Sharing backline

[nilebodgers]

1 hour ago, BigRedX said:

Can some please explain with science why constantly clipping the front end of an amp will cause it to fail, because I can't see any reason for it? 

In 40 years of playing I have only had two amp failures.

One was a very ancient and badly looked after valve amp that I had acquired for next to nothing and which stopped working between sets for no apparent reason the second time I used it.

The other was user error when I inadvertently plugged both sides of a stereo amp into the same speaker cab and released the magic smoke.

It won’t. Any competently designed solid state amp should be able to light up like a Xmas tree and be soundly thrashed without skipping a beat provided it is operated into the rated load impedance.

The speakers are a different story, if their thermal limit or physical cone excursion limit is exceeded then they are toast. 

[BassedinBucks]

46 minutes ago, BigRedX said:

Can some please explain with science why constantly clipping the front end of an amp will cause it to fail, because I can't see any reason for it? 

In 40 years of playing I have only had two amp failures.

One was a very ancient and badly looked after valve amp that I had acquired for next to nothing and which stopped working between sets for no apparent reason the second time I used it.

The other was user error when I inadvertently plugged both sides of a stereo amp into the same speaker cab and released the magic smoke.

The sound signal that gets amplified from guitar is a sine wave; when you overdrive it using the input gain on the amp you clip the top and bottom of the sine wave so that it flattens (or squares it), this distorts the signal and in addition to affecting the sound quality, it causes the amp to overheat a bit. But most damage is done to the drivers in the cab. The overdriven signal creates more higher pitched harmonics which are not present in the original guitar sound source and the crossover in the cab sends these to the tweeter particularly where it will quickly burn out the voice coil; it can also fry the larger cones if the speaker is driven at high volume for long enough. The same can happen if you use an under-powered amp to drive a high powered speaker; the speaker 'demands' more power from the amp and that will damage both amp and speakers; generally, you should use an amp with higher Watt rating than your speakers. And avoid red clip lights everywhere along your entire signal processing path, from guitar to amp, to desk, to FOH speakers - everything green, except vox is nice with a tiny bit of blinking amber.

[Dad3353]

38 minutes ago, BassedinBucks said:

... generally, you should use an amp with higher Watt rating than your speakers...

I'm of the exactly opposite opinion and experience. Typically I use double the speaker power handling compared to the amp (200w amp = 400w cab...). I've worked as a tech for years, and have had many a cab to repair because of amp/cab mis-match (100w cab, 200w amp sort of thing; times ten for PA systems...). Not just in case of mis-use; also 'transients' (power goes off, then comes back on suddenly, or mic unplugged when not muted; the list is long...). To each his/her own, but I've never had an amp or cab suffer from being matched two to one, cab to amp. 

[BassedinBucks]

2 hours ago, Dad3353 said:

I'm of the exactly opposite opinion and experience. Typically I use double the speaker power handling compared to the amp (200w amp = 400w cab...). I've worked as a tech for years, and have had many a cab to repair because of amp/cab mis-match (100w cab, 200w amp sort of thing; times ten for PA systems...). Not just in case of mis-use; also 'transients' (power goes off, then comes back on suddenly, or mic unplugged when not muted; the list is long...). To each his/her own, but I've never had an amp or cab suffer from being matched two to one, cab to amp. 

Blimey! You've been lucky! All advice that you will find on the internet will tell you that your amp must have a higher power rating than your speakers, usually it says at least a third more power, but up to double. If you look at active PA speakers you will see that the power amp in them is usually between 1.6 times to twice the power rating of the cones. You need headroom in your amp that exceeds the power rating of your cones else you could blow the voice coils; this will happen if you run your amp/system very loud for a long period, at a quieter volume you may get away with just some distortion but no damage. Good amps often have a limiter in them to prevent overworking the amp and over-driving the speakers.

I just Googled 'what power amp for my speakers' and the first result produced this;

POWER

The industry says, buy a PA power amplifier that can deliver power equal to twice the speaker’s program power rating. This means that a speaker with a “nominal impedance” of 8 ohms and a program rating of 350 watts will need a power amplifier that can deliver 700 watts into an 8-ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms.

HEADROOM

Extra “headroom” will help you so that only clean, undistorted signal gets to your speakers. Headroom is the difference between the normal operating level of an amplifier, and the maximum level that the amp can pass without distorting. Music has wide variations in dynamic range; without enough headroom, you could find that your gear will clip and distort

[Nail Soup]

I would take the middle ground here.... choose an amp and speakers that had the same power rating.

Not out of compromise, I just don't know any better!

