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Old 13th September 2005, 03:25 AM   #1
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Default Dipole Journey

All this talk on the board has me thinking about converting to "Dioplism" Questions are,

1. Midrange duties, I have and love a pair of Seas M15ch001 drivers, Too small or alright down to 300HZ or so?

2. Woofer/s, A single Eminence Magnum 18LF per side, high sens, sorta low FS and half decent xmax?

3. All of this (along with an undetermined ribbon) in a Dipole/ H Frame of some sort, crossed at approx 300HZ, 2000HZ ?

4. Passive (DOH!! I hear you say) or active if you really twist my arm.

Thoughts?
P>S, Ill get back with the Magnum specs.
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Old 13th September 2005, 03:55 AM   #2
DougL is offline DougL  United States
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Welcome to the dark side.

What you are proposing is not conventional. Most of the designs are 1+" dome, 8" woofer / woofers, Dual 10" or 12" Subwoofers.
Also a few full range dipoles.

Quote:
1. Midrange duties, I have and love a pair of Seas M15ch001 drivers, Too small or alright down to 300HZ or so?
For your 5" to be effective IMHO, you need to have an Fequal lower than or equal to the xover frequency. Above this frequency the M15 plays as loudly as if it were sealed. Below this, the maximum output drops 18 db per octave.
So grab the Linkwitz max spl spreadsheet and look for yourself.

Good Luck;

Doug

PS: I am working on a very similar design.
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Old 13th September 2005, 04:57 AM   #3
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Why not go active on the woofer and passive on the mid/tweet?
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Old 13th September 2005, 05:15 AM   #4
MBK is offline MBK  Singapore
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I second Doug's remarks. Eyeballing it, the Seas should do 300 Hz, maybe 200 even. The lower the better: I had a 6.5" crossed to dual 10" at 300 initially. I went down to 160 Hz and I noticed much improvement in the midrange clarity. Moving mass etc of a small driver just beats large woofers by a wide margin.

Active-passive: you might get away without dipole EQ for the mid/treble. What I did in my current design: make the baffle large enough so that the dipole rolloff starts where the free space to half space transition occurs in the bass (see Linkwitz on the theory of this). In essence, you get a "baffle step" effect of +6 dB from 200 to 100 Hz because the bass will effectively see the floor as a trasition to half space radiation. Result: mid rolls off 6 dB/oct starting at 200 Hz. half space transition picks up the loss by adding 6 dB from 200 to 100 Hz. This works, in my system, with a baffle approximately 40"+ high, 24" wide, with 7" foldback wings.

Below 100 Hz you're out of luck: your woofers will need a 6dB/oct boost, which means separate power amp with at the minimum this single EQ step.

Beware though that for truly excellent results, Linkwitz' many filters in his designs all have very good purposes:

- the delay filter for the tweeter really does it for blending with the mid
- EQ of metal dome resonance modes (may be done passively)
- EQ of peaks in the first maximumof the dipole effect: in your design-to-be, likely around 400 Hz. You can do without it and be happy. I did so for a while. After some RTA testing I added a notch - and went "Aaaaaaaaaaaaaah!!!".

Anyway you can start simple and add complexity later on to iron out the wrinkles.

The basic design I'd suggest:

24" or wider baffle
x-o to mid around 150-200 Hz, 4th order L/R practically a must, passive HP section OK
passive x-o to tweeter ok but well designed
active LP and 6 dB/oct boost for woofers, likely from ca 120 Hz down to 20 Hz with the above baffle dimensions.

Good Luck,
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Old 13th September 2005, 07:37 PM   #5
derf is offline derf  United Kingdom
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Quote:
1. Midrange duties, I have and love a pair of Seas M15ch001 drivers, Too small or alright down to 300HZ or so?
Hmm, if you intend to stick your bass drivers in a H/W/whatever frame, the resonance will kick in prior to 300hz. Taking the 5" a lot lower than 300hz is gonna make it strain.

Quote:
2. Woofer/s, A single Eminence Magnum 18LF per side, high sens, sorta low FS and half decent xmax?
Why don't you go with more x cheaper eminence 18's, one a side really won't cut it. If space is a problem, dipole bass probably isn't the best direction to go in. Just trying to figure out the reasoning behind 1 x 18" driver a side...

Quote:
4. Passive (DOH!! I hear you say) or active if you really twist my arm.
You could go passive, but why bother when one of those Behringer boxes are cheap as chips, can eq room response aswell, leaves you a ton of flexibility.

Quote:
What you are proposing is not conventional. Most of the designs are 1+" dome, 8" woofer / woofers, Dual 10" or 12" Subwoofers.
Covention isn't always best... I mean look at most shop sold hi-fi speakers, 6.5" and 1" dome, fine for moderate levels, but what if you want more?. Isn't this why people start diy'ing in the first place, to break away from convention because it doesn't work for them, no?

Quote:
Moving mass etc of a small driver just beats large woofers by a wide margin.
Moving mass hype is all a bit of a fallacy. Especially when people look at it as the "be all and end all", rather than in relation to other parameters/occurrences. A smaller driver is always going to have to move further than a larger one for any low frequency event.
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Old 13th September 2005, 08:04 PM   #6
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Default Re: Dipole Journey

Quote:
Originally posted by Beau
All this talk on the board has me thinking about converting to "Dioplism" Questions are,

1. Midrange duties, I have and love a pair of Seas M15ch001 drivers, Too small or alright down to 300HZ or so?

Probably fine as long as you make a large enough midrange panel to support the driver down to 300hz with a bit of EQ.. Smaller panels will create a 6db roll off on the bottom end that will make it really hard to get to 300hz with such small drivers.

Quote:
Originally posted by Beau

2. Woofer/s, A single Eminence Magnum 18LF per side, high sens, sorta low FS and half decent xmax?
Positivies: Big SD, Decent 6mm xmax, large VAS is good
Negatices: Qts is a bit low for a dipole, and FS is a too high depending on how low you want to go.. Remember the dipoles won't get any help from box resonance or a port so it will be hard to make Bass below the drivers free air Fs. and the low Qts means it will roll off pretty early and need lots of Xmax to make up for it.

I would choose a driver with a higher Qts or a larger Xmax..
High Q + decent xmax is fine and Low Q + large xmax + digital EQ will be fine as well. I went the low Xmax route in my design since distortion tends to increase with excursion (not always but a good rule of thumb)

Quote:
Originally posted by Beau

3. All of this (along with an undetermined ribbon) in a Dipole/ H Frame of some sort, crossed at approx 300HZ, 2000HZ ?
Similar to my design again I'm using a JP2.0 ribbon and Audax PR170m0 midrange. Cross overs are 2.5K LR24 and 250 LR24. Digital Crossover, seperate amps, and DEQ for room equalization. The hardest part about using a ribbon tweeter is finding a midrange that can keep up with the sensativity and speed of the ribbon. IMHO look for low mass, high sensativity midranges to make this combination really shine

Quote:
Originally posted by Beau


4. Passive (DOH!! I hear you say) or active if you really twist my arm.

Thoughts?
P>S, Ill get back with the Magnum specs.
Behringer DCX-2496 was the way I went. Works great if you can get pro sound amps with gain controls and use balanced connections the whole chain...

pm/e-mail me if you want more details on my design. I'll be posting pics sometime this week as it starts to come together

--Chris
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