Whatever happened to acoustic suspension??

[onplane]

After reading many of the threads on this board, it’s obvious that many of you have been actively involved in the US loudspeaker market over a number of years. My question has to do with the apparent demise of the acoustic suspension design. I say “apparent demise” as the big three AR, Advent and KLH manufacture so few if any acoustic suspension speaker systems.

I’m just guessing, but I suppose some of this has to do with the more “modern” solution of using a subwoofer for the low frequencies. Further, those subwoofers are often powered, which minimizes both electrical and mechanical interference.

Nevertheless, it still begs the question, why aren’t more subwoofers acoustic suspension in design? I did find some, but the price is pretty steep:

http://www.crutchfield.com/S-fEdxcmch47W/c...sp?g=12300&pg=2

http://www.hometheaterhifi.com/volume_12_3...005-part-1.html

I will say I was shocked when I saw the size of the amplifiers in those subwoofers … 1000 Watts and HIGHER!!!

Are those huge amps necessary because of the inefficiency of the acoustic suspension desgn?

I currently own a set of AR-3a’s (I’m listening to them as I type this memo and I’m the original owner), a set of TSW 610’s (not used much) and an AR 8” down firing, ported subwoofer (used for hours every day). The subwoofer I bought on the net and just assumed it would be acoustic suspension, but … it’s NOT! In all fairness it sounds OK, but can’t handle the deep base like my 3a’s.

Now, the TSW 610’s are significantly brighter and appear to have better stereo imaging than the 3a’s, but it just seems like they are “working too hard”. It’s hard to describe, but the 3a’s produce such fantastic sound and so “effortlessly”. Then the deep base in the 3a’s is again superior to the 12 inch TSW 610’s and I have no idea why that should be the case.

My normal listening room is small (approx 120 sq ft), music is 90% jazz and power (based upon an old set of Realistic power meters) averages 0.5 watts. That is, 0.5 watts is for me a very comfortable listening level in my small room.

Before I close, thought I’d share how 30 years ago I ended up with 3a’s. During my years at college I had a little money so started with a set of AR-4x’s. Once I graduated, I sold those and “upgraded” to the 3a’s. I have never regretted the decision to purchase the 3a’s. I do regret, however, the decision to sell the 4x’s. Those little speakers had one terrific sound!

Sorry this was so loooooong,

Jerry

[Guest Bret]

Jerry,

Glad you came aboard and are yet another super-satisfied owner of the legendary 3a.

Let me take a quick stab at answering your question:

Acoustic suspension has this nasty habit of rolling-off faster than a ported system. I'm making the specifics up, but it's useful for a down-and-dirty explanation. . . don't quote me.

If you have a 3a and it has a *system* resonance of 41Hz, the bass will roll-off at 12db/octave below that point to the point of *driver* resonance (about 13-18Hz). So at 20Hz, it's 12db down, and 12db down is a long, long way down. "Usable" bass ends somewhere in the mid thirties.

A quality vented/ported speaker, well designed, is more or less flat down to the port frequency - at which point they tend to fall completely apart and sound like someone's waving a huge rubber-chicken around. . . but they are flat to that lower point. . . more or less.

So it's easier and cheaper to make a ported system that "goes lower" than an acoustic suspension design. The cabinet can be smaller and the driver can be sturdier.

This is one of those things that my ears say "Hey, that makes no sense, the (3a/10pi/11) will rattle the windows with pipe organ pedal tones and the subwoofer that claims it's flat to 30Hz falls apart and gets all blatty and stuff."

(my ears use the term "and stuff" a lot; I've tried telling them how inarticulate they sound, but they refuse to listen )

I know that the engineers have measured. I'm sure the physicists have figured and the chemists. . . have done whatever it is chemists do. I feel *certain* that they all have it right. Flatter, lower bass is easier to get with ported (bass reflex) designs. It's a shame it has to sound like that. Every one I've ever heard sounds like bass reflux to me.

"Doctor, can you give me something for my bass reflux?"

"Okay, here's a quarter."

"That's not much."

". . . not much of a speaker."

