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AR3a - Measurements

gkimeng said:
Zilch is measuring mids and tweets only in a pair of speakers whose woofers have been removed for refoaming (and from the photo he has posted, the stuffing has apparently come out as well). So as measured so far, these speakers have no stuffing.

3a's are loose-stuffed. The stuffing is determined by weight and fluffed to distribute evenly throughout the cabinet, so should not be concentrated in any particular region of the cabinet volume. The mid and high drivers both have closed backs, not open as in the woofer.

I think cabinet-related issues being discussed so far are not resonance, but possible interference caused by portions of the structure that may protrude into the drivers' sound fields.
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Actually, I had sort of figured out what Zilch was doing. I'm quick that way. :D

So the stuffing is determined by weight. That's sensible. How many pounds, would you say, per cubic foot?

Oh, and it sure looks like resonance to me.
 
Pete B said:
I referenced it here, and there is some discussion of the #7 vs. #9 woofer inductor, do you know which is used in the systems you're testing?
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Hi, Pete!

Thank you for the links. It would appear that I'm measuring the same speaker here, including the 1.8 kHz notch. I'll read the original in the Anthology. There's a hint there they were aware of the polar response issues 40 years ago, as well.

These both have #9 inductors. The woofers are refoamed and drying; I should be able to get LF data on them tomorrow.

I'm adding the last update to #1 for now, the L-pad attenuation.... :thmbsp:
 
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gkimeng said:
It may be because I just got in from a dinner out where I may have had a bit too much, but I need to be whacked over the head with obviousness right now. What kind of cabinet resonance do a mid and tweeter with sealed backs produce?
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None of note.

gkimeng said:
Ok, it just hit me. Cross out "interference" in my previous post and substitute "diffraction."
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It's both. Allison tells us what it is, specifically:

Now we reinstall the grille cloth molding and make the front of the molding flush with the inside of the smooth chamber wall. Fig. 5 shows the on-axis response obtained with the level controls still set at maximum. The mere presence of the molding produces increased level (on axis) in the range of 300 to 1000 Hz, a 5 or 6-dB notch at 1400 Hz, and miscellaneous perturbations on up in frequency.
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They didn't publish those curves in the literature, of course.

Continuing, as relates to the polars:

Figs. 6 and 7 are 15° families of the complete system, taken in a horizontal arc, first in one direction away from the system axis and the in the other. The grille molding is in place and the level controls are at maximum. It is difficult to assess performance because the output level changes rapidly, not only with frequency but with small angular increments as well. And one must keep in mind that the output variation has been observed only in one plane around the system.
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They look like the polars I measured and posted at #1.

The balance of the paper assesses whether or not any of this is audible, and Allison's answer is, "No," not in typical living rooms:

When using loudspeaker systems that have low directivity factors at all frequencies, listeners at typical listening positions in virtually all living rooms are well within the area in which the reverberant field dominates.

The reverberant field spectral balance is determined primarily by the acoustic power frequency response of the loudspeaker system. Thus, the single most important factor in assessing the "frequency response" of a loudspeaker system is the integrated output at all angles.
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Which became his "Thing:"

http://www.stereophile.com/interviews/105villchur/index2.html
 
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Zilch,

Thanks for that Stereophile link. I hadn't read that. Very good interview with Roy. I would love to hear a pari of Allisons some day.

Jim
 
gkimeng said:
Must be me, but I'm still confused. If there is none of note, what effects are you measuring that appear to be the result of "resonance?"
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I haven't identified any resonances per se, as yet. They characteristically remain constant no matter the measurement angle. Interferences, on the other hand, will vary as that changes, which is why I pointed Paratima to the polar measurements; off axis in the one direction, the 1.8 kHz null becomes a peak.

More from Allison (1972):

Even when the individual speakers [drivers] in a high-fidelity speaker system radiate energy in a smooth and uniform manner at all forward angles, if each is measured by itself on a flat baffle, the system in which they are used does not do so. Interference between speakers in crossover frequency regions causes reinforcement at some frequencies and cancellations at others. The frequencies at which these effects occur change with the angle from the system axis at which the direct radiation is measured, because the speakers cannot occupy the same space on the mounting plate; therefore, as the microphone is moved around the cabinet, the differences in path lengths change.

