1db is clearly perceptible

[Guest105]

I get that. But my point is, or rather question, volume increase per increment on the pre must be commensurate to total output power of the particular amp. Wouldn't a higher power amp yield a greater increase per increment?

At the same preamp output, two different power amps are likely to produce different output to the speakers (because of different input sensitivities and gain structures). But from that point, the change in output as the volume control is changed will be the same (leaving aside compression/clipping).

For example, the same preamp and speakers might produce an SPL of 85db with one amp and 88dB with another. But assuming the same gain curve in both power amps, a one increment change of the preamp's volume control will yield the same change - upwards or downwards - in power to the speakers and therefore in SPL.

The absolute power capability of the power amp is irrelevant to this equation...up until the point of non-linearity/clipping.

 

[Superampman]

So my statement that at '60' on the pre, any of my amps are 'cookin' may very well be incorrect? I'm very careful not to bring them into clipping and I don't have an spl meter. Time to get one and start a new experiment

 

[Guest105]

So my statement that at '60' on the pre, any of my amps are 'cookin' may very well be incorrect? I'm very careful not to bring them into clipping and I don't have an spl meter. Time to get one and start a new experiment

I don't understand how you came to that conclusion. They may very well be quite loud at that setting.

 

[62caddy]

So my statement that at '60' on the pre, any of my amps are 'cookin' may very well be incorrect? I'm very careful not to bring them into clipping and I don't have an spl meter. Time to get one and start a new experiment

"60" is what o'clock? What is the signal? Is it a very quiet passage or a very loud passage? You can have a lower output voltage output at "60" (say 1:00) than a volume setting at "30" (say 10:00).

The answer is that without knowing the gain structure of the amplifier, the voltage of the preamplifier and finally the loudspeaker sensitivity, there's really no way of knowing what is going on in terms of output power.

Now if you start throwing SPL levels into the mix - trying to calculate output power from actual loudness at the speakers - forget about doing it that way.

 

[62caddy]

So my statement that at '60' on the pre, any of my amps are 'cookin' may very well be incorrect? I'm very careful not to bring them into clipping and I don't have an spl meter. Time to get one and start a new experiment

If by "cooking" you mean the amplifier is producing maximum output - again, there's no way of determining that - purely based on loudness alone.

A speaker rated at 110 dBW will play as loudly with 1 watt as a 90 dBW speaker with 100 watts.

 

[Guest105]

"60" is what o'clock? What is the signal? Is it a very quiet passage or a very loud passage? You can have a lower output voltage output at "60" (say 1:00) than a higher signal at "30" (10:00).

The answer is that without knowing the gain structure of the amplifier, the voltage of the preamplifier and finally the loudspeaker sensitivity, there's really no way of knowing what is going on in terms of output power.

Now if you start throwing SPL levels into the mix - trying to calculate output power from actual loudness at the speakers - forget about doing it that way.

If by output power you mean the signal from the power amp to the speakers, the sensitivity of the speakers has no effect on it (as opposed to their impedance, which does). Sensitivity, of course, determines how loud they will be with a given level of input.

I'm not surprised that the OP's various power amplifiers are producing similar volume levels from his speakers at a given point on the preamp's volume (gain) control. This would be as expected, assuming the use of the same preamp and same speakers in each case (and assuming similar input sensitivities on the part of the power amps).

 

[Montycat]

That's one possibility but it depends what you're trying to ascertain. 1dB difference in level of a tone of a certain frequency or 1dB difference in average volume of from say, 70 to 71dB, when listening to Back in Black.

Completely and utterly false. Back in Black can't be played at less than 110db.

 

[Superampman]

If by "cooking" you mean the amplifier is producing maximum output - again, there's no way of determining that - purely based on loudness alone.

A speaker rated at 110 dBW will play as loudly with 1 watt as a 90 dBW speaker with 100 watts.

Yes, that's what I mean. If I know the speaker dbw, can I not determine output power at a given distance? I sit 13' away from speakers with a sensitivity of 89db. 100db at that distance should be doable with a 200wpch. amp, no?

 

[Guest105]

You could get a somewhat reasonable estimate that way...but I would recommend doing the measurement at 1 meter to minimize reflection/room acoustics. And you really need to know how the speakers were measured in the first place (eg 1 kHz tone, etc). Try to use the same signal when you measure. You can probably assume that the measurement was calculated as continuous (vs peak), so this is the reading you want to refer to.

This measurement - after you do the math (and accounting for speaker impedance) - will give you a gross estimate of the power coming into the speaker.

This approach would not be very useful in determining if the amp is producing its maximum output (assuming that you want to know this value without clipping).

But what are you really trying to determine? There is probably a better/easier/more accurate way to get the answer to your question(s).

 

[Audiovet]

Mostly repeating, but there still seems to be some uncertainty. Perhaps some salient aspects in different words ....

