Variable Tuned PR

[Geoff H]

Quoting Bud in "Beyond the Ariel"

"This was an 8 inch driver with edge wound voice coil on a Kapton former, and worked from 20 Hz out to 2 kHz, crossed over to a 10 inch on the bottom with Mille's patented cross over that turned the 10 inch into a passive radiator at about 60 Hz, in a gradual slope."

For some time I have been thinking of a small enclosure with a full range driver, and a smaller driver as a passive radiator. The idea is not to exploit the radiation from the PR, but to use it to tune the enclosure.
A tuned circuit across the VC of the PR could allow the cabinet to be reduced in size, without resorting to a noisy port.

Not quite the same as Bud quoted, but similar. Just wondering if anyone has any thoughts on the idea, or heard a similar scheme.

Geoff.

[Ron E]

what do you want to accomplish with the tuned circuit? The PR is already a "tuned circuit" - the electrical analogue is a series notch filter....

[kelticwizard]

Originally posted by Geoff H
[B]Quoting Bud in "Beyond the Ariel"

For some time I have been thinking of a small enclosure with a full range driver, and a smaller driver as a passive radiator. The idea is not to exploit the radiation from the PR, but to use it to tune the enclosure.

If you don't plan to exploit the output from the PR or port, why do you want to tune the enclosure?

Originally posted by Geoff H
A tuned circuit across the VC of the PR could allow the cabinet to be reduced in size, without resorting to a noisy port.

Could you please explain why that would be so?

[Geoff H]

Hi Ron, and Kelticwizard,

Thanks for the responses

My thinking was to allow easy adjustment of the PR res. Damping could also be easily controlled.

Substituting C of the enclosure for electrical C across the PR VC. It's still a notch filter, just physically smaller.

X-max could be a problem. If the PR was 1/2 the diameter of the main driver, X of the PR would have to be 4 times that of the driver.

There could be other problems I haven't become aware of.

Geoff.

edit: Kelticwizard beat me.

[kelticwizard]

Geoff:

"Beyond the Ariel" is a pretty large thread. Could you point me to the post where BudP made the comment about the 8 inch?

Thank you.

[Geoff H]

Thought i was going batty there, but found it. Searching for "Mille's" found nothing. "Mille" produced results.

Yes, it is a big, and interesting thread.

Geoff.

http://www.diyaudio.com/forums/showt...18#post1195018

[kelticwizard]

This was an 8 inch driver with edge wound voice coil on a Kapton former, and worked from 20 Hz out to 2 kHz, crossed over to a 10 inch on the bottom with Mille's patented cross over that turned the 10 inch into a passive radiator at about 60 Hz, in a gradual slope.

I must confess I have a problem getting a handle on this entire configuration.

First, the whole idea of an active speaker with voice coil and magnet being hooked up to the amp for some frequencies, but apparently decoupled from the amp for lower frequencies. Seems to me a crossover with very large inductors would be necessary to do this, and that would affect the sound on frequencies in the passband.

Second, the speaker is essentially useless below the tuning frequency. The passband where the PR is adding output extends perhaps an octave above the tuning frequency, so the lowest the tuning frequency is likely to be here is 30 Hz-if it is that low. If that is the case, why bother having an 8 inch going all the way down to 20 Hz? It will never have any appreciable output below 30 Hz, or whatever the Fb of the box is.

Third, I think any woofer with a magnet/voice coil hooked up to an amp for any frequency range runs a big risk if it is used as a PR for the bass range. On loud passages, the excursions put it in danger of extending past it's mechanical range and damaging the unit. On conventional PR's without magnets or voice coils, you don't have to worry about this that much. On PR's with voice coils you intend to actually function, you do.

Having a 10 inch PR for an 8 inch active speaker is a step in the right direction, but I would feel a lot better with two 10 inchers than one. Two 10 inchers, ( 2 times 56 sq in) would be nearly four times the surface area of a single 8 inch, (32 sq in), and give you a lot more leeway on loud bass passages. I suppose a single 10 inch would be okay if it has an excursion twice the 8 incher's excursion.

[Geoff H]

Thanks for the response. It seems we're up against the old box vol, efficiency, bass response triangle again. I was looking for a reduction of box volume. If I was looking for real bass performance I'd go to 15s.

Also, my concept could create an broad z peak, not what we want to maintain bass response.

In the Mille system quoted by Bud, I can't help but think the 10" would go through hefty phase changes, resulting in a big hole in the bass region. Also $10" + $8" = $15" ?? and no expensive xo.

Regards,
Geoff

[kelticwizard]

Originally posted by Geoff H
In the Mille system quoted by Bud, I can't help but think the 10" would go through hefty phase changes, resulting in a big hole in the bass region. Also $10" + $8" = $15" ?? and no expensive xo.

Regards,
Geoff

Just about any enclosed box, except perhaps aperiodic, goes through hefty bass changes. But the spl output can be smooth.

We both probably should ask Bud about this configuration anyway, lol.

As for 10" + 8" = 15", here are the approximate sq inches of all three driver sizes:

8 in = 32 sq in
10 in = 56 sq in
15in = 132 sq in

These are approximations, individual models can vary a little.

[Geoff H]

I know about square law additions LOL. I was using $ in terms of cost of drivers.

ie the cost of 4 8" drivers buys a better solution in a 15" for bass performance.

Gotta agree with your comment re aperiodic. Best solution I've found in small cabs.