The science behind cranking a tube amp...

[Kenny D]

There seems to be more to getting good tone than just burning the tubes hotter.

I have read the Mixerman/Slipperman articles on getting the speakers to really pump air. What is the science behind this? Are we doing some type of comression when pushing the speakers that hard?

Last night I cranked up the amp so loud I could not be in the same room with it. This was the only way I could get the tone I am after. I have a PPIMV mod on the Plexi and the amp normally sounds beautiful in the room without pushing the volume anywhere near what it took to get a good recorded tone.

What is actually going on between the amp, the speakers, the air and the mic?

[RockStarNick]

I mean, a LOT of it has to do with the fact that when an amp is cranked, the power tubes are REALLY working hard, and compressing and overdriving.

To me, that's where the tone comes from. Not necessarily decibel levels. BUT... depending on the amp, you have to reach near-death DB levels in order to get that tube magic happening...

Can you explain the differences in sound, ON TAPE, between the cranked-to-hell sound, and the "normal" volume level?

[mike leary]

We on the other side of the studio, sweated blood when you guys started cranking those amps; our consoles did not have enough pre-amp padding to handle the transients; thus the popularity of the Shure 57.

[Kenny D]

I mean, a LOT of it has to do with the fact that when an amp is cranked, the power tubes are REALLY working hard, and compressing and overdriving.

To me, that's where the tone comes from. Not necessarily decibel levels. BUT... depending on the amp, you have to reach near-death DB levels in order to get that tube magic happening...

Can you explain the differences in sound, ON TAPE, between the cranked-to-hell sound, and the "normal" volume level?

Yes, when attempting to record at "tolerable" levels (still quite loud), the sound is thin and buzzy. When the amp was turned up to deafening levels, the tone smoothed out and became more like what you would hear on a commercial CD. Far less buzzy - much warmer.

I know that cranking an amp really gets the power tumes humping but why would it be so important to get speaker extrusion. Many of Slippy's comments are regarding getting the speakers "really pushing air." This strikes me as something physical that happens to the speaker and the mic.

[lpfella]

I think that an amp with a really interactive master volume is the secret to getting great tones at lower volumes and pushing the tubes without blowing the room out with volume. Some that come to mind are Matchless and Savage. Both have very unique amazing, and versatile master volume knobs.

I know these two suggestions do not help with your amps situation but if you are ever in the market these two amps may be something to look into.

Getting an attenuator to run with your amp to get some of those sounds at lower volumes.

[rob2001]

Heres some info on what I think is a big contributor to all this. The Fletcher-Munson curve. To sum it up as I understand it, the human ear is more sensitive to certain frequencies and that changes with SPL's. So to me, it's more than only getting tubes cooking and my experience with attenuators confirms this. I far prefer the tone from a loud cranking amp compared to an attenuated cranking amp.

Anyhow, heres a link offering a brief explanation of the Fletcher-Munson curve.

http://www.allchurchsound.com/ACS/edart/fmelc.html

I'd add that speakers can add their own compression and breakup. Some people dig it, some don't, but thats another thread!

But all this leads me to believe that it will always be totaly impossible to simulate a loud, cranked tube amp. But as with anything, too much of a good thing isn't always good. IMO, there is such a thing as bad power tube breakup and speakers being pushed too far.

[Kingbeegtrs]

Low Wattage + Volume at 10 (or eleben) = good tones at bearable volumes.

[RockStarNick]

more questions:

Is the preamp for recording on the same setting? or are you adjusting it accordingly when the volume is turned up?

How far away is the mic? What kind is it?

Could it be that the sheer volume and air moving from the speaker is "tricking" the mic into some sort of proximity effect?

[Kenny D]

more questions:

Is the preamp for recording on the same setting? or are you adjusting it accordingly when the volume is turned up?

How far away is the mic? What kind is it?

Could it be that the sheer volume and air moving from the speaker is "tricking" the mic into some sort of proximity effect?

No, I have to adjust the pre down or I'll be red-lining the meter for sure.

I used two mics: Audix I5: 1 foot from the grill, on cone close to the edge of the speaker. Room mic: AKG C1000s about 9' back, off axis, pointing at the speaker.

Both mics sounded better when the amp was turned up way loud but I could not audibly tell the difference myself in the room. I could not stay in the room for very long. Way too loud.

[Tone_Terrific]

Speakers are not linear, either with regard to freq response or output, so they do sound different under heavy power. Sorry, no references.

Ed Degenaro uses an iso cab. I am pretty sure he has posted clips showing that the tone may not change at the mic as much as we think though. i.e. low level, amp attenuated clips sounded like much like louder ones. Maybe he could be roused to restate his techniques.

[GDking]

It is mainly electron dolphins dancing within a matrix of crystalline lattice. Do a search.



:banana

[michael.e]

Low Wattage + Volume at 10 (or eleben) = good tones at bearable volumes.

Disagree.

I mean it sounds ok, but, in the midst of say a rock song, all you get is this compressed "shhshhhhhhhhhhh" noise and some tone.

Basically, what i am saying is that a low watt amp on ten does not equate to what I would consider good tone.


