An omni with dipole bass, upwards mounted U-frame as midbass? - diyAudio
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Old 12th July 2012, 09:48 PM   #1
OllBoll is offline OllBoll  Sweden
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Default An omni with dipole bass, upwards mounted U-frame as midbass?

Hello there,

I've thought some about dipoles but after discussions, some with Stig Erik (Thank you Stig Erik ) I've realized that I don't really want a dipole, I just want an omni without box issues and with the clean bass of a dipole.

The current plan is this:

Dipole subwoofer 20-80 hz.

????? midbass 80-500 hz.

omni midrange 500 + hz. This one will be mounted upwards, like the old sonab carlsson speakers and the pluto. 4x tweeters will be placed in a ring around the midrange to make high frequencies omni also.

The speaker would be designed to stand at below listening level, say 65 cm high.

Now onto the actual question I wish to discuss in this thread:

The big question mark though is how to do the midbass... I've thought about just doing a H-baffle dipole and then place the midrange ontop of it. But that would be a non ideal transition on crossover freq to the omni and I just got an idea...

Would it be possible to make an upwards mounted U-frame midbass? For me that would probably be ideal, dipoleish at lower frequencies but transitioning into an omni at higher. Should mate really well with an omni midrange without any issues.

But would it work with a say 20-30 cm long U-frame with 30-40 cm of free air under?

Last edited by OllBoll; 12th July 2012 at 10:01 PM.
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Old 12th July 2012, 10:56 PM   #2
ScottG is offline ScottG  United States
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I've done this. When done properly it's excellent.

Actually the critical question in the design is not the dipole range, but rather the "omni" midrange and integration with the treble section of the design. (..it *needs to be about 8-9 db more efficient that the rest of the system, and have the correct dispersion profile at the top of its pass-band. It should NOT be below "listening level", but rather *at* "listening level".)

The midbass region should be dipole, with a highpass around 60-80 Hz and a low-pass around 150-300 Hz.

The bass section should NOT be dipole. The reason for this is that you'll need some added compression effects from the non-dipole bass system to "add-to" the midbass section. This compensates for some loss in compression from the dipole midbass that provides more tactile sensation (..i.e. "punch"). It's better to have a lower order crossover between bass and midbass as a result (..to increase the "over-lap" of the respective driver operation).

Despite this however, you'll still want to have a midbass dipole that has as much compression as possible while still having a fast transient nature. This can be accomplished with a high force (relatively) low mass (for sd) driver(s) - i.e. more suitable pro drivers.


ALL of this is quite complicated, and is most easily accomplished with a digital crossover where you can eq. each active section of the design.

*..note - IF you have an active design (with good eq. filtering), then the "requirement" of 8-9 db of "gain" from radial midrange is not necessary provided you have enough power to "boost" the pressure of the driver to compensate (..and provided the driver can take it within the tolerances that you require).
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Last edited by ScottG; 12th July 2012 at 11:04 PM.
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Old 12th July 2012, 11:32 PM   #3
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by OllBoll View Post
4x tweeters will be placed in a ring around the midrange to make high frequencies omni also.
wouldnt that make it a ringradiator, more than omni sorry, I couldnt resist that one
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Old 12th July 2012, 11:33 PM   #4
sreten is offline sreten  United Kingdom
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Hi,

Terms and concepts need to be defined. 20Hz dipole
bass ? have you any idea what this actually implies ?

Any pointing upwards mid bass (80 to 500Hz) dipole
will have no output on axis in the region its dipolar.

Omnidirectional and dipole simply don't match at all,
you can't match dipoles 8 dispersion to 0 omni.

rgds, sreten.
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Last edited by sreten; 12th July 2012 at 11:44 PM.
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Old 12th July 2012, 11:45 PM   #5
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by sreten View Post
Any pointing upwards mid bass (80 to 500Hz) dipole
will have no output on axis in the region its dipolar.
ehh, I suppose you meant to say, it will have no bass output
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Old 12th July 2012, 11:48 PM   #6
ScottG is offline ScottG  United States
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Quote:
Originally Posted by tinitus View Post
wouldnt that make it a ringradiator, more than omni sorry, I couldnt resist that one
It not only sounds ill-conceived, it is.

Best bet is either a small radiating area tweeter without baffle (in a traditional forward firing arrangement), or a radial ("upward firing") tweeter with a small high-freq. 180 degree horizontal dispersion "lens".

The former is basically "omni" up to around 3-4 kHz, increasingly directional above that.

The later is fully "omni" (..horizontally speaking).
Commercial example:
http://www.morrisonaudio.com/morrison_loudspeakers.htm

..utilizing a reflector for the midrange is sub-optimal (.. absorption would have been preferable), as is the lower height of the speaker.
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Last edited by ScottG; 12th July 2012 at 11:56 PM.
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Old 13th July 2012, 05:06 AM   #7
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by ScottG View Post
I've done this. When done properly it's excellent.

