Common amp myths

[fdeck]

Also, don't sacrifice your hearing to these tests. I wear hearing protection whenever I do audio testing with speakers connected.

 

[shakerattleroll]

Well, that's what he's saying and then throwing in all kinds of confusing jargon about gain structure and stuff. I've sat through one too many board room meetings to know when someone is BS'ing their way through something. I'll give him that he probably knows a lot more than I do, but then again, I'm still learning all this stuff.

My thoughts, whether it's a myth or cold hard truth, if millions of people worldwide are perceiving something to be louder than something else, then that should be the REAL test. We are talking about bass ya know?

So if you're still learning, how is it I am wrong because you're confused about my reference to gain structure? I'm not BS'ing my way through anything. I've sat through one too many audio classes to believe a tube watt is louder.

As Bongo more eloquently illustrated, the amps are not inherently equal because they use the power available to them in completely different ways. It's just not a good comparison.

I would choose the SVT over the B series all day, every day, and for anyone to assume I don't know what I am talking about or to assume I've never gigged is ridiculous. Of course perception is important when we pick an amp to play with, but that still doesn't mean that the watts of a tube amp are louder. The tube amp can be pushed beyond it's limits in a way that solid state can't to make us perceive it as louder, but the watts themselves are not more powerful. That's just plain old electrical engineering 101; you cannot have a watt that is worth more than another watt, that's not how energy works.

Millions of people can perceive lots of different things, that isn't good enough to make something "cold hard truth".

 

[shakerattleroll]

Here's an example that might help people to understand one of the reasons tube amps "seem" louder:

Have you ever noticed how commercials "seem" louder than the program you are watching on television? We perceive it as louder, but it isn't. The FCC mandates certain levels that CANNOT be exceeded. So how do advertisers get their commercials "louder"? They compress the living S out of them, and we therefore perceive the commercial to be louder.

This effect, compression, is just one of the reasons we can perceive the tube amp to be louder, but the watts aren't any more powerful or louder, on and on ad nauseam.

 

[shakerattleroll]

Thought you'd never ask!

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Bill, with all due respect, I will take the word of an audio physicist over you. And said audio physicist says bass waves don't need room to develop.

I love that picture. It is tubes, so it is probably louder.

 

[seamonkey]

...
It would be interesting to repeat the experiment an octave up.

Better yet - reference the Carver story, and put a small resistor in series with the SS amp. Play with a couple of different resistors until the frequency response matches that of the tube amp. I expect the SS will do the same thing on the scope.

 

[SpankyPants]

Can i call you Uncle Jimmy?

 

[shakerattleroll]

Uncle Jimmy!!!

 

[JimmyM]

Can i call you Uncle Jimmy?

Not until you wash that crap off your face.

 

[perogato02]

True.
Now my head hurts.
But in order to dubunk the myth, we need to explain why the perception is that the 'bass is louder in the back of the hall' or 'across the park'...?

Low frequency sounds travel further then higher frequency sounds (due to the waveform they don't get reflected that much by obstacles compared with the higher frequencies) ... so the farther away you are listening to music the more the low frequencies stand out in the mix.
This is the reason why you can hear the bass miles away from a festival.

At least, that is what I've been told

 

[SpankyPants]

Not until you wash that crap off your face.

What crap, Uncle Jimmy?

 

[JimmyM]

Low frequency sounds travel further then higher frequency sounds (due to the waveform they don't get reflected that much by obstacles compared with the higher frequencies) ... so the farther away you are listening to music the more the low frequencies stand out in the mix.
This is the reason why you can hear the bass miles away from a festival.

At least, that is what I've been told

Right. Same reason that when you go outside of a building that's blasting music, all you can hear is the bass. It's not that you can finally hear the bass...you can finally hear the bass unencumbered by mids and treble.

 

[Rune Bivrin]

Leaving the SS vs Tubes discussion for a while, my favorite myths are:

Loudspeaker ratings are accurate and complete.
I think most speaker manufacturers (as opposed to driver manufacturers) take the sum of the thermal power handling capacity of the drivers in their boxes and call that the rating of the box. However, playing a bass with the lows cranked you're quite likely to send the drivers into over-excursion with ease (depending on how they're tuned.)

