Help on connecting an active subwoofer QTX sound QT18SA.

[DJ Max]

Hi, I have a Numark Mixdeck Express with 2 sets of phono outputs a 1 set of XLR outputs. I am using one set of phono to power an amp and a pair of passive 15” speakers on stands. I am planning to purchase an active subwoofer which is this one
http://www.whybuynew.co.uk/speakers/...w-dj-disco.htm
I know it’s not the best and (figures are way out) but reviews are good and it’s in my price range and it’s also for occasional use.
My problem is that I’m not sure how to connect it as it only has 1 XLR input. Can I just use one of the xlr’s from the mixdeck to sub? Will this work properly as only receiving one signal? Do I combine left and right output to single input into sub? I thing this will turn everything to mono, am I correct?
Any ideas will be appreciated and thanks in advance.

[DJ Jules]

The bigger issue you have here is that if you're introducing a sub to handle the lower frequencies, you should filter those frequencies away from your Ecko tops. Bass isn't really stereo (the human ear can't discern the direction of low frequencies so there's no point in it being stereo), so in theory you could run the sub off one of the XLR outputs. However, knowing the makeup of the Mixdeck (the XLR outputs are just wired in parallel with the phono ones), this will probably mean a slight reduction in output to the phono channel (meaning you're going to end up with lopsided output to the tops).

You've got a few options:

1. Either you're going to need two subs (assuming that the QTX sub has a high pass output) and you'd run the XLR outputs from the Mixdeck to the sub, and then on to your amp and tops - as you've got passive tops and an active sub, this means running signal cables out to the sides and the back to the amp in the middle again so it's less than ideal. Also, I suspect you don't want to fork out for two subs.

2. You're going to need a crossover to filter the low frequencies off the amp and tops. This is the better option (and not a lot of money) and how it should be done. The signal would come out of the XLR's on your Mixdeck, into the cross over, the cross over would then combine the low frequencies into a single output and filter them off the outputs to your tops. You'd then feed both the sub, and your amp from the Crossover.

3. You can run "cheap" (and :censored - Do what you originally proposed and connect the sub to the XLR output on the Mixdeck. The Low frequencies will run to both the sub and the tops, meaning you might get some odd things sound wise where the subs and tops either cancel each other out or add to each other, but if you really don't have the budget (and/or aren't bothered about how it sounds) then you'd probably get away with it. As I said above though, just watch out that adding the sub doesn't reduce the output to your tops (or if it does, rebalance the two channels using the gain controls on the amp).

Julian

[Excalibur]

Must type faster, Jules has got it bang on. There are other possibilities, but not cheap, and not pretty. Crossover's best idea, this is a good alternative, esp the Alto sub. I like mine.

Two QTX subs, or one Alto TS15 sub. Two channels, no joiners, splitters or resistors. Sadly, at least £100 dearer. Ah well.

[DJ Max]

Julian, thank you for your detailed reply. Option 1 is not ideal as don’t have the money and room to store a second sub. Also I think that the output on the subs is only a link and not filtered but I know what you mean and a good idea!!
I might start with option 3 first and add a cross over if doesn’t sound ok. I have noticed a mono/stereo switch on the mixdeck and I could use mono to balance the outputs a little. I should hope that the QTX active subs have a build in crossover to cancel the high/lows. I know that it’s not ideal and doesn’t act like a crossover but I have a spare small mixer which I can connect in line between the mixdeck and the tops amplifier and lower the bass from the tops that way. Thanks again.

Must type faster, Jules has got it bang on. There are other possibilities, but not cheap, and not pretty. Crossover's best idea, this is a good alternative, esp the Alto sub. I like mine.

Two QTX subs, or one Alto TS15 sub. Two channels, no joiners, splitters or resistors. Sadly, at least £100 dearer. Ah well.

You are always praising those Alto’s! If I could afford one of them I would buy one! Less clutter and would be tidier!!

[Excalibur]

Julian, thank you for your detailed reply.

