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Re: Kurt, I'd like to ask your advice about...

Posted by KCHANG (A) on February 15, 2007 at 18:07:08

In Reply to: Kurt, I'd like to ask your advice about... posted by Russ57 on February 15, 2007 at 12:04:23:

Hi Russ,

Not sure I am "da man." I just happened to have slapped together the biggest OB bass in the suburb of Chicago at one time. Now that I've moved to CA and dismantled the OB bass in connection with the move, I've lost my bragging rights. Nevertheless, I'm happy to discuss about OB.

I've not used or heard the Augie, so I cannot comment on that particular driver. Nevertheless, genearlly I'd rather use a lower-Q bass driver on OB, instead of a driver with a high Q. You can always use an EQ (even a cheap analog 32-band prosound EQ will work) to get the bass to your satisfaction. That's what I did with the eight-18"-woofer OB bass. The 18" drivers I used have a Qts that is more suitable for a vented box. A little bit of EQ (I used a digital Behringer EQ), no more than +6dB max, was enough to get good bass down to 30Hz. The use of an EQ significantly increases the flexibility in the selection of woofers for OB, allowing one to put more emphasis on paraments such as Fs, Xmax, and distortion in choosing the drivers.

A high-Q driver allows the use of a narrower baffle, but it depends on the particular baffle width you want to use and can be too much of a good thing. In this regards,if you read Dick Olsher's writeup about the Feastrex with Augie project, http://www.enjoythemusic.com/magazine/equipment/0107/diy_loudspeaker_project.htm
you'll see that he used a parallel resistor to tame the resonance bump of the Augie. He speculated that the right range of Qts for OB woofers might be 0.6-0.7 (this should be baffle-width dependent). The Q of the Dayton IB woofer is in that range. Thus, you may not need any EQ if you put the Dayton driver on that baffle. Another important parameter is the Xmax. The Dayton IB driver has a Xmax that is twice that of the Augie. For these reasons, unless someone can show me that the Augie has significantly lower distortion figures, I'd pick the Dayton IB woofer over the Augie for my OB projects.

As to the question of which woofer is good for 250Hz, I think that they both should have no problem going that high. The dip in the frequency response of the Dayton driver around 800Hz should not be a problem, especially if you use a 4th-order crossover.

Before I left Chicago, I was playing with the Fostex FE206esr drivers on OB with two 15” woofers on each 3’-wide baffle. I got the woofers on clearance sale for $25 each. They have a Qts slightly lower than 0.4. I used the Behringer CX2300 active crossover and a JVC digital receiver to drive the system. If I recall correctly, the frequency of the crossover was set around 250Hz. Those cheap woofers had no problem at that crossover frequency. The OB bass sounded very satisfactory even without any EQ. The main problem I had with that system was that the FE206esr sounded too bright even when listened to off-axis. Nevertheless, the system sounded very impressive in terms of dynamics and impact. I had a good time playing the Planet Drums CD through those speakers. To my ears, they were as dynamic or better, and with deeper and better bass, than some of the horn speakers I had owned.

Overall, I think most decent woofers can be used on OB, with a bit EQ if necessary. The Qts should not be a dominating factor in the driver selection, unless it is ridiculously low (like those drivers requiring horn-loading) or high (like those cheap Goldwood woofers).

Best,

Kurt

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