What killed off the acoustic-suspension speaker?

[TerryO]

Clue!

Btw I was looking for pics of vintage audio and ran across this cool photo of the AR9, Power Sponge Of The Decade , which contained a link to the designer's thoughts on the engineering behind the 9.

Some of Infinity's a.s. speakers were also known to be difficult loads for many amplifiers, including the beautiful RS IIA, which IIRC also exhibited tricky phase angles electrically-speaking, though to be honest I don't know what that means or how it affects an amplifier.

Difficult loads for an amplifier was almost an Arnie Nudel trademark. OTOH, he did help bring in a lot new technology to speaker design.

Best Regards,
TerryO

 

[clubsport911]

What a terrific thread.

I'm not a speaker designer but have been into DIY audio for over 40 yrs and love this enthusiasm for the hobby we all share.

I am however an engineer and for me, a micron is quite a large unit - certainly you'll be glad I don't have this much contradiction over the laws of physics in my company, when the pilot pulls the stick back on the aircraft taking you and your family on holiday, you will want the aircraft to take off!

Anyhow, coming to the op, I'm so curious to hear opinions of my set up which is that "marmite" of speakers, the KEF 105/3. With its cavity coupled bass (look it up ) and unconventional design it has sent my preconceptions about what "good" bass is into a flat spin.

Until the arrival of the KEF's my main speakers were heavily modified Mission 765's (google Mission 765's for sale) with 2x 8" bass reflex /port loaded to make deep and I thought, powerful bass.

The 105's look very impressive but the bass is totally and utterly different. Not nearly as deep (or is it ?) what is there is simply a magnitude better, more accurate and faster.

I do miss what I think is that "last octave" but every now and again these kefs shock me... When I play material with bass, it's there as large as life. However when playing rock and dance that is loaded with low notes a lot of the boom has simply gone leaving me the impression of no bass.

It has taken me weeks of listenening to remove all my prejudice about what low bass really is and having to adjust my mental models about LF reproduction has not been an easy journey.

Whilst reading this fascinating thread, I went through 5 sides of lp and was never happier that whilst it's been tough "less really is more"

So, my current 105 speakers have 2 x 8" (sealed) speaker systems (connected back to back in me mechanical and electrical anti-phase, driving a central chamber which then vents to room via a massive port. I think the sound is unique, and whilst not de riguer these days, has left me smiling !

Thanks for a thoroughly entertaining and informative read

Steve

 

[Bare]

Understandably that even KEF's sound better
Do note there are many speakers available that make KEF' 105's sound quite poor.
More coin though .

 

[neutron7]

I think it comes down to:

Its cheaper to use a tuned port with a smaller speaker, and the numbers sound better. if you spend the money on a bigger/better driver then you can have better bass in a sealed enclosure, and it doesn't have to be a bigger box. most people dont really care they just want to hear "bass" and the manufacturers do it for them. (listening on crappy m-audio ported "studio monitors" with bass that extends nicely but sounds horrid)

 

[tvrgeek]

Gad, there is so much hearsay here.

"Acoustic Suspension" is the term coined by AR for a sealed box. Nothing else.

Soft surrounds are no problem. Cheap foam is.

The efficiency is set by the driver parameters, not the box.

The market rewards the "wow what bass" from a tinybox. So, a ported box with a hump before rolloff sells better than a larger box with a flat rolloff.

What neutron7 said.

 

[balerit]

>>> What killed Acoustic Suspension?

>>> The Thiele and then the Small papers and all the simulation programs made design of proper vented box designs much simpler.

Bill, what components are used in your speakers in the pic? They look terrific!

When i first read this post i thought sealed is not dead and never will be dead. But yes, Thiele/Small made it easier to design ported boxes that also sound very good.

Personally, i prefer back horns and open baffle... measurements be damned! I'm in this hobby for the SOUND!

Thiele and co really only put mathematic emphasis on James F Novak's work of the '50's, my speakers are based on his ducted phase invertors as they were known.

I personally don't believe in the modern way of testing speakers, the graphs don't look good so everyone is changing their software/simulation to suite the graphs.

And yes measurements be damned.

As a rule of thumb I would say anything under 10 inch should be infinite baffle for small systems and 10 inch and over for bass reflex in larger systems.

Just my 2 cents worth.
Mac

 

[tvrgeek]

Mac,

I do believe in the modern simulation and testing. It is much quicker to get to the place where you start using your ears. It can help weed through the hundreds of possibilities to start with better choices in drivers. What I think you are really thinking, correct me if I am wrong, is that over-reliance on simulation and only technical measurement is what you don't believe in. In that I would totally agree.

If you have not found advantage in the modern tools, could it be you have not had the time available to learn them? Some are very easy to get misleading results and it takes a long time to understand what they really tell you. If there is anything I can say about SoundEasy, is it is not easy! Something like TrueRTA is very easy, but it takes a lot of experience to see what it is telling you. ARTA the same. Sims like WinISD are silly easy, but with enough experience, you get a feel of what it is telling you and what the final build actually measures as. It sure saves a lot of time and money in finding out if that new wonder driver is a 85Hz or a 65Hz driver, or if you are looking at a 20L or 60L box.

