Apologies if this has been asked before somewhere earlier.
What happens at the speaker terminals of an amp when a Sub is wired to a Sub out on the amp where the amp applies a crossover filter to the signal before it is sent for amplification and thence to the speaker terminals, diverting the low frequencies away to the Sub line level out jack on it?
Is any boost then applied to the frequencies that do pass to the speaker terminals? If not, does the fact that amp power is not needed for the low frequency signal result in a higher dB level for the remaining frequencies that are amplified and passed to the speaker terminals such that these sound louder than when there is no Sub present?
I'm not sure where you want to go with this question...
No boost is applied highpassed signal for the speakers.
The sub has its own amp (active sub) and the sub has a volume control, so if configured correctly, the volume of the sub matches that of the speakers.
The sub has its own amp (active sub) and the sub has a volume control, so if configured correctly, the volume of the sub matches that of the speakers.
Right; so all one has to do is to match volume levels manually?
Well, there are some more settings.
Crossover frequency:
You can choose the crossover frequency on your receiver. If you have small speakers with little low range, you want to set it at 100 or 120hz or even higher, so the sub takes over all frequencies below that. If you have large speakers, you want to set it to 80hz.
The sub itself also has a crossover frequency button, however you should NOT use it if you already set the crossover with your receiver. Turn it all the way open.
Phase:
The sub may also have a phase button, to "align" the phase of the sub to the speakers.
If the sub and speakers are out of phase, the frequencies at the crossover will sound weak, because they cancel each other out. In this case you want to adjust the phase, until the the frequencies at the crossover sound loudest.
Location:
The location of the sub will have a huge impact on the sound. The "best" location is usually where the sound is loudest.
However location may also cause a spike or dip in specific frequencies, which is not ideal.
So try different locations and figure out which one is best in your situation.
In reality you probably have only very few locations where you have space to actually put the sub though :).
There are many sites with much more information, so maybe you want to take a look there. I had fun writing this though ;).
Thanks for all of that, my question was only about volume levels though. It arose from a discussion elsewhere about whether the amp, no longer having to power the lower frequencies, would cause slightly elevated sound levels for the remaining ones than when a Sub is not in the mix, at the same volume control setting.
I get that notwithstanding the answer to the above, the sound levels from the main speakers and from the Sub would still have to be manually matched.
It arose from a discussion elsewhere about whether the amp, no longer having to power the lower frequencies, would cause slightly elevated sound levels for the remaining ones than when a Sub is not in the mix, at the same volume control setting.
No. If you were playing a 1kHz test-tone the sound from the speakers wouldn't change.
But, if you crank it up to the point of clipping (distortion) the main channels can actually go louder (without distortion) if they don't have to reproduce the bass.
Things get "more interesting" with DVD or Blu-Ray and home theater receivers... The ".1" channel is the LFE channel for "Low Frequency Effects". That means ONLY booms, vibrations, and explosions. The normal musical bass, etc. exists in the 5 (or 7) main channels. So by default none of that regular bass goes to the subwoofer. If you have full-range main/surround speakers those speakers will reproduce the regular bass.
If you mix-down to stereo, the 5 (or 7) channels are mixed-down, but the LFE is NOT used. You still get the normal bass but the LFE information is lost.
Since most people have smaller main/surround speakers home theater receivers have something called "bass management". That will remove the normal bass from the 5 (or 7) channels and send ALL of the bass to the sub. On my receiver there is a setting for "small" or "large" speakers and if you select small all of the bass is re-routed to the sub.
Thank you for the responses.