8 Ohm speaker with 4 ohm subwoofer?


I run Spendor s3/5r's using the 8 ohm posts on a Jolida tube and have just purchased a Rel q108e which according to the Rel specs runs at 4 ohms. I planned on running the subwoofer directly to the same 8 ohm speaker level inputs on the amp, but now I am worried that may not work because of the ohm difference. Please help so I can decide if I need to cancel the order quick.
j_goughnour
I'm not particularly familiar with that REL model, but I believe that what you would be connecting to the Jolida would be the inputs to the amplifier that is built into the REL, and that the input impedance of the REL's amplifier is something like 100K ohms.

Assuming that is correct, the Jolida would see a totally insignificant load presented to it by the REL, and it is only the amplifier built into the REL that would see the 4 ohm impedance of the subwoofer driver.

Assuming my understanding of the subwoofer configuration is correct, you have no problem at all.

Regards,
-- Al
I have 2 REL Stadium subs and Al's explanation is correct from my experience of them. You have nothing to worry about.
Thank you both for your help!
So when you hook up a sub this way, the amp has no extra load on it? What happens to the amplified signal once it gets to the high level input?
So when you hook up a sub this way, the amp has no extra load on it? What happens to the amplified signal once it gets to the high level input?

That is correct with respect to most or all of the REL subwoofers, when their high level inputs are used. I wouldn't necessarily generalize to other designs.

When the amplified signal gets to the high level input, it goes into the sub's own amplifier, which at its front end has an active stage presenting a very high input impedance (i.e., essentially no load) to whatever is driving it. The high input impedance means that negligible current is drawn by the sub from the external power amp -- the sub's power amp is responding to the voltage going into it, but doesn't require significant current or power. It's just like a line level input going into a preamp or power amp, except that the voltage levels are higher.

The main speakers provide the proper 8 ohm loading to the external amplifier, and the sub's driver provides the 4 ohm loading to the OUTPUT of its internal amplifier, and everything's cool!

What should NOT be done, however, would be to at any time have the external power amp connected to the sub without the main speakers also being connected. Some amps can be damaged, or have their long-term reliability degraded, if they are operated without a speaker load.

Regards,
-- Al
Ok thanks, maybe you could help with a problem I'm having. I'm also trying to hook a sub up to my Jolida 202a ( which is what led me to this thread ) My sub is an older energy with high level in but no outputs. I have speaker wire going from the 8ohm taps to my main speakers ( Fostex Fe1262 single drivers ) then a second set of speaker wire going from the 8ohm taps to the sub. However as soon as the wire to the sub is connected I get a low hum out of the right channel. I'm wondering if I'm putting too much of a load on the amp? Any help would be appreciated.
Rdylan -- Assuming the Energy sub is a powered sub, with a built-in amplifier, and the inputs are high-level/high impedance (rather than speaker-level/low impedance), you are not putting too much of a load on the amp. The REL's are like that, but I have no knowledge of how the Energy's are/were designed.

If the Energy is designed like that, then I would think the hum is due to a grounding problem. If either the Jolida or the sub have 2-prong plugs, try reversing their orientation. If they are 3-prong, try floating one or both of them with a 3-prong to 2-prong adapter (leaving the ground unconnected). Also, try plugging them both into the same outlet or power strip, if they presently are not.

Hope that helps,
-- Al