Splitting a pre-amp channel for sub - good or bad?

Makes sense, thanks for the clarification

10-29-12: Hockey4496
What does that have to do with the question?
Hockey4496 (Threads | Answers | This Thread)

A lot of people read these threads from all over the world. I want them to know there are other options out there. Also, a lot of these threads go into the archives for future reference to help others.

The one I used for an example, can even use speaker level inputs, if the user would choose to. This might be an option for you in the future, if you buy another subwoofer. Too many companies are just giving line level inputs, like Klipsch. Not everyone that uses a subwoofer is running a home theater type of system, and a receiver, or surround processor, with subwoofer outputs. Stereo preamps with a subwoofer outputs, are not common.

What does that have to do with the question?

In addition to my prior post, if adding a subwoofer to a preamp that even has a subwoofer output, with no impedance changes to play games with the signal, still can degrade the sound.

The bass from a sub could mask the midrange and highs easily. Even more so, if you don't set it up right. So do some serious comparisons with, and without it (during and after setup), to see if hear anything that can sound like it is taken away. This can be due to the sub possibly masking, or overpowering, the good part that you are hearing, in comparison to not using it. Other distortions from the added sub, or bass vibration in the room, can exist too.

These companies that make subwoofers, should use amps that are more versatile. Not everyone has a receiver with a subwoofer output. I've seen cheap under $200 subwoofers, with left and right line level inputs, and left and right speaker level inputs in the past. They could have the company that makes their amps (if they don't) supply this type of inputs. I think the speaker level inputs have a high enough input impedance, that the system may not know it's hooked up.

I have an older HSU, beside getting good reviews, it performed as promised. It went down close to the frequency specified,when tested. I don't know about their (HSU) newer ones made nowadays to say anything on promised specs. A lot of other companies promised to go down to a certain frequency, but fell about a full octave short. One was a JBL (I believe) that fell short by about 10 decibels (at -3 db, or -6 db) when tested. That's about an octave less than promised. I only use mine on occasion, to see if I'm missing anything on some new recordings I buy.

There doesn't seem to be many tests done on subwoofers. This lower priced HSU subwoofer has the type of inputs, that makes it easier to hookup. No specs for impedance that I can find though. This variation of hookup options, is a good selling feature in my opinion. It would be nice if the companies read these type of forums, and give their customers a product they could work with, a lot easier. It sure wouldn't hurt for some of these companies, to get more informed. Also, it wouldn't cost them much at all, for them to give these types of inputs, in my opinion.

Consider a sub crossover. Discontinued NHT X2's and Paradigm X-30's are getting hard to find. Bryston 10B Sub's are expensive. There's a European company called Reckhorn that makes something rather unusual, if it's available for US voltage.

Thanks guys, very helpful.

Al- very nice explanation, sounds like you've had a physics class or two before :)

Not a good idea in this particular case. As we discussed in one of your other recent threads, you may already be approaching the point of impedance incompatibility between the preamp and amp. If you split the signal it is likely to make that situation considerably worse.

The input impedance of your sub does not appear to be specified, but line-level input impedances of powered subs are commonly in the 10K to 30K area, sometimes as low as 5K. The preamp will see a load impedance equal to the product (multiplication) of the input impedances of the sub and the amp, divided by their sum. For example, if the sub's input impedance is 20K it would combine with the 33K input impedance of the amp to produce an overall load impedance seen by the preamp of (20 x 33)/(20 + 33) = 12.4K, which is probably too low for the AES preamp, assuming that it uses an output coupling capacitor.

Member Bifwynne resolved a comparable problem very nicely, at modest cost, by using a buffer stage custom made for him by Tom Tutay. Search his posts for more info on that.

Also, driving the sub with just one channel is not a recipe for good sonics. The two channels should be summed together into a mono signal, either by the sub if it provides that capability, or if not then in the buffer stage.

Regards,
-- Al

Splitting is commonly done and typically does not degrade sound quality
Alan

Splitting the channel will work. I'm doing it because I use a tripath amp. You will see a slight lessining in gain.
I'm using a Lightspeed Attenuator and lost less than one hour of gain on the volume knob.
If you listen at 11 o'clock before the split. You might have to go to 12 o'clock after the split.
I didn't notice any degradation in dynamics or attack, just in gain.
I know every system is different, so it might be different in your system.
Good luck and let us know how it works out for you.