Playing bass through a guitar amp?

[wellREDman]

can I damage a guitar amp by playing bass through it?
When I'm teaching i have been playing bass and guitar, and now my twin tele, through an old Carlsboro  bass combo, but we've just had a 40w Marshall valvestate donated, and I would like to use it but I remember as a teenager  I killed a big old hi fi speaker by using it as a bass amp, would i do similar damage to the Marshall if I use the bass part of my twin through it?

[Dave W]

The speakers in a guitar amp generally aren't able to handle the transient spikes of a bass at any kind of volume. For low volume, non-aggressive playing you can get by, but there's a lot of low frequency cancellation with an open back cabinet and the EQ isn't optimal for bass.

[gearHed289]

The AMP will be fine, it's the speakers you need to be careful of.

[Denis]

For fun I played my Danelectro through a buddy's Fender Twin Reverb.
It was not fun.

[Granny Gremlin]

I wouldn't worry about the speaker unless you crank the amp, but that is a concern (the 12" in the Marshall should be mostly fine).  Combos generally have the speaker well matched to the amp's output, though if you crank it with a bass plugged in (especially with solid state amps like your valvestate) the clipping that the low frequencies can cause might blow the speaker (this would be less of a concern with a tube amp, but still).  You should be well safe if your tone is clean (barring an actual distortion effect, whether onboard to the amp or external).  The remaining issues are a) amp voicing, and  b) lack of bass response, as mentioned (which are a matter of tone preference rather than safety).

Many bassists, both famous and not, have used guitar or PA amps for bass (including Marshalls into 12" guitar speakers).  I myself use old tube PA amps (live/jam) and maintain (as I've mentioned before) that one of the best recording sounds I ever achieved was a 60s Gibson EB3 through an older Peavey Bandit guitar practise amp (8 or 10" speaker) which is a pretty crappy amp that has never sounded any good with any other instrument I have plugged in to it (especially guitars).

[Highlander]

I ran my pair of Sound City open back PA columns (4x12 oblong style as opposed to square) until I killed them with my Hiwatt; I also used (and still do) a Marshall 4x12 slope cab which had dual cone speakers (again PA style) but now has a pair of Eminence Governor 75w guitar speakers (and a pair of the old Celestions sort of as blanks) and I'm happy with the sound.
I have often used 2x15 bass cabs (WEM was one I had for some years) with the Marshall.
I always tended to push them as far as I could...
I presently only have a MAG300 with 4x10 combo operational - Hiwatt is still sick...

[westen44]

The AMP will be fine, it's the speakers you need to be careful of.

Exactly. 

[exiledarchangel]

I use my guitar combo for practice, I don't put it over 3-4 and everything is fine.
Its a 25 watt open back thingy from epiphone, and it has an almost nice sound for bass for a guitar combo.
Maybe someday I will test its amp connected with a real bass cab.

[SKATE RAT]

i play bass through a Traynor guitar head and an old Peavey 4 X 12 guitar cab (Scorpion speakers). i play really loud with distortion and have no issues i have been using this set up for years now.

[Dave W]

i play bass through a Traynor guitar head and an old Peavey 4 X 12 guitar cab (Scorpion speakers). i play really loud with distortion and have no issues i have been using this set up for years now.

That's because the Peavey Scorpions can handle bass. But if it's an open back cabinet you're still getting a lot of low frequency cancellation.

[SKATE RAT]

yeah, they can and sound much better with Bass than guitar. i'd like to get a 2nd cab someday

[Granny Gremlin]

But if it's an open back cabinet you're still getting a lot of low frequency cancellation.

A workaround for that (though there aren't too many open back 4x10s out there, aside from combos, that I am aware of) is to make sure the cab is right up against a wall.   Trouble is, a wall just ain't always handy. ... and it might get a bit boomey by nearly eliminating baffel step effect.

Scorpions , although used and marketed as guitar drivers, were also used and marketted as general purpose extended range (on the top side; in the sense of them being not quite fullrange units) woofers and used in some of Peavey's smaller floor monitors and PA speakers.  They might have used them in bass cabs here and there but I'm not sure.  They were kinda like Peavey's answer to the popularity of JBLs.

[slinkp]

A workaround for that (though there aren't too many open back 4x10s out there, aside from combos, that I am aware of) is to make sure the cab is right up against a wall.   Trouble is, a wall just ain't always handy. ... and it might get a bit boomey by nearly eliminating baffel step effect.

What's baffel step effect?

Scorpions , although used and marketed as guitar drivers, were also used and marketted as general purpose extended range (on the top side; in the sense of them being not quite fullrange units) woofers and used in some of Peavey's smaller floor monitors and PA speakers.  They might have used them in bass cabs here and there but I'm not sure.  They were kinda like Peavey's answer to the popularity of JBLs.

