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Cab power handling (farting...)

Fretless55

Fretless55

Jan 6, 2010
562
725
Portland Oregon
#1
I'm confused by this.

What have is (both bought used):

-Older GK 400RB II head

Rated 125w @ 8ohm / 200w @ 4ohm


-Bag End s15d cab

Rated @ 8ohm continuous 200w / peak 400w

Sensitivity 103

My question is this:

With master at noon, and all EQ set flat, it will start to "fart out" at 10 o'clock volume when I dig in on the E.

I understand this is a pretty efficient cab, and it does get loud pretty quick, but I thought it would have more head room in handling what really isn't a high powered amp played with a passive P bass (full volume) with flats.

I'd appreciate any advice from the more technically adroit.

Thanks
 
#2
Well, the power rating of the cab says little or nothing about what power the elements start to fart out at. The speaker element has a motor consisting of a coil in a magnet gap. It is only in its linear range while the magnet gap is covered by coil. Outside that range, movement is no longer linear, and it farts out. The power rating mostly tells what it can take before it overheats.
 
#3
Hi.

^That.

Also, knob positions by themselves mean absolutely nothing, You can reach the max power with any and all positions depending on the input signal strenght.

I don't know whether that GK has a HPF, but if it does, use it.

Most "Hi-Fi" bass amps amplify IMHO too low on the frequency spectrum, and that creates the illusion of a really weak amp. All the power is "wasted" on frequencies that aren't very useful or even useless in a gig situation, but when rehearsing at lower SPL the tone is just heavenly ;).

Regards
Sam
 
#4
What you are experiencing is not the fault of the cab, but of the amp. Speakers dont exactly fart. They distort which sounds like, well, distortion(like a mild-med overdrive), and when pushed really far they bottom out which sounds like somebody hammering the back of the speaker.

If it is a farty square wave synth sound (like a maxed out nasty fuzz pedal) you are hearing, it is most definitely the amp running out of headroom, and clipping.

If you can't get loud enough to cover your gigs or practice, without farting out, with this setup, you need more power. A HPF will help, but it is only a remedy, not a cure.
 
#5
I noticed you didnt say what bass you were using.. I only say this because something like this happened to me recently. I plugged my ACTIVE conklin into my input on my bx1500 head, but in the process of setting everything up i bumped the switch putting the input into Passive mode, Instead of Active.. and instantly the gain was over the top.. Im not saying this is YOUR issue.. just sharing something that happened to me recently.. does your amp have a passive/activie input? or gain know?
 
#6
You've told us nothing about where you set your gain, only master. Could be the head, could be the cab. Neither are especially high power or power handling, but I would think the 115 could take at least a 200w amp running clean, as most modern 115's can at least do that. But they do sound very similar when distorting, so you need to make sure which one is doing the distorting before you decide what to do.
 
#7
First turn the master up to 3:00. 10:00 is pretty early on the volume (input gain) to start getting breakup, check the pickup height to your strings it could be too close. Where do you have the boost set at? You could be tipping into the "G-K growl" but not fully there or the power supply caps may be due for replacement (you said a old used unit).
 
#8
JimmyM said:
You've told us nothing about where you set your gain, only master. Could be the head, could be the cab. Neither are especially high power or power handling, but I would think the 115 could take at least a 200w amp running clean, as most modern 115's can at least do that. But they do sound very similar when distorting, so you need to make sure which one is doing the distorting before you decide what to do.
Click to expand...
You need a really extreme linear excursion to accommodate 200w linear movement without distortion in the bass range. With a sensitivity of 103dB at 1w you would get 126dB at 200w if the response is linear. There is no way a bass cabinet rated to 200w max and 103dB sensitivity is clean and linear all the way to 200w.
 
#9
Shardik said:
You need a really extreme linear excursion to accommodate 200w linear movement without distortion in the bass range. With a sensitivity of 103dB at 1w you would get 126dB at 200w if the response is linear. There is no way a bass cabinet rated to 200w max and 103dB sensitivity is clean and linear all the way to 200w.
Click to expand...
That all depends if they use fartout or voice coil meltage to arrive at the 200w figure. For example, Ampeg rates their SVT 115e at 200w, and it's fully capable of taking it IMHO, and it would probably be rated at 400w if they went by voice coil.
 
#13
Thanks for all the responses so far!

Sounds like most think its a problem with the head, but I'd also be especially interested in hearing from the Bag End cab users out there. Would a higher powered head (ie an Ampeg pf350 or a pf500) really help? Somehow it seems counterintuitive...
 
#15
Thanks for the sustained interest B-string. I can see from your profile you're a GK fan.

I went ahead and set the master at 3 o'clock, the volume at 10, with the boost level at noon. It's OK with a very light touch (I'm a fingers guy) but even with a little "dig" it becomes a non musical bleat. Don't think it's the GK growl...

Thanks again
 
#19
Fretless55 said:
School me!
Click to expand...
Well the boost knob does add dirt to the signal. Of course, that all depends on the level of what's coming into it, but that's pretty much the idea for the boost knob...to cause distortion.

Having said that, B-string knows an awful lot more about GK amps than I do, plus he's a tech, so do what he says. Too bad you don't have a cab that handles way more power than your Bag End to try it out in.
 

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