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Interesting conversation about speakers and ohms
- Thread starter Nephilymbass
- Start date
All good but what headroom?!
A small SS amp that can't overdrive the 8ohm version is the only situation that gets more volume when a 4 ohm version of same cab is used instead. That rare in these days of megawatt micro amps.
If your amp is able to beat up the 8ohm cab there is zero extra volume from 4ohm swap.
Well what do you want from me? Blood?
I'm assuming that there are cabs tough enough to handle these wattages being used.
I'm assuming that there are cabs tough enough to handle these wattages being used.
OK, does damping possibly play a part in what the repair man is seeing? I don't remember the equation, but I seem to remember (my memory is faulty at times, I'll admit) that damping is proportional to impedance. I'd that is true, it COULD mean that the 4 ohm speakers generally experience more physical travel (in addition to the fact that they might be getting overdriven).
As for the too little power killing speakers, I have heard that too, and I believe it. If you drive a SS amp really hard those hard clipped outputs are not kind to speakers. Tube amps clip softly, and, I believe, cause fewer problems.
Everything affects everything in electronic sound chains.
As for the too little power killing speakers, I have heard that too, and I believe it. If you drive a SS amp really hard those hard clipped outputs are not kind to speakers. Tube amps clip softly, and, I believe, cause fewer problems.
Everything affects everything in electronic sound chains.
You heard wrong. How many times do you need it refuted?
A square wave is only square when it's plotted on a voltage vs time graph.
Oh, did I say square? (read it again, please, maybe you read it wrong)
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True and accurate. But we all know what happens when someone has too little power. They crank it up until they get the volume they need. So yes, the cabinet was overdriven by an underpowered amp driven to extremes. No?
So OK, can we agree that: (people pushing) underpowered (SS) amps (past their limits) blow speakers?
Doesn't matter, this is a myth that needs to be finally put to rest. It is not helpful to people wanting to match cabs to their amps, either.
There is simply no such thing as under powering.
I'll accept that. But the real truth is, the cab was overdriven by the user. And it's my opinion that this happens most often when the user brings a system too small for the venue.
Everything in the sound chain matters.
The thing is that the square wave is delivering more power to the speaker than the sine wave is and all the speaker cares about is the watts. It does not care what waveform the watts have, if there are too many watts it will overheat and fail. I think your contention that you can blow a speaker by underpowering it is really based on the fact that if you connect an 800 W amp to a 1000 W cab and then drive the amp into hard clipping, which will feed a square wave to the cab, you can blow the cab. And this is true, but in fact the amp is delivering more than 1000 W to the cab in this case. It is not underpowering the speaker, it is overpowering it. In this case the speaker is "underpowered" only in the sense that it is connected to an amp with less rated sine wave output than its power handling capacity. But the actual square wave output of the amp is greater than the cab's power handling capacity. To a physicist your contention that you have blown your cab by underpowering it is nonsense and the people who are responding to you are thinking like physicists. To an average musician your contention that you have blown your speaker by underpowering it is spot on because they have been there and done that. They don't know that an 800 W amp can deliver 1600 W to cab when driven into hard clipping, they just know that 1000 W is greater than 800 W. Amps are rightfully rated for maximum sine wave power because some people do want/need clean signals. But they should also carry recommended cab power handling level ratings so that people who don't care to learn physics can safely mate cabs to amps. Even people who want clean signals are well advised to use twice the cab power as amp power because mistakes happen and if a setup error drives your amp into clipping your cab can be blown before you can correct the error.
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Sure. But that is still pushing a system past its safe operating limit. In this case it isnt the amp, but the cab which has met it's limitations. It is almost always the limits of the cab.
Not buying it. A cab's limitations are dependant on the cab, not the amp used. Dumbasses will blow their gear regardless of the size of their amp if their cab doesnt meet their needs.
You are missing the point. To the average person an 800 W amp should not be able to overheat a 1000 W cab. You have to understand the difference between sine and square waves and you have to understand that many 800 W amps will deliver far more than 1000 W to a cab when overdriven in order to understand why this is possible. The average person does not understand this so to them the statement that you can blow a speaker by underpowering it is true. They actually have blown 1000 W cabs with 800 W amps so obviously it is true. They don't know that the cab doesn't meet their needs because amps are rated by their sine wave outputs. We who understand physics understand the problem but to the average person it looks for all the world like you can blow a cab by underpowering it.
Ah, you'll have to forgive the crusty responses on this topic. It comes up pretty often and a lot of the TB oldtimers are sick of hearing about it.
Further explanation below...
Damping is indeed proportional to load impedance but it's not an issue in most amps as they typically have low enough output impedance to provide good damping at 4 Ohms. There are a few exceptions (there always are
) but for the most part it's a non-issue.We've sort of been dancing around what is actually happening in the posts I quoted here. A given amplifier has a maximum clean voltage it can put into a speaker and this is set by the DC power supply voltage of the output devices in the amp. That maximum voltage when connected to a load impedance determines the maximum amount of clean power the amplifier can put into the load. If the signal tries to exceed that maximum voltage it cannot and the output waveform is clipped off at the maximum voltage (hence the term clipping). The more the amp is driven into clipping, the more of the waveform is clipped off and the more it tends towards looking like a square wave. One of the side effects is that the clipped waveform will deliver more power into the load than the unclipped one at the same peak voltage. The extreme of this is a pure square wave (which we don't really ever see) which will deliver 2x as much power into a load as a sine wave with the same peak voltage. You probably already know this but I think it's important as a reference.
The long and short of it is that an amplifier can produce more than its rated power when clipped. Sometimes a lot more. It will never reach the theoretical limit of 2x due to power supply and thermal constraints but let's assume it can approach that. So we have a hypothetical 400W amplifier. Under clipping it might be able to put out an actual 700W so you can see how it could potentially damage a cabinet (honestly) rated for 500W under these conditions. However, connect a cabinet that can handle 1000W and the potential for thermally damaging the drivers in that cabinet disappears. So yes there definitely are cases where pushing an amp rated for less power than a cabinet into clipping can damage the speakers, but there's a limit to it and it's actually because the drivers were overpowered. The misconception that underpowering can damage speakers comes out of this.
In the real world, most low frequency drivers are excursion limited long before thermal limits are reached and hence most damage to cone speakers is from overexcursion (creasing, torn surrounds, etc.) rather than thermal damage to the voice coil.
This post was not meant to be condescending and if it reads that way, I apologize in advance.
