# Bass traps or EQ



## F1 fan

I am seeking advice on the best way to deal with a strong axial mode.My small room makes it neccessary to place my subs in the corners which gives me a nice little shot of room gain but on the downside it also excites a nasty 50hz mode.
I am curently using a single band of Parametric EQ to reduce its level but was wondering if corner loaded bass traps like superchunks would be an even better solution.Or is the best approach to combine both traps and EQ? 
What are the pros and cons of each?
What thickness would the trap have to be for it to be effective at 50hz?

Thanks Fred


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## basementjack

Fred, what are the dimensions of the room?

if you are 'trapping a freqency' in your room, that is if exactly half of a 50hz sine wave fits into your room, then no amount of EQ can truely fix the problem (though i supposed you could notch out 50hz from your setup, which would not fix the problem, but would eliminate the source (kind of like cutting off your leg because you have a sore foot - when a padded shoe is really the best answer to let the foot do it's job))

You'll find that a reasonable size (2-4") panel will do well so long as you give it some space between the panel and the wall. A popular technique is to put one diagonally over corners.

ok now here are a few thoughts...
If you have a Radioshack sound meter, and a laptop (or a PC near your theater) - there is free software you can use to measure the response of your room. if you are capable of this, it should be the foundation of anything you do, and you should use it to validate that what you are doing is working.


Its been suggested that a compressed roll of homeowners insulation has decent absorbing properties.
Yes it is ugly. but it is also cheap. if you really want to 'hear' what the difference is in your room with some absorption, 2-6 rolls of insulation would do the trick - once you hear the results, you can decide the best way to treat the room permanently (very likely via commercial panels like GIK or realtraps). if you've used the software and measured before and after, the difference will not only be audible, but it will be documented too, and then you can post back the results here.


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## bpape

Good advice.

Also, IMO, the best way to attack it is to determine what is causing that peak - hence the question above about your room dimensions. Also, would be nice to know the distance from the listening position to the rear wall of the room. 

Corner treatments tend to deal with pretty much everything in the bottom end. That's not a bad thing, just don't expect it to only do 50Hz. You had said it's an axial mode - which dimension if you're sure? Based on that and the other answers, you may find that in addition to the corner absorbtion, it may be beneficial to specifically treat the offending dimension a bit in addition. The EQ is not a bad thing for a sub but IMO should be used in addition to proper treatment.

There is so much more than just FR to deal with that EQ just can't do over a wide range and over a wide number of seating positions. 

Bryan


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## Ethan Winer

Fred,

> What are the pros and cons of each? <

How much are you willing to read to get the answer? I'll give you the Reader's Digest version, but first HERE is a link to the unabridged version. :reading:

Okay, now that you read all that and digested it... :holycow:

The best approach is as much bass trapping as you can manage, then, if more control is still needed, a touch of EQ _cut only_ at one or two remaining offending frequencies can finish the job. I have 40 traps in my living room (no kidding), and I also use the one-band cut-only parametric EQ on my SVS subwoofer to reduce one really low room mode peak by a few dB. That gets me flat within 10 dB, which is about as good as most domestic size rooms will ever get.

--Ethan


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## F1 fan

Jack ,Bryan and Ethan,thanks for the great feedback.:T 


Jack, my room is 19' x 11.2' x8'. Unfortunately I don't have a lap top or a PC near the HT so my only measurements are with the Rat Shack meter and test tones.Doing a mode calc indicated the presence of a 50 hz axial mode corresponding to the width dimension and the measurements and listening confirm a problem.Using the the EQ as a 50 hz notch filter certainly improves things but the three of you seem to be in agreement that corner traps will improve matters even further so I guess I should order some Rockwool.

Bryan ,Iam aware of the broadband coverage but I was wondering what kind of thickness was needed to get any benefit in the 50hz range.My space is limited but I did some checking today to see what the maximum size of trap I could squeeze into the corners.It looks like the max would be a 4' tall triangle shape with a 16" face pointing into the room.The maximum thickness would be somthing like 10 or 11 inches in the center.This is a lot smaller than the Tri Traps but will it be reasonably effective if not 50hz at least for the several modes falling around 150hz?

Ethan, thanks for the link and I will be reading that and many other sections of your very resourseful website.
Wow 40 traps ,I bet that room sounds good.

Thanks all for your help.


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## Wayne A. Pflughaupt

> Jack, my room is 19' x 11.2' x8'. Unfortunately I don't have a lap top or a PC near the HT so my only measurements are with the Rat Shack meter and test tones.


 The good news is you don’t need to have a computer near the HT room. All you need is a cable long enough to reach from the SPL meter to the computer. You could do it easily with a regular coaxial cable with RCA adapters screwed onto both ends. :T Get a coaxial cable with an easy-to-reseal box, and you could return it after you’re done, and save a few bucks.

Regards,
Wayne


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## F1 fan

Wayne A. Pflughaupt said:


> The good news is you don’t need to have a computer near the HT room. All you need is a cable long enough to reach from the SPL meter to the computer. You could do it easily with a regular coaxial cable with RCA adapters screwed onto both ends. :T Get a coaxial cable with an easy-to-reseal box, and you could return it after you’re done, and save a few bucks.
> 
> Regards,
> Wayne


My PC is in the basement and the HT is on main floor but I guess that would be doable if I were to have an access way upstairs.I could temporarilly remove a heating duct.

