AR woofer crossover points in perspective

[Aadams]

15 hours ago, genek said:

 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.

I think you may be on to something regarding the original AR9.

For the last year I have been seeing my AR9s as an expensive 8 inch system sitting atop a finely integrated passive sub woofer.  With side firing woofers, crossing even a little above 200hz would have female voices singing out the sides but why not go lower than 200hz?  After all, the 8 inch could easily get to 80hz.   Maybe power handling?  I am not confident the speaker would perceivably sound better with a lower woofer crossover. 

BTW the 910 was also a 4 way but using all cones and was the last to use an 8 inch low mid before the Classic Series switched to 5.25 low mids.    

Adams

[ligs]

3 hours ago, Steve F said:

 

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.

 

[ligs]

Interesting.  I have 1976 Edition of High Fidelity's Test Reports. I was looking for any  discontinuity of the frequency response of AR 2ax woofer up to and beyond 2000 hz. I could not find any. This brings up perhaps another requirement for good listening: smoothness and paralleling of the response curves over a wide range of angles. Perhaps not just the crossover point( what Hz)but the implementation of crossover design  will determine how good the total speaker will sound. In the crossover design,   the phases of the component drivers need to  compliment each other,  otherwise a disruption  could result in the final frequency response and dispersion characteristic. Without an EE degree, I am not qualified to comment this in any more details. 

George

 

[Aadams]

Below is a list of passive, full range, loudspeakers available today with woofer area and crossover frequency.  All are TOTL or near, most are bass reflex designs and all use 6 inch or smaller LMR and/or midrange drivers.    I only listed speakers for which the manufacturer published performance specs.  Some of the claims for low freq extension seemed dubious to me while others seemed reasonable. 

Adams

[Aadams]

It turns out, from 1979 until 1995 NO AR TOTL speaker had higher than a 300hz woofer crossover.

Interesting facts about the Connoisseur Series:

Note the paragraph regarding the new midrange driver.

The Connoisseur 50 12” 3way with a -3b point of 30hz is incorrect though the misprint may have been intentional.  The correct number is 39.

Adams

[Aadams]

Given the freedom to employ the 12" to its greatest advantage AR consistently chose lower crossover points finally settling on 200hz in their 4way systems.  

The point has been made, that the AR9 side firing woofer configuration may have forced a 4way design to keep the LMR in the front.

The AR9LS, LSi and 98 all had forward firing woofers but AR kept the crossover at 200hz.  I am speculating here with no help from Google---------- in tall columns with large spatial separation between drivers a high crossed woofer at the bottom of the column will make some human voices and instruments seem to move up and down the column.  The same should be true today.  Even though an 8 or 6" speaker can carry a large band of frequencies, when they are used in multiples as woofers in tall columns with a port, the crossover must be placed low enough to prevent this illusion of relocation.  The same applies to powered sub-woofers and satellites.

Apparently AR felt the big 12" was in its best range when cut at 200hz, which implies that anything much higher represented compromise.  

Adams

 

[tysontom]

 

 

>The point has been made, that the AR9 side firing woofer configuration may have forced a 4way design to keep the LMR in the front. [incorrect assumption].

>The AR9LS, LSi and 98 all had forward firing woofers but AR kept the crossover at 200hz.  I am speculating here with no help from Google---------- in tall columns with large spatial separation between drivers a high crossed woofer at the bottom of the column will make some human voices and instruments seem to move up and down the column.  The same should be true today.  Even though an 8 or 6" speaker can carry a large band of frequencies, when they are used in multiples as woofers in tall columns with a port, the crossover must be placed low enough to prevent this illusion of relocation.  The same applies to powered sub-woofers and satellites. [incorrect assumption].

>Apparently AR felt the big 12" was in its best range when cut at 200hz, which implies that anything much higher represented compromise.  [This, too, is an incorrect assumption].

>Adams

____________________________________________

AR did not design the tower speakers with those things in mind.  It just doesn't work that way.  The two 12-inch woofers needed to be placed close to the floor-wall intersection to reduce the possibility of out-of-phase cancellations.  The existing 8-inch Lower-Midrange driver was an existing in-house driver, for the most part, used in numerous other AR systems, and it could easily get down well below 200 Hz.  Also, AR wanted to improve the lower-midrange power-handling capability of the dome midrange and tweeter units, so the 8-inch LMR helped with that as well.

The "art" in the AR9 design is the almost seamless integration between the two 12-inch woofers and this 8-inch lower-midrange unit—working together as though one single unit.  There are no clues that there is any transition from the woofers to the LMR, and AR was most proud of this and considered it to be one of the great achievements in the design of the 9's crossover.

Unless you are listing to your speakers about a foot away, you will never sense that "human voices and instruments seem to move up and down the column."  This just doesn't happen unless you had all large cone drivers operating into the midrange and treble, and thus you might sense a wandering image with highly directional speakers that are projecting to you predominantly first-arrival sound, but these speaker systems are generally objectionable to listen to anyway.

—Tom

[Aadams]

2 hours ago, tysontom said:

Apparently AR felt the big 12" was in its best range when cut at 200hz, which implies that anything much higher represented compromise.  [This, too, is an incorrect assumption].

Tysontom

Thanks

You were so focused on correcting the first two assumptions that you failed to correct the last assumption. After AR embarked on the bifurcated path with the verticals, evidence shows that all 12" systems below TOTL had higher crossovers.

