Efficiency of Two Speakers in Series - Page 2

AndrewJ · 2nd May 2002, 12:55 AM

It looks like this question is destined to be asked and addressed forever and ever, but here is my contribution again

AudioFreak is absolutely correct from a theoretical point, assuming closely spaced drivers at low frequencies, where the wavelength is large relative to the spacing, and the drivers themselves are non directional. This applies in practice to typical drivers at frequencies below around 200Hz.
P.Lacombe is correct in a more detailed analysis where account is taken of spacing and directivity, ie in the region above around 200Hz. However I would take some issue with his statement that the full 3db is rarely achieved. I believe it is at low frequencies.
If we ignore off axis performance, then I can readily show with measurements that the on axis response of a pair of series connected drivers is identical to that of a single driver both in sensitivity and frequency response, given a constant input voltage, and +6dB for parallel connection. This would mean that I get very close to the +3dB efficiency increase at low frequencies.

AudioFreak · 2nd May 2002, 02:30 AM

Quote:

Originally posted by Electro
No, putting two speaker drivers in series will not give you an increase in SPL but a decrease in SPL.

Practical terms, assuming 1W/1M efficiency, it stays the same @ low frequencies and close proximity.

Assuming the 2 drivers are identical or close to it, putting drivers in series shouldnt hurt the sound badly.

mrfeedback · 2nd May 2002, 03:07 AM

Two bass drivers in proximity will increase overall efficiency due to nearfield coupling.
Four drivers is even better - witness a Marshall Quad box - these are sensitive and go REAL loud.
Wiring two voice coils in series destroys damping.

Regards, Eric.

AudioFreak · 2nd May 2002, 03:25 AM

mr. feedback, you are correct regarding damping, it will more or less kill it but then again it wouldnt be worse than running off some of the tube amps available as far as damping factor goes.

mrfeedback · 2nd May 2002, 03:33 AM

True - I meant to add that this lack of damping may or maynot be a good thing.

Eric.

Won · 2nd May 2002, 05:26 AM

Hm. So, what would the best way to wire up 6 speakers then? Also, there is no passive crossover (as I mentioned, biamping), so concern towards that is misdirected. I would also like to avoid using a transformer.

I don't really believe that speaker 1 acts as a crossover element to speaker 2 if they are connected in series, and I'm pretty sure that they will be more or less in phase. Also, I'm fairly certain that damping would not be "killed" but only suffer a little.

The fact that the overall Qes will change does seem valid, and I will look into that.

I suppose I should just have a little amp for each driver, then?

Unfortunately, that isn't going to be a solution that I will pursue. Yet.

-Won

planet10 · 2nd May 2002, 06:34 AM

Another phrasing with a twist:

You get a 3dB increase, whether wired in series or parallel, because you are doubling the radiating surface.

Now if you have a SS amp that almost doubles its power into 4 ohms vrs 8 ohms then you gain another 3 dB if you parallel them, -3dB if you series them. (most home theatre amps and other cheap gear will not -- often these units put out less power into 4 ohms [or just blow-up]).

If you have a tube amp, you change the taps you are using so you get no gain (or loss) in power.

dave

AudioFreak · 2nd May 2002, 06:37 AM

i think this thread is destined to go on and on forever .... i stated the above differences in efficiency in the 2nd post of this thread....

2nd May 2002, 06:34 AM	#17
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III	Another phrasing with a twist: You get a 3dB increase, whether wired in series or parallel, because you are doubling the radiating surface. Now if you have a SS amp that almost doubles its power into 4 ohms vrs 8 ohms then you gain another 3 dB if you parallel them, -3dB if you series them. (most home theatre amps and other cheap gear will not -- often these units put out less power into 4 ohms [or just blow-up]). If you have a tube amp, you change the taps you are using so you get no gain (or loss) in power. dave __________________ community sites t-linespeakers.org, frugal-horn.com, frugal-phile.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

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2nd May 2002, 12:55 AM	#11
AndrewJ diyAudio Member Join Date: Sep 2001	It looks like this question is destined to be asked and addressed forever and ever, but here is my contribution again AudioFreak is absolutely correct from a theoretical point, assuming closely spaced drivers at low frequencies, where the wavelength is large relative to the spacing, and the drivers themselves are non directional. This applies in practice to typical drivers at frequencies below around 200Hz. P.Lacombe is correct in a more detailed analysis where account is taken of spacing and directivity, ie in the region above around 200Hz. However I would take some issue with his statement that the full 3db is rarely achieved. I believe it is at low frequencies. If we ignore off axis performance, then I can readily show with measurements that the on axis response of a pair of series connected drivers is identical to that of a single driver both in sensitivity and frequency response, given a constant input voltage, and +6dB for parallel connection. This would mean that I get very close to the +3dB efficiency increase at low frequencies.

2nd May 2002, 03:07 AM	#13
mrfeedback diyAudio Member Join Date: Feb 2002 Location: Perth, Australia.	Two bass drivers in proximity will increase overall efficiency due to nearfield coupling. Four drivers is even better - witness a Marshall Quad box - these are sensitive and go REAL loud. Wiring two voice coils in series destroys damping. Regards, Eric.

2nd May 2002, 03:25 AM	#14
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	mr. feedback, you are correct regarding damping, it will more or less kill it but then again it wouldnt be worse than running off some of the tube amps available as far as damping factor goes.

2nd May 2002, 03:33 AM	#15
mrfeedback diyAudio Member Join Date: Feb 2002 Location: Perth, Australia.	True - I meant to add that this lack of damping may or maynot be a good thing. Eric.

2nd May 2002, 05:26 AM	#16
Won diyAudio Member Join Date: Nov 2001 Location: Cambridge, Mass	Hm. So, what would the best way to wire up 6 speakers then? Also, there is no passive crossover (as I mentioned, biamping), so concern towards that is misdirected. I would also like to avoid using a transformer. I don't really believe that speaker 1 acts as a crossover element to speaker 2 if they are connected in series, and I'm pretty sure that they will be more or less in phase. Also, I'm fairly certain that damping would not be "killed" but only suffer a little. The fact that the overall Qes will change does seem valid, and I will look into that. I suppose I should just have a little amp for each driver, then? Unfortunately, that isn't going to be a solution that I will pursue. Yet. -Won

2nd May 2002, 06:37 AM	#18
AudioFreak Warp Engineer On Holiday Join Date: Oct 2001 Location: Queensland, Australia	i think this thread is destined to go on and on forever .... i stated the above differences in efficiency in the 2nd post of this thread....