Sirch Sound Posted February 3, 2008 Share Posted February 3, 2008 Hey, this is probably a fairly simple question but im being very stupid about it. I am basicaly looking at getting a sub package. This includes 2x 18 inch and 2x 15inch. However I can get the 18" subs in both 4 and 8 ohms and the 15inch in 8 ohms only. Would it be worth getting the 4 ohm 18inch and the 8ohm 15inch? Would this then take my system down to 2ohms and therefore needing a smaller amp or is it not possible to match 2 different independances? Also these cabs are 600w rms each cab, so 1.2kw rms per side, should I be looking at an amp putting out around 1.5kw rms per side oris this still a bit small? Cheers Rich Link to comment Share on other sites More sharing options...
Shez Posted February 3, 2008 Share Posted February 3, 2008 Can you explain how you're planning on driving these? It sounds like you want to connect a 15 and an 18 in parallel on each side of one amp. If this is the case, you really should be thinking about having a crossover in there somewhere. Unless one or both cabs have crossovers built in of course... Bit more info needed. Link to comment Share on other sites More sharing options...
themadhippy Posted February 3, 2008 Share Posted February 3, 2008 keep it all at 8 ohms,makes the maths simpler if nothing else,2 8 ohms in parallel gives 4 ohms,4 8 ohms in parallel = 2 ohms, a 4 and 8 ohm cab in parallel will give around 2.6 ohms, 2 of each will take you down to 1.3 ohms Link to comment Share on other sites More sharing options...
Trunker Posted February 3, 2008 Share Posted February 3, 2008 ....a 4 and 8 ohm cab in parallel will give around 2.6 ohms....... Plus you have the resistance of the cable run from your amp to your speaker cabs. Link to comment Share on other sites More sharing options...
Rob_Beech Posted February 3, 2008 Share Posted February 3, 2008 ok 2.60003 then. Come on it is al theoretical anyway, the impedance is an active measurement rather than passive resistance, it alters with frequency amongst other things. It's simply a general idea. Are you running these from 1 amp, ie the 18 and the 15 on 1 channel, and the same on the other channel? I'd probably want slightly different settings for the different subs, but I am picky. Link to comment Share on other sites More sharing options...
Sirch Sound Posted February 4, 2008 Author Share Posted February 4, 2008 Are you running these from 1 amp, ie the 18 and the 15 on 1 channel, and the same on the other channel? I'd probably want slightly different settings for the different subs, but I am picky. Yes, I was planning on runing an 18 and a 15 of one channel, linked in paralell. Yes I would like a bit more controll with these cabs, however I dont really have the money, hence the reason I just want to run them off 1 amp. They do have active crossovers built in, however is there anyway possible of running these cabs with 1 amp and still being able to use a crossover? Or is two amps the only way. I would like a bit more adjustability than just using the built in crossovers, however dont really have the budget to be buying 2 amps. CheersRich Link to comment Share on other sites More sharing options...
MarkPAman Posted February 4, 2008 Share Posted February 4, 2008 You can run the 18"s on one side of the amp & the 15"s on the other, provided the amp is happy with 2 Ohms for the 18"s (& 4 Ohms for the 15"s). Depends on how important you think stereo is, for subs I don't usually think it's that important. Link to comment Share on other sites More sharing options...
Rob_Beech Posted February 4, 2008 Share Posted February 4, 2008 If you have an active crossover that has enough features to allow you to do it, and you don't mind your subs being in mono. You can use one channel of the amp to drive a pair of 18's and 1 channel to drive a pair of 15's with a different input signal from a different output on your crossover. Even the Behringer DCX2496 allows you to do this without any effort at all. Simply setup the crossover so input A is left and input B is right. Output 1 for the 18's output 2 for the 15's and 3 and 4 for your tops. (3 4 5 6 for your tops if they are biamp).You'd need to make sure that outputs 1 and 2 both took a summed signal from A+B to allow any LF content from left AND right gets to them. Then adjust the crossover settings to taste, perhaps with the 18's providing a slightly lower extension and with the 15's with a small peak in the upper bass area for that kick, but rolling off earlier than the 18's. Also remember that if the drivers are mounted differently (ie one is reflex the other horn loaded etc, or even just stepped back a few inches) you'll benefit from the delay function in the crossover aswell. The tops then take the left OR right signal. Rob Edit : Beaten to it by Mark. In this instance I'd always go for 8ohm boxes all around. But some amps will still drive the 2ohm load, it is just giving them alot to do. Link to comment Share on other sites More sharing options...
Sirch Sound Posted February 4, 2008 Author Share Posted February 4, 2008 Ok. Cool well I have a dbx drivedranck, not the pa I hasten to add! So basically I need to chip out a little more for a slightly more powerful amp and run in 4 ohms, so the amp isnt working quite so hard. Cheers for all the helpRich Link to comment Share on other sites More sharing options...
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