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Matching Heads with Cabs

kintrap

kintrap

Guest
Apr 6, 2014
63
11
Kansas
#1
For a solid state set up, it is all fairly self explanatory, as far as wattage goes. You want a cab that has a higher wattage rating than the amp, commonly said to be about twice as much to be safe. My question is when dealing with tube amplifiers, knowing they are louder per watt than solid state, wouldn't you need a cabinet with an even higher wattage rating? If so, how much?

For example, if I found myself a tube head with 100w, and I wanted to find a cab, what number should I look for.
Alternately, if I found a cabinet rated at 1200 watts, what kind of tube head can I pair with it?
 
#3
kintrap said:
For a solid state set up, it is all fairly self explanatory, as far as wattage goes. You want a cab that has a higher wattage rating than the amp, commonly said to be about twice as much to be safe. My question is when dealing with tube amplifiers, knowing they are louder per watt than solid state, wouldn't you need a cabinet with an even higher wattage rating? If so, how much?

For example, if I found myself a tube head with 100w, and I wanted to find a cab, what number should I look for.
Alternately, if I found a cabinet rated at 1200 watts, what kind of tube head can I pair with it?
Click to expand...
Scientifically, they are not. It's all perception, because the saturation, overdrive & distortion you get from a tube amp sounds much more pleasing or even desirable compared to a solid state amp clipping. So, scientifically, the watts from a tube amp and a solid state amp that your cabs sees (if they have the same rating or more precisely the same measured output) are the same. So the same rule should apply for both types of amps. With a cab that can continously (RMS) handle 1200 W you are safe either way.
Of course I've also heard the rule, that your amp should be more powerful than the cab rating, because it's easier to hear a cab beginning to be overloaded. An overpowered amp may destroy your cab by clipping, which can't usually be detected before it happens. (maybe that's why people suggested to you to use double the amp's rating on the cab, but I'd be more comfortable trusting my ears).
TB, please correct me, if I'm wrong.
 
#5
kintrap said:
Whoa whoa whoa. So the only difference for tube is just the tone?
Click to expand...
Yep, pretty much.


kintrap said:
I've believed for years that tube power results in higher decibel output.
Click to expand...

Not at all. Tubes (generally) distort in a much more pleasant way to the human ear, so we are cool with running them well into their peak ratings. Also, I believe that most output transformers have a HPF effect, but that varies across designs.
 
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#6
Joce said:
Scientifically, they are not. It's all perception, because the saturation, overdrive & distortion you get from a tube amp sounds much more pleasing or even desirable compared to a solid state amp clipping. So, scientifically, the watts from a tube amp and a solid state amp that your cabs sees (if they have the same rating or more precisely the same measured output) are the same. So the same rule should apply for both types of amps. With a cab that can continously (RMS) handle 1200 W you are safe either way.
Of course I've also heard the rule, that your amp should be more powerful than the cab rating, because it's easier to hear a cab beginning to be overloaded. An overpowered amp may destroy your cab by clipping, which can't usually be detected before it happens. (maybe that's why people suggested to you to use double the amp's rating on the cab, but I'd be more comfortable trusting my ears).
TB, please correct me, if I'm wrong.
Click to expand...
more wrong than right where it counts.
 
#7
You're looking at a serious cab that can do 1200w of continuous bass. Something like a dual sub equipped 3 way.

No everyday tube bass amp does that kind of power so it's all moot.

Yes, a tube amp often makes pleasing overdrive sounds which raise the average power output.

No, clipping isn't a silent woofer assassin.
 
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#10
kintrap said:
Whoa whoa whoa. So the only difference for tube is just the tone? I've believed for years that tube power results in higher decibel output.
Click to expand...

The natural compression from the tubes coupled with the overdrive of the power tubes gives the impression that a tube amp is much louder. The overdrive is occurring in frequencies our ears are picking up easily - therefore we assume it is louder. In the end - it's a tone difference. That is the least technical way to describe it and I know there is more to it than that, but this is a good starting point.

The Ampeg SVT is 300 watts of tube and is used currently into a 810 cabinet rated at 800 watts RMS - works fine for just about everyone in the industry.
 
