Treating the entire front wall - Bob/Z?

Posted: Tue Mar 29, 2005 10:48 pm

Maybe in some HT applications treating the front wall might be advantageous but in others it makes no sense at all. Certain speakers (bipolar and dipolar designs) like the Definitive Technologies have front and rear facing speakers (L/C/R) that reflect sound off of the front wall intentionally. Absorbtion would only kill those reflections and destroy their beautiful sound. Mirage's Omnistats (although not bi/dipolar) would suffer the same fate as the Def-Techs.

My HT has no front wall treatment, I really don't see the point if the rest of the room is treated properly. Just my opinion.

Posted: Wed Mar 30, 2005 1:03 am

Big_D

True true.
Another way to go with the front wall is baffles (aka soffits), of course baffles don't work with bipolar or electrostatic either. Smile

There are lots of options that are specific to various theaters.

Posted: Wed Mar 30, 2005 7:05 am

Just a general comment, more a thought.

Either one absorps, or one doesn't.
And with absorption I mean as linear as possible (flat absorption).

All the rest I feel as absorption to solve specific remaining problems not covered by a general treatment.

One could argue that this front wall is a lot of grazing incidence which should be an advantage for the lows, and the same grazing incidence will diminish others.
But that's all thinking out loud.

Generally: either one aims to solve specific problems, or one absorps as flat as possible.
The idea of covering a complete wall with 1" material feels very strange to me.
At the other hand, DE proved to be a pro, having good results with his approach.

And I also don't accept the fact that reflections are necessary destructive. They can as well be constructive (smooting level by multiple reflections superposed).

As such I'm as well sure that absorbing certain low frequent reflections can cause as well trouble by raping a smoothed level and enhancing the destructive effect of other reflections.

As such, Paul's and Mark's approach is one approach (bit non-environmental like, the get rid of it all approach), but there are certainly other approaches as well.

Just thinking out loud.

Posted: Wed Mar 30, 2005 7:32 am

This HT bussiness is relatively new, so there are loads of opportunities for guru's to come up with new, revolutionary treatment methods.

My cynical 2 eurocent. Twisted Evil

Posted: Wed Mar 30, 2005 9:27 am

The reason many treat the entire front wall (myself included) is very simple. The only thing you want coming at you from the front in an HT environment is the sounds coming from the LCR. You don't want reflections from the back wall then off the front. You don't want direct sound from bipole/dipoles coming off the front wall at you. And on and on. By the time you map out all of those points, you've pretty well got the whole wall covered anyway.

As for biploar designs, many of the people who design with the front wall dead also believe that this type of design has no place as the LCR in an HT environment. I personally agree but that's really just preference. I just can't see deliberately adding out of phase information from the front and then turning around and measuring impulse response and trying to kill all of the OTHER early reflections but leaving those from the rear drivers alone.

Just my 2 cents.

Posted: Wed Mar 30, 2005 9:58 am

Bpape,

I think the question is more:

Why so thin (1") rather than discussing different room acoustic approaches.

What makes that if you absorp, you only absorp mid and high.
What's the use of this approach?

I don't see the reason that reflections at the front should be limited to mid and high.

I've seen that referred is also to whatever furniture which then should compensate.
And I've read about the fear to overabsorp low mids.

Instinctively I shouldn't think about cladding a whole wall with a 1" thick material in function of music, doesn't matter which wall.
In the same way I shouldn't think about using carpet for a whole floor.
I don't speak about targetted problems here.

But I also accept the fact that DE tells he gets good results.

Posted: Wed Mar 30, 2005 10:51 am

Personally, I agree that doing the whole thing in 1" is not preferable for exactly the reasons you mentioned Eric. I like to mix 1" and 2" and back the 1" with drywall or something solid so it looks like the same thickness but doesn't over absorb in the mids. This gets you down a little lower. Also, in the corners, with soft broadband absorbtion, you are getting some bass absorbtion.

In a perfect world, you'd do as much as deep as possible on the front wall to make it all more broadband. Unfortunately, there is no good way I've found to do that without OVER absorbing where things like people, chairs, couches, etc. are good at absorbing.

Actually, I believe DE proposed using something like Linacoustic with the lining toward the room on the front wall which provides very little in the way of HF absorbtion.

