Perceptual Effects of Room Reflections

[Duke]

The problem is absorbing the deepest octaves. If you don't manage to hit those and absorb too much of the rest it obviously will sound terrible.

'Absorbing' the 'deepest octaves' requires quite aggressive wall/corner treatment. Nowadays we have DSP to treat peaks in those octaves, at least.

So basically all I can do is place 17” soffit bass traps on the corners. There is some fiberglass something inside. It can absorb down to 40Hz but with not much efficiency below 50Hz... I kind of don’t care about below 40Hz can’t afford to do much about it.

Just for the record, there is an alternative to extensive bass trapping that acoustician Matthew Poes describes within about 30 seconds from where this clip is cued up to. Of course you can do both, they are not mutually exclusive:

 

[srrxr71]

Fully agree and appreciate such efforts, even enjoyed the Harman Logic 7 upmixer which was a work of David Griesinger in my previous car.

Many people have gotten hooked though their car systems. A lot of people, including people who post here, got their first taste from an Acura DVD-A system.

 

[srrxr71]

Ah no. Would you consider using just any old speaker on and left and a different one on the right for 2 ch?
Much of the negative comments made on multich is done because it's never given a chance to perform it's best.
The base 5 or 7 channels need to be as closely matched as possible, identical if your budget allows.

Only true in the Classical genre, for any kind of modern music discrete use of the base channels is much more the norm.


Yes it is, but if you want your multich experience to be as satisfying as your 2ch, that is what it takes.

Early surround before multichannel music in the form of SACD and DVD-A pretty much had dipole sides.

That changed with ITU R BS. 775. I understand this and that was the point I was making to the poster who had smaller sides.

I guess it’s okay to start. We can’t discourage people simply because they don’t have an extra $10-15k around. If they want to use $90 side speakers to experiment that’s fine. I think we all know it’s not meeting the standard.

Actually I said something similar to my friend that you said and pointed him to the standard. It annoyed the heck out of him. Not very encouraging. The truth is on a sofa it’s hard to get ITU R BS.775 because the cushion occludes the rear speaker.

My friend just like sound coming from everywhere. He has some cheap things sitting in the back and sides. What can I say? He was chasing some rare out of print DVD-A and I told him it was pointless without a proper ITU system. I hope I saved him $360 on that DVD because it is. But he wasn’t happy to hear it.

 

[srrxr71]

Just for the record, there is an alternative to extensive bass trapping that acoustician Matthew Poes describes within about 30 seconds from where this clip is cued up to. Of course you can do both, they are not mutually exclusive:

Thank you for that! Yes absolutely. I’ve trapped the heck out of my room. I’m trying to hit a mode at 60Hz with extra trapping.

However for 20, 30 Hz modes which I have, it’s an exercise in futility. I understand that.

I’m having a 3rd sub delivered in 2-3 weeks. So that would be helpful. Subs one and two have pretty much the same modes at my listening position.

The one question I have is whether I can cut the exact mode frequency with a high Q filter by about 10-15dB to get better waterfalls. Is that a valid way to handle it?

Also the 20, 30 Hz modes i’m actually going to leave alone to get that bass power out of my room. It’s practically inaudible right? It just exists for feels?

 

[Sal1950]

Early surround before multichannel music in the form of SACD and DVD-A pretty much had dipole sides.

I ran a all Paradigm system like that for 10+ years, I never really fell in love with it.

I guess it’s okay to start. We can’t discourage people simply because they don’t have an extra $10-15k around. If they want to use $90 side speakers to experiment that’s fine. I think we all know it’s not meeting the standard.

I understand what your saying, between a rock and a hard place.
The problem is we hear so much of this "multich never sounds as good as pure stereo" but when you find out the kind of multich rig they've experienced you immediately understand why they came to that conclusion. Speaker wise, stereo was 2x more expensive than mono, and done to the same quality level a 5.1 rig is 2.5x more costly than stereo not inclusive of the subwoofer. That's just the hard facts. There are ways to save a lot of money and still get excellent results but you have to do your homework.

 

[srrxr71]

I’m enjoying stereo for now enough to put off my homework. I’ll get there eventually.

 

[dasdoing]

Just for the record, there is an alternative to extensive bass trapping that acoustician Matthew Poes describes within about 30 seconds from where this clip is cued up to

where exactly in the video?

 

[fpitas]

I’m enjoying stereo for now enough to put off my homework. I’ll get there eventually.

Me too. I feel like primitive man, squatting in his cave with old 2 channel technology. Yet, I like it.

 

[Duke]

where exactly in the video?

It starts at 37 minutes and 37 seconds into the video. Or 2257 seconds into the video.

 

[dasdoing]

It starts at 37 minutes and 37 seconds into the video. Or 2257 seconds into the video.

ok, I might be missunderstanding.....but I don't seam to hear nothing about

alternative to extensive bass trapping

in that part.

 

[Duke]

ok, I might be missunderstanding.....but I don't seam to hear nothing about

[an alternative to bass trapping]

in that part.

The alternative is, multiple subwoofers (intelligently distributed):

"I've installed a lot of bass traps in people's rooms, I've filled every corner, the ceiling, you name it, and it didn't make anywhere near as big a difference as four subs did." - Matthew Poes, in the video clip.