I have no idea what you are saying about changing their simulation to match the graphs. It would be pointless to change a simulation graph to match measured results other that to stroke one's ego somehow. Cheating the measured graph to match an overly optimistic simulation is not unheard of. It's called "advertising".

I disagree with your blanket statement "under 10..." It depends entirely on the application. My 3 inch desktop speakers are totally unsuited for OB. In my guest room, the mains are right against a large back absorber. Totally inappropriate for OB. In my living room, OB may work well, but I don't have the space and the WAF is too low, so the mains are rear ported with sealed subs. My experience is that sealed makes for a better blending of subs into a typical living room. So, in the only totally accurate answer for anything in audio, "it depends".

 

[soundaatma]

How about the passive radiator cabinets. They can provide deeper LF extension than sealed, yet be smaller than ported with minimal mid range leakage

Unfortunately, very few drivers with T/S specs suitable for sealed cabinets are available these days for DIYers . The ones that are around usually are for automotive applications and lower quality

 

[tvrgeek]

PR's tend to cost too much, so they are not common. The PR acts just like a very large port. Where you can't fit 20 feet of 4 inch pipe into your box, a 12 inch PR will. Not common, but they do work. Peerless still makes one and recommends it with the 830500.

 

[Cal Weldon]

PR's tend to cost too much

You often make you own from old drivers. Remove the motor, paint the back of the cone with PVA glue a few times and add some slits in the spider if travel is restricted. Extra weight can be added by filling in the dustcap from the backside with extra glue but be careful the suspension can handle it.

 

[system7]

To say that acoustic suspension is just closed box is misunderstanding how it works. AR's bass drivers were very high mass and inductance (ca. 3mH) with soft foam surrounds on a lowish Qts well below the 0.5 you'd use with most closed box. As a result, as mentioned, the Vb is at least 3 times smaller than the Vas. The design also differs from closed box in using a huge amount of glass fibre or similar stuffing.

These days surrounds are much better than in the 1950s and 1960s, and its main justification is past. The AR-3A is still a fine three way design, but the two ways like the AR-4X and AR-6 looked dated and let though a lot of midbass cone breakup around 5kHz which can sound harsh.

It wasn't reflex that competed with Acoustic Suspension in the 1970s , but closed box with more sophisticated crossovers and less stuffing but still using wall reinforcement of bass. Bookshelves, not standmounters.

Overall, I'd say that it wasn't bass that let AS down at the budget end, but the muffled and harsh midrange. Much easier to design a standmounter too. You use a bigger bass coil which makes electronic filtering easier. If I was building a bookshelf type these days, I'd use a low inductance driver for sure. Like this Peerless 830870 4" polycone which is optimised for closed box of 5L:
Peerless 830870 HDS 106 PPB MidWoofer Speaker

 

[davidsrsb]

My TDL transmission lines sounded bass light compared to my Mission 752s until I played some organ music. Closer listening shows the "one note" thump of the BRs

 

[weltersys]

. AR's bass drivers were very high mass and inductance (ca. 3mH) with soft foam surrounds on a lowish Qts well below the 0.5 you'd use with most closed box.
These days surrounds are much better than in the 1950s and 1960s, and its main justification is past.

I don't disagree with most of what you wrote, but the early AR surrounds were a ,treated linen not foam.
The 2 way photo on the left in your post #191 appears to be treated linen , the 3 way on the right, foam.

I recently (unsuccessfully :^( ) used the treated linen surroundss from a pair of ARs from approximately 1959 to replace the rotted foam surrounds on some much more recent "digital ready" Cerwin Vega speakers.

The early foam surrounds rotted quickly (especially when exposed to sunlight), which would have had an impact on popularity, it is a good thing that foam surrounds no longer have to disintegrate so quickly.

 

[Hezz]

* too inefficient vs. bass-reflex, its main competitor?

* people became irritated at paying extra for more powerful amps that could drive acoustic-suspension speakers to their full potential?

* generally speaking, more people preferred the sound of a bass-reflex design i.e. bass reflex is generally "punchier", more "lively" etc?


Through the 60s and 70s acoustic-suspension loudspeakers seemed to be everywhere. But by the early 80s only Infinity, KEF, Advent, Celestion, Boston Acoustics and a handful of others here in the States still sold them. Then by the mid 90s, I believe only Advent and Cambridge SoundWorks (founded by Henry Kloss......who founded Advent!) still sold them and now as far as I can see, at least as far as the mid-fi class is concerned*, no one sells them.

Just curious, as I like the sound of the acoustic-suspension system, though I know that on paper supposedly a bass reflex should sound the same.....but to me they don't.


