What matters about SINAD measurements

[daftcombo]

Another factor in the desire for very low noise levels is the way it is measured and referenced on the datasheet. For a power amplifier, it is typically referenced to full-scale output, thus distortion normally falls as the signal level drops, but the noise floor is relatively constant. That means if the SINAD is dominated by noise, typical at low output, then if you are listening at 50 dB below the max output you are getting much closer to the noise floor. My system can put out around 105 dB or so from a pair of speakers but I usually listen around 65~70 dB (though often louder for music). So if the amp only has 80 dB SNR (or SINAD limited by noise) relative to maximum (full-scale) output the noise floor is only about 50 dB down.

Thanks for the long post. I don't get this part though.
How do you know that "the noise floor is only about 50 dB down"? Calculus or measurement?

 

[DonH56]

Thanks for the long post. I don't get this part though.
How do you know that "the noise floor is only about 50 dB down"? Calculus or measurement?

Actually I should have said 65~75 dB -- I changed from 75 dB to 70 dB based on where I usually set my volume at but forgot to change the calculation. And it is a calculation, but does not require calculus.

105 dB max - 80 dB = 25 dB noise floor, assuming as stated previously that the noise floor is constant. So an amp that can produce 105 dB from my speakers at full volume (maximum amp output) and specified to have 80 dB SNR relative to maximum output (typical way it is spec'd) has a noise floor of around 25 dB in my system. Now if I listen at 65 to 75 dB on average that means the noise floor is 40 to 50 dB below my average listening level. That is, 65 to 75 dB minus the 25 dB noise floor is 40 to 50 dB down from (below) my listening level. I have not measured the noise floor of my current system but the math has held in the past.

Whether or not that is good enough is up for debate but depends heavily on the speakers, how close you sit to them, how loudly you listen, the noise floor in the room, etc. etc. etc. The usual worser case is when a high-power amp is used with highly-sensitive speakers so you are only using a fraction of the amplifier's output. Then hiss may be a problem at normal listening levels. Distortion, probably (almost certainly) not. Audio fora have plenty of posts from folk who bought a high-power pro amp for their 100 dB/W/m horn speakers at home then heard a lot of hiss.

HTH - Don

 

[daftcombo]

Thanks. Could you deduce these 25dB from the speakers sensivity as well?

 

[RCAguy]

I suspect musicians - those with direct experience with musical instruments - would more easily detect added distortions. However, they are rarely the ones to ask about quality reproduction, from what I've read.

I say added distortions, because music is layer upon layer of harmonic distortions. That's part of what gives different instruments their different sound.

Here is the electrical signal of a single note on an electric bass guitar - from the jack on the guitar to the ADC of a Behringer 202HD, to PC via USB, RTA displayed in REW.

No "effects" added.

View attachment 25236

Varying the pick technique will vary the relative levels of the harmonics - which changes the "tone" expressed.

The above was a pretty straightforward lick with a plastic pick, a few tries taken to get a nice series onscreen, without the second harmonic exceeding the fundamental (it is easy to do), so the distortion display would make sense, so the software would not be looking for the wrong sequence of frequencies for the "distortion" measures.

What's the SINAD there? About 5?

Note the "multitone" sequence, with little grass between the frequencies.

How many harmonics are present there? Thirty five or so?

The little spikes at 30 and 40 and 55 are the three lowest strings, not fully damped.

The harmonic structure of a musical instrument is not SINAD - it is tone color. SINAD (or THD+N or IM) are added bogus harmonics that change (distort) the original instrument's tone color. Preserving musical tone color is the holy grail of high fidelity. They are revealed by measurments using pure sine wave with no harmonics so any that show up are non-linearities of the device under test. These are most prevalent in transducers (loudspeakers, phono cartridges, and to a lesser extent microphones) and power amplifiers, which have a much harder job of than preamps and DACs slewing 1000x the current (Amps instead of milliamps).

 

[RCAguy]

Actually I should have said 65~75 dB -- I changed from 75 dB to 70 dB based on where I usually set my volume at but forgot to change the calculation. And it is a calculation, but does not require calculus.

105 dB max - 80 dB = 25 dB noise floor, assuming as stated previously that the noise floor is constant. So an amp that can produce 105 dB from my speakers at full volume (maximum amp output) and specified to have 80 dB SNR relative to maximum output (typical way it is spec'd) has a noise floor of around 25 dB in my system. Now if I listen at 65 to 75 dB on average that means the noise floor is 40 to 50 dB below my average listening level. That is, 65 to 75 dB minus the 25 dB noise floor is 40 to 50 dB down from (below) my listening level. I have not measured the noise floor of my current system but the math has held in the past.

