Loudspeaker perception

[mige0]

Again Earl – I very much would like to discuss that topic with you as I found your knowledge in that area to be the strongest and most eye opening for me.

But - *please* put down the "rambo" for a moment and also pick up *my* point of view - or even better balance Pro and con from a more neutral point of view – shouldn't be that hard for you claiming to be a scientist.

Why is a plane wave desirable? I don't see a reason to assume that.

Me neither. (see above)
But if I have to trade it in for getting fast decay / suppression of room modes – so what?

Multi-sibs CAN act as active absorbers. If I have two subs in a room and I turn on a third and the sound level (averaged arround the room to be precise) goes down (and this is easy to arrainge, just try it), then the third sub IS actively absorbing the sound in the frequency range where the sound level has gone down. This is simply physics.

I must have missed this.
Read the Todd Welty paper some time ago and "active bass absorption" didn't jump on me then.
http://www.harman.com/wp/pdf/multsubs.pdf

Could you please elaborate on this any further – maybe you have some measurements (CSD) about decay behaviour as this is a very good indicator if there is just "FR evening out" or absorption going on?

Active sound sources can decrease the decay along with the levels, but they don't have to. It all depends on how they are setup, phase, amplitude, etc.

"Active sound sources"


"It all depends on how they are setup, phase, amplitude, etc"
so what?

And we should all remember that it is possible for sound decay in real rooms to not be monotonic. Namely, the sound CAN increase before it falls or fall at different rates over time.

Haven't come across that – or at least may not have identified it the way you put it.
Again - could you please elaborate on this any further – maybe you can point me to some measurements for illustration ?

For instance, the frequency of modal decay does not occur at the frequency of the excitation. So the decay could be quite dissonant. The longer a sound exists the louder it will seem to be (up to a point) so both the gain from a mode as well as the extended decay will tend to make that frequency pronounced.

Worth to note now and then – also that the a room mode has some bandwidth / meaning it doesn't happen exactly at a single discrete frequency.

- ---


Besides all above I am not so much interested in uniform frequency response (about 10dB jumps with multi sub as far as I have seen) in the modal region as in short decay – or even better – no decay, as virtually no room modes come into play.

The measurements from Nils at AVS together with that presented by Goertz / Wolff / Naumann in their DBA paper indicate that it *is* possible to have all the cake

Michael

 

[gedlee]

But - *please* put down the "rambo" for a moment and also pick up *my* point of view - or even better balance Pro and con from a more neutral point of view – shouldn't be that hard for you claiming to be a scientist.

Well I am sorry, but I'm not going to deal with someone who insults me that this.

Markus

Inferference is not absorption and won't change the energy in the room. Some points will show a decrease but conservation of energy means that some will show and equal increase.

Why is it so hard to conceive of a source being sink in one frequency band and an source in another. This is easily show theoretically and hence should easily be found in practice. If the DBA setup has sinks then why isn't it feasible that a random setup could likewise as as a sink. The only difference is that ALL of the back wall speakers are sinks and all of the front wall speakers are sources. In the random situation this mix of sources and sinks will tend to be random.

I have never bought into the concept than no modal excitation is desirable. It needs to be controled, but not elliminated.
A pure plane wave in a room would act just like an anechoic chamber - never a good listening space. I want a high entropy modal situation at all frequencies down into the LFs and the plane way situation does not create this.

 

[ScottG]

To clarify about multi-subs versus DBA.

Multi-sibs CAN act as active absorbers. If I have two subs in a room and I turn on a third and the sound level (averaged arround the room to be precise) goes down (and this is easy to arrainge, just try it), then the third sub IS actively absorbing the sound in the frequency range where the sound level has gone down. This is simply physics.

Active sound sources can decrease the decay along with the levels, but they don't have to. It all depends on how they are setup, phase, amplitude, etc. And we should all remember that it is possible for sound decay in real rooms to not be monotonic. Namely, the sound CAN increase before it falls or fall at different rates over time. And active can affet each of these in different ways. It could actually increase the sound before it decays, etc.

My opinion about Floyds question is its both. Modal decay is a complex thing. For instance, the frequency of modal decay does not occur at the frequency of the excitation. So the decay could be quite dissonant. The longer a sound exists the louder it will seem to be (up to a point) so both the gain from a mode as well as the extended decay will tend to make that frequency pronounced.

