Treating my small room with Soffit bass traps and diffusors.

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danvprod

Working on finally treating my playback room. I picked up four of the soffit bass traps to start. Speakers are open baffle GR Research Super Vs. I don't quite have enough ceiling to stack two traps on my right wall (I'm in the attic). Right now I have two stack on the left and one on the right of the speakers.

I'm wondering if it makes sense to hang the one on the right mid-wall, or order a custom length trap and go as high as I can? I also have the forth one positioned directly behind my listening chair. I have an old room model that I need to modify, but you can see the plan view of my room.

Also looking for guidance on the next set of treatments. I am thinking of adding absorption on the first reflections points (sidewalls) and diffusion directly behind the speakers (possibly swapping out the curtains on my window for a window-wide diffusor. Ideas/help welcomed!

I should say that the bass traps have helped the SQ in my room immeasurably already. Very impressed with how big a lever these are. The difference is not subtle in the slightest. Bass is no longer boomy. Some of the structure-born bass transmission is gone, everything just sounds better with a more stable center image. Likely the single biggest improvement I've made in my system in a while.





« Last Edit: 1 May 2017, 01:21 pm by danvprod »

danvprod

Here is a better room model showing what I am dealing with. Note, as shown in the picture above, I have a angle on the right side of the room, which is a challenge. I plan on getting two more soffit bass traps, one custom size (35"), and another full length to go behind my listening chair.

So I need to figure out:
1) What to do with the window? I have a curtain on there now, but I'd like to get diffusors covering the glass.
2) What to do with first reflection points? I am thinking some of the 242 acoustic panels with scatter plates.
3) What to do with the back wall? I am kind of limited because of the doors. I have a pair of closet doors and also the door to the room.
4) Do I need any more diffusion?



danvprod

I should add that I am able to make and post impulse response measurements if anyone is interested.

poseidonsvoice

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I should add that I am able to make and post impulse response measurements if anyone is interested.

Please go right ahead  :thumb:

Best,
Anand.

JWL.GIK

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Hey there.... nice setup for sure! I like the way you have the room arranged, that's exactly what I'd do if I was in that room. If you haven't already, it might help to experiment some with speaker placement to get the best possible bass response via SBIR, while maintaining your soundstage and imaging. The bass traps are also helping, of course.

Regarding placement for your bass traps, if it were me, because the room isn't a perfect rectangle (attic ceiling), I'd do this listening test to find the bass hot spots/pressure zones in the room, and put the bass traps in those locations if possible:
http://gikacoustics.com/video-testing-corner-bass-trap-placement/

Regarding the next set of treatments, I'd go absorption at reflection points on the side walls and ceiling, as thick as possible (244s are great, Monsters even better but thicker, 242s work if space or budget is limited), and possibly more bass trapping to make things even better on that front. You can use scatter plates if you wish, but reflection points are probably the one place in most rooms where I want full-on absorption.

I wouldn't worry too much about the window. The speakers are firing away from it, so other areas in the room will be more important to treat. You could put diffusors over them, but if it were me I'd start with treating the rear wall and the reflection points and see where you are.

The doors on the rear wall may limit us a bit.... ideally we want bass trapping/thick absorption, as well as diffusion back there. Perhaps you can mount panels directly to the door(s), or use freestanding panels or stands for those treatments? That way they can be in place while listening or moved out of the way as needed. I'd consider the thicker Alpha Panels here, the Alpha 6As are very hard to beat for a rear wall since they provide both bass trapping/absorption and diffusion.

That should be enough to get you started.... as always you can contact us and one of our reps will further guide you to make sure you get the right products for your room and your budget.  :thumb:


danvprod

Thanks very much for the thoughts and assessment here. A couple of thoughts:

1) I read about your thoughts on SBIR re: placement with the back wall and pushing the boundary interactions up until past the Schroeder frequency, which is easier to treat with absorption. The issue here is that my GR Research speakers are open baffle, so they need to be pulled out at least 3' from the back wall. Also, I think being open baffle the issue of diffusion on the back wall is higher up on my priority list, at least based on information from Danny Ritchie (GR) and others.

2) I will try do some measurements in the corners and see if the pressure spots are where I've placed the traps. I have noticed that the double-stacked traps on the left wall really knock down the audible flutter echo present between the longer wall with the door.

3) Agree about the first reflection points. The monsters look really nice. 2'x4' panels would work here, I suspect. Perhaps I could get away with two.

4) The Alpha 6As look really nice as well, and I like the look of the diffusors.

Are there any measurements that would be the most productive to take at this point?

JWL.GIK

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understood! There are a lot of different speaker designs out there, and not all are compatible with the close-to-the-wall strategy. So just be aware of SBIR and what it is doing, you can then mitigate the effects with other strategies (bass trapping).

I agree that diffusion on the wall behind the speakers (I call this the front wall, because it's the wall we face when listening) can help, particularly so with speakers like yours.

I like the way you are thinking here in general.

