Common amp myths

[seamonkey]

Based on the scope traces that

Loudthud​

measured, it might make more sense to put the resistors in series with the power supplies. Maybe that's the entire basis for tube power amp "compression."

Either way, I think the effect would be the same. you're turning a voltage source into a current source. Thevenin lets this reduce to a voltage source with a resistor in series. Feeding a reactive load would tend to follow the impedance curve of the load (the speaker) and end up looking like the diagram for a tube amp.

 

[Psycho Bass Guy]

There is no spec that reliably measures loudness. What we perceive as loudness is the result of a complex permutation involving at least a dozen factors, not just two or three.

Exactly. That's the problem with a thread like this. Very complex questions are being addressed, most often incorrectly, by short, pat "layman-speak" answers which give the impression that the issues are cut and dried or easily quantified.

Shoot, just to cover what the term "loudness" means requires one to define frequency, intensity, signal, production and observation transducer efficiency, relative humidity, temperature, altitude, and few others. That's just to define "loudness." Now, add in gain staging, power supply efficiency, signal intensity, equalization, power, and distortion if you want to compare amplifiers, and still there are numerous ways to juggle all those numbers to give a more "marketing friendly" result.

 

[seamonkey]

Speaker cab manufacturers all adhere to standard AES measurement practices. Therefore the specs they tout can be used to compare products, and are to be trusted implicitly. They wouldn't lie, would they?

This must be right. We should just trust those who come to us with goods and services to sell. We do for all other industries and it always works out for the best.

 

[SpectorBass308]

Bass cabinets are heavy

 

[theunknowndude]

Bass cabinets are heavy

+1000

best 'fact' I have seen in this thread for a bit

seriously thanks for all the knowledge in this thread even if some of it is not 100% agreed on...

 

[Psycho Bass Guy]

I do believe they say the same for the orgasm

Nope. Think more along the lines of Kevin Smith.

 

[deggial]

You know, I DO believe in the validity of scientific measurement - but I also believe in real world observation...

I don't mean to take sides on the tube amps vs SS amps argument, as I have no experience for that specific instance, but real world observation or other forms of empirical evidence can be sometimes misleading.

One such instance is the debate about bass waves needing room to develop. The position in a room will indeed play a role, but the actual reason bass sounds different depending on distance is cancelling reflections off walls or other surfaces in a room - and the frequency of a sound wave does affect the degree in which it is reflected. One relevant experiment one can do is use different surfaces to test the sound acoustically. Thin surfaces, such as pieces of paper, will not reflect low frequencies and thus you will not notice any difference on the bass side.

That's not to say that empirical evidence is worthless, but you have to be careful on how to interpret real world observation, especially in uncontrolled conditions.

 

[seamonkey]

lol

i wont take it personally if you don't

FWIW - I use tube sound all the time. Informal blind tests conducted by Jimmy (the OP) have already pointed out that people can't really tell the difference in a real tube versus other solutions. I chose to use other solutions for many reasons.

A myth would be you can only get authentic tube sound from a tube amp.

 

[rag]

I have questions for both Bob @ QSC, PsychoBassGuy, and Robert @ Gallien-Krueger.

Since most consumers are going to use the term "watts" as their basis of how "loud" a particular amp will be, what measurement should the consumer really be using to make that determination? SPL?

As an example: An Ampeg SVP-CL preamp is first plugged into a tube power amp rated at 300W@4 Ohms, and then into a solid-state power amp rated at 300W@4 Ohms. The tube power amp is a lot louder. A watt is a watt, but it does not seem to be an accurate measure how loud the amplifies is. What specification could reliably measure "loudness"?

You pretty much have to listen to it. Most amplifiers are designed to drive real loads, but of course they always end up driving speakers which behave nothing like real loads. Speakers are nasty resonating beasts that fight the amplifier at every turn.

 

[Navybass]

In the electronic field, a watt is a measurement of power and power is defined as the rate at which electrical energy is transferred by an electric circuit. It's equasion is P=IV where;
P= Power (in watts)
I= Current
V= Voltage

Technically, electrically speaking, a watt is a watt no matter if it's generated by a tube amp or solid state amp.

However, most people notice that a 50w tube amp sounds louder than a 50w solid state amp at an equal volume setting. This might be due to a tube amps ability to amplify the harmonic frequencies of the fundamental frequencies better than a solid state amp. Solid state amps tend to attenuate some of the harmonic frequencies. This makes the tube amp sound fuller and could be perceived as sounding louder.

This is just my thought on the subject.

 

[MHensleyJr]

I guess you don't understand the numerous explanations given. LOUDNESS IS NOT A SCIENTIFIC MEASUREMENT!!

+1 End of Thread.

 

[joebingo]

Bass waves need room to develop.

I must admit I always thought this was true. So many audio people used to say it as a mantra when I was starting out. Not true, according to Bill Fitzmaurice, and his explanation is a good one...if it were true, how come headphones work?

Headphones work because of the proximity effect. That page talks about microphones as opposed to headphones, though seeing as they are essentially the same thing, the only thing to change would be:

"The result is that the frequency response of the microphone changes; specifically, it increases at the low frequency (bass) end, as the audio source is brought close to the microphone. This is the proximity effect as it pertains to audio."

to

"The result is that the frequency response of the ear drum changes; specifically, it increases at the low frequency (bass) end, as the audio source is brought close to the ear drum. This is the proximity effect as it pertains to audio."

Obviously if you read the entire article, it explains the physics behind this. (amplitude, frequencies, distance, air pressure, phase etc etc)

The fact of the matter is, I can barely hear myself when playing next to my amp, either at a gig or in practice. However, moving further away from my amp means I can hear myself.

This is not a phase issue. If it was to do with boundaries, I wouldn't be able to hear myself at any point in the room.