Keeping the volume control at 5 uses half the amp power
The correlation between volume control settings and amp power is pretty slim. You can count on an amp getting louder when you turn controls clock-wise, but that's about it. Many instrument amps are designed such that their volume controls have most of the range covered in the first third. That way they'll appear loud in the shop where the potential buyer is expected to think "Wow! If it's this load at 3, just imagine what it'll do at 10!".

 

[Rune Bivrin]

Some other tidbits I've been pondering:

I'm guessing that some of the "loud" tube amps have a relatively poor frequency response below 100 Hz (or somewhere in that range), thus having a lot more power available to the "loudness" creating mids. That combined with the higher output impedance allows the resonance of the speaker to "bloom" so you don't miss the lows.

Solid state amps on the other hand are easily built to reproduce DC faithfully, albeit pointlessly. That in combination with the very low output impedance tames the resonance of the speaker, and you'll wind up spending much of the power in the lower frequencies where they don't contribute much to perceived loudness.

About clipping and DC:
A poorly designed (and poorly used) SS amp can have unsymmetric clipping. That could, in fact, put out a moderate amount of average DC when clipping. Whether that has any perceptible effect on the power handling capacity of speakers I really don't know. DC moves the voice coil off center from the magnetic field and also the cooling effect of the magnet structure. But how much? No idea...

 

[rag]

"Tube watts are more powerful than SS watts.

Watts is watts. The only difference is that tube amps will generally allow you to push past the point of their RMS wattage because distortion kicks in much smoother and less noticeable as an SS amp, so it sounds like clean volume even though it isn't."

actually, tube amps are generally louder than SS amps with the same wattage. That's because they run in class AB, where the amp is not only pushing the speaker foward, but also pulling it back. SS amps, or at least the cheap ones, run in a more efficient class C, D, H, etc. Where the amp really only pushes the speaker out, then the magnet of the speaker pulls it back naturally. for example:

I have a Threshold stereo power amp (designed for high fidelity stereo speakers) that is class A for the first 50% of its power, then its class AB. It's rated at 100 watts RMS per side. I also have a Carver PM 2.0t. I don't know what class it is, but it's definitaly not AB. It's rated at 450 watts RMS per side.

My speakers are barely moving around with the threshold, and totally flapping around with the Carver (at full power) but they both give me about the same loudness.

"tube watts" basically refers to a power amp that is class AB, which 99% of tube power amps are, and 99% of SS [bass] amps are not. Watts are watts, but when you add a speaker in there, "tube watts" are over twice as loud.

Totally not true! Way off the mark. 99.999% of all amplifiers are Class A/B!

 

[bongomania]

Solid state amps on the other hand are easily built to reproduce DC faithfully, albeit pointlessly.

I've never heard that said before. Link to reference?

About clipping and DC:
A poorly designed (and poorly used) SS amp ...could, in fact, put out a moderate amount of average DC when clipping. ...DC moves the voice coil off center from the magnetic field and also the cooling effect of the magnet structure.

The claims you're making here go against the statements made by amp and speaker cabs designers here... again, link to reference?

 

[georgestrings]

What are your criteria for determining maximum usable volume?

Exactly how healthy a wager would you make?

Now, maybe *some* people's criteria is different than mine, but I'm sorta a "where the rubber meets the road" type of guy - and don't get as hung up on specs as *some* do...

So, here goes:


Play a gig with a LOUD metal/hard rock band, with a typical classic rig: an SVT on top of an 810 - then, play the same gig the following week with with a B2RE instead of an SVT, and compare effectiveness... Now, unlike some(apparantly), I have actually done this - and I can tell you, the SVT had PLENTY left "in the tank", while the B2RE "ran out of gas", FAR too early...

Furthermore, as I stated before - I've played more than a few gigs with a Marshall Major for a head, and it worked just fine for a loud metal setting - if you've seen a 200 watt SS amp that can pull the same duty with the same effectiveness, I'd love to see it...

