Double Bass amp wattage - does it need to be higher than the cabinet's?

[BrBss]

I'm confused my V4-B is 100watts max and my 212 cab is rated at 600watts? I always thought you wanted your cab to be a lot higher than your head to help prevent it from blowing up?

For bass cabinets and subwoofers, this can be a good practice. A 100 watt cabinet will likely not take a 100 watt, 50Hz sine wave without reaching the excursion limits of the speakers. That being said, amps have volume knobs- so using a 600watt amp with a 100 watt cabinet can also be fine if the volume is turned low.

 

[drurb]

High frequency is high frequency. Whether it comes from a square-wave synthesizer in a keyboard, a fuzz-type distortion applied to a bass, or a clipped waveform at the output of an amplifier is irrelevant.

No! The amount of energy reaching the tweeter can be much higher in the case of hard, sustained clipping.

 

[BrBss]

Well, because it's going to be at a very high level-maybe twice the RMS rating of your amp. Amps can put out huge amounts of high frequency junk when overdriven hard. Whereas you can run fuzz and other distortion effects at reasonable levels, which won't harm anything. So overdriving an amp can overpower the tweeter and blow it as a result.

So you're saying a clipped amp outputs more power than it is rated for. I agree. Which is another reason why your cab should have a higher power rating than your amp- not vice versa.

Let's say I'm using a 100 watt amp. Whether I'm clipping it or not, a 50watt speaker is more likely to be blown than a 200watt speaker.

Conversely, lets say I have a 100 watt speaker. A 50w amp, even run full blast and clipping, probably won't exceed the thermal limits of the cab. A 200w amp, on the other hand, obviously can.

 

[BrBss]

No! The amount of energy reaching the tweeter can be much higher in the case of hard, sustained clipping.

Well, consider a sending square wave into a 200watt amp and getting a 200 watt square wave output, vs putting a sine wave into a 50 watt amp that is clipping and getting a 100watt square wave output.

Guess what? The 200w amp is putting out more power. So how is that less likely to damage a speaker???

 

[drurb]

http://billfitzmaurice.info/forum/viewtopic.php?t=1886

Over powering, either thermal or mechanical is the only thing that damages speakers.

A fuzz pedal produces its sound by clipping the input signal. Its still a square wave.

What is not recognized in the linked article is that the spectral splatter at high levels can and does thermally stress tweeters.

 

[Hopkins]

Well, because it's going to be at a very high level-maybe twice the clean RMS rating of your amp. Amps can put out huge amounts of high frequency junk when overdriven hard. Whereas you can run fuzz and other distortion effects at reasonable levels, which won't harm anything. So overdriving an amp can overpower the tweeter and blow it as a result.

Exactly my point, clipping does not damage speakers, its over powering that causes damage. The square wave signal thing from clipping is nonsense.

If you push an amp that hard it is going to sound terrible without any noticeable increase in volume.

 

[Hopkins]

What is not recognized in the linked article is that the spectral splatter at high levels can and does thermally stress tweeters.

Its power spikes from running an amp to hard, not the clipped signal itself. That write up has a great description of what a square wave is.

 

[BrBss]

What is not recognized in the linked article is that the spectral splatter at high levels can and does thermally stress tweeters.

What you are referring to IS discussed in Bill's article, under the "average power" / "Crest factor" section. Clipping an amp is effectively changing from a sine wave to a square wave (each with equal amplitude), which results in increased average power. While that increase in average power occurs due to the addition of higher frequencies (spectral splatter), the damaging effect is the increase in power, not the broadening frequency spectrum.

 

[drurb]

What you are referring to IS discussed in Bill's article, under the "average power" / "Crest factor" section.

The mistake he and others make, though, is in the misleading statements to the effect that clipping doesn't do the damage via spectral splatter. His own analysis shows that it does. It's trivially true that distortion, per se, doesn't kill a tweeter. One can feed a tweeter with a highly distorted low-level signal very safely. When you clip an amp at high power, the spectral spread causes massive amounts of high-frequency energy to thermally overload the teeeter.

