SPL phenomenon from different amps

[h3ndrix]

I previously owned a Rogue integrated with 100w driving some 804S’. I liked the sound well enough but sometimes I found myself turning up the amp to and experiment/get more impact. There were a few instances where I was listening in the mid 90s dB to 100dB. A couple of times doing that during some droney, almost frequency sweep-like, parts of music I was listening to—it would cause one of my speakers to crackle. I thought maybe I fried something and ended up replacing the drivers. I couldn’t understand how “juicing” the speakers could cause that. Still don’t.

In the midst of learning about that, it was brought to my attention that maybe I was expecting too much from my 100w amp. So I upgraded to 250w from Rogue.

I like the amp better, noticed I was listening at lower volumes and still finding enjoyment. Now I will “crank” it and get to a measured SPL of 85dB from my listening position (about 6ft). What I think is crazy is… it seems louder than my 100w ever did? Like I understand there might be more detail coming from the speakers now but now I feel like 85dB is almost, just almost, unlistenable where I was able to crank the previous amp before feeing uncomfortable/maybe causing an issue for one of the speakers.

I know my messaging might not be super clear but I’m hoping someone can parse through it enough to help me understand what’s going on.

To reiterate, there’s not really a problem—just a curiosity.

 

[staticV3]

There is simply no playback quality which an Amp can affect, that could make 85dB SPL appear louder than 100dB SPL.

This would become obvious in a direct, unsighted A/B comparison.

I suspect your SPL readings are off.

 

[h3ndrix]

There is simply no playback quality which an Amp can affect, that could make 85dB SPL appear louder than 100dB SPL.

This would become obvious in a direct, unsighted A/B comparison.

I suspect your SPL readings are off.

I suspected the same and measured both amps with a SPL meter and phone as meter to comparable results.

Is there a possibility that the newer amp is driving the woofers more efficiently and producing more low end that affects SPL? I will say there is certainly more low end present at lower level.

 

[solderdude]

At 2m (6ft) your speakers can reach 84dB SPL with 1W(in 8ohm).
Your speakers are 8ohm average but dip to 3ohm at certain frequencies.
To reach 90dB average you will likely have 100-105dB peaks present.
To reach this you require an amp that can supply 28V in 8ohm = 100W.

Is there a possibility that the newer amp is driving the woofers more efficiently and producing more low end that affects SPL?

No.

Maybe you can play the new amp louder. 250W vs 100W (if the ratings are accurate) means the 250W amp can play 4dB louder without hitting distortion.
Maybe it can handle low impedance better.
Maybe your volume control/gain differs given you this idea.
Maybe there is something else at play.

 

[Buckeye Amps]

Decibel level is decibel level. There are many different factors involved in reaching a certain dB level, along with the quality of the sound and a whole host of different variables. But 100dB is 100dB and 85dB is 85dB.

Something is off/wrong between the two measurements you made. Or you are severely biased (unintentionally) in your recollection of how loud 100dB was to you compared to your now 85dB reading.

 

[h3ndrix]

That definitely may be it. I think the volume knob is tricking me as well. On the previous amp, halfway up got me to the “danger zone” of 100dB, on this new amp halfway up is about 85dB give-or-take depending on the record pressing. This is quite possibly all psychological. For some reason the 85dB on this amp feels like “enough” and I feel less reason to turn it up past that. Something with the previous amp made me feel like turning it up searching for more detail when I may have just been getting more.. distortion?

 

[Sokel]

Different weighting could explain it also.
If one measurement was A-weighted and the other C-weighted (both showing 85dB average), the A-weighted one would sound a lot louder, specially with bass-heavy material.

 

[Buckeye Amps]

That definitely may be it. I think the volume knob is tricking me as well. On the previous amp, halfway up got me to the “danger zone” of 100dB, on this new amp halfway up is about 85dB give-or-take depending on the record pressing. This is quite possibly all psychological. For some reason the 85dB on this amp feels like “enough” and I feel less reason to turn it up past that. Something with the previous amp made me feel like turning it up searching for more detail when I may have just been getting more.. distortion?