Firstly, a dB figure is a ratio. An amplifier does not have an 80 dB output, unless stated elsewhere referred to what. Then the dB figure is the same increase/decrease in energy irrespective of whether one looks at voltage or power. The calculation/formula is different, not the amount itself. (3 dB amounts to a doubling of power, a 1,414 increase in voltage or current, etc.)

The 3 dB figure in loudness, popularly described as a 'worthwhile' change in loudness as mentioned, did not itself originate thus. Again as mentioned, the origin was a simple electrical situation i.e. a doubling/halving of power, a situation where the reactive component in an attenuation circuit is equal to the resistive component, a condition of 45 deg. phase shift, etc. The resultant loudness change description came afterwards and fell in conveniently.

Important, again as said, is that audibility of such is quite dependant on the type of programme, signal, etc. It should not be the subject of a 'my-hearing-is-better-than-yours' kind of debate.

 

[Superampman]

kcbluesman, I'm asking hypothetically for interest's sake to learn. You've obviously been very helpful as have you all. I've learned quite a bit as regards pre amp/amp interaction. I had no idea of some of the points brought up.

Put a different way, if I know the power output of the amp(say 200wpch.), and I know the speaker dbw, can I not with precision then calculate max distance possible to maintain a min. 100db spl?

 

[Guest105]

Well, you can calculate it but the result will have a pretty big +/- factor due to the number of unknown variables.

Starting with an amp capable of 200 watts (rms calculation) before clipping and a pair of 8 ohm speakers with 88dB sensitivity:

Add 3dB of SPL to account for the second speaker...so at 3 feet/1 meter, your SPL is 91dB with one watt of power.

To get to 100dB at 1 meter, you would need 8 watts. For each doubling of distance, the rule of thumb is a 6dB drop in SPL in open air. So, at 6 feet, you would ostensibly need 64 watts. This could vary considerably depending upon room acoustics...in an enclosed area, the power required should be less....but I'm not nearly knowledgeable enough to even estimate how to account for this variable. That would take somebody like JBL Guy.

Anyway, at 12 feet and using the same rule of thumb, you would need 256 watts to maintain 100dB.

And of course, I'm not accounting for dynamic peaks in the recording. With 12dB peaks, you would already be well into clipping (you would need an amp capable of delivering 2048 watts to avoid it completely...assuming your speakers could take that kind of power!).

Hope this helps. I'm sure that I've oversimplified this topic, but I'm at the edges of my knowledge level...but I'm sure more technically astute members will chime in to expand/correct my comments.

 

[Superampman]

Cool. I've got 1100 watt peaks available from my TNT200s in bridged mono. The Kappa 9s are 89dbw. Make it or not, they rock the house Roy Esposito built them and assures me they can handle the Kappas. I'm still skeptical though, as they get up to about 150F at the heat sinks. But just one in stereo stays 20 deg. cooler.

 

[Guest105]

I thought that the TNT200's are rated at 200 watts per channel in standard configuration. I doubt that bridging doubles them...but even if it does, how do you get to 1100 watts?

In any case, I'm sure that those beautiful amps can just about make your ears bleed pushing the Kappas.

 

[Superampman]

I thought that the TNT200's are rated at 200 watts per channel in standard configuration. I doubt that bridging doubles them...but even if it does, how do you get to 1100 watts?

In any case, I'm sure that those beautiful amps can just about make your ears bleed pushing the Kappas.

They are 'bridge paralleled'. So they output nearly four times. Stable to nearly a dead short. Each stereo amp is true dual mono. Roy was a principal EE at Acoustat and now runs a shop in Florida dedicated to the preservation of the original Jim Strickland Acoustat line. They were designed to handle their electrostats as you probably know. I have three TNT200s and a 120 he built for me for fully active JBL altered 4345 project that still hasn't gotten off the ground. I have all the parts for a good while now but I'm a lazy guy. I have the Kappas and a bunch of others.

 

[62caddy]

Yes, that's what I mean. If I know the speaker dbw, can I not determine output power at a given distance? I sit 13' away from speakers with a sensitivity of 89db. 100db at that distance should be doable with a 200wpch. amp, no?

As KC has said, it is not the optimal way of calculating the amount of output power actually being delivered, plus you also have impedance variations from the loudspeakers to add further confusion.

In theory, yes it might be possible to get a very rough approximation of what's going on but unless tests are conducted under highly controlled laboratory conditions (more specifically, in an anechoic chamber) with sophisticated test equipment, your power estimates will be extremely doubtful.

You'd be far better off picking up an outboard power meter if you really want to get some idea of what power you're using. But remember, they're really only voltage meters - not watt meters.

 

[whoaru99]

Yeah, well, analysis paralysis...

Nominal impedance figures, amplifier rated outputs, etc. etc. are good enough for general conversation.

The notion that we can't say "exactly" about any given situation implies we can't say anything about anything baffles me. Frankly, I think it's often just obfuscation.