 

[BrBss]

The mistake he and others make, though, is in the misleading statements to the effect that clipping doesn't do the damage via spectral splatter. His own analysis shows that it does. It's trivially true that distortion, per se, doesn't kill a tweeter. One can feed a tweeter with a highly distorted low-level signal very safely. When you clip an amp at high power, the spectral spread causes massive amounts of high-frequency energy to thermally overload the teeeter.

I'll refer you to post#24. Increasing amplifier power, like you suggest, and adding a fuzz pedal is the same thing as clipping a lower wattage amp.

You say that amplifier power should be higher than speaker power, which means you can exceed thermal limits of the tweeter before you even clip.

Put a 10kHZ sine wave into a 100 watt amp and get a 100 watt RMS 10kHz sinewave directly to your tweeter. If your tweeter is rated at 50 watts, you're screwed. If its rated at 200watts, you're fine.

 

[Hopkins]

The mistake he and others make, though, is in the misleading statements to the effect that clipping doesn't do the damage via spectral splatter. His own analysis shows that it does. It's trivially true that distortion, per se, doesn't kill a tweeter. One can feed a tweeter with a highly distorted low-level signal very safely. When you clip an amp at high power, the spectral spread causes massive amounts of high-frequency energy to thermally overload the teeeter.

Please define and explain spectral splatter.

 

[BrBss]

Please define and explain spectral splatter.

It's the broadening of a spectrum (addition of high frequency content) in the frequency domain caused by a sudden change in the time domain (i.e., the vertical edges of a square wave).

Again, the damaging effect to the speaker/tweeter by changing from a sine wave to a square wave is the increase in average power, not the broadening frequency spectrum.

 

[drurb]

I'll refer you to post#24. Increasing amplifier power, like you suggest, and adding a fuzz pedal is the same thing as clipping a lower wattage amp.

You say that amplifier power should be higher than speaker power, which means you can exceed thermal limits of the tweeter before you even clip.

Put a 10kHZ sine wave into a 100 watt amp and get a 100 watt RMS 10kHz sinewave directly to your tweeter. If your tweeter is rated at 50 watts, you're screwed. If its rated at 200watts, you're fine.

If you're prone to overdriving your amp, then the practice you suggest is a good one. Better to increase amplifier power and avoid the problem in the first place.

 

[BrBss]

If you're prone to overdriving your amp, then the practice you suggest is a good one. Better to increase amplifier power and avoid the problem in the first place.

Your initial premise was NOT that you should use an amp with enough power that you don't have to clip it. Your initial premise was that your amp should have more power than your cabinet.

Let's say I clip a 50watt amp because I need more volume. What you have yet to explain is why using a speaker that can only handle 25 watts would somehow be safer than using a speaker that can handle 100 watts.

 

[Hopkins]

It's the broadening of a spectrum (addition of high frequency content) in the frequency domain caused by a sudden change in the time domain (i.e., the vertical edges of a square wave).

Again, the damaging effect to the speaker/tweeter by changing from a sine wave to a square wave is the increase in average power, not the broadening frequency spectrum.

So it is still over powering that damages the speaker, not square waves

 

[mapleglo]

So to answer the op's question, the power rating per se, is not the most important thing, because the numbers are questionable and suspect. My Ampeg PF800 owner's manual says:

800 watts rms @ 4 ohms, 3% THD [PF-800]

which is not extremely useful - what's the frequency range that was used to measure that 800 watts? 20 to 20k? 100 - 10k? who knows? Was that power measured using load resistors on a test bench with a sine wave as the input? Probably. How does that relate to how I use it playing my bass through my SVT810E? My guess is not very closely.

The important aspect is to get an amp with enough power that you won't have to push it into clipping when playing, and to get a cab that can handle it. To determine that compatibility, listen carefully to your rig. If it starts to sound like it's going to break, turn it down, or it most likely will.