It was good advice, Max. I concur with it.

Also I think that the output on the subs is only a link and not filtered

Well done Max, I think you're correct. Initially, I was sure that the variable filter was applied to the output, but now I don't think it is. When all else fails, read the manual It appears to simply alter which frequencies the sub delivers. Not perfect for what you require.


Right, here's a potted treatise on speakers, crossovers, and subs.
Low frequencies are hard to produce, need lots of power therefore, and can " muddy " the higher frequencies being produced in a speaker. The laws of physics ( which incidentally, ye cannae change ) dictate that for best results, low frequencies need large drivers, high frequencies need smaller drivers. The more drivers you can have in a system, the better, as each one has its own little job, reproducing a narrow band of frequencies.
That's why, for best sound quality, sending the low frequencies to subs gives the tops an easier life, and let's them work better, as they now have a smaller range to reproduce. Also, speech/vocals don't work well with drivers above 12".

That's wildly shortened, but illustrates the basic principle. Modern kit with electronic effects tries to get round this to some extent.

Thus, option 3 probably isn't ideal, as the tops are still running full range. On occasion, in the DJ world, this can work well, I've done it before for certain types of function. I know it's more costly, but the crossover option is head and shoulders above every other. The Alto or other twin channel sub is almost as good. Have a look for a s/h one on ebay maybe?




Praising Alto kit? It does what it says on the tin, but not a lot more. Won't fill wembley stadium, but will entertain fifty to a hundred folk in a village hall just fine.

[DJ Jules]

Thus, option 3 probably isn't ideal, as the tops are still running full range. On occasion, in the DJ world, this can work well, I've done it before for certain types of function. I know it's more costly, but the crossover option is head and shoulders above every other. The Alto or other twin channel sub is almost as good. Have a look for a s/h one on ebay maybe?

I'm working tonight in a club that ran for many years with the bass filtered off the bins, but the tops running full range. The previous DJ thought they'd get more bass out of the whole rig this way, but in reality it just made the tops sound really bad, and made the bass response really unpredictable. Changing a couple of cables and playing with the crossover point made the whole thing sound a lot sweeter.

Praising Alto kit? It does what it says on the tin, but not a lot more. Won't fill wembley stadium, but will entertain fifty to a hundred folk in a village hall just fine.

I quite like the Alto kit for sound, but I've anecdotally heard bad things about reliability and customer service. If you want a cheap option that will deliver (and if your amp is up to the job), it's probably best to look for passive subs with a built in crossover - I'd expect you to be able to pick up a pair of something reasonable for not a lot of money - but you would need a pair as you can't really run one side with a sub and one side without.

Switching the mixdeck to Mono will get you round any issues with bass beats being missing if they're delivered through one channel only, but you might still find you have issues with lopsided output that you'll have to compensate for at the amp. The only way to really know for sure is to try it as it really depends on the impedance of the outputs on the mixdeck and on the inputs on the amp and sub.

Julian

[DJ Max]

Thanks all for your professional advice and for sharing your opinions (much appreciated).
I have been experimenting this evening and remembered that I have a small 10” active sub with my home cinema system which has one phono input. I connected this sony sub and can honestly say that although it’s small it made a huge overall improvement and worked nicely connected to one phono channel of the mixdeck. The sound became close to the way I would like it to be. I will definitely add a sub to this system and in the future a crossover too.

[DJ Max]

Praising Alto kit? It does what it says on the tin, but not a lot more. Won't fill wembley stadium, but will entertain fifty to a hundred folk in a village hall just fine.

I have invested in a used Alto Active 15 Sub which I received yesterday but still waiting for the correct cables to arrive.

[Excalibur]

I have invested in a used Alto Active 15 Sub which I received yesterday but still waiting for the correct cables to arrive.

Good man. I'm sure it will do the job admirably.

[DJ Max]

Good man. I'm sure it will do the job admirably.

I have Pm you - hope that you don't mind.