Capacitor in series with mid-bass -anyone else seen this?

Ian J · 23rd January 2012, 04:25 PM

Was checking out an old pair of Goodmans Maxim 2 yesterday - they had been on my mom's stereo since about '87. Noticed v high dc resistance on one so took it apart expecting a loose connection. After removing the xo board attached to the bottom of the cab it became apparent that a 450mF cap was in series with the mid-bass! This has to be for dc protection surely, but I've never seen it before. The maxim2's were a hi-fi starter speaker with some pretension for sound quality - surely the negative of affecting the SQ outways the benefits of saving them from the small chance of an amp frying them? Any one else seen this in a commercial model?

Osvaldo de Banfield · 23rd January 2012, 04:48 PM

Which is the speaker impedance?

Ian J · 23rd January 2012, 04:51 PM

well the mid-bass unit on its own is quite high - about 7 ohms if I remember correctly.

Osvaldo de Banfield · 23rd January 2012, 05:01 PM

If as you tell me the impedance of the spk is about 7ohm, this is a high pass filter with one real pole at 101.05 hz, so the speaker can receive those frequencies below with attenuation augmenting 6db each time the frequency goes down an octave. This apparently is wright.

Good luck !!!

sreten · 05:26 PM

Hi,

I presume you mean a 470uF capacitor. Yes it has been done before.
KEF used it a lot. Basically you add a series capacitor to a sealed
box with a Qbox of around 1. The capacitor reduces the peaking
somewhat, extends the bass a little and does give DC protection
and some subsonic protection also.

Nice little speakers, used them a nearfields on a desk in a studio.

Probably worth replacing the bipolar electrolytics, try
Falcon Acoustics | The Leading DIY Speaker Parts and Kit Supplier since 1972
Make up the 470uF with a 450uF bypassed with 20uF.

rgds, sreten.

http://www.humblehomemadehifi.com/do...20Box_copy.pdf

I've also modelled it in the free demo version of Basta! and it does work.

23rd January 2012, 04:25 PM	#1
Ian J diyAudio Member Join Date: Feb 2003 Location: Oxford, England	Capacitor in series with mid-bass -anyone else seen this? Was checking out an old pair of Goodmans Maxim 2 yesterday - they had been on my mom's stereo since about '87. Noticed v high dc resistance on one so took it apart expecting a loose connection. After removing the xo board attached to the bottom of the cab it became apparent that a 450mF cap was in series with the mid-bass! This has to be for dc protection surely, but I've never seen it before. The maxim2's were a hi-fi starter speaker with some pretension for sound quality - surely the negative of affecting the SQ outways the benefits of saving them from the small chance of an amp frying them? Any one else seen this in a commercial model? __________________ 'We demand guaranteed, rigidly defined areas of doubt and uncertainty!' - Douglas Adams

23rd January 2012, 04:48 PM	#2
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	Which is the speaker impedance? __________________ A veces pongo un circo y me crecen los enanos... "Que se llama soledad", Joaquin Sabina, el capo.

23rd January 2012, 04:51 PM	#3
Ian J diyAudio Member Join Date: Feb 2003 Location: Oxford, England	well the mid-bass unit on its own is quite high - about 7 ohms if I remember correctly. __________________ 'We demand guaranteed, rigidly defined areas of doubt and uncertainty!' - Douglas Adams

23rd January 2012, 05:01 PM	#4
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	If as you tell me the impedance of the spk is about 7ohm, this is a high pass filter with one real pole at 101.05 hz, so the speaker can receive those frequencies below with attenuation augmenting 6db each time the frequency goes down an octave. This apparently is wright. Good luck !!! __________________ A veces pongo un circo y me crecen los enanos... "Que se llama soledad", Joaquin Sabina, el capo.

23rd January 2012, 05:14 PM	#5
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, I presume you mean a 470uF capacitor. Yes it has been done before. KEF used it a lot. Basically you add a series capacitor to a sealed box with a Qbox of around 1. The capacitor reduces the peaking somewhat, extends the bass a little and does give DC protection and some subsonic protection also. Nice little speakers, used them a nearfields on a desk in a studio. Probably worth replacing the bipolar electrolytics, try Falcon Acoustics \| The Leading DIY Speaker Parts and Kit Supplier since 1972 Make up the 470uF with a 450uF bypassed with 20uF. rgds, sreten. http://www.humblehomemadehifi.com/do...20Box_copy.pdf I've also modelled it in the free demo version of Basta! and it does work. __________________ There is nothing so practical as a really good theory - Ludwig Boltzmann When your only tool is a hammer, every problem looks like a nail - Abraham Maslow Last edited by sreten; 23rd January 2012 at 05:26 PM.


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