Help me Select a woffer for my OB

[DougL]

I have a 3-way OB in progress.

I was thinking of using either a pair of
Dayton Classic 15"
or a pair of Dayton RS 270-8

I want to use them up to 250 Hz on an 18" flat baffle.
Either choice should be good to 500 Hz without issues.

In this use, would the Larger drivers with less excursion be better than the Higher Tech 10" drivers?

By the way, my budget for drivers is $500, including tweeter, midrange and woofers for both channels.

Any opinions are welcome.

Doug

[AJinFLA]

Hi Doug,

neither of your choices on an 18" flat baffle will produce anything like bass below 100hz, if that. There is a very simple way to determine what you are looking for. SL's spl calculator: http://www.woodartistry.com/linkwitzlab/spl_max1.xls. The Sd of the 10 will be in the 330 range and the 15 will be about 820 or so.
Your "D" will be only 100 for the 10 and 38 for the 15. Not good.
A MUCH better driver would be http://www.partsexpress.com/pdf/295-560s.pdf
on an at least 24" baffle to get any meaningful bass whatsover.
For even better a bargain 2 of these (per side) will set you back about the same http://www.amazon.com/exec/obidos/tg...nics&n=507846.
A large baffle is a must (see pic). The PE has a nice rising response that you might be able to get away without any EQ. for "woofer" bass.
Good luck building.

cheers,

AJ

[DIY_newbie]

Doug,

Welcome to the world of open baffles, you won't be sorry you tried it.

SL spreadsheet is a great place to start. Howver here are a few tips from my own experiences.

High Sensativity, large diameter, low FS drivers will work very well in open baffles. I'm suing 2x12" drivers with only 2.25 mm xmax in my design but their each 93db efficient and achiving a flat response to 20hz to 250hz with only 12db of equalization across the pass band. However I am using an H-frame which is 18" wide, 24" deep and 30" high. This equates to an open baffle of ~ 42" wide and 54" high.. Less effiecent drivers will need much more excursion. As a good rule of thumb 3db = 2x the excursion required. Wiring 2 drivers in parallel picks up another 6db (3db for 2x surface area, another 3db assuming your amplifier doubles power into 4ohms over 8ohms) So an 87db driver would need 12x the 2.25 mm or 27mm of excursion to produce the same SPL.

You won't need as large a frame or baffle if you have large excursion drivers 14=20mm like SL used. However for most drivers less excursion = less distortion...

Good luck with your project...

--Chris

[DougL]

Thanks for the responses.

Your "D" will be only 100 for the 10 and 38 for the 15. Not good.

That is not my understanding of D from the Linkwitz site. I Estimate that D should be about 250 (mm) for either driver. My understanding is D the average radius of the baffle, measured from the acoustic center of the driver. On an 18", the shortest distance would be about 225 mm. I added 25 mm to be conservative, to account for the "extra" area of a rectangular baffle.

Using these numbers, and assuming half space, I get 99 db at 57 Hz for the 10" and 4 db more for the 15, or 103 db.
I have an IB for 20 to 60 Hz

By the way, I have prototyped this with 12" buyout woofers, and have significant response to 40 Hz.

High Sensitivity, large diameter, low FS drivers will work very well in open baffles.

My limited experience as well.

Doug