This isn't loudspeaker perception specifically (rather like the room construction portion), but:

This is another one of those areas that can provide very good results for an overall modest expenditure.

While there are certain design characteristics I find that produce better quality low freq.s - i.e. a better "sounding" sub or full-range loudspeaker, these design elements are almost always more expensive in parts and construction.

But for an "active" low freq. absorber - you can go pretty low in cost:

Cheap plate amps, cheap high excursion drivers with high compliance (but good motor strength), AND fairly low volume requirements (in a sealed system). Not only can it be relatively inexpensive, ***but it's also extremely well suited to "in-wall" application***.

What's really needed here though, is a good program for determining distribution of these things around the room to achieve a particular type of desired effect for a particular user. Hint, hint - good business opportunity.

 

[mige0]

Maybe the mods should split the thread at this point. We are starting to talk about "Absorption in the modal region".

Maybe yes, but consider also:

The topic of the thread is about speaker perception and as such don't you think we should also discuss the limitations as where "perception of speakers" apply ?
Room modes outright dominate sound performance - and from this perspective it makes sense to keep it in here.

You cannot discuss *anything* seriously without at least illuminating the context IMO.

Room modes clearly affect out perception – not only how a speaker is able to "drive" the room but also to what extent it is possible to establish the illusion of something "real" playing in your room.

For example –
Every room has its sonic patterns and one of the significant patterns is, which modes the listening room actually has – and how the speakers interact when placed differently.

If this pattern of room modes (or how speakers can deal with it at certain places) does or doesn't fit the recording, for sure isn't a bagatelle when it comes to a more holistic impression of "loudspeaker perception" (Earls great take of "dissonant" decay). No?

Well I am sorry, but I'm not going to deal with someone who insults me that this.

What I proposed is to less support what *you* are "bying in" than to discuss the topic. This includes - IMHO – to not only support your point of view but rather to splay all details connected to the topic.
If this is asked for to much .....

Inferference is not absorption and won't change the energy in the room..

You are sure that DBA is dealing with interference only – me not.
Otherwise – it would be hard to show frequency responses like the ones we saw.

Why is it so hard to conceive of a source being sink in one frequency band and an source in another. This is easily show theoretically and hence should easily be found in practice.

I could think of that (in an actively responding set up for example) – but why should a simpel subwoofer do it?
Also haven't seen any measurements yet that backup your claim.

If the DBA setup has sinks then why isn't it feasible that a random setup could likewise as as a sink. The only difference is that ALL of the back wall speakers are sinks and all of the front wall speakers are sources. In the random situation this mix of sources and sinks will tend to be random.

sinks or no sinks – usually you are more decisive – maybe you begin to follow my suggestions ?
What is the benefit of random placed subs in a situation where you don't need it = flat wave form?
In case of DBA there is no need for random placed subs – quite contrary – its a different approach than multi sub placed random (or sort of)
Anybody can gain a good impression of the benefits and restrictions of multi sub placement due to the paper from Todd Welti (thanks Markus for pointing at and reminding me)
and like wise about the DBA due to the paper linked earlier.

I have never bought into the concept than no modal excitation is desirable. It needs to be controled, but not elliminated.

This is no more than a plain belief IMO.
It holds for the concept *you* support – no doubt about that - but not necessarily for *any* other concept .

A pure plane wave in a room would act just like an anechoic chamber - never a good listening space. I want a high entropy modal situation at all frequencies down into the LFs and the plane way situation does not create this.

Have you played around with DBA actually – or is it only an educated guess you state here ?

I am with you in that an anechoic chamber can't offer the charm of a lush listening room – and quite few would feel comfortable in.
BTW one of the concerns I have about scientific findings in such a set up. On the other hand - sound reproduction in open air can be absolutely satisfying.
This points to quite audible imperfections of so called "anechoic" chambers – don't you agree?

Sure – the high entropy situation *you* feel happy with wouldn't happen – but I could state this to be beneficial as well (see the "open air" argument above) – or do you have further considerations to back up your rather personal than scientific claim?


Michael

 

[graaf]

What I proposed is to less support what *you* are "bying in" than to discuss the topic. This includes - IMHO – to not only support your point of view but rather to splay all details connected to the topic.
If this is asked for to much .....

yeah, in fact it was waaaay too much!!

don't You know that the Good Doctor has His important educational AGENDA !!!

maan, You owe Him RESPECT for that !!!

so... don't be surprised now!

in fact it was the final insult ...

