#1741109 - 04/25/07 03:50 PM
HT/mixroom
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Jesse S
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Hi Ethan, I'm at the acoustics stage of my renovation and would like your advice.
The red would be 2" OFI fibreglass mounted on-wall. The green would be 1" fibreglass mounted on the ceiling. The blue is 4" fibreglass for bass-traps run floor to ceiling. The floor will have wall to wall carpet.
Mainly this will be a home theater but I think this design should provide a decent RFZ for mixing.
Do you have any suggestions or alterations to my plan? Should I run the red sections from floor to ceiling?
Thanks in advance.
Edited by Jesse S (05/01/07 12:45 AM)
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#1741677 - 04/26/07 11:21 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Jesse,
That all looks good, but I'd use 2 inches thick on the ceiling instead of only 1 inch.
For the side wall reflection points you could experiment, but covering all of that floor to ceiling might be too much.
--Ethan
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#1741810 - 04/26/07 01:43 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Ok. The ceiling height is only 82", which is why I was wanting to use a thinner material there.
For the bass traps, would going up to 6" thick be useful? Also, I might be able to go deeper with the corner traps in the rear, say 3'. Worthwhile?
One last thing, I'll be using a 7.1 setup with dipoles on the sides and monopoles on the rear wall. Would you put absorbers on the ceiling to catch the first ceiling reflection to the seats?
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#1742320 - 04/27/07 10:37 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Jesse,
> The ceiling height is only 82", which is why I was wanting to use a thinner material there. <
Yeah, but the small loss in height is more than offset by the improved absorption.
> For the bass traps, would going up to 6" thick be useful? Also, I might be able to go deeper with the corner traps in the rear, say 3'. Worthwhile? <
More / thicker is always worthwhile!
> Would you put absorbers on the ceiling to catch the first ceiling reflection to the seats? <
Yes, all early reflection points are worth treating.
--Ethan
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#1744178 - 04/30/07 08:09 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Ethan,
I got a sample of Dazian fabric today that I might use to cover the fibreglass. Some people say that you should be able to blow through it with little restriction for it to work properly. I tried blowing through it and airflow is somewhat reduced though if you hold it up to a light you can see little holes. Can a fabric be too dense/tightly woven that it would interfere with 703 type material behind it?
Also, is fabric enough to contain the fibres or do I need to use a thin layer of batting?
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#1744573 - 05/01/07 03:28 PM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Try putting the fabric in front of the fiberglass and "talk into" the fiberglass with and without it. If it sounds the same with the fabric, and totally dead like talking into a void, then it's probably fine.
Fabric alone is probably enough, but batting never hurts.
--Ethan
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#1756814 - 05/25/07 01:29 AM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Ethan-
I'm going to use the OFI 2" fibreglass as noted above. But I also have 96sq' of Auralex 2" wedge foam that I'd rather not waste. It's specs aren't as good as the OFI but it's decent down to about 500hz
(0.91 NRC), 250hz is 0.30, whereas OFI is still 0.71 at 250hz.
Anywho, since the Auralex isn't quite as good, where would you suggest using it? Front wall or ceiling? I want the better stuff on the first reflection so that's out.
Also, regarding mounting the panels on my side walls, would low end performance go up if they were spaced an inch off the wall?
Lastly (  ) I have a 4 18" infinite baffle subwoofer at the front of the room. I was planning to build a small "stage" just for appearance sake. However, a few people have commented that this will act like a bass trap if it resonates so it would require a boatload of sand to dampen. Any thoughts on this?
Thanks again for your time.
Added a pic
Edited by Jesse S (05/25/07 01:33 AM)
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#1757023 - 05/25/07 01:02 PM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Jesse,
I also have 96sq' of Auralex 2" wedge foam that I'd rather not waste. It's specs aren't as good as the OFI but it's decent down to about 500hz
If you already have a lot of sculpted foam you can increase its performance by placing two pieces face to face and using them as one piece. This makes the combination thicker and solid.
I want the better stuff on the first reflection so that's out.
Actually, this is one place where sculpted foam can be better than rigid fiberglass because the peaks and valleys in the surface absorb better for sound arriving at an angle. Which is what you need at reflection points on the side walls and ceiling. You could make a killer absorber for those places by using three layers of 2-inch foam. Put two layers face to face as above, with the third layer having the sculpted surface facing the room.
I was planning to build a small "stage" just for appearance sake.
If you make a stage from wood I'd stuff it with fluffy fiberglass rather than sand. This way you have at least a small chance for the stage to add a little bass trapping into the room.
--Ethan
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#1757088 - 05/25/07 02:26 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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If I triple it up, that would make 4 2x4' panels of 4.5" total thickness. So a finished panel of 4x4' for each side wall.
That's a great idea. Most of the time I'll only be using the first row of seating and 4x4' would cover all first reflections. If I need to, I can add another 2" fibreglass panel further down the side walls if the room needs more absorption.