Much to do with the amp topography
MUCH to do with the sensitivity/quality of the speakers. And NOT that they are pushing air..

[michael.e]

No, I have to adjust the pre down or I'll be red-lining the meter for sure.

I used two mics: Audix I5: 1 foot from the grill, on cone close to the edge of the speaker. Room mic: AKG C1000s about 9' back, off axis, pointing at the speaker.

Both mics sounded better when the amp was turned up way loud but I could not audibly tell the difference myself in the room. I could not stay in the room for very long. Way too loud.

I LOVE my I-5 for close mic'ing and I use an Audix CX-212 large diaphragm condensor for more ambient micing or low volume/super sensitive/touch sensitive parts.

[TieDyedDevil]

Cranking an amp also reduces the effective bandwidth of the output transformer. (Or at least it tends to: it depends upon the transformer.) You lose lows and highs and end up with more midrange.

[RockStarNick]

Cranking an amp also reduces the effective bandwidth of the output transformer. (Or at least it tends to: it depends upon the transformer.) You lose lows and highs and end up with more midrange.

Very interesting...

Is that the opposite of the way a human ear hears? Like, we hear bass and treble BETTER at higher volumes (hence the need for a loudness button?)

[franksguitar]

I always found it better to use a small very low wattage amp and cranking it so you can maintain the crank factor without being at insane decibel levels for recording as well as doing both close miking on the outside of the cone w/an SM57 and a condensor mike about 6 ft out for ambient sound to make it sound hugh. In some cases for some tracks I use a POD direct to avoid the high volume or amp simulation.

[jcground]

The discussion about Fletcher-Munson curves and loudness controls is key to how people react to the tone at high versus low volumes, IMO.

More about Fletcher-Munson:
http://en.wikipedia.org/wiki/Fletcher-Munson_curves

Tube versus solid state drive, as it was explained to me when I was in college, boils down to the physical limitation of amplifiers when pushed. A tube will "try" to give you more amplification than spec, and the slight rounding of the sound waves at the clip level as it tries to give you more is what people typically find pleasing to hear. By comparison, transistors typically have a harsher clip with less rounding of the sound wave. You can see the difference on an oscilloscope, but the difference is also noticable to your ears.

Digital amplificiation, of course, cannot push at all, so the clip is especially harsh. I don't know anybody who likes the sound of digital distortion. (Note, I'm not talking about digitally modeled analog distortion... I'm talking about pushing a digital recorder into the red.)

The ability of transducers (speakers and mics) to handle high SPLs when pushed will also vary depending on their design. A speaker or mic's behavior at the limits of excursion (as far as it can vibrate back and forth) is bound to be different based on how it's built, what it's built from, how hard you're driving it, with what sort of signal, etc...

To my ear, attenuated amps, cranked low power amps, and cranked unattenuated high power amps sound different on playback at the same volume. Unfortunately, I like the sound of the cranked unattenuated high power the best... but I can't play that way when I practice (too loud) or even most of the places I've ever gigged (would still be too loud). It's also a drag because playing through a really high power rig changes the way you play - muting, finger technique and other aspects of your play have to be more precise or it'll sound terrible. So, IMO, you have to practice to get good at playing really cranked, and it's hard or impractical for most people to do.

Fortunately, in the end, guitar tone is subjective. You can't really talk about goodness in measurable terms like "fidelity" - how an audiophile would about a high end stereo - because you're creating your tone, not recreating it. Whatever tools you use, and how you use them, you'll know good tone when you hear it. :)

[blueprint]

+1 for low wattage amp at full volume.

I have an 18 watts Reinhardt head, and I get amazing tones with it without breaking the walls of my basement.

Moreover, I think that if you record something more or less as loud as human voice you have many many choice of mics.

[Kingbeegtrs]

Disagree.

I mean it sounds ok, but, in the midst of say a rock song, all you get is this compressed "shhshhhhhhhhhhh" noise and some tone.

Basically, what i am saying is that a low watt amp on ten does not equate to what I would consider good tone.


Much to do with the amp topography
MUCH to do with the sensitivity/quality of the speakers. And NOT that they are pushing air..

you don't have to have the guitar's volume at 10

[michael.e]

you don't have to have the guitar's volume at 10
Oh, I understand that fully. I have not kept my volume pot on 10 all the time for about 18 years.

Still....:dunno

[rmconner80]

Aside from the FM curve, yes, pushing the speakers ABSOLUTELY contributes texture and artifacts to the tone. Every single thing from the sensitivity of the mic getting hammered to the (now nearly defunct) tape compression to the non-linearity of the tubes and transformers is making "that sound".

With regard to speakers, you can get into that texture range by using lower wattage speakers and lower wattage amps. But still, obviously, more iron and glass in a push pull 100 watt marshall is always going to sound "bigger."

[LSchefman]

Guitar speakers distort under power. That's a big part of it. Speaker distortion is part of the "sound."

And to some degree, the cabinet resonates to the loud tones, and the mic picks up some of the room (very little in some cases, but that's another matter). Hence, the "moving air" argument.

I agree that sometimes you have to crank it up to get what you want, and this is particularly true in the case of heavier tones.