Regarding tweeters, I never had much use for them in the context of a bass rig. Any time the cab had one, I usually just turned it off anyway. Never liked them.

My guess is that your 800 watt head will work just fine with your 800 watt rated cabinet, used sensibly.

 

[fdeck]

So to answer the op's question, the power rating per se, is not the most important thing, because the numbers are questionable and suspect. My Ampeg PF800 owner's manual says:

which is not extremely useful - what's the frequency range that was used to measure that 800 watts? 20 to 20k? 100 - 10k? who knows? Was that power measured using load resistors on a test bench with a sine wave as the input?

You're wise to be skeptical about ratings. In this case it's probably possible to read between the lines due to engineering conventions and commonalities about how amps work. Also, "rms" has a legal definition in the US, and Ampeg is a reputable maker who would be very much under the microscope if one of their amps didn't meet its ratings.

But it's convoluted. The rated wattage is inferred from the voltage measured at 3% THD into a (most likely) 4-Ohm resistive load. From an engineering standpoint, I'd interpret that rating in terms of a voltage amplitude at clipping. And it's a no brainer for an amp to cover 20 to 20k.

Probably. How does that relate to how I use it playing my bass through my SVT810E? My guess is not very closely.

It's a YMMV situation, but at least the behavior of a mainstream ported cab is not a mystery. For better or worse, while this information is useful to engineers, It's a toss up how useful it is for musicians. I just happen to be interested in this stuff because the engineering side is a hobby of mine.

 

[fdeck]

Just a side note. Most of the new "micro" heads have a built-in compressor limiter to avoid problems encountered when switchmode power amps are driven to clipping. Both of my amps do. (GK MB200 and EA Micro300). As a result, clipping these amps under normal conditions is unlikely. But a different matter arises. In my experience, it's pretty annoying to be riding a compressor all night long when playing dynamically is so important to our craft. So, I would still consider sizing an amp so it's unlikely to be pushed to the limit at your typical volume levels.

 

[Major Softie]

Speaker wattage ratings are relatively valuable . . . as in: if you look at the ratings relative to other speaker cabs from the same manufacturer, usually they will be useful for relative comparisons. Okay, not always, but usually.

Otherwise, fairly useless.

 

[drurb]

Well, consider a sending square wave into a 200watt amp and getting a 200 watt square wave output, vs putting a sine wave into a 50 watt amp that is clipping and getting a 100watt square wave output.

Guess what? The 200w amp is putting out more power. So how is that less likely to damage a speaker???

It's not! I didn't say it was! Go run a square wave at 200 watts into a cab with a tweeter rated at 200 watts. POOF!

Your initial premise was NOT that you should use an amp with enough power that you don't have to clip it. Your initial premise was that your amp should have more power than your cabinet.

Let's say I clip a 50watt amp because I need more volume. What you have yet to explain is why using a speaker that can only handle 25 watts would somehow be safer than using a speaker that can handle 100 watts.

This is ridiculous. That was the underlying premise of what I said was that one wants to avoid clipping. I went on to explain about that. I didn't merely quote some silly rule. The point was that one should not worry about having an amp that is rated as having a higher continuous output power than the rating of the speaker cab. So, given that one's goal is to avoid clipping, you really want a powerful amp. The truth is that, so long as you are not clipping the amp, the cab can have a power rating lower than that of the amp. You don't want to overdrive the cab either, so the cab's rating could be higher as well. It's absurd to think and to interpret what I said as meaning that a cab with a lower power-handling spec would somehow be better. What I said was geared toward not having an underpowered amp that would go into clipping. If a cab is overdriven by a clean signal, it usually warns the user prior to any real damage. So, all-in-all, if one device is going to have a lower rating than the other, you're better off with an over-powered amp. One neither wants to clip the amp nor overdrive the cab. One should be intelligent about these things. Perhaps I should not have (over)simplified. More damage has been done by underpowered amps (to tweeters, especially) than by over-powered amps.