What is the purpose of this design? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 18 Old 05-18-2019, 03:40 PM - Thread Starter
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What is the purpose of this design?

What do you suppose is the purpose of the inward-firing underwoofer in this design?

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post #2 of 18 Old 05-18-2019, 03:41 PM - Thread Starter
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My guess: directional bass control using the radiation from the back of the cone as active cancellation. How well it works, I have no idea. Could be wrong.

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post #3 of 18 Old 05-18-2019, 03:53 PM
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Quote:
Originally Posted by Soulburner View Post
What do you suppose is the purpose of the inward-firing underwoofer in this design?

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Would need to see more of the speaker.

If it isn't ported, then one of those drivers is probably a passive radiator.

To me, in this type of speaker, it solves a problem that doesn't have to exist.
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post #4 of 18 Old 05-18-2019, 11:11 PM
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What brand/model is it, or is this some DIY Frankenspeaker?

It's a VIRTUAL channel unless stated otherwise.
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post #5 of 18 Old 05-18-2019, 11:26 PM - Thread Starter
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Quote:
Originally Posted by RayGuy View Post
What brand/model is it, or is this some DIY Frankenspeaker?
Probably the latter. And I couldn't find anything about it, even with an image search.

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post #6 of 18 Old 05-18-2019, 11:27 PM - Thread Starter
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Quote:
Originally Posted by PrestigeAudio View Post
Would need to see more of the speaker.

If it isn't ported, then one of those drivers is probably a passive radiator.

To me, in this type of speaker, it solves a problem that doesn't have to exist.
I see what looks like a port sticking out behind the bottom driver.

Good call on the passive radiator. I suppose that is plausible, assuming the driver has the right properties.

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post #7 of 18 Old 05-19-2019, 05:49 AM
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If the top driver is an active driver, it might be a push-pull design. M&K used to use this design approach:










However, in the picture you posted it does look more like a PR.


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post #8 of 18 Old 05-19-2019, 07:59 AM
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This appears to be a now discontinued model from Wilson Benesch


From the description the inverted driver is supposed to act almost like a port turboocharger


http://www.soundstagenetwork.com/rev..._discovery.htm
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post #9 of 18 Old 05-19-2019, 08:27 AM
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It's a 3-way speaker, OP, with a pair of woofers facing one another on the bottom of the cabinet. The isobaric arrangement (technically a misnomer) of two motors and doubled moving masses allows a smaller internal volume than would a single woofer. The driver over the tweeter is a midrange in its own sub-enclosure.
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post #10 of 18 Old 05-19-2019, 09:17 AM - Thread Starter
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Thanks guys, mystery solved.

Now, why don't we see this tactic used more? Is it simply a fear of how people will react to the driver sticking out? I guess it's not how a "finished" speaker is "supposed" to look. I guess most stands wouldn't work, either. And, there is a 3dB loss to efficiency.

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post #11 of 18 Old 05-19-2019, 09:27 AM
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Quote:
Originally Posted by Jon Lane View Post
It's a 3-way speaker, OP, with a pair of woofers facing one another on the bottom of the cabinet. The isobaric arrangement (technically a misnomer) of two motors and doubled moving masses allows a smaller internal volume than would a single woofer. The driver over the tweeter is a midrange in its own sub-enclosure.
Jon, in an isobaric configuration one of the woofers has to be wired out of phase to the other respectively right? So that there is no cancellation? Otherwise, they would cancel each other out right?


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post #12 of 18 Old 05-19-2019, 09:35 AM
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Quote:
Originally Posted by audiofreak38 View Post
Jon, in an isobaric configuration one of the woofers has to be wired out of phase to the other respectively right?
Correct - here the external driver is wired in reversed polarity. It and its mate effectively become a single driver with modified parameters.

See Design principles, and note the last paragraph as to what this arrangement becomes.
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post #13 of 18 Old 05-19-2019, 09:43 AM
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Quote:
Originally Posted by Jon Lane View Post
Correct - here the external driver is wired in reversed polarity. It and its mate effectively become a single driver with modified parameters.

See Design principles, and note the last paragraph as to what this arrangement becomes.
If the both woofers function as a single driver, then that would also double the Xmax effectively moving more air mass? Can the coupling of the woofers allow for deeper extension then? Obviously, it will account for more in volume w/less distortion. In other words, can isobaric arrangements allow for deeper extension? Just curious Jon. Thanks for taking the time to educate us. Hope all is well your way.


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post #14 of 18 Old 05-19-2019, 09:52 AM
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Originally Posted by audiofreak38 View Post
If the both woofers function as a single driver, then that would also double the Xmax effectively moving more air mass? Can the coupling of the woofers allow for deeper extension then?
Compared to a single identical driver Xmax is unaffected. Air volume (behind the inner woofer) can be halved and bass cutoff is unaffected.

From the link:

Quote:
The two drivers operating in tandem exhibit similar behavior as one loudspeaker in twice the cabinet. The cabinet is defined as the space behind the rear driver ... The new driver will have the same resonant frequency ... as one driver ... Because the impedance is also halved, the performance of an isobaric speaker is achieved with twice the power. The new efficiency is thus 3 dB lower than with one loudspeaker. ... the new combined loudspeaker has twice the moving mass compared to the single driver but also half the compliance because of the doubled suspension. ... the coupled driver pair (iso-group) can now produce the same frequency response in half the box volume that a single driver of the same type would require.
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post #15 of 18 Old 05-19-2019, 10:05 AM
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Quote:
Originally Posted by Jon Lane View Post
Compared to a single identical driver Xmax is unaffected. Air volume (behind the inner woofer) can be halved and bass cutoff is unaffected.

From the link:
Thanks Jon. Reading up on the link that you provided. At least I got part of it right......LOL!!!! Physics is so fascinating. Much appreciated!


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post #16 of 18 Old 05-19-2019, 02:46 PM
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NOT a Passive Driver (cuz it APPEARS to have a PAIR OF WIRES connected to it)....and NOT ISOBARIC (see fol. descriptions...esp. note how closely coupled the two speakers are...and they move in the SAME Direction, so that it has Twice the Force to drive the same Cone Surface Area):
https://www.kicker.com/how-to-build-a-subwoofer-box
https://www.vueaudio.com/isobaric-subwoofer-design
https://jlaudio.zendesk.com/hc/en-us...nclosure-Types

"Isobaric" means CONSTANT PRESSURE...which is what you get In-Between the two Woofers when they move in SAME Direction against a fairly SMALL enclosed Volume of Air [as opposed to Out-Of-Phase, trying to Compress the Air In-Between them]:
https://en.wikipedia.org/wiki/Isobaric_process
PS: If Front and Bottom Woofers move in SAME Direction [so Sound Radiation is IN-PHASE], then Air In-Box is alternately Compressed and Uncompressed...and if move in Opposite Directions, In-Box Air Pressure differences are less....but internal reflections result in it NOT being Isobaric.

It's simply a Sealed Box [unless there is a Port on the Back] with Two Woofers...[or perhaps a Woofer and a Sub-Woofer]....as is found in MANY other products on the market, although usually with one located above the other....with an unusual radiation pattern due to Woofer Locations....and suspension in mid-air....

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post #17 of 18 Old 05-19-2019, 03:12 PM
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post #18 of 18 Old 05-19-2019, 03:27 PM
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A-HA....Interior view shows us that the Driver on the Bottom is one-half of an Isobaric Sub-Woofer PAIR, mounted Cone-to-Cone!!!!
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