# Room Treatment round two



## fredk (May 14, 2008)

For those that may want to read it, round one is here.

Sketchup of Room:








Recap:
The main area of my apartment is 20x20 with the kitchen set in the middle of one wall. The 'outside' walls, ceiling and floor are poured concrete, the kitchen walls are probably plaster on metal lathe. Initially I looked at my space as 20x11 (main livingroom) with extensions.

At the main seating positions, I saw a nasty peak at 52Hz and nulls at 42Hz and 76Hz. I build one set of traps 4'x2'x6" and noted significant improvement at 42Hz and a narrowing of the 76Hz null.

It was not until near the end of round one that I realized I was basically dealing with a square concrete room. The monster peak at 52Hz made sense as this matched with axial and tangential modes of 20'. This made me curious to know what a wider set of measurements would show, hence round 2.

So, here is a set of measurements taken at the points in the room where you see circles. The one at the very front of the room behind the display and the one in the dining area are not in this set.









Just look at the consistancy of the peak at 52.5Hz through all but one of the measurements.

This leads me to one question. Given that this peak seems to be consistant over the entire main listening area, and given that it is addative (a peak), does this make it an ideal candidate for the dreaded equalization?

In an odd twist of fate, the best measurement came from the dining area where 22-40Hz is almost flat. That explains why music sounds so good when I am sitting at the table for dinner. :bigsmile:


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## thewire (Jun 28, 2007)

That isn't brought up to often so let me see what I can recall. Some things that come to my mind are:

Difussers (front of the room?) and a dead front wall.

Ceiling Helmholtz Resonators (lots of boxes aimed at a target frequency)

Thick panels hung envenly around the room or maybe some tube trapping would be better.

Changing the height of the floor. (sloped)

Adding splayed walls.

I realize some of these are all somewhat impractical but it's the best I can think of. :huh:


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## bpape (Sep 14, 2006)

To answer your question - yes. It's consistent so it will be effective for all seats - AND - it's purely in the subwoofer range so it's not impacting sound quality in the mains. 

All of that said, ignore ANY measurement that is not where a seat is - it's totally irrelevant. Also, make sure you measure where the ear will be height wise. 

Bryan


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## fredk (May 14, 2008)

Thanks Bryan. It looks like my next acoustic investment should be a Feedback Destroyer. It should clean up a large part of the boomieness I hear.


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## bpape (Sep 14, 2006)

Just understand that EQ will only deal with the frequency response aspect. It won't help any to deal with excessive decay times and ringing in the room - nor will it deal with nulls in response. Treatments will. Usually the best option is to do things in the following order:

- placement
- treatment
- EQ

Bryan


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## fredk (May 14, 2008)

Yup, I understand. No amount of treatment is going to remove that peak. Placement just seems to move the peak in frequency. Surprisingly, ringing is not as bad as I would have expected.

The plan is to eqaulize that peak to see what it gets me, and then continue on with treatments. I still need to work on the upper end as well.


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## bpape (Sep 14, 2006)

Most likely, since the peak is pretty much everwhere in the room, it's either:

- height related

OR

- boundary response issue due to sub placement

Bryan


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## fredk (May 14, 2008)

?

Given that a mode calculator gives axial and tangential modes at 56Hz for a room of 20' I would have thought this peak more likely relates to that length/width. Particularly since in reality my system is in a square room.

I would have thought that the 71-76Hz null I see around the room is related to height. Again, it matches with a predicted mode at 71Hz.

Edit: It probably at least has a boundry component as the only two places I can put it at the moment are in a corner or along the one wall. If I remember I will move the sub out from the wall and do some measurements just to see what happens.

Either way, it matters not. It needs fixing.


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## bpape (Sep 14, 2006)

If it was purely the combination of axial and tangential, it would change or disappear in different places in the room which vary with length. Your measurements indicate that it doesn't - except for one trace that just has it reduced in intensity (likely a null overlaying it). 

You're right though, it needs fixing. 

Bryan


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## fredk (May 14, 2008)

Good point. I was expecting the null to dissapear or shift as I moved to the narrow part of the room. This acoustics stuff is an odd beast.


