Choosing a Subwoofer

Looking for some simple advice here. Following my Ear Fatigue thread that morphed into a philosophy - technique - advice column I’m looking to get my hands on a subwoofer. My setup at the moment is a Focusrite feeding signals to two JBL LSR305’s. I know I need an active sub (or do I?), which means I have to get a sub that receives its signal from the Focusrite, and then in turn provides signals to the JBL’s. Do I have that correct?

And while browsing the literally thousands of subs out there, I see a bunch of subs that have inputs, but speaker terminal outputs. Some of these subs are listed as studio subwoofers. Is it possible to use these subwoofers in my setup, or should I specifically aim for ones with XLR input and outputs?

Thanks in advance for the good advice I know I will get!

I also have a set of the JBL LSR305’s and I love them… I even love them for general music listening. I settled on these because they seemed to get very good reviews and they were in the range of my rather limited budget. I’m not really sure I need a sub, but I’d be interested to hear about any affordable options that might be out there. It doesn’t make sense for me to pay $400 for a sub when my monitors only cost about $250 for the pair. :slight_smile:

I got my JBL’s from a local store after trying to buy some Mackies. The guy in charge of the sound room told me to read some reviews because as he put it “we barely get a chance to put the JBL’s on display because they sell so fast”.

Have you had any luck with subs? I’m currently scouring the second hand sites to see if there’s anything there.

I’ll preface my remarks with, I was schooled in @madpsychot 's Ear Fatigue thread too and am still learning a bunch myself.

The JBL site lists the frequency response of the JBL LSR305 to be 43Hz - 24kHz. If you want to hear anything below 43Hz, you’ll need a sub. My M-Audio BX5’s are only rated down to 56Hz, so it is more of an issue for me…

To answer your questions about the inputs and outputs, most subs will have a line input which is generally used for a dedicated subwoofer output from a preamp or receiver that would limit the signal to 80 hz and down. This is especially prevalent in 5.1 or 7.1 systems, where the ‘.1’ is the sub channel information.
If you had an interface with a line level subwoofer output you would use that. If you don’t, you use speaker cables as the input, and bridge out to the monitors. In this case, the sub is getting a full range input, so you use the crossover adjustment on the sub to blend it with the low frequency capabilities of your monitors, and try to make sure the sub is set so it extends the low end of your monitors without doubling anything. Read the specs of your monitors carefully; if they are 43hz to 20khz ± 1db, your sub needs to only add 40hz and down. If they are ± 3 DB or more, the sub will need to be crossed over at 80 to 100hz., and be adjusted to the right volume level for a flat eq curve, or as close as you can get in your room.

Sorry to sound dumb, but I’m going to ask anyway…

My interface simply has outputs (multiple to take care of surround sound setups. It has no subwoofer output, so if I was to hook up a sub to another output, I would simply be routing full audio to the sub.

The subs with dedicated XLR and balanced TRS ins and outs are easy to understand.

For the subs that simply have speaker terminals as their ins and outs I’m curious of this routing:

I would take the output of my interface, and feed the subs inputs with those wires. I would then take the outputs of the sub, and in turn feed each monitors inputs with those wires. Is that correct? The sub would get full audio, to which I can adjust the crossover point to get bass coming out of the sub, and the rest of the frequencies coming out of the monitors. So my question is this: how would I take an XLR connector coming out of my interface, and the route that wire to speaker terminal inputs on a sub? Is this not taking a balanced output from the interface and turning it into an unbalanced signal in the sub?

This is confusing me somewhat, as there are quite a few “studio” subwoofers that seem not to have XLR inputs at the back, and rather having speaker terminal connections.

You will need to avoid using any speaker level connections on a sub since your current monitors are internally powered and don’t provide a way to output a speaker level signal.
If the sub has rca (unbalanced), TRS or XLR (balanced) input you can use another output from your interface and route full spectrum audio to it. The sub will have an internal crossover that filters out high frequency signals.
Another option is to use a y cable that splits the signal and routes one to the outputs to your JBL and the other to the sub.

Exactly right, I wasn’t aware the JBLs were powered. It’s okay to send full range to the sub from the interface, you just adjust the crossover down to where you’re extending, not doubling what the JBLs are already giving you. Sorry if I added to the confusion. In my setup, I use an audio receiver to drive my monitors, so the speaker outputs of the receiver go to the sub first, then out of the sub to the monitors. In your case that won’t work.

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Thanks @JayGee - this is exactly my though but needed it confirmed. I’m got to be looking for a sub with XLR inputs and outputs. I can route an output from the interface to a subwoofer, but the thought of having to adjust the mix bus to take care of an extra output is not something that appeals to me.

Hey Bob, would you mind explaining this statement? I don’t see a “±” anywhere on my monitor specs, just the 56Hz-22kHz Frequency Response.

To have accurate specifications, speakers need to give you the variance on the level of all frequencies. If a speaker is down 6db at 43HZ compared to where it is at 1Khz, then it is not really displaying a flat response. Most speakers will give you their response as + or - 3db, so you know that it is relatively accurate within the listed range. If it doesn’t, then you really don’t know how accurate it will be. JBL is a very good line, I’m sure they list it somewhere.

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Anyone have any experience with the Monoprice 10-inch Powered Studio sub? It has both XLR and TRS in’s and out’s and looks to be quite affordable at about $220.