Cab farts

[lownote]

Played a three hour ouside gig yesterday in the heatwave .  My band's loud so I had had gain on 1 o'clock and master set to around 2 on my Markbass LM3. My 4 ohm BF Two 10 kept farting. Could it have been heat?  Or do I even more totally not understand these things more than I thought?

Edited July 19, 2022 by lownote

[jazzyvee]

Hmm, most likely the drummer. 🤣.

Seriously though, maybe the pre-amp in the rig is overheating and clipping??. Maybe try a lower pre-amp setting and open up the master volume a bit more to get the same overall volume and see how that works out? 

 

Having not had many bass rigs I most likely understand far less than you do. Hopefully someone more knowledgeable on these things might offer some insight. 

Edited July 18, 2022 by jazzyvee

[Acebassmusic]

2 hours ago, lownote said:

Played a three hour ouside gig yesterday in the heatwave .  My band's loud so I had had gain on 1 o'clock and master set to around 2 on my Markbass LM3. My 4 ohm BF Two 10 kept farting. Could it have been heat?  Or do I even more totally not understand these things more than I thought?

 

From my experience, playing an outside gig tends to swallow up the bass so expecting a 2x10 to keep up with a loud band could be a little optimistic (even though BF are good). I'm also assuming that as you were outside your cab wasn't near any side or back walls? If it wasnt then you lose any boundry effect that helps boost the volume from the cab.

 

What EQ settings did you have? If, due to the lack of boundry effect etc, you've boosted the lows to compensate this could be contributing. Also as @jazzyvee says if your input gain is slightly too high it can cause distortion / farting from the cab.

 

Have you tried the amp / cab since and noticed any problems?

[lownote]

@AcebassmusicAt practice room volumes since it sounds fine. Alex has just come back and said I've not got enough output happening.  Is that the same as you saying I'm overcranking the gain, and got the master volume turned down too low?  I remember once Dave Green at Ashdown telling me gain should be whacked wide open, and only use the master ouptput volume to control volume.

Edited July 18, 2022 by lownote

[Acebassmusic]

5 minutes ago, lownote said:

@AcebassmusicAt practice room volumes since it sounds fine. Alex has just come back and said I've not got enough output happening.  Is that the same as you saying I'm overcranking the gain, and got the master volume turned down too low?  I remember once Dave Green at Ashdown telling me gain should be whacked wide open, and only use the master ouptput volume to control volume.

 

Good to hear it sounds ok at rehearsal levels, hopefuly means that no major damage has been done 🙂 I'm not quite sure what Alex means by "not enough output happening" 🤔

 

As far a whacking the gain right open I've always understood it that you should push the input gain until it only occasionally clips on your very loudest notes and then use the master for your overall volume setting. I've just plugged into my Eden 500 and VK 210 and with the gain cranked I can create some exceedingly awful farty sounds at very low volume. 🤣

[lownote]

Hmm, that makes sense. I didn't look for the clipping light (it being bright sunlight, like).  Reading Alex' email again he says I could be clipping. So maybe my answer is to be careful with the gain and thrown the master wide open.

[Acebassmusic]

4 minutes ago, lownote said:

So maybe my answer is to be careful with the gain and thrown the master wide open.

 

For me its a balance between the 2 - set the gain for clean undistorted sound and then boost as required with the master volume.

[gjones]

I was under the impression that the master on a class D amp can be turned to max and you can then use the gain to adjust your volume.

 

Which means that your gain shouldn't clip, unless your band is seriously loud.

Edited July 18, 2022 by gjones

[itu]

The basic idea in amplification is to set the input gain to fill the channel. But you should not overdrive it, if that is not the idea. This way your amp is amplifying the signal, not the noise. Otherwise your amp is a) noise generator, or b) distorting.

 

When the channel is full of the bass signal, you can open up the master/volume/whatever as much as the situation and you need.

 

The signal is always a mixture of the wanted content (the bass), and unwanted (noise). If your adjustments are not functional, your output from the cab has lots of something that warms the amp, but not your audience.

 

The comment from @gjones is somewhat questionable. If the adjustments are named unconventionally, this may be true, but the input gain is the thing you set and forget. All other adjustments can be tweaked while playing. (Although every eq pot should be seen as a bandwidth limited gain. Use the eq wisely along with input gain.)

[gjones]

21 minutes ago, itu said:

The comment from @gjones is somewhat questionable. If the adjustments are named unconventionally, this may be true, but the input gain is the thing you set and forget. All other adjustments can be tweaked while playing. (Although every eq pot should be seen as a bandwidth limited gain. Use the eq wisely along with input gain.)

