# Room Acoustics Opinions



## t6902wf (Nov 14, 2008)

I seem to be blessed with good room acoustics, I think. The system sounds good to me but I have not been in many home theaters. I can not hear it during a movie but I can hear a flutter echo if I clap.

The room is 16 x 13 with an 8.5 foot drop ceiling. There is an 8" riser in the back.
I have the walls treated in a 1" fiberglass with an extensive wood gridwork (see photos). Behind the rear seats the two center panels are what the fabricator described as diffuse panels. They are 1/4" of fiberglass with 1/4" pegboard backed by 1/2" fiberglass.
Above the drop ceiling I have 12 x 24 batt fiberglass around the entire perimeter , I read it acts as a bass trap so I thought I would give it a try. The center 4' (total of 6 feet) in front of the screen also has 12" x 24" batts, I had extra so I placed it there.

In the front corners there are 2 x 4 drywall bump outs, they were done by the builder. They are hollow and are not sealed above the drop ceiling (see the photo) I am beginning to suspect they act as a bass trap. I was also considering blowing cellulose into the hollow bump outs. But I might be better leaving well enough alone.

Here are two photos of the front and the back of the room.

















Here is a graph of the bass without EQ, I use Audyssey as my EQ.









Here is a graph of the room with Audyssey on and Dynamic Eq on which is how I watch movies.









Here is a waterfall of the room










Is this good or do I need to work on something? I was considering getting the new SVS-EQ1 for bass but I am not sure what it would do for me. I might get it measure and listen to the results and return it if it has no significant positive effect.
Any comments or suggestions welcome.

Thanks in advance for your help.

Bill


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## bpape (Sep 14, 2006)

I'd fill the bumpouts.

I'd also be suspect of the measurements as you have a rising response all the way down to 10Hz. The ceiling insulation is helping with bass taming.

EQ - not sure it's going to buy you a lot. You do need additional bass control in the room though as is evidenced by the waterfall plots

Bryan


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## t6902wf (Nov 14, 2008)

bpape said:


> I'd fill the bumpouts.
> 
> I'd also be suspect of the measurements as you have a rising response all the way down to 10Hz. The ceiling insulation is helping with bass taming.
> 
> ...


_Posted via Mobile Device_

Bryan, will the bass go through the 1" through the drywall and reflect back into the room?
If that is true filling the corner bump outs should help. It will be interesting to do before and after measurements. in any event.


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## Prof. (Oct 20, 2006)

Is that flooring a hard surface?


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## t6902wf (Nov 14, 2008)

Prof. said:


> Is that flooring a hard surface?


Under the carpet is cement. The back row is 2x8's with 3/4 plywood. It is hollow no insulation.
_Posted via Mobile Device_


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## Prof. (Oct 20, 2006)

Ah..It looked like you had some sort of floor tiles....Interesting carpet pattern..
Your riser should really be filled with insulation..That might help some with the clap echo problem..


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## t6902wf (Nov 14, 2008)

I am afraid that ship has sailed. I am not tearing up the carpet and plywood. I am surprised that that floor would add to it. I thought it was the ceiling tile. They are very hard.
_Posted via Mobile Device_


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## Prof. (Oct 20, 2006)

Any large hard surface area can contribute to echo..

*Above the drop ceiling I have 12 x 24 batt fiberglass around the entire perimeter*

If you only have these batts around the perimeter, then I would suggest adding more batts to the overall ceiling area will help to reduce echo..


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## thewire (Jun 28, 2007)

If you were to use Quiet Batt above the ceiling you would not need to worry about the fiberglass making a mess as it is up there with particles, being itchy, etc. It's actually very light. I use them laying directly on my tiles in the front of the room, and may eventually get more someday for the back of the room also.


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## eugovector (Sep 4, 2006)

96dB at 10HZ does seem quite unlikely. What were you using to measure?


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## t6902wf (Nov 14, 2008)

I used a Radio Shack Meter. Two HSU-ULS15's should be able to get to 10hz in such a small room.
I don't doubt the Radio Shack meter is weak. I am not really concerned with below 20 to be honest.


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## bpape (Sep 14, 2006)

Any time you have any sort of cavity, it should be filled with insulation. Otherwise, it's basically a drum resonating at a frequency determined by it's depth and the mass of the face. 