Actually the critical question in the design is not the dipole range, but rather the "omni" midrange and integration with the treble section of the design. (..it *needs to be about 8-9 db more efficient that the rest of the system, and have the correct dispersion profile at the top of its pass-band. It should NOT be below "listening level", but rather *at* "listening level".)

The midbass region should be dipole, with a highpass around 60-80 Hz and a low-pass around 150-300 Hz.

The bass section should NOT be dipole. The reason for this is that you'll need some added compression effects from the non-dipole bass system to "add-to" the midbass section. This compensates for some loss in compression from the dipole midbass that provides more tactile sensation (..i.e. "punch"). It's better to have a lower order crossover between bass and midbass as a result (..to increase the "over-lap" of the respective driver operation).

Despite this however, you'll still want to have a midbass dipole that has as much compression as possible while still having a fast transient nature. This can be accomplished with a high force (relatively) low mass (for sd) driver(s) - i.e. more suitable pro drivers.


ALL of this is quite complicated, and is most easily accomplished with a digital crossover where you can eq. each active section of the design.

*..note - IF you have an active design (with good eq. filtering), then the "requirement" of 8-9 db of "gain" from radial midrange is not necessary provided you have enough power to "boost" the pressure of the driver to compensate (..and provided the driver can take it within the tolerances that you require).
Ofc it will all be active and EQed with DSP, While I'm intererested in such an unconventional idea I'm not mad enough to try to do it in a passive design

And since the whole point of this would be to have dipole bass and so it would kinda destroy the purpose if I use a monopole subwoofer.


Quote:
Originally Posted by sreten View Post
Hi,

Terms and concepts need to be defined. 20Hz dipole
bass ? have you any idea what this actually implies ?

Any pointing upwards mid bass (80 to 500Hz) dipole
will have no output on axis in the region its dipolar.

Omnidirectional and dipole simply don't match at all,
you can't match dipoles 8 dispersion to 0 omni.

rgds, sreten.
A subwoofer with a figure-8-pattern? Also very big drivers for very little bass so no THX movies. Currently the plan though on how to solve that issue is 2x IB15 in a W-frame which should give me all the bass I could ever want even when run dipole. The only remaining issue would be if smart placement can make such that I get about equal power output everywhere in the room to make transition easier to the two speakers.

The question about midbass nulls are if they really would be hearable, sine the U should shift them downwards and the low mounting height of the speaker.

And if I'm not mistaken others here have already tried to combine monopole omni with dipole subwoofers, and supposedly it worked great. So my wish is to test if this transition can work higher than they tried.

Quote:
Originally Posted by ScottG View Post
It not only sounds ill-conceived, it is.

Best bet is either a small radiating area tweeter without baffle (in a traditional forward firing arrangement), or a radial ("upward firing") tweeter with a small high-freq. 180 degree horizontal dispersion "lens".

The former is basically "omni" up to around 3-4 kHz, increasingly directional above that.

The later is fully "omni" (..horizontally speaking).
Commercial example:
Audio Products

..utilizing a reflector for the midrange is sub-optimal (.. absorption would have been preferable), as is the lower height of the speaker.
But I want a true omni at high frequencies, and I know no tweeters which can be crossed reasonably low and have great dispersion at over 10 khz. The method of using multiple tweeters pointing in different directions to solve high frequency omnidirectionality is already tried and proven to work beautifully so that I will keep. There was a whole line of omni speakers here in Sweden that used tweeters in such a way, and they sound great

The current plan is to test to build a U-frame, put it in my room and then let the measuring begin to see if it works well.

Last edited by OllBoll; 13th July 2012 at 05:26 AM.
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Old 13th July 2012, 05:13 AM   #8
ScottG is offline ScottG  United States
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..oh well, sometimes my advice fails at the start.
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Old 13th July 2012, 12:14 PM   #9
el`Ol is offline el`Ol  Germany
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This is how it could look like.
Top plate must be large in order to preserve omni-character. The dipoleness becomes dominant if you don't care.
If you add side walls you get "box issues.
Attached Images
File Type: jpg omnidip.JPG (11.0 KB, 127 views)
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Old 13th July 2012, 03:09 PM   #10
puppet is offline puppet  United States
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At low(er) listening levels this might be an OK idea. I think this is generally correct for an up firing "omni" arrangement. ... and overall volume needs are subjective.
but ...
When one starts to push the SPL up, the additional reflective surfaces .. ie. the ceiling, seem to "confuse" the overall presentation. The more you push it the worse it seems to get ... depending on the room.
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