What's a safe max to have my amp on?

[Bankai]

Well basically I've started using a limiter in the FX loop and currently have it set to cut at +10dB. It's not there for sound quality it's to safeguard the amp/cab against my (or far more likely someone else's) clumsy fingers.

Amp is running around about 200wts RMS into 8 Ohms (Little Giant 350).

The cab is 8 Ohms and is rated 200wts RMS.


Is having the limiter at 10dB too high to prevent excessive/dangerous volumes or is it too low?

Edited March 17, 2010 by Bankai

[Mr. Foxen]

Should probably calculate the excursion limit of the speakers and the voltage required to get there, then set a voltage limiter to below that.

From what you have told us there is no way to tell you how to set your limiter. Probably best do it by ear, find where your speakers protest and make sure it doesn't get that far.

[Phil Starr]

It isn't usually the peaks which destroy modern speakers which are designed to mechanically limit this problem. They burn out when they are driven by excessive amplifier power over long periods of hours rather than minutes or seconds so it is your average power that matters. The peaks may sound like the aftermath of a mega chilli but they won't necessarily damage the speaker.

A compressor restricts the peaks but will also boost the average level which is why the ads sound louder on TV. Having said that you shouldn't have any problems unless you run into distortion. Keep your speakers sounding clean and stop worrying.

[Stylon Pilson]

[quote name='Phil Starr' post='778363' date='Mar 18 2010, 10:29 AM']It isn't usually the peaks which destroy modern speakers which are designed to mechanically limit this problem. They burn out when they are driven by excessive amplifier power over long periods of hours rather than minutes or seconds so it is your average power that matters.[/quote]

In the context of bass speakers, I was under the impression that it was the other way round.

[quote name='Phil Starr' post='778363' date='Mar 18 2010, 10:29 AM']The peaks may sound like the aftermath of a mega chilli but they won't necessarily damage the speaker.[/quote]

Again, I'm doubting that you know what you're talking about here.

S.P.

Edited March 18, 2010 by Stylon Pilson

[Mr. Foxen]

The long periods thing is the power compression you get in live PA applications, the subs are working hard, the voice coil warms and it's impedance increases, making them go quiet, they get turned up and get warmer etc.

With bass speakers, the are running 'full range' or at least much broader range than a PA sub, and without all the processing (compression, limiting, filtering etc.), so they have less low end high power hitting them, and more low power time to cool off. If the signal is not limited, potentiall a peak can push the speaker past it's Xlim (breaking point) and destroy it, farting kicks in after Xmax (clean limit), so those speaker specs are important, and not just the realms of Claber and Fitzmaurice.

Course, with the compressed by distortion sub bass drone in Caricatures, the smell of hot voice coil was not unfamiliar.

[Phil Starr]

[quote name='Stylon Pilson' post='778372' date='Mar 18 2010, 10:38 AM']In the context of bass speakers, I was under the impression that it was the other way round.



Again, I'm doubting that you know what you're talking about here.

S.P.[/quote]

No, I do try to be accurate in technical answers and all of this is in various texts. Rating a loudspeaker is surprisingly difficult for manufacturers. They really need to get as close as possible to the likely use of the speaker which is usually playing music but music is such a complicated thing that it is impossible to model objectively. Pure sine waves are nothing like music because apart from anything else there is only one frquency. You could use a random mix of all the frequencies (white noise) but music doesn't have energy evenly distributed so instead we usually use white noise filtered to more accurately resemble music (pink noise). Various test conditions are used (EIA,AES etc) but basically this 200W speaker probably got its rating by having pink noise passed through several samples for several hours (different for each standard) with none of the samples failing.

The problem with this test is that it simulates every sound being at full volume all of the time. A bassist playing 16 beats with a heavy pick and driving the amp into clipping wouldn't be close to getting this much power. Speaker manufacturers then try to give other indications of power handling by quoting 'peak' ratings either at specified distortion levels or as a 6dB crest value (Eminence,Fane do this). None of this really describes real life. If you play with a dynamic range of,say, 40dB then your average power is 20dB down on your maximum power, so if this 250W amp is not being driven into clipping it is only actually developing an 'average' of 2.5W of heating and even at moderate distortion the long term average is likely to be less than 20W. The speaker shouldn't fail because of overheating.