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## fredk (May 14, 2008)

Woohoooo! Picked up a used BFD 1100 today. Now all I need is some cables and I can make those REW graphs do all kinds of funky things. :bigsmile:


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## fredk (May 14, 2008)

WOHOOOOOOO!!!!

It worked! Exactly the way REW predicted! Exactly!

Well, colour me impressed. I defined the filters in REW based on my last set of extensive measurements. I used the auto-generate tools in REW on my main seating position. REW gives me a set of numbers to enter into the DSP1100. I added a filter for the worst peak at 56.2 Hz.

I then did the calibration stuff with REW and did two measurements: one with the filter, one without. It took a 14db cut to pull that peak down so I do not know what effect that will have on the overall quality of sound.









I then loaded the filters I had created on the without filters graph to compare the actual result to that predicted by the filter and I'll be if it didn't exactly match the predicted filter result. Talk about dead simple.

I also did a quick check to see how the filters would affect the other measured positions, and for the most part, I think it will improve sound in almost every measured position.

I'm off to listen to a Balrog have a dissagreement with Gandalf to see what the difference is with the filter on and off.


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## fredk (May 14, 2008)

It has been an interesting evening. I added 3 more filters tonight and did some listeining. The filters were at 23, 29 and 34 Hz. I wanted to see what impact a broad range of filters together would have.

For music, the difference was very, very subtle, and only for stuff with low low bass. Listening very carefully to several tracks from ELP's debut album, I could hear a slight difference in the kick drum; like someone toned it down a little. The same could be said for some pipe organ stuff. I don't think it was super low though.

One interesting thing, with the EQ on, I think I noticed the hole at 40-45 Hz a little more as the organ notes moved through that range, you could feel the notes weekening and strengthening again.

Most of the bass boom is still there. Looking at waterfalls, the shape of the ridge at 56Hz is exactly the same, just reduced.

I put on LOTR the Cave troll and Balrog scenes. Here the difference was more noticable but still subtle. There was a noticable reduction in boom in some scenes and some of the effects were more defined, like those when parts of the bridge collapse.

Looking at the output LEDs on the BFD there is WAY more low frequency output from LFE than music.

So, the EQ did not have nearly as much effect as I had hoped it might, despite dropping the 56Hz, frequency by 14db. Most interesting.


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## bpape (Sep 14, 2006)

All a matter of frequency response adjustments vs. getting decay times right.

EQ has it's place - but it's the last adjustment to make behind proper positioning of seating, subs, and speakers - and bringing the bass decay time into line

Bryan


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## fredk (May 14, 2008)

So it seems. I also wonder if some of the boom that I atributed to 56Hz may well be higher than I thought(bass guitar).

We see so much focus on the stuff below 30Hz on these forums, that it is easy to forget that bass extends up much higher than that.

I am beginning to see a patern where any given change is quite subtle, but [hopefully] the sum of multiple changes will be strikingly different.

I believe that I had one corner position where the 40-45Hz hole was eliminated, but the 56Hz peak was shifted down quite a bit. If that peak is as consistant as the 56Hz one, I can EQ it as well. I was originally worried that I would not be able to effectively treat it with bass traps because it is so low.

After that I will go back to additional bass traps along the front wall.


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## fredk (May 14, 2008)

As usual it seems to take a few days for things to sink in.

So, if I understand correctly, the boom I am hearing could still be from the 52Hz region. The reduction in ringing from 700 to 500 ms. due to the 14db reduction in volume is not enough for me to perceive any reduciton in boom.

Ah well, onward. My next step is to try the sub in my rear corner where the 42Hz null was eliminated last time I measured. Unfortunately I have no way to do an A/B comparison of the two positions for what I would expect to be a subtle differences.


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## bpape (Sep 14, 2006)

What most people describe as 'boom' is considerably higher than 25 Hz.

Also, reducing the amplitude of a frequency in relation to the other frequencies has no impact on decay time in and of itself. That doesn't mean that proper treatment can't be both. I just wanted to make sure that you understand that they're not necessarily always going to go together.

