AR woofer crossover points in perspective

[tysontom]

On 4/30/2018 at 2:58 PM, Aadams said:

3 posts prior.  LST is cited as not having this problem but the LST also had a completely different approach to achieving "spectral balance".    I have never heard an 11 or a 10pi  and not seen a graph for either and don't know if that same notch at 575hz is present.  I also stated in the previous post that the problem could be solved with a 1/3 octave equalizer.   IMO neither the world's most powerful tweeter nor a simple treble control adjustment around 5khz will restore the missing harmonics and overtones, between 600 and 1600hz, so you can clearly hear what Ellen Foley is singing, which is the origin of this thread.

Good to see you back.

Adams

Addendum: I found this in archives:  A letter from Allison to Hoffman, 1970.  Items D and E give insight into the thinking of the creator about the objective of the 3a design-----------Clearly, not drum demos in club sized rooms.   There are no response curves for the ADD designs to be found.

 

 

On 4/29/2018 at 7:07 PM, Aadams said:

The modified chart below is what I see based on the clarification above and the tendency of owners to keep the 3a mid output at around the attenuator mid point.  Maybe the 10Pi addressed this.  I know the LST did. 

Adams,

You have completely misinterpreted the AR-3a  response curve above, and you're "reading into it" what you think you are experiencing in your setup at home.  The "blue zone" and the "green zone" are not at all what you actually hear: the tracing above shows superimposed individual-driver response curves all on one chart for reference purposes, done for transparency by Acoustic Research. 

There is a huge amount of interaction and blending that occurs with drivers at the crossover frequencies, and that "Diminished-output-of-important-voice-and-harmonics-and-overtones" insert you put at the top is actually meaningless and incorrect.  You need to look at the power response or rta response to see what you are or are not hearing from the speaker.

 

 

 

 These curves give a better idea of what you hear from the AR-3a

—Tom Tyson

[Aadams]

Tom Tyson

Thanks.  I can work with this too.  I actually thought there must be blending.  I don't have time tonight but I will make a new chart showing a 3db and 6db down tracing. It seems logical turning the pot down any degree from max has to proportionally diminish output of all frequencies handled by driver so the graph line should be pretty much the same slope and linearity.   Should it not?  It seems almost impossible that I could be totally incorrect on this.   

Aadams

[ligs]

Normally, attenuation of the individual driver changes not only the spl but also the slope of the crossover of the driver and could make the overall frequency response more ragged as seen in the illustration. A true L-pad which provides a constant impedance may be better but I can not find an example for it. 

[Aadams]

TysonTom

Here is the new chart.  Of course, I see the same issue I saw in the previous chart regarding diminished output in the critical human voice mid range.  I tried to be objective and welcome  your critique.

I repeat myself by saying, IMO the 3a does not generally have a problem with voices, only certain voices.  When a musical instrument, other than voice, drops a couple of db in a portion of its timbre range humans don’t notice but certain male and female voices are very recognizable and those timbre shifts can be detected by ear.

I will concede this may only be an issue at my house but if the 3a curve was the sine qua non for speaker quality the AR9 would have the same curve.  Someone with influence at AR saw an opportunity for improvement in an area important to retail purchasers.

Bonus Question- I think you have intimated that absolute clarity and dispersion are mutually exclusive features.  Does this mean if AR could have taken the dome mid-range down to 200hz that voices would have been more dispersed but somehow perceivably less defined?

 Adams

[ligs]

Just for completeness, I like to include additional response curves for AR3A from the net. I assume the on-axis anechoic response response is at the axis of the tweeter. Measuring multi-way speakers system  is always problematic, IMO.

 

 

[Aadams]

This not supposed to be a 3a thread, but this last chart reminds me of what can be found among ancient CSP writings.  A prominent example: Before my time here, Zilch, a man full of speaker knowledge and who is recently deceased, found great joy in winding up the AR Iconophiles at this site by using all sorts of analysis,graphs  and relentless,articulate, argument to cast the 3a as an inadequate antique.  One thread shows a hemispherical measurement of 3a dispersion uniformity, using color intensity, that he produced.  To paraphrase his words, it was a mess.