Whether or not that is good enough is up for debate but depends heavily on the speakers, how close you sit to them, how loudly you listen, the noise floor in the room, etc. etc. etc. The usual worser case is when a high-power amp is used with highly-sensitive speakers so you are only using a fraction of the amplifier's output. Then hiss may be a problem at normal listening levels. Distortion, probably (almost certainly) not. Audio fora have plenty of posts from folk who bought a high-power pro amp for their 100 dB/W/m horn speakers at home then heard a lot of hiss.

HTH - Don

Your analysis if good. The solution, after including speaker sensitivity in your calculations, it's is not to size a power amplifier too large, but so that audio system noise is 15~20dB below room noise. This scaling is tantamount to "gain staging" inside a device. Every application has a correct power for the job such that, within the DNR of recordings played on the system, no amplifier noise will be audible, and no onset of distortion will be reached.

Simplified formulae for power amplifier requirements and system SNR in an acoustically treated room at SMPTE standard 85SPL (105 peak per channel) are…

1) Amplifier power rating (comfortably below the onset of clipping to allow for aging) = LD^2 * (105-SS)

Where LD is listening distance in meters; SS is speaker sensitivity in dBSPL/w/1m.

Example for LD of 2.5m (8ft) and typical consumer speaker SS of 89SPL/w/1m, the minimum undistorted power required is 6.25 x 16 = 100w. (I’d go for 150~200w for up to 3dB margin). This permits undistorted reproduction of 105dBSPL peaks IF the speakers are capable of undistorted output at that power at any frequency. (Less power is required in a more live space, although modes and comb filtering will affect individual listening positions.)

2) Then ideally the minimum power amplifier SNR (>15dB below a typical domestic listening room with weighted noise 30~35dBA, or <15dBA) = >90dBA below the amplifier power calculated above. (Assumes the power amplifier is the noise culprit of all links in the audio system chain.)

In the above example, any more power is unneeded (a waste of money) and might introduce more noise than -90dB below 105SPL, which only need be just below audibility in a relatively quiet domestic listening space. Equipment with these ratings are quite ubiquitous for reasonable money, although one must be careful that the ratings are honest and meaningful, i.e. ___ watts across the range 20~20kHz with all channels driven.

 

[DonH56]

Your analysis if good. The solution, after including speaker sensitivity in your calculations, it's is not to size a power amplifier too large, but so that noise is 15~20dB below room noise. This scaling is tantamount to "gain staging" inside a device. Every application has a correct power for the job such that, within the DNR of recordings played on the system, no amplifier noise will be audible, and no onset of distortion will be reached.

Agreed, and in my day job designing the gain structure is critically important for balancing noise and distortion for optimal performance at the output of the system. Same thing happens in digital filters when gain scaling and optimization is used to provide the greatest dynamic range at each tap/stage in the filter. Setting a target below the room noise is another way of defining the problem, perhaps a better starting point. I have thought about applying the intercept point concept to audio chains.

 

[RCAguy]

I suspect musicians - those with direct experience with musical instruments - would more easily detect added distortions. However, they are rarely the ones to ask about quality reproduction, from what I've read.

I say added distortions, because music is layer upon layer of harmonic distortions. That's part of what gives different instruments their different sound.

Here is the electrical signal of a single note on an electric bass guitar - from the jack on the guitar to the ADC of a Behringer 202HD, to PC via USB, RTA displayed in REW.

No "effects" added.

View attachment 25236

Varying the pick technique will vary the relative levels of the harmonics - which changes the "tone" expressed.

The above was a pretty straightforward lick with a plastic pick, a few tries taken to get a nice series onscreen, without the second harmonic exceeding the fundamental (it is easy to do), so the distortion display would make sense, so the software would not be looking for the wrong sequence of frequencies for the "distortion" measures.

What's the SINAD there? About 5?

Note the "multitone" sequence, with little grass between the frequencies.

How many harmonics are present there? Thirty five or so?

The little spikes at 30 and 40 and 55 are the three lowest strings, not fully damped.

