Woofer technology - isn't it surprising...

[rdepelteau]

Just for fun... here's the wiring diagram...

 

http://www.freescale.com/files/graphic/block_diagram/SG2026BD.gif

[TimR]

I'm not sure that Teflon frying pans were that expensive in the 70's, but just wait another 35 years and they'll be using those acuators in 'sound transmission devices' everywhere.

 

Try contacting their R+D, see if they've any jobs going, you might be able to borrow a few at the weekends..

[rdepelteau]

I lost their address.

[butcherNburn]

Originally posted by Big Red 67:

Back in the day they had something called a passive radiator. I think it was a gimmick. Just a floating cone that looked knida like a speaker.

A long time ago I had a set of JBL StudioMaster's with 12" passive radiators. I don't know how much they contributed to the sound but they were some kick a** speakers.

[alexclaber]

Passive radiators seem a really cool idea but they generally don't work as well as ports due to all the mechanical imperfections of the moving diaphragm system. The main reason they are used is where the size of the port would be prohibitive.

 

When designing a port you need to consider the maximum air displacement (Vmax = Sd x Xmax) of the driver, and then calculate the resulting speed with which air will be forced through a port of given area. The maximum speed allowable is 0.045 Mach - any greater and port noise is likely to be problematic.

 

Once you know the minimum port area that you can use, you then simply extend the length of the port until the mass of air in the port resonates on top of the air spring caused by the cabinet volume at the frequency you want.

 

This is all well and good until you're trying to design a very compact speaker cabinet. In this case the small internal volume raises the spring constant of the helmholtz resonator thus requiring a particularly large air mass, i.e. a large port length (as increasing the area would increase the strength of the air spring). And the problem here is that the port simply won't fit in the cabinet.

 

Enter the passive radiator - simply a speaker missing the motor section. This can be tuned by changing the surround stiffness and cone mass and can totally replace the port in a reflex design. My in-car subwoofer uses one of these as the cabinet is tiny - about 10" cube - and is tuned really low and the long-throw 8" woofer moves a lot of air. It works really well.

 

The Mesa/Boogie Scout is a really nifty design because not only does it have a passive radiator but it also has a tuned port. I presume this is because the PR used has insufficient excursion so by tuning a port at the same frequency the load is shared. Cunning.

 

Alex

[Gruuve]

The sub in my SUV has is a passive radiator design...200 watts and it's tiny, and IIRC the frequency response drops into the low 30's. It rocks...maybe some more focus on the passive radiator approach would be worthwhile?

 

Dave

[alexclaber]

Originally posted by Dave Sisk:

The sub in my SUV has is a passive radiator design...200 watts and it's tiny, and IIRC the frequency response drops into the low 30's. It rocks...maybe some more focus on the passive radiator approach would be worthwhile?

I doubt it. Good bass in cars is just SO easy. IIRC you get 12dB/octave gain in the bass.

 

Alex

[rdepelteau]

I think the area of the radiator should be maximised, always. The reason being that a larger area is displacing more air, so a larger area doesn't have to travel as much to move the same air mass as the speaker. It can also be made of a flexible heavy membrane such as rubber, to flex and absorb a lot of sound and vibration. I think that is better than just a speaker cone radiator the same size or smaller than the speaker.

 

I would try to make the whole back of the speaker from a heavy rubber membrane with enough flex to maintain internal air pressure to within specified limits, to dampen vibration and sound waves coming from the back of the speaker. Perhaps even a two stage dampening device.

[Big Red 67]

WOW! Passive radiators have come a long way. Like I said the ones I saw where allways in really big cabs. Other then the recent examples.

[rumpelstiltskin.]

Originally posted by rdepelteau:

I would try to make the whole back of the speaker from a heavy rubber membrane with enough flex to maintain internal air pressure to within specified limits, to dampen vibration and sound waves coming from the back of the speaker. Perhaps even a two stage dampening device.

while a properly selected membrane might aid you in maintaining exact internal volume, it won't help reduce vibration and sound waves from the back of the speaker. in fact, it would enhance such vibrations at the back of the cabinet compared to a rigid cabinet material like MDF or plywood. i'd also question the value of maintaining strict internal volume.

 

another way of approaching this question is to examine the effects of the proposed actions. for example, when the loudspeaker moves out, the resulting rarefaction inside the cabinet adds force to re-center the driver. the only other return force is in the form of the suspension components (spider, surround) pulling the driver back to center in the face of decreasing electrical signal.

 

if we are to remove this rarefaction by maintaining internal volume vis a vis internal air pressure, increased stress is placed on the supsension components of the driver to maintain driver position. essentially what you are doing is removing the air spring, which is the purpose of building a cabinet.

 

but i'd encourage you to give it a try, if only to verify my educated guess. or to bear out your theory. however, i'd suggest you bring more of your engineering background to bear in your experiments. blind repetition is often less productive than a single calculated attempt. spend some more time analyzing your ideas and doing research (the web is a wonderful thing), and you'll be better able to separate good ideas from those that have already been conceived and rejected, or tried and failed.

 

robb.

