Question on coils

glynnw · 4425

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Offline glynnw

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on: November 01, 2011, 02:05:09 PM
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.

PC, J River software, opticaRendu, Schitt Ygg DAC,Tortuga Pre, Torta Radu tube buffer, Linear Tube Audio ZOTL10, Spatial Audio X5w/pair of GR Research dual 12" open baffle servo subwoofers tamed by DSpeaker Dual-Core DSP , Audience AU24 SE  spkr cable, handmade silver interconnects,


Offline Paul Birkeland

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Reply #1 on: November 01, 2011, 06:29:24 PM
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 "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline Paul Joppa

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Reply #2 on: November 01, 2011, 07:32:52 PM
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!

Paul Joppa


Offline glynnw

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Reply #3 on: November 02, 2011, 07:24:02 AM
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.

PC, J River software, opticaRendu, Schitt Ygg DAC,Tortuga Pre, Torta Radu tube buffer, Linear Tube Audio ZOTL10, Spatial Audio X5w/pair of GR Research dual 12" open baffle servo subwoofers tamed by DSpeaker Dual-Core DSP , Audience AU24 SE  spkr cable, handmade silver interconnects,


Online Doc B.

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Reply #4 on: November 02, 2011, 07:32:47 AM
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.

Dan "Doc B." Schmalle
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Bottlehead Corp.


Offline glynnw

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Reply #5 on: November 02, 2011, 09:38:29 AM
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.

PC, J River software, opticaRendu, Schitt Ygg DAC,Tortuga Pre, Torta Radu tube buffer, Linear Tube Audio ZOTL10, Spatial Audio X5w/pair of GR Research dual 12" open baffle servo subwoofers tamed by DSpeaker Dual-Core DSP , Audience AU24 SE  spkr cable, handmade silver interconnects,