You troll!!

You know...

best regards!
graaf

 

[mige0]

yeah, in fact it was waaaay too much!!

don't You know that the Good Doctor has His important educational AGENDA !!!

maan, You owe Him RESPECT for that !!!

so... don't be surprised now!

in fact it was the final insult ...

You troll!!

You know...

best regards!
graaf

Wow !

 

[gedlee]

When I agree with you guys all is fine, but when I disagree I'm "Rambo", opinionated and not objective. Sorry I don't play those games.

 

[ScottG]

When I agree with you guys all is fine, but when I disagree I'm "Rambo", opinionated and not objective. Sorry I don't play those games.

Actually I don't think anyone has a problem with you disagreeing on any particular topic. What they would *like* however is some discussion from you that was more "process" based and less "conclusive", OR *if* "conclusive"/argumentative - to argue as many different "sides" as seem practical (i.e. at least 2: for and against). Frankly I thought this response: "To clarify about multi-subs versus DBA", pretty much achieved that sort of "process" response .

Yeah, the "rambo" thing was a little rude (even if the intent wasn't there), and graaf's more so (which most certainly was intended). (..both "pointed", but also a little and a lot excessive.)

I've personally tried out the active bass absorption technique. Its an easy experiment to do.

(..for others)

(low or no cost): Go into you typical "mega-store" electronics outlet where they have several subs WITH a cheap spl meter and a cd burned with some modal range test-tones in a format that a cheap in-store cd player can handle. (..make sure you select a time of business when the room is likely un-occupied.) Turn off amplification to everything but the loudspeakers you want to listen to (and in the case of subs - disconnect the power on all of them). Select loudspeakers that are moderately "full-range" (i.e. have an extended low freq. response.) Play the tones and pick a few areas of the room to get spl readings. Then re-connect one of the subwoofer's power cord and turn it on, BUT DON"T HAVE A SIGNAL GOING TO IT. Now make another sweep at the same multiple areas in the room and look to see a difference. I've never NOT noticed a difference (assuming a broad range of locations) - and virtually always in some locations the difference is plainly audible.

Of course the spl-meter will cost you if you don't already have one.. But they are fairly cheap (usually select an analog (readout) meter vs. a digital one.) OR you can always purchase and return the meter (provided that the law allows it) claiming the calibration was *way* off (..and it always is)

 

[ScottG]

I once suggested in this thread looking at the sometimes *very* different opinions at the Rmaf 2008 thread here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=131174

But here is something I found particularly interesting - Panomaniac's post (#93):

http://www.diyaudio.com/forums/showthread.php?s=&threadid=131174&pagenumber=4

..Didn't like the Orions++, but did like the Plutos. What's interesting about this is the un-said context: Panomaniac's loudspeakers (which I'm assuming he substantially prefers), are open baffles (at mid-to-lower freq.s). I.E. - he does like his dipoles, but doesn't like the Orions.

IMO - this just "highlights" that dispersion character is not necessarily the dominate factor with why some prefer open baffle operation (..at mid-to-lower freq.s).

 

[Russell Dawkins]

In the same vein, I find Panomaniacs reply #13 here: http://tinyurl.com/6gfwvh
intriguing, considering the cost/performance ratio and relative simplicity of the PAudio 18" "solution".

 

[graaf]

But here is something I found particularly interesting - Panomaniac's post (#93):
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131174&pagenumber=4

In the same vein, I find Panomaniacs reply #13 here: http://tinyurl.com/6gfwvh
intriguing, considering the cost/performance ratio and relative simplicity of the PAudio 18" "solution".

perhaps it was not a problem with the speakers
after all according to Mr Panomaniac:

All the OBs there seemed to have the life sucked out of them.

and the above statement refers to very dissimilar speakers in various setups

most probably there was something wrong with other elements of "listening process", perhaps with speaker room/interface or even perhaps just panomaniac had one of these worse moments/hours/days when everything sounds like "life sucked out"

best regards!
graaf

 

[graaf]

interesting to read that many people at RMAF liked Plutos even more than Orions, Mr Panomaniac included

perhaps this was because they were more optimally placed in the room:
http://www.diyaudio.com/forums/showthread.php?postid=1634295#post1634295

ha! actually it is the placement I advocate for omni speakers here on the forum:
http://www.diyaudio.com/forums/showthread.php?s=&postid=1484811&highlight=#post1484811
(see the image attached to the post)




on the other hand for Orions the placement was clearly suboptimal:

http://www.diyaudio.com/forums/showthread.php?postid=1634297#post1634297

almost pushed in the corner with no reflective wall behind how could they sound alike? they are not designed for that!

room-speaker interface is everything!

best regards!
graaf

 

[Salas]

Did they play as boundary speakers in the RMAF or the pictures show them merely put away not to obstract the Orions?

