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Old 20th May 2008, 01:53 PM   #1
maghen is offline maghen  Sweden
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Default dipole or not?

Hi all,

I'm a newbie looking for answers.

I am about to either choose or build the tweeters for my line array project.
Most DIY ribbon tweeters I have seen have "open backs" to radiate sound both ways.
Is this a suitable design for a tweeter, meant to match midrange and bass speakers that are boxed in a traditional way? Or should all drivers in a speaker be "open baffle" for best results?

I am a bit suspicious about dipoles in general, since I don't really see how they can reproduce recorded sound correctly, but feel free to convince me!

/Magnus
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Old 20th May 2008, 03:26 PM   #2
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If you're interested in learning about dipoles, I would start by reading and digesting these two websites:

www.linkwitzlab.com
www.musicanddesign.com
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Old 20th May 2008, 06:07 PM   #3
maghen is offline maghen  Sweden
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Default is it wise?

Ok, I have looked into the concept before and found both sites quite interesting.

I understand that dipoles won't suffer from "box distorsions", and perhaps I shouldn't worry about all the delayed reflections, since it is explained that the human brain automatically ignores them...

But is it wise to use dipole tweeters together with boxed mids and bass? Any comments?
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Old 20th May 2008, 06:53 PM   #4
gedlee is offline gedlee  United States
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Dipoles are not a panacea. What about edge diffraction and baffle resonances. Dipoles have as many problems as boxes do. And the claim that they "excite few modes" have been totatly debunked. There are a lot of false claims out there about dipoles. I am not totally opposed nor totally on board, but I do look at all the problems with my eyes open.
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Old 20th May 2008, 07:13 PM   #5
badman is offline badman  United States
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Default where possible, it's best to pattern-match

Always best to pattern match as much as possible, to get consistent power response. This means horns with horns, direct with direct, dipole with dipole, etc. Sometimes you can mix and match, like a midrange/treble horn matched to a 12" or 15" that's already beaming. This is possible because the beamwidth tapers as the 12" or 15" becomes directional, but does so slowly, rather than an abrupt transition at the crossover freq.

Another (becoming more common) combination that has some promise is dipole at lower frequencies and directional (horns, waveguides) in the higher frequencies where horns are more modest sized. This saves you the need for huge enclosures.
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Old 20th May 2008, 07:44 PM   #6
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Hi Magnus,

Only your ears can provide the final dipole vs. monopole answer, but you can avoid mistakes and do-overs if you can find local audio stores or friends that have dipole line sources like Magnepan or Apogee, mixed monopole bass and dipole ribbon tweeter like DALI MegaLine, monopole bass and planars like VMPS or kits that follow Jim Griffin's line array design rules. The easiest DIY might be copying a well reviewed closed box Jim Griffin line array design using planar tweeters.

http://www.audiocircle.com/circles/i...hp?board=127.0

http://www.audioroundtable.com/misc/nflawp.pdf

http://audioroundtable.com/ArraySpeakers/

If you DIY a monopole ribbon tweeter, you will need to have extensive rear sound absorption material to keep the rear waves from reflecting back upon the ribbon foil..

If you DIY a dipole ribbon tweeter, a full 3-way dipole line array design would match the best products.
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Old 21st May 2008, 01:20 AM   #7
ucla88 is offline ucla88  Tahiti
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It's important to note that the "rear wave" issue is often looked at incorrectly.

A monopole radiates sound rearward as well-this is a key point that gets lost. However, it's rear radiation is limited to below the bafflestep region. Above, it only goes forward into 2 pi space. This is the source of the on axis/power response problem of a monopole.

The dipole solves this, however, more energy is radiated higher up in the spectrum, making placement/rear wall interaction more important.

If you read SL's and John k's site, as well as the thread/comments by Dr. Geddes and John k on cardioid bass, you'll see that the simulations below 100 Hz have trouble showing a clear advantage to a dipole vs a mono or cardioid. (That doesn't mean that one doesn't exist-but hey, we're scientists. There may be a subjective difference in dipole bass, but...)

However, there is a clear difference between a monopole and a dipole in the 100-1.5k range or whatever is the practical upper limit to dipole radiation. The radiation pattern/power response is more uniform (not considering the space into which the radiation is occurring). Rear wave absorption is not an issue with dipoles. Panel resonances are difficult to assess. The motion of a dipole panel will likely be higher, but there is generally less panel to radiate in a dipole. I think the winner would be design specific.

Which way to go? Difficult question. You have to build and listen to better examples of each to decide. No design is inherently better.

Maybe we can get a set of Orion's or NaO's at the next Burning Amp festival, as well as one of Dr. Geddes DIY horns. I will bring my RST panels if they are finished by then.

A well done line array would be cool as well
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Old 21st May 2008, 01:40 AM   #8
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Quote:
Originally posted by ucla88

If you read SL's and John k's site, as well as the thread/comments by Dr. Geddes and John k on cardioid bass, you'll see that the simulations below 100 Hz have trouble showing a clear advantage to a dipole vs a mono or cardioid. (That doesn't mean that one doesn't exist-but hey, we're scientists. There may be a subjective difference in dipole bass, but...)


This is taking the 'simulations' too far.

There are clear, measurable and audible advantages in using a dipole bass system over a monopole.
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Old 21st May 2008, 01:52 AM   #9
gedlee is offline gedlee  United States
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Quote:
Originally posted by Magnetar



This is taking the 'simulations' too far.

There are clear, measurable and audible advantages in using a dipole bass system over a monopole.

Prove it - don't just spout nonsense.
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Old 21st May 2008, 01:53 AM   #10
ucla88 is offline ucla88  Tahiti
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Quote:
Originally posted by Magnetar



This is taking the 'simulations' too far.

There are clear, measurable and audible advantages in using a dipole bass system over a monopole.

Well, I guess that's open to debate. I don't disagree that dipole bass sounds different. But this is subjective. Nothing wrong with that. And, simulations are fraught with error.

I think you have to accept that the jury's still out. You can choose dipole bass over monopole if it suits you, but how clear the "measureable" advantages are is still a bit uncertain. I think if anything, proponents of dipoles have more ground to stand on in the 100-1000+ hz range. Or, at least that's the way I see it.

PS- I'm in my dipole phase. See my project at RST dipole

So, I'm not against dipoles. But let's try to not overgeneralize or state a preference, however based in science, as science/dogma
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