Way back around 1982 when I had a TNT-130 with a single 15", I remember that you had to pay extra to get a "Black Widow equipped" amp.  I did not pay extra.  Was mine a Scorpion?  Or were there other driver models?

Tangent: Later, I bought a Randall head, and before I sold the Peavey I tried running the Randall preamp out into the Peavey power amp in. This convinced me that the reason I disliked Peavey bass amps of that era was only because of their preamps. With the Randall preamp, the Peavey power amp and cab sounded totally fine, after years of being unable to dial in a sound I liked from the Peavey.

I used that Randall for 8 years or so, driving a poorly constructed homemade cab with an EVM-15L, which miraculously accidentally sounded pretty decent - enough so that in college, a couple other bassists used to borrow it from me.   That rig lasted until I finally blew the EVM and replaced it with an old Ampeg 2x12 with Eminence drivers, and then the Randall head got stolen and replaced with a GK 400RB.  I liked that GK / Ampeg rig, although it didn't have anything like the low end depth I like nowadays.

[Granny Gremlin]

What's baffel step effect?

You know how they ( home theatre salesmen/installers/manufacturers etc.) tell you that bass is non-directional (so having a single sub anywhere in the room in a stereo/surround system will work just fine)? ... but then they never tell you at what point exactly this happens.

The reason is that it is not a fixed universal frequency at which bass becomes non-directional.  It is determined by the the size of the speaker baffle - the point where the shortest dimension (i.e. either the width or height of the speaker) = 1/8 of the frequency.  At this point the sound waves wrap around the back of the speaker and radiate in all directions vs just forwards at the listener resulting in a -6db shelf (in terms of output; SPL) from that point down (and a -6db per octave slope down to that point).  Putting a speaker right up against a wall (or soffit mounting it in a wall) reduces/eliminates this effect because the soundwaves can't go backwards (or not very far before they bounce back).  Some speaker systems (notably pro studio monitors and hi end hifi) have circuits or other mechanisms (such as a duplicate woofer on the rear crossed over around the transition point) to compensate for this.  This is another reason (aside from the oft-cited "larger cones move more air" thing) that smaller woofers tend not to produce as much bass (smaller woofer goes in a smaller box, with a higher transition point).

Anyway, the things to take away from this bit of info are:

- if your amp/speakers are too boomy, move them away from the wall  *
- if your amp/speakers aren't bassy enough, put them up against a wall ... if already up against a wall try a corner *
- never buy a hifi/theatre system that has really really tiny main (L + R) speakers (we've all seen those little cubes, or superthin towers poles) + sub and expect a nice smooth integration between them (unless you litterally put the mains right up on/in the wall).  You likely will not be able to adjust the crossover point high enough, and if you did, the top end of the sub's response would be directional and make things weirder.

* Some amp/speakers (mostly studio monitors, as far as I have seen)  have a room mode selection switch - you can use this instead (and not just as intended, if a weak bass speaker you may opt to have it up on a wall and set it for middle of the room mode for more bass).  Labelling on the switch varies from the simple English "corner", "wall", "in room" (or similar) to the a more technical description of the dispersion pattern based on speaker placement: 2pi (forward only, i.e. up against or in a wall), 4pi (away from walls or other boundries), pi (corner), pi/2 or 1/2 pi (tri corner, like where the corner meets a floor or ceiling) or sometimes a middle of the road sort of thing (just to confuse people) of "full space" or 1 (out in room),  1/2 space (wall) , 1/4 space (corner) and 1/8 space (tri corner). Not all implementations have all 4 options.

Way back around 1982 when I had a TNT-130 with a single 15", I remember that you had to pay extra to get a "Black Widow equipped" amp.  I did not pay extra.  Was mine a Scorpion?  Or were there other driver models?

They had other models that they used as well.  Dunno what you had, but not all the speakers Peavey used had Metal names like these 2. I'm not sure whether all the speakers they used were branded Peavey or not, but another example of a Peavey-branded speaker is the Sheffield line.

[hollowbody]

One of my favorite speaker cabs was a Scorpion equipped Peavey 412F with ports on the top and bottom. I foolishly though that I had to have an 8x10 to go with the SVT Classic head. I regretted selling it immediately.

As far as guitar amps for bass, I'm currently using a Fender Super Twin. I know that they were never a very good guitar amp, but 180w RMS is perfect for bass. It doesn't sound very Fender-y to me, thankfully. I've never been a big fan of the Fender tone stack for bass. It sounds more like a Sunn to my ears.