* I know that term will bother someone but I don't know what else to call the Advent/Infinity/etc price point

In my opinion what killed off the AS speaker was a couple of different things. One was blindness. The AS design can make good sounding bass but the system was optimized for the low end transients. And the smaller AS systems tend to have an un-natural sounding mid-bass, lower midrange and midrange. This could have been fixed had they limited the woofer to work in the low bass only. But most were designed to run up to 2khz or higher. The more successful AS three-ways are the ones that limit the woofer to 200-300Hz or lower and use a sealed mid-bass chamber that is tuned towards a more critical damping for the mid-bass enclosure.

All of the important music fundamentals are between about 60-2000Hz. And the speaker covering this range needs to have an air spring which can tune itself to different frequencies. It's just like a car suspension that works great on big bumps. But take it on a dirt road with cyclical washboard bumps and the suspension can't do it's job.

AS only works well for a narrow range of frequencies. And all the attention was on the low bass response. However, the bigger the box the better it seems to work since at higher frequencies the air spring looks more and more like an infinite baffle to the drivers.

Had a wide range midbass been employed with aperiodic tuning in an isolated enclosure combined with the AS woofer the speaker would have been more successful. But combine the public's desire for a somewhat elevated bass response with the annoyance of unnatural sounding mid-bass and lower midrange. You have a recipe for disaster.

 

[TerryO]

You often make you own from old drivers. Remove the motor, paint the back of the cone with PVA glue a few times and add some slits in the spider if travel is restricted. Extra weight can be added by filling in the dustcap from the backside with extra glue but be careful the suspension can handle it.

This thread is ALIVE!(again).

We used to mess around using old drivers back in the day. In the late 90's we talked Dan Wiggins into designing a high quality "Passive Radiator" after the old "Bass List" design group finished "The Official Bass List Subwoofer" which was subsequently introduced to the general public as the "Shiva" Subwoofer.

The last I heard (a year ago) the downfiring Subwoofer I desighed and helped build for "Shiva #1" was still in use and going as good as ever.

Best Regards,
TerryO

 

[speaker dave]

To say that acoustic suspension is just closed box is misunderstanding how it works. AR's bass drivers were very high mass and inductance (ca. 3mH) with soft foam surrounds on a lowish Qts well below the 0.5 you'd use with most closed box. As a result, as mentioned, the Vb is at least 3 times smaller than the Vas. The design also differs from closed box in using a huge amount of glass fibre or similar stuffing.

These days surrounds are much better than in the 1950s and 1960s, and its main justification is past. The AR-3A is still a fine three way design, but the two ways like the AR-4X and AR-6 looked dated and let though a lot of midbass cone breakup around 5kHz which can sound harsh.

It wasn't reflex that competed with Acoustic Suspension in the 1970s , but closed box with more sophisticated crossovers and less stuffing but still using wall reinforcement of bass. Bookshelves, not standmounters.

Overall, I'd say that it wasn't bass that let AS down at the budget end, but the muffled and harsh midrange. Much easier to design a standmounter too. You use a bigger bass coil which makes electronic filtering easier. If I was building a bookshelf type these days, I'd use a low inductance driver for sure. Like this Peerless 830870 4" polycone which is optimised for closed box of 5L:

Much "opinion masquerading as fact" as my old boss Laurie Fincham would say. Acoustic suspension is closed box. The only distinction we might make is that there are high alpha and low alpha designs. Alpha is the ratio of driver compliance to box compliance, or Vas to box volume. A high alpha design is one where a relatively compliant woofer is put in a relatively small enclosure. 3 to 1 (not “3 times less”, certainly a non sequitur) is quoted as the borderline, but the distinction is purely arbitrary. We can talk about acoustic suspension at one end of the continuum and infinite baffle at the other but they are all modeled and analyzed the same and are simply closed box or second order systems.

Similarly, the amount of stuffing used doesn’t create a distinction. Whatever the Alpha of the design the stuffing will give a similar compliance increase and standing wave damping in proportion to the percentage of box filling. High percentage stuffing does not equate to Acoustic Suspension.

Wall reinforcement of bass means?

The “muffled and harsh midrange” (those are not opposites?) wouldn’t be a characteristic of AS designs as it is purely a function of response curve and crossover network. Certainly large Alpha and small Alpha designs alike could have similar characteristics if (poorly) designed to do so. I also don’t see how a “bigger bass coil” is an attribute of either vented or large or small sealed box.

A few facts:

Just about any woofer can be made to work in either vented or sealed designs (as long as the Q isn’t too high).

For a given woofer a proper vented design requires nearly double the box volume of the proper sealed design.

Frequently the manufacturers don’t allow for twice the volume so many vented systems are peaked in the bass.

With proper design, a vented box can have well damped transient response, although it will be a higher order system than sealed.

Vented systems will have less mid-bass excursion but possibly more excursion below cutoff.

Vented systems are not inherently more efficient for a given woofer. You can redesign the woofer, pick up efficiency and have the same LF cutoff, but it requires complete redesign with more magnet, hence more cost.

The big difference between the early Acoustic Suspension systems (AR, KLH) and their peers was not high compliance but the willingness to pile on the mass and give up midband sensitivity. “Acoustic suspension” just made for a more marketable concept than “massy cone”.

Regards,
David