power amp for subwoofer duty

Discussion in 'Location Recording' started by rockstardave, May 30, 2011.

  1. rockstardave

    rockstardave Active Member

    i've been on a kick checking out power amps to run my subwoofers. so i've read up on a few things and here are some of the amps i'm considering to run 2 or 4 cheap subwoofers, each at an 8-ohm load.

    Crown XTi4000
    Crest VS1500 (if i use 4 subs i'll need 2 of these)
    QSC RMX series

    i already have an XTi4000 for my tops, and if i had 2 of them i would just use their onboard DSP for xover and EQ. but i've heard they're not the best for subs

    the Crest i like because of it's high damping factor (1000 !). a bit heavier and larger than i would prefer, but the xti only has a damping factor > 500.

    RMX amps are also heavy, but there's something to be said for amps that are forgiving with line voltages.

    .. THOUGHTS??
     
  2. dvdhawk

    dvdhawk Well-Known Member

    The XTIs (and the like) are great for tops and monitors. But I prefer a heavy amp for subs - something with a big heavy transformer to help you ride out the deep transients. To my ears the heavy transformer style amp seems to have more reserve that results in more muscle. There are some truly exceptional lightweight amps, but they're in a completely different ballpark price-wise.

    Lightweight amps have improved in a lot of ways, but there is a trade-off when it comes to the ability to convert the power coming out of the AC receptacle into useable thump.

    I personally use middle-weight Crest on my tops and subs and the XTIs on monitors.

    Hope that helps.
     
  3. rockstardave

    rockstardave Active Member

    yes that's right along with what i've read and heard anecdotally.

    which Crest amps are you using? i really like the DSP and my xti for my top-boxes , but maybe with such a light weight amp, i can "afford" to toss a heavy amp in the rack.

    what do you think about Crest VS series against RMX amps?
     
  4. dvdhawk

    dvdhawk Well-Known Member

    Crest, Crown, QSC - all good in my estimation. A lot of my friends use nothing but QSC and sound great, some use nothing but Crown and sound great. I use a combination of Crest and Crown selected for the specific job at hand. Even their fly-weight amps have a proper place. I'm sure you're on the right track, just by the fact you're researching the topic.

    So I think it gets down to the reason I prefer the sound. I think the big transformer can store enough power to thump regardless of the instantaneous draw on the venue's electrical supply. The heavy power supply minimizes the peaks and valleys in line voltage. Where a lightweight amp is really dependent on AC line voltage to get anywhere near it's theoretical peak output - even if the thing momentarily draining the line voltage is the amp itself pounding out a kick drum.


    I've used the V-series with good results for low-mids and subs. (But I thought they stopped making those 10 years ago.)


    For a while we were using a Crest Pro 9200 on the subs and a Crest Pro 8200 on the tops;

    9200: 2-rack space, 22 lbs. theoretical 2200w/ch @4Ω
    8200: 2-rack space, 22 lbs. theoretical 1450w/ch @4Ω
    and it was lightweight, ferociously loud, and really defined and punchy - but...

    When my partner at the time wanted to pull the 200-series out of the system to do solo stuff, I replaced them with the CC series. The CC's are 2x the weight, but 1/3 the price, so I bought four of them and was still 'money-ahead'. The subs with the CC's are still tight and well defined, but there's more depth to the sound - with the exact same cabinets. Beefier sounding. When I first got the CC's we had a chance to run 2 subs and 2 tops with the 200-series amps plus 2 sub and 2 tops with the CC-series. With a good A/B comparison the CC's held there own in every way and we both thought the subs were fuller sounding. It might look like we lost watts on paper, to me the system sounds even bigger. It quickly becomes an electrical issue running 4 big amps vs. 2 big amps, so I can scale the system to the venue.

    CC-4000: 2-rack space, 44 lbs. theoretical 1350w/ch @4Ω
    CC-2800: 2-rack space, 40 lbs. theoretical 965w/ch @4Ω

    So it was punchy before, but a different kind of punchy with the heavier amps. Kinda punch in the face vs. knee to the gut.

    (Even at 44 lbs. the CC is still a lightweight by comparison to the classic Crest 8001's and 10001's of old.)


    I remember back in the good old days working on the crew for some big shows, and the Carver PM1.5 and Crown Macrotechs would be rolling down the ramp in 18-space racks 3 ft. high. Then there would be this short rack, barely 10 inches tall with 4-inch casters on it. That's was a single Crest 10001 for the subs, at about 145 lbs. 15000w of program mono bridged at 2Ω. It took four guys to keep it from running down the ramp too fast and breaking somebody's leg.

    A boat anchor for sure, but wow what an amp.
     
  5. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    Pick speakers first, then select amps to drive them to your target SPL. Deciding on amps first is putting the cart before the horse.
     
  6. Davedog

    Davedog Distinguished Member

    I'm with Dave on this one. Large power supply, fast slew rate, iron for breakfast.....the big notes stay firm. Since you're limiting the bandwidth, look at the burst for rises in the frequencies you want to amplify....Flat or better way down low with a lot of efficiency is good.


