# Bass traps



## Fincave

Some basic info first: 

Room is 4.95m by 3.9m by 2.4m. Floor is laminate ie hard and very reflective, have one carpet on the floor, natural fiber but pretty thin so not doing much for absorption. I have acoustic panels made from rigid fibreglass on the walls, left wall coverage is probably about 45%, right wall coverage 15%, front wall coverage is about 25% and cannot place much more as my screen takes up the rest of the available space. The ceiling is entirely untreated and made of concrete covered in plaster, same as the walls. 

Installing the panels improved my sound quite dramatically, I had a lot of echo before doing the 'clapping test', now there is none. My speakers are Amphion Argon2's and can probably be described as very accurate monitors, some people have said that mid and higher frequencies are harsh sounding, I have no problems in that regard. Bass is take care of by a BK Electronics Monolith, more than ample for my small room. Am also using a BFD to tame the subs response, the response is not ruler flat by any means yet, but still pretty good, at least to my ears. 

The problem: My only problem is to some of the bass sounding boomy and I was wondering would traps work to solve this?

I was thinking of building my own traps and putting them in the four corners of the room. They would be triangular in shape and would consist of a wooden frame with the front face being a rigid fibreglass panel 30mm in thickness. Am not sure what would be the best material to fill them with, fibreglass or rockwool, both are available here in varying densities. The traps that would be in the front of the room would have a volume of roughly 55 litres and in the rear 110 litres.

1: Will traps solve the boomy sounding bass?

2: What would be the best material to fill traps with?

3: Will the traps I have described be big enough?


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## F1 fan

A triangular shaped corner trap called Super chunks seems to be popular and effective.It is made up of many wedges of OC703 rigid fibreglass. Here is a link to one way of doing it .see about half way down the page.http://www.radford.edu/~shelm/acoustics/bass-traps.html


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## JCD

Ethan Winer has a link to his DIY bass traps -- here.

Will it fix your problems? Probably not entirely, but it should help A LOT. 
Hopefully Bryan Pape and/or Ethan Winer could chime in with some additional info.

JCD


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## Fincave

Thanks for the replies! Have actually read both the articles mentioned. The 'super chunks' idea seems to very doable, the only problem being all of the rigid fibreglass panels that I have seen available here in Finland have a coating on the front, presumably to make them acceptable appearance wise and to restrict loose fibres from becoming airborne etc. Cutting up these panels would become quite pricey, probably end up costing about $400 for the two traps I have planned for the front corners, double that for the rear corners. Filling the traps with fibreglass and using a panel for the front face would bring the price down to about $160 for all the traps but am not sure as to how effective they would be. Have to pay another visit to the hardware store and have a look at the available materials.


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## drf

nice, please keep us posted on how you go with this, I have a very similar sized room which will require similar treatment but am unsure of the best path to take. 

I can't imagine you would need 4, but then I am not an expert... yet. Are there particular frequencies that boom?


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## bpape

You can fill the back with a less dense material as long as you fill it completely. A bit of compression won't hurt either. 

It's hard to say if it will be enough as you specificed the volume but not the surface area exposed to the room which is a critical piece of information.

Bryan


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## Fincave

The front face of the smaller traps would be 60cm X 60cm, the rear traps 60cm X 120 cm high. The traps would be triangular in shape with the sides being roughly 42cm X 42cm X 60cm and would not be placed flush into the corner, probably a gap of 2-3cm all around though they could be flush mounted if it would be beneficial. Hope this info makes sense! Thanks for all assistance!


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## bpape

Those will help some but may not be enough. For that size room, I'd want a minimum of 4 of the 60x120's. Get them flush into the corner if you can.

Bryan


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## Fincave

Have done some more reading on the subject of bass traps and came across DIY tube traps. The tubes are apparently available here and are not expensive at all. Anybody with any experience of these traps? The tubes that are available here come in different sizes, wall thickness of 5cm or 10cm, diameter of 10cm, 12,5cm, 16cm and 20cm, all the tubes are 120cm tall. They would be easy to place in the corners and could also be placed in a row along my rear wall behind my sofa. The question being are these effective at all? 

