Tube Amp & Cabinet Matching

[carbonfold]

I know, I know, I know.... sticky sticky sticky or search engine, however, hear me out. Looking for more math/science vs. opinion here that I haven't really seen address exactly.


There is so much talk about over or under powering speaker cabs due to their maximum RMS capabilities. We know that SS amps can offer more control over clipping than tube amps so that they may be dialed to the “T” with the maximum speaker RMS efficiently. This would lead you to believe that when properly dialed up, you may safely run a 1000w SS amp on a 1000w RMS speaker system (or lower). However, this may not always be safe in the music world due to happy fingers that have the urge to keep cranking it up thus back into the world of clipping.

Currently I’m running a Marshall VBA400, a 400w (400w @ 4 or 2 ohms) tube amplifier, in a GK 412 Neo, a 4 x12 cabinet @ 1200w RMS / 2400W Peak with 102dB Sensitivity & 133dB Maximum.

I’m trying to understand clipping possibilities that tube amplifiers have over their actual output rating. Seems to be little information (that I have found) on this due to biasing issues ect ect… but the funny thing is that the manufacture of this amp has a recommended 4x12 cabinet (VBC412) to match this amp that is only rated at 400w RMS. I would fear that if the amp hit a clipping state over 400w, it could distroy the cabinet rather easy. But, I don't want to run a cabinet to much over the amp rating and lose out on head room.

So, where am I going with all this? I'm wondering if there is some % based math to calculate an approx amp output power rating to cabinet output power rating (for best match of output and efficacy *** AKA best of both worlds). Would it be more efficient running a 400-600w RMS w/ 102dB vs a 1000-1200w RMS w/ 102dB ? Would it even have an effect on headroom?

[BassmanPaul]

For starters, under powering is a myth.Taking it to its extreme, if it were true the cabinet would blow if it wasn't connected to an amp.

[AwkwardLoudness]

A cabinet's thermal rating, i.e. power handling, (XXX watts RMS, YYY watts peak) isn't particularly useful data since most speakers reach their excursion limit before reaching the reported thermal rating. Speakers can fail if pushed to the excusion limit too much. The amp's EQ, not just output power, affects speaker excursion. Another factor that makes reported thermal ratings even more useless is the fact that ratings are arbritarily determined using different methods by each manufacturer.

Clipping from tube amps will not damage speakers (like SS clipping) as long as the excursion limit is not reached.

"Underpowering" damage to cabs is a myth - at least in the manner that the issue is often described - but certainly solid state clipping (in amps without safety mechanisms to prevent it) can occur before a cab is driven hard.

Originally Posted by carbonfold

Would it be more efficient running a 400-600w RMS w/ 102dB for headroom vs a 1000-1200w RMS w/ 102dB (such as Bergs and the Ampeg Heritage line) ?

The efficiency of a cab is not related to thermal rating.

[carbonfold]

So there is no sound output differences here and would give me the same response?

400w tube amp with 1200w 102dB 412
Vs.
400w tube amp with 600 w 102dB 412

See what I'm saying. I'm just interested in the actual truth to maximizing tube amp and cab matching. Or does it not really matter as long as nothing truly exceeds maximum handling? That whether it has a thermal rating that is a perfect match or 3 times over, it will "sound" the same?

Also as for under powering being a myth.... I know where you are going with that but I fully understand how amplifiers going over their rating during clipping and then going over the cabinets rating cause overheating ( aka fry ) so it is not "truly" underrated rather than eventually going over due to clipping. However, that is not where I want to go with this thread. I've seen countless threads on that topic.

My main question is how much a tube amp can peak over it's rating to properly match a cabinet without having an excessive difference. Not saying to run a cab under the amps rating, rather asking the question should a amp & cabinet's output rating match or a % threshold over tube amp rating. But as Awkwad stated the issue would be more of thermal ratings rather than maximum watts. So with that being said, there has to be a science to it or am I asking a pointless venture of knowledge ?

Originally Posted by AwkwardLoudness

A cabinet's thermal rating, i.e. power handling, (XXX watts RMS, YYY watts peak) isn't particularly useful data since most speakers reach their excursion limit before reaching the reported thermal rating. Speakers can fail if pushed to the excusion limit too much. The amp's EQ, not just output power, affects speaker excursion. Another factor that makes reported thermal ratings even more useless is the fact that ratings are arbritarily determined using different methods by each manufacturer.

Clipping from tube amps will not damage speakers (like SS clipping) as long as the excursion limit is not reached.

"Underpowering" damage to cabs is a myth - at least in the manner that the issue is often described - but certainly solid state clipping (in amps without safety mechanisms to prevent it) can occur before a cab is driven hard.

The efficiency of a cab is not related to thermal rating.

[NKBassman]

There is no such thing as underpowering a cabinet. Why would putting 400W into a 1200W cab be a bad thing? You may not be utilizing the full potential of the cabinet, but you're not going to hurt anything.

Taking Bassman Paul's "extreme" example in a slightly more realistic direction, could you ever imagine damaging an 810 cab with a 5W tube head?

