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Old 15th October 2010, 10:53 PM   #1
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Default DIY dipole to replace Apogee Diva?

hello,

I've had planars/ribbons for years (Magnepan 1.6s, rebuilt Apogee Duettas, rebuilt Apogee Divas), and with the Apogees have been multiamping with crossovers generated by Acourate software.

I like the big line-source ribbon sound, but the Divas have obvious weaknesses in sensitivity, dynamic ability, bass, etc. It is possible to obtain a new, 'modern' Apogee but the cost is *very* high... and I have never trusted the design of the planar bass panel.

The obvious thing to do would be to build a linesource dipole speaker using (just for example) Revelator or Accuton ~6" mid drivers and (again for example) Raal tweeters. The slightly less obvious thing to do would be to build a Horbach Keele dipole.

I am not constrained by crossovers (Acourate can generate anything I could really want) or by amplification. By DIY standards cost is also not a major constraint. I do have a small room now (12 x 17 x 9, roughly) but I've heard IRS Vs sound great in a room only slightly larger, so I am not giving up hope just yet.

Has anyone here been in a similar position and found a good solution? I'd also be interested to know about professional audio engineers who might take on a side project.

all best,

Brandt
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Old 16th October 2010, 12:55 AM   #2
ScottG is offline ScottG  United States
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I don't know of a true ribbon dipole driver that is efficient and is also a *long* line source - that is commercially obtainable.

The resident expert on DIY long ribbon drivers would be Paul W. (..but he has personally moved on to large horns).


These people appear to do custom orders on longer line ribbons, but list neither the cost nor the measurements:

Transmission Audio Inc.


Because you have an active (digital) solution for crossover, the things you need to be more concerned with are dispersion patterns horizontally (and vertically if you plan on stacking an array), linear decay, non-linear distortion, and basic operational limits.

IMO ribbons are best suited to higher freq.s and in particular long very narrow line sources for very wide horizontal dispersion. IF you build yourself such a driver, or have one made, then you need to consider other drivers better suited to different bandwidths.

Now consider the midrange panel. Electrostatic panels, line source planars, line array planars, and line array cone drivers.

Hint: Think line array planar..

BG corp. just released their "10" version which is suitable as a midrange driver in an array. See measurements here:

Zaph|Audio

In an array of 8, and depending on the size of the baffle and the order of crossover, you could use these to around 150 Hz.

(Note that you could also use an array of the Neo 8's for a treble line array as well, but they might not have quite the detail of a true ribbon, nor would they have a horizontal dispersion pattern as wide and stable a more narrow line source.)


Finally there are the lower freq.s to consider. There are planar base panels available:

INFRAPLANAR : haut parleur isodynamique plan pour grave

..but not exactly cheap.

IMO a line array of bass drivers should do the trick, and in particular these drivers and their amplifiers:

SW-12-16FR - SW-12-16FR

Again, an array of 8 per loudspeaker. 2 "stacks" of 4 wired in parallel with one of these amplifiers per stack:

H600PEQ - H600PEQ
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Last edited by ScottG; 16th October 2010 at 01:02 AM.
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Old 16th October 2010, 01:51 PM   #3
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Let me back up. Ignoring for a moment (?) the specifics of the drivers, is there a dipole line source configuration superior to that of the Infinity IRS V? I.e., something better than a curved, wide baffle for the mid-tweet array? I wouldn't be able to make the baffle quite as wide as the IRSV baffle (room too small for that to be practical) but let that go for the moment.

If I can determine the overall configuration of the speaker, then I can move on to the drivers.

thanks,

Brandt
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Old 16th October 2010, 11:00 PM   #4
ScottG is offline ScottG  United States
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Quote:
Originally Posted by seaspeak View Post
Let me back up. Ignoring for a moment (?) the specifics of the drivers, is there a dipole line source configuration superior to that of the Infinity IRS V? I.e., something better than a curved, wide baffle for the mid-tweet array? I wouldn't be able to make the baffle quite as wide as the IRSV baffle (room too small for that to be practical) but let that go for the moment.

If I can determine the overall configuration of the speaker, then I can move on to the drivers.

thanks,

Brandt
Most dipole drivers will have some inherent advantages over drivers run front and back out of phase.. like the IRS V.

Frankly the IRS V also had over-damped drivers (closed-back planars), and the surface area was inadequate for the midrange panels. Additionally, a full line source for the treble will not have combing effects.

As far as a basic design.. of a large baffle for a dipole line source being better (or not), that really depends on the drivers.

The more surface area AND displacement you have - the lower/louder you can go. The larger baffle is there to partition the rear out-of-phase signal with the frontal in-phase signal. Less baffle requires more surface area and greater excursion.

You can play around with free-ware apps like the Edge and the Baffle Diffraction Simulator to see the effects of spl-loss from a reduction in baffle area and dipole cancellation.

Home of the Edge

FRD Consortium


One thing to note: most designs do not have a true dipole radiation pattern. The larger the baffle the *less* the pattern resembles a dipole. (..that cancellation that is removed by a large baffle provides those side nulls in the pattern that are part of a dipole.)