Here are some of the links I have been looking at:

the tubes

diy 1

diy 2

info


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## geekwithfamily

According to Jon Risch the pipe insulation traps don't do anything because the material is too dense. He has instructions to make ASC-esque tube traps by compressing fiberglass insulation around an open cylinder. I just made his "quick and dirty" traps and they helped my room boom (absorbing bass overhang). The great thing about the quick and dirty's is you can just buy some packaged rolls of fiberglass insulation and throw them in your room's corners and see if bass traps help at all. If they don't work out just return them (as they're still in the package) or further insulate your home.


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## brucek

> If they don't work out just return them (as they're still in the package) or further insulate your home.


Great idea.........


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## Fincave

Thanks again for the info and links! Had a thought, not sure if it is doable or feasible so correct me if need be. Basically have two discs, say MDF 2,5cm (1") thick and give them a diameter of 40cm (15,75"), join them using a sturdy dowel rod about 100cm (40") long. Wrap fibreglass insulation around the dowel using duct tape or wire to hold the insulation in place if need be. Not sure how tightly they would need to be wrapped/packed? Then ask my girlfriend very nicely to make a cover for them out of material. I could then place these in the corners and maybe somewhere along the side walls, these could then be used as stands for plants or lamps etc. Suggestions and comments most welcome.


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## Ethan Winer

> According to Jon Risch the pipe insulation traps don't do anything because the material is too dense. <

That's bad advice. Pipe insulation absolutely works.

--Ethan


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## Fincave

Probably going to try the tube traps as soon as I can get to the hardware store. Should they not do anything I amy well try the 'quick and dirty' traps. Have more questions though, is BIGGER BETTER? What influence will the internal diameter have and should I go for the thicker wall size. Also, would fiiling the inner cavity with fibreglass have any effect, it kind of makes sense to me that it would make a difference. In the articles I have read both suugest leaving half of the tube reflective and half not, WHY? Am sure will have more questions still. Thank you for all the assistance thus far


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## bpape

Bigger is better (deeper at least). 

I'll sit on the fence between Ethan and Jon. Jon is incorrect that the issue is density. He is correct in that per area of floor taken up, there are a LOT better, more effective, cheaper solutions than pipe insulation. It's not that it can't work. 

IF you fill the tube with fluffy stuff, it can work pretty well - if you can get maybe a 16" or larger diameter tube. But, think how far that will stick out into the room. A 2' wide chunk in the corner provides more surface area exposed directly to the room and takes up half the floorspace.

There CAN be issues with density if you expect the tubes to be broadband absorbers. For the same reason that less dense materials work better for reflection absorbers when you have shallow angles of incidence. With a tube, you have TONS of refections at those shallow angles. This is only an issue from say 1kHz up but I personally don't want that area spraying around randomly in my front soundstage.

Bryan


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## basementjack

I have built a few of the tube traps using the instructions at http://www.teresaudio.com/heaven/traps/traps.html.

They weren't that hard to build, but they weren't that easy either.

The problem for me, being a perfectionist, was the circle tops and bottoms, I used a router and a circle jig and cutting down 1/8 in at a time made a nice template, then I used a 'tracer' bit, mounted to a router in a table, and stacked the template on a roughly cut piece to make the others. It was time consuming and the circle gig, and template bit ended up costing me about $50 USD

I can settle the density question - I weighed a piece after removing the foil, and caluclated how many cubic feet were in the piece I weighed - (these were Knauff 1000deg pipe wrap) - it came out to 3Lb/cubic foot.

I made 2 approx 22 inch diameter, 2 inch wall thickness traps, and 4 appox 13 inch diameter 1.5" thickness traps.

I have to say I didn't notice a huge difference with them.

I will take some room measurements and post them at some point in the next few weeks.

In the mean time, I think the idea insulation rolls from the home store is a great one - as pointed out - it's cheap, easy, and easily reversible.