Bryan


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## fredk (May 14, 2008)

When I talk about boom, it is the sound of a specific note or set of notes and how they sound in relation to others close to them in frequency. To me, it has nothing to do with a specific frequency range. The way I would describe it is that, in addition to the difference in sound, I can feel addtional preasure on my ears for certain notes.

It could still be that what i am calling boom matches your description and is coming from higher up. If this is the case, then additional broadband traps should reduce this.

Once I have moved the sub to play with it a bit in the corner, I will get back to additional absorbtion to see what that does for me.

Where do decay times need to be in order to perceive a meaningful reduction in boom?



> Also, reducing the amplitude of a frequency in relation to the other frequencies has no impact on decay time in and of itself.


Agreed. I was only commenting that, starting from a lower amplitude, you get to zero (or the 45db floor on the graphs) sooner. In my case that was 45db ~200ms sooner. It looks like a reduction on waterfalls, but is not meaningful in how those frequencies sound. I think this is where the confusion arises that EQ can reduce ringing.


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## bpape (Sep 14, 2006)

What you're describing as boom sounds to me like modal peaks where 1 or 2 notes are considerably louder than other surrounding tones. Excessive decay times only exacerbate the issue. Having the 20x20 dimensional issue makes the peaks even more intense

I'd like to see the decay time from 100Hz down to be no more than 400ms

Bryan


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## fredk (May 14, 2008)

> I'd like to see the decay time from 100Hz down to be no more than 400ms


The decay time at 52Hz is just over 500ms and for the peaks as 34 and 24 it is above that. Hmmm. So I am close on my largest peak and the one that is in the range of most bass. I think I should take a few measurements with my mains included to see what is happening up around 80-150Hz.


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## fredk (May 14, 2008)

I think I could measure in my bathroom or bedroom closet and I would find a peak at 52 Hz.

Sub in the center of the room, ear hight (red) vs. right wall:









Main seating position at various heights from seat level to 5':









1.5 feet in front of the main seating position from 1' off the floor to 5':









Maybe an ancient audioholic placed a curse on the ground my apartment building was erected on and I will forever be haunted by a 52Hz. peak. I dunno. :coocoo:

I am going to try placing my two bass traps on the seating area and measuring to see what happens. It looks like the whole area from about 58Hz up to 90Hz is room height related.

Sigh, I keep looking for hints on where I should put my next set of bass traps to try to effect that darned 52Hz peak. Maybe I should order a container load of 3lb. board and just stuff everything but the area between the main seat and the display. :joke: :dumbcrazy:


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## thewire (Jun 28, 2007)

I have a 20 X 20 garage I could try and see if I could improve since my HT is rather out of commission (projector went out and bringing in a tv) until I get some more treatments other than listening to music. There is a drop ceiling with no insualtion above it, some various shelving against a wall with a window, a door in the corner, some steps off the side of the right middle of the wall, and another window on the opposite side. Besides some traps I could pretty much take a large amount of insulation in there from my ceiling also and see what I could come up if you like.


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## bpape (Sep 14, 2006)

If you're convinced it's all height related, (I'm not - especially based on the graph where you measured from 1' to 5' off the floor and the peak was there for all of them) - then put a good absorber right over your head.

Can we get a rough sketch of how you're actually set up now and what the height of the room is?

Bryan


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## fredk (May 14, 2008)

Bryan. I don't particularly think its height related, but in post #7 this guy suggested, based on the graphs in post #1 that he thought the peak might be either height or boundry related. 

I decided to explore those two options with the last set of measurements.

OK, Picture recap:









The blue dots represent the 12 measured points represented in my first post. The red x is where I placed the sub in the middle of the room to eliminate boundry effects. The two height related measurements were in the prime seating position and at the blue dot just forward of that position.

Not shown in the picture is a set of traps in the upper left corner measuring 4'x8'x6".

Room measurements are 22' (front to back) x 20' wide x8' high. The section where the kitchen is is 11' wide.

All my REW measurements show a 52Hz peak no matter where in 3D space I have measured. I am still convinced that it is based on axial modes based on length and width further reinforced by a tangential mode at 51.xHz.