Now, people can throw all the specs, and scientific jargon at this that they want, however - those are cold hard realities that cannot simply be ignored...

For the record - I use hybrid amps for my gigs these days, and don't even own an all-tube head for bass - so it's not like I have any emotional investment in taking the position I have - just real world experiences...


- georgestrings

 

[rag]

wow.. this needs to be stickied.. when I was starting out this thread would have answered a lot of questions for me.... Great thread!

so here is a question.. not necessarily a myth.. but is there REALLY a difference in the sound of an 8 ohm cab vs a 4 ohm cab if they are both receiving the same amount of wattage? (300 watts @ 8 ohms into an 8 ohm cab vs. 300 watts @ 4 ohms into a 4 ohm cab) I have heard people tell me that the 8 ohm cabinet will sound cleaner and the 4 ohm cab will be slightly louder. Is that really true or just a load of myth?

(this is also assuming the cabinets are otherwise completely identical)

It depends on the impedance of the drivers. In general, higher impedance drivers are more efficient than low impedance drivers. This is because high impedance drivers use finer voice coil wire (round wound coils) that pack better and therefore get more wire in the gap. Let’s take a 4x10 eight Ohm cabinet and compare it to a 4x10 four Ohm cabinet from the same manufacturer. Most manufacturers use eight Ohm speakers wired in series parallel to get eight Ohms, and sixteen Ohm speakers wired in parallel to get four Ohms. In this case the 4x10 four Ohm cabinet will be more efficient than the 4x10 eight Ohm cabinet because it uses high impedance speakers.
In our case (GK) we make our own drivers and therefore are able to make both our 4x10 eight and 4x10 four Ohm cabinets with high impedance speakers wired in parallel. For the eight Ohm 4x10 we use thirty two Ohm speakers wired in parallel, for the 4x10 four Ohm cabinets we use sixteen Ohm speakers wired in parallel. So in our case the eight Ohm cabinet is more efficient than the four Ohm cabinet because 32 Ohm speakers are more efficient than 16 Ohm speakers. Another point of interest, when you loose one speaker in a series parallel cabinet you also loose it’s series partner so half your speakers drop out. If you loose a speaker in a completely parallel configuration you only loose that speaker, the other three keep working. Thirty two Ohm speakers are more expensive to make but we feel the benefits are worth while.

 

[Rune Bivrin]

I've never heard that said before. Link to reference?
...
The claims you're making here go against the statements made by amp and speaker cabs designers here... again, link to reference?

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You'll find a wealth of information at this site, and any solid state amp designer will know that it requires an effort - if only a small one in the form of a capacitor - to block DC at the input from appearing amplified at the output. It's really operational amplifier design 101.

Tube amps - at least the vast majority - have a transformer on the output which effectively block any net DC from reaching the speaker.

 

[jezzamac]

Has anybody mentioned the efficiency of the speakers being driven by said watts? Edit: Yes!

 

[georgestrings]

You guys both miss the point completely. The B2RE is not a valid comparison, because it is incapable of using its watts efficiently in terms of "loudness". But that is not strictly because it's solid state.

If the choice given was between an SVT with its EQ set flat, and an equivalent-wattage solid state amp plus a good compressor plus a good overdrive pedal plus adjusting the EQ of the ss amp to match the preset EQ voicing of the "flat" SVT, then you might have a fair comparison.

Sure, you can argue that the SVT's inherent compression, distortion, and EQ shaping make it an easier choice over a rack of complicated SS gear, but the fact is all the gear I mentioned in the second example can be 100% solid state. And using it in a manner that carefully recreates the described qualities of the SVT will get you equal "loudness".

Do you work in politics??? - 'cause that sure was a nice spin job...

Let me see if I've got this straight - a tube amp and an SS amp with the same output ratings, but to be "fair" in your world, the SS amp needs to have a compressor, an OD pedal, and be EQ'd to match the tube amp's sound while FLAT???

Yeah, sounds about right - hahaha!!!


- georgestrings