I'll also comment that The traps look ridiculous. I honestly think the marginal improvement in acoustics doesn't justify the look on my wifes face. There has got to be a better way....


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## bpape

Looks is certainly an issue - hence my point on the slabs straddling a corner taking up a LOT less space.

Now, if you take that same 22" tube and fill the middle with fluffy fiberglass, I think you'd notice a larger difference in the bottom end.

Bryan


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## Fincave

Will be picking up some high density rockwool panels tomorrow and ave decided to cut them into wedges and stack them in the front corners. From one package I will be able to get two traps which will be 50cm across and 100cm tall, plus some wood for a frame and some material to cover them and the total cost should be about $25. Hopefully they will make a difference and depending on the results wil make another two for the rear corners. Once I have made the traps will post as to any results.


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## JCD

Since I'll be working on my room soon (hopefully) and will be addressing the accoustics as well, I look forward to your impressions of the results.

JCD


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## F1 fan

I am also interested in your results as I plan to to build a pair of these.
May I ask what is the density and thickness of the Rockwool you are using? 
I don't think the OC703 product is available in Canada but I have found a Roxul Rockwool product that may work.It is called Drain Board and is 1" thick with a density of 8lbs pcf.It is even dense enough to cut on a table saw.


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## bpape

Actually, if you want to emulate 703, see if you can get some Roxul RHT40.

Bryan


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## F1 fan

bpape said:


> Actually, if you want to emulate 703, see if you can get some Roxul RHT40.
> 
> Bryan


Thanks Bryan for the tip,it should be no problem getting the RHT40.

The Roxul site states it has a density of 3.5lbs pcf.Would the product I mentioned (see link)with a density of 8lbs pcf be even better suited for bass trapping duties or is that too dense? 
http://www.roxul.com/graphics/rx-na...nboard/Synergy_DrainBoard_English_5-12-06.pdf


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## bpape

Depends on how you do it. If you're going to use 4" straddling a corner then the 8lb would be a better option. If you're going thicker or even chunking it, no need to spend the extra money. As you increase thickness, you can slack on the density a bit and still get good performance.

For the same money, I'll take 8" of 4.5lb over 4" of 8lb any day.

Bryan


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## Guest

If you're looking to eliminate unwanted bass at frequencies below 100Hz, you'll need to have some type of material that actually absorbs the acoustic energy. Obviously, right? But typically, fiberglass insulation - even dense 705 FRK mentioned in Winer's article - is acoustically transparent below 100 Hz. So you need another level of function, some type of material or process to swallow up these 10' + energy packed waves.

I've used hanging absorbers in the isolation booth of my studio derived from the formula in 'Acoustics and Psychoacoustics' by Argus. After they were built, I subscribed to Sound on Sound magazine out of the UK and discovered an even handier bass trap built by Paul White, Editor in Chief of SOS. This design is unique in that it's similar to a Helmholtz absorber, yet instead of pegboard, it uses a neoprene type material hung loosely over the rockwool (think, 'rigid insulation') barrier. This hanging sheet is what gobbles up the bottom end, not the rockwool. Between these three features; 1) the airgap between the absorber and the wall, 2) the rockwool, and 3) the hanging sheet of neoprene, you have a very effective wide-spectrum absorber.

If you're looking for a cost-effective design, these traps appear to be just the ticket as they're frequently built and added to the many home and semi-pro recording studios (think, 'poor') that are featured in SOS. If you search the last three or four issues of SOS at www.soundonsound.com there are some plans to build these using 1x4's, burlap and the materials mentioned above.

Best Regards,
TJ


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## basementjack

Fincave, 

Do you have a PC setup that you could use to measure the response of the room before and after the traps? They have some free software at this site called RoomEQWizard. It'd be really neat to see how much of a difference the corner traps made.

I built some tube traps, - I'll try and measure the room without and with the traps this coming week (it might be the weekend) and I'll post a link to the results.