Posted: Wed Mar 30, 2005 12:38 pm

z60611 wrote:

Quote:

DE isn't building an absorber. He's building a massively analized room. As Russ Herschelmann says, "start with the chairs".

Thank you! I had forgetten that point posting earlier in the thread. Dennis designs total environments, not individual components.

More completely;
Andre

Posted: Wed Mar 30, 2005 12:55 pm

Greetings

I don't agree with this 'over-absorbing' notion.

Once you've got 1" of absorption ( or even 1/2" )already killed all highs 100%

You can't kill 200% of highs by increasing the absorption to 2"

Trouble is kiilling all the highs by putting lots of THIN absorption everywhere, leaves you a boxy muddy room, as the mids and lows are still flying about everywhere.

And yet a lot of people mistakenly think that by adding even more absorption it's gonan make the room even more duller.

Nope, Adding MORE absorption, rebalances things, by absorbing the mids and depending on the thickness the lows.

Mark's Studio Build has full wall absorption on EVERY WALL, and the ceiling.

Does it sound sound dead and boxy. Nope, it sounds EXCELLENT!

Completely Absorbing the Front wall is a great idea. But ONLY if you use a decent amount of absorption. particularly as the rear and sides of a speaker cabinet emit a very HF rolled off response.

Absorbing the total front wall in some ways gives the benifits of soffit mounting. i.e taking the front wall out of the equation.

If you don't have any front wall absoprtion, the reflections will come back at ya bass and low mid heavy. Sticking 1" of absorption on the front wall will only make that WORSE.

However absorbing the front wall properly can yeild great results.

Incidentally, while I was building my soffit wall, for a few days I had a situation where I only had the studwork and absoprtion. hence a totally absorbed front wall

Even though there was no other absorption in the room, it sounded great in there.

Lastly I think only 1" of absorption is pointless anywhere. Very unbalanced!

That's what I think anyway. feel free to flame me Smile

Paul

Posted: Wed Mar 30, 2005 1:21 pm

Bob,

> I remember posting some polar plots for you. <

Really?! I've been trying to find this for a year now, and finally hit pay-dirt the other day when I apparently discovered the magic words Google needed.

First, let me say I don't want to turn this into bashing DE. Yes, his statements are my main motivation for this bit of research, but so many people treat their rooms this way - whether because they're following DE or because they read about LEDE somewhere else - it seemed important to investigate.

> I remember DE once saying that even if you stand behind a monopole speaker one can still hear the words. <

Yeah, sure, but by itself that statement is meaningless. What matters here is magnitude. If a speaker sends 18 dB more out the front than the rear at 500 Hz and above, as do most of those speakers, that's enough to avoid comb filtering.

> DE has mentioned several times that in his style of rooms the big problem is over absorbtion at 200hz <

I agree with Paul. That's just plain nuts.

> It matters much less how much LF bounces off the front wall because the wavelengths are so long that at least it's still in phase even after the bounce <

Huh? 100 Hz has a quarter wavelength of 34 inches!

--Ethan

Posted: Wed Mar 30, 2005 1:28 pm

BP,

> You don't want reflections from the back wall then off the front. <

The main problem is reflections that arrive within about 20 milliseconds of the direct sound. Further, to do much damage those reflections need to be pretty strong - say, 10 dB or less below the direct sound. Are either of those conditions likely or even possible after a second bounce in a typical size room?

> You don't want direct sound from bipole/dipoles coming off the front wall at you. <

Agreed, and that's why I specifically excluded them early in my article.

--Ethan

Posted: Wed Mar 30, 2005 1:42 pm

I agree that 2" is NOT going to do anything more to the highs than 1" or 1/2". It will though go down further into the mids where people and chairs are already sucking up a good portion and where drywall walls are absorbing some too. THAT's where the overabsorbtion can happen IMO.

Again, we're talking an HT environment here, not a studio. There will likely be 6-8 or more overstuffed chairs and 2-8 people in the room doing a wonderful job of hogging upper bass and mids. Putting say 2" space 2-3" off the wall on the WHOLE front wall would likely overdo the upper bass through lower mids from an absorbtion standpoint.