I had better start spending some time at the REW thread to learn about the software.I may have to seek your assistance on the finer points of it.

Thanks Fred


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## Ethan Winer

Wayne A. Pflughaupt said:


> The good news is you don’t need to have a computer near the HT room. All you need is a cable long enough to reach from the SPL meter to the computer.


Or he could download the 1 Hz test tones from my company's site, burn a CD on his computer, and play that CD through his system with the RS meter in the same room. That SPL meter is portable, yes? :neener:

:rofl:

--Ethan


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## F1 fan

Ethan Winer said:


> That SPL meter is portable, yes? :neener:
> 
> :rofl:
> 
> --Ethan


yes Ethan I paid the extra and got one of the portable models :bigsmile: 


:help: before I buy the supplies I would like to get the experts opinion on my planned triangle corner trap and its potential benefits and any suggestions for changes to improve on my plan.

The design I had in mind was a 40-48" tall lite wooden frame with a 16" open front facing into the room.I was thinking of using 3lb/cf mineral wool to pack it with.The front would be covered with material.

I would likely mount them in the upper half of the four corners to maybe get some additional reduction of hi frequency reflections as the top half of my room is still fairly lively.

Is this big enough to have some effect in the bass range?

Is there anything I should do different?

Thanks Fred


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## Wayne A. Pflughaupt

Ethan Winer said:


> Or he could download the 1 Hz test tones from my company's site, burn a CD on his computer, and play that CD through his system with the RS meter in the same room.



Oh, a wise guy, huh? :heehee: 

Sure, he could do that, but in the time it takes to play and measure _two_ of those tones, REW would be finished and showin' the graph on the screen! :bigsmile: 

So - take that! :neener:

Just kidding, I hope you know! :joke: 

Seriously, I've done the tones, I've done REW - I'm done with tones! :T 

Regards,
Wayne


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## Ethan Winer

Fred,

> Is this big enough to have some effect in the bass range? <

Some effect? Sure.

> Is there anything I should do different? <

Make them bigger?

--Ethan


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## Ethan Winer

Wayne,

> So - take that! :neener: <

I _love_ that smiley!

BTW, below is a large size version of the ROFL guy. Use it as you see fit. :T

--Ethan


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## Wayne A. Pflughaupt

Yeah, that’s a great one! :T I’ve got it book marked now – probably the only smiley face I’ve ever book marked! 

Regards,
Wayne


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## F1 fan

Ethan Winer said:


> Fred,
> 
> > Is this big enough to have some effect in the bass range? <
> 
> Some effect? Sure.
> 
> > Is there anything I should do different? <
> 
> Make them bigger?
> 
> --Ethan


Well I guessed someone would recommend making them bigger but WAF and placement issues limit me to that size.As long as they will have some benefit I will go ahead and build the first pair this weekend and give them a try.

Thanks Ethan.


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## F1 fan

Ok I was able to quickly slap together 2 frames tonight .I will purchase some mineral wool tomorow.


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## basementjack

The frames look great.

I have a thought for you...

often we try and cram an acoustical solution on top of an existing room, instead of trying to design it into the room...

If you look at many high end home theaters, you'll notice that many have columns and sofits.

those are both 'room features' that can have tremendous acoustic benefits.

For example, you could build a wooden frame work for soffit - for example, on the left and right sides of the room. Cover this sofit with a neutral tight weave fabric that blends in with the ceiling color, and most people would never notice it's fabric. then under the fabric you can put what ever you want - You'll gain a **** of a lot more absorption than you will with a few corner traps, and most people won't even notice.

Columns on the sidewalls can be used for the same thing.

I made the mistake of building some tube traps... they did help, but not enough to continually answer the 'what are those' questions I get from people over and over again. If I had spent the same effort (and money!) on making acoustic sofits, I'd have a much nicer solution.


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## Ethan Winer

Wayne A. Pflughaupt said:


> I’ve got it book marked now


That GIF file will stay on my web site permanently, but you can also right-click and use _Save Image As_ to keep a copy locally on you own hard drive.

--Ethan


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## bpape

The corners will not only help in general frequeny response but will also help with general decay time issues that an EQ can't deal with effectively.

If the mode is width related, consider shifting your entire setup about 6" right or left (speakers and seat so you're still centered with relation to the speakers). This assumes you're sitting dead center now. This is a freebie thing that is often a good thing to do.

Bryan


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## F1 fan

basementjack said:


> for example, you could build a wooden frame work for soffit - for example, on the left and right sides of the room.


Jack,I like the soffit idea and had thoughts about doing something like this a while ago but I don't think I could make it look good enough to pass the WAF test in the combined living room /HT.If I had the option of building a dedicated HT room from scratch it would be easier to build in something or just buy a commericial product.


Bryan ,thanks for the tip about shifting things off center,I might give this a try.


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## basementjack

Fred, 

Have you seen the program CARA before? It's an acoustic modeling program.

You design up your room in 3d and it can calculate what the frequency response will be at the listening position. It also has a cool feature that shows where peaks and valleys will be in your room for a given frequency.

You could use something like this to experiment with different options before commiting to anything.

