Impedance/Underpowering question

[socknroll1]

We all know that over-powering a speaker cabinet is much safer than under powering one. My question is, if I'm going to knowingly under power a cab, how far can I go?

Here's a setup I want to try:

500w head @ 4 ohms
1 250w 8 ohm cab (getting 250 right?)
1 400w 8 ohm cab (getting 250 right?)

Will my 400w cab explode?

I have tried this at low-ish volumes and it sounded fantastic. If I crank up halfway, will I be screwed?

[Bass_Pounder]

Originally Posted by socknroll1

We all know that over-powering a speaker cabinet is much safer than under powering one. My question is, if I'm going to knowingly under power a cab, how far can I go?

No we all don't know.

Underpowering is a myth - if it were true, your cabs would explode when your rig was turned off

[Von Felgenhauer]

The only real cabs that can be underpowered are the ones with magnets the size of the speaker itself, and even then it's just to get the cone moving, not to damage speakers. Your best tool as a musician is your ears. Wattage handling specs tell you nothing pretty much. Just listen with your ears and you will be ok.

[Floyd Eye]

Originally Posted by socknroll1

We all know that over-powering a speaker cabinet is much safer than under powering one.

What the................????????????

[billfitzmaurice]

Originally Posted by Bass_Pounder

No we all don't know.

Underpowering is a myth

+1. In addition, thermal power ratings are next to worthless. Cab output is limited by driver excursion capacity, not the power rating. Said excursion limited power handling tends to run around half the thermal rating.

[socknroll1]

To clarify: many bassists have recommended rigs in which the total output of the head is more than the total handling of the cab(s). Example being a 1000w head with a 750w set of cabs. I've been told that is safer than the opposite, because if your head was not loud enough for your cabs and you pushed it very hard, you would be putting a distorted signal through your cabs. With a higher powered head, no matter how much you turn up, you're pushing a clean signal.

THat was my logic and my impression from many sources. Is that fundamentally wrong? I'm ready to learn here boys! Spill the facts!

[Electricblue]

Underpowering has been beaten to death on a daily basis. I would consider it better to have cabs rated at least twice as much as what you are putting into them. This can "make extra room" for bass-heavy EQ settings.

However, figures are only a rough guideline. Listening with your ears is where it's at.

[billfitzmaurice]

Originally Posted by socknroll1

Is that fundamentally wrong?

It is. If there was any truth to it at all guitar players would have to replace drivers nightly, and there would be no such thing as fuzz boxes or synthesizers, as their clipped waveforms would kill every driver they played though. Your source is seriously misinformed.

[Electricblue]

Originally Posted by billfitzmaurice

It is. If there was any truth to it at all guitar players would have to replace drivers nightly, and there would be no such thing as fuzz boxes or synthesizers, as their clipped waveforms would kill every driver they played though. Your source is seriously misinformed.

Doesn't a clipped waveform only break tweeters? That's what I heard.

If it was true, wouldn't every big venue's PA be ruined after a Metal gig?

[MysticMichael]

I just knew that Bill couldn't resist this thread...

MM

[Sartori]

The tweeters in bass cabs are at risk from a clipped signal only because of the extra highs such signals usually have, more than the tweeter is supposed to be seeing, and therefore overpowering the tweeter.

The woofers don't really care whether the signal is clipped or not. If they can handle the power they can handle it, and if they can't, they'll probably fart out and blow.

[B-string]

Originally Posted by socknroll1

To clarify: many bassists have recommended rigs in which the total output of the head is more than the total handling of the cab(s). Example being a 1000w head with a 750w set of cabs. I've been told that is safer than the opposite, because if your head was not loud enough for your cabs and you pushed it very hard, you would be putting a distorted signal through your cabs. With a higher powered head, no matter how much you turn up, you're pushing a clean signal.

THat was my logic and my impression from many sources. Is that fundamentally wrong? I'm ready to learn here boys! Spill the facts!

Many bassists are WRONG! If your 750 watt set of cabs reach their max. cone movement at say 500 watts. You crank your 1000 watt amp at a outside gig and send over 500 watts to them, do you think burned out or "hung" speakers are a good thing? Just because the cab says 750 watts does NOT mean they handle 750 watts at low bass frequencies (and could never handle 1000 "clean" or not).

[seamonkey]

I keep wondering how many "expert authorities" go around repeating this myth over and over. Some guy in a music store, somebody who played bass in the 70's, somebody who plays a doctor on TV.

These authorities believe what they say, they have somehow witnessed it first hand and so repeat it. And it's easily believed by those who believe the authority with not proof.

And this is just one of many myths.

[socknroll1]

So you're all telling me, NO my cab will not be more likely to explode than if I had 2 x 250w cabs? I'm feeling better...i guess.

[B-string]

Your worry is the 250 watt cab as it is at its limit, the 400 watt cab should be fine.

[Bassamatic]

You CANNOT damage your cabs by underpowering them (whatever that means) unless you cause the amp to clip consistently. Clipped signals become mostly high frequencies, over loading and blowing the tweeters unless they have protections circuits. Might also damage a crossover if clipped severely. Woofers are unaffected by the extra highs

Overpowering a cab by a large margin will eventually damage the drivers.

[wcriley]

Originally Posted by Gio S

You CANNOT damage your cabs by underpowering them (whatever that means) unless you cause the amp to clip consistently. Clipped signals become mostly high frequencies, over loading and blowing the tweeters unless they have protections circuits. Might also damage a crossover if clipped severely...

Wouldn't this be a sign of poor design and components that are not up to the task? It doesn't seem to be a problem PA cabs.

[billfitzmaurice]

Originally Posted by wcriley

Wouldn't this be a sign of poor design and components that are not up to the task? It doesn't seem to be a problem PA cabs.

PA cab high frequency sections will start sounding really bad before damage will occur, and only a total bonehead at the desk would fail to reduce the HF level to compensate. Electric guitar amps leave tweeters out completely, because tweeters sound nasty when fed clipped waveforms. Bass players who run with lots of distortion should also forgo tweeters.

[Bob Lee (QSC)]

A clipped signal might have additional HF content, but not always. In fact, the intensity of the higher-order harmonics that are generated drops off rapidly, and the clipping action itself often obliterates much of the higher-frequency energy in the original signal.

For example, if you severely clip a full-range signal of say, a regular music recording, you might find that it sounds tubby and high frequency content like cymbals and vocal sibilance gets lost--that's from the lopping off of HF content in the clipped portions of the waveform--but also harsh and raspy, and that's from the various harmonics generated that tend to be dissonant from much of what's going on in the music.

[babebambi]

Originally Posted by seamonkey

These authorities believe what they say, they have somehow witnessed it first hand and so repeat it. And it's easily believed by those who believe the authority with not proof.

And this is just one of many myths.

I am curious as to what they actually witness that lead them to such conclusion.