From dfischer at usol.com  Thu Aug  3 18:32:50 2006
From: dfischer at usol.com (Duane Fischer)
Date: Thu Aug  3 18:32:52 2006
Subject: [Vintage-Audio] Dual Voice Coil For Woofer?
Message-ID: <200608032221.k73ML077026640@smtp.usol.com>

Hi Bob, 	
	
The reason for this old post is because I am using my vintage Compaq
Prosario 1210 laptop as I wait for HP/Compaq service to arrive tomorrow
morning with a new mother board for my seven month old bullet proof super
computer. The audio card, integrated to MB, failed Saturday. I called HP as
I have a three year - all parts - all labor - on site contract, they got me
a new MB and a tech n less than 24 hours.	
	
I got the three CDS, thank you. Some unusual and interesting sounds there! 
 	
	
That is some kind of stereo, or 5.1, setup that you have! I wish I could
hear how the changes in the stock audio that you made sounded.	
	
I have no anti-virus software on this Windows 95A system anymore, so better
get off line. 	
	
Talk to you soon Bob. Again, thank you.	
	
Duane W8DBF	


----------
From: wolfbob <wolfbob@csnsys.com>
To: Vintage home and professional audio equipment from 1975 back
<vintage-audio@mailman.qth.net>
Subject: Re: [Vintage-Audio] Dual Voice Coil For Woofer?
Date: Wednesday, December 28, 2005 2:25 AM

I think it was an easy way to get subwoofer performance from 
both channels without an additional amplifier to bring the 
two channels together and equal to the rest of the speaker 
system. Very low frequencies have no directional or spatial 
contribution so only one sub-woofer is required for very 
good stereo sound, but how do you combine the two stereo 
channels and get them up to snuff unless you do something 
clever such as the dual voice coil speaker. The very low 
freqs in the two channels are averaged, but that is still 
OK.

WBob


----- Original Message ----- 
From: "Duane Fischer" <dfischer@usol.com>
To: "Vintage home and professional audio equipment from 1975 
back" <vintage-audio@mailman.qth.net>
Sent: Tuesday, December 27, 2005 10:49 PM
Subject: Re: [Vintage-Audio] Dual Voice Coil For Woofer?


>I spoke with Judith Fulkerson, Oxford, Michigan today. She 
>has been
> rebuilding speakers professionally since 1976. The only 
> brand she knew of
> that were set up like this one was made by Infinity.
>
> I believe the phasing is not as simple as you assert. A 
> speaker cone can
> not travel in two different directions at the same time. 
> How is this
> compensated for?
>
> You make reference to more than one amplifier, this 
> involves only one.
>
> Keep in mind this was when the so called "sub" woofer was 
> a new concept.
> Much has changed since this was developed. Personally, I 
> would call this a
> woofer being shared by two channels, as you can not have a 
> sub-woofer
> without a woofer, right?
>
>
>
> ----------
> From: Matt Johnson <matt34_mn@yahoo.com>
> To: Vintage home and professional audio equipment from 
> 1975 back
> <vintage-audio@mailman.qth.net>
> Subject: Re: [Vintage-Audio] Dual Voice Coil For Woofer?
> Date: Wednesday, December 28, 2005 12:54 AM
>
>> The 15 inch speaker has two voice coils, one for the
>> right channel and a
>> second one for the left channel. Somehow the two
>> signals are put in phase
>> and fed to a single speaker.
>>
>> How did they cause the two voice coils to work with
>> one speaker?
>
> Its simply two voice coils wound on the single former
> that are electrically isolated from each other. The
> signals applied to each are magnetically summed
> allowing each amplifier channel to be added without
> electrically connecting them.
>
>>
>> Was doing this common or unusual?
>
> Quite common actually, many passive subs use this
> arrangement. It is even more common is car audio
> though. Often people will connect both coils to a
> common amplifier channel to obtain a lower drive
> impedance (provided they have a current capable amp!).
> Of course it is vital that proper phasing is observed
> since low bass is usually in phase. Connect the
> channels out of phase and the net drive to the cone is
> zero!
>
> The shame in this situation is that there is a high
> level crossover between the amp and the passive
> woofer. To really drive a sub the voice coil needs to
> be connected directly to the amp with no reactance in
> line to harm damping factor. Also having a low level
> crossover ahead of the amps will allow the amps to
> deal with their respective frequency bands reducing IM
> distortion between the seperate systems. I had a
> friend of mine that had an older Cerwin Vega 12"
> passive sub like this that removed the passive
> crossover replacing it with a plate with connectors on
> it. When he drove the system with a pair of amplifiers
> and a low level crossover I was simply amazed at the
> performance. My JBL 2235H still did much better
> though!
>
> Regards,
>
> Matt
>
>
>
>
> __________________________________
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From dfischer at usol.com  Tue Aug 29 13:15:09 2006
From: dfischer at usol.com (Duane Fischer, W8DBF)
Date: Tue Aug 29 13:15:49 2006
Subject: [Vintage-Audio] Re Michael
Message-ID: <00c601c6cb8e$b041ba90$f4ec1240@hpdc5100mt>



I trust that Michael Salmons is alive and well, and just too busy to respond 
to e-mail.

I need to speak with you Michael, so send me a private note and tell the 
best day and time to call.

Thanks.

Duane W8DBF

From salmonsm at missouri.edu  Wed Aug 30 09:59:38 2006
From: salmonsm at missouri.edu (michael salmons)
Date: Wed Aug 30 10:00:10 2006
Subject: [Vintage-Audio] Re Michael
In-Reply-To: <00c601c6cb8e$b041ba90$f4ec1240@hpdc5100mt>
Message-ID: <C11B03FA.1F6D%salmonsm@missouri.edu>

Hi Duane, feel free to call me today at 573-884-5242. I may be busy but
you'll get a hold me eventually.

Michael


On 8/29/06 12:15 PM, "Duane Fischer, W8DBF" <dfischer@usol.com> wrote:

> 
> 
> I trust that Michael Salmons is alive and well, and just too busy to respond
> to e-mail.
> 
> I need to speak with you Michael, so send me a private note and tell the
> best day and time to call.
> 
> Thanks.
> 
> Duane W8DBF
> 
> _______________________________________________
> Home: http://mailman.qth.net/mailman/listinfo/vintage-audio
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer@usol.com ** 

