[eclein]

Wayner---looks great and I'm sure it sounds great too......I have seen you refer to that Andreas V. album a few times but never was nearby my rig when I read about it....its finally playing right now...This could be the next stuff I wear out....LOL...very cool!!!!

[dB Cooper]

The problem with "acoustic suspension" is the distortion, especially when using a small woofer. If you try and squeeze too much bass out of it at some point the distortion becomes gross distortion.

I'm not absolutely sure about their efficiency, but I'm thinking that woofers designed for acoustic suspension aren't all that efficient either, they have long throw, overhung voice coils, never a lot of turns in the gap.

?
Low distortion bass was always one of the hallmarks of good acoustic suspension designs, such as the AR line, the Advents, and the Allisons, just to name a few. Any speaker will distort badly if it is driven to its xmax. Yes, acoustic suspension woofers are theoretically less efficient; the design was impractical in the era of ten watt amplifiers. Watts were cheaper by the fifties.


Here is an excerpt from an interview with Edgar Villchur, co-inventor of the acoustic suspension design:

David Lander: You've said you turned your attention to loudspeakers because, back in the early 1950s, they were the weak link in the hi-fi component chain.

Edgar Villchur: In those days you could buy an amplifier for home use with 0.5% distortion or less, even at the frequency extremes and at full rated power. Loudspeakers showed distortion levels in the low bass of 20 to 100 times that amount. The problem was the mechanical suspension that held the cone in place. When the cone moved a large distance, the suspension would stretch. It wouldn't allow the cone to travel the full distance in response to low-frequency waveform peaks. I thought, Well, what we need is a linear restoring force, one that doesn't bind, one that allows the cone to move a large distance and brings it back elastically. That's when the light went on. This linear spring had been there all the time. The cushion of air in the cabinet was exactly the kind of spring I wanted.

Lander: So you decided to reduce the springiness of the mechanical structure and replace it with air.

Villchur: By reducing the stiffness of the mechanical cone suspensions and then reducing the size of the air cushion—which is to say, reducing the size of the cabinet. The latter is something you have to do; it won't work otherwise. You end up with a linear restoring force, radically reduced low-frequency distortion, and—as an extra dividend, not a primary dividend—a small cabinet.

Full interview at http://www.stereophile.com/interviews/105villchur

Here is a page from the Allison brochure of late 70s- early 80s vintage, for the Model Three, showing distortion levels for inputs of 2.8 watts (90 db reverberant spl), 14 watts, and 70 watts. Allison pointed out in their brochure that they had never seen this type of data published for inputs of over 20 watts, and neither have I.

[Æ]

?

So, do you think Acoustic Suspension typically has less distortion than Bass Reflex?

[dB Cooper]

Yes. Both harmonic and phase distortion. I've owned both.
I have furnished some data to support my contention, based on a middle of the line (but well engineered) acoustic suspension speaker. Let's see some distortion plots for 70W input into your favorite phase inversion (the technically correct term for bass reflex) box. We'll see if they match the 30+yo Allison.

There have been both good and crappy acoustic suspension designs, and good and crappy vented designs. I don't know what your blanket statement was based on.

Driver and enclosure engineering have improved over the years but the laws of physics haven't.

[Æ]

Yes. Both harmonic and phase distortion. I've owned both.
I have furnished some data to support my contention, based on a middle of the line (but well engineered) acoustic suspension speaker. Let's see some distortion plots for 70W input into your favorite phase inversion (the technically correct term for bass reflex) box. We'll see if they match the 30+yo Allison.

There have been both good and crappy acoustic suspension designs, and good and crappy vented designs. I don't know what your blanket statement was based on.

Driver and enclosure engineering have improved over the years but the laws of physics haven't.

My statements are based on the obvious market trend that seems to like ever smaller and smaller loudspeakers. That is the reason there are so many bass reflex designs. Squeezing bass from as small of an enclosure as possible. Like this little teeny tiny set of desktop computer speakers that are plugged into my computer. I don't use them for music appreciation, I just have them there so I can hear whatever it is they have to say, but the darn little things are actually ported!