Regarding the stage, those who commented on it "resonating" were of the mind that this was a bad thing, i.e I build the monster sub and then I would "lose" a bunch of output to a rattly stage.
I can see the logic as I've seen rooms where things like a vibrating window actually convert a lot of SPL to vibration. Such that if you touch the window and stop the vibration, an SPL meter actually jumps a good 6-10db. But if you think it's still doing positive bass trapping, I'll try with fluffy instead of sand (wasn't looking forward to hauling a wackload of sand in anyway )
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#1757454 - 05/26/07 09:44 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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> those who commented on it "resonating" were of the mind that this was a bad thing, i.e I build the monster sub and then I would "lose" a bunch of output to a rattly stage. <
Everyone's a damn expert. 
You know about speaker isolation like Auralex MoPads, yes? So a "rattly" stage would be similar in the good sense. But you don't want rattles or self-resonances. Hence the fiberglass stuffing.
--Ethan
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#1758341 - 05/28/07 03:29 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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The OFI-72 costs 50% more than the OFI-48 (4.5lbs/cu' vs 3.0).
I could use 6" of the 3lb for the same cost as 4" of 4.5lb.
I also have 60 sq' of a 2" Roxul product that is something like 7-9lb/cu'. That's enough for one 2" layer for each of the 4 corners, then 1-2 more layers of the lighter stuff
e.g
Roxul 2" 7lb --------
OFI 2" 3lb --------
OFI 2" 3lb --------
or
Roxul 2" 7lb --------
OFI 2" 4.5lb --------
Ideally it'd be roxul/ofi 4.5/ofi 4.5 but I have to keep costs down wherever the cost/benefit isn't great enough.
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#1758728 - 05/29/07 12:05 PM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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More thickness is generally better than more density. Also, mineral wool costs less than rigid fiberglass, but it's not as nice to work with and it tends to sag. Just something to consider when deciding what to buy.
--Ethan
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#1766135 - 06/13/07 02:05 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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This is my pre-bass trap measurement of the IB subwoofer.
The blue line is a near-field placement.
The back (top graph) seems pretty good for a blank room with no eq. This particular "left" (bottom graph) position is kinda wonky. There don't seem to be any nulls at least. Do you think 6" traps in each corner can smooth most of this out?
Edited by Jesse S (06/13/07 02:06 PM)
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#1766505 - 06/14/07 11:21 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Yes, 6-inch thick traps in every corner will help a lot.
--Ethan
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#1770506 - 06/23/07 03:32 AM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Interesting to see how close the predicted modes are to actual
I just happened to put 2 cuts on my behringer FBD at 33 and 63hz and when I checked the modes again now, that's where they should be. Currently the room has no traps, except for a sealed bail of roxol insulation, which I put in the rear left corner.
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#1772292 - 06/26/07 05:10 PM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Jesse S
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Ethan-
My room isn't finished yet but I had 1 bale of insulation in the back corner. It didn't seem to do much for the bass but I didn't try with/without. For fun, I dragged another bale in and stuck it in the front corner. It works (!) I compared the same song with/without the front bale and the kick drum was signficantly improved. Quicker decay and more definition. Bass guitar was also more defined. Of course you know traps work but until we hear it for ourselves it's not quite real.
Anywho, can a 4" or 6" thick trap equal the relatively huge thickness of one of these insulation bales? They are probably 2' wide by 16" deep and the density is pretty good when they are packed. If just 2 bales can make this noticeable of an improvement, I'll be interested to see what full height traps in all 4 corners can achieve.
Edited by Jesse S (06/26/07 05:11 PM)
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#1772295 - 06/26/07 05:17 PM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Jesse S
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Oh, one other thought. Rather than use a triple layer of Auralex panels, I was thinking of using 1" of fibreglass with the Auralex on top of that. That would give 3" total and should extend the effective NRC down to around 300hz. That would leave me with enough Auralex to cover the first reflection points and the ceiling, though I may just use Auralex alone on the ceiling due to the height restriction.
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#1772591 - 06/27/07 10:20 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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can a 4" or 6" thick trap equal the relatively huge thickness of one of these insulation bales?
Who knows? You'd have to test both side by side to be sure.
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#1853763 - 12/09/07 09:14 AM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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I finished my traps finally. They are 2'x7' and 3" thick of Roxul 12 lb/cu'. I measured the FR manually with the rat shack meter and applied light correction with a BFD. There are no nulls and the largest correction I needed was -6db at 63hz. This used to require more like -12db. The bass decay is very different (fast) compared to having no traps. There are 4, 1 for each corner. I would do more but the screen at the front and a heat radiator at the rear are limiting extra places for traps. I only measured to 125hz so past that is inaccurate.
The blue line is a chair on the left, the purple is a chair on the right. I'm pretty impressed with how similar the response is in multiple locations, but then that's the point of using traps - less room interaction. I'm waiting for an ecm8000 and mp13 mic pre so that I can use REW/True RTA.