 

[markus76]

Originally posted by ScottG I've personally tried out the active bass absorption technique. Its an easy experiment to do.

(..for others)

(low or no cost): Go into you typical "mega-store" electronics outlet where they have several subs WITH a cheap spl meter and a cd burned with some modal range test-tones in a format that a cheap in-store cd player can handle. (..make sure you select a time of business when the room is likely un-occupied.) Turn off amplification to everything but the loudspeakers you want to listen to (and in the case of subs - disconnect the power on all of them). Select loudspeakers that are moderately "full-range" (i.e. have an extended low freq. response.) Play the tones and pick a few areas of the room to get spl readings. Then re-connect one of the subwoofer's power cord and turn it on, BUT DON"T HAVE A SIGNAL GOING TO IT. Now make another sweep at the same multiple areas in the room and look to see a difference. I've never NOT noticed a difference (assuming a broad range of locations) - and virtually always in some locations the difference is plainly audible.

THIS IS NOT ACTIVE ABSORPTION! For active absorption to work, sound needs to be generated.
Your measurements only showed the tolerance of your SPL meter and the deviation caused by not measuring at the very same locations you measured before. It's just impossible to do a repeatable measurement when you don't mark the locations to the millimeter. Have you ever noticed how much the sound field changes when moving the meter only a few inches? Even opening a door or moving people changes the modal field. Within a store where people interact constantly with objects, doors, windows, etc. no meaningful acoustic measurement can be taken.
Btw can the weighting of your SPL be switched off?

 

[ScottG]

THIS IS NOT ACTIVE ABSORPTION! For active absorption to work, sound needs to be generated.
Your measurements only showed the tolerance of your SPL meter and the deviation caused by not measuring at the very same locations you measured before. It's just impossible to do a repeatable measurement when you don't mark the locations to the millimeter. Have you ever noticed how much the sound field changes when moving the meter only a few inches? Even opening a door or moving people changes the modal field. Within a store where people interact constantly with objects, doors, windows, etc. no meaningful acoustic measurement can be taken.
Btw can the weighting of your SPL be switched off?

We are talking about something different, and I could well have misinterpreted Earl's comments. If so, I apologize. As for what I was describing:

"Active" in the sense I intended - is the use of an amplifer. External pressure hitting the "active" sub's driver is converted from motion to heat - "sinking" energy. The amplifier's electrical damping *actively* resists inward and outward changes by the driver caused by external pressure changes.

Of course all of those unpowered speakers and subwoofers will ALSO trigger a change - "passive". (note however that the "passive" change can also cause a reactive *addition* in spl.) Now you could argue that the change was the result of going from that "passive" condition to an "active" one (i.e. that the "passive" condition was making the change and the "active" one negating it). I wouldn't completely disagree with this, BUT I've also tried a subwoofer in a room "active", and not in a room - with changes.

Note that you don't have to move the meter from the location for the before an after for any single location - so it most certainly is NOT impossible. However, I've always found locations (dominate modes) where the average changed enough that it was most certainly an effect caused by the powered (but no signal) sub.

As for the meter, its a standard 2-setting "weighted" meter. Note that you aren't looking for extreme accuracy, what you ARE looking for is a substantial change. Something that *is* within the means of these cheap toys.

 

[ScottG]

perhaps it was not a problem with the speakers

most probably there was something wrong with other elements of "listening process", perhaps with speaker room/interface or even perhaps just panomaniac had one of these worse moments/hours/days when everything sounds like "life sucked out"

best regards!
graaf

Its possible - and at least to some extent likely, but there were OB's he liked at the show more than others.