[Combed20]

I think ultimately, it would be a NO from me. When my band organises a gig where we are sorting everything ourselves, we normally offer kit share. It saves space in the venue and prevents lots of faff between bands. But it's our event. In the case of the OP, I neither want to drop my rig off the night before, or get to the festival first thing and be there all day to babysit my rig through a dozen different bands. I can certainly see the advantage of everyone using the same backline, but it wouldn't be mine!

[Dad3353]

3 hours ago, BassedinBucks said:

Blimey! You've been lucky! All advice that you will find on the internet will tell you that your amp must have a higher power rating than your speakers, usually it says at least a third more power, but up to double. If you look at active PA speakers you will see that the power amp in them is usually between 1.6 times to twice the power rating of the cones. You need headroom in your amp that exceeds the power rating of your cones else you could blow the voice coils; this will happen if you run your amp/system very loud for a long period, at a quieter volume you may get away with just some distortion but no damage. Good amps often have a limiter in them to prevent overworking the amp and over-driving the speakers.

I just Googled 'what power amp for my speakers' and the first result produced this;

POWER

The industry says, buy a PA power amplifier that can deliver power equal to twice the speaker’s program power rating. This means that a speaker with a “nominal impedance” of 8 ohms and a program rating of 350 watts will need a power amplifier that can deliver 700 watts into an 8-ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms.

HEADROOM

Extra “headroom” will help you so that only clean, undistorted signal gets to your speakers. Headroom is the difference between the normal operating level of an amplifier, and the maximum level that the amp can pass without distorting. Music has wide variations in dynamic range; without enough headroom, you could find that your gear will clip and distort

No, I'll not be lending you my amps/cabs, even if you ask nicely. My bass amp (Hiwatt 200w valve amp...) would wreck a 100w cab in seconds at half power. It was designed to power two of these (so four cabs, two each side...), rated at 400w...

 

I used this rig for many years, for PA, in the '70s; it could get very loud indeed. We use the amp now for bass,  with an HH 2x15 folded horn, rated as 200w. We rarely get past a quarter on the dial, and I wouldn't want to push my luck with full tilt. The walls would crumble anyway..! 

 

Edited May 7, 2021 by Dad3353

[Downunderwonder]

Hooboy, the great underpowering myth surfaces at BC.

One backlined gig I did I almost turned around to go get my own gear. Ancient Trace Commando 100w 12'' combo appeared to be in good condition. It had just enough poke with a bit of bass in the monitor on the far side of the stage iirc.

The kid band on first had other ideas. Horrible distorted mess for their whole set. Not enough power to blow up the speaker so I got to play through it and it was fine.

If I had brought in my 250w Trace and 210 it would have been end of days for the 210, from too much power.

[Woodinblack]

I would always make sure that my speakers were rated for the at least the maximum power of the amp. I have blown speakers, but not ones with a higher power rating than the amp.

[Nail Soup]

So what is the speaker/ amp power ratio in a combo?

[MichaelDean]

I thought it was great when I played in Japan. Every venue had an 8x10 with an Ampeg SVT450 or Hartke HA3500, drums minus breakables, a guitar combo (usually a Roland JC120) and a Marshall half stack plus keyboard stands etc. It made it really easy to play there because we knew we didn't need to bring amps, plus the sound guys know all of the foibles of the equipment. I guess if you trash the gear, word gets round and you don't get invited back too! Seemed like a really efficient way of doing it. Not sure you'd convince many venues round here to do that though!

[Ed_S]

21 minutes ago, MichaelDean said:

I thought it was great when I played in Japan. Every venue had an 8x10 with an Ampeg SVT450 or Hartke HA3500, drums minus breakables, a guitar combo (usually a Roland JC120) and a Marshall half stack plus keyboard stands etc. It made it really easy to play there because we knew we didn't need to bring amps, plus the sound guys know all of the foibles of the equipment. I guess if you trash the gear, word gets round and you don't get invited back too! Seemed like a really efficient way of doing it. Not sure you'd convince many venues round here to do that though!

That does sound great!

Probably won’t be a popular idea, but I wonder whether it’d work for venues with bands on all the time to get a decent shell-pack and guitar/bass cabs, and get people to chuck a few quid in a jar for the pleasure of using them, then put that money back into maintaining the kit so that it was always in good order and people wouldn’t mind donating to its upkeep. I’d chip-in to use a decent, well maintained cab that I didn’t have to carry round.

[Lozz196]

A good few venues I’ve played in the UK have this sort of set up, and do prefer the bands to use these house cabs & shells, makes it quicker on changeovers plus the sound man doesn’t have different sounding bass drum & rack toms for every band.

[bartelby]

Last year I gave a local venue an Ashdown 8x10” and a Laney 4x10” for their in-house backline, they used to have an unnamed 1x15” of dubious condition to use. Hopefully they’ll get some use at some point this year.