Elliptical enclosure - reflection/diffraction issues?

[novec]

Please take a look at this simplest one:
M-AUDIO - Audio Buddy - Budget Microphone Preamp
It has anything one need for the all kind of measurements via decent sound card or a good one integrated, only line in and outs are needed & with minimal additional voltage dividers (diy) one can convert
any PC/MAC into powerful all kind audio measuring place. 😉

Cheers

Doesn't look too bad, but I think the ART USB Dual Pre would be an even easier solution when you're only interfacing with a computer anyways. Don't know if it's any good, though, I just googled it 🙂

Edit: Something like the MXL USB Mic Mate is even simpler, and can be had for 40 bucks. Judging by the few comments I've read so far it seems decent enough for our needs.

 

[djn]

I have these in the screened in porch at our cottage. I still have to sand down the second barrel. They are genuine Jack Danials barrels.

 

[dfidler]

I have these in the screened in porch at our cottage. I still have to sand down the second barrel. They are genuine Jack Danials barrels.

Where are the drivers going to sit in these? Will they be inset or will it be flush with the apex of the barrel and the sides protrude out (on a cylinder perhaps)?

 

[djn]

The woofs are behind the cone made of mesh in the woof holes. The woofs are Dayton 12", the horns are Magnivox, and the tweets are pro Peizos. I bought they from a guy that built them 30 years ago. All the drivers were shot and all the slats (stays) were loose. I had to take them all apart and used Liquid Nail to reassemble.

I plan on sanding down the other one this summer. They have a simple single order crossover that I designed.

 

[dfidler]

So they're actually inset into the enclosure; interesting and really neat. I've often wondered what doing that would do to the sound. Would doing this create any diffraction artifacts?

Do the long wavelengths of the low-end make it so that it doesn't matter or will that sharp edge at the end of the channel be a prime example of edge diffusion? (I suspect the latter).

 

[novec]

Nice barrels! Perfect look for semi-outdoor speakers.

But back to my speakers - bear mentioned that the height of the woofer might be bad in respect to floor reflections. Any other comments on that? I've also considered separating mid and tweeter in a separate enclosure, isolated from the woofer box with spikes. Good or bad?

 

[badman]

So they're actually inset into the enclosure; interesting and really neat. I've often wondered what doing that would do to the sound. Would doing this create any diffraction artifacts?

Do the long wavelengths of the low-end make it so that it doesn't matter or will that sharp edge at the end of the channel be a prime example of edge diffusion? (I suspect the latter).

That inset is a worst-case diffraction scenario- still REALLY cool looks though! You could put a bevel around the woofer cutout to make it a very ideal setup.

 

[djn]

The "pavilion" is just for hanging out so I've never done an analisys on them, but they sound great.

 

[djn]

Nice barrels! Perfect look for semi-outdoor speakers.

But back to my speakers - bear mentioned that the height of the woofer might be bad in respect to floor reflections. Any other comments on that? I've also considered separating mid and tweeter in a separate enclosure, isolated from the woofer box with spikes. Good or bad?

I think the woof should be off the floor as much as possible. It makes for a cleaner sound. I also like the idea of a seperate cab for the mids and tweets. Less vibration interference.

 

[dfidler]

I also like the idea of a seperate cab for the mids and tweets. Less vibration interference.

Is that really an issue?

The sub cab is going to be vibrating at a frequency that is slightly less than that of the frequency of the woofer (mdf/ply is denser than air meaning that it will slow the vibrational frequency down some).

Therefore, I would think that any vibration would be well below what could be considered a problem for any mid and even less so for a tweet.

I might be worried about it the other way though; the mids causing ripple across the woofers cone, but again, I'm not sure that would matter, would it?

The only real issue that I see is if you left all of the drivers open to each other in the same chamber but even this is easily rectified.

Having said that, bwaslo once said to me:

... Two or more cheap subs in the right places will also usually work a lot better than one sub of high price. For heavens sake, don't restrict your low bass to have to come from the same place as your mids and highs! They have different acoustical placement requirements and the odds of the best place for subs being the same place as for tweeters is very nearly zero. Putting them in the same cabinet is a compromise right from the start.

