PA+another power amp?

Discussion in 'Amps and Cabs [BG]' started by Nickthebassist, Apr 11, 2005.

  1. I was thinking, perhaps me and my band could purchase another 1200watt power amp, and send a line out signal from the Peavey 696F, and basically double its power? We could have 4 1x15s, and 4 1x12.......... :cool: Is it possible to do this?
  2. Jack


    Sep 6, 2003
    Newcastle, UK
    Yes, but the question is why?
  3. LOUDNESS! If we have our own PA, we don't have to hire one for gigs. People in York like it LOUDDDDDDD.
  4. Passinwind

    Passinwind I Know Nothing Supporting Member

    It's certainly possible, but if your goal is to be twice as loud, it'll take 10 times the power to get there, and your speakers will need to be able to handle the power as well. What kind of horns are you going to run with the 15s and 12s?
  5. +1.

    Point well made - probably for about the 10,000th time!! :D :D
  6. Horns? What are they? Aren't they for treble? ;-) No seriously, it's all an idea, nothing serious yet. For now, we're gonna get a couple of 1x15s and some 2x10s with the horns built in. Should handle most of the range.
  7. BassManPatsFan

    BassManPatsFan Supporting Member

    Feb 20, 2004
    San Francisco
    vaild point here.
    I learned last week from my band director a little something about volume that i had never known before. Him being a trombone player, he told us this in terms or tromboners(age?). What he said was that when you have one trombone player playing at a normal volume, they will be playing at a certain decibel rate. In order to double this, most people would think you just add a second trombone player, but in reality you would need to add 7-8 more trombones to this section. I'm not sure however if the same is applicable to power amps (obviously they aren't powered by a human if that has anything to do with it) but it seems like it would be logical. I have no idea if this is common knowledge among the rest of you, but I sure found it interesting. :hyper:
  8. karrot-x

    karrot-x Banned

    Feb 21, 2004
    Omicron Persei 8
    Why don't you go with 18's? They'll really hit the floor hard.
  9. TheChariot


    Jul 6, 2004
    Boston, MA
    Oh they'll hit the floor alright...

    And after they hit the floor... they will drag... and sag... like a floppy pile of crap.... until the tone dies and gets sucked away forever. But hey... if your looking to ruin the great tone of your 12's and 15's... bingo!

    Dude... you do not need that much PA for a gig. We've got 600Watts of PA, and its PEEERFECT for a Marshall guitar Halfstack and Bass Fullstack. As for drums... I'm the drummer... and Dave Grohl is pretty much my drumming idol... so... I can pound and keep up.

    Take a look at Club PA's. They have PILES of friggon power amps! That's what it takes to actually make a difference in volume via power. PLus you would need MONSTROUS power handing from your speakers. Like... CLUB QUALITY cabs.

    Eventually, it gets to the point where having your own PA is just limited. You cant take 10 speaker cabs with you to a gig. Something will break... or get stolen.... its more liability than you can imagine. I would limit myself at 600Watts at the MOST... with 4 cabs. That's a TON right there.... enough to rent out to other bands, even!
  10. rockstarbassist

    rockstarbassist Banned

    Apr 30, 2002
    The Woodlands, TX
    Endorsing Artist: HCAF
    What kind of 18's are you playing through? I'd hardly call the badassed JBL's we play through anything wimpy. I don't hear them drag, sag, and sound like a floppy pile of crap... I'd try upgrading from that Hartke cab you're using for your PA and get some real pro audio gear... That kind of statement isn't just dumb, it's plain ig'nant! :eyebrow: :scowl:
  11. HMmmm, it's just our Peavey doesn't seem as loud as our old PA that was about 150 watts(we think, it's an obscure make). Now, the Pevaey is designed to run at 4 ohms, but we're using 8ohm speakers, so I expect it will get a lot louder when we start connecting things up in parallel. The speaker we're thinking of getting can handle 275 watts each. The PA puts out 600 watts through two channels. I take it if we get two 8ohm speakers that handle 275 watts, and connect them in paralle, this will make it 550watts of handling power at 4ohms? Or am I wrong?
  12. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Watts, watts, watts. Watt's up with the talk about watts? It seems that as soon as the last thread explaining the fact that watts mean nothing with respect to loudness disappears another one pops up. So once more, but this time with feeling: Watts don't measure sound levels. Decibels do. Watts and decibels have no direct correlation. If your system isn't loud enough adding more watts in the form of either amplification or more speakers is the least effective way of curing the problem. Instead of power you need to be considering the sensitivity and bandwidth of your PA speakers. Before you do anything else read a book about soundsystem design. 'Sound Reinforcement Handbook' (Davis & Jones) or 'Sound System Engineering' (Davis & Davis) are two good ones.
  13. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    My very recent bass rig upgrade sure reminded me of that!