The FFT of a bass guitar is not SINAD - it is the instrument's musical "tone color" - the holy grail of high fidelity audio. SINAD (or THD+N or IM) are bogus added harmonics due to non-linearities of audio devices, most notably transducers (loudspeakers, phono cartridges, and microphones) and power amplifiers, which must slew 1000x the current (Amps not milliamps) that do preamps and DACs. Audio devices are tested using pure sine waves with no harmonics so that any artifacts that show up are distortions of tone color.

 

[RCAguy]

Ah, a misunderstanding, my apologies. Too little sleep lately...

The thread is about SINAD, so noise and distortion are included. Noise we've discussed. Distortion I find a little trickier to define. Like most folk, I can tell if distortion around 1% (-40 dB) is added to music, but frankly that is an A-B comparison. Given the complexity of most music I might not tell at -40 dB for some music or complex passages, but for a solo flute (about the closest to a pure tone) or other solo instrument I know well I might detect around -60 dB (0.1%). At least so I have found in my brief recent excursions into adding distortion to sounds.

Another thing to consider is that IMD (intermodulation distortion) happens whenever you have harmonic distortion, is not harmonically related to the signal so is easier to hear (i.e. is more obnoxious), and for e.g. two tones of equal amplitude whose sum matches that of a single tone's peak amplitude the IMD will be about 9.542 dB higher in amplitude than HD (harmonic distortion) thus roughly twice as loud. I find it much easier to detect 0.1% IMD than the same level of HD even on a pure tone.

Another factor in the desire for very low noise levels is the way it is measured and referenced on the datasheet. For a power amplifier, it is typically referenced to full-scale output, thus distortion normally falls as the signal level drops, but the noise floor is relatively constant. That means if the SINAD is dominated by noise, typical at low output, then if you are listening at 50 dB below the max output you are getting much closer to the noise floor. My system can put out around 105 dB or so from a pair of speakers but I usually listen around 65~70 dB (though often louder for music). So if the amp only has 80 dB SNR (or SINAD limited by noise) relative to maximum (full-scale) output the noise floor is only about 50 dB down. Different speakers, different amps, and the result may be better or worse. 100 dB from a high-power amp driving sensitive horn speakers may not be good enough while 60 dB driving insensitive speakers might be fine.

Finally, you have to watch how noise is weighted when it is reported. A weighting mimics our hearing but also weights out LF and HF noise. Broadband results often yield 3 to 10 dB worse SNR. I tend to look more at wideband noise specs, especially when the noise gets dominated by HF hiss (alas, not much a problem for me anymore) or LF power spurs (typically 50/60 and 100/120 Hz depending upon where you live). Those power supply spurs can be obnoxious and thus are one thing I pay attention to in Amir's results.

IME/IMO/HTH/etc. - Don

Right on, Don, about IMD - my go-to measurement. Just to paraphrase your point, IM is harsh\obnoxious\not "euphonius," and therefore easier to detect subjectively than THD. Where THD is present, IM is too, and v.v., so either is a measure of non-linearity and non-fidelity.

 

[RCAguy]

I may not have made myself clear.
The data that amirm presents is about measured performance. One product often compared to another. There isn't much to discuss unless one believes the data is wrong. Based on that data amirm states that one product performs to a higher specification than another.
At this point the reader has then to decide what level of performance is important to them.
One can always apply the' fit for purpose' argument to products. The problem is often each application requires differing levels.
We do have a measure of what is and what isn't audible. A brief tour of the various 'hi fi ' boards should show that this measure of what is audible isn't accepted by many.
You may believe and possibly even have some data to present, that backs up your view that a particular set of measurements is 'good enough'.
However, while it may be true that under test conditions one can demonstrate that the 'good enough' standard is indistinguishable from a higher standard, if one applied that to say automobiles then we would all be driving Volkswagen beetles equipped with speed limiters.
Thankfully, my scientific/engineering background isn't in domestic audio, or even 'professional' audio. I was an Avionics engineer working with acoustics for military applications so much of the nonsense that gets applied to 'recreational' audio didn't get established in my views.
For me domestic audio is a hobby. I build much of my own equipment, used to belong to an audio club where the hobby aspect dominated.
I rather like amirm's measurements. They allow me to make a better informed choice should I wish to purchase a product based on a data set rather than the many opinions of audiophile experts, be they domestic or 'professional'.

