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Speaker Farting...Why?

N

no_flags

Dec 31, 2009
14
0
#1
Ok I know this has been discussed ad nauseam but after reading through the faq threads about it I still don't know what to think.

Here's the scenario: a Hartke LH500 into a Avatar 410 neo. The amp is 500 watts the cab can handle 1000. If I turn the amp up enough the speakers will fart out. Is this from the amp clipping? If so, why are seemingly all solid state amps designed so that they clip when turned up all the way? Why not just decrease the gain range to a safe level? Or is it from the amp supplying too much power to the speakers? I don't see how that would be possible unless the amp was clipping since it is only 500 into a 1000 W cab.

Also, what exactly is speaker "farting"? Is it when the input signal to the speakers is trying to drive them farther than their maximum excursion?

Thanks to anyone who can help enlighten me on this. :confused:
 
#3
wicked_child said:
imho, this phenomena occurs even before the signal reaches the speakers. yep, my vote is that the amp is clipping.
Click to expand...

This has been happening with my Avatar 2X12 and my Peavey Tour 700.

Head: 500 watts at 8 ohms
Cab: 500 watts (8 ohm cab)

My gain was at about 12 O clock, and now it is at about 8 or 9, and it is not happening.

Even when my speakers would fart out with higher gain, the clipping LED wouldn't turn on, so I don't think that could be the problem. It also only happens when I have my bass tuned to CGCF, not drop D or standard.
 
#4
Hmm mine's just in standard tuning. I will say I have a pretty bass heavy sound...that seems to make it happen more but I don't exactly understand why. I don't think it has anything to do with the avatar brand though. I ran into the same thing with my old swr cab.
 
#5
no_flags said:
Hmm mine's just in standard tuning. I will say I have a pretty bass heavy sound...that seems to make it happen more but I don't exactly understand why. I don't think it has anything to do with the avatar brand though. I ran into the same thing with my old swr cab.
Click to expand...

This is my first head/cab, and I still have nothing bad to say about Avatar...

Whats your EQ looking like right now? I put everything flat, and boosted more mids then anything, and put the gain back to about 12 o clock, and all of the farting seems to have gone. Maybe I was giving just a little bit too much bass with the head.

I'm still messing around with it to find my sweet spot with all of the EQ options that are available with the head, though. And playing in drop C, I want to have a very boomy sound. Maybe I'll be ordering in my other 2X12 sooner then I thought.
 
#7
If you boost some bass, those 10" drivers will bottom out with the quickness. Takes somewhere around 50 watts per driver @ 40-60hz, IIRC.

As to your other question: Why are solid state amps designed to clip before you turn them all the way up? Because different people send different strength signals to the power amp.

If you boost a bunch of anything you're sending a hotter signal to the power amp.

Think of it like this: If you send a signal of +4dBu to the power amp, and turn the master all the way up, you are probably getting very close to all 500 watts the amp has to offer. Now add +6db of bass. Your signal is very likely not +4dBu anymore, probably more like 6-10dBu.

So now, you probably only have to turn your master volume knob to 1/2 to be railing your amp.

There are tons of gain stages in bass amplification that can overdrive your power amp, overdrive your preamp, or whatever. Say you use a very hot bass into an 18v boost pedal and crank it up, then slap and pop like Flea, you could be sending a hot enough signal to overdrive your preamp and power amp at quite modest volume settings.

That's kind of a generic explanation but suffice it to say, different amounts of gain before the power amp will make the amp clip earlier or later. That's why. It's not like all solid state amp manufacturers are stupid or something :)
 
#8
deliciouspesto said:
It is clipping somewhere in the signal chain and it is being passed on, they have gain in case you feed it a low signal.. obviously you are already giving it a lot, so lower your input.
Click to expand...

I used my stack for the first time in a band situation (only a guitarist, no drummer at the time), and my input was only on about 3. The stack has power, I just think I had too much bass dialed in.
 
#9
Regarding speaker farting, it's one of three things generally:
1- overdriving your preamp (too much gain before or within the preamp - adding lots of eq with a hot signal, cranking the gain, turning up all your preamp knobs on your bass). This can sound good or not depending on your ear and the design of the pre.

2- overdriving your power amp (say you have a powerful preamp that's hard to clip like say, a Gallien Krueger or EA, you send too hot of a signal to the power amp and it clips (tries to reproduce a signal level it is incapable of).

3- your speaker is pushed past Xmax. Some speakers (guitar speakers, primarily) sound good when distorting. Some sound farty.

Any of the above could be causing it but most likely thing to cause what people think of as farting is either clipping in the power amp or speaker distortion. The LH500 is a tube preamp, and rates to have a fairly gentle clip at the preamp stage.
 
#10
My eq is a little scooped, so mids cut a bit and lows and highs boosted. Nothing too drastic though. And it does get extremely loud before the speakers start to fart. I guess I was just wondering theoretically why this happens. If it is the amp clipping then why do all the companies make solid state amps that will clip when dimed? Couldn't they just decrease the amount of maximum gain? Perhaps they are trying to accommodate a wide range of input levels but how much variation could there be between basses besides actives being louder than passives?
 
#11
rpsands said:
Think of it like this: If you send a signal of +4dBu to the power amp, and turn the master all the way up, you are probably getting very close to all 500 watts the amp has to offer. Now add +6db of bass. Your signal is very likely not +4dBu anymore, probably more like 6-10dBu.

So now, you probably only have to turn your master volume knob to 1/2 to be railing your amp.
Click to expand...

That make alot of sense. Thanks!
 
#12
dukeisdog said:
This is my first head/cab, and I still have nothing bad to say about Avatar...

Whats your EQ looking like right now? I put everything flat, and boosted more mids then anything, and put the gain back to about 12 o clock, and all of the farting seems to have gone. Maybe I was giving just a little bit too much bass with the head.

I'm still messing around with it to find my sweet spot with all of the EQ options that are available with the head, though. And playing in drop C, I want to have a very boomy sound. Maybe I'll be ordering in my other 2X12 sooner then I thought.
Click to expand...

:)
 
#14
I generally make the power amp carry the load so the pre-amp makes a clean job of the input.

Set Guitar volume at about 8 (out of 10). This leaves some adjustment under your fingers.
Set the Master Volume (power amp) at 5 & the Gain (Pre-amp) at 3.
Increase the Master to 8, slowly, then bring up the Gain, if you need more sound. Spinal Tap legends about amps that go to 11 aside, you need to find & respect the limits of the equipment. Keep an ear out for clipping. Adjust either Master or Gain to fix it. One of them should fix clipping with a small tweak. That 1 is the weak link in the chain. If you push hard on the weak spot often, something will break.

I know you've heard this before but, it's worth repeating. If you're driving your amp hard you should protect your hearing. A pair of ER-20's from [Invalid or Expired Link Removed] will protect you & still let you hear everything that is going on around you while you play.

Hope that helps 8-)
 

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