I was having a typo moment and typed gain when I should have typed master.

 

As far as I am aware, there is no noise to amplify on a class D head, so you can turn the master to full and then use the gain to adjust your volume. 

 

When the amp starts to clip, as you adjust the gain, you know that's as loud as you can go (assuming your cab is good enough to take that level of input).

Edited July 18, 2022 by gjones

[itu]

7 hours ago, gjones said:

As far as I am aware, there is no noise to amplify on a class D head...

As far as I am aware, a system without noise is... wait a moment, where could I find one? The bass pickups and pots produce noise. The preamp in the amp is a noise source. Downright everything produces noise and the amp is very able to amplify it. No matter which alphabet you have, the story actually starts: Let there be noise.

(And light came later.)

 

The channel is working the same way as is every preamp. The most efficient way of using it, is to fill it. Then the power amp can use its potential to the max. This is true also at low levels. Why would we want to warm the room with noise, while we could move the cones with the same energy?

[Downunderwonder]

Farting is the sound you get from an excess of power applied to low end frequencies. I think it's entirely likely your 500w amp is fully up to the task of farting your 4 ohm BF cab without clipping itself.

 

Outdoors you have no wall behind the cab to add the usual 6dB of low end reflective bass. Effectively that's a 'phantom' 6dB cut on your EQ ie the knobs haven't moved. To compensate you boost your lows or pluck nearer the neck without realizing.

 

Fart city for the cab getting four times the low end power to get it sound like it does with a wall behind it.

[lownote]

Here's Alex (Captain Barefaced)'s definitive opinion, FYI: “Either your amp is clipping or you're overloading the drivers. With the 10CR they gradually overdrive in a fairly 'nice' way but solid-state amps tend to clip more suddenly and harshly. Either way it sounds like you don't have enough output… not loud enough or able to produce enough lows at that loudness - the answer is more speakers and/or more amp power.”  Which is counter-intuitive to me.  I thought cabs farted because they're not wo/man enough for the amp; seems it's the other way round.

Edited July 19, 2022 by lownote

[jazzyvee]

I play quite a bit of reggae and hence need a lot of bottom end at fairly high volumes. And I have found that to get the least noise/distortion and risk of farting out from my rig (rack), I put the power amp (class D) on full or virtually full and set my bass to about 3/4 full volume then start to increase the gain on my preamp till I get to the volume I need for the gig. That way I get a clean sound, lots of clean headroom and less chance of farting at low volume from my cab. If I do it the other way and set the pre-amp high and then use the power amp to set the stage volume i tend to get more hiss from the preamp and more chance of the cab farting out at low or high volumes.
 

It i'm using a standard type of bass head, the ones i have tried are too hissy if i turn the master volume to full and then bring up the pre-amp gain. That said my Mesa boogie Walkabout has never made my cabs fart out but can start to be edgy if it's  up to loud and it is quite hissy if up loud. 
The worst for causing farting out I have found are those heads with a sub/octave button, i turn those off.

[Welshbassist]

Just wondering, are you absolutely sure the cones themselves are in in good condition? I had a similar issue where a dust cover became slightly detached, and made a horrible farting sound but it was only noticeable at high volumes when I was using a low b/with the bass turned up. Might be worth removing the grille and inspecting the speakers.

Edited July 20, 2022 by Welshbassist

[mcnach]

On 18/07/2022 at 10:56, lownote said:

Played a three hour ouside gig yesterday in the heatwave .  My band's loud so I had had gain on 1 o'clock and master set to around 2 on my Markbass LM3. My 4 ohm BF Two 10 kept farting. Could it have been heat?  Or do I even more totally not understand these things more than I thought?

 

I doubt it has much/anything to do with the temperature. A lot of people use these amps in locatons where this is just normal summer temperatures, and not that hot.

However... playing outside tends to mean you need to pump out the bass harder than usual (as others mentioned, you usually lose wall reinforcement among other things) so I suspect you were trying to get more from those cabs than they're ok to give. Especially if you used a single Two10. I use a couple generally, with a Mesa D800... it's great, it's loud... but outdoors without reinforcement they can only do so much. A single cab I would not consider other than for use as monitors.

 

[Merton]

On 19/07/2022 at 11:56, lownote said:

Here's Alex (Captain Barefaced)'s definitive opinion, FYI: “Either your amp is clipping or you're overloading the drivers. With the 10CR they gradually overdrive in a fairly 'nice' way but solid-state amps tend to clip more suddenly and harshly. Either way it sounds like you don't have enough output… not loud enough or able to produce enough lows at that loudness - the answer is more speakers and/or more amp power.”  Which is counter-intuitive to me.  I thought cabs farted because they're not wo/man enough for the amp; seems it's the other way round.

