Sub advice

[matt the cat]

I have been happily using a pair of 300w speakers on stands for a while now as most of my work is in average size pubs.

I have a few jobs coming in from a local WMC which has a large room (150-300 people) and a fantastic proper old fashioned stage, i have done 1 gig in there and the sound wasnt too bad (i went on the dance floor at its busiest) but as im going to be there a lot more im looking at purchasing a Sub.

My question is do i need two Subs or is one enough? i have seen one for sale nearby (600W passive) but having never used a sub before im not even sure what leads i need?

My speakers are passive and connected by speakon from the amp but if i connect a sub do i connect it from one of my speakers and if so does it matter which one or do i connect it straight from the amp

I know i sound like an idiot but im not a techno head and have only just worked out Sky +

[WWDJ]

There is no right or wrong on this as there are many ways to swing a cat (pun intended)

There are 2 routes you can go. Active or Passive.

If you go the Active route, the amp is already built into the Sub, so you need to split the signal before it gets to your current amp or route a line level signal from your current amp if it has such output. This will connect to the input on the amp which will then amplify the bass. Do not connect an amplified signal to the input on an Active Sub.

If you go the Passive route ideally you need 2 things in addition. Some sort of crossover to split the bass and other frequencies as the other thing you will need is an additional amp to drive the bass. You could in theory drive all the speakers from one amp, but you are increasing the load on the amp which will make it run hotter and more likely to overheat if you are pushing it hard.

On the subject on one sub or 2. I ran one for a while perfectly fine and I now run 2 so either is fine, it depends whether you like the tops over subs look or are happy with it looking unbalanced symmetrically and whether you want the extra volume/expense.

It also depends on how much space you have to carry subs and how loud the subs are, as to what you need.

[Excalibur]

My aversion to active speakers is well known, but: For people wishing to dip a toe in the water with one sub, it's an ideal way. One passive sub is tricky.

Right, options in order of simplicity. :
1) One active sub. Mixer outputs L and R into sub, both hi outs from sub back to inputs of existing amp. Simples. ( Except a few active subs don't have hi outs. Only a few )

2) Two active subs. Mixer left to left sub, right to right sub, corresponding hi outs back to existing amp.

3) Two passive subs. Two choices here. If the subs have an internal crossover, connect the amp outputs to the sub inputs, and the hi outs from the subs to the tops. It works, it's simple, but it's not the best way.
The best way. Active crossover, as below, sub amp not bridged.

4) One passive sub. In this case it's very tricky to use one amp only ( and a very bad idea ) so for prerefence we need an active crossover ( Behringer CX2310 or similar ) and a second amp. Run mixer outs into crossover, hi outputs from here into amp driving tops. Lo outs into sub amp inputs, amp run in bridge mode. ( if the amp can't run at 2ohms per channel, don't connect a 4ohm sub up like this, it has to be 8ohms. Don't ask why, just believe it )

As a very very rough guide ( cue someone pointing out you can't hear watts ) the output of your sub(s) ought to be twice that of the tops.

That should do to be going on with, hope I made it fairly simple.

[matt the cat]

Cheers guys for some great advice, i have a second amp which has only been used twice so guess i will be using it a lot more often now

[Dynamic Entertainment]

Matt...chuck up a bit of info on the makes and models of your gear and we can go from there...not much else to add right now as Peter and Daves posts were bang on.

[addoaddo]

Although for sound you only need one sub as generally there is no directional sound at these frequencies most people use two as it looks more balanced even though they often use them in mono
You will need a crossover somewhere in the system to remove all the higher frequencies. Active, (power speakers) will normally have this in. Some seperate amplifiers like the Yamaha also have this built in to the amp.
Alternatively your mixer may have a Sub out.

If you do only get one speaker, run the amp in bridge mode and conenct the two inputs to the amp to your normal LR signals.

As for power it depends on the efficency of both sets of speakers but the sub generally has to be more powerful than the rest of the sytem.

[djeddie]

...If you do only get one speaker, run the amp in bridge mode and conenct the two inputs to the amp to your normal LR signals...

I don't know of any amp that will 'mono' the signal inputs when in bridge mode. Every amp I've ever known will use either channel input as the bridge input.

[Excalibur]

If you do only get one speaker, run the amp in bridge mode and conenct the two inputs to the amp to your normal LR signals.
.

Well yes, but: If you were to buy a big 4ohm sub, and connect it to a bridged amplifier not rated to run at 2ohms per channel, then the result would be excessive heat and a burning smell. And it could be even worse. I'm repeating myself here, but it bears repeating. Hence why I advocate only bridging amps if you're well up on the subject. There are pitfalls for the unwary.

I don't know of any amp that will 'mono' the signal inputs when in bridge mode. Every amp I've ever known will use either channel input as the bridge input.

It's taken me three goes to understand that. I think what you're referring to is that while the amplifier outputs are summed, the inputs may not be , thus the signal could only be from one audio channel.
However, all may not be lost. Mixers such as the Denon X-500 have a dedicated sub output, which is summed already. Most active crossovers have a summed sub output which could be used. And the simplest and cheapest option is a cable where the left and right channels are joined into one connector, along the lines of http://cpc.farnell.com/pulse/pls0012...-2m/dp/AV18928 depending of course on what connectors you're dealing with on your equipment.

And finally, bear in mind that even if you were only to amplify the low frequency output of one channel, it's quite likely that the outcome will sound fine.

[djeddie]

It's taken me three goes to understand that. I think what you're referring to is that while the amplifier outputs are summed, the inputs may not be , thus the signal could only be from one audio channel.

You're kind of on the right lines. But the outputs of a bridged amp are not summed, they are the inverse of each other.

When bridging an amp Channel A, for instance, becomes the input and the Channel B input connector is bypassed, the Channel B gain is "hard wired"* to full and the input to Channel B is fed the phase inverted signal from Channel A. The speaker is then placed between the Channel A and Channel B positive outputs. So instead of the output signal modulating* around 0V the output signal is the difference between the two output signals.
Technically speaking an amplifier in bridge mode 'should' produce four times the output into double the impedance but due to current limiting of the power supply will normally produce twice the power into double the impedance of the single channel.
For instance, a 100W at 4Ω per channel amplifier should be able to produce 400W at 8Ω, but usually will be 200W at 8Ω

I've put that in layman's terms and sincerely hope I'm not trying to teach anyone to suck eggs.

* - for want of a better phrase.