Bi-amping, guitar head, p.a. speakers...

Discussion in 'Amps and Cabs [BG]' started by AngryHammer, Jun 6, 2019.

  1. AngryHammer


    Jun 25, 2017
    Eureka CA
    So, here is what im thinking ive got an empty open back 2x12, i want to find some full range p.a. speakers to put in it for my overdrive.

    I play metal and punk, right now i am bi-amping my rig with a bass tube head running to a 4x10 for my low end and a 100 watt guitar head into a 15 inch black widow for my overdrive. The black widow is a bass speaker and doesn't sound killer with the guitar head, but i don't want to put guitar speakers in because i don't want them to get blown from the bass frequencies. Thats where the full range p.a. speakers come in.

    What do y'all think? Go ahead, smash my dreams.
  2. JimChjones


    Aug 6, 2017
    SE England
    Why don't you roll the bass off to zero on the guitar head? If its got a reasonably powerful tone control that should cut the bass right down to what guitar speakers can cope with. Better yet you could put a high pass filter or an pedal eq of some kind ahead of the guitar amp to cut them down even more.
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  3. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    An open-backed enclosure provides no loading to the drivers contained therein, so the uncontrolled bass frequencies are going to endanger the drivers no matter what kind you use. You'll need employ some sort of device to filter out the LF signal to those speakers. And I don't know what you're referring to by full-range PA my world, that would refer to a full-range speaker system with separate components for highs and lows, etc. If you're thinking you can find a regular cone driver that will give you some nice, bright high end, but still robust enough to handle the low freq signals, a guitar speaker is probably exactly what you're looking for.
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  4. Wasnex


    Dec 25, 2011
    Since you are not using a crossover over I suggest the term mult-amping is more appropriate to describe what you are doing. Use whatever term you prefer, but most people assume you mean something different when you say biamping.
    Multi-amp guitar rigs - Wikipedia
    Multi-Amp Rigs 101

    I am not sure which 15" Black Widow you have, I attached the spec sheet so maybe you can see why you don't like the sound.

    In general, a PA driver will probably be fairly flat in the mids. A guitar speaker will likely have a lot more colorful tone.

    If you run a suitable HPF and high powered guitar speakers, the speakers should be fine, especially if you install them in a sealed back cab. In the past I ran a pair of JBL E120s and a blackface Fender Twin. As long as I kept the bass control below about 4, I could run the amp just under clipping and the speakers were fine, even in an open back cab. For context a blackface Twin should be considered about an 85W amp.

    For awhile I actually biamped my SVT and the Twin with a Orban 672A set to a 200Hz crossover point. I could have run the crossover a bit lower with the JBLs, but 200Hz is the limit of the Orban's LPF section. I did some experiments where I ran the HPF lower and it tended to muddy up the sound a bit. I think this was because of the open back cab and possibly introduction of phase errors from misaligning the crossover.

    I think a Marshall 1960A or similar cab with Vintage 60s would probably be fine with a 100W head if you ran an HPF around 100Hz. Might even be okay running full range, but I think it would probably sound better with the HPF so it doesn't fight with your 410 in the low end. I wouldn't subject Greenbacks to this sort of abuse.

    Good luck and have fun!

    Attached Files:

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  5. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    +1 ...but stand by.
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  6. Wasnex


    Dec 25, 2011
    I can't wait :nailbiting::woot:
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  7. AGCurry

    AGCurry Supporting Member

    Jun 29, 2005
    St. Louis
    If you put an open-back cab in the vicinity of a closed-back cab, you are liable to encounter phase problems.
  8. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    I'm not sure that this has been my experience...but I'm willing to listen to an elaboration. Is it different from the 'phase problems' between the front-facing and rear-facing waves in that same open-backed speaker?
  9. Even if it's a closed back. That is a big reason why folks bi-amp instead of multi-amp.
  10. Wasnex


    Dec 25, 2011
    From what I have read, an open back cab will behave largely as a ported design with an very high tuning (see below). There is a lot of phase shift and group delay that occurs around the port frequency. So yes, I would expect some phase issues around the resonance of the open back cab if you paired it with a close back cab.

    An open back cabinet functions like a ported cabinet with a really big port. There is a fairly long thread that gets into the technical matters somewhere here on Talkbass. I believe Fb is typically in the 100 to 150hz range, so too high for bass. This may be the thread: Detuned Cabinets?
    agedhorse likes this.
  11. Redbrangus

    Redbrangus Supporting Member

    Nov 19, 2018
    Under The X In Texas
    I think these are two different issues. As far as phase relationships are concerned, I figure an open-backed enclosure is approximately equivalent to a open, flat baffle that has the dimensions of the baffle plus the sides in the same plane. The destructive phase cancellations occur because of the negative-going waveform wrapping around the baffle...I don't think the resonant system of enclosure and driver, such as it is, contributes much to this effect.

    My over-all point is: how are the 'phase problems' that occur when an open-backed cab is combined with a closed-back cab different from the phase problems that occur when the rearward wave of an open-backed enclosure is combined with the forward wave of that same enclosure?

    In either case, I don't endorse using an open-backed cabinet for any sort of bass signal that hasn't been high-passed pretty aggressively. In fact, I don't endorse using an open-backed enclosure for any sort of bass signal at all, but use (experiment?) with whatcha got.
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  12. Wasnex


    Dec 25, 2011
    :thumbsup: Although I suspect it probably depends somewhat on how much back paneling is involved.

    Here's an example of a fairly extreme amount of rear paneling, that is more of a large shallow port than open back. I have one of these (Mojave) cabs loaded with Celestion Blues and it has huge lows.