- Jack


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## F1 fan

basementjack said:


> Fred,
> 
> Have you seen the program CARA before? It's an acoustic modeling program.
> 
> You design up your room in 3d and it can calculate what the frequency response will be at the listening position. It also has a cool feature that shows where peaks and valleys will be in your room for a given frequency.
> 
> You could use something like this to experiment with different options before commiting to anything.
> 
> - Jack


No I have not heard of this program before but it does sound interesting.I am interested in learning more about it ,would you by chance have a link?
Thanks Fred


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## basementjack

Cara can be found at www.cara.de (main site)
or www.rhintek.com (us distributor - I believe related to the author in some way.)

I would look at the website in the US, and if it looks interesting, give them a call.

I first found out about it via a forum suggestion, but wasn't sure.

After talking to the guy for 15 minutes, I was sold.

The product is pretty cheap for what it does, and how specialized it is.

It'll set you back about $75 for the current version with the tutorial CD - the Tutorials are top quality - and very helpful - acoustics is a fairly complex subject to begin with, and while the program isn't hard, the tutorials really help point out all that the program can do.

- Jack


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## F1 fan

Thanks Jack I will check it out.


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## F1 fan

Here is the finished product.I plan to mount them on the upper half of the corner and may add a solid pine end cap on them to dress them up a bit.


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## basementjack

Wow Fred, those look great, and it sounds like you threw them together pretty quickly.
I wish I would have done something like that - I suppose I still can.

I spent a pretty good amount of time and effort building some 'tube traps' - and while I'm sure they're doing _something_, they are pretty imposing - your traps blend right in.

What did you end up using for insulation?


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## Sonnie

Nice work... :T


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## F1 fan

Thanks Jack and Sonnie.



basementjack said:


> what did you end up using for insulation?


I used this 3" mineral wool. http://www.roxul.com/graphics/rx-na/canada_us/products/AFB/AFB-English-5-16-06.pdf

I just cut it into wedges and stacked them until the frame was full.

I'm quite pleased with the look and was surprised how easy it was to do.Im not sure what the blue cover material I used is made of (I still had some left over from my wall panel project) but it is a pleasure to work with.It stretches nicely in all directions without bunching up.


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## BoomieMCT

I think you are on the right track. I've always heard that one should try to deal with problems using treatments first and EQ what that won't fix (peaks only!). In my case treating a nasty 63Hz dip had the side effect of solving a 95Hz dip and a big 50Hz peak. 

Once you finish your corner traps (very nice BTW) I think you'll see improvements elsewhere as well.


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## bpape

Nice job on the corner absorbers. They look really good and I'm sure are performing well.

Just a little addition to the above post.

- Deal with what you can first via placement of seating, speakers and sub.
- Treat the room to deal with modal issues and to bring overall decay time into place using broadband treatments
- Use tuned absorbers if feasible to deal with narrow, more stubborn issues
- Use EQ to deal with the last few peaks in response.

Bryan


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## F1 fan

Thanks Bryan and Boomie for your complimentry words and advice.

I have only finished two of the traps but I placed them in the lower front corners and did a bit of listening .Even with just the two there was a very noticable improvement in the bass range.I listened to among other things Pat Metheny and Charlie Hadens ,Beyond The Missouri Sky which is a very well recorded disc of mainly acoustic guitar and acoustic bass.

I find this recording a good bass articulation test and on my system the acoustic bass tended to sound a bit bloated and some notes were a little too resonant.With the traps installed these same bass notes tightened up considerably and became more detailed and natural sounding. Similar results were noted with other recordings.

I am pleasantly surprised by the degree of improvement and so far it looks like the $30 and 1.5 hours spent building these was well worth it.Now I have to build two more and see if that brings even greater rewards.


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## bpape

Welcome to the world of the believers. Setting things up right and treating your room appropriately are the most cost effective upgrades you'll ever make. You're seeing and hearing that for yourself right now.

You'll find yourself listening to things you haven't heard in a while and hearing them in a whole new light.

Enjoy!

Bryan


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## Guest

[EDIT: Oooo000PS! I just realised I hadn't seen the entire thread before I posted this . . . looks like I'm a little late in my replies! DOH!!! :duh: I was going to just delete the post, but on second thought I'll leave it here in case anybody else might happen across it and find it helpful.  Anyway . . . congratulations, Fred! Nice job. ] 





F1 fan said:


> Bryan ,Iam aware of the broadband coverage but I was wondering what kind of thickness was needed to get any benefit in the 50hz range.My space is limited but I did some checking today to see what the maximum size of trap I could squeeze into the corners.It looks like the max would be a 4' tall triangle shape with a 16" face pointing into the room.The maximum thickness would be somthing like 10 or 11 inches in the center.This is a lot smaller than the Tri Traps but will it be reasonably effective if not 50hz at least for the several modes falling around 150hz?


If you have the right density of material, you might be able to make something in that size that will help out at least down to the 150 Hz range, and maybe marginally down in the 50 Hz range. The 150 Hz range is more important for music anyway. For example, the low E on a bass guitar or bass fiddle is right around 40 Hz, but most of the energy of the sound of that note actually comes from the 1st harmonic, at 80 Hz (which is why you can hear the bass notes even on tiny speakers that roll off much higher than that.

There is no getting around the fact that you need mass to deal with low frequencies, so more would be better. You'll want to make sure you *at the very least* treat all four vertical (wall/wall) corners if it is at all possible. If you can't do that, then you'll want to look at treating horizontal (wall/ceiling or wall/floor) corners if you can.

