Amplifiers....how big

Edreams75

ive read the Amplifiers....how big in the faq and am now more confused. i built the pa thinking i was doing well with the amps i got but now think i under powered my system. i want to get clarification before i start replacing my amps. my band uses the pa for practice and the small clubs without a in house system. we run vocals, kick drum, synths and electronic percussion through it(low end heavy sources...tr808). i have 2 B-52 mx15 for the mains. 8 ohm cabs rated at 300 watts. they are powered by a crown xls1500 rated at 300 watts @8 ohms per channel. subs are 2 B-52 mx18s. 8 ohm cabs rated at 550 watts. they are powered by a crown xls1000 run in bridged mono. 2 8 ohm cabs put a 4 ohm load on the amp, it is rated at 1100 watts @4 ohms bridged mono, which gives each sub 550 watts. the faq post says you should have 2-4 times the rated power on the speaker......so im way under powered according to this. i am thinking of buying another crown xls1000 and running each main cab on one xls1000 in bridged mono, that would give 700 watts @8 ohms in bridged mono going to each main cab. then buying a crown xls2000 for the subs, that would be 2100 watts @4 ohms bridged mono...so 1050 watts to each sub cab. should i replace the amps or is the way i have it ok/good enough?????

Gadget

Ok... clarification...

For Dj work, using heavily compressed music:

B-52 mx-15... rated 300/600/900 (RMS /program/peak) power needed = NO MORE THAN 600 watts

For Live sound, dynamic, rock music: Duty cycle of amps no more than 1/3 power)

B-52 mx15...rated 300/600/900 power needed = 600-900 watts per cab...

Live rock is MUCH more dynamic than canned music. Therefore you need more power to re-produce it. The problem with canned music is it's so heavily compressed the dynamics are happening all the time and so the duty cycle of the amps exceeds the max of 1/2 power (running more then 1/2 of the time) this heats up the voice coils and can destroy the speakers.... but the live sound business has no such limitation, and occasional peaks that exceed twice the program power are possible...

Now, if you hook up the system, and it does what you need, when you need it, your golden, your most likely not in any danger of burning your speakers if you don't clip the amps,

If, however, you run out of gas, can't get the sound you were looking for.. you don't have enough rig for the gig...

Now..the bad news... With B-52's CRAPPY spec sheet you have NO idea what 300 watts means... that could well be 150/300/900 watts (and very well could be) or 300/600/900...

600 watts isn't a lot for live sound tops, but then if your using TR808 samples they aren't like live drum sounds either... so perhaps were back to program value max again...only you can decide if you have enough rig... remember this, to get twice as loud as your 300 watts.. you would need 10 TIMES THE POWER... double the power will only elicit 3dB more sound...

Does that help?
G

Edreams75

It does help a bit. The mains seem to be fine volume wise, we aren't pushing anything to the max and it's still able to be heard. Main thing is the subs, they just aren't the earth shaking chest exploding volume we were expecting. I am going to contact B52 and find out what the watt figure is (program/rms/peak)

Gadget

When you do.. find out what driver they have in the subs... I see it's a 3.5" voice coil.. and I assume stamped basket? Sorry but no matter HOW much power you throw at those.., they will NEVER produce chest thumping bass...sorry.. you'll need something like the Peavey SP218 with about 4000 watts per cabinet for that experience... (and that's the LEAST expensive sub I can think of that will do that... maybe get into the Yorkville subs too...
G

Edreams75

i went with the B-52 mx18s subs for price and the fact that they get down to 30hz. everything else in that price range (even some of the "high end" subs) only got down to 40-50hz.....thats not a sub! the peavey sp218 only goes to 51hz. i saw the 3.5" voice coil and thought it was close enought to a 4" and assumed that it was a cast frame.....a stamped frame on a sub is STUPID! the guy i needed to talk to at B-52 is at lunch....figures

Gadget

i went with the B-52 mx18s subs for price and the fact that they get down to 30hz.

