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Old 31st March 2010, 01:36 PM   #1161
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Originally Posted by graaf View Post
? in what sense?
I can only offer you where to look for information but I don't write lengthy educational posts because I'm not a teacher.
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Old 31st March 2010, 01:40 PM   #1162
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Yeah yeah you can quit the guessing anytime. Your speakers are most likely not tightly matched. You ever try to null cancel test them?
I consider my Nathans "tightly matched". I would even go so far to claim they are tighter matched than the majority of speakers. If your "system" relies on an unusual tight speaker matching, then probably not many people will use it because it just would not work for them.

Can you describe the "null cancel test"?
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Old 31st March 2010, 03:49 PM   #1163
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Originally Posted by markus76 View Post
I can only offer you where to look for information but I don't write lengthy educational posts because I'm not a teacher.
thank You
then can You kindly tell me where can I look for information that "there are none" (omnidirectional speakers) please?
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Old 31st March 2010, 03:53 PM   #1164
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Read the book!
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Old 31st March 2010, 03:55 PM   #1165
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Quote:
Originally Posted by markus76 View Post
Can you describe the "null cancel test"?
perhaps this is it:

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Under the general heading of tests it may be relevant to describe Quad's own routine test, which I watched at the factory. A square pulse is fed to one loudspeaker, and the audio output from a B & K microphone observed on a storage oscilloscope, which shows an incredibly good representation of the original pulse. Next, pulses of opposite polarity are fed simultaneously to two units, with the microphone in front and between them. Moving the microphone produces a null, which becomes a straight line with no more than 0.5 dB adjustment to one inputl
http://www.quadesl.org/Album/Intervi...3rev1981p2.doc
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Old 31st March 2010, 04:15 PM   #1166
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Originally Posted by markus76 View Post
Read the book!
oh Markus

You know very well in what sense Ferstler (and also myself) used the word "omnidirectional"

real world "omnidirectional"

perhaps better word is polydirectional or reflecting speakers like Allison, Hegeman/Morrison, Shahinian, Walcott, Sonab/Carlsson, Ohm, German Physics, B&O, Mirage, MBL, Duevel, Time Domain (Jp), Linkwitz's Pluto and so on

they ARE (or were) there

yet they are not covered in the book, none of them

Toole discusses various contemporary and also historical designs but none of the above

this fact makes the book quite uninteresting to me
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Old 31st March 2010, 04:18 PM   #1167
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Hi,

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Originally Posted by markus76 View Post
Can you describe the "null cancel test"?
There are many versions. With the Speakers I helped design we actually close the ports (no sound out of the back) and place the two units of a pair face to face with around a 5mm gap, then we play out of phase (between channels) mono pink noise (I made a test/setup CD that includes such a track mainly actually for speaker setup).

The sound that remains is the sound that is not cancelled because there was no perfect channel match between drive units, crossover, amplifier and CD-player.

I remain positively surprised with just how much attenuation of the noise we gain, especially as in my reviewer days I used practically the same method to "burn in" review loudspeakers and hence I know just how often the cancellation is not very good (implying poor pair matching).

Note that my method described above includes the whole system from the CD/PC track onwards, including different DAC non-linearity between channels all the way to badly tracking volume controls and driver mismatches. If you have a tube that has a significantly higher amount of distortion in one of the units in one channel that too is audible in this setup, though I normally look at the FFT graphs from the QC testing to figure out something like that is amiss.

Ciao T

Last edited by ThorstenL; 31st March 2010 at 04:33 PM.
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Old 31st March 2010, 04:43 PM   #1168
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in this very old review of Ohm speakers in Stereophile I have found observations that can shed some light on why omni speakers are considered by many audiophiles as having poor imaging:

Quote:
Sonic Impressions
The Ohm Walsh 5 started things off in the "dead" end of my dead-end/live-end listening room. No matter where I positioned them in that end of the room, however, their imaging magic was not to be heard. The almost palpable and spacious soundstage I had experienced under show conditions was gone. Instead, the soundstage width was restricted to the solid angle subtended by the edges of the speakers, and the solidity of individual spaces within that soundstage was marginal.

Acting on the suggestion of Don Bouchard at Ohm, I repositioned all of the absorbent material in the room so that the dead end became the live end and vice versa. It worked! The transformation was incredible. The dimensions of the soundstage stretched clear out to the sidewalls with excellent depth. The diffuseness of individual spaces within the soundstage increased somewhat, but each space took on a convincing 3-D quality. The focus within the soundstage was not ultra-tight, being more typical in extent of what you might experience from the back of the concert hall. It might be more accurate to say that the whole end of the room appeared to come alive; I got the distinct impression of peeking into a real space. A very enjoyable experience. One may conclude that the Walsh 5 does need a fair bit of room reflection really to shine, and that the dead-end/live-end arrangement suits it quite well.
see: Stereophile: Ohm Walsh 5 loudspeaker

it seems that omni speakers are not tolerant of typical audiophile listening room acoustics that is rather on the dead side
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Old 31st March 2010, 04:59 PM   #1169
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Toole discusses various contemporary and also historical designs but none of the above

this fact makes the book quite uninteresting to me
Toole discusses the basics that are necessary to developed and understand any reproduction concept. That fact should make this book interesting for anybody talking about sound reproduction.
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Old 31st March 2010, 05:04 PM   #1170
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Originally Posted by ThorstenL View Post
we actually close the ports (no sound out of the back) and place the two units of a pair face to face with around a 5mm gap, then we play out of phase (between channels) mono pink noise
I'm not sure if this is a feasible test because the setup is essentially a ported single speaker design. Have to think about it.

Best, Markus
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