This leaves me wondering if there is even a possibility of treating it. Even if I try, where do I start? I could see myself putting a lot of $ into treatment without much effect.

By the way Bryan. I geatly appreciate your help so far. I know you are busy and have lots of paying customers to take care of as well.

P.S. Here is a waterfall to give some idea of where ringing shows up:


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## fredk (May 14, 2008)

Thanks for the offer Steven. Is that garage concrete all the way around? It would be interesting to see a second set of measurements of a similar room, but thats a lot of work for you to haul equipment up to your garage.

If there is one thing that can be learned from all my measuring is that square concrete rooms are to be avoided at all costs!!

Maybe I should save up all the pennies I am tempted to spend on treatments and put it into my house fund. Buying a better room seems like the best option right now. :devil:


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## bpape (Sep 14, 2006)

Well, it can't be length related or you'd be seeing it when you move forward and back - but you don't. What we need to do is find a place to put the sub that will deliberately create a dip at around 50Hz. Lemme dig through some tools that I have when I have time and I'll see what I can do.

Bryan


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## thewire (Jun 28, 2007)

fredk said:


> Thanks for the offer Steven. Is that garage concrete all the way around? It would be interesting to see a second set of measurements of a similar room, but thats a lot of work for you to haul equipment up to your garage.


Hauling one of my subs to the garage isn't much trouble really. The garage isn't concrete except for the floor. My HT has the concrete bellow. Taking my 100+ pound television down two flights of stairs and taking the 100+ pound projector off the ceiling is going to much worse than that. I have taken my sub up to my room before, and done some experementing with it in the garage to check soundproofing in my bedroom. Your right however it would be alot of work, and I should probobly save my energy for the HT.


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## fredk (May 14, 2008)

Bryan. It just occured to me that I may be doing something counter-productive during the measuring process. In REW there is a check levels button in the measurment window that you can use to make sure that your measurement level is in the appropriate range. I have been using this to 'level match' each measurement.

So, if the 'check measurement' process told me my input level was at -18db for the first measurement, I would adjust the volume for each subsequent measurement so that the level check is at the same -18db level. I typically see a 2-4db difference between each measurement. Perhaps in doing this I am distorting what the graphs should be showing??


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## bpape (Sep 14, 2006)

I'd keep everything as close as possible with no adjustments. If there is 4db of difference between one measurement and another, something else is going on.

Bryan


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## fredk (May 14, 2008)

I finally got around to a measurement set with traps above the mic.

The mic was in the main seating position about 3 feet above the floor. The traps were only a couple of inches over the mic, but that was the only practical way to set things up.

The red is a baseline without traps, green is with a 4'x4' x6" area covered, blue is 2'x4'x12".









As expected, there was no effect on the 52Hz peak. Surprisingly it had more effect everywhere else than any other position I have tried the traps in. Go figure.

Bryan. You didn't happen to dig up those tools did you?


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## bpape (Sep 14, 2006)

Sorry - been absolutely buried and it's on a PC I've not used for a while. Hope it still works as I'm not sure I can find the install media.

Bryan


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## fredk (May 14, 2008)

In this economy, busy is a good thing. 

Is this a software package I can get hold of somewhere at a reasonable price?

At this point I am uncertain how to proceed. Maybe I should just move on to treatment for the mids and highs for now.


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## bpape (Sep 14, 2006)

This is probably the best commercial product that's somewhat reasonable

http://www.cara.de/ENU/index.html

I have a couple of other things that are older and need to upgrade to this anyway. 

Bryan


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## fredk (May 14, 2008)

I checked out the website last night. The software looks pretty interesting. So, you are suggesting something to model my room instead of something more complex like RplusD to measure it?


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## bpape (Sep 14, 2006)

Cara will help you identify best seating and speaker location given the room so you're starting off in a good position with the fewest anomolies.

You'll still need to treat (and potentially measure) the room so you can get the reflections and decay times under control as well as identifying more specific issues that need to be addressed. Honestly, the software here at the Shack (Room EQ Wizard) does an excellent job and it's free.


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