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Author Topic: New speaker idea Alpair 12P / Lowther DX-3 / Acoustic Elegance Dipole 15  (Read 6304 times)

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Marvey

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Since the Rag turned out better than I thought, I have decided to build a floor standing speaker to make the most of what it (and the Gen V) can do. Came up with a simple list of requirements:
  • Must be cheap relatively speaking. The prototype must be as shitty looking as possible.
  • Open baffle bass. Based on prior experiments, OB seems to reduce the amplitude of room nodes by 50%. OB should be helpful for those annoying dips which are impossible to correct without multiple subs. Quality bass without room interactions is something most headphone people take for granted.
  • Decent frequency response. Don't want to have to depend upon digital EQ, so I can use turntables and CD transports.
  • Simple crossover circuits. Goes with cheap. Complex crossover / EQ circuits can result in excellent frequency response, but at too huge of a cost to reduced dynamics and microdetail. Been there. Done that.
  • Bi-amping with dedicated amp for OB woofers, possibly with line level passive crossover and bass roll-off compensation.
  • Moderately to highly efficient at 90db+ Less of a priority since Rag is being used. But efficiency is never a bad thing. Efficient drivers tend to sound more lively too.
  • Three way or more. More drivers playing within their operating areas should result in less intermodulation distortion. Not a huge priority though.
  • Use of drivers which are readily available. No more unobtainable stuff like Moth Cicada drivers.
« Last Edit: January 14, 2015, 06:18:20 AM by marvey »
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Marvey

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Re: New speaker idea
« Reply #1 on: December 03, 2014, 10:32:09 PM »

Idea #1

Keep Eminence Beta 15" woofer from old project. Alpha has higher Qts at > 1.0 which will have much better bass extension in an OB. However that high of a Qts may be too uncontrolled for my taste. The Beta 15" with Qts ~0.50 will have to do despite less bass extension. I don't remember the Betas producing anything significant below 45Hz. Might need a sub to fill in up to 45. Oh well. IMO, OB benefits > downsides. The Acoustic Elegance 15" drivers look nice, but again, want to keep this project cheap.

Mark Audio Alpair 12P (8" driver) and Alpair 7P (4" driver). Paper drivers from Mark Audio. Realistically probably about 90db efficient. $135 + $79 respectively. Using the 8" wide-bander alone might be asking too much and the driver may be too beamy. Hoping the 4" will help a little bit in smoother high-end extension and vertical dispersion. Same cone material and similar construction should result in a more cohesive sound.

Concerns:
  • How much more effective would the 4" would be in terms of dispersion width or treble performance? I haven't measured these drivers myself. I haven't see off-axis measurements.
  • Use of first order crossovers will result in combing and funky vertical off-axis response.
  • Imaging diffuseness.
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Marvey

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Re: New speaker idea
« Reply #2 on: December 03, 2014, 10:48:19 PM »

Idea #2
  • Similar to above with same OB bass driver but with following changes on mid/treble:
  • MTM arrangement with 2 x 6" Alpair 6P paper drivers which are around ~90db efficient. Choosing to double up the 6" for better efficiency and less excursion. Also hoping the 6" can extend better than the 8" before handing off to the tweeter.
  • In between the woofers would be sandwiched a HiVi RT2C isodynamic planar tweeter. A RAAL with the amorphous core would be nice, but again we are talking cheap. The 70-20 RAALs which can take more punishment are not available to the general public. And any smaller RAAL will likely blow without a complex crossover. In any event, I'm letting the 6" do most of the work and letting the RT2C act as a semi-super tweeter.
  • The faceplate HiVi RT2C of the tweeter will assure good horizontal dispersion and limit vertical dispersion, which in this case would be a good thing to prevent comb filtering effects. Thinking about trying something borderline like crossing over at 6kHz first order. If that doesn't work, maybe a wide notch circuit somewhere below the crossover point. At $80 a piece, they are relatively cheap and can be experimented upon.
  • Finally, the RT2C isn't a dipole (at least I don't believe so), so maybe this setup might image better withoutsome of the higher frequency backwave hitting the back wall and causing too much of a diffuse stereo image.
CONCERNS:
  • Questions about HiVi RT2C power handling with first order crossovers
  • Cohesiveness between the HiVi (iso planar) and Alpair 6" (paper cone)
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zerodeefex