People tell me I only feel that way because I've never heard a good bass reflex system. Well, I've heard plenty of expensive ones, but ultimately they are right. I've never heard a good one.

[Carlspeak]

>After reading many of the threads on this board, it’s obvious

>that many of you have been actively involved in the US

>loudspeaker market over a number of years. My question has to

>do with the apparent demise of the acoustic suspension design.

> I say “apparent demise” as the big three AR, Advent and KLH

>manufacture so few if any acoustic suspension speaker

>systems.

>

>I’m just guessing, but I suppose some of this has to do with

>the more “modern” solution of using a subwoofer for the low

>frequencies. Further, those subwoofers are often powered,

>which minimizes both electrical and mechanical interference.

>

>

>Nevertheless, it still begs the question, why aren’t more

>subwoofers acoustic suspension in design? I did find some,

>but the price is pretty steep:

>

>http://www.crutchfield.com/S-fEdxcmch47W/c...sp?g=12300&pg=2

>

>http://www.hometheaterhifi.com/volume_12_3...005-part-1.html

>

>I will say I was shocked when I saw the size of the amplifiers

>in those subwoofers … 1000 Watts and HIGHER!!!

>

>Are those huge amps necessary because of the inefficiency of

>the acoustic suspension desgn?

>

>I currently own a set of AR-3a’s (I’m listening to them as I

>type this memo and I’m the original owner), a set of TSW 610’s

>(not used much) and an AR 8” down firing, ported subwoofer

>(used for hours every day). The subwoofer I bought on the net

>and just assumed it would be acoustic suspension, but … it’s

>NOT! In all fairness it sounds OK, but can’t handle the

>deep base like my 3a’s.

>

>Now, the TSW 610’s are significantly brighter and appear to

>have better stereo imaging than the 3a’s, but it just seems

>like they are “working too hard”. It’s hard to describe, but

>the 3a’s produce such fantastic sound and so “effortlessly”.

>Then the deep base in the 3a’s is again superior to the 12

>inch TSW 610’s and I have no idea why that should be the

>case.

>

>My normal listening room is small (approx 120 sq ft), music is

>90% jazz and power (based upon an old set of Realistic power

>meters) averages 0.5 watts. That is, 0.5 watts is for me a

>very comfortable listening level in my small room.

>

>Before I close, thought I’d share how 30 years ago I ended up

>with 3a’s. During my years at college I had a little money so

>started with a set of AR-4x’s. Once I graduated, I sold those

>and “upgraded” to the 3a’s. I have never regretted the

>decision to purchase the 3a’s. I do regret, however, the

>decision to sell the 4x’s. Those little speakers had one

>terrific sound!

>

>Sorry this was so loooooong,

>Jerry

>

Take a look at Parts Express website. They offer some subwoofer kits with moderately powered amps which, I believe, are of AS design. If you're into speaker building, they also offer an even broader selection of sub amps you can select from. They also have technical service help. You can get recommendations for woofers and box designs if you start with an amp.

With regard to the apparent demise of AS speakers, there has been a lot of debate as to which gives better bass. Vented or AS? AR found the right combination of materials and design that pleased thousands of customers. If you look around you can still find AS speakers - depending on who manufactured them. It seems to be a personal preference thing. Each has it's advantages and disadvantages. Although, at this AR posting area, the opinion is obviously in favor of AS.

Remember, it's all about the music

Carl

Carl's Custom Loudspeakers

[kkantor]

Speaking as a designer who has chosen both vented and sealed approaches, let me give my personal perspective....

Both types of enclosure have their own strengths and tradeoffs. There are four general reasons why vented systems are popular now:

1- Economics. The kind of raw driver that will work best in an acoustic suspension design requires a compliant, "floppy" construction. This kind of woofer is harder to assemble on an automated production line, due to the nature of its "soft parts." It is also more complex to test this kind of woofer during manufacturing. For this reason, the woofers used in vented systems tend to cost a little bit less money.

2- Ease of design. For an acoustic suspension speaker to work properly, the woofer and the cabinet must be exactly matched. There is very little fine-tuning that can be done. This means that during the design process, many different woofer prototypes may be required to get the sound the design engineer wants. This time consuming, and requires a very cooperative and experienced manufacturing facility. On the other hand, one can easily buy a woofer that is roughly correct for a certain size vented box, then dial everything in just by changing the port dimensions. This is a valuable benefit to amateur designers, and professionals on a deadline.

