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UNDERpowering speaker cabs

dancehallclasher

dancehallclasher

Jul 21, 2000
6,730
205
44
San Ramon, CA
#1
ok, take a bag end S15-D, handles 200W continuous. say i hook it up to my SWR workingman 15 combo, thereby running 100W into it. is this really bad, and if so, only bad at high volumes or what?

i'm wondering because i've heard of those little smokey amps powering 4x12 guitar cabs, in fact they recommend it on the website. so what's the skinny?
 
#2
Underpowering a cab is in itself not dangerous. The danger with not having enough power/headroom is that if you turn up the amp until it starts clipping, which will cause damage to the speaker (at least with SS amps). If you have lots of power available you'd be able to get the desired volume without stressing the amp.

And my favourite band rocks. ;)
 
#3
Underpowering a speaker is dangerous only

A. if you run the amp into heavy clipping, and

B. if the amp is powerful enough to damage the speaker when it clips.

An amp's power rating is measured with sine waves and with little or practically no distortion. But with severe clipping, the waveform shape will approach that of a square wave, which has a lot more power and a lot more distortion.

For example, an amp rated at 200 watts with a sine wave could put out up to 400 watts with a square wave, at least for a short time. And if the signal is high enough to cause clipping that severely, even when it drops below clipping it'll be at a very high level. Therefore, the average power will be extremely high, and at times possibly higher than the amp's 200-watt rating.

Therefore, if the amp is driving a speaker rated at, say, 250 watts or so, there's a strong chance that it could burn out.

But if you're badly overdriving a 50-watt amp into a 500-watt speaker, you're not likely to damage the speaker even though you're underpowering it and also driving the amp into severe clipping. But it'll sound like crap.
 
#7
Originally posted by 72beetle
VERY nice! Hey, check out the <a href="http://www.minibosses.com">Minibosses</a>, they do great video game soundtracks too!
Click to expand...
Thanks man! I've been wondering for a long time if there was someone who shared my perversion for old video game music! I will definitely check them out! :D
 
#8
lol Oyster!

I was just playing that game (Castlevania IV) the other day and thought about how cool the basslines are in some of those songs...

Excellent job on the bass, man!

Didn't mean to hijack the thread there.

Also, I don't think I can add much to what Bob said, since he pretty well knows all when it comes to amps and things. :)
 
#9
wouldn't another speaker give me more volume anyway?

i'm kinda confused here... does adding another speaker have any effect on whether the amp clips or not? because currently i'm not using any extension speaker, and i don't drive my amp into clipping, so would adding another speaker change that?
 
#11
Originally posted by dancehallclasher
wouldn't another speaker give me more volume anyway?
Click to expand...
Yes, and add to that it would allow you to run your amp at the full power rating.
i'm kinda confused here... does adding another speaker have any effect on whether the amp clips or not? because currently i'm not using any extension speaker, and i don't drive my amp into clipping, so would adding another speaker change that?
Click to expand...
It will change to the better - since you will have more power available from your amp (running in 4 ohms as opposed to 8 without ext. speaker) and increased speaker area will "fill the room" more than the single speaker on your combo.
 
#12
Originally posted by Da5id HeX
lol Oyster!

I was just playing that game (Castlevania IV) the other day and thought about how cool the basslines are in some of those songs...

Excellent job on the bass, man!
Click to expand...
Try playing some of the lines in that and other games - many of them are have quite unorthodox rhythms and patterns... loads of fun! :)

I think I will put some more work in that MP3, though - the playing is a bit sloppy, the strings were rather dead (never heard such a dull slap sound before ;)) and I feel a need to develop the MIDI instrumentation, especially the drum track (I borrowed the whole MIDI backdrop from www.vgmusic.com and only added bass, some EQ and reverb).

This is definitely the wrong thread for this, though. ;)
 
#13
Originally posted by dancehallclasher
wouldn't another speaker give me more volume anyway?

i'm kinda confused here... does adding another speaker have any effect on whether the amp clips or not? because currently i'm not using any extension speaker, and i don't drive my amp into clipping, so would adding another speaker change that?
Click to expand...

It might. A lower load impedance will draw more current from the amp at any given output voltage, and that heavier load will make the amp clip at a somewhat lower output voltage.

For example, let's say your amp clips at 40 volts RMS into an 8-ohm load. (That's 200 watts.) You add another 8-ohm cabinet, so now it's got a 4-ohm load. If it's got a good, strong power supply, maybe it'll clip at 36 volts now (324 watts). If it's got a soft, wimpy power supply, maybe the clipping point will sag down to 32 volts (256 watts) or lower.

But for any point below clipping, you'll still have twice as much power as before (a 3-dB increase), and if your cabinets are close together and facing in the same direction, you can get as much as another 3 dB of acoustic coupling (meaning the acoustic power from the two cabinets will reinforce straight out to the front, but may cancel to the sides or at other angles).
 
#15
ok, thanks everybody. so i guess the final verdict is, i will be good to go as long as i don't crank it and try to cause earthquakes, right? cool.

see, i don't have enough dough to buy a good full rig at once, so my long-term plan is

1) get the bag-end cab, use it as an extension.
2) sell my combo and buy a carvin power amp for the 15", with my sansamp as a preamp.
3) get another 15" or a 4x10 or both, eventually, as the poweramp does 350 watts/side at 4 ohms.
 
#16
Originally posted by dancehallclasher
ok, thanks everybody. so i guess the final verdict is, i will be good to go as long as i don't crank it and try to cause earthquakes, right? cool.

see, i don't have enough dough to buy a good full rig at once, so my long-term plan is

1) get the bag-end cab, use it as an extension.
2) sell my combo and buy a carvin power amp for the 15", with my sansamp as a preamp.
3) get another 15" or a 4x10 or both, eventually, as the poweramp does 350 watts/side at 4 ohms.
Click to expand...


That's the cool thing about combo amps that can hold extension speakers.
I used to have a Peavey 210TX.
I bought my Peavey 410TXF to add to it, later got my Firebass head, then just last year got my 115BXBW. :)
 
#19
Originally posted by Blisshead
Hi Bob could you take a look at my thread about power amps and maybe give me some advice? It's the power amp, how would you do this? thread. Does QSC make something along those lines? Thanks -Josh
Click to expand...

Hi Josh, I looked at your thread, but I'm not clear on what you want to know.
 

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