    I upgraded my cab, but not my head (that's next, after some more gig-money rolls-in) - so I'm still running a 140W-rated, $120 amp (the famous "beginner's" amp: the Hartke 1400!). Last Saturday The Mole Patrol played a not-small hall, and I had TOO MUCH amp power - I tried sneaking the volume up past "11:00" twice, and had to turn it back down!

    Yes in-deedy, my new cab is 100dB-efficient JBL PA cab with 2X15 and a horn, and boy-oh-boy, can you tell the difference over my old 4X10 -- but Bill: may I add something else to even further make a case for, and somewhat build upon your already valid and thought-provoking speaker vs. power amp wisdom?..

    Something I still haven't seen addressed here (I mean anywhere on TB!), is how dispersion factors-in to efficiency. You can't describe how much audio power a cab is putting-out by only measuring on-axis sound pressure!! An SPL measurement is only measuring ENERGY, not power; You're missing a whole dimension of the physics when you try to reconcile the energy at a point in space with the acoustic/music power being contributed to a room. That's a fact.

    The REAL issue with efficency is electrical power IN, to acoustic power OUT. It's really unfair (to put it nicely - I'd tend to say 'deceptive' - I'm serious...) to claim that comparing the energy at a point (SPL) to the input power that produces that energy is somehow describing 'efficiency', especially when an enclosure is well known to have a dispersion that drastically and continuously varies with frequency! It simply is NOT describing efficency in any practical, musical sense, and an on-axis-only measurement is always going to be an unrealistic best-case for a speaker cone that's bigger than a couple inches across. To compare power to power, you have to 'intergrate the energy over the area of interest' (our 'interest', of course, should be the music venue that we're playing in).

    Picture this: Say I had some sort of "sound Lazer" - like a speaker that shot a 'beam' of sound. Let's say I had it on stage, and I aimed it right toward an open window on the back wall of the hall. You understand now, that this sound energy would contribute nothing to the music in the room, unless you were standing 'in the beam', right? It wouldn't matter how 'efficient' the system was at converting power-in to energy that's present somewhere within that beam - it's pretty much musically worthless in that room. This 'beam' scenario is not unlike what really IS the case with MOST bass cabs in the mid- and high-frequency portions of the musical spectrum! Cones have a bad enough beaming problem as it is, and the common convention of running drivers side-by-side very much exacerbates the effect. What makes it worse is that unlike a horn-lens or the like, where the energy is being 'concentrated' by efficiently narrowing and 'redirecting' the sound dispersion, the beaming that occurrs with a cone doesn't offer any extra gain on-axis as the dispersion is narrowed with increasing frequency - the narrowing is due to nothing but off-axis DESTRUCTION of the useful energy; it's only 'fighting itself', and cancelling-out it's own sound.

    You don't have to do The Calculus to understand this: just look at a simple polar chart of horizantal dispersion, at different freqs, for a 10" or 12" or 15" speaker. See how at the lowest frequencies the dispersion is pretty-much omni-directional - now if the dispersion stayed this way at all frequancies of interest, then it WOULD be 'fair' and reasonable to compare electrical input power with SPL energy at a point because the dispersion is uniform - but look at the higher-frequency plots: just try to picture the area that's bordered by the plot-line. You see less area; you're seeing LESS POWER! Notice that the higher the frequency, the less POWER is present!

    Speaking practically and musically, if your cab sounds good right in front of it, and as soon as you begin to progressively move off-axis your highs at first - then even your mids - just go-away, you're wearing rose-colored glasses if you stand on-axis and imagine that's how it sounds to the majority of others out there on the stage or in the audience.

