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In Reply to: High effeciency open baffle woofer? posted by Rick Barton on February 8, 2007 at 09:22:55:
Hi Rick --If it were me, I'd probably go with the Alpha 15A. But, I wouldn't think that you could cross any of them over much higher than 1.2k or so, which makes tweeter choice pretty tough -- compression drivers on a horn/ waveguide is about your only option. If you're willing to go coax, the Hawthorne Silver Iris might be right up your alley. Another possibility would be to go Fostex 6.5" + Eminence 15" and crossover >200hz.
Follow Ups:
Unless the 15" or 18" driver it's expressly intended for vocal / wideband use, or has a good reputation as a wideband driver, you should probably plan to cross it low (under 1KHz).Therefore, for a simple set-up I'd suggest:
An 8-ohm fullrange 6-10" driver, run down to the lower mids (somewhere around 200Hz).
Two bass drivers, in parallel (4 ohm minimum). Put a couple of big inductors in series with this - eg. a pair of the biggest inductors I could get locally would give about 18mH of inductance and 2ohms resistance. So < 50Hz, the amp would "see" a minimum of 6ohms resistance.
Personally, for the bass drivers, I'd let *price* dictate the decision. For OB bass, you need a lot of displacement. Two $100 15" drivers will have an easier time hitting a certain volume than one $200 15" driver.
The exact Qts of the bass driver doesn't matter hugely, since you can tweak them so many ways. If you get lower Qts drivers that seem bass-shy, you can boost the bass by:
- using Eq
- placing the baffle nearer a wall / corner
- placing the drivers lower on the baffle
- making the baffle bigger
- adding wings.
Sometimes it is practical to raise the Qts of a woofer by cutting away part of the spider. I know a fellow who did exactly that and got really good results on OB with a bunch of small, inexpensive woofers.
Personally, I'd be too scared of axing the driver to try it on anything that cost more thatn $50 :-)
You mentioned the Silver Iris, I am very interested in that system and intend to get a pair w/augies once I sell the Lowthers.
Two reasons:1) The higher Q should provide some eq in the bass region. You shouldn't have much problems getting to 50hz pretty flat on a moderate size baffle.
2) Because Martin King uses them in his OB setup and likes them very much. I tend to ascribe a fair amount of weight to opinions held by people who know what they're talking about. As long as I'm shilling, if you're really interested in building OBs from scratch, do yourself a favor, spend the $25, and get a license to use his worksheets. The one for OBs is invaluable.
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