The Objectives of a Loudspeaker in a Small Room

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gedlee said:


Well it is pretty difficult to place room objects, dampers, etc. in a manner that is pleasing to everyone.

IMO the room behind the speakers needs to be dead with no diffracting or refelcting objects nearby. These objects set up early diffraction and reflections and obsure the image - this alone dictates a lot of problems. The speakers should be symetrical to the listener - as well as can be achieved in the room. Then the nearest walls where the first sidewall reflections occur should have a diffuser (I build a special kind here) and this is usually a problem on top of the above requirements. The ceiling reflection must be disipated, the same with the floor. Then the listener must be near the center of the room away from reflecting boundaries. And finally the room from the listener position back should be without any sound absorption at all.

Now get all of this into your "living room" and you are a wizard!!!
[

For the first part, the room behind the speakers, what would you think about solutions that eliminate this room totally instead of making it acoustically dead. The result would be a 'in wall' or more realisticly a very flat 'on wall' speaker system.
Actually, I have started working on a flat (~ 6 inch deep) 'on wall' system, 2-way with a waveguided 1" dome tweeter and 12" woofer. First messurements of a test set up were quite promising, so I would be very interested on your views about such an approach.


gedlee said:

I do not believe that Toole ever said that very early lateral reflections (<10 ms.) are a "good thing". If you know of a statement of his that claims that I'd like to read it.

[

I can't see a benefit of early lateral reflections either, but in the attached document, Toole is quoted:
Toole has concluded that normal reflections in a typical small living room seem not to interfere with perception of the recorded space. He has also determined that early lateral reflections (<50ms) have a beneficial effect on intelligibility similar to raising the dialog level, and that the reflection pattern is more important than reverberation.

edit: jzagaja already quted that, sorry! ...that happens when awnsering phonecalls while typing... :rolleyes:

best, martin
 

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gedlee said:
IMO the room behind the speakers needs to be dead with no diffracting or refelcting objects nearby. <snip> And finally the room from the listener position back should be without any sound absorption at all.


There are definitely 2 schools of thought on which end of the room should be dead.

20~30 years ago the "dead end behind the speakers" fad was sweeping the recording industry. Everyone seemed to be building or renovating control rooms for this type of sound.

I'm of the other school. Somewhat reflective behind the speakers, no reflection from behind the head. Similar to what is done in performance halls. That's the type of room that has always sounded best to me.

A matter of taste, I suppose.
 
Cal Weldon said:


:D

Chris, you devil you.


jus trying to amuse myself -

Maybe the "best sounding" room is one that allows you to relax enough to enjoy the music and ignore everything else. So I guess that means one with a really quiet "beverage storage / dispensing" unit.
Now those in the know will recognize the reference to casa Weldon.

( DIY jet powered beer coolers need not apply)


edited fore typoze
 
lovechild said:


For the first part, the room behind the speakers, what would you think about solutions that eliminate this room totally instead of making it acoustically dead. The result would be a 'in wall' or more realisticly a very flat 'on wall' speaker system.
Actually, I have started working on a flat (~ 6 inch deep) 'on wall' system, 2-way with a waveguided 1" dome tweeter and 12" woofer. First messurements of a test set up were quite promising, so I would be very interested on your views about such an approach.
...
Throwing in some personal experience. Eliminating the room behind speakers is a positive approach. However, the wall around any on wall design would still benefit from a concrete type back wall with good absorption characteristics in the higher frequencies. The speaker in my avatar is only 11cm thick, and the wall still makes a difference.

lovechild said:


I can't see a benefit of early lateral reflections either, but in the attached document, Toole is quoted:
Toole has concluded that normal reflections in a typical small living room seem not to interfere with perception of the recorded space. He has also determined that early lateral reflections (<50ms) have a beneficial effect on intelligibility similar to raising the dialog level, and that the reflection pattern is more important than reverberation.

edit: jzagaja already quted that, sorry! ...that happens when awnsering phonecalls while typing... :rolleyes:

best, martin
Early reflections <4ms and room modes still affect imaging and spacial perception, unless one is not critical of the differences. This becomes personal preference.
 
Orthoperspecta

graaf said:
Re: PeteMcK

one of the most interesting three-channel systems is Stereolith from Switzerland: http://www.stereolith.ch/

the center channel is only from around 2 kHz and up and probably L+R but I'm not sure

and here is a review of heavily modified Stereolith Monitor 232: http://magazine-audio.com/essais-hi-fi/essais-enceintes-hi-fi/22

That reminds me of an invention "Orthoperspecta".

Here is a short story about it:
But I really want to tell you about another man than Dr. Matti Otala:

In Finland we had one certain genuine world class amp designer, the grand old man. Somewhat sensationally, Dr. Otala has publicly given praise for the TIM ideas to this man as the originator. His name was Tapio M. Köykkä. This man invented (I cannot translate this word correctly!) the counterphaseamplifier (please correct!) in 1953 which was later applied throughout the world. Electro-Voice was the first asking for a licence and Westinghouse invited the man to work with them in U.S. with no success. He stayed in Finland.