Shadrach, I take your well-said points. True the audio hobby isn't "rocket surgery," and various audio applications certainly do require "differing levels." However audio engineering is about more than sizing (scaling) for each application\level. (As I've practiced it for 58yr that ranges from to designing and integrating studios, home theaters, and Movies in the Park (audiences up to 1,000). For domestic music reproduction, the requirements I allude to as "typical" share a narrow range of ambient noise, speaker sensitivity, and that commercially distributed recordings are limited to a dynamic range of so many dB, topping at no more than 100 for classical and 10dB for pop\rock (kidding somewhat). So the math is not hard; for larger spaces and systems it is more involved.

 

[DonH56]

Your analysis if good. The solution, after including speaker sensitivity in your calculations, it's is not to size a power amplifier too large, but so that audio system noise is 15~20dB below room noise. This scaling is tantamount to "gain staging" inside a device. Every application has a correct power for the job such that, within the DNR of recordings played on the system, no amplifier noise will be audible, and no onset of distortion will be reached.

Simplified formulae for power amplifier requirements and system SNR in an acoustically treated room at SMPTE standard 85SPL (105 peak per channel) are…

1) Amplifier power rating (comfortably below the onset of clipping to allow for aging) = LD^2 * 105-SS

Where LD is listening distance in meters; SS is speaker sensitivity in dBSPL/w/1m.

Example for LD of 2.5m (8ft) and typical consumer speaker SS of 89SPL/w/1m, the minimum undistorted power required is 8 x 16 = 128w. (I’d go for 150~200w). This permits undistorted reproduction of 105dBSPL peaks IF the speakers are capable of undistorted output at that power at any frequency. (Less power is required in a more live space, although modes and comb filtering will affect individual listening positions.)

2) Then ideally the minimum power amplifier SNR (>15dB below a typical domestic listening room with weighted noise 30~35dBA, or <15dBA) = >90dBA below the amplifier power calculated above. (Assumes the power amplifier is the noise culprit of all links in the audio system chain.)

In the above example, any more power is unneeded (a waste of money) and might introduce more noise than -90dB below 105SPL, which only need be just below audibility in a relatively quiet domestic listening space. Equipment with these ratings are quite ubiquitous for reasonable money, although one must be careful that the ratings are honest and meaningful, i.e. ___ watts across the range 20~20kHz with all channels driven.

Very good info! Think there's a typo in the first equation, however, needs parenthesis:

1) Amplifier power rating (comfortably below the onset of clipping to allow for aging) = LD^2 * (105-SS)

 

[RCAguy]

Very good info! Think there's a typo in the first equation, however, needs parenthesis:

1) Amplifier power rating (comfortably below the onset of clipping to allow for aging) = LD^2 * (105-SS)

Correct and thanks Don - I'll edit my post. (First time I've taken these simplified firmulae out for a spin.) I should remember to "Please Excuse My Dear Aunt Sally" (parenthesis, exponent, multiply, divide before add & subtract).

 

[DonH56]

Correct and thanks Don - I'll edit my post. (First time I've taken this math out for a spin.) I should remember to "Please Excuse My Dear Aunt Sally" (parenthesis, exponent, multiply, divide before add & subtract).

No worries. I plugged in my system and the results were... interesting, without the parentheses. For a second there I thought I needed a whole lot bigger amp! I usually do OK on mathematical operator precedences. Logical precedence sometimes messes me up, most recently when one programming language handled an old "if" construct differently than the language we are using now. I have to write test scripts and such but as a programmer I'm a pretty good trumpet player... Should just stick to analog circuit design.

 

[RCAguy]

No worries. I plugged in my system and the results were... interesting, without the parentheses. For a second thre I thought I needed a whole lot bigger amp! I usually do OK on mathematical operator precedences. Logical precedence sometimes messes me up, most recently when one programming language handled an old "if" construct differently than the language we are using now. I have to write test scripts and such but as a programmer I'm a pretty good trumpet player... Should just stick to analog circuit design.

I'm a piano player - maybe we can jam? After using the correct math operations, what amplifier power did you calculate for what LD and SS?

 

[DonH56]

I'm a piano player - maybe we can jam? After using the correct math operations, what amplifier power did you calculate for what LD and SS?

My wife's the pianist of the family, but sure...

I usually send people to this on-line SPL calculator: http://myhometheater.homestead.com/splcalculator.html ALl of them have problems (Dr. Toole really dislikes them) but I find they are useful to provide some sort of relative reference.

Your equation assumes fall-off with distance squared which is not always true in real life. More reflective or more absorptive means deviation from the ideal 4-pi rolloff, plus of course directivity of the speakers enters into the SPL at the MLP (main listening position). There are others on ASR who pay more attention than I; my grad acoustics course was a long time ago and my career took a different direction.