Overpowering cabs is bad. Clipping SS poweramps into square wave distortion is bad. But underpowering? Nah.

[carbonfold]

Again..... This isn't what this thread is about

I'm gonna scratch some verbiage at the top to get us refocused on what this thread is really about.

Originally Posted by NKBassman

There is no such thing as underpowering a cabinet. Why would putting 400W into a 1200W cab be a bad thing? You may not be utilizing the full potential of the cabinet, but you're not going to hurt anything.

Taking Bassman Paul's "extreme" example in a slightly more realistic direction, could you ever imagine damaging an 810 cab with a 5W tube head?

Overpowering cabs is bad. Clipping SS poweramps into square wave distortion is bad. But underpowering? Nah.

[nysbob]

The numbers have some meaning, but your ears and common sense trump them.

[recreate.me]

I think I can see what you are asking, and I believe the answer is no.

As far as I know there are way to many variables in play to give an actual value. And i think that if you did calculate the range it would be just as good as your estimate and you then need a cab in the range or 400 - 800watts.

The tough part is speaker excursion because that isn't measures by watts, so I you ignore it you get the question your asking, what is the peak power of a maxed tube head.

Okay so how do you get the max power o your tube head ? Turn your eq to max, and volumes and gains to max and play hard and measure every note.

That might work, but it won't address excursion that you could do trial and error with every note max eq and varying volume levels.
That would only apply to your head and those tubes.
Question answered.

[carbonfold]

true... not that I'm stating I have none but seeing 2+2=4 does mean something.

Originally Posted by nysbob

The numbers have some meaning, but your ears and common sense trump them.

[AwkwardLoudness]

Originally Posted by carbonfold

So there is no sound output differences here and would give me the same response?

400w tube amp with 1200w 102dB 412
Vs.
400w tube amp with 600 w 102dB 412

A 1200w cab vs a 600w cab from the same manufacturer? Or different manufacturers? Each manufacturer determines these arbitrary numbers using their own methods. Even speaker/cab efficiency ratings are embellished sometimes.

You need to worry more about cab design (internal volume, porting, bracing, damping) rather than bull**** numbers.

FWIW, I've own a ~440 watt clean RMS all tube amp that can fart out 8x10 cabs with "1600w RMS" (or more) thermal rating.

[beans-on-toast]

I understand what you are asking. It is a reasonable question. I don't know if there is a reasonable answer.

For one thing, you never know what the true specs of the amp and cabinet are. Is your amp output really 400W? Does it peak at 600W? 800W? Do the drivers really have a 102db sensitivity? Is one driver better equipped to deal with those peaks than another, despite their published specs?

Some manufacturers smudge the truth to better market their products. They also cut corners in their designs to maximize profit. At the same time, they want their product to sound as good as possible and survive through the warrantee period.

If you know what the true specs are, then you can apply a reasonable rule of thumb for matching an amp and a cab. I find that spending some time with the products and using your ears to determine what the limitations are as to how far you can push a rig is the best approach. The specs are a guideline at best that give you a reference to start.

[Bass_Pounder]

The problem is - there is NO answer to your question.

Thermal ratings of speakers mean nothing.

*Most* people assume that a 1,000 watt rated cab can handle a 1,000 watt amp, and it is just not true.

You need to know the T/S parameters of the speakers in the cab so you can calculate when it hits displacement limitation, and no cab companies provide that info.

[carbonfold]

Originally Posted by recreate.me

I think I can see what you are asking, and I believe the answer is no.

As far as I know there are way to many variables in play to give an actual value. And i think that if you did calculate the range it would be just as good as your estimate and you then need a cab in the range or 400 - 800watts.

The tough part is speaker excursion because that isn't measures by watts, so I you ignore it you get the question your asking, what is the peak power of a maxed tube head.

Okay so how do you get the max power o your tube head ? Turn your eq to max, and volumes and gains to max and play hard and measure every note.

That might work, but it won't address excursion that you could do trial and error with every note max eq and varying volume levels.
That would only apply to your head and those tubes.
Question answered.

NOW WE ARE COOKING!! I mainly had brought up this because seeming some higher end cabs with lower RMS (I know bs verbiage) but it was interesting to see why they will rate from 600-800w cabinets vs other company's giving these outlandish RMS ratings.

Originally Posted by AwkwardLoudness

A 1200w cab vs a 600w cab from the same manufacturer? Or different manufacturers? Each manufacturer determines these arbitrary numbers using their own methods. Even speaker/cab efficiency ratings are embellished sometimes.

You need to worry more about cab design (internal volume, porting, bracing, damping) rather than bull**** numbers.

FWIW, I've own a ~440 watt clean RMS all tube amp that can fart out 8x10 cabs with "1600w RMS" (or more) thermal rating.

Well, let's say cab for cab, they were exactly the same (brand and everything) besides one was thermal rated @ 600w and the other was at 1200w . Both were pushed with the same 600w head. If there was no clipping involved at all, would the speaker output / response / headroom be the same if the amp was running @ 100%?