 

[Scott in Dallas]

Square wave distortion blows speakers.

This is the second most repeated myth. Supposedly it puts out a wave that's the opposite of how a speaker works and shreds them. If it were true, how could you amplifly an analog synthesizer?

That's sort of like saying, "if snakes are dangerous, how come a picture of a snake won't bite you?"

 

[Bob Lee (QSC)]

I have questions for both Bob @ QSC, PsychoBassGuy, and Robert @ Gallien-Krueger.

Since most consumers are going to use the term "watts" as their basis of how "loud" a particular amp will be, what measurement should the consumer really be using to make that determination? SPL?

As an example: An Ampeg SVP-CL preamp is first plugged into a tube power amp rated at 300W@4 Ohms, and then into a solid-state power amp rated at 300W@4 Ohms. The tube power amp is a lot louder. A watt is a watt, but it does not seem to be an accurate measure how loud the amplifies is. What specification could reliably measure "loudness"?

Honest amp power ratings are generally reliable in that they might be different varieties of apples but at least aren't apples and oranges.

The biggest variable is the conversion from one type of energy to another. Dynamic loudspeakers inherently waste more than 90% of the power put into them. IOW, nearly all the power turns into heat, and only a small amount turns into acoustical energy, or sound. Different loudspeaker system designs can squeeze a little higher proportion of acoustical energy than others, and therefore get more SPL per watt, but that may come at the expense of other desirable performance characteristics. For example, a cabinet might have a more uneven frequency response--which would be undesirable in a monitor or PA cabinet but might not be bad for an instrument system--and be louder overall for a given drive signal than a cab that has a very flat, accurate response.

And the process for converting sound into sensory stimulus--that is, human hearing--is even more complex and variable. Our hearing isn't at all flat, and furthermore, it's a lot more uneven at low sound levels than higher ones. Acoustical energy at a given SPL will sound a lot louder if it's concentrated in the 500 Hz to 4 kHz range than if it's 20 Hz to 160 Hz, even though both frequency ranges cover two octaves. That disparity in perceived loudness will be greater at low SPLs and less so at higher ones. This is one way that EQ can often make something sound louder without actually increasing the power in the signal.

There are other factors that influence loudness, so it's a complex thing to measure unless you identify those factors and control for them. Most loudness comparisons are analogous to cutting two pieces of string and measuring to see which one's longer.

One way or another, you must have enough loudspeaker, and enough amp power to drive it/them, to do what you intend to do.

 

[BWB]

Bass cabinets are heavy

Tube amps are light, easily transportable, and reliable.

 

[Bob Lee (QSC)]

Headphones work because of the proximity effect. That page talks about microphones as opposed to headphones, though seeing as they are essentially the same thing, the only thing to change would be:

"The result is that the frequency response of the microphone changes; specifically, it increases at the low frequency (bass) end, as the audio source is brought close to the microphone. This is the proximity effect as it pertains to audio."

to

"The result is that the frequency response of the ear drum changes; specifically, it increases at the low frequency (bass) end, as the audio source is brought close to the ear drum. This is the proximity effect as it pertains to audio."

Obviously if you read the entire article, it explains the physics behind this. (amplitude, frequencies, distance, air pressure, phase etc etc)

The fact of the matter is, I can barely hear myself when playing next to my amp, either at a gig or in practice. However, moving further away from my amp means I can hear myself.

This is not a phase issue. If it was to do with boundaries, I wouldn't be able to hear myself at any point in the room.

No. "Proximity effect" applies to directional microphones, not headphones.

Headphones work like small loudspeakers because that's what they are. Sound waves are waves of alternating compression and rarefaction, and low frequencies don't need space or distance to "develop."

 

[Bob Lee (QSC)]

In the electronic field, a watt is a measurement of power and power is defined as the rate at which electrical energy is transferred by an electric circuit. It's equasion is P=IV where;
P= Power (in watts)
I= Current
V= Voltage

Technically, electrically speaking, a watt is a watt no matter if it's generated by a tube amp or solid state amp.

However, most people notice that a 50w tube amp sounds louder than a 50w solid state amp at an equal volume setting. This might be due to a tube amps ability to amplify the harmonic frequencies of the fundamental frequencies better than a solid state amp. Solid state amps tend to attenuate some of the harmonic frequencies. This makes the tube amp sound fuller and could be perceived as sounding louder.

This is just my thought on the subject.

How do you define "equal volume setting?"

 

[Bob Lee (QSC)]

That's sort of like saying, "if snakes are dangerous, how come a picture of a snake won't bite you?"

Your analogy is flawed.

Jimmy points out a simple truth: despite the myth that square waves are dangerous to loudspeakers, the fact that an analog synthesizers producing square wave signals have been successfully amplified and fed into loudspeakers with no ill effect disproves it.

 

[Jonyak]

Your analogy is flawed.

Jimmy points out a simple truth: despite the myth that square waves are dangerous to loudspeakers, the fact that an analog synthesizers producing square wave signals have been successfully amplified and fed into loudspeakers with no ill effect disproves it.

that and the fact that millions of people everywhere use fuzz pedals, which basicaly amplifies your signal alot and clips it into a square wave, on a daily basis, while feeding that into a speaker.

 

[Scott in Dallas]

Your analogy is flawed.

Jimmy points out a simple truth: despite the myth that square waves are dangerous to loudspeakers, the fact that an analog synthesizers producing square wave signals have been successfully amplified and fed into loudspeakers with no ill effect disproves it.

Yes, the analogy is flawed. That was my point. It's a meaningless analogy because it doesn't address what actually blows the speakers, it just explains it away by suggesting that waves of different types are the same just because of the shape. It's much the same as saying that you shouldn't listen to Van Halen because the recording of the guitar distortion is bad for your speakers.