Loudspeaker perception

[poptart]

I suppose one could say that the need was identified in my PhD. thesis back in 1981, it was certainly discussed, but that work was aimed more at rooms for sound testing than for critical listening, however, the need and concepts are exactly the same. This thesis was used in the design of several sound studios including the ones for the satellitte radio companies studios.

Coincidentally, RPG's products were used in both the Sirius and XM satellite radio studios as well. Their specialty is diffusion products but they make some low frequency absorbers. There seems to a mushrooming of companies that make room treatments these day so recognition of the need must be growing.

The plate absorbers mentioned have the plate facing into the room? Good for low frequencies but a big mirror for highs. It would be nice to combine the two ideas, punch a stiffer plate with the BAD pattern so you keep the panel resonance the same but gain diffuse instead of highly specular reflections above 1K.

 

[mige0]

To me OB does 2 things that give it a sense of superior subjective purity in the power region 200-800Hz over a box. 1. Does not smear the 1st msec as much. 2. Gives a means of radiation control there. I.e. figure of 8 is a type of control.
It asks for more space and money, but that is a discussion of another order.

What the "pitch & catch" / SBA / DBA subwoofer array arrangement (developed by Goertz, Wolff, Naumann
http://www.sennheiser.com/klein-hummel/globals.nsf/resources/tmt2002.PDF/$File/tmt2002.PDF) has in common with open baffles is that it does NOT pressurise the room – independent from which type the subwoofers are .

This makes it really appealing for me. I think I have to run some simulations on the room simulation program CARA next.
My guess is that there might be a way to lower the count of speakers needed for some special cases.

Would be fascinating if we could extend the frequency range of transparency - we can get from OB's 100Hz and up - down to the bottom.

Greetings
Michael

 

[mige0]

Coincidentally, RPG's products were used in both the Sirius and XM satellite radio studios as well. Their specialty is diffusion products but they make some low frequency absorbers. There seems to a mushrooming of companies that make room treatments these day so recognition of the need must be growing.

The plate absorbers mentioned have the plate facing into the room? Good for low frequencies but a big mirror for highs. It would be nice to combine the two ideas, punch a stiffer plate with the BAD pattern so you keep the panel resonance the same but gain diffuse instead of highly specular reflections above 1K.

Yes the metal plate is faced towards the room as intended by the inventors.

Should be no problem to apply some acoustic foam to the front as well if you want to have *not only* LF absorbtion.
Alternatively you could simply "turn the Schnitzel"


Keep in mind that acoustic foam isn't that absorptive to high frequencies as stiff fibre glass for example.

 

[mige0]

You are quite correct. I don't believe that I have ever argued against OB on a purely theoretical basis, only that the "apparent" advatages do not "appear" to outweigh the "apparent" disadvantages. I find them impractical and problematic to work with. I find the need for active crossovers and multiple amps a very bad use of limited funds in a sound system setup. If cost were no object I would sell lots more speakers than I do. The fact is that cost IS ALWAYS a major factor. The OB pushes up the costs far more than I believe it would push up the performance.

Earl, regarding active setups - besides some very good technical arguments there are sonic benefits very obvious to at least some people.
For them its not a question / discussion what's "mass market's" desire. As long as I can afford, I *always* will go active, simply for its sonic superiority (as I perceive it for some decades now).


Not to say there aren't any beautiful passive speakers.

Greetings
Michael

 

[JPV]

Small ? – not sure – well, at least as small as a 200+ seat cinema actually is.

Basically it was full range as there were roughly a dozen surround speakers each side available.
Though I tailored the frequency response to taste. If too much HF the result doesn't convince of.

For home use – no, I didn't

For LF only is a pretty hypothetical case as you don't easily get into a situation where you have more LF absorption in small rooms than HF absorption


Greetings
Michael

Let's suppose that a small room has enough bass attenuation, would this method give optimal bass restitution?

JPV

 

[markus76]

I would suggest that you use the wording (acoustically) "small room" as it is defined in the literature: a room the size of a "typical" living room. 200+ seats is more the office/worspace type of space. Next category would be spaces the size of concert halls.
The soundfield in each category differs significantly!

Best, Markus

 

[JPV]

I would suggest that you use the wording (acoustically) "small room" as it is defined in the literature: a room the size of a "typical" living room. 200+ seats is more the office/worspace type of space. Next category would be spaces the size of concert halls.
The soundfield in each category differs significantly!

Best, Markus

Yes exactly,

The question is related to have an impression ( in the LF) of well behaved decaying LF sound field which is nice to hear and this in a mode prone environment ( small room )

JPV

 

[gedlee]

has in common with open baffles is that it does NOT pressurise the room

And "pressurizing the room" is bad because ...?