Typically, for bass traps, you should use at least 703 or 705 rigid fiberglass panels (705 offering more bass absorption than the 703, due to a higher density), and it needs to be at least 3 to 4 inches thick. The thing is that these come in 2' x 4' sheets . . . which means that you'll have to do some cutting to get them to a 16" width for the face of the traps, and cutting fiberglass or rockwool is not exactly a whole lot of fun. 

With 703 or 705, you don't necessarily need to actually fill the whole corner with fiberglass, as having an air gap behind the panel actually increases the amount of absorption over having the same panel with no air gap behind it. You may be able to get a small improvement by stuffing some lower density fluffy fiberglass behind the 703 or 705 panels. 

You could also just fill the entire corner space with 703 (I'd say the 705 isn't necessary if you are going this route, and the 703 would be more cost effective). For this, you'd get a bunch of 703 panels and cut them into triangles (here again, having a 24" face is going to make for less cutting and less wasted material), and just stack the triangles until you reach the desired height.

You can also get a bit of improvement in the bass absorption of these panels if you use the FRK version of the 703/705 across the face of the traps. The FRK panels have a kraft paper facing, which will act as a limp mass membrane. Mind you . . . you will need to sandwich several panels of 703 or 705 to acheive the 3-4 inch thickness you need for low frequency absorption, but you will only want the FRK facing on the outermost panel! 

You don't want to have layers of kraft paper in between the 703/705 panels, as this would actually DECREASE the effectiveness of the panels, because you will impede the gas flow through the thickness of the fiberglass. In large part, the absorptive behaviour of the fiberglass material is acheived via the tortuous path the sound pressure is forced to take through the fiberglass, both on its way in, and then on its way back out, as it is reflected back through from the walls behind the trap. If you have multiple layers of membrane, you quite drastically change the way the air pressure moves through the absorber, to a detrimental effect. The preceding is, of course, a grossly over-simplified explanation of how it actually works, and I started to write a more detailed one, but then I decided not to bore you with the details.


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## bpape

Scott makes good points. 

Don't be discouraged. A solid chunk of 703/705 with a 16" face and 10" thickness in the corner will absolutely have some effect at 50Hz - certainly way below 150Hz. 10" of 703 will have close to a 1.0 coefficient down to around 100Hz. Is it going to be 1.0 at 50? No. Can it be .4 or a bit more? Yup.

In short, you do what you can.

Bryan


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## F1 fan

Hi Scott, thanks for chiming in with a very informative post.Im glad you didn,t delete it.And I assure you a more indepth explanation would not have been boring.
Does this sound reasonable?with the next traps I build I was thinking of using higher density mineral wool (6lbs/cu ft instead of 3) to maybe get better absorbtion at lower frequencies.I would like to use OC 703 or 705 but unfortunately it is not readily available in Canada.I will be cutting it into triangles and stacking them into the wood frames.Yes I agree it is not the nicest stuff to be working with.

By the time I'm done I should have about 75 percent of the vertical wall corners treated.

Thanks again for your input.
Fred


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## F1 fan

bpape said:


> 10" thickness in the corner will absolutely have some effect at 50Hz - certainly way below 150Hz. 10" of 703 will have close to a 1.0 coefficient down to around 100Hz. Is it going to be 1.0 at 50? No. Can it be .4 or a bit more? Yup.
> 
> Bryan


1.0 down to a 100hz and .4 at 50hz .I like those numbers Bryan:jump:


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## Guest

F1 fan said:


> Now I have to build two more and see if that brings even greater rewards.


There is absolutely NO QUESTION that it WILL bring greater rewards. Not only will you have more actual absorption in the room, but you will be treating the room modes from FOUR problem spots instead of only two.

There are some very good animations that show how room modes work, and how sound pressure displaces the air particles in a room, here:

http://www.isvr.soton.ac.uk/SPCG/Tutorial/Tutorial/Tutorial_files/Web-standing-rooms.htm

You can see how the modes gather in the corners and then shoot back out into the room -- this is where the sound pressure gathers velocity before being reflected back into the room. I think the above-linked animation is helpful in understanding why it's important to treat the corners of your room as adequately as possible, and that dealing with this reflected sound is really the only way to effectively deal with room modes. 

If you are able to impede enough of the velocity of the wave front at those critical spots to reduce the amplitude of the reflected sound, you will reduce the amount by which the reflected sound will distort the direct sound (from your speakers), which it does by either canceling out the direct sound (where the reflected sound is out of phase with the direct sound) or by enhancing it (where the reflected sound is IN phase with the direct sound).

When you EQ your room, you aren't changing the way the sound travels through the room or the way it interacts with the room boundaries. So the problems are still there. I don't deny that you can get a *subjective* change in the overall frequency response of the room (though the actual effect of EQing a room is very positionally specific down to within less than a cubic inch, and it really doesn't fix the modal ringing -- it might reduce the amplitude of the modal ringing at a given frequency along with the amplitude of the direct sound, so there is a subjective change, but the ringing is still there in roughly the same ratio to the direct sound, and it's still acoustic distortion), but you aren't really fixing the problem -- you're simply masking it . . . a bit like putting a band-aid on a broken arm. 