    I remember those older Crest amps!! I worked a stage years ago with 4 of the 8001's in a couple of racks running those old Meyer Sound subs with the 18" in em....You couldnt get within ten feet of those things without running to the can......talk about remodeling yer innards.......
     
  7. rockstardave

    rockstardave Active Member

    davedog- i was searching into this the last few days and i found an old thread about how "better" sub amps may decrease volume compared with budget amps. the upside, of course, being a more uniform output across frequency bandwidth, as well as a tighter sound. your comment "big notes stay firm" sort of scares me. i want ALL notes to be firm! (y)

    boulder - i already own speakers, thanks for asking.

    for what it's worth, i'm probably going to loan an XTI4000 for this gig. power is reliable at this venue. OR maybe i'll just bite the bullet and buy a VS1500.

    follow-up question: how much does the damping factor actually matter?
     
  8. Ripeart

    Ripeart Active Member

    Are any of you using line conditioners on your power amps? Why or why not?
     
  9. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    Then specific advice would need specifications of the speakers to have much value. Recommendations without the specs are just shots in the dark.
     
  10. Davedog

    Davedog Distinguished Member

    I was referring to the subs only in this case. Which you really want to stay firm. I hate PA with clear highs and mids and an unarticulated wash of 100cycles and down...
     
  11. rockstardave

    rockstardave Active Member

    davedog- i meant all notes that the sub amp will be reproducing. we were on the same page.

    boulder - i disagree. think of this as an "all else being equal" scenario. which amps provide better bass response? which amps have good circuitry? that's the sort of thing i'm trying to ascertain. for what it's worth - my top speakers are garbage. dirty cheap dual-15"s.
     
  12. bouldersound

    bouldersound Real guitars are for old people. Well-Known Member

    I guess it seems a little misdirected to be shopping for good amps to power speakers you described as cheap. Amps won't make anywhere near as much difference as the speakers themselves. Practically all modern amps have effectively flat response when operating within their rated power levels, so that's a non-issue. The specifics of the circuitry is essentially irrelevant beyond its impact on cost, weight and reliability.

    There are some people who swear by non-switching amps for sub duty. At the same time there are major productions using switchers for all pass bands. I haven't seen any independent scientific confirmation that "big iron" amps as a category have any advantage over switchers for subs. It's possible but I'm not convinced.
     
  13. Davedog

    Davedog Distinguished Member

    You probably cannot find a sheet of paper that would tell you whether this is actually true and we may be getting into the elusive 'figment of the imagination' or 'suggestive hearing' , but I think the 'big iron' stuff on the bottom makes sense and I think I can hear the difference. I'm not in the PA game any longer but having two BGW 750's on the subs meant that they werent going to crap out anytime soon. JBL 4530 X 4 on their sides. Not perfect but they'd take the roof off of any club I ever worked. Old Skool !!!

    I worked one show in a small auditorium where they had a flown in place rig and the bass was lacking so we got a chance to put the old Betsy's on top of each other for that BIG outdoor sub-horn config...They really worked well like that. I've heard old Martin sub-bins with that amp on em too....Marvelous.

    Like I said....Its all Rocket surgery these days and I like those 22 lbs power monsters.
     
  14. dvdhawk

    dvdhawk Well-Known Member

    I don't need to see a whitepaper on this one. All I need is my ears to tell me the difference. I'm not trying to convince anyone that you can't get loud without a big transformer in the amp. I've owned a fair number of Carver PM1.5 amps, and the Crest 200-series, Crown XTi and heard plenty of big boys using lightweight QSC and Lab Gruppen for big outdoor shows. But the big boys have access to something you don't always get doing clubs, festivals, and fairgrounds - massive electrical services dedicated to the stage, or rolling generators that could run an entire hospital in an emergency.

    You'll notice a HUGE difference in performance in the lighter amps doing a show somewhere with a barely adequate generator, or any other place with significant voltage drop in the real world of dicey power. On the other hand, if the gig is at a venue with excellent line voltage - the lightweights come to life. I don't dislike the lighter amps. I often use that sort of thing on tops and monitors. I've used and installed my fair share of them. But given a choice, I prefer (by a significant margin) the more muscular tone I get from 'big iron' on my subs. It may not be everyone's taste, but I know what I like. I would be thrilled if we could blow the roof off the dump with a short stack of 12 pound amps.

    The major production companies using lightweight amps A) often have endorsement deals and B) are going to sell them off after about 6 months of rigorous touring. They factor that into their operating expenses. They know it's hard on them and they would rather recover a large percentage of the cash than do the maintenance, or risk failure in the field. Back in the day, we bought some of our Carvers from just such a production company. Experience taught us, we (I) would need to change out the big dual caps that make them tick shortly after we got them. The ones we bought new ran years before showing signs of weak caps.

    Believe whatever you want. Do an A/B comparison and you may not hear a difference, or like they sound. But at some point your back, your wallet, and your ears will have to come to some sort of understanding.
     
  15. rockstardave

    rockstardave Active Member

    great post dvdhawk!
     

Share This Page