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Does the amp "see" the subwoofer?

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Posted on March 3, 2017 at 13:54:30
Raymond Leggs
Audiophile

Posts: 748
Joined: November 25, 2007
 When you have a passive sub and you run the amp through the X-Over and out to the speakers does the amp "see" the subwoofer as a load between the speakers?

 

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RE: Does the amp "see" the subwoofer? , posted on March 4, 2017 at 04:41:18
Dave_K
 If its a passive sub, the amp is powering the subwoofer, so of course it sees it as a load.

If it's an active sub with a high level crossover, and you are running the main speakers through its high pass filter, then the amp sees a different load from the main speakers due to the high pass filter.

If you're running the main speakers full range, and you run an extra pair of cables to the high level inputs of an active subwoofer (ala Rel) the amp doesn't really notice the sub. There's a teensy bit more capacitance from the extra cables, but it's miniscule compared to the load of the speakers.

 

My amps have been looking for a sub-woofer for years..., posted on March 3, 2017 at 18:17:22
Ivan303
Audiophile

Posts: 48887
Location: Cadiere d'azur FRANCE - Santa Fe, NM
Joined: February 26, 2001
 They ain't found one yet!




First they came for the dumb-asses
And I did not speak out
Because I was not a dumb-ass

 

Absolutely, posted on March 3, 2017 at 14:52:02
E-Stat
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Posts: 37673
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 Every speaker is a load to some amp.

I trust you refer to attaching both speaker leads first to the sub where it's crossover "keeps" the low frequencies and sends the high pass signal to the main speakers.

 

RE: Absolutely, posted on March 8, 2017 at 11:15:32
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 Yes of course... If you are driving "through" the Sub's speaker connection it is loaded buy the combination of the Passive (Speaker Level) High-pass filter built into the subwoofer, and the Load of the loudspeaker connected to it. That means the possibly inexpensive Choke/Cap filter is right there in circuit with the main speaker.

That is why it is preferable to use the line level input to a sub and the receiver/preamp's line level HP crossover. Though since these are in two different components it is likely that they are not optimized for each other.
A stand alone crossover - or tuneable Bass management or DSP crossovers it likely to yield optimum results.

Because of room response irregularities - actual optimization is best left to measurements or by ear.


"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: I should add..., posted on March 9, 2017 at 12:01:38
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 There are a few plate amp subs that pass the signal full range at the speaker level. Then the 10kOhm or so amplifier input impedance is all the driving amplifier "sees"




"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: Absolutely, posted on March 3, 2017 at 15:39:15
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 I could be wrong, but I understand the INPUT impedance of speaker level inputs of a sub are very high.
Too much is never enough

 

RE: Absolutely, posted on March 3, 2017 at 18:33:17
FenderLover
 I would imagine an amp "sees" all speakers attached to its input. Isn't this why speaker's impedance should match the amp's output impedance?

Now, if that were an active sub-woofer, attached to the output of the pre-amp or gain section of the amp... maybe not. At least not the secondary windings of the OPT.

 

RE: Absolutely, posted on March 3, 2017 at 19:08:07
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Sub connected by speaker level wiring doesn't consume much / any real power. That tells me very high input impedance. At least this is true with powered subs.
SS amps are theoretically best with the Lowest output impedance. That measure drives damping factor on which most modern speakers thrive.

I'm speaking to active subs.

When speaker level was mentioned, I was thinking (dangerous at best of times) that this was as opposed to line level inputs.
Too much is never enough

 

RE: Absolutely, posted on March 4, 2017 at 08:07:16
E-Stat
Audiophile

Posts: 37673
Joined: May 12, 2000
Contributor
  Since: April 5, 2002
 At least this is true with powered subs.

Which is not the case here. The amp is driving the passive sub.

 

RE: Absolutely, posted on March 4, 2017 at 10:11:49
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Yes, I re-read the original post and I'm not on track.
Too much is never enough

 

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