Conversely, if you do as much as you reasonably can to fix the REAL cause of the problems, and ONLY THEN put a band-aid on the smaller problems, you'll be able to get a lot closer to what the artist and the recording engineer intended you to hear. But keep in mind that EQ in itself is an introduction of a distortion of the sound source (in a number of ways, including the introduction of phase errors to the direct sound!), and, again, it cannot change the physics of how sound travels and interacts with room boundaries.

This concept is ESPECIALLY important when it comes to small room acoustics, because, unlike larger rooms (like concert halls, etc.), there is no delay (that your ear can discern) between the reflected sound and the direct sound -- particularly at lower frequencies, and the sound doesn't get a chance to decay on its own before it hits the next boundary problem spot (i.e., it's once again gathering in a corner to be reflected again) as it would in a large room (e.g., the size of a high school football stadium or a good sized concert hall), so you have to focus on reducing the *amplitude* of the reflected sound. If there is enough delay between the reflected sound and the direct sound, then your ear/brain will be able to distinguish the two sounds (to varying degrees, of course, also depending on the relative amplitude of the reflected sound to the direct sound). This stuff is hard wired into our brains (known as psychoacoustics), and it is part of the way our ear and brain are together able to determine the relative location of sounds, and hence the reason we can get a three dimensional image from only two speakers.

Sorry to ramble on about this, but the EQ v. acoustic treatment comes up so regularly, I thought it might be helpful to some people to discuss it in the above terms. Obviously each individual/room/family, etc. will have various different criteria as to the meaning of "reasonable" when it comes to treatment, given factors like WAF, multi-purpose use of a room, aesthetics, budget, etc., but I think a lot of people try to use EQ as a replacement for proper acoustics treatment because (a) it's the path of least resistance, and (b) they don't understand the above information. Or they will continue to spend thousands in upgrading their electronic gear, when a small investment in a bit of acoustic treatment will give them a FAR greater return.

As a recording engineer, I always try to get the sound right at the source first. That will usually mean dealing with the acoustics as much as possible up front, and then finding the right mic, preamp, and, prehaps more importantly, mic position for the particular instrument I'm recording and the acoustical conditions I'm dealing with. In pretty much all cases in which I have the option, I'll change mics, mic positions and, where possible, the acoustic conditions before I reach for EQ to "fix" the sound.

As a professional musician (drums) who has played in literally hundreds and hundreds of different rooms of all types and sizes over the years, and who has performed in said rooms on everything from the very finest instruments to student/entry level drums, I can tell you that for the most part I'd rather play an entry level drum kit in a nice sounding room than a very expensive top level instrument in a bad sounding room.


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## Guest

Yes, I agree with Bryan that you should be able to get some absorption down to 50 Hz with your current design. I didn't mean to say that it wouldn't help at all (perhaps I shouldn't have used the term "marginal") . . . I meant it more in relative terms, that larger traps would help more if you could do it.

But perhaps even more so, I wanted to point out that you can be less concerned about a 50 Hz room mode than you would want to be about modes at ~80 Hz and up. One reason is that the majority of the speaking range of even the lowest instruments is in the 80 Hz and up range, because we hear the first harmonic louder than we hear the fundamental of these instruments. If you play any given music CD through a spectrum analyser, even stuff that is fairly bass heavy, you'll see that there is a lot less energy down around 50 Hz and lower. And that is because, again, the "speaking range" of these instruments is at the first harmonic.

Actually, the first stage of mastering for music recordings often involves applying a high pass filter at around 30 Hz or so, which gives a noticeable roll-off curve from 60 Hz down to 30 Hz. 

But your room (as with most small rooms) is more likely to have much bigger problems in the 80-500 Hz range.

I ran ModeCalc on your room and took a couple of screen grabs of the results, and you will see that you have MUCH bigger, and much more noticeable issues in that range. And if you look at the one that gives you a graphics plot, you'll see where you have numerous modes from each of the dimensions bunched up right next to each other. It's that kind of stuff that can really make the overall frequency response of your room look like the Swiss Alps (as most small rooms do!).

[EDIT: Yikes! How to I upload a picture here? I thought I had done it right, but I don't see the pic! :scratch: ]

If you get some of those modes sorted out, things start to become much clearer, and because there is more power there it can punch through any mud/rumble that can come from a mode in the range of 50 Hz or below.

If it's a home theater system, and you like to watch movies with lots of explosions and earthquakes in them, you'll have stuff with more energy down in that range . . . but who's gonna care if an explosion or an earthquake rings a little longer than it's supposed to. Noam sayin'? 



F1 fan said:


> Does this sound reasonable?with the next traps I build I was thinking of using higher density mineral wool (6lbs/cu ft instead of 3) to maybe get better absorbtion at lower frequencies.I would like to use OC 703 or 705 but unfortunately it is not readily available in Canada.I will be cutting it into triangles and stacking them into the wood frames.Yes I agree it is not the nicest stuff to be working with.


Just to clarify, when I say 703 or 705, I'm basically using these terms as generic references to rigid fiberglass or mineral wool panels of essentially 3 lb or 6 lb density, respectively. Performance should be roughly equivalent, if I'm not mistaken.

I'm not absolutely certain off the top of my head (I'd have to look up the data, etc.), but I would guess that the 6 lb density fiberglass/rockwool, etc might be overkill for using it in this way, where you are filling the entire corner. (Maybe Bryan or others can give you some more precise info on this.)