The next failure condition that causes problems is over excursion. The speaker is pushed beyond its limits of travel Xlim. as the coil moves out of the magnetic gap the electrical forces on it diminish. back in the 1930's speakers failed because designers didn't compensate for this and there was more of this in the 1950's and 60's when electric guitars and bass were used with what were essentially domestic speaker designs. The designers can get round this by making sure the suspension mechanically limits the excursion by proper design of the suspension. Celestion, Fane and eminence do this and so I expect do all the 'name' manufacturers. It is hitting the mechanical limit which causes the farting noise.

The other reasons for failure are corrosion of the metal parts (beware aluminium coils) and fatigue due to the repeated high accelerations a speaker is subjected to.

I could go on but I suspect most people won't be interested. The only other thing is that when driven into distortion an amp heats the speaker more than under undistorted sine wave conditions, up to root two (1.414) times the power for maximum distortion. This is more relevant to synths than bass.

So matching speakers to amps for power is a little subjective. If you want to be completely safe then use a speaker better than 1.414 times the amps rated power but be aware that you will only be using a fraction of the speakers power handling. If you use a moderately clean sound you will have no trouble using speakers roughly matching the amp. If you really want a clean sound then there is nothing wrong with using a little amplifier overhead. PA engineers often use 6dB extra in the amps because amp clipping sounds worse than momentary speaker limiting. This means using 1000W amps with 250W speakers (but they do monitor for clipping). Some bass players do this too to get clean peaks.

Obviously the harder you work your speaker the greater the accelerations it is subjected to and the sooner it will start to fatigue but regard the power ratings as a guide only. Under normal conditions this 200W speaker will work happily with a 250W amp for many years, just be aware that it is slighly under powered and if it distorts, turn it down.

[Bankai]

Ok. Well referring back to the actual amp head.

If it was a 200W amp (as is the case here) and was being run at full power. Presuming that the signal being fed into the power amp is 0dB, it'd be hitting the RMS bang on. Any fluctuation over 0dB would be more than the 200W RMS?

Or is this not the case? You see the signal coming from my preamp into the power section is usually hitting 10dB on the beat so I'm worried that if I'm running the amp at full it'd be hitting higher than 200W, thus maybe damaging the speaker?

[escholl]

[quote name='Bankai' post='781005' date='Mar 20 2010, 06:20 PM']Ok. Well referring back to the actual amp head.

If it was a 200W amp (as is the case here) and was being run at full power. Presuming that the signal being fed into the power amp is 0dB, it'd be hitting the RMS bang on. Any fluctuation over 0dB would be more than the 200W RMS?

Or is this not the case? You see the signal coming from my preamp into the power section is usually hitting 10dB on the beat so I'm worried that if I'm running the amp at full it'd be hitting higher than 200W, thus maybe damaging the speaker?[/quote]

Where are you getting this measurement of 10dB from? What nominal input level is the power amp looking for? Is is looking for +4dBu?

The important thing to do is just to listen to your amp -- does it sound distorted? If it doesn't, then you've nothing to worry about. As the saying goes, listen with your ears, not your eyes.

[bumnote]

[quote name='Phil Starr' post='780480' date='Mar 20 2010, 08:47 AM']I could go on but I suspect most people won't be interested.[/quote]

I found that very interesting thanks

[Badass]

Yeah I found that very interesting too Phil.

As for the original question...I always stick to something I was told many moons ago. If you need to turn to master vol above 5 often, then it is time to buy a bigger combo / amp + cab. Back in the 70's the cones rated at 100watts I used had to be reconed more often that I used to like. I was always on the lookout back then for another speaker. Ah the good old days

[karlthebassist]

[quote name='bumnote' post='781449' date='Mar 21 2010, 10:27 AM']I found that very interesting thanks[/quote]

As did I. Cheers.

[The Burpster]

11 of course!

[Phil Starr]

[quote name='escholl' post='781437' date='Mar 21 2010, 10:17 AM']Where are you getting this measurement of 10dB from? What nominal input level is the power amp looking for? Is is looking for +4dBu?

The important thing to do is just to listen to your amp -- does it sound distorted? If it doesn't, then you've nothing to worry about. As the saying goes, listen with your ears, not your eyes.[/quote]

I'd go along with this. Meters are a useful indication but not all power amps run off 0dB and the impedance needs to be taken into account too. If your ears say the setting is clean then that is usually good enough but male sure that you stick on or below these settings at gigs where the temptation to turn up is greater and the ability to hear distortion reduced.

[Bankai]

Alright then. Thanks

[Toasted]

I just wish Alex was here to do a graph for us.