So, how would a 6.5 inch acoustic suspension design stack up against a 6.5 inch bass reflex design? The epitome of a two way is most often a 6.5 mid-woofer with a 1 inch tweeter in a bass reflex enclosure. I also wonder how the two would compare in the efficiency department. There must be a reason why acoustic suspension has slipped into near oblivion.

Doesn't really matter what the phase is, as long as the port output doesn't cancel the woofers output. Never really a problem with a properly designed 4th order alignment.

The more correct term which really makes sense, is Helmholtz Resonator.

[Wayner]

I think acoustic suspension cabinets, as a general rule, are smaller, then ported enclosures. May not be a steadfast rule, but from my observations, it seems to be the trend, at least in the past.

My Advent Model 3's will hold their own in a shoot out (with a volume limit) with anything within it's comparative size. It has a 6 1/2" acoustic suspension woofer, and the box measures about 10 x 6.5 x 16. Surprising bass for such a small cabinet.

As another general rule, acoustic suspension speakers are less efficient then ported speakers. Just guessing, the AR-4x is probably somewhere about the 86-87 db/m/w category. It simply needs a little more nudge to get it to the same levels as, say my Dynaco A25XLs (slot loaded, 91db/m/w).

Wayner

[dB Cooper]

My statements are based on the obvious market trend that seems to like ever smaller and smaller loudspeakers. That is the reason there are so many bass reflex designs. Squeezing bass from as small of an enclosure as possible. Like this little teeny tiny set of desktop computer speakers that are plugged into my computer. I don't use them for music appreciation, I just have them there so I can hear whatever it is they have to say, but the darn little things are actually ported!

So, how would a 6.5 inch acoustic suspension design stack up against a 6.5 inch bass reflex design? The epitome of a two way is most often a 6.5 mid-woofer with a 1 inch tweeter in a bass reflex enclosure. I also wonder how the two would compare in the efficiency department. There must be a reason why acoustic suspension has slipped into near oblivion.

Doesn't really matter what the phase is, as long as the port output doesn't cancel the woofers output. Never really a problem with a properly designed 4th order alignment.

The more correct term which really makes sense, is Helmholtz Resonator.

That seems different from the original argument, which as I understood it was that acoustic suspension fell out of favor due to high distortion levels. I wonder if Wayner is hearing high distortion from his AR's. I certainly didn't from the pair I listened to at length. It is a small 'bookshelf' model with an 8" woofer, so I wouldn't expect it to rattle windows in a big room, but a pair of Allison Ones (for example) would.

I too have seen ported computer speakers. While some are certainly legit, I have observed some with ports that are about an inch and a half deep. I haven't done the calculations to determine the resonant frequency of a one and a half inch deep port, but I have a dollar that says it's well above the bass range. It's there because people expect to see a port these days. In other words, it's there for marketing reasons, not for any acoustic reason. I am just saying that that marketing reasons have something, maybe not everything, to do with the disfavor acoustic suspension has fallen into.

Many of the speaker makers in acoustic suspension's heyday- AR, KLH, Advent and Allison come to mind- made their own drivers. Only a small handful do today and most of those are "deep end" ($$$$) boutique brands.  So most speaker companies today outsource their drivers and are basically designing the enclosure and crossover around available drivers. And when driver manufacturers gear their product line towards what sells- a driver suitable for acoustic suspension has very different characteristics than one suited for a ported box- a snowball effect ensues: fewer sealed designs>fewer suitable drivers offered>even fewer sealed designs. The speaker driver manufacturer has a mortgage to pay too.


I believe the port tube is a Helmholtz resonator and 'phase inversion'  refers to the enclosure as a whole, but I don't want to get bogged down in terminology. I just wanted to challenge the assertion that acoustic suspension=high distortion.

