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Old 17th May 2006, 06:52 PM   #1
punk is offline punk  Italy
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Default Open Baffle project with FR

So this is what is my mind now :

Plain open baffle speakers with wings, total size more or less 20" x 50" (50x110 cm). Fostex FX120 placed off axis ~1/3 of the distance from the top. No tweeter, no filters. I'm not going to change this great speaker and all I really want is to reinforce the lower frequencies range. don't need want to force the fostex too low, I'm not concerned with on-axis peaks, eventually I'll only adjust the level, killing a few dB to make the woofer job easier.

Woofers ? I've been reading about this topic for a while and am quite confused. So, according to S. Linkwitz a low Qts woofer gives a better impulse response and is easier to design active EQ. Surely well implemented in his sytem, but it's a complex design to start with. Some people try to extend the range of one speaker only with EQ. Maybe it's ok for a high-quality and larger speaker, but I know my fostex's bass is poor in sealed and ported enclosures.

Others prefer high Qts speakers that will roll of more gently and this is what I want to try.
Eminence alpha 15" would be the best candidates, ~95dB low Fs and Qts of 1. Less than 60$ each.
But I'm also tempted to try two 12" or 15" goldwood speakers (9.50$ to 27$ each) per channel. they have a qts close to 2(!), small magnet, huge Vas and response up to 1-2kHz, ~same sensitivity as the FR. Ultimatley, crossed with a good fullrange driver they only have to do some sound "reinforcement" up to 200-250 Hz where the FR takes over.

Do you think it might be worth a try without active EQ? Or the dB drop on OB is too significant in that frequency range ? what about using woofers 10 dB more efficient than the FR ?

thanks,

Lorenzo
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Old 17th May 2006, 07:25 PM   #2
ScottG is offline ScottG  United States
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http://www.hawthorneaudio.com/drivers.htm

The "Augie" (at the bottom of the page) is specifically designed for what you want. Giving you more low freq. response then the other cheap woofers AND probably a much lower THD (when comparing similar low freq. cut-offs).
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Old 17th May 2006, 07:58 PM   #3
punk is offline punk  Italy
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not sure about the iris driver. Besides Xmax, I don't see why it is better than the eminence alpha 15a. Also, 88dB instead of 95 ?
Iris speakers are look like (and very likely built by) Eminence woofers, but the price is 2-3 times as much!


L.
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Old 17th May 2006, 10:02 PM   #4
ScottG is offline ScottG  United States
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Quote:
Originally posted by punk
not sure about the iris driver. Besides Xmax, I don't see why it is better than the eminence alpha 15a. Also, 88dB instead of 95 ?
Iris speakers are look like (and very likely built by) Eminence woofers, but the price is 2-3 times as much!


L.

The "Augie" not the "Iris"..

The Augie has a much lower fs (..and this is why its about 6db less effiecent). It also has the best suspension eminence provides (..found only on the "Definimax/Magnum" series). It has almost 3 times the magnet that the Alpha has - while still retaining a large qts value. Futhermore it has a copper faraday ring to reduce distortion. Finally the basket is cast rather than stamped.

Now if you need something that will only go down to 50 Hz then a pair of Alphas should work well. If however you want a driver that will go to 30 Hz then the Augie is what you want.
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Old 17th May 2006, 10:59 PM   #5
Rudolf is offline Rudolf  Germany
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Lorenzo,

MJKs new Open Baffle worksheets at www.quarter-wave.com are a big help at looking deeper into your problem.

In the first diagram I have combined the FX120 (green) with the Eminence alpha 15" (blue). The resulting response is red. This simulation is calculated for a listening distance of 2 m and includes the influence of the floor. Crossing over at 550 Hz you can elegantly eliminate the floor bounce.

The second diagram shows the additive effect of a front wall behind the driver. The reflections from that wall can push up the SPL around 100 Hz, but you will need some kind of EQ for sure.

High and Low pass certainly can be further optimized. Please note that both drivers are running on the same level. There is no boost or attenuation of any driver involved.

If you could lead me to some TS parameters for those Goldwood speakers, I could look into that combination too.
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File Type: gif fast fx120_1.gif (13.5 KB, 756 views)
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Old 18th May 2006, 02:47 AM   #6
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I find those Goldwoods intrigueing as well. Of course they are not the greatest but I used boxplot to model the Pismo15" in an IB and 4 of them produced pretty high output and -3dB at 20Hz. It had a pretty big bump at 30Hz but people often boost that range anyway. At < $30 a piece... maybe not without merit.

mike
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