Realtraps Diffusor

zybar · « **on:** 13 Oct 2006, 11:21 pm »

Ethan,

Can you go into detail about this new product?

Why is it designed for behind the listener and not behind the speakers?

Thanks,

George

ted_b · « **Reply #1 on:** 13 Oct 2006, 11:45 pm »

from Ethan's website:
"All untreated listening rooms suffer from comb filtering, a particular frequency response error that creates numerous peaks and deep nulls. Comb filtering is a problem in smaller rooms especially, because of the proximity of the listening position to the rear wall behind. Numerous peaks and nulls occur at predictable quarter wavelength distances from that wall, badly skewing what you hear. For audiophiles and other critical listeners the result is a colored, often boxy and congested sound. For mix engineers comb filtering is even more troublesome - if you can't hear the music as it really sounds, it's much more difficult to achieve an excellent mix.

When placed on the rear wall behind the listening position the RealTraps Diffusor scatters mid and high frequencies, while low frequencies pass through the reflecting well membranes to be absorbed by rigid fiberglass behind. The membranes also increase bass absorption beyond what fiberglass alone could provide. Thus, comb filtering artifacts are reduced dramatically over the entire effective range."

Ethan Winer · « **Reply #2 on:** 14 Oct 2006, 02:14 pm »

George,

> Why is it designed for behind the listener and not behind the speakers? <

Well, it could also be used there, and at first reflection points in a larger room. Other than planar speakers, most speakers send their sound forward to the listener, so the primary reflection places that need treating are the side walls and ceiling (and floor), followed by the rear wall. Especially when someone listens near the rear wall, reflections from the rear are the most damaging. To my way of thinking, the front wall is the third place to worry about. With normal front-firing speakers sound goes past your head, strikes the rear wall, then has to go all the way back to the front, then back to you, before the front wall reflections are much of an issue. And after that much distance the reflections are pretty well attenuated anyway.

This is not to say that diffusion on the front wall is never useful. But most small rooms have too much ambience, not too little, around the front of the room near the loudspeakers. I call that excess "early" ambience chatter - all the reflections are short because walls are usually close by, and that clouds intelligibility.

--Ethan

zybar · « **Reply #3 on:** 14 Oct 2006, 02:53 pm »

Thanks Ethan.

In my space where my speakers fire down an almost 30' long length, I sit a good 11' from the rear wall This rear wall has your MiniTraps in the corners and a large cd rack with about 1200+ cd 's in the middle of the wall.

Would the diffusor still help in this situation?

BTW, the distance from my listening seat to the rear wall is basically 38% of the room length. This location was picked based on listening and measurements from the TacT preamp. Of course, this is the distance you suggest in your website as well.

George

Ethan Winer · « **Reply #4 on:** 14 Oct 2006, 04:14 pm »

George,

> This rear wall has your MiniTraps in the corners and a large cd rack with about 1200+ cd 's in the middle of the wall. Would the diffusor still help in this situation? <

Yes, our diffusor will be infinitely better than a rack full of CDs. I don't know where the "conventional wisdom" comes from that suggests a CD (or LP) rack offers useful diffusion, but it's definitely a myth. It's really easy to tell which sounds better just by "talking into" both. That's my standard test for diffusion and absorption. Just stand six inches in front of a proposed material and say loudly, "Testing, 1, 2, 3" and you can easily hear exactly what it's doing by the tonality of what is reflected back at you.

> Of course, this is the distance you suggest in your website as well.

<

But of course! (Though I have to credit studio designer Wes Lachot as the source of the 38 percent "rule.")

--Ethan

AB · « **Reply #5 on:** 17 Oct 2006, 01:23 am »

I have a question for you, Ethan.

I have a phenomenon in my room where if I move my head just a few cm left or right a center image vocal will flatten out or thin out or drop back in the SS, actually all three of these. It is the strangest thing and I am finding it difficult to describe. I would like to eliminate or at least minimize this. I suppose this is comb filtering.

I have stacks of Real Traps in the room - 4 mondo traps, one in each corner - 4 2x2 mini traps, one in each tri corner and 2 4x2 minitraps mounted in the horizontal ceiling/wall behind the speakers.