[Russell Dawkins]

Many of the speaker makers in acoustic suspension's heyday- AR, KLH, Advent and Allison come to mind- made their own drivers. Only a small handful do today and most of those are "deep end" ($$$$) boutique brands.

My understanding is the opposite - in "the day" most speakers used drivers made by CTS (Chicago Telephone Systems) of Paducah Kentucky. This included AR and even Altec Lansing, apparently. CTS would build precisely to supplied parameters, whether defined by physical dimensions - top plate thickness, etc. - or performance criteria.
This is lifted from another site:

 Bob Gault worked for CTS which was indeed in Paducah. He split off in '66 to start Eminence. According to the Eminence website:

In 1966, Bob Gault founded what was to become the world's largest loudspeaker manufacturing company after working as an engineer for Magnavox and CTS (Chicago Telephone Supply). Ironically, Gault started Eminence hoping to maintain three 18" speakers per day, based on a commitment from Ampeg's Everett Hull. Under the leadership of Gault and most recently his son, Rob, the company's capacity has grown to over 10,000 speakers per day, employing nearly 200 people.

As I understand "the old days", as CTS started to decline a lot of the customers came over to Eminence and Bob stuck with a lot of the same vendors, hence the similarities like the Wendy's magnets. I worked there after Bob retired but he came in a couple of times a week between rounds of golf (he was a serious golfer even with both hips replaced) to check on things. He was a great guy (passed in '02) and his son is too.

[Æ]

That seems different from the original argument, which as I understood it was that acoustic suspension fell out of favor due to high distortion levels. I wonder if Wayner is hearing high distortion from his AR's. I certainly didn't from the pair I listened to at length. It is a small 'bookshelf' model with an 8" woofer, so I wouldn't expect it to rattle windows in a big room, but a pair of Allison Ones (for example) would.

I too have seen ported computer speakers. While some are certainly legit, I have observed some with ports that are about an inch and a half deep. I haven't done the calculations to determine the resonant frequency of a one and a half inch deep port, but I have a dollar that says it's well above the bass range. It's there because people expect to see a port these days. In other words, it's there for marketing reasons, not for any acoustic reason. I am just saying that that marketing reasons have something, maybe not everything, to do with the disfavor acoustic suspension has fallen into.

Many of the speaker makers in acoustic suspension's heyday- AR, KLH, Advent and Allison come to mind- made their own drivers. Only a small handful do today and most of those are "deep end" ($$$$) boutique brands.  So most speaker companies today outsource their drivers and are basically designing the enclosure and crossover around available drivers. And when driver manufacturers gear their product line towards what sells- a driver suitable for acoustic suspension has very different characteristics than one suited for a ported box- a snowball effect ensues: fewer sealed designs>fewer suitable drivers offered>even fewer sealed designs. The speaker driver manufacturer has a mortgage to pay too.


I believe the port tube is a Helmholtz resonator and 'phase inversion'  refers to the enclosure as a whole, but I don't want to get bogged down in terminology. I just wanted to challenge the assertion that acoustic suspension=high distortion.

The only real way to know at what frequency a bass reflex port is tuned, would be to run an impedance curve or close mic the port output. The port is not independent of the woofer and the enclosure, so physically measuring the port all by itself is kind of meaningless.

But I do agree with you as far as having an appearance. I've seen plastic boom box radio, enclosures with fake ports that didn't go anywhere, they were obviously there for the looks.

Try giving an acoustic suspension design some baffle step correction and see what happens to the distortion.

[Russell Dawkins]

Full interview at http://www.stereophile.com/interviews/105villchur

Thanks for the link, dB - a good read. He, along with Henry Kloss, are two of my heroes in American Audio.

[dB Cooper]

Back atcha, Russell; thanks for the history. (I am listening to my Tivoli One radio, designed by Kloss, right now.) I remember mfr literature from Allison and Advent claiming they made their own drive units. Advent woofer cones were supposed to contain ground up newspapers and felt. Allison had those unique midranges and tweeters.

