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Speaker Level Inputs

post #1 of 12
1/6/13 at 7:27pm
Thread Starter 
I'm a bit confused about speaker level inputs on a sub. I recently bought a surround bar that has a passive wired sub. In reviews of the unit, there have been references made to replace the passive sub with a larger powered sub that has speaker level inputs to improve the bass performance. If the sub out on the surround bar is powered, such is the case with mine, to power a passive sub, wouldn't it be wrong to route this to the speaker level inputs as aren't they powered on an active sub as well?
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post #2 of 12
1/6/13 at 8:05pm
Subs can have both a speaker-level input and a pre-amp (line level) input. What exactly do you have?
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post #3 of 12
1/6/13 at 9:12pm
You can surely add a second sub with the current subwoofer , using the speaker wire from the surround bar that goes to the "subwoofer". I would not remove the current "sub" as it is most likely be a woofer than a subwoofer, removing it might (read as would) create whole in the frequency response. Just make sure the sub you buy has speaker level inputs.
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post #4 of 12
1/7/13 at 1:30pm
Thread Starter 
Quote:
Originally Posted by lovinthehd View Post

Subs can have both a speaker-level input and a pre-amp (line level) input. What exactly do you have?

It has both. I'm told by several people to use the speaker level, but that concerns me.
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post #5 of 12
1/7/13 at 1:31pm
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Quote:
Originally Posted by qguy View Post

You can surely add a second sub with the current subwoofer , using the speaker wire from the surround bar that goes to the "subwoofer". I would not remove the current "sub" as it is most likely be a woofer than a subwoofer, removing it might (read as would) create whole in the frequency response. Just make sure the sub you buy has speaker level inputs.

If the replacement sub has a high enough cross over point, that does not concern me.
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post #6 of 12
1/7/13 at 3:44pm
Quote:
Originally Posted by bluemark81 View Post

It has both. I'm told by several people to use the speaker level, but that concerns me.
Speaker level is used if you have a stereo receiver that does not have an LFE output. If you have an x.1 receiver use the LFE output to a line level input on the sub.
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post #7 of 12
1/8/13 at 9:03am
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

Speaker level is used if you have a stereo receiver that does not have an LFE output. If you have an x.1 receiver use the LFE output to a line level input on the sub.

I know that is what is suggested, but somehow I guess I'm not understanding the internal circuitry. If I use the speaker level inputs, this must bypass the subs own amp because my soundbars sub terminals are amplified. Is that the case?
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post #8 of 12
1/8/13 at 9:13am
Quote:
Originally Posted by bluemark81 View Post

I know that is what is suggested, but somehow I guess I'm not understanding the internal circuitry. If I use the speaker level inputs, this must bypass the subs own amp because my soundbars sub terminals are amplified. Is that the case?
Powered subs often have speaker level inputs to allow them to be used when there is no line source available; they're not there to allow the sub to be run as a passive. It's easy enough to test, see what happens if you turn the sub amp off.
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post #9 of 12
1/8/13 at 9:21am
As usual, what bill says. As I understand it, in effect, the first thing the speaker level input to a powered sub "sees" is a resistor to keep the current that would be supplied at speaker impedances from overloading the input section of the sub's amplifier. So the input stage in essence converts the speaker level signal into a line level signal so that the amplifier inside the sub can deal with it.
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post #10 of 12
1/8/13 at 11:23am
Quote:
Originally Posted by JHAz View Post

As usual, what bill says. As I understand it, in effect, the first thing the speaker level input to a powered sub "sees" is a resistor to keep the current that would be supplied at speaker impedances from overloading the input section of the sub's amplifier. So the input stage in essence converts the speaker level signal into a line level signal so that the amplifier inside the sub can deal with it.
+1. Transformers might be used as well, I've never looked at the circuitry to see what they do.
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post #11 of 12
1/9/13 at 6:03pm
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

Powered subs often have speaker level inputs to allow them to be used when there is no line source available; they're not there to allow the sub to be run as a passive. It's easy enough to test, see what happens if you turn the sub amp off.

So, if my soundbar has a sub output power of 100 watts for the passive sub that came with it, and I end up purchasing an active sub with 500 watts to replace it, am I still getting 500 W out of the sub?
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post #12 of 12
1/9/13 at 7:34pm
Quote:
Originally Posted by bluemark81 View Post

So, if my soundbar has a sub output power of 100 watts for the passive sub that came with it, and I end up purchasing an active sub with 500 watts to replace it, am I still getting 500 W out of the sub?
Yes, because the output of the soundbar amp is moot, you're not driving a speaker with it. But I'd still drive the sub with the receiver LFE output.
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