3- Technical performance. It is often the case that a slightly better response can be coaxed from woofers between 8" and 10" in diameter by using a carefully-tuned, vented box.

4- Electronics improvements. Properly recorded digital media do not suffer from the excessive and uncontrolled very low frequency signal output that records tend to exhibit. This used to be a problem, but it isn't now. Also, there are a number of signal processing strategies used to try and optimize vented enclosures.

These are real benefits in today's marketplace. Fewer companies are rewarded for squeezing the absolute sonic best of their products these days. People want convenience and price, dealers want lots of new models, factories want mass-production-friendly devices.

Even though there are many vented systems using woofers smaller than 8", they can run into trouble with very deep bass, and so most experienced speaker designers avoid them. At the larger end of the range, an acoustic suspension design will give the most accurate results in a no-holds-barred, all-out, big subwoofer design, and this is where you find it used most. (For home speakers, at least.)

In favor of acoustic suspension, you have:

1- Just about the best transient response possible in a practical design.

2- Typically lower distortion in the deep bass.

3- The ability to work in compact enclosures without difficulty.

4- Much slower rolloff below the bass cutoff. (Brent mis-spoke about this one item. AS rolls off a 12dB/oct, vented rolls off at 24dB/oct.) This factor can mean more total bass energy in the room, even below the systems main range of operation. It also makes bass EQ more practical.

[Now, if you really want to get esoteric, many of what LOOK like modern vented designs operate as acoustic suspensions over some of their range. Some of what look like acoustic suspensions are really sealed "finite baffle" designs.]

Hope this answers your questions. If not, jump in with more!

[onplane]

Ken, thanks ever so much for that great explanation!

I can’t help but wonder, whether there have been driver improvements over the years as well. Prior to acquiring a set of AR-4x’s I had a set of 12 inch Jensen vented speakers. While they worked great on rock (bass guitar), they were awful on jazz trios with their double bass. In short, they couldn’t handle the very low frequencies at all. Then the Jensen mid range was muddy at best. Nothing even close to the clarity of the 4x’s.

Now, today’s 8 inch vented systems with good tweeters and mid range are decent on double bass. Nothing like my bi-amped AR-3a’s, but decent.

In thinking about it, the creative work that AR did on tweeters and mid range, is found today in all modern speaker systems.

Regards,

Jerry

[dynaco_dan]

Hi jerry;

There is no such thing as too loooong in our hobby.

Welcome.

[dynaco_dan]

Hi Ken;

Great write-up as always, thank you.

[kkantor]

Thanks for the thanks, but no thanks needed....

This is the FUN part for me!

[kkantor]

No thanks, needed! Happy to respond to such thoughtful questions.

You are absolutely right about drivers getting better. Materials, such as magnets and surrounds, have improved. Even more significantly, (in my opinion), is the huge impact on driver design that computer measurement and modelling has had. When I was in school, it was state of the art to predict mathematically very basic elements of driver and system behavior, such as resonance and Q. Now, most larger companies have the capacity to prototype and optimize on paper. In practical terms this has improved several things, for example:

1- Price/performance ratio.

2- Power handling.

3- Distortion.

4- Maximum excursion, (Xmax).

It's not that the very best of the old-school drivers were slouches in these regards. It's just that in 1965, a 12" woofer with an Xmax of >25mm was not feasible. Certainly, an 8" woofer with an Xmax of 9mm and a power rating of 200 Watts wasn't on the designer's menu. So surely, there are small speakers around now that can audibly out-perform their earlier counterparts, sealed or vented.

I also noticed you had asked about subwoofer power ratings. Watts are pretty cheap these days. It's a simple spec that the average customer can easily understand and compare, and so there is a bit of an "arms race" mentality going on in subs. Also, active equalization is very much in fashion, mostly to get better bass cutoff numbers. Equalization burns up Watts very quickly, so you need a lot of reserve available.

OK, enough fun, back to real work...