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## Ethan Winer

tjschuhow said:


> fiberglass insulation - even dense 705 FRK mentioned in Winer's article - is acoustically transparent below 100 Hz ... an even handier bass trap built by Paul White, Editor in Chief of SOS. This design is unique in that it's similar to a Helmholtz absorber, yet instead of pegboard, it uses a neoprene type material hung loosely over the rockwool (think, 'rigid insulation') barrier.


Just to clarify, rigid fiberglass is absolutely effective at frequencies much lower than 100 Hz. However, its absorption is improved by the addition of a membrane. I wouldn't charactertise Paul White's bass trap idea as a Helmholtz trap, but it might work better than plain rigid fiberglass.

You can see a comparison of three densities of rigid fiberglass, without and without the FRK facing, in this report:

www.ethanwiner.com/density/density.html

There you will see rigid fiberglass only three inches thick making a small, but very real, improvement even at the room's lowest 42 Hz mode.

--Ethan


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## Fincave

No progress as of yet, just more questions! Went and had a look at one store today and they have rigid rockwool panels that are 100cm X 60cm X 5cm, no mention of density on the packaging and no salesman in sight (no saleslady either). The panels are sold in packs of five though I may be able to get loose ones if I ask nicely. From the above package I would be able to get: 

1) One trap with front being 78cm, sides being 50cm and 60cm and 100cm tall

2) Two traps, front of 60cm and both sides being 42cm and being 100cm tall, the second trap would have a face of 50cm with both sides being 35cm and 100cm tall

3)One trap (oblong) with sides being 60cm X 25cm and being 100cm tall

Of the above options what would be the best, options 1&2 are both triangular in shape and would fit nicely in the corner. Is option 3 being oblong a problem or not, appearance wise it would not bother me! While I was in the shop I happened to notice sacks of loose rockwool, roughly 100cm X 40cm X 30cm and weighing 20kg, these would be the cheapest, easiest and ugliest option though easy to cover in material.

I seem to be getting the hang of REW and will use it to take measurements before and after treatments, as soon as I decide on what traps to build.

Once again any and all input will be most appreciated. Thank you in advance.


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## F1 fan

bpape said:


> Depends on how you do it. If you're going to use 4" straddling a corner then the 8lb would be a better option. If you're going thicker or even chunking it, no need to spend the extra money. As you increase thickness, you can slack on the density a bit and still get good performance.
> 
> For the same money, I'll take 8" of 4.5lb over 4" of 8lb any day.
> 
> Bryan


Thanks , I will use the RHT40 and shoot for a 8-12"thickness.


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## bpape

TJ.

Yes - those can work nicely - but they'll only work for maybe a couple of octaves. That may not be what is desired. And, I can assure you that if you use 6-8" of even 703, you'll get significant absorbtion well below 100Hz. Even 6" of 703/705 straddling a corner will be pretty effective down to the low 60's/high 50's.

Bryan


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## Guest

Here's a link that will give you more things to think about for your project. As if that's going to help! http://www.sae.edu/startpage/support.php Maybe you've already checked SAE out, but go to the 'Free Reference Material' center panel and click on '1. Audio Studies.'

You'll find clear answers related to traps, absorbers, layout, design, materials, coefficients of absorption, acoustic transparency, etc. There's even a Helmholtz Resonator Calculator - my personal favorite.

If you get information overload, I won't fault you if you chuck all the data and stuff a couple bundles of old bluejeans in the corners of the room. It worked in the '60s, right?

Regards,
TJ


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## Fincave

Great, more reading! Seem to be spending more time reading than listening to music. Seriously, thank you for the link, will have a more in depth look soon. May well end up changing my plans yet again or even just throw bundles of jeans in the corner, quick and easy!


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## Fincave

Small progress report. Have purchased some rockwool panels and have cut them to size. Need to buy some wood for frames and then assemble them. Couple of bad pics included.


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## basementjack

Finclave -that looks like a lot of work!

What did you use to cut them?


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## Fincave

Cutting them did take some time. I would have wanted panels that were thicker but the thickest that were available were 50mm, there are 56 pieces in total. When I asked what would be the best way to cut the panels I was told that they have a special knife for the job that resembles a bread knife, being a chef with a good collection of knives I decided to use my oldest and worst bread knife, worked a charm though the knife is not quite the same anymore!