    This is why I chose a 90X50-degree dispersion HORN, crossed-over at 2000Hz for my rig. You can really HEAR the difference all over the room.

    Gotta run (I'm at work)! I hope we can all see this subject expounded upon here on TB. There is a general dark-ages kind of misunderstanding and mis-information going on in the bass-world regarding this subject.

  14. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Dispersion is a huge factor. For all intents and purposes sound is omnidirectional below 80 Hz, and typical speakers doesn't really get directional to around 300 Hz or so. The problems start once the diameter of the driver exceeds 1 wavelength. With a ten, with a true cone diameter of perhaps eight inches, that frequency is about 1700 Hz. For a fifteen the limit for reasonable off-axis response is closer to 1kHz. So while the on-axis response of a typical speaker may be very respectable up to even 5kHz the off axis response, what everyone who isn't directly on-line with the driver axis, may be quite poor. There are a couple of reasons why you sounded so good through the JBL. One was a properly designed cabinet actually capable of reaching low notes. As you noted the other was the high frequency horn, one designed for good off-axis response. I do think that 2kHz is a bit high for a crossover to fifteens, and if your driver/horn will stand it you should try going lower. If not think about adding a six inch mid to fill in the 1kHz to 2kHz range.
  15. Toasted


    May 26, 2003
    Leeds, UK
  16. Joe P

    Joe P

    Jul 15, 2004
    Milwaukee, WI
    My original plan was to go with one or two Avatar NEO-15s with a selenium horn and driver suspended and time-aligned above it. I chose the horn and driver to both be rated fully useable down to 400HZ (though the continuous power-handling of the driver was a bit derated down there, as compared to a 1000Hz min; also the horn did have a little odd lobing behind it in the 500Hz plot). I'd still love to hear what that would sound like - if from nothing else but a technical-standpoint, I love horns. This would have cost me at least $600, and that's if I went with a passive 800Hz crossover (800Hz seemed to be where the 90-degree horn pattern best matched with a typical 15" driver dispersion) - an active with a stereo power amp and a bass preamp was getting monitarily prohibitive.

    I was experimenting with our little band PA, and also looking into some PA cabs at music stores a little (as well as much book-study, of course). I saw this JBL JRX125, with two fifteens and a horn in a vertical alignment and read some sales promo on it. I finally convinced - don't even get me started.. - the salesman (no: CLERK!) to allow me to connect a bass head to it. That thing sounded so good, that I considered postponing my big, experimental project for a while; I still need a new head yet, and the other idea would have taken many months of gig-money (I sort of made a deal with my wife about only spending gig-money on music stuff...). I'm glad I did (BOTH: Made the deal with my wife AND got the JBL.. now I can spend ALL my gig-money with only Talkbass consultation - no wifely-input reqired! We made a deal...).

    Aaaaanyway: I agree that 2KHz is high, but I figure all that can mean is a reasonable EQ-change at the fringes of dispersion; a dip between 1000Hz and 2000Hz - that's not the worst place for a 'scoop', I'm a mids-meister myself (I BOOST'em!), so out there at the edges I'll probably still have more mids than many bassists do ON-axis!

    Gotta run!

  17. BassJunkie730


    Feb 3, 2005
    :eyebrow: Nick aren't you the guy that so vehemently defended a certain tone from a certain bass player from a certain band? Well I think you need to do two things before posting (I try but there is always that one thread that answers my question that I couldn't find).

    All you have to do is seach watts or decibels or more volume from speakers or something. That's why people get frustrated with newbie TB'ers that come in and ask the same old question again, and again, and again.

    Second. OPEN YOUR MIND, I don't know if you benefitted from the nickelback bass overdrive thread, but if we cannot convince you that percieved volume and wattage are not directly related and that getting another power amp will not make you louder (if your speakers can handle it it WILL give you more headroom, which has it's bonuses like people thinking "Oh THAT's what he's singing") Then please do not waste our time or at least those of us who REALLY know what they're talking about. That other thread was exhausting - funny at times but exhausting.

    I'm not trying to jump to conclusions - but remember there are many opinions, personalities, ego's, beliefs, but most importantly many minds with tons of useful information at Talk Bass. open your mind - you may learn something - or at least save yourself from buying the wrong componet for your rig.

    over and out.