[rdepelteau]

Thanks robb

 

I did not say to maintain 'strict' internal pressure, but 'within specified parameters'. I understand that vacuum act on the speaker to pull it back. And probably, a complete rubber back is not necessary, a flexible seal around a dampening device may perform just as efficiently. That's certainly the route I would investigate should I build my $50Gx36" speakers, since it's obvious that a lot of air would be moved by such a large cone. Maybe a hybrid port/damper like the car speakers Alex spoke about. For one thing, instead of a surround and spider to pull back, I would consider a floating design, more like a piston in a sleeve, with rings around the perimeter. And use a certain amount of vacuum or springs to pull back and limit travel. But that's all hypothetical since I'll never build one.

 

I don't intend to build a prototype, or devote any more time on this issue that I already have. I have plenty of work ahead of me in R&D. I only wish my mathematical skills were better. Tensors and differential equations are the tools of the engineer. Unfortunately, I didn't finish my mechanical engineering, but I know when and where calculations are needed. Mathematical modeling is necessary in today's research. Trial and error is not necessary anymore as material science and computers is all that is required to model exact prototypes. And that can save companies tons of money and effort that would be spent uselessly going down a dead end road.

 

When I suggested an actuator instead of the conventional method, I knew that automotive actuators were already on the market, so I researched these, to find out their specs, and see if they were capable of driving speakers. I like to work with what is on hand. Handbooks provide a lot of ready made solutions, and over the counter components can save a lot of time, when they can be found.

 

A lots of speaker companies devote a lot of time and effort to put out products that is a step ahead of the competition. Since I have no desire to go into the speaker manufacturing biz, and compete, I might as well join the kibitzing party, and see if I can contribute some useful ideas.

 

I am satisfied with pure research, it would be very encouraging to see this design being produced somewhere and delivering a superior sound. It wouldn't be the first time I come up with something interesting.

[getz out]

What about using lasers? They have done wonders in hard drives.

 

In general, you want the box to be as rigid as possible so you do not lose energy through sympathetic resonance of cabinet.

[Tom Capasso]

I'm not qualified for the depth of technology that this thread has moved toward. I've found the discussion at times to be interesting, over my head, and "out there".

 

I think all of the scientific research is cool, and the economics always take time to catch up.

 

At one point, someone (wisely) wanted to define the problem so we're on target. The original question was about woofer technology, noting that it hadn't changed much. That's interesting, but it's not a problem. If we want to move air with bass frequency more efficiently, that's a "problem".

 

My feeling is that the best answer within our current tech/cost is more speakers. Phil Jones cabs start down this path (thanks to Lug for the picture), but my experience is that you need more speakers placed throughout the audience. Bose line arrays help get more "throw", but not in our frequency range. So I would advocate more powerful amps (or arrays of amps) that feed speaker groups/cabs that are distributed. You don't need as much volume (there isn't as much "waste" because you're throwing for shorter distances). And it resolves many local acoustic issues (having played in lots of echo-y churches, I know about this).

 

I know, I know. That will work fine in established venues with "mounted" systems (though I haven't seen it much). But what about when I go out with my band? For now, that's an issue I don't have an answer to - go out with 20 cabs and the wiring and power to drive them? It would be a lot to carry and set up, but the technology to do that is here.

 

Anyway - that's my less than interesting contribution. Drive through please.

 

Tom

[TimR]

They do this at big outdoor events, with speaker stacks positioned further and further away from the stage. Each stack has a 'delay line' on it so that the music is produced from the stack at the same time as the sound coming from the speaker in front arrives, this stops phase problems and echo type effects.

 

You could do it a gigs with small speakers and a wireless system, but I'd bet some idiot would start unplugging stuff and messing with settings so the gear would have to be set up in the right place.

[rdepelteau]

Tuned ports....

 

I was thinkin, a tuned port is just an opening tuned to a particular frequency. So what if, instead of a fixed port size, there was an aperture like the shutter of a camera, that was computer controlled, to open and shut so as to tune the port on the fly ?

[Tom Capasso]

The "tune on the fly" sounds interesting. The latency issue would probably kill it for anything faster than half notes. Imagine the "blooming" of a note as the port adjusts just after the note starts to sound. And chords?

 

Interesting though - keep thinking!

 

Tom

[Bobby LowTones]

I would think once the port size is pretty well defined, then the

tube length sould be controlled instead of the aperture.

 

Now is the time to use a linear actuator to slide a secondary tube

over the main one...

[jeremy c]

More grist for the mill.

"more bass, less space"

Tymphany home page.

Wood cone speakers

[rumpelstiltskin.]

the tymphany LAT drivers have been around for a year or so. funny you'd add them here, because my friend just emailed me about them today. the wood cone speakers have been around for a while, too. we got a good laugh out of them at peavey. did you catch that they're soaked in sake?

 

for another take on flat-panel compatible bass, check out my employer's infinity cascade loudspeakers featuring MRS drivers .

 

robb.

[TimR]

Sorry just had to bump this!

[Big Daddy from Motown]

We are sorry too!

[TimR]

LOL. Just thought someone was asking about how magnets work and remembered this very humorous thread.