Mr. Köykkä also used a specific amp design curing transient distortion from 1955 (no feedback over many amp stages) and he wrote an article about the crucial transient distortion in 1969 taking heavy critics from scientific engineers as the idea was against the accepted dogms. A bit later Mr. Matti Otala grabbed bravely this controversal idea and continued to study it and showed that Mr. Köykkä was right - the muddy sound of amps was caused by transient distortion.

If I have understood this correctly, it seems that Mr. Otala took the international fame for curing the transient distortion and made his career using it. But later at least in Finland, Mr. Otala admitted openly, that Mr. Köykkä really invented the whole idea. Mr. Köykkä was sitting on the first row in the 40th anniversary seminar of Finnish Assoc. of Acoustics when Mr. Otala started his keynote speech by nodding to Mr. Köykkä saying out loud that it was really him who originally invented the TIM phenomenon. Mr. Köykkä said later, that he had blushed then.

Mr. Köykkä also created so-called Orthoperspecta system (pat. appl. 1962 - being the mother of quadrophonic stereo) which employed a big whole range mid speaker and small high freq. side speakers working with turned phase. For instance Bang & Olufsen had to pay to Mr. Köykkä by violation of his patent in Finnish markets. Mostly Mr. Köykkä created tube amps called VOIMA. The most important model being the receiver VOIMA OP3. People keep telling it could give quite astonishing concert phenomenon with it's 3 spkrs. Later, transistor design from 1976 was called WATTRAM and finally rivalled the tubes by the creator.

We could also say that PRaT was first realised by this man. He kept talking about the leading edge at least from the 60's. He geniously showed how important the leading edge is by playing a tape wrong way. Exactly the same information looses all it's intensity, when it is played backwards. And still there is everything. Only when genuine transient start a chord, the music has it's original power (!).

He also said that measuring an amp by a sinewave is like testing a camera by shooting a white screen. And squarewave is the worst measuring signal, he said, by masking the problems. He insisted testing with information instead and appreciated measuring IM distortion.

Mr. Köykkä was a real character being in his own spheres when not too many understood hifi too well. He gave demos using classical music from vinyls in the backroom of his workshop in Helsinki. His company was called Voimaradio. And he was telling people in 60's and 70's that speakers don't spoil music but amps do. Thus the speakers he did use were truly simple and primitive.

This man invented many things. Also the multispark idea for car engines for lower fuel consumption. So the Alfa Romeo's Twinspark etc. is originally from his brains.
Source:
http://www.pinkfishmedia.net/forum/showthread.php?t=27155&page=5
 
Hey guys, try Googling "fourth wall".

I'd like to throw a couple of ideas into the ether...

- How about loudspeakers with a hyper-cardioid dispersion pattern, which is quite wide but only in a forward direction to minimize reflections from the wall/corner behind them? AFAIK, dipoles attempt something similar by cancelling out the DC component of that reflection but I suspect that the response could be "tuned" in some way.

- Also, having just 2 measurement points is completely insufficient for anything "3d". The "one microphone for each ear" thing was designed to work for headphones, not loudspeakers with close to 100% crosstalk.
 
CeramicMan said:
Hey guys, try Googling "fourth wall".

I'd like to throw a couple of ideas into the ether...

- How about loudspeakers with a hyper-cardioid dispersion pattern, which is quite wide but only in a forward direction to minimize reflections from the wall/corner behind them? AFAIK, dipoles attempt something similar by cancelling out the DC component of that reflection but I suspect that the response could be "tuned" in some way.

There is no DC component in sound. The DC component we experience is called atmospheric pressure.

It is certain that dipole speakers very efficiently cancel any side radiation when listened from the side at 90 degrees angle. A large flat diagraphm is also very directional sound radiator.
 
Re: Nikolas Ojala

>Mr. Köykkä also created so-called Orthoperspecta system (pat.
>appl. 1962 - being the mother of quadrophonic stereo) which
>employed a big whole range mid speaker and small high freq.
>side speakers working with turned phase.

very interesting, thank You for a very interesting post

the main difference between Orthoperspecta according to your brief description and that Stereolith thing is that the Stereolith is really a three-channel system and that the L and R channels in Stereolith are in phase
somewhat similar (in contrapositioning of L and R channels) was Grundig "Space Fidelity" system
 
Re: CeramicMan

>having just 2 measurement points is completely insufficient for
>anything "3d". The "one microphone for each ear" thing was
>designed to work for headphones, not loudspeakers with close
>to 100% crosstalk

I respectfully disagree on both points.
I believe that Moulton is right: http://www.moultonlabs.com/dave_more/nick_batzdorf_interview

His statement that "loudspeakers are perceived in stereo as early reflections of a sound whose direct version we missed" is IMHO axiomatic and cannot be refuted. This is a basic psychoacoustical fact.
From this logically follows that can't be any problem with crosstalk AS SUCH.
BUT crosstalk can BECOME problematic when positioning of the loudspeakers in the listening room combined with specific directivity of the loudspeakers results in psychoacoustical inconsistencies

IMHO for "3d" a two channel system is perfectly sufficient
although it's potential has not yet been fulfilled because of misunderstanding of the problem of "room/speaker interface"

"room/speaker interface" was the principal problem of audio reproduction in Stig Carlsson' "orthoacoustics" and rightly so IMHO:
http://www.carlssonplanet.com/downloads/uploads/carlsson_ortho.pdf

Deficiency of realism we experience with our stereos is first of all a question of lack of psychoacoustical constistency and soundfield completness as Fcserei so accurately put it
 
I would prefer to get this discussion back on topic - its not about amplifiers, atc.