Earl, regarding active setups - besides some very good technical arguments there are sonic benefits very obvious to at least some people.
I *always* will go active, simply for its sonic superiority (as I perceive it for some decades now).

Not to say there aren't any beautiful passive speakers.

I have not experinced any technical or sonic benifits to active, only very large additional costs and mores "toys" to play with.

 

[Paul W]

Markus,
With the bass arrays, you mention "two additional subs in back". From that, I believe you tried something other than the 1/4 and 3/4 width and height sub locations. What sub versus wall locations are represented in the SBA and DBA plots you posted?
Paul

 

[markus76]

Paul, all subs were at 1/4 wall length from the side walls but they were standing on the floor. So I guess that's why we don't see an impact on the 70 Hz mode.

Best, Markus

 

[mige0]

Let's suppose that a small room has enough bass attenuation, would this method give optimal bass restitution?

JPV

JPV, yes I think so – but haven't done this, so my answer is no more that a good guess.

Keep in mind that you don't get it without adding some "synthetic" reverberation. Just playing back what the mic's are recording (with some delay) did not sound good / right.
So its not exactly *restitution* you get but rather creating an ambience at will.

What I got back then dropped my jaw, considering the very low effort I made.

Basically it was
- relatively cheap AKG boundary mics
- a simple (Mackie) mixer as mic pre
- a TC electronics two channel reverb

Most astonishing of all - it was *only* two channels

Now I would use a more sophisticated PC solution with the mighty possibilities of convolution reverb you get for free today.

I would suggest that you use the wording (acoustically) "small room" as it is defined in the literature: a room the size of a "typical" living room. 200+ seats is more the office/worspace type of space. Next category would be spaces the size of concert halls.
The soundfield in each category differs significantly!

Best, Markus

Sure.

And "pressurizing the room" is bad because ...?

Frankly - no clue. (except maybe that there are very few instruments that can pressurize a room)

As long as everybody is looking for some light in the dark, I think best is to state the obvious first – look out for similarities / differences next – try to construct some hypothesis and proof of concept last.

I have not experinced any technical or sonic benifits to active,.

What a pity – though I already felt almost sure about that

Paul, all subs were at 1/4 wall length from the side walls but they were standing on the floor. So I guess that's why we don't see an impact on the 70 Hz mode.

Best, Markus

Markus, if the CSD plots are measurements of that setup in your room they are darn good
How did SBA / DBA sound then?



Michael

 

[bwaslo]

Markus,

Good point about the non-rigid walls. I've also wondered about furniture in the room and doorways and windows affecting the DBA scheme. Very elegant idea, though. I was once involved in using a similar thing for generating reflection coefficients to test RF amplifiers (done in a matched cable arrangement, a much more controlled situation than a listening room of course).

Though the plots you show make the DBA look better to me (big resonance near 70Hz being a bigger concern than one near 30Hz that would seldom become excited).

I'm using the multisub approach with active servoed woofers, placed and adjusted by trial and error. It does work very well. I like the active approach for the woofers rather than passive. It appears these days (with class D amplifiers, switching supplies and the like) that a strong power amp can cost less than a high quality woofer -- or even its cabinet, in a lot of cases. And active crossovers are just opamps, resistors and capacitors (jelly bean parts) though that doesn't stop companies from charging crazy prices for same. Making the arrangment active makes it all a lot easier to get it to play flat, particularly if servo feedback is used.

bwaslo , what I found is that a DBA might only work well in a perfectly rectangular room with very rigid walls, i.e. creating a plane wave makes sense at all. That's something not found very often. In a real room where calculated modes and real modes don't match very well the multisub approach seems performs better.

Multisub in DBA configuration:

An externally hosted image should be here but it was not working when we last tested it.

DBA (delay and phase invertion of rear subs):

An externally hosted image should be here but it was not working when we last tested it.

Best, Markus

 

[ScottG]

Scott, I can actually think of lots of reason for "a perception of superiority by others". Its just that none of them are acoustic - they are all psychological. (And I prefer to avoid those kinds of discussions because its not my field.)

Thats true, and its always something that anyone needs to be extremely wary of. "Blind" and (double blind) testing can be done at home, but most won't expend the effort (..in fact I've rarely done this myself).

Still, I have heard differences effectively "double blind" between open baffle midbass operation vs. monopole operation. There were however multiple differences in the two different systems and also different placement within the room. (..I did swap equipment and loudspeaker placement to get a "feel" for the "character" of these changes, but it did take place over a more extended time period (over an hour).) HOWEVER, I'm reasonably confident that differences were SO apparent in particular instances (drums especially) that it wasn't simply a psychological effect.

