Acoustically coupled radiators

Jstas

I'm sitting here thinking about bandpass subwoofer boxes and trying to think about what makes them so poor in frequency range yet play so loud. Simple, it's the design. It's efficient even if it has a truncated frequency range.

So how do you gain a wide frequency response range yet attain high volume levels? Use multiple drivers. Multiple drivers take up room though and require tons of power.

What kind of enclsoure do you use for those multiple drivers? A sealed, acoutic suspension enclosure will certainly give you the accuracy and range one looks for in a musical bass sound but a bass-reflex (i.e.: ported) enclosure gives you that mind-numbing, thumping volume everyone looks for.

So where is the compromise to get that small yet powerful but accurate subwoofer? Well, Polk Audio uses a passive radiator in the SDA speakers to achieve a low end frequency response that is similar to the performance of a large, powered driver but does not have the same power requirments nor does it affect sensitivity of the overall speaker. It helps keep power requirments down and effectivly increases the performance of the speaker system. The problem is that a passive radiator network usually has to have twice the radiating surface of the active, direct-radiating driver.

So what is my point? Well, Infinity has a BassLink system for trucks with one active driver and two raditors. It's loud and efficient but large. The benefits to the passive raditor is that you get the volume of a ported enclosure but the accuracy of an acoustic suspension enclosure. You need space for an arrangement like the Infinity system but what if one was to use a standard sized bandpass box? The sealed side of the enclosure would have the passive radiator(s) in it and the other side would still be ported like a bandpass box. This way you get one driver performing like two, using half the power will a full frequency response range but the impact that the power of a bandpass sub box can provide.

Part of the reason bandpass boxes are so muddied is because the direct radiating driver is not really radiating directly. The sound is reflected inside the ported side of the box and exits through port tubes which have port noise, resonance issues and standing wave problems. This doesn't mean that the driver itself is poor but rather the enclosure is poorly designed. A bandpass box amounts to a horn-loaded driver in a sense and it's physical limitations are presented by the shortcomings of the enclosure's design. By placing the passive radiators in the sealed side of the box, you regain that direct radiating surface so your frequency range returns but you retain that sonic impact from the enclosure gain of the ported side of the box.

Now I'm sure that I am not the first fool to think of this nor will I be the last but I was wondering if anyone has heard of this idea being implimented or ever heard such an enclosure in person. I suppose I could test it out myself but if there is sufficient evidence that such an enclosure exists and it is shown to sound particularly bad then I'd abandon all ideas for it. Otherwise, I might just try it out.

MacLeod

Ive never heard of anything like that but Im far from knowing it all.

Im not sure if it would be worth the effort of tuning and designing though. You think it would really sound any better than a properly built sealed enclosure?

neomagus00

so, to clarify, you're talking about a standard 4th-order bandpass box, with a passive radiator on the other side of the sealed section?

if so, i think it's an idea worth testing, though the issue of tuning comes into question... is the bandpass box not a very specific alignment?

RuSsMaN

VMPS uses such a design in some of thier home audio subwoofers. Slot loaded (from the rear) active driver, firing into a sealed chamber with a pr.

Remember, a PR is acting just as a port would. Actually, a lot of manufacturers refer to PR's as simply 'expensive ports'.

audiobliss

This reminds me of my neighbors' (well, used to be...they moved.....anyhow) speakers. They were old (old, old) Onkyos. I know they don't make good speakers now, but I'm convinced that they did then. They had a super-tweeter, tweeter, mid, and 2 woofers. The thing was, the bass section was sealed off from the rest of the enclosure. Only the top driver was powered, and the bottom one was a passive radiator. Besides sounding like an awesome idea, it actually did sound awesome. In a large room with a 20' (about; probably higher) ceiling, you could turn it up and get the bass to go through you. I'm not that critical a listner, so I can't really testify to the accurateness of the bass, but there was a lot of bass there.

So I guess what I'm saying is, that it is a very cool, efficient design.

Of course,.....I could be totally wrong....