*shrug*

 

[djn]

It is true that it might not interfer with the frequency, but the mechanical vibration in the motor of the mid and tweet "could" cause issues.

 

[Smiley 09]

Good PRICE....

Doesn't look too bad, but I think the ART USB Dual Pre would be an even easier solution...

I agree for that price it's a bargain...
For best performance it is necessary then to disable the all other
audio devices on the particularly PC either in the bios for on board sound card
or phisically remove any other audio card from PCI or PCIe slots and just before
removal uninstall related drivers.. and til then instal this new USB audio intrface
to obtain the lovest ps/ns jitter ratio. The only S/N ratio is maybe to bo be
considering for eg. low level audio apps measurement.
But it is adequate for All sort of speaker measurement..

 

[bear]

Floor bounce causes a big notch somewhere in the frequency response. So it matters what the height above the floor is, otoh if the notch is out of the passband of a given driver it may be of some benefit. Real problems in the response come when the notch is in the intended passband (like if the woofer runs up above ~300 Hz as typically floor bounce will end up below that freq...).

The issue with drivers in the same volume is the seal between them. Any leakage can cause IM in the form of modulation due to the energy from another driver pumping the enclosure or via actual holes/leaks.

This is still somewhat common in commercial speakers where the tweeter inhabits the same enclosure as the woofer, and the assumption (a poor one) is made that the tweeter is "sealed". Most tweeters, even the ones sold as "sealed back" tweeters are not really completely sealed.

_-_-bear

 

[novec]

Thanks, bear. I don't suppose you have a quick equation for calculating that frequency?

Each driver has a properly sealed volume for itself in my current design, so that part's taken care of. I was just wondering whether it might be a good idea to physically disconnect mid and tweeter to minimize vibrations from the woofer. But I have a feeling it won't make much of a difference.

 

[bear]

It is not quite that simple as it also relates somewhat to the distance you are sitting at...
It is in effect the time it takes for a wave to reflect back to your ears (or microphone) 180 degrees out of phase... so a 1/4 wave path to a surface and out to the ears = 180 degrees out?
Multiples count too... but not as much.

I have measured a massive notch between about 100Hz. and 200Hz. when a midbass was placed about 30" above the floor... the midbass was supposed to cover down to about 80Hz... no way, it measured like there was a flaw in the measurement gear... of course as always, YMMV.

_-_-bear

 

[dantheman]

The Front wall, ipsilateral side wall, and floor will all cause big issues. The contralateral wall, ceiling, and possibly even the rear wall could also come into play in a small room I imagine. As the distance gets further, the less problem it will cause.

I believe this is the equation for the front wall where the bounce will be coming back off the wall on to itself so to speak:
Cancellation notch frequency = [(344m/s) divided by (4 times the distance from the speaker to the wall behind it in meters)]


and this for other significant boundaries:
notch frequency = [(344m/s) / 2(the distance of speaker to the listening position via the reflecting surface - the direct path distance from the speaker to the listening position)]

This picture may help with visualization:

Just substitute a person for the microphone.

Dan

 

[dantheman]

OK, can you tell I'm exhausted? Here's my pics to illustrate my point.

Front wall:

Cancellation notch frequency = [(344m/s) divided by (4 times the distance from the speaker to the wall behind it in meters)]

All other near boundaries:

notch frequency = [(344m/s) / 2(the distance of speaker to the listening position via the reflecting surface - the direct path distance from the speaker to the listening position)]

Dan

 

[speaker dave]

Dan the Man has the picture and equation right.

Here is a typical floor bounce measurement. For testing the two speakers were about 3 feet off the floor and 3 feet 10 inches from the mic. At a normal listening distance the cancelation frequency would go higher (floor bounce path and direct path get closer in length) and room modes would start to obscure the dips.

Note a third harmonic at around 400Hz.

David S.

 

[vdi_nenna]

Dickason says spheres are the perfect box, but not easy pull off.

How about these?

 

[novec]

The general shape looks a lot like mine. Do you have any other pictures showing driver placement etc?

Spheres aren't a big problem once I get my CNC mill operational. Might be worth looking into.