I don't know if Zilch or anyone, outside of NASA, or Harman has the tools and talent to perform accurate objective measurements of any loudspeaker. I am skeptical of anyone with a home setup.  AR was careful with their data collection and measurement, concerned that the results should be repeatable by anyone following the protocols. 

The point is:

----------These Murphy charts show zero resemblance to anything published by AR.  

----------The Zilch chart also shows zero resemblance but is of a type not possible 50 years ago.

The common result of both measurements of the 3a

----------Murphy says, “Still it sounds better than you might think”

----------Zilch, a CSP gadfly who actually had a lot of speaker cred, said, – to paraphrase- “Maybe this explains why the 3a sounds so good in certain rooms” and “The problem with the 3a is it needs the right room which most people don’t have.”  Zilch felt that modern waveguides (horns) were more appropriate for most situations and liked big JBLs.

On balance, however, I am in no position to say their work was any less valid than that of someone who fabricates graphs to support a subjective opinion.

Adams

[Aadams]

Below is an excerpt from a Roy Allison technical presentation made in 1970.  The full paper is in the library. 

And, I know this document has been referenced in other threads.

http://www.classicspeakerpages.net/library/acoustic_research/special_sections/additional_ar_documents/the_sound_field_in_home_lis/

Three impressions I took away.

1------The “typical” Boston area listening rooms that were used for home measurement are NOTHING like the “typical” rooms in which you find systems today or even then.

2-----The 3a was optimized for recreating a live performance experience.

3------He concluded it is beyond the capability of a speaker to reconcile concert hall, reverberant field, sound with the listening room experience of sound captured through near field microphones. The best suggestion he had at the time was to encourage liberal use of amplifier tone controls.  This was before the availability of inexpensive equalizers.  

 

 

[tysontom]

On 5/3/2018 at 11:15 AM, ligs said:

Just for completeness, I like to include additional response curves for AR3A from the net. I assume the on-axis anechoic response response is at the axis of the tweeter. Measuring multi-way speakers system  is always problematic, IMO.

 

 

Ligs,

In my opinion, this MurphyBlaster AR-3a measurement really doesn't mean a great deal.  With all due respect, this guy is/was an economist by training and a speaker-DIYer as a hobbyist.  I'm sure his intentions are creditable, but I have no idea how he got that measurement or what it means.  Like so many hobbyists, this guy gets some measuring equipment and soon considers himself an expert in the field of acoustic measurements.  Notice that the curve is all over the place with apparently reflections and interaction from any number of things.  You cannot decipher anything whatsoever about the performance of the speaker from those response curves.  For example, he says, "...The woofer also had a big humb at the top of its range, whcih colored the sound.  Still, it sounds better than you might think...."

—Tom Tyson

[ligs]

Tom,

My point was"Measuring multi-way speakers system  is always problematic, IMO" 

In " The Sound Field in Home Listening Rooms by Roy F. Allison and Robert Berkovitz" ,  response curves of muti-way speakers can look very different depending on the test chambers(2 pi or 4 pi or where in room) and even with or without the cabinet molding. If a speaker is placed well into the room without reinforcement from the wall or floor it could conceivably sound like that measured in a 4 pi chamber which is labeled as Figure 8. 

George

[tysontom]

5 hours ago, ligs said:

Tom,

My point was"Measuring multi-way speakers system  is always problematic, IMO" 

In " The Sound Field in Home Listening Rooms by Roy F. Allison and Robert Berkovitz" ,  response curves of muti-way speakers can look very different depending on the test chambers(2 pi or 4 pi or where in room) and even with or without the cabinet molding. If a speaker is placed well into the room without reinforcement from the wall or floor it could conceivably sound like that measured in a 4 pi chamber which is labeled as Figure 8. 

George

George,

I don't disagree with your statement.  The graph you attached shows predictably the effect of measuring anechoically into a 4π, 360˚ solid angle, as you noted, which shows the attenuation in bass as though the speaker was being suspended from a rope in the middle of a room.  Also, the grill molding affects the system measurement fairly dramatically, but at different angles.  All of these things add up to the difficulty in testing "full-system frequency response."