30 hz???? ya right.. from a single sub? A B-52 sub? Maybe (20-30 or more) dB down from the USABLE frequency response...
Do you think that if the Peavey SP218 with it MASSIVE Low Rider drivers can only do 31hz @10dB down.. and are rated @ 49-300 hz that utilize a cabinet made of Baltic Birch...with a 600/1200/2400 watt rating...for a single driver...

If they can't hit those numbers with that setup... the B-52's with a 3.5" voice coil and a 550 watt rating under 100 lbs is probably made of MDF... that THIS is going to actually hit 30hz? That cabinet would fly apart at those frequencies..

It's called TRUTH IN ADVERTISING... or the LACK there of...It's all a game of numbers and half truths...To be honest, there are only a handfull of loudspeakers that can produce below 40 hz 3dBdown... and it usually takes a few of them to to even approach that number. 30 hz... that's a WHOLE lot harder to hit. ... and in groups of one? I can think of only a couple, and they are manufactured by Danley sound. One has 20, 15" woofers, and 20,000 watts of power built in... called the Matterhorn, another is the TH812, which has 8 12" drivers in one box.

Sure there are some home theater boxes, and I know Bill Fitzmaurice claims 30 hz on some of his stuff.. but they won't be able to put out 30hz in any kind of medium venue size place, or outdoors at all.... maybe a living room, or car or van...

Sorry to be the bearer of bad tidings... but they are OUTRIGHT lying about that spec... within any REASONABLE dB down figure. I bet those boxes are 10dB down @ 45hz...and are much more likely a 55 hz box...

gadget

Edreams75

Awesome, that pretty much blows everything I thought I knew out of the water. Sucks cause I got talked into the B-52, claimed they were damn good speakers for the money. I wanted to go with peavey. Would have been the pv series so they may not have been much better. Well I got what we paid for so I need to get the most out of it!!!! Which brings up a new question, I had the hpf of the low xover set to 30hz cause that's what I thought those speakers got down to. What should I set it at

Gadget

Naw... the PV series is no better... but I wouldn't go any lower than 45hz BW18...maybe 50 would be better. I did discover that it's a cast basket woofer... it's probably a 500 watt program woofer, so you could have an amp as high as 1000 watt in peaks..(but if you ever get a hold of the guy ask him...

G

Sorry to bust your bubble... but I just HATE the whole process of blowing the specs all out of proportion... I mean 30 hz... they KNOW that's a joke!

Gadget

BTW we DO have a DIY sub in the FAQ section that really kicks ass, and isn't hard to build. About $500-600/pair
G

Edreams75

I'm starting to get a rather unpleasant taste in my mouth with b-52. Tried all day to get a hold of the tech guy there......out to lunch, not at his desk, went home for the day! Knew I should have gone with peavey, never had a problem getting a hold of a tech guy there! Gonna check out the DIY subs, may end up doing that or the sp218 somewhere down the line

Dra

Devil's advocate.
It is Christmas, so he may be hard to reach.

The B-52 are definitely marketed to DJ's. You may be able to sell them at a small-ish loss and do the upgrade sooner rather than later, since they are new. Did you buy them at a store? Maybe they will give you a good trade in.

DRA

Edreams75

Good point!!! no we bought them on ebay so probably cant return them. ill probably wait till we pay these off(6 months) and try to sell them. been researching stuff and think im gonna go with peavey....sp2 and sp118. its double what we paid for the b-52 speakers but lesson learned you get what you pay for

Edreams75

Finally talked to the guy at B52. He said that the watt rating stated is rms.....he thinks!!!! Not very reassuring! And the only info he has on the driver for the sub is that it's a cast frame. Def should have gone with peavey!!!!!

Gadget

And if you want to buy once, cry once... If NSL still has the DAS line (you'd have to call and verify...) the RF1264 for a little more money would get you a VERY good top...that measures up well with the DIY subs I mentioned earlier...Dr. J has this setup and he is SUPER happy with it, and he has been blowing away all the sound guys in his area with the setup.. (plus he already has tunings for them)

G