I think I'd almost rather see you spend the difference in cost between the 703 and the 705 on getting more of the 703 and making larger (taller) traps if you can swing it (i.e., lovely wifey would permit, etc.).

If you were making panel traps to straddle across the corners, rather than filling the entire corner space with rockwool as you are here, then the denser 705 panels would make more of a productive difference, I think. The design you are using (filling a corner) and a panel trap have similar, but subtlely different, behaviours in play that cause them to perform the way they do.


Yikes . . . it's late and I'm gettin' sleepy. But I do have a couple of suggestions I could offer on how you might improve on what you've got there without adding too much complication. More on that tomorrow.


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## Guest

OK. Got it sussed now. Here's the second ModeCalc screen grab. Attaching both in one post made for a very W-I-D-E thread! :duh:

Looking at these numbers, you can also see why using REW to analyse the frequency response of your room is going to give you a much better read than using test tones of even as fine as 1 Hz increments!


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## F1 fan

Scott, thanks so much for taking the time to post the Mode calc results.
I see what you are saying about problems well above the 50hz range.Things do seem to get a bit ugly from 150-500hz.
As you suggest I will stick with the 3lbs/cu ft mineral wool for my remaining traps.
Fred


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## Guest

Fred, see my comments in this thread (both of my recent posts there) regarding a similar design to yours.

Also . . . I might suggest that, instead of building a frame for your trap that consists of wood panels, you would probably do better with a more sparse frame, more closely resembling a triangular box kite.

Triangular frames (open) at the top and bottom, and support struts at each corner (I'll attach another quick and dirty sketch here as well).

The wood panels up against the wall are redundant, and waste a certain amount of space that could be used for either additional absorption material or an air gap, either of which would increase the amount of absorption you are getting from that space.

Further, you want as much absorption material exposed to the room as possible. Having the top surface exposed will also increase the amount of absorption you can get with these traps.

Better yet for you, if you can swing it, would be to simply go from floor to ceiling with the "superchunk" style traps you are building (again, see my comments in the other thread. 

First picture is open top frame, second is side view of the trap frame. Again, very rough sketches here. Also (just to be clear), with regard to the side view, the support struts can be flush with the corners of the top and bottom frame, rather than being inset as the diagram shows.


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## bpape

While the piling up of frequencies at or above 150Hz is certainly worse than lower (and almost always is), this does not negate the need for decay time control down that low. Also, look at the offending frequencies that are piling up. They're almost all primarily interactions between the length and width multiples. Addressing the fundamentals of those dimensions will help the multiples also.

Also, remember 2 things:

- Predictions are very useful and should be paid attention to - but they're just predictions. Real world measurements will almost certainly be very different.

- ModeCalc only addresses the axial modes of a room. Axials are by far the most powerful of the room modes. However, the tangentail and oblique modes of a room are MUCH lower in frequency. They can also easily pile up on each other and on the axials to turn somewhere that looks innocent enough into a place where you have many different things piling up on each other. Please don't get me wrong. I'm not trying in any way to minimize ModeCalc or it's usefulness. It's very handy to get a quick look at the main axial issues in a room.

- Calculations of a rooms modal issues look at the information in a void. They do not take into account the position of the speakers, the subwoofer, or the listening position(s) - all of which can be used to your advantage (or against you) to address frequency response related issues to a certain extent. 

I'm not trying to minimize the use of ANY room mode calculator. I simply want to make sure that you don't make decisions on how deep your absorbtion NEEDS to go based simply on an axial modal analysis that looks like most of your modal overlap happens above 150Hz. This will ignore the issues I stated above - not to mention the general decay time issues that will be present in pretty much every room.

Bryan


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## F1 fan

Scott,I think I will cut large openings in my triangle tops and just cover it the same way with the material.

Bryan and Scott ,thanks for sharing your expertise, your informative posts have been very helpful .


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## bpape

Good luck. Post some pics of them.

Bryan


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## F1 fan

bpape said:


> Good luck. Post some pics of them.
> 
> Bryan


I will, and if I get real ambitious I will try to learn REW and post some room measurements with and without the traps.


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## Guest

Quick question. for bass traps is it necessary to run the foam trap up the lenght of the wall to the ceiling? or just lay one on teh ground?


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## cyberbri

It's not necessary to have it go the full height of the wall. Doing so would provide more absorption and improve the sound more. But it is fine to have a panel or corner wedge, etc., sitting on the ground covering half of the corner height.


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## allredp

What a great thread!!! Wow, thanks Scott and Bryan for the truly professional (if somewhat dizzying :rubeyes: ) help. 

My question regards my room which has strange "corners"--meaning that my back L is about an 11' angle wall with a fireplace in it, my back R has a 4' closet on it (meaning 2 corners) and my front R has a door close to it with the SVS parked there, and the front L has a double door right to the corner. Overall room size is 15D x 27W x 8H. 

I'm a newbie so I don't know how to post a pic! 

So, if I were to use a "corner" trap--where would it be? and how effective could it be (especially considering that the one backwall corner actually faces away from the SVS).

Much thanks for the help!

Phil


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## jmprader

This is a great thread. Just wanted to put in my $.02.