On the other hand, MurphyBlaster's measurements of the AR-3a were more or less random, and it is difficult to separate meaninful speaker performance from interaction, diffraction and so forth.  For this reason, I think the MurphyBlaster response graphs were not useful.

—Tom

 

[Pete B]

4 hours ago, ligs said:

Tom,

My point was"Measuring multi-way speakers system  is always problematic, IMO" 

In " The Sound Field in Home Listening Rooms by Roy F. Allison and Robert Berkovitz" ,  response curves of muti-way speakers can look very different depending on the test chambers(2 pi or 4 pi or where in room) and even with or without the cabinet molding. If a speaker is placed well into the room without reinforcement from the wall or floor it could conceivably sound like that measured in a 4 pi chamber which is labeled as Figure 8. 

George

 

This is a good chart to study because a B&K frequency response test system provides some averaging

depending on the speed.  These were probably done very slowly so that the diffraction effects can be seen,

whereas the other charts provided by AR have some averaging.  I posted this many years ago:

http://www.classicspeakerpages.net/IP.Board/index.php?/topic/1571-ar-3a-4pi-anechoic-measurements-from-1970-aes/

It is interesting to note that with modern advances involving diffraction control and crossover design 

it is possible to get very respectable curves, sometimes, even without averaging.

http://www.soundstagenetwork.com/measurements/revel_concerta_f12/

[tysontom]

On 5/4/2018 at 10:06 AM, Aadams said:

This not supposed to be a 3a thread, but this last chart reminds me of what can be found among ancient CSP writings.  A prominent example: Before my time here, Zilch, a man full of speaker knowledge and who is recently deceased, found great joy in winding up the AR Iconophiles at this site by using all sorts of analysis,graphs  and relentless,articulate, argument to cast the 3a as an inadequate antique.  One thread shows a hemispherical measurement of 3a dispersion uniformity, using color intensity, that he produced.  To paraphrase his words, it was a mess.

I don't know if Zilch or anyone, outside of NASA, or Harman has the tools and talent to perform accurate objective measurements of any loudspeaker. I am skeptical of anyone with a home setup.  AR was careful with their data collection and measurement, concerned that the results should be repeatable by anyone following the protocols. 

The point is:

----------These Murphy charts show zero resemblance to anything published by AR.  

----------The Zilch chart also shows zero resemblance but is of a type not possible 50 years ago.

The common result of both measurements of the 3a

----------Murphy says, “Still it sounds better than you might think”

----------Zilch, a CSP gadfly who actually had a lot of speaker cred, said, – to paraphrase- “Maybe this explains why the 3a sounds so good in certain rooms” and “The problem with the 3a is it needs the right room which most people don’t have.”  Zilch felt that modern waveguides (horns) were more appropriate for most situations and liked big JBLs.

On balance, however, I am in no position to say their work was any less valid than that of someone who fabricates graphs to support a subjective opinion.

Adams

Adams, in response to your comments above about Zilch.

"Zilch"

"Zilch," Evan R. Flavell, who died about seven years ago from lung cancer, was definitely one of the more knowledgeable and accomplished home-style speaker testers.  He was a major JBL-style contributor to AudioKarma's Speaker Forum, and his measurements always seemed reasonably accurate for the type of testing he was doing.  He certainly understood what he was doing, but his preference was near-field fr testing more than acoustic-power testing, and it appears that he preferred flat on-axis output from a speaker rather than rolled-off highs.  Nevertheless, he did a lot of polar-response and off-axis testing as well. 

At one time, Zilch had been a conditioning coach for the swim team at UC Berkeley and developed a "swim bench," a dry-land exercise device for swim teams.  He was an engineer and held several patents in the field of exercise equipment. 

Zilch used his engineering background to delve into the field of audio-loudspeaker design, and he developed (and marketed) a crossover network to incorporate a constant-directivity horn-tweeter, the "Econowave," as a replacement device to add the benefit of a "flat curve" to replace the old "rolled-off" high frequencies of speakers such as ARs, EPIs and Advents, etc. 

