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Old 2nd February 2015, 03:16 PM   #1
kuer is offline kuer  Canada
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Default Passive subwoofer power ?

I have a 1978s passive subwoofer, non-powered, M&K 12" volkswoofer, hooked to speakers B output of a 2ch amplifier, A output is used for main speakers. functionally it is ok.

But the problem is subwoofer sounds too tiny accordingly, seems no subwoofer at all. When I turn off the main speakers, I can hear the bass out of the subwoofer, and the bass is up with the amp volume turning up.

Does this subwoofer need a dedicated amp to pump up? or what can I do for this subwooer if I want to obtain adequate bass?

Thanks.
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Old 2nd February 2015, 03:29 PM   #2
18Hurts is offline 18Hurts  United States
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The reason you can't hear the sub is an efficiency miss match with the mains.

Generally speaking, subwoofers are not as efficient as main speakers so running them passively will show this. To get an idea, run one channel with the sub only and the other with the regular speakers and adjust the balance between channels to get it to what you want. If the balance control is pushing the sub with more power than the mains, that would indicate you need either a more efficient sub, add more subs, EQ the sub, less efficient mains or running an amplifier to the sub and boost the power.

I used a passive subwoofer 25 years ago--it blended well because it was slightly more efficient than the mains and was loaded in a corner to increase the loading. The passive crossover cut the mains at around 70Hz from what I measured so it worked fine. Much, much, MUCH easier to have an electronic crossover, phase control and amp gain to do the same thing but with better results.

Good luck!
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Old 2nd February 2015, 03:37 PM   #3
AndrewT is offline AndrewT  Scotland
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Some low bass speaker drivers are very inefficient.
80dB to 85dB/W @ 1m is common.
Satellite/main speakers are commonly 85dB to 90dB.
That means the low bass speaker generally needs 5dB more power (nearly 4times) to get the same SPL.
It can be even worse if the low bass has rolled off due to using a small box to get the price of the speaker down. 10times as much power is not that uncommon.
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Old 2nd February 2015, 04:14 PM   #4
kuer is offline kuer  Canada
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Join Date: Jul 2014
Quote:
Originally Posted by 18Hurts View Post
The reason you can't hear the sub is an efficiency miss match with the mains.

Generally speaking, subwoofers are not as efficient as main speakers so running them passively will show this. To get an idea, run one channel with the sub only and the other with the regular speakers and adjust the balance between channels to get it to what you want. If the balance control is pushing the sub with more power than the mains, that would indicate you need either a more efficient sub, add more subs, EQ the sub, less efficient mains or running an amplifier to the sub and boost the power.

I used a passive subwoofer 25 years ago--it blended well because it was slightly more efficient than the mains and was loaded in a corner to increase the loading. The passive crossover cut the mains at around 70Hz from what I measured so it worked fine. Much, much, MUCH easier to have an electronic crossover, phase control and amp gain to do the same thing but with better results.

Good luck!
Quote:
Originally Posted by AndrewT View Post
Some low bass speaker drivers are very inefficient.
80dB to 85dB/W @ 1m is common.
Satellite/main speakers are commonly 85dB to 90dB.
That means the low bass speaker generally needs 5dB more power (nearly 4times) to get the same SPL.
It can be even worse if the low bass has rolled off due to using a small box to get the price of the speaker down. 10times as much power is not that uncommon.
Thank for your replies. Yes, it's all about the efficiency. Now I know that a dedicated amp can be used with the passive subwoofer with no issue.

Just pulled out an unused vintage HK amp and connected to the subwoofer to power it seperately. Woo, for music it's fantastic, I will never use it for movies anyway. can't believe this subwoofer sounding, made 30+ years ago, is still tight, smooth and fast. That saves this "juck".

Thanks again.
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Old 4th February 2015, 04:29 PM   #5
kuer is offline kuer  Canada
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Previosly I used Y split from cd player to main amp and subwoofer amp, although the sound was nice, there was some noise out of main speakers.

Today, use a pair of rca cable from main amp's Tape-out (no pre-outs) to subwoofer amp's AUX in, everything seems perfect now.

Very happy. but this way ( using Tape-out or pre-out) is good way to connect? Thanks.

Last edited by kuer; 4th February 2015 at 04:32 PM.
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Old 5th February 2015, 07:53 AM   #6
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
Tape Out usually has a much higher output impedance than Pre-out.

If you are using the Tape Out ONLY for a bass only channel, then the loss of treble due to the higher output impedance is irrelevant.
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Old 5th February 2015, 04:34 PM   #7
kuer is offline kuer  Canada
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Quote:
Originally Posted by AndrewT View Post
Tape Out usually has a much higher output impedance than Pre-out.

If you are using the Tape Out ONLY for a bass only channel, then the loss of treble due to the higher output impedance is irrelevant.
Thanks, Andrew.

Just for bass output. When I did it, I was thinking of this matter. Wonder if I could find a special adapter (or something like that) to split the main amp pre-out? one connection is for subwoofer amp, the other for the main amp itself.
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