SUB input speakers in vs line level - AVS Forum
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post #1 of 5 Old 10-01-2012, 10:08 PM - Thread Starter
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Dear AVS Forum,

I have read certain articles about subwoofers and have learned a lot of therical basics. The problem is that when i want to confirm the theorical with the practice i've found some diferences. Explanation:

At the following link (i think it;s a good reference for newbies):

Speaker-level inputs
If you have an older receiver and subwoofer combination that doesn't offer an LFE connection, then you can also use speaker-level inputs. They also bypass the receiver's built-in crossover and send an amplified signal to your subwoofer. Just hook up your sub from your receiver's front left and right speaker outputs using ordinary speaker cable. This will be a full-frequency signal, but the sub's built-in filter will block the higher frequencies. Then, connect your stereo speakers via the subwoofer's speaker-level outputs. Your sub will pass on the unfiltered, full-frequency signal. If your sub does not have speaker-level outputs, you can wire the sub and stereo speakers in parallel using your receiver's speaker terminals.

Just keep in mind that you will be sending an amplified signal from the receiver, which will be reduced to line-level by the sub, then amplified again by the subwoofer amp, so this isn't an ideal way of doing things. This method should only be used if you can't make either an LFE or un-filtered line-level connection.


Two main issues:

1. If i connect as said the sub's built in filter (crossover potentiometer), the stereo speakers will only be sending mid to high frequencies (the unfiltered). So my question is, if i am connecting speakers with these specifications:

Tweeter1" (25mm) polyurethane dome
Woofer6 1/2" (165mm) injection-molded polypropylene/graphite cone, with integral Santoprene™ surround
Frequency Response 55Hz - 20kHz ±3dB

This speaker will not be able to reproduce the midbass frequencies because they have been filtered by the active sub, so in this case i assume this connection is not the best because i am missing some frequency range of the speaker. Am i right?


2. The article mentioned that the speaker level input will be reduced to line level by the sub and then amplified again. I have connected the input and output speakers at my sub. I found that if i power off my sub, the speakers output keep playing. So, my question is, if i power off my sub the speakers output should be disable? because if the sub made the speaker to line level convertion it should need the power from the sub to amplified the signal. Am i right?

I really want to clear all this doubts to make sure which connection is the best and will gives me the best performance. Hope somebody with more experience could help me.

CHeers!
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post #2 of 5 Old 10-02-2012, 06:26 AM
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Quote:
Originally Posted by franciscom View Post

Dear AVS Forum,
I have read certain articles about subwoofers and have learned a lot of therical basics. The problem is that when i want to confirm the theorical with the practice i've found some diferences. Explanation:
At the following link (i think it;s a good reference for newbies):
Speaker-level inputs
If you have an older receiver and subwoofer combination that doesn't offer an LFE connection, then you can also use speaker-level inputs. They also bypass the receiver's built-in crossover and send an amplified signal to your subwoofer. Just hook up your sub from your receiver's front left and right speaker outputs using ordinary speaker cable. This will be a full-frequency signal, but the sub's built-in filter will block the higher frequencies. Then, connect your stereo speakers via the subwoofer's speaker-level outputs. Your sub will pass on the unfiltered, full-frequency signal. If your sub does not have speaker-level outputs, you can wire the sub and stereo speakers in parallel using your receiver's speaker terminals.
Just keep in mind that you will be sending an amplified signal from the receiver, which will be reduced to line-level by the sub, then amplified again by the subwoofer amp, so this isn't an ideal way of doing things. This method should only be used if you can't make either an LFE or un-filtered line-level connection.

Two main issues:
1. If i connect as said the sub's built in filter (crossover potentiometer), the stereo speakers will only be sending mid to high frequencies (the unfiltered). So my question is, if i am connecting speakers with these specifications:
Tweeter1" (25mm) polyurethane dome
Woofer6 1/2" (165mm) injection-molded polypropylene/graphite cone, with integral Santoprene™ surround
Frequency Response 55Hz - 20kHz ±3dB
This speaker will not be able to reproduce the midbass frequencies because they have been filtered by the active sub, so in this case i assume this connection is not the best because i am missing some frequency range of the speaker. Am i right?
2. The article mentioned that the speaker level input will be reduced to line level by the sub and then amplified again. I have connected the input and output speakers at my sub. I found that if i power off my sub, the speakers output keep playing. So, my question is, if i power off my sub the speakers output should be disable? because if the sub made the speaker to line level convertion it should need the power from the sub to amplified the signal. Am i right?
I really want to clear all this doubts to make sure which connection is the best and will gives me the best performance. Hope somebody with more experience could help me.
CHeers!

no you are not right. The sub converts the signal to line level for purposes of feeding it to the sub's monophonic apmlifier. It passes the speaker level signals straight through, with prehaps a high pass filter applied. Your receiver's amps still power the left and right speakers.
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post #3 of 5 Old 10-02-2012, 10:56 AM - Thread Starter
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thank you JhAZ for your repply,

Let me understand it. So what you said is that my amp will still power the speakers output connected to the subwoofer by passing the speaker signal but the important thing is that the sub internally filters a high pass through it? So is not a full range signal? If you are telling me this, i would prefer a connection directly from my amp to the speakers (covering a full frequency range) and the sub will be connected via a line level.

Thanks for all.
Cheers!
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post #4 of 5 Old 10-02-2012, 12:56 PM
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Originally Posted by franciscom View Post

thank you JhAZ for your repply,
Let me understand it. So what you said is that my amp will still power the speakers output connected to the subwoofer by passing the speaker signal but the important thing is that the sub internally filters a high pass through it? So is not a full range signal? If you are telling me this, i would prefer a connection directly from my amp to the speakers (covering a full frequency range) and the sub will be connected via a line level.
Thanks for all.
Cheers!

Depends onthe sub but I think most with high level speaker outs filter. Could be wrong. You can google your sub and find out. But the problem if you add a sub to a full range system is that wherever the (unnown, can't trust the manufacturer'sspecs especially once the room is factored in) and the subs overlap you'll have bloated too loud sound and the deeper bass will appear to be turned down compared to (lets say) midbass.
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post #5 of 5 Old 10-02-2012, 02:48 PM
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I had a listen to a cabasse santorin 25 using high level inputs and the sub sounds punchier but wont go quite as deep as when it would be in the normal lfe output.
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