This system has apparently had (and perhaps still has) a good following, and the system actually sounds pretty good from my brief experience.  I think Roy C of our forum has had experience with that setup with very satisfactory results, and Roy might elaborate on the Econowave design.  Insofar as Zilch was marketing his Econowave horn tweeter replacement, he had an ax to grind concerning speakers like ARs, and he frequently offered rather extensive measurements made on some of the old speakers, including many ARs.  His measurements were generally much more comprehensive than most of the other DIY measurements and these were not terribly different from the anechoic measurements done in AR's anechoic chamber.

DIY Measurements of the AR-3a

What this comes down to is that for years the AR-3a, and many other AR classic speakers, have been tested a dozen different ways from Sunday by numerous and enthusiastic DIY audio testers—most folks equipped with inexpensive digital software and non-calibrated electret microphones—in an effort to quantify that the AR-3a speaker wasn't really all that great or to explain that the speaker system might have been overrated because it didn't measure so well, even though it seemed to sound great. Of course, no two tests were the same and few resembled each other, and virtually none was governed by the old standards of measurements used in the hi-fi industry! 

The fact that the AR-3a received such great commercial success and stellar reviews (except for CU's comments at one point) only compounded the dilemma.

One thing stands out: there is 100% disagreement by most "weekend warriors" on the measurement standards used to test the speakers.  Chart speed, levels, vertical resolution, smoothing and testing conditions in general rarely resemble each other.

Some amateur reviewers tested the AR-3a outdoors and some indoors; some were done at 1 meter for the entire system while other tests are tested at 2 or 3 meters.  Some testers tried rta measurements while others tried full-system frequency response tests, most with the notion of proving why the speaker sounds "rolled-off" in the high frequencies, yet ironically, most testers agree that the speaker always sounded much better than it appeared to measure.  It appears that most amateur testers also strongly believe that what you measure when you put a microphone in front of a speaker is what the speaker "is doing."   

—Tom

 

[ligs]

I don't know John Murphy in person but I believe he is the designer behind Phiharmonic Audio speakers

http://www.philharmonicaudio.com/

and the author of " Introduction to Loudspeaker Design. 2nd Edition. 

https://www.trueaudio.com/ild_abt1.htm

More about Murphy.

https://rhythmaudiodesign.com/pages/dennis-murphy

And perhaps he could chime in this discussion. 

 

George

 

[Pete B]

The Murphy Blaster work was done by Dennis Murphy, an economist by profession, who learned 

to drive measurement and design tools a long time ago.  He is currently the person behind Philharmonic

speakers.  From their website:

"Philharmonic speakers were developed by Dennis Murphy, who has a proven track record in crossover designs for Salk Sound, Ellis Audio, and many popular public domain kits, such as the MBOW1 and CAOW1.  The cabinets for our 3-way speakers are hand-crafted to order in the USA.  Click on the "Cabinets" tab for details on the cabinet makers and available veneers."

John Murphy, unrelated to Dennis as far as I know is behind True Audio and the book.

I've known John Murphy online since the mid 1990s, and Dennis since early 2000 from the Madisound forum.

Dennis provided the switched cap test speaker that I refer to in the "Capacitor Myths" thread and it caused

a huge upset on the Madisound board.

[Pete B]

This is interesting, speaker B the anechoic curve vs. in room:

http://www.classicspeakerpages.net/library/allison/other/technical_articles_by_roy_f/technical_articles_by_roy_f_8.html

[ligs]

38 minutes ago, Pete B said:

The Murphy Blaster work was done by Dennis Murphy, an economist by profession, who learned 

to drive measurement and design tools a long time ago.  He is currently the person behind Philharmonic

speakers.  From their website:

"Philharmonic speakers were developed by Dennis Murphy, who has a proven track record in crossover designs for Salk Sound, Ellis Audio, and many popular public domain kits, such as the MBOW1 and CAOW1.  The cabinets for our 3-way speakers are hand-crafted to order in the USA.  Click on the "Cabinets" tab for details on the cabinet makers and available veneers."

John Murphy, unrelated to Dennis as far as I know is behind True Audio and the book.

I've known John Murphy online since the mid 1990s, and Dennis since early 2000 from the Madisound forum.

Dennis provided the switched cap test speaker that I refer to in the "Capacitor Myths" thread and it caused

a huge upset on the Madisound board.

Thanks for the clarification.

