[dwarfed centipede]

Hey everyone, I just had an idea.  What if when you are building a speaker "box" you put fins of certain lengths sticking out?  Would these fins help radiate certain frequencies depending on their length?  Say if you make the box out of some kind of hardwood instead of MDF to allow sound waves to radiate.  Any thoughts?

[Vapor Audio]

Thoughts?  Bad idea ... the goal is for the enclosure to contribute nothing to the sound.  Even if you could engineer radiating fins, the sound they radiate would contribute nothing but even order distortion products.  It would be impossible for them to be anywhere close to in phase with the drivers. 

[dwarfed centipede]

What if you didn't hear the driver?  Say enclose it inside the box and use fractals to radiate every frequency?  Maybe even use metal fins instead of wood.  Just thinking outside the box here, this probably won't end up being practical or even sound good.

Thought of something else, use the fractal antenna for frequencies where they could be practical and use a series of bandpass enclosures for the low end.  Then you wouldn't have any direct interference from the driver.  Although, I wonder what would happen with the time delays from the different wave propagation?

[Russell Dawkins]

Outside the box, ooooh yeah!!

http://www.youtube.com/watch?v=8Q7FFjUpVLg

[Vapor Audio]

That's certainly an outside the box idea.  I'd have to say you're better off scrapping that idea though 

If you wanted play with something similar, get some of the NXT type surface exciters. 

[planet10]

I have used an exo-skeleton for bracing.

Bösendorfer uses techniques similar to what you describe.

http://www.gerhardfeldmann.com/bony-history/Floorstanding.htm?page=category&cid_name=Floorstanding

dave

[Russell Dawkins]

I have used an exo-skeleton for bracing.

Bösendorfer uses techniques similar to what you describe.

http://www.gerhardfeldmann.com/bony-history/Floorstanding.htm?page=category&cid_name=Floorstanding

dave

I don't see the connection between what I see on that site and this ... whimsy(?). Actually, from all I can see, the Bosendorfers (how do you get that umlaut over the "o"?) are pretty conventional boxes, aren't they?

Russell

[dwarfed centipede]

Those speakers just use the same kind of wood as they use on pianos.  I bet they sound very rich.  The design I was thinking would be completely different.  Has anyone ever built an enclosure out of metal?  What does that sound like?

[Mike Dzurko]

Generally speaking, metal rings like a bell . . .  bad. However, metal, when bonded to mdf or wood can provide additional mass damping . . . good.

[Vapor Audio]

Generally speaking, metal rings like a bell . . .  bad. However, metal, when bonded to mdf or wood can provide additional mass damping . . . good.

I've put a 2-way in a 24"x12" steel tubing extrustion just for an experiment and it certainly didn't ring.  The accelerometer had trouble picking up any energy at all.  In a metal enclosure you need some thick damping on all internal walls though, or else you get a fair amount of sound transmission - that's different than resonances.  The problem though was the weight, that piece of tubing alone was 120 pounds. 

But forget metal - if you want to go nuts make a cabinet out of a canvas or paper phenolic.  Tensile strength higher than steel (depending on what phenolic you choose exactly), and great internal damping to boot.  The problem you run into then is cost.  I make baffles out of a canvas phenolic, and just the raw material for a 1" thick, 18" x 10" piece is $120 ... and that's with my 'buddy' discount.  You could make a cabinet out of 1/2" thick phenolic though and get it to a reasonable cost.   But oh, another problem will be cutting it ... and gluing it    You can't cut it with your table saw, I got lucky to find a CNC machine that works with stone and can handle phenolic.  And you need special (expensive) adhesives to glue pieces together.  But varieties of phenolics are what Wilson uses for all the X-Material, M-Material, etc. 

[planet10]

I don't see the connection between what I see on that site and this ... whimsy(?). Actually, from all I can see, the Bosendorfers (how do you get that umlaut over the "o"?) are pretty conventional boxes, aren't they?

On some of them the midbasses sit behind a sounding board that is designed to radiate.

dave

[planet10]

The design I was thinking would be completely different.  Has anyone ever built an enclosure out of metal?  What does that sound like?

Not many have, but done right is can be really effective. High stiffness means that they can have their panel resonances pushed up very high where they won't ever get excited. Sure they can ring like a bell, but a bell doesn't ring unless excited.

dave

[Wylie Williams]

Some designers have swum against the stream. Back in the 70's Jeff Martin of Speaker Craft told me of an old man speaker builder who would occasionally bring in his home-made speaker for comparison to their kits. His secret to sound was that he made the cabinet like a violin. Same thin varnished wood, etc. To him the resonance of a musical instrument was only able to be reproduced if the cabinet resonated like a musical instrument. Jeff reported that the sound was actually not so bad, at least on violin music. In the 80's one British maker, Mission,  admitted that they designed a resonance in their smallest bookshelf speaker to contribute warmth. 

[Russell Dawkins]

Some designers have swum against the stream. Back in the 70's Jeff Martin of Speaker Craft told me of an old man speaker builder who would occasionally bring in his home-made speaker for comparison to their kits. His secret to sound was that he made the cabinet like a violin. Same thin varnished wood, etc. To him the resonance of a musical instrument was only able to be reproduced if the cabinet resonated like a musical instrument. Jeff reported that the sound was actually not so bad, at least on violin music. In the 80's one British maker, Mission,  admitted that they designed a resonance in their smallest bookshelf speaker to contribute warmth.

...and in the early 70s, Yamaha designed an ear shaped woofer for the (dipole!) NS-230, reasoning that it made sense that the diaphragm should ideally be ear-shaped since our ears are that shape. 
http://tinyurl.com/64gulpq

Also, in the early 70s some other Japanese maker - I can't remember who - stated that his design intention was to make a speaker that resonated like a beautiful violin, not to make a lifeless non-resonant item.

In reality, though, all cone speaker-based designs juggle the resonant characteristics of boxes and/or drivers, with the spoils going to the best compromise. Open baffle cone speakers, of course, are not exempted.

[Vapor Audio]

Some designers have swum against the stream. Back in the 70's Jeff Martin of Speaker Craft told me of an old man speaker builder who would occasionally bring in his home-made speaker for comparison to their kits. His secret to sound was that he made the cabinet like a violin. Same thin varnished wood, etc. To him the resonance of a musical instrument was only able to be reproduced if the cabinet resonated like a musical instrument. Jeff reported that the sound was actually not so bad, at least on violin music. In the 80's one British maker, Mission,  admitted that they designed a resonance in their smallest bookshelf speaker to contribute warmth.

The truth about this approach is that ANY resonances in the cabinet, intentional or not, produce their own separate waveform which will sometimes sum with the drivers waveform ... and other times cancel.  It's nothing more than even order distortion products, and will be wildly and uncontrolably out of phase with the wavefrom coming from the drivers themselves. 

I can't imagine any situation in which this would be desireable.  The job of the drivers is to reproduce the recording as accurately as possible ... anything the enclosure contributes is only going to contaminate the waveform created by the drivers. 

[Mike Dzurko]

Amen, and beautifully stated. I can simply state that in my 30+ years of designing speakers, I found this to be absolutely the case.

The truth about this approach is that ANY resonances in the cabinet, intentional or not, produce their own separate waveform which will sometimes sum with the drivers waveform ... and other times cancel.  It's nothing more than even order distortion products, and will be wildly and uncontrolably out of phase with the wavefrom coming from the drivers themselves. 

I can't imagine any situation in which this would be desireable.  The job of the drivers is to reproduce the recording as accurately as possible ... anything the enclosure contributes is only going to contaminate the waveform created by the drivers.