The way I read that he’s saying that either your amp was the source of the farting (through clipping pre or power amp) or the drivers really were farting probably because of too much LF content.

If the amp was the source, then you need a more powerful amp. If the speakers were the source then you need more speakers.

Hope that makes sense?

[miikebass]

Had the farty sound last night at a pretty loud gig. 
Noticed toward the end of the night. More noticeably Bb on the E string. 
 

Running Ampeg PF500 (gain at 2 o’clock and not clipping), Hartke 2x10,

Gibson Midtown.

I just removed the grille and checked the speakers. All looks good.  Voice coils move smoothly. 
 

Was it just my settings?  Gain a bit too high?  Have I damaged my cab?

[Dan Dare]

If the input gain clip light isn't flashing and the cab farts, you're either causing the power stage of the amp to clip (too little power - amp cannot produce sufficient power and cuts/clips the peaks from the signal, resulting in a near square wave) or pushing the drive units too hard (too much power from the amp causes them to hit their extension limit), as Alex at BF points out. Could be a combination of both.

 

Modern compact cabs with a single 12 or a couple of 10s and compact amp heads are very capable, but there are physical limits to how much they can do. Playing outdoors or very loud calls for a lot of power and sufficient drive units to shift enough air, especially for bass.

 

A brief fart from the cab won't cause damage, but if you don't turn down and keep blasting away, it will.

[Baloney Balderdash]

A HPF is your freind.

[Rberry7777]

Without limiting (or heavy compression) or judicious gain control of the overall signal chain, a wicked thumb or palm muted heavy pick in the right place can result in a nasty fart -possibly worse.  Open the amp and watch how its fed. Experiment - find the cause. Adjust accordingly.

[Obrienp]

I had terrible farting noises at certain frequencies ( mostly B on the E string)  from my BF Two10 shortly after I bought it secondhand. Thought I had been sold a pup but my local luthier/amp technician helped me track it down to a loose mounting bolt on one of the speakers. It had worked its way so far loose that the captive nut had come free from the back of the baffle board and when I turned up the volume, the rim of the speaker was vibrating against the board, making a terrible farting noise. We had to remove the speaker and relocate the loose captive nut on the board (fortunately it hadn’t chewed up the wood yet). We then refitted it and made sure all the bolts on both speakers were nice and tight. Quite a few of them were quite loose. It now sounds absolutely fine. I now tighten the nuts every couple of months to make sure it doesn’t happen again. I don’t know whether this is a specific BF issue: they mount the speakers from the front, rather than the back of the board but the retaining bolts do seem to loosen quite quickly. When I can raise the energy, I’m going to take each bolt out in turn and put Loctite on when I refit them.

[DGBass]

11 minutes ago, Obrienp said:

a loose mounting bolt on one of the speakers. It had worked its way so far loose that the captive nut had come free from the back of the baffle board

I had the same with a pair of BF 1x10s ( early 100s serial numbers) where t-nuts worked loose from the rear of the baffle causing an audible vibration in the low to low-mid sound range. Luckily the t-nuts stuck to the magnet assembly when they fell off and were easily retrievable. I was able to fix this myself but had to rotate a driver slightly to get fresh baffle as I could see the wood in the original position was splintered away at the rear and there wasn't much for the t-nuts to grab onto. The baffle board wasn't very thick. I did mail BF about it first time it happened but was happy to keep the cab rather than send it back. I was using an ABM 500 with my two 1x10s at the time and they always sounded fairly farty because I was driving them too hard in the low frequency dept and they didn't like that at all. 

[Obrienp]

@DGBassInteresting. I wonder if this is a general BF issue, or just with a particular series/build time. Unfortunately, the serial number is missing from my Two10, because it was converted to an S (4-12 ohm switch) at some stage, so I can’t tell if it was made around the same time as your cab. I might contact BF to find out if they came up with a fix. I’m thinking spring washers, or some kind of Nyloc captive nut.

[DGBass]

@Obrienp I Couldn't say, but it was mentioned that this hadn't happened previously. The first 1x10 I had started buzzing within a week of use. The second one after about a month of use. I only contacted BF about the first one and when it happened on the second, I fixed that and both cabs were fine. The bolts were quite small, maybe M4 or M5 and I did refit them with spring washers and new t-nuts before selling the cabs on.