 

George

[Aadams]

Leaving 3a measurement behind and getting back to the thread topic of why AR continued to lower the crossover of the 12" woofer.

1 hour ago, Pete B said:

This is interesting, speaker B the anechoic curve vs. in room:

Page 18 of the Roy Allison paper on speaker and listening room integration.  Note the very last paragraph of the article.

Is uniform room loading another reason the woofer crossover was dropped to 200hz in the 4 way systems?  The Allison 1 used 350hz in its 3 way design.

Adams

[Pete B]

Probably.  The PSB Stratus Gold literature states that the woofer is placed (somewhat) low, 

and the midrange high.  The crossover point is chosen so that neither driver has the floor

bounce dip in the passband.  Don't recall where I read this, might have been by Keele in

the Audio review.

[tysontom]

On 5/7/2018 at 6:32 PM, Aadams said:

Leaving 3a measurement behind and getting back to the thread topic of why AR continued to lower the crossover of the 12" woofer.

Page 18 of the Roy Allison paper on speaker and listening room integration.  Note the very last paragraph of the article.

Is uniform room loading another reason the woofer crossover was dropped to 200hz in the 4 way systems?  The Allison 1 used 350hz in its 3 way design.

Adams

Adams:

Once again, AR lowered the crossover on the AR-3a from the earlier AR-1 and AR-3 levels because the new midrange could operate lower in the midrange, thus keeping the woofer out of the higher frequencies.  This was always the goal.  The problem has to do with off-axis response, smoothness and linearity of the large woofer cone; the lower crossover was not related to vocalist clarity or midrange intelligibility. 

With the AR-3, the lowest Villchur could operate the 2-inch phenolic-dome midrange was ≈1000 Hz, thus the 1 kHz crossover.  The AR-3's woofer thus had to operate up to 1000 Hz, and even though the woofer is flat, on axis, from 38-1000 Hz within ±1½dB on axis, the off-axis response is compromised.  With the 1½-inch AR-3a soft-dome midrange, the resonance frequency was a half-octave lower; therefore, AR could lower the midrange crossover was set to 575 Hz.  The result was improved dispersion in the midrange and upper-bass frequencies.

What Roy Allison is referring to is the boundary dip that is caused by a reflected, out-of-phase low-frequency wave from the woofer cone that bounces off the floor or wall and returns and partially cancels the front wave, causing a dip in the response at certain frequencies in the upper bass.  By placing the woofer(s) close to the floor-wall boundary, and crossing over below that frequency, the dip can be avoided.  The AR9 was also designed with this in mind, of course, with the two woofers close to the floor on each side (instead of in front up high).  This has come to be called the "Allison Effect." 

There is still debate on the efficacy of trying to remove the dip (do recording studios compensate in recordings for a dip they may or may not get from their studio monitors?), as it may cause some "softness" in certain frequencies, but in general that dip is there and can be avoided.  It is possible that you are losing some intelligibility around the frequency of the boundary dip.  If you re-mount your AR-3a speakers flush with a wall or bookcase, you can avoid this problem.   

 

—Tom

[Aadams]

13 hours ago, tysontom said:

Once again, AR lowered the crossover on the AR-3a from the earlier AR-1 and AR-3 levels because the new midrange could operate lower in the midrange, thus keeping the woofer out of the higher frequencies.  This was always the goal.  The problem has to do with off-axis response, smoothness and linearity of the large woofer cone; the lower crossover was not related to vocalist clarity or midrange intelligibility. 

And I repeat, I absolutely agree. 

For at least 4 reasons. 

1-------In 1968 Roy Allison was still on a quest for concert hall realism above all else

2-------Distortion in the 12” was very low and voice was well presented

3-------AR had no small cone speaker to cover the low-mid range if they had desired to do so.

4-------The men pictured below are not concerned about deciphering the lyrics to Louie Louie.

I have reviewed the entire thread and cannot find any post where I said the woofer crossover was lowered to get vocal clarity.  Though I did wonder if voice may have been better in the 3 vs 3a because almost all of it originated in the woofer but, I did not say so in a post.

I did say, the woofer crossover point was lowered with every succeeding generation of TOTL speakers containing dome mids.  Lowering the crossover point for whatever reason eliminated, from the woofer, fundamental frequencies of the low mid-range, whence nearly all voice originates.