Yes, if you want to do some testing, it can be quite edifying. I recommend using Room EQ Wizard software with a measurement mic. There is an intro to this sort of testing here:
http://gikacoustics.com/room-eq-wizard-tutorial/

I'm mostly interested in the bass response (under 400Hz) with the waterfall graph (so you can see resonances), and also the ETC response, about which you can find details here:
http://www.gikacoustics.com/unpacking-etc-time-domain-measurements-early-reflections/

Note that if this sort of testing seems overwhelming, it's not strictly necessary.... it will give you a ton of info about your room, but we kind of already know the solution to the problems it will reveal. Some people enjoy this sort of thing; if that's you then test away and have fun learning about your room. If this seems like more of a chore then don't worry about it.  :thumb:

danvprod

I made measurements in each of the corners of my room C1-C5 with the left speaker alone and with the right speaker alone. I also made a measurement at the listening position. First set is without any traps in the room and the second set is with traps in the position in the picture above.
Waterfall (Top before traps, bottom after traps).  This is left speaker -> listening position.

ETC (sorry, top after, bottom before) This is left speaker -> listening position:

FFT (Left and Right -> Listening position before and after traps, bigger nulls are before):

danvprod

This is the after left and right speakers -> listening position. Interesting that the left bass array seems to be a few dB down. The XO frequency is set at 80 Hz.

poseidonsvoice

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danvprod,

Let's settle your LF issues first. Like JWL.GIK said just concentrating on 20Hz up to the Schroeder frequency or a little more like 300-400Hz.

Can you post a graph with both speakers playing at the same time (not individual speakers), use no smoothing or 1/48 octave, and make sure your vertical scale is about 5 dB or less? That will show more detail that is relevant.

It looks like one channel's bass array may compensate for the other looking at your previous graph which can be a good thing.

After that, we can look at the waterfalls.

Best,
Anand.

danvprod

Thanks, Anand.
As requested. Both speakers playing at the same time 20 Hz - 300 Hz w/ vertical scale of 5 dB. 1/48 octave smoothing.



danvprod

Sorry that my graphs are hard to read -- I reformatted and plotted again using a difference piece of software, which gives me a lot more control vs. REW for presentation.

These were made this morning after tweaking the crossover frequency and gain on the right speaker. I turned up the gain a bit and also increase the crossover frequency to about 100 Hz.



JWL.GIK

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Looks like you are on the right track. Your test results look pretty typical for a small room. From here you have a few options:

1. further experiment with placement of what you already have in the room. Here I mean moving the listening position, speakers, and bass traps you have now. This can help but given the amount of tweakage you've already done, I think improvements here will be incremental.

2. Add more bass traps. This is the ticket to making bigger improvements. The ones you have are already clearly helping. More will be even better.  :thumb:

Bendingwave

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I have wood laminate floors so I put the bass/isolation pads directly under my speakers and it worked for me as it had a pretty discernible change in sound. It looks like you have carpet so I am not sure how much change in sound will occur but you can give it a try and see if it makes a difference for you.

danvprod

Added four Skylines I was able to find locally behind the speakers to help aid in diffusing the back wave of the open baffle Super Vs. Might consider 1Ds in the future, but these were local, available, and within my budget.



I've been doing some further research on active bass trapping. I found Clayton's black hole generator (no longer made) and the Bag End e-trap. I am considering that to work in tandem with the passive traps I have now. I still am planning on getting the custom height soffit bass trap to add to the right corner behind my right speaker.

I think the black hole generator and/or the e-trap would be effective in taming the axial model associated with the short wall (width) of my room. It's ~ 39.3 Hz according to the amroc room mode calc. I know the soffits are not going to be able to deal with something down that low, and I'm thinking that EQ won't help either (although I certainly can try with the PEQ on the A370 amps of my GRs.
 

danvprod

Measurements at the listening position with the Skyline diffusors on the wall. I don't expect them to change anything in the low frequency measurements because they are effective > 1.7 kHz given by well depth max.

Blue is left, red is right, black is both.



danvprod

I am impressed at the effectiveness of even just the four soffit bass traps. Here is a before and after waterfall:
Before:

After:


To my eyes I see a drastic reduction in the modal ringing. It's still there in the "after", but is out of the way much quicker. I see the same thing in the EDT in the 63 Hz octave band (going from .61 -> .3).

I still need more trapping (and maybe some active trapping to tame the rest of the 40 Hz axial mode), but I think I am well on my way here.

drummermitchell

perhaps some GIK Scopus tuned traps to target those specific frequencies.
Perhaps I'm old school but even using an Equalizer studios,sound guys only use them if absolutely necessary.
For me any thing electronic to fix rooms for me is a last resort.

JWL.GIK

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Definitely they are doing their thing.  :thumb:

I agree that I would do everything you can acoustically first, at which point you may realize you don't need any sort of electronic correction. If you do, I would use it only to bring down any remaining stubborn peaks by a few dB. I would never use EQ to try to raise a null, for various reasons.

danvprod

Added a Spatial Black Hole Generator to help with the low bass modal ringing to compliment the soffit bass traps. I positioned this on my back wall to deal with the axial mode for the room's width.


This is at the listening position, where a reduction of mode's peak amplitude is reduce by nearly 3 dB and also the early decay time is reduced by quite a bit.