Hi,
I was watching some videos from Audiophile Junkie on YT where he's covering the Montreal Show.
I saw this new speaker that looks like a G Clef that has the woofer / mid as a face to face isobaric design.
In their design It looks like each speaker is in a sealed 1/2 shell and there's a gap of about 2 or 3 inches. (Estimate from looking at the video and pictures)
see:
https://www.stereohifi.nl/loudspeak...aker-t/stereowise-l-speaker-treble-clef-audio
I'm trying to understand the benefits of a face to face isobaric design.
In some other speakers, it looks like you have both speakers facing each other attached to the same baffle so there is no gap.
So here's the questions...
1) Benefits of isobaric in general?
2) Benefits of face to face isobaric.
2a) One side sealed, other side open? (A different speaker design...)
2b) Both sides sealed, but there's a gap between the two drivers.
3) The gap between the two speakers... advantages/disadvantages ?
3a) Is there any math concerning the width of the gap?
4) What other considerations?
I mean its an interesting design... I'm curious about the acoustics. Imagine taking a 6.5" purifi woofer (extended range.)
The data sheet says sealed bottom frequency is ~77Hz, Ported drops to ~44Hz. What could you expect from a face to face isobaric ?
Is there any good material on isobaric speaker design?
I know that Mon Acoustic has an isobaric speaker (face to rear)
I realize that doing this sort of design gets expensive really quickly and its more of a thought research project while I'm out walking my Husky.
Thx
I was watching some videos from Audiophile Junkie on YT where he's covering the Montreal Show.
I saw this new speaker that looks like a G Clef that has the woofer / mid as a face to face isobaric design.
In their design It looks like each speaker is in a sealed 1/2 shell and there's a gap of about 2 or 3 inches. (Estimate from looking at the video and pictures)
see:
https://www.stereohifi.nl/loudspeak...aker-t/stereowise-l-speaker-treble-clef-audio
I'm trying to understand the benefits of a face to face isobaric design.
In some other speakers, it looks like you have both speakers facing each other attached to the same baffle so there is no gap.
So here's the questions...
1) Benefits of isobaric in general?
2) Benefits of face to face isobaric.
2a) One side sealed, other side open? (A different speaker design...)
2b) Both sides sealed, but there's a gap between the two drivers.
3) The gap between the two speakers... advantages/disadvantages ?
3a) Is there any math concerning the width of the gap?
4) What other considerations?
I mean its an interesting design... I'm curious about the acoustics. Imagine taking a 6.5" purifi woofer (extended range.)
The data sheet says sealed bottom frequency is ~77Hz, Ported drops to ~44Hz. What could you expect from a face to face isobaric ?
Is there any good material on isobaric speaker design?
I know that Mon Acoustic has an isobaric speaker (face to rear)
I realize that doing this sort of design gets expensive really quickly and its more of a thought research project while I'm out walking my Husky.
Thx
Ok?
Forgive me... Is there a difference due to the gap between the two 1/2 shells?
Wouldn't they behave the same as isobaric face to face?
Forgive me... Is there a difference due to the gap between the two 1/2 shells?
Wouldn't they behave the same as isobaric face to face?
For isobaric the drivers need to be acoustically coupled, the photo's show a open gap between the shells and at the rear the sides of the shells are open as well, almost as if they are OB
Hmmm.
Ok... it makes sense... Would you invert the drivers or keep them the same?
I'm trying to imagine the sound coming out and if they would cancel?
That could explain the width of the gap relative to the driver size?
I mean its an interesting thought experiment. No?
Ok... it makes sense... Would you invert the drivers or keep them the same?
I'm trying to imagine the sound coming out and if they would cancel?
That could explain the width of the gap relative to the driver size?
I mean its an interesting thought experiment. No?
Just to follow up...
yes I googled ripole subwoofer and found.
https://jazzman-esl-page.blogspot.com/2011/01/ripole-subs-are-underway.html
yes I googled ripole subwoofer and found.
https://jazzman-esl-page.blogspot.com/2011/01/ripole-subs-are-underway.html
Looks more like a face-to-face push-push sealed. Given the small size likley EQ? A ripole would be the “OB” version of this arrangement. A technique used by Monitor Audio in their flagship.
dave
I have built a LOT of speakers and have never found isobarik loading to be worthwhile on any level.
I've been told that this isn't isobarik but repole ?sp? design.
Which is kind of interesting.
I guess we should close this thread because its a bit misleading on my part.
Which is kind of interesting.
I guess we should close this thread because its a bit misleading on my part.
Smaller enclosure, about one-half of the size for equivalent bass extension.
Simpler fabrication. Less wasted space between the woofers, which does not count toward the cabinet volume needed for the bass extension.
Not sure what you are envisioning. In an isobaric design only one side of one woofer interfaces with the acoustic suspension or ported enclosure. The other woofer has one side interfacing with the first woofer and another side interfacing with the room (or an open cavity into which it is firing).
You want enough to make sure the woofers do not touch each other.
Not that I am aware of.
If wiring the woofers in parallel, make sure the impedance is not too low for your amplifier.