I know, I know..... damn these "what if" scenarios! haha

[nysbob]

Originally Posted by carbonfold

true... not that I'm stating I have none but seeing 2+2=4 does mean something.

Yes, when the numeric values are absolute you can comfortably write a valid equation.

When you're talking about stated amp and speaker specs, there is no reliable continuity in measurement, so consequently any derivative equation is speculative at best.

[koobie]

Originally Posted by carbonfold

So there is no sound output differences here and would give me the same response?

400w tube amp with 1200w 102dB 412
Vs.
400w tube amp with 600 w 102dB 412

At least as far as guitar amp drivers are concerned, higher-wattage versions (from the same manufacturers) don't always sound the same as their lesser wattage versions. Do you have two specific cabs (from the same manufacturer) in mind?

Originally Posted by nysbob

The numbers have some meaning, but your ears and common sense trump them.

I agree with Bob. If your cab clacks, flubs out or sounds strained, back off the volume. I don't like to operate anywhere near the limits of a given speaker, not worth the risk.

[AwkwardLoudness]

Originally Posted by carbonfold

Well, let's say cab for cab, they were exactly the same (brand and everything) besides one was thermal rated @ 600w and the other was at 1200w . Both were pushed with the same 600w head. If there was no clipping involved at all, would the speaker output & response be the same if the amp was @ 100%?

The two cabs could not be the same (beyond thermal RMS rating) because one would either have twice the number of speakers as the other, OR they would not have the same speakers. I'd go with the so called "1200w" cab though epecially with a 400w tube amp. Or, maybe I'd want a pair of the 600w cabs if the amp's output impedance options would allow it, and especially if it would double the number speakers....more speaker area = more volume all else being equal.

[Bass_Pounder]

Originally Posted by carbonfold

Well, let's say cab for cab, they were exactly the same (brand and everything) besides one was thermal rated @ 600w and the other was at 1200w . Both were pushed with the same 600w head. If there was no clipping involved at all, would the speaker output / response / headroom be the same if the amp was running @ 100%?

I know, I know..... damn these "what if" scenarios! haha

Again, without the specs of the speakers it's all just a guess (and they cannot be identicle speakers because changing the thermal rating of the speaker also changes the rest of the T/S values due to the difference in size/weight of the voice coil).

Other than super speakers like the Eminence 3015LF that can take all the power it's thermally rated for, *most* commercially available speakers hit their mechanical limits at 1/2 to 2/3 the thermal rating depending on how you EQ.

So, my best guess is that - NO, they would not be the same.

[recreate.me]

No, it might be true If you had a 100watt head, but it's generally a good assumption that your head when maxed will put out a higher wattage then it's rates at.

Sounds weird but you have to remember RMS is not peak, so changes like dropped turning or eq in more bass or hotter pickups might cause high peaks, and peaks cause problems!

I had a can that would fart I I dropped my e to a d. But I'd I didn't it was great as loud as I wanted.

What you should be worrying about, as we are all pointing to is excursion.

[John D]

Originally Posted by beans-on-toast

I understand what you are asking. It is a reasonable question. I don't know if there is a reasonable answer.

For one thing, you never know what the true specs of the amp and cabinet are. Is your amp output really 400W? Does it peak at 600W? 800W? Do the drivers really have a 102db sensitivity? Is one driver better equipped to deal with those peaks than another, despite their published specs?

Some manufacturers smudge the truth to better market their products. They also cut corners in their designs to maximize profit. At the same time, they want their product to sound as good as possible and survive through the warrantee period.

If you know what the true specs are, then you can apply a reasonable rule of thumb for matching an amp and a cab.I find that spending some time with the products and using your ears to determine what the limitations are as to how far you can push a rig is the best approach. The specs are a guideline at best that give you a reference to start.

@ OP
If this thread lasts 1000 posts, you won't get a better answer than this. IMHO

[carbonfold]

Hopefully most people here will not misunderstand me think that I'm failing to use "the ear" concept. I use it everytime I'm rolling gear. You may ask me, "what would this information even matter in the real world?". Well I guess it does to me but may not to the next person. To me, it explains a general consensus of what you are looking at or the numbers would not exist. However, though I'm a "ear" person and what may work for me may not work for you, I also have the personality of numbers and math. Numbers state the way something "OUGHT" to be, whether or not it truly is. You dig?

To get that base line, you have to forget imperfection. Think perfection and the way something ought to be. After that you can guess-a-mate the +/- variances. However, we are in the real world and equipment isn't made on a perfect standard. With that said, let me throw out there something that would be a perfect world situation:

A speaker company named Company X makes two 15 inch subs. One is rated for 600w @ 4ohms and one is rated 1200w @ 4ohms (lets disregard cabinet design yada yadas for a moment).

Now, lets pretend we are in a perfect world and these two subs are "truly" rated at their handling ablities. One at 600w & the other @ 1200w. If you are using an amplifier rated at 600w (no clipping issues), would there be any benefit using a 600w vs the 1200w? Would the 1200w respond and handle different than a 600w speaker with a true clean 100% 600w load? Or would it just be the same in the end? Yes, I'm being "technical".