Another source of similar perturbations in the system's radiation pattern is diffraction, which is really a form of self-interference. Mounting surface discontinuities, the grille cloth molding, and the dimensions of the cabinet itself all produce diffraction that affects the direct-wave radiation in a complex manner dependent on the angle of the cabinet with respect to the microphone.
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The paper illustrates these effects using anechoic measurements of AR3a, which are remarkably similar to the quasi-anechoic results I have measured and posted here, 39 years later.... :yes:
 
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Zilch said:
I haven't identified any resonances per se, as yet. They characteristically remain constant no matter the measurement angle. Interferences, on the other hand, will vary as that changes, which is why I pointed Paratima to the polar measurements; off axis in the one direction, the 1.8 kHz null becomes a peak.
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Oh, ok. When you used that nodding smiley, I thought you were agreeing with him that the results looked like resonances.
 
I missed that you added the polars - the 1.8 kHz thing has to be interference.
1 wavelength ~ 7.3 inches
1/2 is 3.67

I'd say interference with the raised edge to the left of the mid, which might be about 4 inches away. That's my guess.:thmbsp:
 
packrat said:
I'd say interference with the raised edge to the left of the mid, which might be about 4 inches away. That's my guess.:thmbsp:
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That's what Allison said it was, nearly 40 years ago.

He also said it is inaudible, postulating that it is "filled in" by the reverberant sound field, which dominates the direct in normal home listening environments using AR3a.... :dunno:
 
packrat said:
I'd say interference with the raised edge to the left of the mid, which might be about 4 inches away. That's my guess.:thmbsp:
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That was what I thought, before I managed to confuse myself last night.

Zilch said:
That's what Allison said it was, nearly 40 years ago.

He also said it is inaudible, postulating that it is "filled in" by the reverberant sound field, which dominates the direct in normal home listening environments using AR3a.... :dunno:
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So now you have to go find an anechoic chamber somewhere... :scratch2:
 
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Zilch said:
That's what Allison said it was, nearly 40 years ago.

He also said it is inaudible, postulating that it is "filled in" by the reverberant sound field, which dominates the direct in normal home listening environments using AR3a.... :dunno:
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Eventually, AR delt with the diffraction when they designed the AR3a "Improved" version which sold primarily overseas. The large, picture-frame edge on the cabinet was minimized to address what they knew was a diffraction problem. See pic attached.
 

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Ultimately the "Max dispersion, max artificial soundstage" approach fell out of favor, and loudspeaker designers focused instead upon cleaning up the direct field to achieve improved imaging and accuracy, while minimizing reliance upon room reflections and the reverberant field.

[Except at least one well-known purveyor of "Direct-Reflecting" technology.... ;) ]
 
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Zilch said:
Ultimately the "Max dispersion, max artificial soundstage" approach fell out of favor, and loudspeaker designers focused instead upon cleaning up the direct field to achieve improved imaging and accuracy, while minimizing reliance upon room reflections and the reverberant field.

[Except one well-known purveyor of "Direct Reflecting" technology.... ;) ]
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I suspect a large part of it was that quadraphonic sound was reincarnated as Dolby Surround and manufacturers discovered that this time around they really had figured out how to get people to buy more speakers...currently up to eight, counting subwoofer.
 
When the ambience is in the program, and we can reproduce that accurately, we certainly don't need the room messing with it.

Op. cit.:

In the light of thise findings we believe that typical operating settings for loudspeaker high-frequency balance controls should be well below the settings which produce flat acoustic energy if the objective is a spectrum similar to that produced at a concert hall seat. In view of the variations found in both living room and concert hall frequency balance, and the manner in which these variations occur, we think that home listeners should be encouraged to make more liberal use of amplifier tone controls.

Certainly, in view of current recording practice, flat electrical response in the playback system is more likely to be wrong than right, particularly if the loudspeaker systems used for playback are able to deliver nearly flat acoustical power output and are adjusted to do so.
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http://www.classicspeakerpages.net/...l_control_se/ar-3a_and_ar-5_level_contro.html

AR was about replicating the concert hall in small rooms; that's the why and the wherefore of the white dots.... :yes:
 
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Zilch said:
Ultimately the "Max dispersion, max artificial soundstage" approach fell out of favor, and loudspeaker designers focused instead upon cleaning up the direct field to achieve improved imaging and accuracy, while minimizing reliance upon room reflections and the reverberant field.

[Except one well-known purveyor of "Direct-Reflecting" technology.... ;) ]
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Does this include the good Doctor Geddes?
 
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