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Old 20th September 2007, 10:07 PM   #11
ronc is offline ronc  United States
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Good paper Martin.

ron
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Old 21st September 2007, 12:49 AM   #12
MJK is offline MJK  United States
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Thanks for the positive feedback everybody. I appreciate it. If people walk away with just two concepts, I hope they are as follows.

1) After reading the article the relative efficiency requirement for the woofer with respect to the rest of the system should be clear. In a passive system this means that the woofer probably needs to be at least 6 to 10 dB more efficient, while in an active system this means that additional boost may be be applied to the woofer to help produce this increased efficiency.

2) Another important point is that a Qts value of 1.0 to 1.2 is an advantage for an OB, in particular with respect to baffle size, and does not automatically mean that the response will boom. I have proven this to myself both analytically and with experience gained from the Lowther OB system using two 15" woofers with significantly different Qts values.

Remember, an open baffle speaker is a system and the alignment of the bass is driven by the woofer's Qts, the baffle size and shape, and the low pass crossover. It is really not that difficult to design and get right if you pay attention to the details.
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Old 21st September 2007, 03:36 AM   #13
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Martin,

You make it all sound so simple. I guess it is when someone else has collected all the information and put it in one place.

Thank you!
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Old 21st September 2007, 04:06 AM   #14
Pano is offline Pano  United States
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Yeah, nice paper Martin. Very clear and easy to follow.
The choices you make are well explained and easy to understand.

So you have well achieved your goals #1 & #2.
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Old 21st September 2007, 11:25 AM   #15
Vix is offline Vix  Yugoslavia
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Now we hope for the next article, with Nelson Pass fingerprints on it. You may have guessed: An active two way crossover, designed by Nelson Pass. Then, both of the shortcomings that Martin mentions , could be overcome...

I'll tell ya that I have a pair of Eminence Beta 15's and a pair of Visaton B200's. According to Martins article, they won't match very good in a passive configuration due to the high efficiency of the B200 compared to Beta 15. So, I guess I'll need to go active and equalize the Beta...

Greedy boy...

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Old 21st September 2007, 09:36 PM   #16
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Yep. Designed with OB and FR in mind. I have a nice one
now, but it's going through a revision. If you come to RMAF
you can listen to it.

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Old 22nd September 2007, 09:29 AM   #17
Geoff H is offline Geoff H  Australia
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Yes, good article Martin. It should help those who enjoy OB have the bass that OB deserves. Also, it provides targets for driver modification for OB use, esp considering Qts.

Geoff.
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Old 22nd September 2007, 03:22 PM   #18
renfrow is offline renfrow  United States
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How about putting an L-Pad on the full range speaker, wouldn't that help to tailor the efficiency?

Tom.
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Old 22nd September 2007, 03:58 PM   #19
MJK is offline MJK  United States
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Quote:
How about putting an L-Pad on the full range speaker, wouldn't that help to tailor the efficiency?
Sure would. I guess it comes down to how much efficiency are you willing to give away? Maybe I could keep my Lowther's sound but reduce the efficiency to 90 dB/W/m with the correct amount of padding and end up with a smaller baffle. An interesting idea.
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Old 22nd September 2007, 05:35 PM   #20
klykx is offline klykx  France
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Does this mean that I am doomed to active with my EX3's (soon to become DX3's) and 2 parallel alpha 15s and could only go passive with 4 per side?

I assume that is the case if I don't want to damp down the Lowthers?

Peter
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