Corner traps are easy, even I, with no juxtaposed thumbs (but a brother with tools!) managed a pair, and they work great (and augment the performance gains from sub eq). Mine are combo oc703 and acoustical cotton in a minimal framed enclosure found in this thread:

http://www.hometheatershack.com/forums/home-audio-acoustics/736-corner-traps-wall-treatments.html

If I can do it, so can anyone lurking here. And they work great. So do my diy oc703 wall panels.

Even the wife can appreciate the difference.

Another tip of the hat to Ethan, Bryan, Scott and others who preach the gospel on this subject. :T


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## bpape

I had forgotten those pics - still get a kick out of the Marshall logo!

Bryan


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## F1 fan

I finally finished my second pair of corner traps and as hoped they did bring about further improvements.The biggest improvements are most apparent when listening to music with bass guitar and acoustic bass.Midbass is much tighter and more detailed sounding with much less overhang. This was the frequency range I really wanted the traps to be most benificial and they did'nt disapoint.

Adding the traps along with the previously built acoustic treatments certainly has been the most bang for the buck tweak that Ive done.My room is small but I was able to fit quite a bit of treatment into it without it taking up much space or making it look too ugly.(although my Wife may not agree with that last statement) 

Here is a list of treatments.

2 corner traps in the lower front corners.

2 corner traps in the upper rear corners

2 8" thick rockwool panels behind the main speakers(for SBIR reduction)

2 3" rockwool panels at the side wall first reflection points

several small 2"fibreglass panels on the upper rear wall to reduce reflections.

Im soon going to be removing the thick pile carpeting and replace it with a harwood floor.This will probably make the room much more lively so I may need to treat the ceiling.But That may be a bit of challenge.


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## allredp

That's exciting F1--could you post some pics of your "treated" room for us?
Thanks,
Phil


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## F1 fan

Ok here are some pics.


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## F1 fan

A few more.


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## basementjack

HOT DOG F1!

Did you build all these traps since you started with the corner traps at the beginning of this article?


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## allredp

Nice job, F1. You inspire us...


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## F1 fan

Thanks Jack and Phil.



basementjack said:


> Did you build all these traps since you started with the corner traps at the beginning of this article?


No just the 4 corner traps. I built the others previously.


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## Guest

I am building 88" 24x17 corner traps. I was wondering if you have any tips on stretching the fabric. I built frames last night and will order some 703 and GOM over weekend.


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## F1 fan

Hi crg,I bet those large traps will work great.
As far as tips , I just started on one side and secured the fabric the full length of the frame with an electric staple gun.I then pulled it as tightly as possible to the one side then stapled it.Then the top then the bottom.Im not sure about the GOM but the fabric I used was very strecthy so it was easy to get tight so that there were not any wrinkles.

Good luck and when you get them done be sure to post some pictures.


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## Guest

Well, I got the frames done this weekend (with a little help).


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## F1 fan

Wow those are huge,I wish I had the space for something that big.NicelyDone.

btw your helper is a little cutie.


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## Guest

Thanks for the compliments. Lucky for her she looks like her mother.

Looks like it will take a few weeks for the 703 to get here so I'll post more pics then.


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## Guest

The fiberglass came in sooner than I thought it would. I cut it up and filled the cavities of the two 88" ones today. I had 1 panel left and set it in the front of the smaller 48" trap. Used a utility knife and electric carving knife as suggested elsewhere. 

I have some left over 1/2" linacoustic that I hoping to attach to the front so that when I cover it it will produce a smooth surface. Also, while I understand its best to fill the cavity of the 48" in corner trap, especially since its only 1 panel 2" thick, will filling it with left over linacoustic work well or is there somethingelse I should consider that I can get from HD or Lowes?


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## mike c

hey F1, do you have pics of the backsides of your DIY creations? 

the corner trap, wall panel, and free standing panels?


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## bpape

Filling with Linacoustic would provide some benefit - though not as much as 703 in the deepest octaves.

Bryan


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## Guest

Well I finished the two larger traps. I did not use GOM due to expense and used burlap instead. I was largely pleased with the finished results except the edges. I may re-wrap it later after working on my technique a bit with the smaller trap. 

I think my mistake was that I cut the top and bottom of the frame for exactly a 24" width & 17" sides. When I cut the 703, the front corners extend just bit past the frame. For the smaller frame I am going to make plates an inch or 2 longer to see if that will work.

Any way attached are some pics. Once in the room they really blend in nicely. I finished before the wife got home. Took her down to the room and she did not immediately detect what was different (a major plus).


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## Guest

I recalibrated the system and got to listened to a few tunes (Neena Freelon - Soulcall) before the wife callde me to eat. This is a piece of work I enjoy lstening to every now and then. The cello on Better Than Anything seems to have more definition and a little more punch. Good start1:bigsmile: 

Attached are before and after REW graphs. The before was with 1st reflection point and rear traps in place. "After" adds front corner traps to the "Before".


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## bpape

Lookin good! Yeah - it's not an exact science. An extra .5" here and there will gain you a ton of looks. Though, I will say that they look nice in the room

Bryan


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## F1 fan

mike c said:


> hey F1, do you have pics of the backsides of your DIY creations?
> 
> the corner trap, wall panel, and free standing panels?


