Limiter, 350w head, 400w cab..

[Tuomas]

I have Ampeg B2R 350w head which has Limiter. Manual says that it keeps the power amplifier's output clean at extreme volumes but gives you less watts. I was wondering that is the Limiter ment to be used if you have a cab that cant take 350w? So should i use Limiter if i have 400w cab or can i damage 400w cab with b2r? Sorry 'bout my english but i hope someone gets the idea..

Thank you.

[Mr. Phil]

Well I don't see a problem if you are running 350 watts through a cab that can handle 400 watts... Thats headroom for the cab. You won't overdrive it.

[rumpelstiltskin.]

the risk you run in using a cabinet rated at or above the wattage of your head is that you can overdrive the head before reaching the power limits of your cabinet.

 

in that case, the limiter may actually do more harm than good. in general, if you're not loud enough, play quieter or understand that you need to buy a bigger amp or another cabinet.

 

robb.

[a boy named sue]

Won't the built in limiter stop his head from clipping, meaning that he can't damage his cab., even though the head is too small?

[rumpelstiltskin.]

what is clipping? i ask that only semi-facetiously, because most people understand that clipping is bad without having any idea what clipping actually is.

 

for example, if you have a limiter and you turn up a little bit, the peaks of your signal get heavily compressed -- they get flattened at the extremes of the waveform. if you turn it up a little more, a little more of the waveform gets flattened. if you turn it up a lot, a lot of the waveform gets flattened -- it begins to resemble a square wave.

 

what else resembles a square wave? if you said clipping, you're right. a true square wave is alternating DC: the speaker goes to maximum excursion in one direction and then goes to maximum excursion in the other direction. it's very stressful to speakers to do that. it's sort of the down-ups of audio. over-limiting your signal will result in just as damaging a signal as simple clipping.

 

so what good is a limiter? what the limiter does is limit the peaks of the waveform, bringing the quieter parts up in volume. you're actually putting out less maximum power because the limiter stops increasing the gain on the signal before it can reach the peaks it normally would. however, because the quieter parts come up in volume, the overall perceived loudness is increased.

 

why would you want to increase perceived volume while decreasing actually power? perhaps if your cabinet can't handle the power you're putting to it. in other words, when the power rating of the cabinet -- or more accurately when its maximum excursion -- is not sufficient to handle the output of your amplifier. a limiter would not help you when your cabinet can handle the power the amp can make, yet remains not loud enough.

 

i mean, it would help a little, but eventually you'll have such an overcompressed mess of a sound that it wouldn't be worth it. if you're only a little bit not loud enough, that's one thing. that's when the band or the stage is really loud and you need just a little bit more to cut better.

 

if you are running out of power regularly and significantly, there's no secret trick or magic box to get more power. you just need to buy a bigger amp or another cabinet.

 

more power + more speaker cone surface area = more loud. learn it. love it. live it.

 

robb.

[g.]

A good limiter design CAN easily allow one to get 3dB-6dB more apparent gain while sounding great. This is regardless of supposed head/amp wattage or cab rating. But of course, setting things right for the various combinations of amps and cabs will allow this to work - or not work well.

 

As long as the gain before the limiter is not so excrutiatingly high (limits I think robb has been alluding to), you can get something extra. But as robb says, don't expect the laws of physics to be suspended.

 

And all limiters are NOT created equal. The key is to keep the amplifier from clipping levels while still sending higher average current, and the best do this very well. Squarewaves have little to do with it; you won't hear anything that resembles clipping, or artificial distortion.

 

Also, take a page from the sound reinforcement world. It is not uncommon to have amps with TWICE the RMS as the cabinets they drive (especially for subwoofers, cabs without tweeters/horns). This gives 3dB headroom so limiters are not used to get more volume, they are merely set to keep the power amps from ever clipping from excessive input gain.

 

And vice versa (this should be patently obvious). Once can drive a cab with WAY less wattage than it is rated for. But if you are not getting enough volume before clipping, already are using compression/limiting to bring up the average, as robb says, YOU NEED MORE.

 

Using weak head-type ore combo amps (with their higher THD ratings) with more speakers is not always the answer though. Not by iteself. Clean headroom still beats driving cabs with un if you want incredible transients and clear tone. Look at guitar rigs: punchy, convincing "clean" tone is harder to come by than overdrive.

[a boy named sue]

so my understanding of a limiter as a thing that applied a fractional gain to the input so that the peaks didn't exceed a particular value was...um how do I say this...limited.

 

oh has there been a compressor vs limiter thread, explaining the difference?

[g.]

To understand the differences in classic definitions of compressing and limiting just think about the two words, and what they would mean. Limiting typically has meant, after threshold is reached more absolute upper bounds to output, compression has meant ratios (1.5/1, 4/1, etc).

 

Over the years many approaches in product and circuit designs have hybridized, combined, and placed the concepts in the same signal chain within one unit. So the same units can often perform one, or the other, or both simultaneaously.

 

The picture is further muddied by companies who describe it oddly (think guitar: where whammy bars are often called tremelos, when in fact they make vibrato), and stomp box compressors which are about SUSTAIN as much as they are a change of gain. Many hybridizations of what controls are available to users have occurred.

 

In the context of the discussion so far in this thread it is useful to think of limiting at the final stage before the actual power amplifier, giving the ability to keep a signal from driving the amplifier's input gain hard enough to cause it to clip at output.