    Also, the size of the baffle and depth of the cab can make a pretty significant difference regarding how much low end the cab can produce, even if there is not much rear paneling. Believe it or not, I actually gigged in a cover band playing bass through my Fender Twin. Obviously this would not have been possible with the stock drivers, but the JBL E120 has a stiff suspension, a very powerful motor assembly, and a power rating of 150W RMS 300W program.

    The rear of my Twin would have looked something like this.
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  13. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010

    Without sounding 2 generic get a 810
    And just run that.

    But open back speakers getting mentioned around here is just asking for smashed dreams lol.

    I'd buy a used 412 sealed back for the same money you'd spend on a pair of pa drivers.

    Used guitar cabs come up all the time.
    I have used a 810 and 412 Guitar cab.
    Ran 412 v30 loaded cab with fender wanna be Model T reissue. Which I can say has a pretty fun pre and all tube output.

    Stopped using 412 ran 810 instead. 2 of them. Same deal just ran different heads. Until I gave up on that and ran just both cabs one head. Ran it hard, used pedal once while go evil.

    No pedals just head distortion. Then hit a gritty fuzz for some changes. Didn't miss running extra head for distortion

    If you get lucky alot used carvins with v30s or the some of the Eminence v30ish drivers came in the carvins too. They had alot ugly rattle fur ones. But had a series with a blueish vinyl and look cool and are dirt cheap.

    Isn't many pa 12" that work well open back. Gotta use squaky guitar speakers. Technically they'll work. Won't sound much different than a Widow really.

    Scorpion loaded 2x15 Peavy could work. Dirt cheap. Scorpions are bright. Few scorpion 10" and widow 18" cabs out there too. All in one box. Sealed with crossover. And indepent inputs for the 10" and 18"
    Last edited: Jun 6, 2019
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  14. AngryHammer


    Jun 25, 2017
    Eureka CA
    ok nix the pa speakers idea.

    I had a cheap front ported guitar 212 that did not work for this, my 412 works but I don't want to lug it. The Black Widow incidentally is in a front ported old Carvin cab. Its either the 1502DT-8 or the 1505DT- 8.

    I run the guitar rig so- bass- 2, mid- 5, treble- 8

    My empty cab is actually just a home made plywood box with a removable back and some blown 10s in it, I was just gonna cut the holes bigger to fit some 12s, but im sure this is inadvisable for a reason or two.

    seems like if i'm gonna spend money maybe just get a sealed guitar 212...
  15. JeezyMcNuggles

    JeezyMcNuggles Supporting Member

    Feb 23, 2018
    Santa Maria, CA
    I suck, but nobody really notices
    Why dont you just play through a single amp, and a bass cab? What's the preconceived notion that your set up cant deliver what you want by itself? All you need is a drive/distortion pedal. Problem solved, and load cut in half. I dont get it.
  16. AngryHammer


    Jun 25, 2017
    Eureka CA

    Why buy one amp over another? or one bass over another?

    I like the way it sounds this way, I've got three overdrive pedals sometime I use one for a boost for soloing but overall they just knock out too much low end. I like sound of overdriven power tubes. Why would you assume its a preconceived notion? I've played though a number of different amps, cabs and pedals, and this is the sound I like best so far, (I'm looking for a substitute speaker set up for the 412 so I don't have to carry it.) Maybe all you need is a drive/distortion pedal, but I like weird junk.
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  17. Wasnex


    Dec 25, 2011
    I think this approach is valid, but it does involve carrying a lot of extra gear.

    Have you tried parallel processing? Split your signal into two paths. Run distortion on one side and compression on the other. Distortion has a bit of built in compression, so running compression on the clean side will help the two signals integrate better when you combine them. You can also run heavy distortion on one side and light OD and compression on the other.

    Another trick you might try with parallel processing is running EQ inline with your OD/distortion. Try it before and after the pedal to see how it changes the sound.

    Lots of options, but the main idea is one side of the signal path retains a nice tight low end.
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  18. Jazz Ad

    Jazz Ad Mi la ré sol

    Using a guitar amp for overdrive along the bass amp is a proof method to get a killer tone, with huge defined lows and great dist.
    Many bands use it, mostly power duos and trios. Clatter and Royal Blood are 2 proponents of this approach. I'd say you're on the right track

    I did it for years. My approach was to use whatever bass amp I had at hand with an Akai Unibass going to a 30W Laney guitar combo. This way I was an octave higher and didn't threaten the speakers.

    Guitar loudspeaker is essential to proper tube overdrive. They have a specific voicing to get to it. All you need is a mean to protect it.
    A hi pass filter set at 100 Hz will do it just fine. You can use a dedicated unit like a fdeck for example but for experimentation on a small budget, a small multi like a Zoom MS60B or B1on will do a fine job at this function without taking much space or energy.
    Another approach is to split the signal. Either with a proper crossover or with more exotic solutions. Some people use a Boss Bass chorus set at 0 rate; used this way its outputs split between full range on one side and only highs on the other. Therea re
    You can also use a high octave device and then send it into the guitar amp.

    Since you only use it for overdrive, 100W is too much. To get into power tube overdrive territory you will need to push it way beyond reason and overpower your bass amp and the rest of the band, especially with a 212. 30 to 50w would be more adept.

    For the loudspeaker it all depends on what kind of tone you want, comfy overdrive or something tighter. In your case I'd go with decent quality 2nd hand and see how it goes.

    With the signal process being so different on both chains, risks of phase issues are minimal but they exist. It's hard to predict how they may manifest before trying.
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  19. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    Yep. I'm working up a new rig like that for slide bass right now. I used to do the duo thing with just drums and myself, and if and when I get back to that a guitar amp would come in handy for the parts where I played guitar too. So I reckon I'll just build one...[​IMG]
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  20. Adienn7


    Jan 26, 2007
    If you wanna run the rig.. Do a crossover.. Rolls makes a cheap one.