Difference in dB output at the "same" volume setting between two amps usually comes down to differences in the gain stage/setting and/or how the amps are connected (RCA vs XLR vs internal/integrated amp)

Someone using a Denon AVR with say 120w per channel and a gain of 29dB can upgrade to a 1200w per channel amplifier with a gain of 26dB but find they may need to actually turn the volume setting up more to get the same desired dB output at their seat. Etc etc. A lot more is in play than just watts.

 

[MaxwellsEq]

That definitely may be it. I think the volume knob is tricking me as well. On the previous amp, halfway up got me to the “danger zone” of 100dB, on this new amp halfway up is about 85dB give-or-take depending on the record pressing. This is quite possibly all psychological. For some reason the 85dB on this amp feels like “enough” and I feel less reason to turn it up past that. Something with the previous amp made me feel like turning it up searching for more detail when I may have just been getting more.. distortion?

It seems that the different amplifiers have different gains. Over the last few decades power amplifier gain has steadily reduced as outputs from domestic and professional sources have increased. Even so, there's no "standard gain" for a power amplifier.

ASR is full of discussions where people are confused by this. They replace their 70W 1980s power amplifier with a gain of 30dB with a new 400W amplifier with a gain of 23dB and are mystified as to why the 400W amplifier is "so much quieter" than the 70W amplifier. Or they complain that their volume control used to be too loud at 12 o'clock and now needs to be turned to 3 o'clock to sound as loud. I think this has a psychological affect. The markings on the dial or the dial rotation all have no meaning.

 

[h3ndrix]

It seems that the different amplifiers have different gains. Over the last few decades power amplifier gain has steadily reduced as outputs from domestic and professional sources have increased. Even so, there's no "standard gain" for a power amplifier.

ASR is full of discussions where people are confused by this. They replace their 70W 1980s power amplifier with a gain of 30dB with a new 400W amplifier with a gain of 23dB and are mystified as to why the 400W amplifier is "so much quieter" than the 70W amplifier. Or they complain that their volume control used to be too loud at 12 o'clock and now needs to be turned to 3 o'clock to sound as loud. I think this has a psychological affect. The markings on the dial or the dial rotation all have no meaning.

Can you help me understand what the volume is actually doing? Can it be thought of as just an attenuator where it’s “maximum” would be no attenuation and any position before it is a varying amount of attenuation based on a curve that it was designed with? Is this what you are referring to as gain? When I hear gain, I think amplification like the volume knob is some sort op-amp that is now boosting the signal like a fader on a mixing board past unity

 

[MaxwellsEq]

Can you help me understand what the volume is actually doing? Can it be thought of as just an attenuator where it’s “maximum” would be no attenuation and any position before it is a varying amount of attenuation based on a curve that it was designed with? Is this what you are referring to as gain? When I hear gain, I think amplification like the volume knob is some sort op-amp that is now boosting the signal like a fader on a mixing board past unity

Almost all preamplifiers have gain. Especially so when amplifying phono signals of course!

The volume control moves between attenuation at lower dial numbers through to gain at the highest numbers on the dial. However, for digital sources feeding modern power amplifiers, you often only need attenuation, which is why some people use what is sometimes known as a "passive preamplifier" - just a potentiometer.

 

[h3ndrix]

Almost all preamplifiers have gain. Especially so when amplifying phono signals of course!

The volume control moves between attenuation at lower dial numbers through to gain at the highest numbers on the dial. However, for digital sources feeding modern power amplifiers, you often only need attenuation, which is why some people use what is sometimes known as a "passive preamplifier" - just a potentiometer.

Got it. And Rogue even confirmed to me “whereabouts” the gain starts. Funny enough, it’s around 12 o clock. My follow question:


If the phono preamp brings the micro voltages to line level, why is signal (or voltage) less than what most digital sources would provide?

 

[solderdude]

Because in the good old days line level was around 300-400mV for tuners, tape/cassette decks and phono-pre-amps around '0dB'.
And ... as the gain is fixed the actual output level also depends on the cartridge.
The thing is that one can easily have signal peaks up to 6dB higher so around 0.8V

For CDP it mostly is around 2V for 0dB but the catch is that the average levels are much lower (5-15dB lower) because in digital there is no signal above 0dBV where in analog audio there often is.

In general CDP/DAC is about 6dB to 12dB 'louder' than the old 'line level'.

