[Vintage-Audio] Dual Voice Coil For Woofer?

[Duane Fischer]

Bob, 	
	
Makes sense to me. Thanks!	
	
FYI: The two Advent 2002 speakers have been reconed and are ready to come
home. Now I have to get a ride to go get them. They should sound nice in
harmony with the woof woof!	
	
Duane W8DBF	


----------
From: wolfbob <wolfbob at csnsys.com>
To: Vintage home and professional audio equipment from 1975 back
<vintage-audio at 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 at usol.com>
To: "Vintage home and professional audio equipment from 1975 
back" <vintage-audio at 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 at yahoo.com>
> To: Vintage home and professional audio equipment from 
> 1975 back
> <vintage-audio at 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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