Acoustical Treatments Master Thread - Page 241

No problem.

Ethan:

You have stated that you use 38 traps in your living room. How big is each trap? Does a trap that goes from floor to ceiling in a corner count as a single trap or a combination of several?

For 1st reflection absorption in a home theater, you seem to recommend 2" rigid fiberglass. Dennis Erskine seems to recommend 1" on the grounds that 2" may be too deadening. Have I understood your position accurately? What is appropriate thickness for side reflection? This is where the art takes over from the science
perhaps. Or perhaps, your personal preference for a music listening room vice Dennis' for home theaters dictate different treatments? For example, you are no fan of dipole surrounds, but I am sure that Dennis would not want a good home theater without them.

My planned theater is rectangular (28' deep, 18' wide at screen, 16' wide at rear row, and 8.5' high ceilings) with a carpet floor. I will follow your advice on traps and 1st reflection treatment. Should I consider ceiling reflection absorption as well if my floor will be carpeted? (For what it is worth, I plan to use Atlantic Technology speakers and the manufacturer tells me that their 8200 THX model is designed to not have much significant vertical dispersion (ie. towards the ceiling))

Also, given my 28' long room, I am planning on putting a sub towards the rear vice front to put it closer to the listening position for greater effect. (I'll bass trap all corners). Is rear positioning OK or is the front preferred? Putting it in the front would mean requiring more power to drive it I think. Closer to seating would require less. Edit: I came across this article: http://www.realtraps.com/art_sub-placement.htm Will read it in full

Thanks

Ethan:

Do you mean 12 'edges'? I consider a corner to be where the walls/ceiling or walls/floor meet. So, 12 edges and 8 corners. Correct?

Very useful. How and why does FRK affect absorption? It is such a thin layer that I thought it would have no effect! But, it does.

Why does adding facing INCREASE bass absorption?

Check out the photos and videos of his room on his site. Each trap is 2' X 4' except some at corners that are 2'x2' iirc.


I would be very surprised if Dennis at any time said 2'' is less good than 1'' for side panel thickness. That would contradict every measurement I have seen.

One might reasonably argue that sometimes diffusion is better than absorption but essentially never that one wants thinner absorption.


That's gonna be a nice space! You should consider starting a dedicated build thread with photos and details of the plan and progress. You'll get lots of good encouragement and maybe some good advice

about sub placement: Unless you are sitting next to a sub for tactile reasons, placement close or far is not the key. The key is how the sub interacts with the room modes. It is going to have to "fill" the room ("pressurize" it). Placement should be determined by where it sounds best when doing that. A quick search on the "crawling" method for sub placement will show you what I am talking about.

Yep.

FRK = Foil Reinforced Kraft paper (a.k.a. FSK = Foil Scrim Kraft paper, a.k.a. Scrim) - it has a thin layer of metallic foil (thin but not very porous).

Nathan:

Thanks. I recall reading that suggestion from Dennis Erskine on this thread. Check this post from him
It is post #6 on this thread.

My build thread is on my signature below. If you look at the voting button that I have established, the naysayers and cheering squad are about evenly split

I'm gonna say, in context, Dennis was talking about very large areas (full front wall and side wall all around up to ear level) being problematic (=leaving one open to absorbing too much). Stick with less coverage (eg, first reflection points) and thick panels at those points, for more reliable results.

Nice build thread! That's gonna be a great space.

The thread poll is pretty general, so it's not clear what the pro and con votes indicate....

Actually, I have 55 panels now.

The photos below are fairly recent, and Yes, I think I'm done!


The thicker the better, always. First reflections are mainly a mid/high frequency issue, but more bass trapping from using even thicker panels is always welcome. A panel thicker doesn't absorb more per se. Rather, it extends the same absorption to lower frequencies. So while even one inch thick is adequate, thicker is only better. And Yes, absorbing ceiling reflections is important too for most speaker types.

--Ethan

There are four corners where each wall meets another wall, four more where each wall meets the ceiling, and four more where each wall meets the floor. I'm talking about "normal" corners, not tri-corners where three boundaries meet. There are eight of those in a rectangle room.

--Ethan

The membrane vibrates when sound waves strike it, and the fiberglass the membrane is bonded to damps that vibration.

--Ethan

Thanks for your answers. Should the membrane be facing into the room or away from it? I would think the latter, right?

Into the room.

I am confused. Dipoles are used as side and rear surrounds on the side and rear walls, respectively. Where is the 'front wall behind dipole speakers'?

Dipole speakers with mostly diffused front wall.

That's a sexy picture. What brand/model are those diffusers?

Auralex Acoustics: T’Fusors / Q’Fusors

Ethan:

How does one fashion a theater seat riser into a bass trap? Is it effective? Thanks for all the education that your website provides.

How would you modify your recommendations here for placing the LCR behind an acoustically transparent screen? Would you still toe-in the speakers?

Ethan W gave me advice on that for my riser, read here:
riser: Broadband bass trap
(Based upon Dennis E work/articles also.)

Is it effective? Yes - every bass trap helps.

Ethan:
Is an air gap recommended for the absorbers at the 1st reflection points, or can the absorber be mounted right against the wall? Thanks

Mtbdudex, Vinyl: Thanks for your responses.

Mtbdudex: What is the theory behind the design of risers as absorbers?

I found this article on risers as bass traps: http://www.audioholics.com/tweaks/do...ter-seat-riser. Elsewhere I found a critique of this design that essentially said that front facing holes are not quite as effective as 1/4" x 48" slits on the top of the decking.

Air gaps help increase the range of frequencies that are impacted by a trap -- typically a good thing when that means more bass is trapped -- hence the emphasis on "broad band" treatments...

Nathan:
So, you would recommend a gap for the 1st reflection points as well? If so, how much? What is the point of diminishing returns from a gap (if any)? Thanks

http://www.avsforum.com/avs-vb/showt...9#post20007129

[quote=Ethan Winer;20071042]Actually, I have 55 panels now.

The photos below are fairly recent, and Yes, I think I'm done!



The thicker the better, always. First reflections are mainly a mid/high frequency issue, but more bass trapping from using even thicker panels is always welcome. A panel thicker doesn't absorb more per se. Rather, it extends the same absorption to lower frequencies. So while even one inch thick is adequate, thicker is only better. And Yes, absorbing ceiling reflections is important too for most speaker types.

--Ethan

Ethan:
With all this treatment what does the frequency response at your listening position look like?

Rule of thumb rather than science I can cite is the gap should not be thicker than the panel itself, and in practice is often 1 or 2 inches for a 2 to 4 inch thick panel.

That said, in ceiling installations people often leave an even bigger gap, and in corner straddling installations of course the gap is bigger, so there is no reason to shy away from using the space if you have it.

Given how terrible the LF response and ringing are in most rooms, I think mine is very good. This is an older plot, from before I added the last round of traps:

Ethan,

Have the 705 foil out in some areas. Would a light dusting of flat spray paint cause any problems? The reflection shows through the GOM 701 at some angles.

Thanks,

I'd be concerned that the "dust" would come off and become airborne. I'm pretty sure that it will not adhere. And the foil will definitely flex.

Something to ponder.

Jeff