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Old 24th March 2008, 01:26 AM   #1
jimluu is offline jimluu  United States
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Default New project inspired by 'beyond Ariel'

I've been watching the thread 'beyond the Ariel' for what seems like years now. I was hoping that some one would make something so that I can copy, but seems like its more of a cerebral exercise only up to this point. So here I go off to my first open baffle project. I don't have any open baffle experience and my measurement 'lab' is still not set up yet, so if anyone have any ideas, I would appreciate your input. I have a reasonable budget, but very little time. So I'm willing to play with expensive parts, but it may take me a while to finish.

This will be the first of my 2 OB experiments:

I have a pair of Hemp acoustics OB12 coaxial speakers at hand, and 4 diycable xj-15 subs. I also have a pair of partsexpress 500watt plate amps (with parametric eq). I plan run the coax with 2 woofers per side driven by the plate amps. This will be a flat baffle 50" x 18".

I need advice on a couple of areas:

1. I'm concerned about the bass drop off of such a narrow baffle. Some of this can be compensated by the parametric eq of the amp. But I want to make sure that the bass is strong enough to keep up with the coaxials. Would a pair of 18" Emminence Kilomaxs be better? They have higher fs, lower qts....but are much more efficient. With the added cone area and some eq, would they be much better or worse than my current subs.

2. I've spoken with Perry at hemp acoustics. He stated that hemp cones don't suffer some of the break up problems as other materials. Of course I have no way to test this. I was thinking of running the mid/bass section of the coax at full range and a simple cross over to the HF driver at around 3k. Does anyone have experience with hempcone material?

Thanks.
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Old 24th March 2008, 05:30 AM   #2
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Hi C-B,

acoustic elegance speakers is a small company that took over production of several Lambda Acoustics speakers. I have not purchased from them, but did buy 50 speakers from Lambda because of the natural sound.

http://www.aespeakers.com/

The 15 " Infinite Baffle woofer might be worth your review. If your bass amp can drive 3-4 ohm loads, wiring two in parallel will give 92 db/watt SPL, and four in 8 ohm parallel-series 95 db/watt. There may be an introductory sale, 4 for $400.

T/S Parameters:
FS: 16.0Hz
Qts: 0.70
Vas: 439L
Z: 8ohm
1WSPL: 86.0dB
Pe: 500W continuos

Lynn Olson favors all four bass speakers near the floor for reflective gain, but a tall WW -coax- WW might be worth consideration. A tall, narrow dipole baffle will modestly lower the 6db dipole frequency as Linkwitz and other baffle equations estimate. The Steinway WMTMW dipoles are BEAUTIFUL.

http://www.steinwaylyngdorf.com/

For a Lynn Olsen TM(2W)(2W) wide base baffle dipole design, the AEspeakers' four IB15 bass, one TZD12M midrange and one DIY dipole ribbon would be an interesting paper design to review.
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Old 24th March 2008, 07:40 AM   #3
jimluu is offline jimluu  United States
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Picture of the 12OB and subs.

12OB specs:


http://www.hempacoustics.com/CO12OB_-_Hemp_Spec_Sheet_ready.pdf
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Old 24th March 2008, 07:40 AM   #4
jimluu is offline jimluu  United States
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picture of Hemp Coax and subs
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Old 24th March 2008, 05:53 PM   #5
jimluu is offline jimluu  United States
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I just got my email reactivated. (was hijacked) and found my old name and password. crazybastard no more: now jimluu.

Thanks for the suggestions. I think that my current subs are better than the AE dipoles. Mine were the 'errors' from diycable, qts too high. Makes them perfect for OB use. I do plan to use AE lambda dipole in my next open baffle project though.

My concerns about the woofer is the volume displacement issue. The current 15" woofers have an xmax of around 27mm, which is quite substantial. I worry that in order to generate as much air displacement as an 18" driver, the 15" have to utilize some 50% more excursion. Will this cause excessive movement to the baffle? I also wonder that if a woofer has to move 2x the distance for the same volume, then it has to move 2x the distance to return to its 'resting' position. This takes time. Is the 15" with high excursion then 'slower' than a 18" that doesn't have to move as much to produce the same output?
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Old 25th March 2008, 06:34 AM   #6
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The Amazing Magnetar built one large WMTMW dipole using dual 21" Woofers 45-330 cycles 99 db sensitive

WMTMW Open Baffles

WMTMW Open Baffles

and then updated to five 10" woofers TMW which he felt had much improved bass dynamics..."more slam"....a big improvement over the 21"

Sensitive Wide Range Open Baffles

Sensitive Wide Range Open Baffles


Magnetar and Lynn favor low moving mass and high SPL sensitivity from multiple drivers to get the big air movement.

I use four Lambda 15" dipoles per speaker with 90 grams Mms 14mm Xmax underhung motors, Qts=0.9, and 92 db/watt SPLs. Multiple drivers seems to be the cost for good dipole bass without a sub.

The Steinway WWMTMWW dipole uses four 12" woofers per speaker.
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Old 26th March 2008, 03:26 PM   #7
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Looking interesting Jim, I have plans for something similar, driven with 2 tubelabSE and an active filter (and something for the bass).
I have not totally decided me for the driver, The price for 2*hemp is 2600$ here in Denmark, but I think that the HEMP's look very good on paperso I would love to hear some positive feedback before spending my 'car-savings' *gg*
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Old 3rd May 2008, 06:30 AM   #8
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Jim.

I'm curious to hear about your listening impressions of the Hemp Acoustics coax. There isn't a whole lot of information anywhere on these drivers....including subjective opinions.

Thank you for your time,

Chris
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