 

[MaxwellsEq]

Because in the good old days line level was around 300-400mV for tuners, tape/cassette decks and phono-pre-amps around '0dB'.
And ... as the gain is fixed the actual output level also depends on the cartridge.
The thing is that one can easily have signal peaks up to 6dB higher so around 0.8V

For CDP it mostly is around 2V for 0dB but the catch is that the average levels are much lower (5-15dB lower) because in digital there is no signal above 0dBV where in analog audio there often is.

In general CDP/DAC is about 6dB to 12dB 'louder' than the old 'line level'.

Exactly. It's the sort of thing for which everyone expects a "fix" but even if you have gain adjustments for each input, you need to account for hot cuts and clicks or bangs not causing overload. Consequently, properly set-up vinyl playback woll always be quieter than digital.

 

[h3ndrix]

Exactly. It's the sort of thing for which everyone expects a "fix" but even if you have gain adjustments for each input, you need to account for hot cuts and clicks or bangs not causing overload. Consequently, properly set-up vinyl playback woll always be quieter than digital.

This all makes perfect sense! I wasn’t thinking it through about how analog sources don’t necessarily have a hard limit.

 

[Ropeburn]

Cartridge output can also vary a lot, so a phono amplifier has to account for that as well. MM models for example vary between 2-8mV easily, that's 12dB difference, or factor 4. If you use a regular phono stage with a fixed gain of 40dB (factor 100), you can get 200mV output or 800 just by changing the cartridge. That's quite a difference.

 

[CDMC]

Almost all preamplifiers have gain. Especially so when amplifying phono signals of course!

The volume control moves between attenuation at lower dial numbers through to gain at the highest numbers on the dial. However, for digital sources feeding modern power amplifiers, you often only need attenuation, which is why some people use what is sometimes known as a "passive preamplifier" - just a potentiometer.

Just to add to this, for analog volume controls that use a potentiometer (i.e most of them), ideally you want it where max volume is your clipping point and you only need to use it to attenuate a small amount (i.e. have the volume at 3 o'clock). As you turn down the volume with a potentiometer, you get more imbalance and potential distortion the further you turn the knob down. Some manufacturers used to purposely put too much gain in their preamp sections to make their amps seem more powerful, so the volume knob would be lower for the same output as another manufacturer. In extreme cases, it would result in clipping at the 9 o’clock position.

 

[kemmler3D]

Depending on how the SPL is measured and weighted, and the spectrum of the music playing, 85dB on the meter can sound subjectively louder or quieter despite showing the same value SPL. In the extreme example, a pure tone at 3khz vs. 20hz will sound a lot louder at the same SPL.

In this specific case it's a little hard to say how it could actually happen and I think variations between measurements might be the most likely explanation. Otherwise I would guess the 100w amp was soft clipping and bass peaks might have been reduced, something like that. Depending on the meter that might not be easy to capture.

A full RTA measurement in REW would give more clues as to whether anything is really going on here.

 

[h3ndrix]

Depending on how the SPL is measured and weighted, and the spectrum of the music playing, 85dB on the meter can sound subjectively louder or quieter despite showing the same value SPL. In the extreme example, a pure tone at 3khz vs. 20hz will sound a lot louder at the same SPL.

In this specific case it's a little hard to say how it could actually happen and I think variations between measurements might be the most likely explanation. Otherwise I would guess the 100w amp was soft clipping and bass peaks might have been reduced, something like that. Depending on the meter that might not be easy to capture.

A full RTA measurement in REW would give more clues as to whether anything is really going on here.

Yeah I do want to say what I’m experiencing is solely psychological. Which is why I referred to it as a phenomenon. Like I think I’m finding a comfort zone at a lower level than I did before. Which is honestly why I was interested in a new amp. Something that might be able to handle what I was throwing at it. The “near discomfort” I was feeling when I wrote this post has actually changed to “this is the sweet spot, I’m extremely happy with how things are sounding”

I also neglected to mention that I had also recalibrated my sub and moved it between amp
use and measurements, so that may also have factored in.

 

[kemmler3D]

had also recalibrated my sub and moved it between amp
use and measurements, so that may also have factored

Aha... I think this is probably the most likely explanation then. That's very likely to produce a noticeable change in the bass region, but depending on the SPL meter / weighting, bass tends to be under-counted, so it would show a smaller change on the meter.