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## Fincave

Short progress report. Have two traps basically ready. Decided against making a wooden frame as the other half said it would be easy to just cover the traps in fabric. Purchased fabric and came to the conclusion that sewing triangular bags is not the easiest ting in the world. My girlfriend made the first one and then decided that maybe need to re-think the covering of the traps, me being stubborn decided sewing can not be that hard, can it? I gave it a go and well it is pretty difficult though I managed to not break the machine or sew my hand to the material or anything like that. Have now placed the cut panels into the two bags and they are having the final seam put in by hand. Should get the last two bags sewn up today or tomorrow morning and will then be able to first do a listening test to see if the boominess has been reduced, also have a look if thee are any changes in the subs response. Here are a couple of not very good pics.


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## Sonnie

Nice work Fincave... :T


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## JCD

Not bad! And yeah, I can see how sewing things up could be a huge pain.

Since I'm lazy and don't want to read through the thread again, where are you going to put the four traps you're making? Obviously in the corners, but one in each corner? Or stacking two in the front corners?

And I can't wait to see how they help your room.

JCD


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## Fincave

At first I plan on putting one trap in each corner, I have two traps that are 60 cm tall for the rear corners and two that are 80 cm for the front of the room. Depending on the listening results I may end up stacking them and make another two that would be 140 cm tall.


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## brucek

> Depending on the listening results


You haven't touched on your testing methods in this thread too much. 

Will you be using REW to do a before and after using response and waterfall? 

What results are you hoping for?

brucek


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## Fincave

brucek said:


> You haven't touched on your testing methods in this thread too much.
> 
> Will you be using REW to do a before and after using response and waterfall?
> 
> What results are you hoping for?
> 
> brucek


I will be relying mostly on my ears, not the most scientific method, I know! I will also use REW to have a look at the subs response before and after. I am using a BFD and have achieved a response that I am happy with, not perfect but good enough for my 'tin ear'. The main reason for builiding the traps was to get rid of some boominess I have when listening to certain music, Nick Cave and the Bad Seeds in particular, the boominess could well be in the mixing? Boomy bass may be a slight exaggeration as the problem is definitely is not severe by any means. Am not sure if the traps will make any difference, they may only make a difference that only I can 'hear', or may only serve as conversation pieces for visitors.

Probably won't use the waterfall as I do not really understand what I am looking at when looking at the results?


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## brucek

> Probably won't use the waterfall as I do not really understand what I am looking at when looking at the results?


But isn't the waterfall plot the exact tool you want to use to evaluate the effectiveness of traps?

See this very interesting acticle on the subject of EQualization using a BFD versus using Traps, where they use waterfalls to test the results (with comments by member Ethan Winer). Perhaps he could comment further here.

Wayne P. also talks about waterfalls here.

With great respect to your ears, I think with all the nice work you're putting into this project, it would be a nice idea to do some REW testing, so we can all evaluate along with you. 

brucek


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## Fincave

No need to respect my ears, they are not that great!:R Thanks for the links, had a look at both, must say that as it is a little late here Ethan Winer's stuff did not get the attention it deserved. Wayne P's post in the second link does make some kind of sense and probably will make more sense after the second reading. As soon as I get the next two traps ready I will take some measurements using REW, will also do some waterfall plots after doing some more reading. Using REW is still a bit intimidating but am getting the hang of it!


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## brucek

Here's another thread on waterfalls where I show my complete ignorance on the subject and where I learned a few things...... It seems quite important to set up the x and y axis and time. Waterfall is simply a response in slices of time after the main response to show how it decays....

brucek


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## Guest

*Fincave*

Hay mate that is a doodle thanks, I’ll check into the pricing for the materials, I doubt it will cost much and the glue as well to stick the separate pieces together.

If I didn’t see it written mate, how many slabs of rockwool was needed to create the triangular shapes?