What I just did was take one of the stand mounted mondo traps and place it directly behind my listening position - about 2 feet behind my head. I tried it both forward facing and backward facing. With the back - the non membrane side - toward the front of the room this "comb filtering" pretty much disappeared.

Now it is not very cool to have a free range mondo trap just standing there in the room.

Will the diffusors work similarly but at a greater distance - say against the back wall? The back wall is only about 5 - 6 feet from my head.

Will you build a diffusor that will have the well side covered in an acoustically transparent fabric? The way they look now they make a strikingly modern statement that might not work for everyone, taste being what it is and all.

Thanks for your help.

Daygloworange · « **Reply #6 on:** 17 Oct 2006, 01:35 am »

AB,

That sounds a little extreme that it would change that much if you move just a little.This might sound a little silly, but I've seen it more than once, check the polarity of your speaker cables.

Cheers

Rob Babcock · « **Reply #7 on:** 17 Oct 2006, 02:02 am »

Is the panel stand-mounted or must you buy that separately?

woodsyi · « **Reply #8 on:** 17 Oct 2006, 03:35 am »

Quote from: AB on 17 Oct 2006, 01:23 am

I have a question for you, Ethan.

I have a phenomenon in my room where if I move my head just a few cm left or right a center image vocal will flatten out or thin out or drop back in the SS, actually all three of these. It is the strangest thing and I am finding it difficult to describe. I would like to eliminate or at least minimize this. I suppose this is comb filtering.

I have stacks of Real Traps in the room - 4 mondo traps, one in each corner - 4 2x2 mini traps, one in each tri corner and 2 4x2 minitraps mounted in the horizontal ceiling/wall behind the speakers.

What I just did was take one of the stand mounted mondo traps and place it directly behind my listening position - about 2 feet behind my head. I tried it both forward facing and backward facing. With the back - the non membrane side - toward the front of the room this "comb filtering" pretty much disappeared.

Now it is not very cool to have a free range mondo trap just standing there in the room.

Will the diffusors work similarly but at a greater distance - say against the back wall? The back wall is only about 5 - 6 feet from my head.

Will you build a diffusor that will have the well side covered in an acoustically transparent fabric? The way they look now they make a strikingly modern statement that might not work for everyone, taste being what it is and all.

Thanks for your help.

Diffusors in the back will definitely get rid of the comb filtering and put some air in your music.

You don't list micros on your early reflection points. Do you have them?

AB · « **Reply #9 on:** 17 Oct 2006, 04:23 am »

The speakers are wired correctly. It's not a speaker positioning issue. It's not a balance issue.

The effect I hear is subtle and I am not sure it would be as annoying to most people as it is to me. I have a bit of hearing loss in one ear so I suspect I am sensitive to this. It only effects vocals - to my ears - and it is best described as a flattening of the image. Rather than the vocal hanging in space with a 3D image about 2 feet in front of the speakers it falls back, narrows and shifts to the left. The vocal completely losses its lifelike-ness-ism.
When I get my head out of the sweet spot it is very noticeable. It really sounds like a phase problem but it only happens with left and right changes in my listening spot.

The first reflectons are handled by a window covering on the left - a triple cell Hunter Douglas type, and a large opening into another very large room on the right.

The rear wall is about 6 feet from my listening spot but there is a wide hallway/entryway on its right side. The floor is carpeted. The ceiling rises from eight feet at the front of the room to about 14 mid and then drops back to eight in the entryway.

The experiment with the stand mounted mondo trap really made a difference. There was still a small amount of the problem but it was very much reduced from what it had been. I just can't have a mondo trap standing directly behind my chair in the middle of the room plus I assume the diffusor will do a better job in any case.

I would like to add another mini trap to the ceiling just above and forward of the listening position. The sloped ceiling does a good job of focusing its reflections back behind the listening spot but I can still detect some and this might be adding to the combing.

My wife has been very tolerant of these things but I think I have reached or am about to reach a critical mass. Doing the most with the least is an issue now. No more holes in the ceiling either. Or else. Oh, and get those amps out of the living room and, please, do something with all those damn boxes...

Sorry, I was channeling there.

Thanks

srlaudio · « **Reply #10 on:** 17 Oct 2006, 11:00 am »

Say, We might be able to help with the room sound and the WAF.....just a thought...