My speakers are rated ~86.4 dB/W/m (they use 2.83 Vrms but the speakers are nominally 6 ohms; I'm too lazy to do the math to correct it and this is just a relative comparison anyway). They are about eight feet away so I'll use your ~2.5 m number.

Your equation is Pamp = Ld^2 * (SPLdesired - Sspkr) = 2.5^2 * (105-86.4) = 6.25 * 18.6 = 116.25 W.
Plugging 116.25 W into the online calculator for one speaker in a corner I get 105.3 dB; pretty close, but that is for corner loading. Not sure what is off

The catch is my room is heavily treated, so if I select instead "away from walls" I get 99.3 dB. Under those conditions I need about 450 W to achieve 105 dB SPL. My amplifiers are rated around 500 W into 4 ohms and my speakers are pretty close to 4 ohms across most of the midrange down so I think I'm in decent shape. Plus I usually listen at around 70 dB SPL so 150 W gets me 30 dB headroom for peaks. I'm OK with that.

 

[RCAguy]

My wife's the pianist of the family, but sure...

I usually send people to this on-line SPL calculator: http://myhometheater.homestead.com/splcalculator.html ALl of them have problems (Dr. Toole really dislikes them) but I find they are useful to provide some sort of relative reference.

Your equation assumes fall-off with distance squared which is not always true in real life. More reflective or more absorptive means deviation from the ideal 4-pi rolloff, plus of course directivity of the speakers enters into the SPL at the MLP (main listening position). There are others on ASR who pay more attention than I; my grad acoustics course was a long time ago and my career took a different direction.

My speakers are rated ~86.4 dB/W/m (they use 2.83 Vrms but the speakers are nominally 6 ohms; I'm too lazy to do the math to correct it and this is just a relative comparison anyway). They are about eight feet away so I'll use your ~2.5 m number.

Your equation is Pamp = Ld^2 * (SPLdesired - Sspkr) = 2.5^2 * (105-86.4) = 6.25 * 18.6 = 116.25 W.
Plugging 116.25 W into the online calculator for one speaker in a corner I get 105.3 dB; pretty close, but that is for corner loading. Not sure what is off

The catch is my room is heavily treated, so if I select instead "away from walls" I get 99.3 dB. Under those conditions I need about 450 W to achieve 105 dB SPL. My amplifiers are rated around 500 W into 4 ohms and my speakers are pretty close to 4 ohms across most of the midrange down so I think I'm in decent shape. Plus I usually listen at around 70 dB SPL so 150 W gets me 30 dB headroom for peaks. I'm OK with that.

Don, I plugged my example above (that also required a correction) into the online calculator and got 104.3SPL, close enough to 105. I used "2~4ft to wall" which is typical for most of us, but 1 speaker because coupling is not factored into my 105SPL-per-channel model. (The calculator adds 3dB for 2 speakers, which is ideal coupling for speakers touching, but not applicable with a spaced stereo pair.) I stated in my post above with the formulae & example that I assumed a treated room, for which the inverse square law holds approximately for listening distances up to about 2.5m if the room is significantly larger.

I am glad to hear that, not surprisingly, you have acoustically treated your listening space. Your relatively inefficient (not at all implying a bad thing) 6ohm speakers produce 86.3SPL with 1.33w (P=E^2/Z=8/6). So at about 86PL/1w/1m (I'm too lazy at the moment to convert precisely that 0.33w), your speakers require ~3dB more, i.e. double, the power needed for the mid-efficiency 89SPL/1w/1m speakers in my example above. As no recording will require 30dB of headroom, and listening at 70SPL RMS, I would say you are somewhat overpowered. However that matters not if the system noise is -90dB. (My quick take, I might give a rethink.)

A working audio consultant, my own three work systems use a mix of higher efficiency passive speakers and self-powered ones, so my power amplifier requirements are no more than 150w/channel for undistorted peaks of 105SPL, even in a 500m^3 studio. At the other extreme is a transportable municipal Movies in the Park system, in for annual maintenance, with 4000w of surround sound (amplifiers in photo), and that measures 105SPL for up to 500 listeners on blankets (1,000 in seats) in a 100ft diameter outdoor space - the turf providing good acoustic "treatment." The Crown digital amplifiers produce only 0.04%IM (measured) at any power level, with no audible noise even in my 25NC studio\lab. If THX had an outdoor system category, it would likely meet certification, and it has gotten good comments from audiophiles.