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#11
kintrap said:
For a solid state set up, it is all fairly self explanatory, as far as wattage goes. You want a cab that has a higher wattage rating than the amp, commonly said to be about twice as much to be safe. My question is when dealing with tube amplifiers, knowing they are louder per watt than solid state, wouldn't you need a cabinet with an even higher wattage rating? If so, how much?
Click to expand...

Self-explanatory - but inaccurate. When matching a cab to an amp, isn't necessarily the case that you need a cab with a higher power rating than your amp will produce - to be safe, or for any other reason. The cab'(s) thermal rating (probably the number you've been using) is not a reliable indicator of how much power it can actually take in real-world application. Your best bet against damaging the speaker(s) resides in your ability to turn the master volume and/or gain controls counter-clockwise whenever necessary. Knowing when it's necessary requires actually listening to your cab. It will tell you when it's had as much as it can take.

MM
 
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#14
Thermal ratings are no more than a vague basis for guesswork when judging a bass cab for folks who play bass [as opposed to highs or mids] because for such users the speakers fail at excursion limits [achieved by making bass notes] - not thermal limits [achieved by from making squeaky noises].

Also - key step in getting past the "tube watts are louder" miasma is understanding that watts do not equal loudness - loudness must be weighed so as to take the frequency content and transient behavior into account = you can make a dangerously loud device [upwards of 130 dB] with a $6 piezo horn and a few volts - obviously utterly pointless however in the context of a bass rig.

Tube amps aint more powerful, they just change the signal [distort], especially at the top end of there output range, in manner which then yields more apparent power [loudness] to the human ear. You can use a SS amp to feed volts to a cab with similar distortion components as a comparably voltage swing capable toob amp and there will be no loudness difference.
 
#15
I wish cab makers would stop "rating" cabs for specific wattages. That information isn't useful, or accurate, in determining how much power you can actually use with them. For that matter, the actual power being output by any given amp varies constantly and is seldom anything like the maximum the amp is rated for. Thus, you're back to the most reliable means of judging, your ears.

I know this isn't going to happen, because cab makers use the "ratings" for marketing, and because many buyers believe those numbers tell them something useful. (Is it true that my 400watt cab is better than my buddy's 300watt cab?). Of course, that's a silly example and a silly question, and there are an awful lot of players who just don't understand much about electronics. There are also those who do understand electronics and have differing opinions as to whether, for example, the amp or the cab should be higher rated. These are honest differences of opinion and can be respected. However, if cab rating would go away, there would be no more problem.

Myself, I just ignore the cab wattages, but I do lament that they tend to confuse some folks and add very little to understanding a system.

Raf
 
#16
What tube head are you looking at? Watts are watts, but since tune amps sound good at their peak values and can run that, id grab something that can take it, but that's my approach with cabs in general. Go higher with the power handling because underpowering can't hurt you, overpowering can.
My advice would be, if the head is 300 watts, get a 600 watt cab.
Also can someone with the facilities to do so measure a tube amps output versus a solid state amps output and give us an imperial test of watt to watt comparison.
 
#17
Raf Seibert said:
I wish cab makers would stop "rating" cabs for specific wattages. That information isn't useful, or accurate, in determining how much power you can actually use with them. For that matter, the actual power being output by any given amp varies constantly and is seldom anything like the maximum the amp is rated for. Thus, you're back to the most reliable means of judging, your ears.

I know this isn't going to happen, because cab makers use the "ratings" for marketing, and because many buyers believe those numbers tell them something useful. (Is it true that my 400watt cab is better than my buddy's 300watt cab?). Of course, that's a silly example and a silly question, and there are an awful lot of players who just don't understand much about electronics. There are also those who do understand electronics and have differing opinions as to whether, for example, the amp or the cab should be higher rated. These are honest differences of opinion and can be respected. However, if cab rating would go away, there would be no more problem.

Myself, I just ignore the cab wattages, but I do lament that they tend to confuse some folks and add very little to understanding a system.

Raf
Click to expand...
Even more than that I wish they all had to use a uniform rating. I love my swr cabs because they give peak and rms but advertised rms. Haven't steered me wrong either!
 

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