[Æ]

Thanks for the link, dB - a good read. He, along with Henry Kloss, are two of my heroes in American Audio.

I think everyone already knows this, but just in case.
http://www.nytimes.com/2011/10/18/business/edgar-m-villchur-hi-fi-innovator-dies-at-94.html

[dB Cooper]

Try giving an acoustic suspension design some baffle step correction and see what happens to the distortion.

Let's see some data.

[Æ]

Let's see some data.

I don't have to drive a car into a telephone pole just so I can see whether or not it will smash in the bumper, grill and hood.

Do you even know why or what BSC is?

So, you take an already somewhat low efficiency woofer and then you depress, attenuate the upper bass and midrange by 3-6dB. That already inefficient woofer now has to move even farther than before bass wise, to achieve the same midrange SPL as previously. Resulting in even more distortion. Simple concept applicable to all systems employing passive BSC.

[dB Cooper]

That's what I thought.

Yes, I do, but I don't choose to interact with someone who apparently is just looking for an argument. You have yet to put up one piece of evidence supporting your blanket statement that acoustic suspension has inherently higher distortion than bass reflex. Every response from you has seemed to be oriented around demonstrating your mastery of acronyms is better than mine. My contention (which is only that acoustic suspension does not in and of itself equate to high distortion) is based on years of extensively owning and/or listening to Allisons, ARs, Advents, and many others, as well as ported speakers of many stripes, as well as the longstanding, well-known reputation of this design for delivering low distortion bass. I have yet to determine what your position is based on despite attempting several times to find out. Your snide tone shows you are not interested in having a real discussion. Buh-bye. On 'ignore' you go; suggest you follow suit as we are apparently destined only to annoy one another.

BTW the upper bass depression  you talk about was specifically addressed by Allison in their designs 35 years ago (I thought frequency response anomalies are not the same thing as distortion, but WTF do I know, apparently not much) :



Say Wayner, how are those AR-4x's working out?

[Quiet Earth]

Bass Reflex vs. Acoustic Suspension,,,, CD vs. Vinyl,,,  .... when will we outgrow these silly arguments?

 


 

[dB Cooper]

Bass Reflex vs. Acoustic Suspension,,,, CD vs. Vinyl,,,  .... when will we outgrow these silly arguments?
 

Your point is well taken, Quiet Earth. I was actually trying to have a discussion, not an argument, but it didn't quite work out. Think I'll just put on some tunes instead next time, or choose a more neutral topic, such as POLITICS... 

[Quiet Earth]

No biggie, we all get caught up in it. I am just as guilty (as charged  ).

I can imagine that we have all heard great examples of many different speaker building techniques, so it is probably not so much of a question of which method is superior but more of a question of "how did you get that to sound so good?".

I am fascinated with the old stuff and how they got so much out of so little.

[Wayner]

The ARs are fun! Spent much of Saturday afternoon listening to many good quality LPs and at my usual volume levels, they were very enjoyable. Solid bass, creamy mid-range and very detailed high end. Hard to believe that inconspicuous little driver can make nice.

I haven't put them on the Ultravalve yet, but I'll give it a week or so more so I am comfortably "learned" on how these speakers reproduce. I'm just glad to have been lucky enough to find a pair that was in this good of condition to do a restoration that would be worth while.

I just wanted to have one nice pair of ARs in the collection.

Wayner

[dB Cooper]

As I mentioned early on, the AR-4x was in the first real "hi-fi" system I ever heard and gave me my first case of "audio goosebumps." An impressive little speaker. Almost bought AR6's for my own first system but settled on original Dyna A25 instead. Probably a good thing- I believe the AR6 used foam surrounds (which would be long gone now) while my ex-brother-in-law still has my old Dynas and they still work.

I would expect droolworthy sound from these playing off the Ultravalve.