use a PA ampli for sub

[cld1354]

Hi,

I'm realizing a sub as a part of a multiamp system
and I will cut this at about 150 hz.
The drive is a Monacor sph 380 double coil.
What do you think about the idea of powering this sub with the PA ampli Alesis RA 500 putting this in bridged mode (500w on 8 ohm)?

Thanks
Marco

[pinkmouse]

Should be fine

[OMNIFEX]

The Alesis is more of a recording studio amp, than PA
amp.

I'm not saying it won't do the job, just letting you know
it wasn't designed for high current use.

A Fan would safeguard you from any problems.



Best Regards,

[haldor]

The Alesis is rated for 4 ohm loads so it should be safe driving an 8 ohm load bridged. Make sure your sub is really an 8 ohm load however, since the actual impedance of your speaker will often be less than the nominal value. For running bridged, I prefer an amp rated as being able to handle 2 ohm loads.

Unless you are getting the Alesis at a fire sale price I think you can get a lot more amp for your money by looking at the QSC RMX family. QSC is one of the best brand names in amps (top three are Crown, Crest and QSC). Lab Grupen is coming up fast to join them as well.

The RMX850 sells for $270 US and will deliver the following power:

Bridged into 8 ohm = 600 W
Bridged into 4 ohm = 860 W

The RMX1450 sells for $360 US and will deliver the following power:

Bridged into 8 ohm = 900 W
Bridged into 4 ohm = 1400 W

All the RMX amps are rated for 2 ohm loads so they should have no problem driving your 8 ohm sub.

Northern Light and Sound is my favorite vendor (lowest cost with good service) in the USA to buy QSC amps from. http://www.northernsound.net/Sales/P...s/qsc/qsc.html

Northern Light and Sound has a system of showing you their real price on their website. They show the MAP (minimum advertised price) that they are allowed to show and the planets and moons displayed after the price show you their discount from MAP. Each planet = 10%, Each moon = 5%. The RMX amps mentioned are available at 10% below MAP.

I have purchased amps and rack gear from Northern Light and Sound in the past and they are an excellent vendor.

P.S. Alesis has a pretty bad name in pro sound gear for reliability and sound quality. Their rack gear (compressors, eq and FX) are generally reviled as being the lowest of the low. I haven't seen their amps, but I have personal experiance with both their compressor and their graphic eq. They make pretty nice door stops, but that's about it.

Phil

[pinkmouse]

Sorry Phil, I have to disagree...

The only reason they have a bad reputation is that they have a low price point, ( apart from the graphics, they are fine in a studio or home situation, but are not robust enough for touring), so snobbery takes over!

To give an example, on all the Pink Floyd Tours since the late 80's they have had racks of Alesis reverbs and compressors for the kit and percussion. Floyd could easily afford better if they wanted, but the kit they have is reliable and sounds good, so why change?

[usekgb]

I've used quite a bit of Alesis gear doing sound over the years, and it is pretty mediocre. All of the RA series power amps have no punch or depth of field. They also have a fairly high failure rate. We had so many of them returned to my store that we stopped carrying them. Stick with something from Crown, Crest or QSC. If your going with Crown, stay away from the XLS series. The price is right, but they just don't perforn like a Crown should at the bottom end.

As far as the other Alesis gear goes, it's hit or miss. Their compressors tend to pump, their EQ's are noisy, and most of the reverbs have no depth. Even so, I own a Nanocomp that I use as a spare compressor when I need another channel of gain control.

To sum things up, If an RA500 is all that will fit your budget, by all means get it. If you can, try and save up for a better quality high current amp. Even the Crown CE1000 will do the job. If you do get the Alesis, you may just want to uprade the power supply a little bit to open up the bottom end some. (That is if you're not afraid of voiding the warranty) Either way, best of luck to you. This sure is fun, isn't it?

[OMNIFEX]

cld1354,
If your having second thoughts on the Alessis, you
can get an OLD Peavey CS 800. I picked up these
a few years back on Ebay for 150 a pop (185 with shipping)

800 watts RMS 20 - 20Khz 0.03% THD 8 ohms Bridged.

They are old, but, are built like tanks.

[usekgb]

Duh!?!?!?!? I completely forgot about the Peavy. They're actually not that bad. They're not the best sounding amps in the world, but they don't suck. Plus, they last forever. Not a bad idea.

Cheers,
Zach

[haldor]

Originally posted by pinkmouse
Sorry Phil, I have to disagree...

The only reason they have a bad reputation is that they have a low price point, ( apart from the graphics, they are fine in a studio or home situation, but are not robust enough for touring), so snobbery takes over!

Actually the reason the compressors have a bad reputation is they pump audibly if used at much higher than a 2:1 compression ratio. Plus the frequencies printed above each of the graphic eq sliders bear very little relationship with the actual frequency bands adjusted, plus flat isn't. The MEQ230 clips easily as well, which is loads of fun since it's usual position in the signal chain is right before the power amp.

Don't take my word for it, here are a just a few choice comments about Alesis. I can find several hundred more if you'd like. Do your own search, if anyone has ever had a good thing to say about Alesis rack gear on the LAB I'd be very surprised.

http://www.live-audio.com/messages/archive4/135796.html

Note: Several of the posters in this particular thread recommend a Behringer compressor as a much superior alternative to the Alesis. Behringer is hardly snob gear.

I've got a NanoVerb that I find the odd use for, but every other piece of Alesis gear I have ever used sucked far more than I would have believed possible.

I'll second the comment about the CS800. My church still has a couple of them in use driving vocal monitors. They never stop working.

Phil

[uli]

Originally posted by haldor
The Alesis is rated for 4 ohm loads so it should be safe driving an 8 ohm load bridged. Make sure your sub is really an 8 ohm load however, QSC is one of the best brand names in amps (top three are Crown, Crest and QSC). Lab Grupen is coming up fast to join them as well.
Phil

Hi folks,

This sub is a lo cost 2x 8Ohms woofer, so better spending more
money for a Hi end sub than to one of those heavily overpriced
PA amps like QSC and Crown!

Uli