Sorry Mike I don't have pics of the backs but if you look at post #15 in this thread you can see how the frame of the corner trap covers the back almost completely.The free standing panels are open in the back except for 2 4"wide strips of hardboard (masonite) runing from top to bottom on each side to hold the mineral wool in place.The backs of the wall panels are completely covered with masonite.

crg,those traps do blend in nicely with the room.It looks like you have a real nice setup.:T


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## mike c

thanks for the info F1.


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## brucek

> Attached are before and after REW graphs


crg, I believe that you are using the old Radio Shack meter calibration file. Best to use the new one that associates with your model found here. The files are new in the last month after Sonnie had his ECM microphone professionally calibrated and we re-did the files.

I really think your low frequency response can be bettered by equalization. You have a nasty peak around 28Hz and others that could be easily corrected with a BFD. There's nothing wrong with correcting very low frequency peaks with equalization. Certainly well executed acoustic treatment improves response over a larger physical area than does EQ, but at very low frequency peaks (such as you appear to have), the size of the treatment would be huge. A cut filter with a matching Q and inverse gain would help reduce the peak.

When you post your graphs use a vertical scale of 45dB-105dB. The RadioShack meter is not reliable above 5Khz, so no use using a horizontal scale that goes to 30KHz. In this case where we are looking for effect of a low frequency mode, perhaps use a horizontal scale of 15Hz to about 500Hz (and measure same to look for low frequency modes).

brucek


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## bpape

Agreed. Looks like 4 bands of parametric would bring things pretty nicely in line. The treatments will help quite a bit and deal with the decay time part of the equation. The EQ is the finishing touch to deal with the last few stubborn peaks that can be caused by any number of things.

Bryan


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## Guest

F1 fan said:


> Here is the finished product.I plan to mount them on the upper half of the corner and may add a solid pine end cap on them to dress them up a bit.


Is there a reason why you built it not with facing the corner in the room? Would be more efficient.
Lamda 1/4 :reading: 

br Gerd


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## F1 fan

gto said:


> Is there a reason why you built it not with facing the corner in the room? Would be more efficient.
> Lamda 1/4 :reading:
> 
> br Gerd


Hi gto,sorry Im not really sure what you are asking,but to clarify it is triangular shaped so it is meant to fit tight into a corner with the absorbative side facing into the room.
If it were a regular 4" flat panel then straddling it across a corner so that there was an air space behind it would increase it's effectiveness.


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## Guest

Hello F1 fan,

If it is not too much trouble, could you please post steps of making it and materials also cost?
Your help is greatly appreciated!
Kev.



F1 fan said:


> Here is the finished product.I plan to mount them on the upper half of the corner and may add a solid pine end cap on them to dress them up a bit.


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## Guest

F1 fan said:


> Hi gto,sorry Im not really sure what you are asking,but to clarify it is triangular shaped so it is meant to fit tight into a corner with the absorbative side facing into the room.
> If it were a regular 4" flat panel then straddling it across a corner so that there was an air space behind it would increase it's effectiveness.


Its not easy to explain with my poor english.:crying: 

Lets take a pic.:bigsmile: 
 

Hope this is understandably?

br Gerd


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## bpape

Yes, that would buy you a little bit of extra extension at some angles of attack - at others it would be pretty much the same or less. Think of the waves that come down hugging the side walls. How much absorbtion do they go through turned around vs. tucked in the corners? 

Plus, tucked in the corner take up a LOT less room and still provide excellend absorbtion.

Bryan


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## Guest

IMHO its a question of what your room needs. 
In kind of acoustic principles/physics its clear, that you loose absorbtion in deeper frequencies.
But out of my experiences its a question of what your measurings show you.
If you want to perform well, then you should look for a evenly respons over a max frequencierange.
And only a good measuring with RT60 shown on watterfall will tell you whats needet.

No question, that it is allways a balance between waste room, how it looks like and how far I am willing to go.  

br Gerd


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## F1 fan

gto said:


> Its not easy to explain with my poor english.:crying:
> 
> Lets take a pic.:bigsmile:
> 
> 
> Hope this is understandably?
> 
> br Gerd


OK gto now I see what you meant. I would think further gains would be had if you also filled the big air gap with some more mineral wool or fibreglass thus making it a cube instead of a triangle.That would substantially increase material thickness.


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## F1 fan

Tigerkn said:


> Hello F1 fan,
> 
> If it is not too much trouble, could you please post steps of making it and materials also cost?
> Your help is greatly appreciated!
> Kev.



Hi Kev,no trouble at all.These are very easy and inexpensive to build. 

1)The frames consist of only four pieces-Using 1/2" plywood I cut two triangles one for the top,and one bottom.Then the support and back pieces were cut to length.Measure and see what the maximum height and width that you can fit into your corners.The bigger the better.

2)For assembly I used some nails and wood glue. see post #15 in this thread for a pic of the finished frame.As an alternative you could use crg's method (shown in post #59) of building the frames. 

3)Cut mineral wool or fibreglass into triangles the exact same size as the top and bottom panel of the frame.I used a utily knife and one of the plywood triangles as a cutting guide.Stack them on top of each other until frame is full .For reference see crg's pics in post #62.

4)Cover the front (and top or bottom if needed)with some acoustically transparent material that matches with your decor.I used an electric staple gun to staple the material to the back of the frames.

approximate costs.

1 bag 3" Roxul brand mineral wool - $25 

plywood -$25

cover material $10-15

I hope that is helpfull.


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