 

[DonH56]

30 dB (1000x in power) is often cited as the max headroom required for movies. 75 dB average and 105 dB max (115 dB for subs) is from Dolby and/or THX (I forget). The number I remember from long ago for music is 17 dB, a power factor of 50, from some AES paper I do not recall and do not have at hand. I have not tried to measure DNR for ages; some time ago I measured around 20 to 25 dB peak-to-average on some Sheffield CDs and a total dynamic range in the 60~65 dB range. Most recordings seemed more in the 40-50 dB range. But I did not have the SW tools for analysis available today so did not look at a lot of them. Some rock CDs were around 15-20 dB, not much range at all.

The 3 dB is for two quasi-independent sources; I thought it was 6 dB for tightly coupled sources? Again not my day job and I got them mixed up recently on another thread so may be wrong again.

I had my IHF certified audio consultant's license for a while decades ago but never really used it past college (1984). That system of yours sounds pretty impressive!

 

[RCAguy]

30 dB (1000x in power) is often cited as the max headroom required for movies. 75 dB average and 105 dB max (115 dB for subs) is from Dolby and/or THX (I forget). The number I remember from long ago for music is 17 dB, a power factor of 50, from some AES paper I do not recall and do not have at hand. I have not tried to measure DNR for ages; some time ago I measured around 20 to 25 dB peak-to-average on some Sheffield CDs and a total dynamic range in the 60~65 dB range. Most recordings seemed more in the 40-50 dB range. But I did not have the SW tools for analysis available today so did not look at a lot of them. Some rock CDs were around 15-20 dB, not much range at all.

The 3 dB is for two quasi-independent sources; I thought it was 6 dB for tightly coupled sources? Again not my day job and I got them mixed up recently on another thread so may be wrong again.

I had my IHF certified audio consultant's license for a while decades ago but never really used it past college (1984). That system of yours sounds pretty impressive!

Hi again, Don. The "headroom" I quote is the SMPTE standard for movies, which I mixed for 30yr. My music recordings (I was for years the recording engineer for the Greenwich Village Symphony, and of quite a few albums in stereo and surround) follow the same SOP. Every movie sporting a Dolby or DTS logo has a company consultant present during mixing who monitors instantaneous peaks short of digital Full Scale (FS) by 20dB (18dB in Europe). That is codified in the standard as 85SPL reference and 105SPL peaks (more precisely waveform crests), summing partly uncorrelated, so partially-coupling, to about 108SPL all five channels driven, and LFE peaks reproduced 10dB higher to 115SPL as you say. Dialog spoken at a normal level is -31FS, called "dialnorm." These numbers apply to theatrical exhibition, including my park system described above, but are somewhat compressed for home DVDs, where the typical reference level is reduced to ~75SPL, peaks of 95SPL/channel, "set" defacto by the typical clipping of low-end home-theater-in-a-box systems. The original CD headroom SOP was 16dB, higher than the best tape and vinyl at about 12 in my experience. I have measured pop\rock CDs squashed to only 3~4dB peak to RMS, and have seen evidence of at least one label that mandates its engineers master, after normalizing to the ceiling, even higher until 4% of samples clipped - intended to play "loud" on boom boxes that typically have little headroom to clipping. In the extreme case, reducing peak capability from 20dB to 3dB would reduce the capabilibty and therefore cost of consumer players by 98%, to 1/50 (100x to 2x). With DSP, it is very alluring to over-process, and easy to clip exactly 4% of samples. Perhaps the abuse is acceptable to the hoards; digital, which should have been a boon to audiophiles, has been turned in many instances into a scourge.

 

[andreasmaaan]

THX calls for 85dB continuous with up to 105dB for peaks IIRC, ie only 20dB of headroom.

 

[DonH56]

As I said, not my day job, thanks for the corrections.

 

[RCAguy]

Just a reminder to put "20dB of headroom" into perspective: 20dB is about 1/6 our total 120dB of hearing dynamic range (DR), and more typically for listening to recorded music or movies at home; a quarter of the 80dB range between the noise of a very quiet room and instantaneous peaks of 105SPL "full scale" (FS). It is 100 times the power of -20FS, the RMS reference level that falls at the top 1/3 point between unclipped peaks and quiet noise - our desired operating DR. Food for thought.