 

[graaf]

Don't You think that posts from No 265 and on should be moved to a separate thread?
they adress various issues of bass reproduction and subwoofers
but nothing about "loudspeaker perception" - completely off-topic

best!
graaf

 

[ScottG]

..only that the "apparent" advatages do not "appear" to outweigh the "apparent" disadvantages.

Yes, but beyond what has been discussed, how much further have you thought about - what is, and is not, "apparent"?

This disadvantages are fairly apparent and easy to discuss, and most have been discussed. But perhaps any advantages are far less apparent (..from a technical perspective).

As far as what is *practical* in a loudspeaker, well - that really isn't what this thread is about, nor is it a major concern for an enthusiast - at least for the point of discussion. Also note that what is and is not practical is a personal "choice" that may not have much to do with one forum member to the next.

 

[gedlee]

Still, I have heard differences ... HOWEVER, I'm reasonably confident that differences were SO apparent in particular instances (drums especially) that it wasn't simply a psychological effect.

Another common "flaw" in many assesments is to assume that "differences" mean "better". This isn't necessarily true and this is where bias plays a strong role. It has been shown time and time again that audiophools prefer "differences", rating a change "better" far more often that a "degradation".

One can actually make a change, a second change, and finally a third change back to the start, taking opinions at each step and find that things got better all the way along. "Change" is not conserved in "audiophool" algebra. I've done this to evaluate the evaluator.

To me no opinion of a change can be valid without some quantifiable measure of the change that can explain the opinion. Otherwise the circular problem can be insidious.

 

[gedlee]

Yes, but beyond what has been discussed, how much further have you thought about - what is, and is not, "apparent"?

This disadvantages are fairly apparent and easy to discuss, and most have been discussed. But perhaps any advantages are far less apparent (..from a technical perspective).

As far as what is *practical* in a loudspeaker, well - that really isn't what this thread is about, nor is it a major concern for an enthusiast - at least for the point of discussion. Also note that what is and is not practical is a personal "choice" that may not have much to do with one forum member to the next.

If its not "apparent" then I guess that it hasn't dawned on me

We certainly differ on the "practical" point of view because I find discussions and pursuits of the "impractical" to be academic and somewhat pointless, but certainly a waste of time. Everything that I do is from the point of view of practicality. Its the definition of "practical" that is up for grabs.

 

[ScottG]

Don't You think that posts from No 265 and on should be moved to a separate thread?
they adress various issues of bass reproduction and subwoofers
but nothing about "loudspeaker perception" - completely off-topic

best!
graaf

Bass reproduction generally is part n' parcel with "loudspeaker perception".

The topic of "subwoofer" is something of a misnomer for both Earl and the pro industry in general (from the perspective of nomenclature). The bandwidth of these so-called subwoofers not only extends into the bass region where substantial fundamentals reside, but also often extends into the lower mid-range.

IMO "subwoofer" is more properly described as an additional device that extends freq. response below virtually all fundamentals - specifically into the infrasonic region.

 

[ScottG]

Another common "flaw" in many assesments is to assume that "differences" mean "better". This isn't necessarily true and this is where bias plays a strong role. It has been shown time and time again that audiophools prefer "differences", rating a change "better" far more often that a "degradation".

One can actually make a change, a second change, and finally a third change back to the start, taking opinions at each step and find that things got better all the way along. "Change" is not conserved in "audiophool" algebra. I've done this to evaluate the evaluator.

To me no opinion of a change can be valid without some quantifiable measure of the change that can explain the opinion. Otherwise the circular problem can be insidious.

Audiophool or not, at least in the case I mentioned - I'll state this for a certainty:

What I heard was not only DIFFERENT - it was CLEARLY *BETTER* AND DESCRIBED in a manner that most would actually consider as BETTER.

If it was not more ACCURATE, well then either a series or different recordings were horrible in this respect, OR IT WAS ALSO AT LEAST A LITTLE MORE ACCURATE.

mige0 has expressed a similar sentiment on this thread alone. He may not have gone through similar testing, but somehow I doubt he is "phooling" himself either.

 

[graaf]

Bass reproduction generally is part n' parcel with "loudspeaker perception".

then nearly everything is "part n' parcel with "loudspeaker perception""

the topic of this thread is very specific:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=130352
http://www.diyaudio.com/forums/showthread.php?postid=1618806#post1618806

frankly speaking I don't know where did the title "loudspeaker perception" came from?
perhaps it is imprecise

best regards,
graaf