Toole has concluded that normal reflections in a typical small living room seem not to interfere with perception of the recorded space. He has also determined that early lateral reflections (<50ms) have a beneficial effect on intelligibility similar to raising the dialog level, and that the reflection pattern is more important than reverberation.

As regards the Toole quote - This is also NOT a direct quote of Toole, but of someone elses interpretation of what Toole believes. It is also a very weak statement ("seem not to interfere") and the reference is once again to the "perception of the recorded space". I do not seek to reproduce the recorded space, but to create the perception of a local space into which the muscians have been placed - quite a different goal (this was discussed earlier). "intelligability" is quite a different thing than reproduction quality - they tend to go in opposite directions - so the claim about Toole and early reflections being contrary to mine is not at all clear from this statement.


How about loudspeakers with a hyper-cardioid dispersion pattern,

This is an attractive option for the mids, and maybe the bass. My book has an extensive discussion about how to achieve this in practice. Unfortunately it is an expensive option - the better solution requiring DSP, multiple amps, etc.


For the first part, the room behind the speakers, what would you think about solutions that eliminate this room totally instead of making it acoustically dead. The result would be a 'in wall' or more realisticly a very flat 'on wall' speaker system.

I've consider this, but I would be more inclined to use the corners to get the system to toe inward for better image at multiple seating locations. I just have not found the situation where this could be implmented with any effectiveness.

Somewhat reflective behind the speakers, no reflection from behind the head. Similar to what is done in performance halls. That's the type of room that has always sounded best to me.

First, small listening rooms ARE NOT concert halls and any comparison of the two is doomed to be misleading.

I suspect that you have never heard the correct setup of speakers and room as I have proposed since my personal experience and that of virtually all who audition my listening rooms, is quite contrary to what you have experienced. And the more important aspect is the nearby diffractions. This has a big effect on imaging. The cleaner the first few ms are WRT the direct sound and nearby reflections and/or diffractions the better the speaker can image what is on the original recording. Those very early aberations to the sound have a substantial detrimental effect that increases with absoulute SPL.
 
Re: Gedlee

>This is also NOT a direct quote of Toole

of course, as I said before "unfortunately only an abstract of his presentation is available to me"
A therefore I asked: "Is anything wrong with that abstract? Is any misinformation there?"

the orginal AES paper is certainly easily available to You (not so for me here where I'm :( )
If Toole is misquoted in that abstract could You kindly clear it up?

BTW as an academic teacher I wouldn't say that "seem not to interfere" is "a very weak statement" in an scientific paper.
I would say that this is perfectly normal scientific language when someone is formulating a hypothesis based on results of concluded research. After all in experimental science we are only making hypotheses and our only results are "it seems to be" and never "it is". At least not in a "good" science.

>I do not seek to reproduce the recorded space, but to create
>the perception of a local space into which the muscians have
>been placed - quite a different goal (this was discussed earlier).

that is most interesting distinction - "recorded space" vs "local space" - and something new for me. To save Your time just tell me where it was discussed please

>"intelligability" is quite a different thing than reproduction
>quality

well, of course, thit is why Toole says "interestingly enough":
"reflected sound appears to enhance the music listening experience and, interestingly enough, to improve speech intelligibility"

and THIS is a DIRECT quote

>the claim about Toole and early reflections being contrary to
>mine is not at all clear from this statement

May I ask You to check the original AES paper (You certailny have it) and clear it up please? :)
so that we can move on :)
 
post post scriptum

>>distinction - "recorded space" vs "local space"

>is it the question of "You are there" vs "They are here"?

if so than I can understand Your remark as to the limits of realism of sound reproduction at home

to place a big orcherstra in a local space i.e. "listening room" i.e. to create "they are here" experience is unachievable indeed

the question of "You are there" vs "They are here" seems to be the most fundamental
ambiophonics e.g. is about "You are there"

I wonder why nobody speaks about third imaginable option i.e. realistic "They are there" i.e. something like having a "sonic hologram" before You
neither "You are there" not "They are here" nonetheless more realistic than both alternatives because more psychoacosutically consistent
 
Nikolas Ojala said:


There is no DC component in sound. The DC component we experience is called atmospheric pressure.

Have some imagination man! Allow me to rephrase it as: "low frequencies approaching DC", considering that true DC is infinite.

Anyway, what I was referring to was an interesting property whereby the interference patterns of dipoles are basically the inverse of those produced by monopole loudspeakers. Where monopoles undergo "room gain" at low frequencies, the opposite occurs with dipoles. At higher frequencies, interference peaks correspond to nulls and vice versa.

Whilst I'm wary about designing speakers that might produce unnatural phasing effects when listening off-axis, it's just another thing to consider.
 
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