Ethan Winer · « **Reply #11 on:** 17 Oct 2006, 04:08 pm »

> I have a phenomenon in my room where if I move my head just a few cm left or right a center image vocal will flatten out or thin out or drop back in the SS, actually all three of these. It is the strangest thing and I am finding it difficult to describe. I would like to eliminate or at least minimize this. I suppose this is comb filtering. <

Yes, I'm sure it is comb filtering. You mentioned having RealTraps in corners, but none at first reflection points. That placement is key for avoiding this problem.

> Will the diffusors work similarly but at a greater distance - say against the back wall? The back wall is only about 5 - 6 feet from my head. <

Yes, diffusion or absorption behind you will avoid comb filtering from that direction (or reduce it, anyway), but I'd first tackle the first reflection points on the side walls and optionally the ceiling.

> Will you build a diffusor that will have the well side covered in an acoustically transparent fabric? <

We hadn't planned on it, but I suppose it's possible.

--Ethan

AB · « **Reply #12 on:** 17 Oct 2006, 04:22 pm »

Ethan, will you have these diffusors with you in Denver at RMAF?
Thanks

ctviggen · « **Reply #13 on:** 17 Oct 2006, 06:12 pm »

Ethan, do you have an estimate of the high value for diffusion. This calculator:

http://www.digitalaudiorock.com/cgi-bin/qrd.cgi

gives less than 4,000 Hz, but I'm not sure exactly what the dimensions are for your device. (3390 Hz if using a max depth of 6 and width of 2 inches and 5 wells per period.)

ctviggen · « **Reply #14 on:** 17 Oct 2006, 06:14 pm »

By the way, I performed a test with using or not using two micro traps between the speakers. The microtraps definitely stabilize the imaging and increase the depth of the soundstage. I'm interested in these diffusive elements, and diffusive elements are very expensive and hard to make yourself.

Ethan Winer · « **Reply #15 on:** 18 Oct 2006, 02:03 pm »

> will you have these diffusors with you in Denver at RMAF? <

Unfortunately no. We built one prototype (well, actually many, but only one final version), and shipped it to the AES show last week in San Francisco. FedEx banged it up so badly we couldn't even show it there. And we won't have more until they go into production in a few weeks.

--Ethan

Ethan Winer · « **Reply #16 on:** 18 Oct 2006, 02:06 pm »

Bob,

> do you have an estimate of the high value for diffusion. <

Our calcs show about 800 Hz to 4 KHz. By ear it sounds as it should (very good), though I understand that's not a scientific test.

>The microtraps definitely stabilize the imaging and increase the depth of the soundstage. I'm interested in these diffusive elements, and diffusive elements are very expensive and hard to make yourself. <

It's a good thing you live near us.

I'm sure we can arrange a loan for a few days.

--Ethan

Rob Babcock · « **Reply #17 on:** 19 Oct 2006, 02:58 am »

Quote from: Rob Babcock on 17 Oct 2006, 02:02 am

Is the panel stand-mounted or must you buy that separately?

ctviggen · « **Reply #18 on:** 19 Oct 2006, 03:57 pm »

Thanks, Ethan. Maybe I'll drive to the construction facility and pick two up for comparison with what I have now. The only thing is finding the time, which always is the limiting factor. My (new) wife and I have had an unbelievably brutal summer, and my list of things to do keeps growing. Luckily, things have quieted down somewhat, and I've been able to chip away at some of the list. I still have a few weekends of performing outside work whilst there's still time to do those things. And, I'll likely just not do some of the stuff I planned on doing, which might also free up some time (though not until Thanksgiving).

Anyway, your device seems like a good combination of reasonable frequency response for the price. I've been wanting to try diffusive elements for some time, but haven't been able to find anything that wasn't obscenely priced.

Ethan Winer · « **Reply #19 on:** 19 Oct 2006, 05:11 pm »

Rob,

> Is the panel stand-mounted or must you buy that separately? <

I'm so sorry - I can't imagine how I missed that earlier!

The stand is an optional accessory. Most people will mount the diffusor permanently, just as they would a bass trap or any other acoustic panel. We used a stand for this photo just for expedience, though a stand is also useful when there's a window in the way, or another reason someone prefers to avoid permanent mounting.

--Ethan