 

[dasdoing]

The alternative is, multiple subwoofers (intelligently distributed):

"I've installed a lot of bass traps in people's rooms, I've filled every corner, the ceiling, you name it, and it didn't make anywhere near as big a difference as four subs did." - Matthew Poes, in the video clip.

ok, he must be talking about FR?
with bass trapping you manly target the decay of the modes. getting the FR flat with treatment realy is something near impossible. you would have to be able to absorb ALL the energy of the mode.
multi subs wont do anything for the decay

 

[NTK]

Low frequency room modes are minimum phase behaviors. Correct the FR (with minimum phase filters), the time domain errors are corrected too.
References:

https://www.harman.com/documents/LoudspeakersandRoomsPt2_0.pdf

https://www.harman.com/documents/LoudspeakersandRoomsPt3_0.pdf

 

[srrxr71]

ok, he must be talking about FR?
with bass trapping you manly target the decay of the modes. getting the FR flat with treatment realy is something near impossible. you would have to be able to absorb ALL the energy of the mode.
multi subs wont do anything for the decay

So the trick I tried over the weekend. Use the GRADE report to find the more frequencies down to the decimal point.

Introduce a high q filter and drop it by 10dB. I did mine at 60.3Hz only thinking that is the only audible mode I have.

Then I duplicated that and also attacked the 35.3Hz mode and the 20.3Hz modes.

I can switch between them at will.

This is just my opinion. Anyone can replicate this and compare themselves. No ABX just subjective opinion.

The bass is so tight and clean now. Really just like all other instruments and tracks are just chilling in the mix ready for you to partake now the bass notes are also chilling there for you to partake.

No need to concentrate on the bass line. I’m at just there and it’s so tight and clean.

When I went back I capsule clearly hear the muddiness on bass notes. Much harder to follow the bass lines. Keep in mind already on GLM corecyee bass it’s so much more clear than any other system I heard.

This little tweak really helped. I hope other try it and report back.

I have extensive treatment already and my waterfalls reflect it. I will be upgrading my bass traps hopefully they will arrive this week. Still it might help the 60.3Hz at best but it’s not going to touch 35.3Hz or 20.1Hz. It’s surprising how much attacking those helped. Those are “inaudible” and probably no notes go down there so one does not expect it to help.

My acoustic consultant said if you have these frequencies hanging out in the room for example 0.81ms they just combine with and interfere with other bass notes. I’m seeing this is true.

 

[srrxr71]

Low frequency room modes are minimum phase behaviors. Correct the FR (with minimum phase filters), the time domain errors are corrected too.
References:

https://www.harman.com/documents/LoudspeakersandRoomsPt2_0.pdf

https://www.harman.com/documents/LoudspeakersandRoomsPt3_0.pdf

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So i’m using about -10dB with Q 13-15 exactly on the mode frequencies. Sounds so much better to me. Bass is so clean it amazes me.

 

[srrxr71]

Me too. I feel like primitive man, squatting in his cave with old 2 channel technology. Yet, I like it.

It sounds so good in a treated room that I couldn’t be bothered to chase anything more. The entire soundscape is chilling in front of me. What more can I ask for? Yeah I’ll be a Neanderthal. A happy Neanderthal.

 

[srrxr71]

Low frequency room modes are minimum phase behaviors. Correct the FR (with minimum phase filters), the time domain errors are corrected too.
References:

https://www.harman.com/documents/LoudspeakersandRoomsPt2_0.pdf

https://www.harman.com/documents/LoudspeakersandRoomsPt3_0.pdf

View attachment 241842View attachment 241843View attachment 241844

Oh yeah that confirms it. Great info!

 

[Duke]

ok, he must be talking about FR?

Yes. And since the in-room frequency response predicts perception at low frequencies, he is also talking about "how it sounds".

with bass trapping you manly target the decay of the modes.

Speakers + room = a "minimum phase system" at low frequencies. So when you correct the frequency response, you have simultaneously corrected the time-domain response, and vice-versa.

Bass trapping directly affects the time-domain behavior and therefore improves the in-room frequency response.

Multiple subs intelligently distributed directly affects the in-room frequency response and therefore improves the time-domain behavior.

To put it another way, it is the in-room frequency response peaks which take longer to decay into inaudibility. Smooth those peaks (whether by multiple subs or EQ or bass trapping or whatever), and those frequency regions no longer take more time to decay than the rest of the spectrum.

(Toole reports in his book that we perceive the frequency response peak, and not the ringing in and of itself, which implies that fixing the frequency response is fixing the problem. See post #493 above by @NTK.)

getting the FR flat with treatment realy is something near impossible. you would have to be able to absorb ALL the energy of the mode.

Absorbing all the energy in the modes = anechoic conditions = not practical.

Matthew Poes is not the first person to conclude that a distributed multi-sub system is more effective than bass trapping at improving the in-room bass, but his extensive hands-on experience with both techniques qualifies him to comment from experience rather than from theory. I first learned the theoretical side from Earl Geddes in January of 2006.

Of course you can do both if space and resources allow, but most of the improvement will probably come from the distributed multisub system.

multi subs wont do anything for the decay

Multiple subs make the decay much more uniform across the spectrum and throughout the room, the "throughout the room" aspect being something that EQ of a single sub cannot accomplish for modal effects.

(Disclaimer: I have been manufacturing a distributed multi-sub system since 2006, so you are welcome to discount or dismiss my opinion since I am commercially involved.)

 

[tuga]

The problem of listening to loudspeakers in an anechoic chamber actually is that the soundstage can get quite close to the one of headphones which many people don't like. Thus especially for the inherently limited stereo reproduction for example side wall reflections are desired by many as they can increase the envelopment.

It's a bit like listening to an unamplified orchestra outdoors. An experience I urge you to avoid.

 

[srrxr71]

It's a bit like listening to an unamplified orchestra outdoors. An experience I urge you to avoid.

The Cleveland orchestra has been doing that for years in the summer.