Sorry for the late reply - got a bug and had to rebuild my machine. 

Bryan


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## t6902wf (Nov 14, 2008)

bpape said:


> Any time you have any sort of cavity, it should be filled with insulation. Otherwise, it's basically a drum resonating at a frequency determined by it's depth and the mass of the face.
> 
> Sorry for the late reply - got a bug and had to rebuild my machine.
> 
> Bryan


Bryan, if it was resonating shouldn't it show up in the frequency plot? I'll probably fill it in the spring in any event. 

I think I would like to bring down the sound from 20 to 10hz and make it flat. I watched the new Batman movie last night and some of the bass was just a little too much. I set the levels with Audyssey and using the receivers tones it measures flat.


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## bpape (Sep 14, 2006)

Do you know it's NOT showing up in the plots? I'm sure it's accounting for some of the low frequency ringing in the waterfalls. How much? Hard to say.

Bryan


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## t6902wf (Nov 14, 2008)

bpape said:


> Do you know it's NOT showing up in the plots? I'm sure it's accounting for some of the low frequency ringing in the waterfalls. How much? Hard to say.
> 
> Bryan


Good point, I hope that is what is causing that ramp up from 20Hz to 10 and the ringing in the waterfalls. It may take a while but I'll post the before and after plots when I am done. It is inexpensive to do, but bit messy.
Thanks :bigsmile:


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## bpape (Sep 14, 2006)

I'm sure it's some of the waterfall ringing. I wouldn't count on it being the rise from 20-10Hz. I personally still think there is something funky with the measurements given that rise. That just doesn't happen that low.

Bryan


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## t6902wf (Nov 14, 2008)

What could do that. The microphone/meter?

Might that also explain the unusually flat response?

I've considered upgrading the meter but for the price I am not sure if it is worth it.


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## bpape (Sep 14, 2006)

Did you run a calibration on the soundcard before taking measurements? Do you have a correction file for the mic/meter you're using?

Bryan


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## t6902wf (Nov 14, 2008)

Yes I calibrated the sound card, the plot had the shape shown in the help files.
I also used the Radio Shack meter correction file. My meter is around 12 years old.

The next time I pull it all out I will redo it all to see if the result changes.


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## thewire (Jun 28, 2007)

RS meter dial on 80. :yes:


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## t6902wf (Nov 14, 2008)

thewire said:


> RS meter dial on 80. :yes:


I don't think so, like I said I will re-visit it when I have time.


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## eugovector (Sep 4, 2006)

thewire said:


> RS meter dial on 80. :yes:


With REW, that shouldn't make a difference, should it?


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## thewire (Jun 28, 2007)

eugovector said:


> With REW, that shouldn't make a difference, should it?


If I measure with the meter lower I get more extention, flatter looking response. A few days ago I had it set to 60 on accident thinking the 6 was an 8 and I think I had a measurement flat to around 10Hz after I told the REW SPL meter it was a 75dB target. I had forgotten to look at the input VU meter. When I use a -18dB sweep I get a 85dB target with the VU meter in the settings calibrated. To get a 75dB target I must tell REW the SPL meter is lower, or turn down the master volume on the pre/pro level -10 and have the VU meter read around -24 on the input where as the output reads -18.


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## eugovector (Sep 4, 2006)

Good to know. It certainly shouldn't be like that (the mic should just pass through whatever it's "hearing").


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## t6902wf (Nov 14, 2008)

bpape said:


> I'm sure it's some of the waterfall ringing. I wouldn't count on it being the rise from 20-10Hz. I personally still think there is something funky with the measurements given that rise. That just doesn't happen that low.
> 
> Bryan


Bryan if I fill the cavities will they act as a bass trap or will I just be stopping the resonance? 

Thanks 

Bill


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## bpape (Sep 14, 2006)

A bit of both. Due to the size of the cavity, the resonance (and absorption) are likely pretty low.

Bryan


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## t6902wf (Nov 14, 2008)

For proper care and feeding of my obsession:coocoo: I ordered a Galaxy C140 Meter.
I'll redo REW's setup to make sure I am getting accurate readings.
I'll also do and post before and after readings of filling those bump outs.
Might be interesting to someone.


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