 

[graaf]

Did they play as boundary speakers in the RMAF or the pictures show them merely put away not to obstract the Orions?

of course I am not sure as I haven't been there

on the picture it surely looks like they were plugged in and connected to the electronics
in fact it looks like they are being presented - the listeners are clearly looking at them

Linkwitz recommends that in normal situation - in a suitable room:

PLUTO should be listened to from closer distance and be placed at least 3 feet (1 m) away from large reflecting surfaces,

we know that they were presented at the show, people listened to them
well, I can't see how they could be reasonably positioned for listening in such a narrow room?
"at least 1 m away from side walls" normally required would mean 1-1.5 of stereo base width in this case
that is clearly not enough

boundary placement seems to be the only reasonable option in such a room for omni speakers

but how it was actually?
perhaps someone has been there and can clarify

best regards!
graaf

 

[mige0]

When I agree with you guys all is fine, but when I disagree I'm "Rambo", opinionated and not objective..

Not exactly Earl,
but yes - I feel sorry about my words did have such bad resonance and you feel insulted.


*But*, Earl – actually – its kind of the other way around (and I agree *if* we keep on continuing - we will go in circles (game playing as you put it))
.
If you can – see it as a feedback about how *I* felt when you started (...here we go again...) with what I call the DampfWalze in Germain
As you have some knowledge of our language, you might get the picture.
"Rambo" might have been not exactly the best translation though as its connotation for you might be different than for me and "SelbstIronie" isn't exactly your strong point AFAIKT.


Well – *I* can stand your manner (though don't like) – no problem – but consider that several others (and not only in this thread !) might feel quite similar without giving you back their impressions.

Besides that "kind of feedback" on a more personal level (your feelings / my feelings) I really would enjoy you to open up – on a professional level - to what Scott obviously was able to put into better words then me with "scientific approach to a topic":

What they would *like* however is some discussion from you that was more "process" based and less "conclusive", OR *if* "conclusive"/argumentative - to argue as many different "sides" as seem practical (i.e. at least 2: for and against).

Hope - but not sure - that you feel better now, Earl.


Back to the topic of double bass array :
In the scope of the thread it should be underlined that multiple bass array placed randomly by definition restricts them to mono playback.

As I would like to explore that border of stereo impression towards low/ very low frequencies rather myself then to believe in what psycho acoustics may take for granted - multiple subs like favoured by you ain't my first choice.

DBA wasn't exactly invented for stereo operation – but may be adaptable.

THIS IS NOT ACTIVE ABSORPTION! For active absorption to work, sound needs to be generated.
Your measurements only showed the tolerance of your SPL meter and the deviation caused by not measuring at the very same locations you measured before. It's just impossible to do a repeatable measurement when you don't mark the locations to the millimeter. Have you ever noticed how much the sound field changes when moving the meter only a few inches? Even opening a door or moving people changes the modal field. Within a store where people interact constantly with objects, doors, windows, etc. no meaningful acoustic measurement can be taken.
Btw can the weighting of your SPL be switched off?

Any good examples on "true" active absorption?
Haven't tried Scotts measurements but from own listening experience have no doubt that other speakers – be it plugged or unplugged alter the room's behaviour – or at least add some sonic patterns.

Still not sure about that "active absorption" thing.
If we look at it from an other perspective - a wave front transfers its impulse energy to the next "air" molecules in the radiating direction.
If there is no air to hit in the radiating direction but for example a loudspeaker membrane the energy transfer is sub optimal and a large percentage of energy is reflected.

*If* we actively mimic air with our loudspeaker membrane we could "catch" the energy and dissipate it in the amp.
*But* its only the energy of that area of the membrane – and that's way too low to be useful for LF absorbing.

Hence above must be sort of too simple picture.
Anybody that can help?

Toole asked an interesting question: "Do we hear the spectral bump or the temporal ringing?"

Best, Markus

He didn't have a DBA at hand to compare with – did he?




Michael

 

[graaf]

and "SelbstIronie" isn't exactly your strong point AFAIKT.

STOP insulting Dr Geddes AT ONCE!

what can You know about "SelbstIronie"???!

He knows EVERYTHING

haven't You got any morals!!??

behave! behave!
for CHRIST SAKE!!

 

[mige0]

perhaps it was not a problem with the speakers

most probably there was something wrong with other elements of "listening process", perhaps with speaker room/interface or even perhaps just panomaniac had one of these worse moments/hours/days when everything sounds like "life sucked out"

best regards!
graaf

Or with the electronics?

I have found my OB to be *very* revealing in this – occupying more time in electronics investigation - on subtle emotional aspects - than about edge diffraction at the moment.