I have a great idea for an MTM design and would like comments (1 Viewer)

[Mike SJ]

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[Brian_J]

Sounds good to me! I am also one who is interested in high quality diy speakers but only if they actually look like high quality speakers!

Brian

 

[ThomasW]

Over the years there have been some quality control and other issues with US Enclosures, so caveat emptor, as they say ......

 

[Mike SJ]

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[MattD]

Here you go Mike

 

[ThomasW]

Know that spheres are probably the worst shape for the creation of standing waves inside the enclosures.

Asymetrical enclosures are a better option. This is why several designs have used egg shaped designs for a TM sitting on a bass bin

 

[Mike SJ]

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[ThomasW]

A symetrical shape like a sphere will certainly create standing waves.

And as with any enclosure, appropriate use of internal baffles and or proper damping materials will eliminate the problem

 

[Mike Keith]

I still don’t know where everybody gets that Spheres are so acoustically bad, if the back wave pressure emanated from the center of a sphere they you would have equal distances from all sides and thus standing waves at nearly all frequencies. But that’s hardly how it ever happens, the driver is mounted on the face and the back of the driver is far closer to one side then the others, and all distances are not equal. Anyway just to be sure I was told to suspend a ball of poly-fill in the center of the sphere which I did. I have already bought a Sphere from US Enclosures and done much experimenting using a SS8530-K00 driver and 2 1.5" vents on either side of the driver, all I can say is no box could beat the sound and smooth baffle roll off. Making a MTM would be a challenge though, I have already tried it and unless you can figure out a way to mold a tweeter in-between two spheres and make it look good, which I could not, then I would go a more conventional route. The tweeter needs to be as close as possible unless your crossover point is very low.

 

[ThomasW]

The little Revelator drivers are so inherently so smooth, they'd sound good playing in a tin can ...:wink:

 

[Mike SJ]

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[ThomasW]

Wave propagation info .

 

[Mike SJ]

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[ThomasW]

Some how I doubt that you're going to be using a 24" dia sphere................

You may want to refer to the enclosure articles in AudioXpress, and the enclosure studies published by the AES in recent years.

Good luck and have fun with your project.

Regards
Thomas

 

[Mike SJ]

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[Mike Keith]

ThomasW:
Don’t get me wrong this was not a statement to argue what you said, but more of a question. Your knowledge is well beyond mine, I have read many of your posts and consider your experience very valuable. However I did extensive listening with a Sphere and many other enclosures without FR measurements and it was subjectively in favor of the sphere, although I cannot prove this. Since I could not get the tweeter close enough to the mids I went with the next best thing, a tapered polygon, which after some modifications sounded as good as the sphere IMO.

I read the article in Audio Express I for one don’t believe it, they did no experimenting with the so-called internal problems of a sphere but did only the baffle interaction response. Their findings dispute many other peer reviewed acoustic experiments that all say that a sphere on the outside is defiantly better then a box. One of these reviews is available on the US Enclosure site. As far as the interior problems of a sphere I still haven’t heard a good argument of why there is a problem, the logical part was about the driver being offset to one side and therefore not equal distance to the other sides, I could be wrong here but so far every time I mention this no one responds to this specific idea, I only here technical quotes about a sphere being bad on the inside and no logical reason for why this may be true in the real world. I would love to hear about why this may be true, I’m not too proud to admit I am wrong, I’ve been wrong about most things concerning Audio theory, I just have a hard time understanding the why.

I have pictures of the sphere but none on a web site that can be linked to.

My DIY Projects
http://www.geocities.com/kingdaddyke...?1078331805978

 

[MichaelAngelo]

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A symetrical shape like a sphere will certainly create standing waves.

And as with any enclosure, appropriate use of internal baffles and or proper damping materials will eliminate the problem
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MacGyver? bahh,

Remind me *not* to get on your bad side

 

[Mike Keith]

MattD:

Nice drawing, looks interesting, but wait until you actually try doing that, carving into one of these composite gel-coated spheres and making it seal up and still look good is a serious problem, I know I've been there.

Also the back wave need only be attenuated as much as possible before it hits the back of the cone, in those drawings they don’t show haw many times the wave will bounce around before returning to the source, and this doesn’t account for the benefits of whats going on in front of the baffle, which is where a sphere is really doing it's magic.

 

[Mike SJ]

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[Mike SJ]

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