Edited by Jesse S (12/09/07 09:17 AM)
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#1854301 - 12/10/07 10:26 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Great!
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#1912322 - 03/19/08 09:29 AM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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and back again 
I'm looking now at doing the ceiling, from about the front of the room to the project with an 8'x8' of 2" OFI-48 (same as 703).
Would it be better to butt the pieces together or to leave a 3-4" space for a little irregularity?
One thing I wanted to mention about my Auralex 2" studiofoam. I've been using them on my sidewalls at the first reflection and they really weren't doing a great job. I laid 3 2x4' panels of this 2" fibreglass in front of them and the difference was staggering. The Auralex specs are almost equal to 2" 703 except in the 250-500hz range, *but* it definitely doesn't perform the same even in the mid and high range. If you talk into either panel, the Auralex doesn't absorb nearly as well. When you talk into the 2" fibreglass it just swallows up the sound where the Auralex allows quite a bit to reflect back. It will be relegated to the less important areas, perhaps up high or at the back of the room as absorbers/diffusors.
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#1912447 - 03/19/08 12:28 PM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Just make it all continuous.
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#1912759 - 03/19/08 08:20 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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I suspended 4 panels in an 8'x4' grid, phenomenal improvement.
It's amazing how huge and deep the soundstage can be with just a stereo setup, when you absorb most of the early reflections. The HR824's + IB sub are really shining now.
A month ago with just my bass traps and Auralex I was finding all music to just sound shitty. Now virtually everything sounds great and I can really appreciate the mixes. Movies are greatly improved too. I watched the opening titles for Spiderman 2 and 3 and the orchestral sound was fantastic. Dialog clarity is enhanced as well. I'll have to do some new measurements with REW.
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#1913166 - 03/20/08 11:22 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Excellent 
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#1920463 - 04/02/08 06:10 AM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Here's my latest readings with REW. Having big problems with a dip in the 40hz range.
The green is 2" fibreglass suspended from the ceiling a few inches. The seating area is the elipse and is generally in the 38% range from the back wall.
The graph above is with no EQ. I can boost at 42hz and it pulls the dip up at least 10db so it's not a null.
I tried various things yesterday. At the back I added 6" of 703 type stuff to each trap, no real benefit. I tried putting 6" all along the rear floor/wall intersection at 45 degrees, again almost no benefit. I tried 6" on either side of the listening position at the floor/wall, no difference.
560/42hz = ~13.3'. That doesn't really correlate with the room dimensions of 12.5x18x6'9.
1/6th smoothing makes it look "nicer", but is that a true representation of what it sounds like? Any thoughts?
Edited by Jesse S (04/02/08 06:15 AM)
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#1920470 - 04/02/08 06:20 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Jesse S
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One thing occurs to me, I need wider traps to absorb lower, not necessarily thicker. Maybe I'll try 4' wide traps at the rear today. That's gonna gobble up space
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#1920651 - 04/02/08 10:23 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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Wider and thicker and more of them. 40 Hz is very low for fiberglass type bass traps.
--Ethan
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#1920700 - 04/02/08 11:32 AM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Should I just not worry since eq seems to bring the response up? 16db at 42hz is quite a boost. My sub/amp has no problem with it at reference level.
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#1921176 - 04/03/08 07:50 AM
Re: HT/mixroom - Please help Ethan
[Re: Jesse S]
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Ethan Winer
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I really hate to see anyone use a lot of EQ boost to fix a null.
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#1921427 - 04/03/08 02:38 PM
Re: HT/mixroom - Please help Ethan
[Re: Ethan Winer]
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Jesse S
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Using this crazy tool called modecalc ( ) one of the primary room modes is 45hz in the 12.5' width of the room. It doesn't overlap with a mode in the length or height but it's still seems to the be root cause.
I moved my traps to be 4' wide in the rear but it still had little effect down low, maybe 3db reduction.
If it was a null, boosting wouldn't correct the dip correct? I'm getting almost full benefit from the boost so it's not the typical "black hole" type null, perhaps since it only derives from 1 room dimension.
What smoothing amount is valid when viewing the sweep results? Even with just 1/12th octave smoothing the dip is less drastic.
Here is today's result, first with no eq. I thought the dip at 90hz was another mode but some tweaking of crossover and subwoofer distance totally eliminated it. No smoothing.
This is with 6 bands of eq at approx 25, 28, 41, 45, 55 and 85hz and only 1/12th octave smoothing.
It sounds pretty even from the main listening positions. It might be horrific if I ever setup a 2nd row of seating and they don't have the dip (they'll be getting the big 45hz eq boost).
I'm planning to add midbass arrays to the left and right speakers, which would run from 50-200hz. Those might help with the dip. The only other tweak I can think of is a tuned resonator.
Edited by Jesse S (04/03/08 02:40 PM)
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