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Old 16th April 2008, 05:37 PM   #1
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Default Mono subwoofer on stereo amplifier possible?

Hello everybody,

I've got a question and i hope there is somebody who can help me. I've got an
little Dynacord PA set. The amplifier has an output capacity of 2x 400 Watt
continous @ 4 Ohm. This amplifier drive's 2 "satellite" speakers with 10" woofers
and 1" drivers.

I would like to add ONE subwoofer to this set, so i'm looking for a passive filter
that will "combines" the low frequencies for both channels. The higher frequencies
(from approx. 125Hz) must be stereo!

When i was searching the internet, i found an Dynacord LM15-1 subwoofer. This woofer
does the same what i want, but Dynacord doesn't build them anymore. But in the datasheet
off this speaker i found a schematic diagram.

It says that both channels are combined but have it's own coil, like this:


Channel A: -----Coil 6.8mH-----+
...........................................+
...........................................+
...........................................+----- To subwoofer
...........................................+
...........................................+
Channel B: -----Coil 6.8mH-----+


I would like to know if this design works, and if so, if it works without afecting
the stereosignals for the satellite speakers?

Are there any other designs?
Sorry for my bad English!

Here you'll fine a datasheet of the Dynacord LM15-1 subwoofer:
Dynacord LM15-1
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Old 16th April 2008, 10:22 PM   #2
Netlist is offline Netlist  Belgium
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Default Re: Mono subwoofer on stereo amplifier possible?

Quote:
Originally posted by Audio Johnny
I would like to add ONE subwoofer to this set, so i'm looking for a passive filter
that will "combines" the low frequencies for both channels. The higher frequencies
(from approx. 125Hz) must be stereo!
This design seems to have been developed to do exactly what you want. I can't do the math for you and the -3db point seems a bit lower in the graph but I can see no reason not to try it.

/Hugo
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Old 16th April 2008, 11:19 PM   #3
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I would like to try it, but the coils are not cheap ( 34,50 each). I'm gonna try it, but does this solution not "destroy's" the quality of the sound? Thank you and sorry for my bad english!
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Old 16th April 2008, 11:21 PM   #4
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What about a dual voice coil woofer?
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Old 16th April 2008, 11:27 PM   #5
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And don't forget some variable resistance element to pad sound levels to match satellite to subwoofer....very pricey for high power levels and that is the Achilles heel of this setup.
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Old 16th April 2008, 11:35 PM   #6
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I would like to buy a subwoofer with has the same finishing as the satelite speakers. A dual cone woofer doesn't fit in this housing (T&S parameters) and i dind't find a SERIOUS dual cone speaker, only brands like carpower, monacor etc.

The satelite speakers aren't so powerfull, so the pad resistors doesn't need to be heavy types.

Thank you for all your responds and sorry for my bad english!
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Old 17th April 2008, 03:19 PM   #7
bjorno is offline bjorno  Sweden
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Quote:
I would like to know if this design works, and if so, if it works without afecting the stereosignals for the satellite speakers?
Yes, it will work with blameless drawbacks for the mains if you choose a sub driver, derived from the known sensitivity of your mains and a suitable driver Re (somewhere between 4 and 8 Ohm) to hit targeted XO frequency.

The sensitivity of the bass driver should be a couple of dB higher (calculations are needed).
See submitted pictures where you can find that with the given components, you obviously should use an 8-Ohm type of driver.

The series LCR network in parallel with the driver must be used for best integration performance (low VSWR).

b

1(2)
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File Type: gif 1-sum_bass.gif (32.1 KB, 275 views)
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Old 17th April 2008, 03:21 PM   #8
bjorno is offline bjorno  Sweden
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2(2)
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File Type: gif 2-sum_bass.gif (32.4 KB, 242 views)
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Old 19th April 2008, 06:45 PM   #9
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Sorry for this late reaction. I would like to thank Bjorno for his measurments! It has take a couple of day's before i understand everything, but i'll think that 2 coils are a good solution for my problem! I would like to thankt everybody for his reply!
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Old 21st April 2008, 11:31 PM   #10
Thawach is offline Thawach  Thailand
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bjorno your pics are good. u try and try to explain. but i try to see and see your explain. i think the pics are good sometime i will copy it for explain to someone in thailand. but now i'm afraid of your licence.LOL i think again...oche when i copy u cannot see. LOL


Audio Johnny u can try this circuit. but i think that why the 6.8 mh is expensive very much. but it's easy to made.

Thanks for my super guy that try and try/
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