Adams

[tysontom]

On 5/12/2018 at 4:01 PM, Aadams said:

Tysontom

Thanks

You were so focused on correcting the first two assumptions that you failed to correct the last assumption. After AR embarked on the bifurcated path with the verticals, evidence shows that all 12" systems below TOTL had higher crossovers.

Adams

Adams your last sentence was not necessarily an incorrect assumption (as I hurriedly stated) except to say that AR knew from the beginning that driving the 12-inch woofer too high represented a slight compromise. 

However, with the AR-3a, that compromise was reduced significantly, because the 12-inch woofer works well on- and off-axis up into the 500 Hz region.   The cone is not terribly directional in that region, but around 1000 Hz, it is becoming more directional.  Obviously, 200 Hz is better yet with the main consideration of the 8-inch LMR handling much of the lower midrange, protecting the midrange dome and increasing power-handling capability. 

 

[Aadams]

1 hour ago, tysontom said:

However, with the AR-3a, that compromise was reduces significantly, because the 12-inch woofer works well on- and off-axis up into the 500 Hz region.   The cone is not terribly directional in that region, but around 1000 Hz, it is becoming more directional.  Obviously, 200 Hz is better yet with the main consideration of the 8-inch LMR handling much of the lower midrange, protecting the midrange dome and increasing power-handling capability.

I was not thinking of the 3a and 500hz crossovers.  I was referring to 700hz, the crossover for all 3way 12” systems through the TSW series, excluding the Connoisseur and MGC.

You seem to be saying the use of the 8inch LMR was all about power handling----that the 8inch did not add to the refinement of the sound.   I have a 58s pair, very similar to a 91, that I have compared to the AR9 and while, once equalized, they do sound similar, there is no way the 58s sounds as good as the 9 between 200 and 1000Hz.  AR said the 91 was its premiere 3way system. I have never heard one with its acoustic blanket, but I have not read anything by anyone claiming it sounded like a 9 with less bass.  We see the 90 discussed as a baby 9 but never the 91 as such.

My point is, the lower woofer crossover and the single 8 inch speaker for the critical mid-range between 200hz and 1200hz makes an audible difference-----or is it my imagination?

Again, I am not talking about the 3a but about where AR was headed.  Here is part of their pitch for the new mid-range in the Connoisseur series.

“the 6.5” midrange operates between 200hz and 4kz so that phase shifts are minimized in the critical mid-range.  Crossover points are consequently avoided where the ear is most sensitive and the low-bass-to-mid crossover point results in very low IM distortion.”

Adams

[Aadams]

And finally, from The Man himself, Mr Tim Holl, on why 200hz was the target.

Adams

[Aadams]

On 4/28/2018 at 12:04 AM, tysontom said:

The big thing that is happening here is the effect of wide dispersion of the AR-3a at those midrange frequencies and how it affects the perceived clarity of voice or instruments.  It also occurs to me that if you are mounting your AR-3a on a stand or table (above the floor but back against the front wall), your AR-3a will be susceptible to the "Allison Effect," a boundary-caused dip of several dB as the reflection from the wall behind the speaker (and the floor) interact with the direct output of the woofer and cancel (null) certain frequencies to some degree, usually around 300 Hz or so.  This could impact intelligibility at those frequencies, of course, and the way to fix this problem is to mount the AR-3a flush with the wall or in a bookcase flush with books around the speaker so that the woofer sees a true 180 solid angle.  It's not always easy to do it that way!

 And also

"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. "

The question of clarity was not the main topic of this thread but I have been bothered ever since about having been obstinate and even worse ? potentially incorrect in my perceptions.  I publicly acknowledge tysontom is exactly correct.  The clarity issue regarding the 3a is resolved, at least in my house.

Aadams   

[Pete B]

I'd like to throw in a bit about what I think went on in the design of the AR-3a.  The emphasis

was wide dispersion through the use of a small dome mid and tweeter.  Dome mids do not

generally have much Xmax and as a result also low volume displacement.  This results in 

rising distortion with lower frequency and higher output.  They probably would have liked to

crossover at 300 Hz but then the distortion would have been higher for the target max output

level.  Let's remember that the 3a dome was 1.5", very small, and an educated guess for the

Xmax is 1 mm.  The PSB Stratus Gold has a 5" cone (6.5" frame) with 3mm Xmax allowing for

a 200 Hz crossover point - and plenty of headroom.

 

Aadams asked why not cross lower in the AR-9, the woofer inductors are huge in the 9 and they'd

have to be even larger for a lower passive XO.

 

Ligs posted a measurement of the 3a woofer distortion and noted that it was higher at 300 Hz.  I

believe that the test was of the full 3a system and at 300 Hz it is likely that there is enough drive

to the midrange driver to cause it to add mostly distortion to the measurement.  In fact, if I am

correct this supports my first point in this post.  Some may say that 100 dB is well beyond the 

requirement for any sane listening level but note that Keele tested the PSB Stratus Gold and 

Wilson WATT/Puppy as providing peak outputs above 150 Hz well above 110 dB often hitting 120 dB.

Well into hearing damage range but they could do it.

[veshzop]

in my opinion the AR 12" speakers with the lowest woofer crossovers sound better, in the music packed human voice octaves, than those with higher crossovers. 

Edited April 29, 2023 by genek
Deleted unidentified links.

[dayamafor]

speakers with the lowest woofer crossovers sound better, in the music packed human voice octaves, than those with higher crossovers. 

Edited April 29, 2023 by genek
Deleted unidentified links.