Question on coils

[glynnw]

Hope you guys don't mind a general crossover design question.  Whenever I post on the other sites I always get a smartass answer from someone and, being the jerk I am, we get into a shouting match.  I am building an open baffle speaker that calls for a 12mH coil on the woofer.  The cost of a custom air core coil is just too much - can I use a metal core coil for this?  I notice on my BassZillas Dick Olsher actually specifies iron core in a couple of places.

[Paul Birkeland]

I don't think you have a lot of choice in the matter with a value that high, unless you want to use multiple inductors to get that value ($$).

These look reasonably tempting, but there have been some nice speakers made with channel frame metal core inductors in the crossover. 

[Paul Joppa]

What is the driver, and what are you driving it with?

Usually open baffle woofers need to have a Q that is relatively large, like 1.0 or more. Resistance increases the Q, so if your driver is low Q then the DCR of the inductor will increase it. Depending on the source resistance of the amp and the QT of the driver itself, a cheaper coil may actually be better...

Gotta say though that the Jantzen 12mH 18 AWG is over 2 ohms and still $40+ ... not cheap!

[glynnw]

I am building the small open baffle from the Lowther site that was exhibited at VSAC 2008 - however initially I will be using either 1 or 2 Fostex 206e drivers (2 will give me the 16 Ohms the crossover wants to see) along with the 12" Tone Tubby per side.  I am using the Fostex drivers now in an experimental open baffle and many aspects of the sound please me more than my BassZillas, which use a more expensive Fostex driver.  Last night I did more research on coils and now have on order 2 of these magnetic core Erse coils (http://www.parts-express.com/pe/showdetl.cfm?Partnumber=266-948) to get a low DCR.

If these work out I may spend the bucks and get the proper Lowther driver that the speakers are designed for - but currently my total cost is under a grand and I'd like to keep it that way.

[Doc B.]

For what it's worth I think Jon Ver Halen said he had a pair of the field coil drivers in stock. To my ear they make that speaker a whole different animal.

[glynnw]

Yeah, but they'd make my checkbook a whole different animal as well.  According to their site, they have designed 2 different OB speakers.  The small one uses 12" Tone Tubby woofers and the PM6A speaker.  This is what they had at VSAC 2008.  The larger one uses a newly made version of the Altec 416A woofers and Lowther field coils.  I'm sure the larger one is much better, but just too spendy for me.