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## Fincave

Brucek: Thanks for the link again, will look into it and post results as soon as I have some.

JBL-4645: I did not even glue the separate pieces together, just placed then into the triangular shaped bag of which the rear seam was left open, the final triangle had to be cut into two and then the seam is done by hand. The bag is cut pretty much to exact size and so it is quite a tight fit. I purchased one packet of panels as the store where I bought them will not sell loose panels, some stores will though. Panels were 120cm by 60cm, cut into half giving 60cm by 60cm, these were then cut into four triangles giving a size of 60cm by 42,5cm by 42,5cm. I used seven 50mm panels and got eight pieces from each panel for a total of 56 triangles, am using 16 triangles for each trap that I am placing in the front corners and 12 triangles for the rear traps, giving a height of 80cm and 60 cm respectively. It would have been handy if the rockwoll slabs were thicker as then the cutting would have been less, the ones I am using can be had as thick as 130mm but were not in stock and would have cost considerably ore as transport costs wuld have been added. Total price for panels was 45€ and about 14€ for the black sheet material, not expensive at all, especially if they work.


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## Guest

*Fincave*

Gotcha, thanks mate, did you spray paint them, not sure but from the look of the image it looks as if they where coloured, could have been the light on the camera?

Estimated cost for argument sakes?

PS. £45.00 UK pounds?


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## Fincave

Just covered in material, no spray paint. 60€ is about £40


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## Guest

*Fincave*

Hay mate, I’m going to put together a few Bob, that means money and get some (ridged rockwool) fabric makes sense! 

I take it you have to glue the sides of it to stick to the walls, (liquid nails) you know that stuff that keeps it from falling off the wall!?

Thanks mate that’s all the information I need, thank you.:T


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## Ethan Winer

brucek said:


> Here's another thread on waterfalls where I show my complete ignorance on the subject and where I learned a few things...... It seems quite important to set up the x and y axis and time. Waterfall is simply a response in slices of time after the main response to show how it decays....


Indeed, waterfall plots are useful because they show ringing as well as the raw low frequency response. Excess ringing is just as damaging as peaks and nulls, and it's the main cause of what's euphemistically known as "one note bass," where every bass note sounds more or less the same regardless of its pitch. Besides the links already provided, this article on the RealTraps site explains how I use the ETF software, which is similar in function to REW:

www.realtraps.com/art_etf.htm

--Ethan


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## basementjack

In addition to using something for your before/after measurements (REW/ETF/Etc)- it might also be neat to use some real time Analyzer software - feeding it with the output of your preamp - I've seen posts where someone does this to watch the 'source' so they can visually confirm bass heavy/weak recordings.

Are you a PC or Mac user?


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## Fincave

basementjack said:


> In addition to using something for your before/after measurements (REW/ETF/Etc)- it might also be neat to use some real time Analyzer software - feeding it with the output of your preamp - I've seen posts where someone does this to watch the 'source' so they can visually confirm bass heavy/weak recordings.
> 
> Are you a PC or Mac user?


PC user, though must admit that often enough it seems as though the pc is using me! Using REW has been trying enough for me.


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## bpape

Hang in there - you'll get it. It's worth the effort.

As for the RTA, it makes your life SO much easier when trying to find just the right place for seating/subs.

Bryan


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## JCD

So, have you finished your project yet?

JCD


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## Fincave

The traps are ready and I have purchased a new external soundcard. Unfortunately am too busy with work and a hundred other things that need taking care of and so have had no time to even listen to a few songs to see if I hear a difference. With a lot of luck I may have a couple of days off soon and may find the time to do some measurements. Will post all results here.


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## Fincave

Finally have some measurements. Played around with REW this morning and set some filters on the BFD, the response is ok and the filters were set with the traps in room. I then removed the traps and took some more measurements leaving the filters engaged. I realsie that I should have also taken measurements without any filters and with and without the traps, something to do at a later date. Here are the results, the first two attachments are the filtered response withe the traps, the next two are without the traps.

Traps
















No Traps


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## kermyb123

Looks like very little change under 80hz - to me...


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