Subwoofer Connection.

[rollo]

Well for years my sub was connected to the output of my preamp via ICs. One output from the Pre is for the amps and the other for the sub. At the request of an Engineer who visited my home for our meeting suggested that I try running the sub off the speaker terminals in lieu of the Preamp. His reasoning was that when both components draw from the Pre together neither get the proper signal. So without all the engineering stuff that I DO NOT understand, I tried it today.
   Results were more dynamics and a tighter and focused bass line. I had tried this before connecting from the amp directly to the sub. However there was a hum of hums present so that idea did not even have a chance. So went back to the old set up. The desired polarity is now easier to discern. I cannot believe I thought the bass was OK until the change.
   So boys if you do not do this already give it a try you will be happy happy happy. Have fun.



charles 

[rollo]

Oh I almost forgot a high pass filter for the amp was his other suggestion since I do not want an active crossover. Both my main speakers and sub have a 24db slope.


charles

[BobM]

Your sub has to be able to take a high level input to do this. Normally an RCA line out from the pre to the sub is a low level input signal, just like what comes out of a CD player and such. Connecting a sub to the amp speaker terminals (or from the speaker terminals themselves) delivers a signal much different from those RCA's and usually requires 3 wires (R+, L+, and one of the - from either R or L).

This is the common hookup for REL subs.

One question I always had though, since my pre inverts phase ... do I hook the sub up as A or B, below?

(A) R+, L+, and one -
(B) R-, L-, and one +

Of course there's a phase switch on the sub that lets me invert it if necessary, but since the pre inverts phase I always wondered which one actually makes sense from an engineering prospective (I always just used A).

[bacobits]

I have always connected my sub through the speaker terminals.
I invert phase on the sub via the switch.

When I had my Audible Illusions M3a it inverted so I just changed my main speaker wires.
So does the MFA MagusB I had.
The Sub again, I inverted phase via the switch.

I have the 24db slopes on the crossover. I have to cross over pretty high round 55hz otherwise it pressurizes the room too much and will jitter my cartridge on the turntable. Lower you wont hear it as much as you will feel it. It is nice to have a 12" sub working but might be overkill for the size of my room right now.


Den

[BobM]

The crossover point on a sub is always a matter of contention. If you look at any of the crossover graphs on Stereophile reviews you will see that crossover points start dropping early, forming a V shape when you look at the individual drivers. But when you sum both drivers it looks smooth without that notch.

So crossover points on a sub should be lower than the drop off point of your regular bass driver, otherwise you sill get an unnatural loading at those low frequencies in the room.

Use the volume control on the sub to adjust the balance between the 2 drivers. Bottom line, if you can hear the sub and tell it's on and where it kicks in then it is probably not adjusted correctly. It should be a semaless extension of the regular bass driver.

The other lie that I found when adjusting my sub is that of corner loading. This always seemed to overload the room in my experience and produce muddy (but deep) bass. I found it better to have the sub somewhere between the speakers on that front wall. My REL is down firing, which worked nicely enough, but I got a big boost in seamlessness when I turned it upside down and had the driver firing upwards. I put a board on top with something to weigh it down. Of course the volume needed to be turned up a tad to compensate for the lack of corner loading, but the integration is phenominal (thanks Charles for this suggestion long ago - it definitely worked for me).

[rollo]

Your sub has to be able to take a high level input to do this. Normally an RCA line out from the pre to the sub is a low level input signal, just like what comes out of a CD player and such. Connecting a sub to the amp speaker terminals (or from the speaker terminals themselves) delivers a signal much different from those RCA's and usually requires 3 wires (R+, L+, and one of the - from either R or L).

This is the common hookup for REL subs.

One question I always had though, since my pre inverts phase ... do I hook the sub up as A or B, below?

(A) R+, L+, and one -
(B) R-, L-, and one +

Of course there's a phase switch on the sub that lets me invert it if necessary, but since the pre inverts phase I always wondered which one actually makes sense from an engineering prospective (I always just used A).

Bob if your pre inverts phase do you reverse the phase at your main speakers ? If so do same for sub. BTW the REL is passive or active ? Your losing me with the third wire. Would that be for ground loop issues ?
    There is a sure fire way to set the polarity of the sub. Here goes. Reverse the polarity of the main speakers. Leave sub connections as is and play a test record tone with a bass line then adjust the subs phase [ polarity] to when you hear no bass. [ you will need someone to adjust the phase as you listen]. When the bass cancels out ju got it . Give it a try .


charles

[BobM]

The REL is active and it has 2 ways to connect. Low level RCA signal from the pre, and high level 3 wire from the amp speaker terminals. You can't connect your low level RCA sub input to the amp speaker terminals or it will probably fry it.

The 3 wire is L+, R+ and common ground - so you get both channels summed. This is particular and fairly standard to a high gain sub input.

[rollo]

The REL is active and it has 2 ways to connect. Low level RCA signal from the pre, and high level 3 wire from the amp speaker terminals. You can't connect your low level RCA sub input to the amp speaker terminals or it will probably fry it.

The 3 wire is L+, R+ and common ground - so you get both channels summed. This is particular and fairly standard to a high gain sub input.

HMMMMMMMM, very interesting. The ol ground wire eh, no shoot. My Carver has either IC or speaker term connections, go figure. I tell ya man since connecting from the speaker binding posts to the sub after using the IC connector from the Preamp there is no going back. Huge difference for the better for me.


charles

[jcoat007]

Oh I almost forgot a high pass filter for the amp was his other suggestion since I do not want an active crossover. Both my main speakers and sub have a 24db slope.


charles

Did you ever try the high pass filter?  I am wondering how this would work if your mains and your sub are running off of your amp.  Wouldn't the high pass filter take out the low level information so the mains and the sub would only get the highs? 

[TomS]

Just a caution to be REALLY careful connecting subs this way (particularly +r, +l, and common grounds).  Some power amps have floating or bridged outputs (typically connected between the left and right hot outputs) that will not like having their low side speaker outputs tied together or even a single to negative connection to ground through the sub amp itself.