Subwoofer Advice

[Megamix]

I'm thinking of adding a single active subwoofer to my passive 15" cabinets.
My speakers weigh 25kg and I don't really want to buy anything much heavier.
Would a 12" subwoofer (e.g. db Technologies Sub12 Active Subwoofer) be OK or do I need 15"?
I'm just after a wee bit more bass - only small venues

[TONYTIGER]

I'm thinking of adding a single active subwoofer to my passive 15" cabinets.
My speakers weigh 25kg and I don't really want to buy anything much heavier.
Would a 12" subwoofer (e.g. db Technologies Sub12 Active Subwoofer) be OK or do I need 15"?
I'm just after a wee bit more bass - only small venues

It would be helpful if you post the details of your passive cabs,make and any technical information you have as one 12" might not keep up with them.

[yourdj]

Hia, There are a few post recently on this matter that will help.

Maybe not mine as its for satellites, but i did one post on a compact powerful sub and someone else in the last week or two (i think):

check this selection out however - nice range:

http://www.thomann.de/gb/active_subwoofers.html

[Megamix]

It would be helpful if you post the details of your passive cabs,make and any technical information

Thanks Tony, yes of course, Warrior PSR15 Speakers and QSC RMX 850 Amp

[Tom]

Being 15" drivers, they should produce quite a bit of bass already. The cab has a max calculated spl of 129db.

The PSR15 already go down to 40hz, where as the SUb12 also goes down to 40hz. The Sub12 can only give 127sb spl output. At what peak that is I don't know but I don't think it will give you what you are after.

[Megamix]

fair enough Tom - I am relatively pleased with the Warriors (for what I paid) - just looking to keep improving on sound quality

[csg]

also bear in mind that just adding a subwoofer to play alongside full range speakers may result in less bass, not more...

might seem strange, but when 2 different speakers that are not of the same design, nor designed to work together are playing the same frequency range, differences in the phase and time domain response may cause the output from one to cancel out the output from the other...

so, try before you buy!

[yourdj]

also bear in mind that just adding a subwoofer to play alongside full range speakers may result in less bass, not more...

might seem strange, but when 2 different speakers that are not of the same design, nor designed to work together are playing the same frequency range, differences in the phase and time domain response may cause the output from one to cancel out the output from the other...

so, try before you buy!

Is that the reason for a reverse phase switch then? How do you know there is problem - is there a delay in the bas and top end?

[csg]

well, not really. Phase reverse switches are usually there to correct phase reversed leads or reverse wired equipment ( some older, usually american equipment was wired pin 3 hot instead of pin 2 hot that is the convention)

phase differences between different loudspeaker designs are rarely 180 degrees out of phase, and will change in angle difference depending on the frequency in question. As such it is very difficult to correct the difference over a range of frequencies.

This in itself can produce very boomy or un-even bass as some frequencies are produced in-phase, so will sum, whereas others will be produced out of phase so will cancel.

so, in short, try before you buy, and in preference either get more of the same, or invest in some subs that can produce all your bottom end, and use an active crossover to prevent two differing systems from producing the same frequencies and therefore introducing issues

[Digital Jack]

Another thing worth mentioning is the fact that phase problems can arise if you vary the distance between sub and main speakers.
For example , run your main speaker whilst it is 18'' from your sub and have a listen.
Now move your sub 36'' away from your main speaker , if you don't notice the change in response you shouldn't be in charge of pa equipment.
It is instances such as this that the phase invert switch helps too.

Try to picture ripples on a pond in relation to sound waves in the air.
Oh this is so frustrating , I know how it works I just can't put it into words.