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Power amp for PA subs

#41
s0c9 said:
Well, I didn't read the entire thread and not sure of the entire issue (volume?), but I can tell you that a PLX 3002 isn't even close to being able to power TWO LS808's. One in bridged mode should give enough headroom for ONE!!
Why do I say this? I've run PA's for many yrs, and yes I play bass too.
I have a tri-amp PA. My 3002 powers my 4-ohm 15" mids (1050w per side). I power my 2" 120w HF drivers with a GX3.
Both gain levels are balanced/limited with my DR260.

The LS808 is rated 1400w program, 2400 peak at 8 ohms.
The 3002 produces 625w per side at 8 ohms.
Bridged, the 3002 will give you 2000w at 8-ohms. That's enough to run a single LS808 at program and have enough headroom for peaks.
Rule of thumb for powering passive speakers is an amp that produces 1.5 to 2.25 times the RMS/Program rating of the speaker. So basic/minimum for the LS808 would be 1.5 * 1400 = 2100w. This allows for transients, and headroom.

My subs are 2 LS800P's.. and like Zooberwerx states have the most bang for the buck of any sub out there. Yes, they need a little EQ to get the best out of them - mine are crossed and 95Hz and EQ cut around 55Hz. Sound awesome. Mostly I use only ONE for bar gigs.

If you are selling, buy some LS801P's.. (my $0.02)
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If I could keep the 808's side by side,they could be usable. We put them together in the middle of the rehearsal space with the 3002 amp,and it shook the whole house at about 75% on the amp. Split them up and all the volume and bottom end goes away.Is this something that happens with just this style of cabinet?
 
#42
73jbass said:
If I could keep the 808's side by side,they could be usable. We put them together in the middle of the rehearsal space with the 3002 amp,and it shook the whole house at about 75% on the amp. Split them up and all the volume and bottom end goes away.Is this something that happens with just this style of cabinet?
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Yes. As I mentioned, subs should be clustered, preferably centered (...but not an absolute), and never separated left & right. Your experience is a spot-on representation of both scenarios. No room front & center? You can stack them either stage left or right for the best performance.

This should explain everything: http://www.talkbass.com/threads/subs-missing-on-dance-floor.707523/page-2#post-10597176

Riis
 
#44
73jbass said:
Funny thing is,in my last band we had the typical single 18" JBL sub with a 15/horn on top. Plenty of bottom end in every venue we played. And that was with a 1600 watt power amp.
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Not so funny. Separating the sub enclosures also serves to accentuate the sonic voids you've described. Clustering allows the drivers to act as a single enclosure where they complement each other's presence (gross oversimplification). IME, throwing a dedicated 3002 on each sub, if separated, would have no discernible benefit and may actually exacerbate the problem at hand. Save your money and do some spatial re-shuffling as I've described and you have witnessed firsthand.

Riis
 
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#45
I get clustering,but why is it that my old setup sounded much better and louder with half the power? Typically the JBL subs were at least 30 feet apart,and usually not backed into a corner or against a wall. But there was plenty of low end. See my confusion?
 
#46
73jbass said:
I get clustering,but why is it that my old setup sounded much better and louder with half the power? Typically the JBL subs were at least 30 feet apart,and usually not backed into a corner or against a wall. But there was plenty of low end. See my confusion?
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Not a clue but it could be the ol' apples & oranges thing. Were they of the same configuration, i.e. folded horn, direct radiating, whatever?

Riis
 
#47
Just the standard JBL front loaded 4 ohm sub. Like this one.
 

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#48
73jbass said:
Just the standard JBL front loaded 4 ohm sub. Like this one.
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That JRX118S cannot be compared to the LS808. It's peak power rating is 1400w, which matches the LS808's program (RMS) power rating.
In essence, the JRX is a 1/4 the sub the LS808 is.
Yes, clustering subs will give you "power alley" type bass, but they should work just as well when placed on either side of the stage. Wall proximity should not be relevant on a 1400w sub indoors in a club/bar size venue. Larger JBLs - like the SRX718S (comparable to the LS808) - are WELL known to need lots "power" before they come to life and sing. They are 8-ohm subs like the LS808, whereas the JRX are 4-ohm. Less voltage is needed to drive the JRX to rated power (lower impedance) than the LS808, which may be where you get your perception of louder with less power.

You have something wrong with your setup. Sensitivity on the JRX is 96dB, peaking at 133dB vs the LS808 sensitivity at 105dB, peaking at 139dB. The LS808 should be REALLY LOUD if properly powered. As I mentioned above, the 3002 is only enough for one LS808 in bridged mode. You should try that on one LS808 and see what you get. A SINGLE LS808 should blow away both of your JRX118's.
 
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#49
73jbass said:
Ok,the amp works fine. We hooked it up to a pair of OAP full size 18" folding horn subs about 50 feet apart,and it sounded great. Same setup with the Yorkvilles,not great. Put the Yorkvilles side by side and its a different story. Wow. Problem is,I don't know of any club around here where we can set the subs up together up front. So it looks like they may be up for sale. Possibly looking at the B52 or Cerwin Vega folding horn subs,which he said were great cabs. Open for ideas here!
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OK yeah, something ain't right. Both of those options are jokes compared to the 808, one 808 would probably beat two of either one.
 
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#50
I saw a house pa last night that had 2 CV folding horn cabs on stage right. One facing foward, and the other directly behind it facing backwards towards the wall. It sounded really good and pretty even throughout the room. The 808s are being sold today and I need something that will match the poweramp I have. Im guessing something rated at about 1000 program each? Open to suggestions.
 
#52
73jbass said:
Question, Will I get the same effect of clustering 2 cabs by using a dual 15 or dual 18 cab on its side? Or does it have to be separate cabinets to the the clustering effect?
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Should work although I can't speak with any authority (...although it's never stopped me before) on whether dual driver enclosures sharing some air space differ from (2) clustered single driver enclosures. Here's one of the higher-end Carvins. Apparently, there's more to the design than just sticking two drivers in a crate and hoping it works:

[Invalid or Expired Link Removed]

Riis
 
#53
I saw those and that is way out of my price range. I was looking at these,Invalid Link Removed. More in my price range and I should be able to run them with the amp I have. I also have a pair of PLX1602s I can run bridged mono into each of these if needed.
 
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#55
73jbass said:
I saw those and that is way out of my price range. I was looking at these,Invalid Link Removed. More in my price range and I should be able to run them with the amp I have. I also have a pair of PLX1602s I can run bridged mono into each of these if needed.
Click to expand...

That would work. I'd also consider two of the 1801's and run a 1602 (bridged) into each.

Riis
 
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#57
Because I dont want to have to buy another 3000 watt poweramp to drive 2 subs. The LS808s only work well if coupled together. In the clubs around here there usually isnt much stage area,if any at all. So putting 2 huge subwoofers on the floor in front of a band with no stage isnt practical. I have limited rack space and not much more trailer space. Thats why I'm looking at the dual 18. I can drive it with the amps I have,and get it in the trailer.
 
#60
The way I read the suggestions was that your amp was just right to power one 808 cabinet and that one 808 cabinet with your amp should outperform both of your previous cabinets together. Sounded to me like your issues stemmed from phase cancellation when you had the two cabinets on opposite sides of the stage. Subwoofers (IMO) should be a single point source and shouldn't be separated .. else you get comb filtering - regions of strong, in phase bass alternating with regions of weak phase cancelled bass.
 
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