The voice clarity and timbre issue was introduced in this thread when I referred to a difference in clarity between the 3a and the 9 not 3 to 3a. 

I have agreed with you the 3a vs 9 difference is probably due to a frequency imbalance caused by a couple of things and has nothing to do with simply crossing over in the middle of the voice range.  You say In 1968, or even now,  this problem could be addressed by mounting the 3a in the wall.  I would say this was a last resort solution for men who expected to be single or needed to find a use for " The Story of Civilization".   Today I would use an adequate equalizer. 

13 hours ago, tysontom said:

What Roy Allison is referring to is the boundary dip that is caused by a reflected, out-of-phase low-frequency wave from the woofer cone that bounces off the floor or wall and returns and partially cancels the front wave, causing a dip in the response at certain frequencies in the upper bass.  By placing the woofer(s) close to the floor-wall boundary, and crossing over below that frequency, the dip can be avoided.  The AR9 was also designed with this in mind, of course, with the two woofers close to the floor on each side (instead of in front up high).  This has come to be called the "Allison Effect." 

There is still debate on the efficacy of trying to remove the dip (do recording studios compensate in recordings for a dip they may or may not get from their studio monitors?), as it may cause some "softness" in certain frequencies, but in general that dip is there and can be avoided.  It is possible that you are losing some intelligibility around the frequency of the boundary dip.  If you re-mount your AR-3a speakers flush with a wall or bookcase, you can avoid this problem.   

Regarding the above:  Thank you. Though I wonder how many non-classical recordings these days are actually produced using anything other than headphones and 6” monitors for evaluation of sound.

Adams

[genek]

Were there any 4-way AR speakers other than the ones with side-firing woofers? I'm wondering if the reason they were 4-way was just that they wanted lower midrange coming from the front instead of the sides.

[ra.ra]

1 hour ago, genek said:

Were there any 4-way AR speakers other than the ones with side-firing woofers?

These two models come to mind.

[Aadams]

The AR Classic Series of the 1990s, did not include a 4 way but 3 of the 4 systems in the line up crossed over the woofer at 200hz.  This was also the first and last time AR used 5.25 inch cones to span the mid-range from 200hz to 2khz.

[Stimpy]

The higher in frequency, a large driver is expected to perform, the more directional said driver will become.  The more it 'beams', the worse dispersion becomes, and more extreme toe in will be required, to aim the woofer, for proper balance.  So, were the shifting crossover points, just a simple experiment, to find a sweet spot, where the 12" woofer didn't 'beam' at the top of it's pass band?

[Steve F]

Let's inject a little logic and math into this discussion. Take 13560 (the speed of sound in inches/sec at sea level) and divide that by the piston diameter of the driver. That will give you the frequency at which the driver starts to become objectionably directional (when the diameter exceeds the frequency being played).

13560/11 (the piston diameter of a 12-inch woofer, minus the 1/2" surround on each side) =  1233Hz. A 12-in woofer is "good" to 1200. 1200! So an AR-3 crossing over at 1000Hz is just fine, no sweat. That is why the Large Advent with a 10/12-in woofer crossing over at 1000 always sounded fine, from a directivity standpoint. (I'm not talking tonal balance or anything like that, I'm talking directivity.)

Will the dispersion improve if the driver is crossed over lower than its upper limit? Of course, but things are not as bad as they seem.

13560/4.25 (the piston diameter of a 5 1/4-in driver = 3190 Hz.

A 1-in tweeter is good to 13,560, obviously, while a 3/4-in dome is good past 18kHz.

Here's an interesting one--a 10-in driver (9-in piston) is directional at 1506Hz (13560/9 = 1506). So the AR-2, 2a, and 'old' 2ax were all "wrong" because they took a 10-in woofer up to 2000Hz, way past the point where it becomes directional. So does everyone here on the Forum criticize these speakers for being objectionably beamy in the midrange? Do we hear constant complaining from everyone about, "I just can't stand the way my 2a's beam that midrange. It's horrible! These are horrible speakers!"

Nope. Not a peep.

Ponder that.

Steve F.