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Croosover info required

  • Pro Audio
  • Audio
Last response: in Home Audio
June 4, 2010 11:54:11 AM

hello i have a pair of 2 x 15 em series martin audio bass cabs and a pair of em 12 inch cabs on top ,can anyone tell me what crossover setting i should set my rack mount passsive croosover unit to,i use this rig in my band and so the drums bass guitar keyboard and vocals are running thru it,i have a 1200 watt amp on the bottom and a 1200 hundred watt amp on the top which i think is wrong ,should i turn the top amp down a bit ,cheers

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June 4, 2010 3:50:43 PM

hello i have a pair of 2 x 15 em series martin audio bass cabs and a pair of em 12 inch cabs on top ,can anyone tell me what crossover setting i should set my rack mount passsive croosover unit to,i use this rig in my band and so the drums bass guitar keyboard and vocals are running thru it,i have a 1200 watt amp on the bottom and a 1200 hundred watt amp on the top which i think is wrong ,should i turn the top amp down a bit ,cheers

It's really better to run the subs at the lowest point manageable, like 70-100hz. If you cross the subs at a higher frequency, you wind up with a big hump in the frequency response, which causes low frequency feedback and ringing, and you wind up tuning out the hump with your equalizer.
You see, crossing the subs at a higher point seems to make the system louder, but you lose the loudness when you get the feedback out with the equalizer.
And you SHOULD be using a 31 band 1/3 octave equalizer, if you do not have that, get one.
Then another problem is the highs are too loud, and the mid range is not loud enough. Turn the highs down if they are adjustable, use just enough highs to balance with the mids and the lows. The highs should be at a much lower level than the mids and the lows.
You see, this is always a problem, because the efficiency of one horn is equal to six speakers. So if you have two horns, you would need twelve speakers to balance it out. And that is why the horns are used at minimum level, the speakers are used at close to maximum level.
And then if the highs are not adjustable, separate from the mids, you are really having problems.
Now for the power, 1200 watts is not too much, not really. You see it's not power that blows speakers, it's distortion. As long as the power is clean, the speakers won't blow. As soon as the amp goes into clipping and produces distortion, then the speakers blow. That's why we use an amp with more power than we need, the amp never clips, the amp never distorts, the speakers don't blow.
So if I use a smaller amp, say 200 watts, the amp clips much sooner, then the speakers blow much easier. The extra power is called HEADROOM. The HEADROOM is the safety zone which keeps the amp from producing distortion, therefore keeping the speakers safe from distortion.
So now you can see that a 1200 watt amp is not really too much, as long as the highs are adjusted down to match the mids and lows.
June 7, 2010 8:17:51 PM

Good explanation soundguruman
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June 7, 2010 8:22:14 PM

Did you really like it?
I have the hardest time explaining why you could run a 200 watt speaker on 600 watt power amp, it's safer. Most people don't get that.
June 8, 2010 2:31:13 AM

Watts = Volts x Amperes.

Look for a high amp current. High voltage and Low amps vs Low voltage and High amps will technically both produce the same amount of electrical power, but excessive voltage will cause voice coil failure.

When people say the amp is clipping, basically the excess power produced is coming from too much voltage gain; once the amp runs out of clean amperes the distortion starts to shoot through the roof, even though it continues to produce additional watts of power.

As long as you have plenty of clean amperes you have plenty of power handling. The problem is, high current amplifiers tend to be pretty big (a Class A/B 500Wx2 @ 8Ωamp weighs about 150lbs).
June 8, 2010 5:53:43 PM

Its like doing 70mph (Legal UK limit) with a 4.2 litre instead of a 1.8 litre. They will both do it, but the 4.2 is sweeter
June 8, 2010 5:54:44 PM

With power to spare if you need it
June 8, 2010 8:19:44 PM

Preferably, 80% of the power in a system should never be used, but should be there for headroom.
June 20, 2010 4:32:43 PM

hi soundguru man thanks for the advice i agree ,it works better this way ,but just to be sure do you recommend turning down the top amp and buying a bigger amp for the bottom .say 1000 watts per side leaving some head room cheers,martin
June 20, 2010 7:43:31 PM

You should be using an electronic crossover, the crossover has volume controls for hi and low. Yes you will be turning down the top.
Three way mono electronic crossover would be better, or run the tops in stereo and the subs in mono, like with a Rane stereo crossover, which has a mono sub output.
Yes you do need a bigger amp for the bottom, the bottom subs always need mucho power.
The thing is that the subs don't need to be in stereo, low frequency is omni directional, so making the subs stereo does no real good.
June 21, 2010 12:07:56 PM

thanks very much for your help mate its very apreciated ,cheers
June 21, 2010 1:33:12 PM

Sorry to bore you mate, but I have 2 more questions, i'm using a peavy cross over not great I know. It's two way stereo or 3 way mono, my top cabs are martin audio 2 way cabs so the built in crossover takes care of the highs. My crossover doesn't have a low mono out so should i bridge the amp, it's a crown 602 .2x600 watts. I have the crossover set at 250 and the top amp turned down as you advised.

Question 2 is I have boosted the bottom input signal to 2 o'clock and cut the top cab input to 10 o'clock though the reduced top input doesn't seem to have much effect. Should both inputs from the crossover be set at 12 o'clock then with top amp turned down sort everything out with the equalisation. Thanks a lot and sorry to keep on. Cheers, Martin
June 21, 2010 2:36:03 PM

You should run the crossover mono, you should cross at about 70 Hz, you should use a Y cord to feed both sides of the sub amp from a mono crossover source. If the subs in parallel, for mono, and each sub is 8 ohms, then will the amp drive a 4 ohm load bridged? Probably not. 2 X 8 ohm subs in parallel equals 4 ohms. If you cross at 250 system will be louder, but out of balance, and that's why you cross it lower for flatter frequency response.
You set the crossover to where ever the highs lows and mids are balanced. It will help to balance it out if it's tri amped. Doesn't the martin cabinet have inputs for highs and lows separate? (bi amp inputs)
If the martin does not have separate inputs, have a tech modify them for bi amp.
use the system 3 way mono instead, you will have much more control over the balance of the system.
it's OK to ask. I'm going away till the 30th, talk to you then.
June 21, 2010 6:38:57 PM

ok thanks ,there is a mono sub out im using the stereo low outs as i thought the sub out was too low. the martins only have one speaker input speakon ,no other ins or outs at all,the crown is 600 watts per side at 4 ohms and the cabs are 4 ohm 800 watts rms they peak at 2300 watts which in itself seema very ambitious to me,they are 2x15 bass cabs and so i dont think they come under sub bass catorgory maybe they do maybe they dont not sure,im worried if i go that low then that leaves a lot of bottom end going to the 12 inch cabs,cheers mate
June 21, 2010 9:29:08 PM

The crossover point also relates to what the top boxes are capable of (and of course where the the sub is made to be crossed). I actually cross mine higher and the top boxes at 162 with a slope...
June 22, 2010 10:09:16 AM

yes ,this is the point im trying to get confirmed,its a 2 way system not 3 way so if i crossover at 70 then surly i will blow the top cabs ,12 inch speakers cant handel frequncies that low can they ???? the tops have their own croosover or filter to seperate the horn,im just trying to get the most efficiant sound without spending a million quid on 3 way system and racks of gear,after all its only a pub band were not playing the nec yet,i do have a 10 band graphic on the mackie cfx 12 desk. cheers dude, martin
June 22, 2010 4:08:54 PM

im a thicky my croosover is active,cheers