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Re: New speaker idea
« Reply #3 on: December 03, 2014, 10:54:18 PM »

are you co-locating the woofers with the rest of the drivers? so 2 woofers total probably?

Idea #1:  I mean, Qts of ~.5 is probably okay, but that number is taken in a vacuum. What's system Q in this case, .7? I'm guessing open baffle low-Q of .2, right? I'd try to go for woofers with Qts ~.8 if you can and forego the separate subwoofer(s).




Edit: Idea #2: see if you can get the 64-10 OEM somewhere. Reach out to Dennis Murphy or Jim Salk offline and see if either will sell you a pair of 70-20s or 64-10s they've taken as returns or something like that.
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Marvey

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Re: New speaker idea
« Reply #4 on: December 03, 2014, 10:55:32 PM »

In the spirit of making this cheap and looking as horrible as possible, a simple scaffold or frame for the drivers will be first constructed. Cutout cardboard from moving boxes will then be mounted onto the frame be used as the baffle. This will allow for easy experimentation of baffle widths and shapes.

After baffles are finalized, polycarbonate or aluminum baffles can be machined so my wife does not kill me.
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Marvey

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Re: New speaker idea
« Reply #5 on: December 03, 2014, 11:00:35 PM »

are you co-locating the woofers with the rest of the drivers? so 2 woofers total probably?

Idea #1:  I mean, Qts of ~.5 is probably okay, but that number is taken in a vacuum. What's system Q in this case, .7? I'm guessing open baffle low-Q of .2, right? I'd try to go for woofers with Qts ~.8 if you can and forego the separate subwoofer(s).

These would be ideal: http://www.aespeakers.com/drivers.php?driver_id=47

0.82 Qts $339 each. More xmax than the cheap Eminence. Also magnet strength probably more even throughout the excursion range of the voice coil. Might be a good idea just to bite the bullet and save on PLLXO design. There is something charming (in the sense of fuck you high-end) with $75 15" Eminence drivers though. I don't think I even had to use compensation in the room to get down to 45Hz.

For idea #2, still looking for 6" driver alternatives. Must be a real ~90db sensitive though.
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DaveBSC

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Re: New speaker idea
« Reply #6 on: December 04, 2014, 01:21:00 AM »

Have you considered doing a full mirror of the drivers? I don't think I've ever seen this done in a fully open baffle configuration.

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Ringingears

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Re: New speaker idea
« Reply #7 on: December 04, 2014, 02:48:17 AM »

I own a pair of Dunlavy speakers that use that array. They are my favorite. They are sealed so in a larger room I have trouble getting enough bass. Flat response, just not enough bass energy for a big open room. Sounds like a Quad that goes down to 20 Hz, just doesn't rattle the china. Have thought about doubles subs at some point. Like when I win the lottery!

I think it is a variation of a D,Appolito array. Crossovers where 1st order. Put a lot a stress on the tweeter, so he had to spend time trying several until he found one that could handle it.
« Last Edit: December 04, 2014, 03:13:37 AM by Ringingears »
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DaveBSC

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Re: New speaker idea
« Reply #8 on: December 04, 2014, 03:18:18 AM »

Dynaudio also uses it in their Confidence and Evidence lines, which are far superior to everything else they make.

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Ringingears

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Re: New speaker idea
« Reply #9 on: December 04, 2014, 03:34:22 AM »

I just really like the sound of this array, done right. The best of the Quad sound, with bass that goes low. And they can rock when need be.  :)p7
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