IF you are more interested in a *mostly* dipole pattern then look to JohnK's Nao Note. Also see cubono's design.

NaO Note preview

Violet DSP Evolution - an Open Baffle Project



You *could* go with an array of cone drivers (midrange portion) with linear excursions significantly exceeding +/- 1mm, and "boost" the lower freq. response for use with a much less wide baffle. Perfect 8 does this (as does the ribbon manufacturer I provided a link to). The problem with this is the mass of the drivers in relation to the treble unit, and the differences in excursion between the two drivers. (..the treble unit is hundreds of times less mass than the cone driver array and the excursion levels are also radically different.) These differences tend to result in dissimilar sound between the two lines. This becomes less important as you go lower in freq.. BUT for some it's still a problem.
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Old 17th October 2010, 12:33 AM   #5
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Ok, thanks -- that's helpful (sorry to be asking such noob questions...).

I take your point regarding the baffle width and making the polar response 'less like a dipole.' I also recognize that a true dipole driver may be better than pairs of closed drivers run antiphase (as in the IRSV).

So how do I know if a midrange driver has enough displacement?

And have you seen any true dipole tweeters suitable for an array? Raal makes a dipole tweeter, but the shape of the faceplate makes it unsuitable for array use. Mundorf has an AMT suitable for line source use 'in development.' Beyma's AMT looks a bit rough from a fabrication point of view, and has a somewhat large faceplate, but can be run as a dipole... have you seen anything 'real world' that looked good?

cheers,

Brandt
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Old 17th October 2010, 01:09 AM   #6
ScottG is offline ScottG  United States
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Quote:
Originally Posted by seaspeak View Post
Ok, thanks -- that's helpful (sorry to be asking such noob questions...).

I take your point regarding the baffle width and making the polar response 'less like a dipole.' I also recognize that a true dipole driver may be better than pairs of closed drivers run antiphase (as in the IRSV).

So how do I know if a midrange driver has enough displacement?

And have you seen any true dipole tweeters suitable for an array? Raal makes a dipole tweeter, but the shape of the faceplate makes it unsuitable for array use. Mundorf has an AMT suitable for line source use 'in development.' Beyma's AMT looks a bit rough from a fabrication point of view, and has a somewhat large faceplate, but can be run as a dipole... have you seen anything 'real world' that looked good?

cheers,

Brandt

You can play with this calculator:

Piston Excursion calculator

Note it is an "infinite baffle" and you'll have to adjust for surface area.

Again, the BG Neo 8 is suitable in an array format. Note however that NONE are really optimal. The problem is that they aren't narrow enough, nor are they full lines. (..ideally it should be half an inch wide and about 5+ feet long.)

Again, I don't know of any manufacturer of dipole ribbon (..or even a planar) that meets those requirements (or is even efficient).

Even if Mundorf produces a dipole driver that has amazing off-axis character, it almost certainly won't be over 3 foot in length.
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Old 17th October 2010, 01:56 AM   #7
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Would a 0.5" ribbon be able to get down to ~200Hz and move enough air to be useful? That seems awfully narrow... I understand that it would have great horizontal dispersion but at a cost, no?

The BG Neo 10 looks like an interesting driver.
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Old 17th October 2010, 02:44 AM   #8
ScottG is offline ScottG  United States
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Quote:
Originally Posted by seaspeak View Post
Would a 0.5" ribbon be able to get down to ~200Hz and move enough air to be useful? That seems awfully narrow... I understand that it would have great horizontal dispersion but at a cost, no?

The BG Neo 10 looks like an interesting driver.
No - a ribbon like that should be good for 1 kHz.. maybe a little lower. Below that it should transition to Neo 10's, or other panel or driver array. That should push the array low enough in freq. that combing shouldn't be a problem, nor directivity in general. Sure there is a cost, but it isn't performance, and it *shouldn't* be one of value (particularly if you DIY the ribbon).

The Neo 8 can be used down to about 400 Hz in a line array (with an appropriate filter and baffle). You can also achieve better high freq. dispersion via the Neo 8 PDR version (..with only a marginal loss in efficiency.) (..while I know budget is not as much of an issue for you, this is pretty much the least complicated and most value-oriented way to achieve a good "dipole'esq" open baffle implementation.)
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Last edited by ScottG; 17th October 2010 at 02:49 AM.
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Old 17th October 2010, 05:39 AM   #9
oublie is offline oublie  United Kingdom
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BARE RIBBONS - Ribbon tweeter midrange speaker drivers for DIY speakers and speaker tweaks.

Newform research do a huge ribbon the r345 a pair of these mated to a suitable woofer line should do the trick.
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Old 17th October 2010, 09:34 PM   #10
ScottG is offline ScottG  United States
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Quote:
Originally Posted by oublie View Post
BARE RIBBONS - Ribbon tweeter midrange speaker drivers for DIY speakers and speaker tweaks.

Newform research do a huge ribbon the r345 a pair of these mated to a suitable woofer line should do the trick.

I'm aware of Newform Research.. none are dipole. (..they also aren't terribly efficient.)
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