Ethan,

I agree that the BIGGEST problems are those within 20ms and those within 10db of the original signal. In a smaller home theater, the dipoles coming off the front wall would absolutely qualify. Off the back then off the front? Maybe not. BUT that doesn't mean they are not issues - just not BIG issues. If I have a signal that is say 24db down and at around 40ms - is that a problem? Yes - just not as big a problem as the ones in the range as you describe.

Posted: Wed Mar 30, 2005 2:39 pm

bpape wrote:

I agree that 2" is NOT going to do anything more to the highs than 1" or 1/2". It will though go down further into the mids where people and chairs are already sucking up a good portion and where drywall walls are absorbing some too. THAT's where the overabsorbtion can happen IMO.

Yeah, but the people and chairs are also absorbing the Hi-mids and Highs. In this respect they're far more balanced at absorbing, ( and IMO almost worth taking them out of the equation in this respect ) so that still leaves an unbalanced state of absorption if you're only using thin absorption on your walls/ceiling.....

Quote:

Again, we're talking an HT environment here, not a studio. There will likely be 6-8 or more overstuffed chairs and 2-8 people in the room doing a wonderful job of hogging upper bass and mids. Putting say 2" space 2-3" off the wall on the WHOLE front wall would likely overdo the upper bass through lower mids from an absorbtion standpoint.

... so I still don't agree with over absorption.

Let me just qulaify that though.. I'm not suggesting an anechoic chamber is the aim by any means, but for an EVEN Balance of absoprtion across the whole range ( Excepting the low bass which would involve filling too much of the room with absorption, leaving no sapce to get in there Wink

) means a LOT of absorption.

Ethan,

I agree that the BIGGEST problems are those within 20ms and those within 10db of the original signal. In a smaller home theater, the dipoles coming off the front wall would absolutely qualify. Off the back then off the front? Maybe not. BUT that doesn't mean they are not issues - just not BIG issues. If I have a signal that is say 24db down and at around 40ms - is that a problem? Yes - just not as big a problem as the ones in the range as you describe.[/quote]

The differences between a HT and a Studio Control room is interesting actually.

Control Rooms aren't designed to be anechoic of course, but one way of looking at it is this....

The sound you are listening to in any listening room like a HT or Hi-FI Room have been tweaked and mixed in a control room.

I've had the chance to listen to a hit album ( Level 42 ) in the control Room it was mixed in. And lemme tell ya, it sounded fucking EXCELLENT! Much better than anything I've ever heard in any listening room.

So what's wrong with a school of thought that says make your listening room like a control room?

Paul

Posted: Wed Mar 30, 2005 3:04 pm

Paul,

I suspect that one day you and I will agree on pretty much everything.

> So what's wrong with a school of thought that says make your listening room like a control room? <

That's exactly what I think too. Some/many/most audiophiles and home theater designers dispute this vehemently. But I can't for the life of me understand why. These guys with their $40,000 loudspeakers and $12,000 CD players and $17,000 power amps and $6,000 speaker cables, ad nauseum, would crap their pants if they ever heard what every day competent pro audio gear in a great room really sounds like.

--Ethan

Posted: Wed Mar 30, 2005 3:16 pm

Ethan Winer wrote:

Paul,

I suspect that one day you and I will agree on pretty much everything.

> So what's wrong with a school of thought that says make your listening room like a control room? <

That's exactly what I think too. Some/many/most audiophiles and home theater designers dispute this vehemently. But I can't for the life of me understand why. These guys with their $40,000 loudspeakers and $12,000 CD players and $17,000 power amps and $6,000 speaker cables, ad nauseum, would crap their pants if they ever heard what every day competent pro audio gear in a great room really sounds like.

--Ethan

Yup. but the Audiophile community is driven by the placebo effect, not by real effects.

There's absolutely NO DIFFERENCE between a $5 power cord and a $400 power cord in terms of sound quality, yet the $400 power cord WILL sound better to the Audiophile because he BELIEVES it will.

Paul

p.s I once succesfully trolled an audiophile forum years ago, by claiming to have found a huge increase in quality by keeping the speaker cables absolutely STRAIGHT! The responses were amazing in their seriousness Smile

Once I've finished my studio and have some leisure time again, I'm gonna do something similar again. Great entertainment.

This topic sponsored by: