Why so few acoustic suspension designs?

[tom67]

Now down to a few like NHT, Yamaha etc......years ago, the reason was lack of efficiency,but not a problem now with new amps...the design has a few strong points like good tight bass in a small enclosure and easier to tune to a given box size.....a few have efficiency of 90db or better just like the ported designs....

 

[Exit]

In the late 60s and early 70s acoustic suspension was dominant. Ported speakers were generally perceived as boomy and only a few companies such as BIC were selling them. I think ported design must have gotten a lot better over the years. I still have acoustic suspension speakers from the early 90s and I like them a lot.

 

[R-Carpenter]

Because you can go 1/3 octave lower in the same size ported design. Or, you could design a smaller speaker with good base extension. Commercial manufacturer has to appeal to as wide of a crowd as possible and not every wife will put up with huge boxes in the living room. Ported vs Acoustic suspension have their own advantages and disadvantages in terms of sound but that's another story.

 

[Pat D]

Thiele and Small

Thiele and Small worked out the mathematics for low frequency behavior in loudspeakers and evidently their work became well known in the early 1970s. Designing ported loudspeakers became less a matter of trial and error and more a matter of designing and achieving predictable results.

Also in the early 70s, some started using computer aided design techniques, which was possible because the mathematics was known. I had the old Kef 104, which I believe was about the first to employ such technology (1973). It had a passive radiator rather than a port, and it had quite good low frequency extension for a large bookshelf speaker, with useful bass down to about 30 Hz.

The bass driver in a ported speaker is not controlled below the resonance, if I understand it, and with record warps and such, this could cause problems with the undamped driver flapping away at frequencies too low for it to reproduce and sometimes causing intermodulation distortion. This could also potentially damage the woofer. I know I got a pair of WarpKnots (low filters rolling off 6 dB per octave below 30 Hz) for my old Kefs as a safety measure, though I really had little problem. I still use 'em for records.

With a sealed speaker, the air trapped in the speaker enclosure helps protect the woofer from large excursions which could potentially damage them.

Digital recordings do not have record warps (down in about the 8-14 Hz range) and so this sort of thing is seldom a problem, although if you try to get a small ported speaker to reproduce high level 16 Hz tones from 32 foot organ pedals, you could have a problem.

http://en.wikipedia.org/wiki/Thiele/Small

If you do a Google search, you will probably find more than you want to know about them. Some of the DIY speaker folks should be able to tell you more.

 

[irishtom]

The reason I use vented speakers is because the woofers that IMO make the best midrange and upper bass aren't suited for acoustic suspension use but are well suited for vented use. These drivers are unsuited for AS use because they have light diaphragms and very powerful motors which is probably why they sound so good in the upper bass and midrange. Such drivers are also more efficient than those with weak motors and heavy cones which is why vented designs can be more efficient---they work with efficient drivers.

I think it was Ray Newman at EV who designed the first commercial speakers using TS specs, he wrote several articles on the techniques in the early 70s and several EV speakers such as the Sentry III and Interface series made use of the new techniques.

 

[tom67]

Pat D hit on something...one problem with AS designs was uncontrolled cone excursion.....similar effect to vibrations on subwoofer cone....in the 70s, we were concerned about the damping factor of a given receiver....today, no one ever mentions that stat....

http://en.wikipedia.org/wiki/Damping_factor