If the outer woofer is itself firing into a cavity, wherein the cavity has an opening to the room, that will change the frequency response. Essentially, the cavity acts similar to a bandpass filter.
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That is a dual opposed slot loaded woofer design, not an isobaric design.
This explains isobaric: https://en.wikipedia.org/wiki/Isobaric_loudspeaker
just a pic to get something in the minds eye for comparison
It is the sealed volume that makes a speaker box / system isobaric.
google sourced definition of isobaric:
an isobaric process is a process where the pressure of a system remains constant (ΔP = 0), while other properties like volume and temperature can change.
so with this definition isobaric speaker systems are pseudo isobaric because ΔP ~ 0
Jeremy
It is the sealed volume that makes a speaker box / system isobaric.
google sourced definition of isobaric:
an isobaric process is a process where the pressure of a system remains constant (ΔP = 0), while other properties like volume and temperature can change.
so with this definition isobaric speaker systems are pseudo isobaric because ΔP ~ 0
Jeremy
From "Loudspeakers for music recording and reproduction" by Philip Newell and Keith Holland, section 3.7 considers Isobaric loudspeakers. They say:
"At low frequencies, the two drivers behave as a single driver with twice the moving mass. The result is a downward shift in resonant frequency to about 70% that of just one driver in a sealed enclosure. The reduced back pressure exerted by the enclosure on the external driver will result in lower distortion because the inner loudspeaker is tending to keep the pressure in the outer chamber constant. However, in practice, the two drivers tend to function as one due to the strong coupling by the trapped air mass"
Book browsable here https://archive.org/details/loudspeakersform0000newe
"At low frequencies, the two drivers behave as a single driver with twice the moving mass. The result is a downward shift in resonant frequency to about 70% that of just one driver in a sealed enclosure. The reduced back pressure exerted by the enclosure on the external driver will result in lower distortion because the inner loudspeaker is tending to keep the pressure in the outer chamber constant. However, in practice, the two drivers tend to function as one due to the strong coupling by the trapped air mass"
Book browsable here https://archive.org/details/loudspeakersform0000newe
That is a bit different of a description than I have otherwise seen. The following is more consistent with the general explanation:
"Fs and Qts do not change their value regardless how many (identical) speakers you add. It’s easy to clarify...
...
When you wire the 2 speakers together, you have the same 2 choices : series or parallel. The most popular choice is parallel, so we are going to focus only on that. Parameters that change :
- Vas is halved.
- No is reduced by -3 dB (efficiency).
- Re is halved.
- Le is halved.
- +3 db efficiency for wiring in parallel.
"The result is that 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." https://en.wikipedia.org/wiki/Isobaric_loudspeaker
I built a few isobaric subwoofers back in the day. I can confirm that the I achieved the same frequency response in half the box volume, meaning that the Vas was halved. It was particularly useful in car audio. Now days, though, I just use a servo controlled subwoofer, which also allows for a smaller cabinet, but also offers other advantages.
I like to test a pair of drivers clam-shell isobaric over a closed tube (so effortless!). Empirically a small gap ~1cm let out even more & lower bass. For example old small-magnet high-Fs Peavey 15" Scorpions (total four) delivered much better bass in less than half the original Vas. Push-pull dipole worked well too, projecting bass axially. And for some reason a gap also increased SPL (there have been threads debating this).
I am quite tempted to build a rudimentary version of this, with the Ripole bass made from 4 wooden salad bowls and 4 of these SB Acoustics woofers:
https://sbacoustics.com/product/10″-sw26sfc38-8-paper/
Cross around 250Hz should be fine, I think. Only tricky part is correcting for baffle step above that with the mid. Perhaps that necessitates an Active design with digital crossover.
I have some unused Wavecor 6" midwoofers and some SB Acoustics tweeters sitting around. Could be a fun summer build.
https://sbacoustics.com/product/10″-sw26sfc38-8-paper/
Cross around 250Hz should be fine, I think. Only tricky part is correcting for baffle step above that with the mid. Perhaps that necessitates an Active design with digital crossover.
I have some unused Wavecor 6" midwoofers and some SB Acoustics tweeters sitting around. Could be a fun summer build.
Makes the box size = half Makes needed power= double
Not very useful unless you need a small box.
Easier to just use low Qts speakers.
Which is a very powerful motor to get there.
Having a need for isobaric just means your using junk motors
Or take it to the extreme and use high Qts isobaric and have a very very small box.
Not very useful unless you need a small box.
Easier to just use low Qts speakers.
Which is a very powerful motor to get there.
Having a need for isobaric just means your using junk motors
Or take it to the extreme and use high Qts isobaric and have a very very small box.
Even in an ideal situation, half the volume is cube root of 1/2 in each dimension, or 0.8 in each dimension. So not so much reduction in physical size.
But it not even that, because you have the physical volume of an additional driver, the air gap between them, and the mechanical structure holding them apart.
None of the naïve calculations on the web take the practicalities of loudspeaker construction into account.
But yes - indeed servo control, or even current drive rather than voltage drive, of single subwoofers, both work well up to around 200 Hz.
The other approach with subwoofers is to use two drivers, but put each on opposite faces of the enclosure. So the box is force balanced and does not have the tendency to rock as a single driver moves.