spherical speaker enclosure

hello

try to upload jpg's using

spherical enclosure causes we don't need a filler, but you can try.

i think 4mm is not enough. i would use 1.5-2.5cm, but i'm not sure it's the right material.

regards

The earthenware matkas you are using have such thin walls that they would resonate like hell for starters. They would need to be very rigid with walls at least 25mm thick and they would need to be of the correct volume for any specific driver.

An example of commercial spherical speakers

These examples appear to be 'tuned port' type of a bass reflex design. A sealed container of any design would need to be 'infinite baffle' type - stuffed with heavy sound absorbing matieral and using a driver that depends on 'air resistance' to prevent excessive cone excursions.

Luhan Monat (luhanxmonat-at-yahoo^dot^com)

You could try applying a layer of adhesive backed sound absorbing fabric/felt to teh inner surface of the enclosure, but perhaps more likely to work with the stock wall thickness and typical of rectangular enclosures would be some kind of bracing. The difficulty being that the mouth of the container you're using is probably smaller than the interior diameter of the enclosure.

You definitley need to select an appropriate driver for closed cabinets this can easily be broken down by the Q-ts ratings of a speaker driver, if memory serves well, the smaller the Q-ts the better suited to closed/sealed applications.

My other suggestion might be to look atcreating a face plate and using smaller 5-6 inch dirvers with whizzer cones that can more acuratley reproduce a wider range of frequencies.

Best of luck. The enclosures are beautilful

-andrew

That would be debateable. I suspect you may be remembering that a spherical *source* is best for omnidirectional sound radiation, but there is no easy way to get that with an enclosure. Some folks have tried covering a spherical enclosure with many small drivers. The problem there is that, as with any multi-driver system, you have interactions between the driver coverage patterns. A driver's output pattern is dependent upon frequency, especially toward the top of its range. So if you try to position the drivers so that their fields just meet for perfect coverage at one frequency range, then at other ranges the fields will have overlaps or gaps. That gives ragged frequency response due to phase cancellation, etc.

The pot "enclosure" you describe would be a classic Helmholtz resonator... the exact opposite of what you want for sound REproduction, though it might be a great musical instrument on its own. The polyfill will help you somewhat, but I suspect that the bigger problem is that the walls themselves are resonating like a big bell. If you are determined to follow through with this (for the sake of art, say) then you might want to try coating the pot walls (inside or out) with something dense and viscous, like pitch. As another post notes, these walls are pretty thin to start with, which is making the problem worse.

Best regards,

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Yes spherical enclosers can work quite well because they do not have sharp edges causing troubling acoustic diffraction patterns. These patterns can color the sound by causing peaks and valleys in response and are partly responsible for the "lousy" sound of some boxes. A spherical enclosure does not automatically improve things, however, it has to be properly made of the right volume and be properly damped without resonance. The boomy sound you report was most likely was caused by too large a volume and or air leaks causing a "porting effect." A second order system requires a "sealed" box so be sure that all air leaks are sealed up and that there are no holes or gaps anywhere in the sphere or speaker mounting. Yes, you should fill the volume with fiber glass, dacron or some other material which will damp resonances and increase the speaker loading. The volume needed should be calculated: Vb = Vas/((Qtc/Qts)^2 - 1). Where Vb is the required box volume (liters), Vas is a speaker parameter (liters), Qts is the speaker Q and is a combination of the electrical and mechanical Q (Qts = Qe*Qm/(Qe + Qm)). These parameters can be measured but are usually supplied with a given speaker. Qtc is the required closed box Q and should be around 0.7 for a second order system. The final closed box cut off frequency will be: Fc = Qtc*Fs/Qts. Where Fs is the free air resonance of the speaker. If you follow these design guides and use a well made rigid clay sphere of the right volume, Vb, you should wind up with a good speaker system. Of course, this discussion is based on one speaker, the bass unit. Midrange and tweeters have to be similarly handled. Bob

My speakers have sperical enclosures and sound quite phantastic, but the spheres are made with 3 different layers and inside there is a lot of dampening material and they are closed cabinets. See my page: