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What is Your Signal to Room Noise?


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I think there are some serious errors posted here.

 

18 hours ago, PeterSt said:

This means the amplification is always at full gain. Say that the RMS power is 30W with the notice that this counts for each of the individual drivers in there, but for the woofers it is a little more than 50W.

 

1. The fact that there's no input attenuation on the power amp does not mean that it's "always" dissipating 50W at the speakers.  It will do so if (and only if) its input signal reaches the voltage at which it achieves its rated output.  The input levels generated by the low level noises under discussion here would be millivolts at the most and would therefore not "...  be blasted through closed doors of the listening room".

 

18 hours ago, PeterSt said:

And as we know, cranking up the volume isn't really the solution (like 40dB + 70dB is seriously too much).

 

2. Decibels are a logarithmic metric, so the ambient noise floor and the output of an audio system in that location are not additive.  If the difference in SPL between two sound sources is more than 10 dB, the total SPL is the same as that of the louder source.  Here's a simple chart showing you how to add two signals based on the difference between them in dB:

 

db_summation_chart.jpg.fd0ab864024c11e5d719feff8668abf3.jpg

 

3. The 40 dB noise floor has no measurable effect on the combined SPL of the speakers' output & the noise because it's 30 dB below the louder source.  Although it may have effects on the perception of the program material being played, noise at 40 db will only be clearly and directly audible if and when the SPL of the program is below 50 dB.  And with a 30 dB or more differential between two audible signals, the louder will mask the quieter to the point of virtual inaudibility.  

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Probably most of the noise is at a low frequency.  You can get RTA apps that will give a readout by octaves or less.  Of course most phone microphones drop off below 200 hz.  

And always keep in mind: Cognitive biases, like seeing optical illusions are a sign of a normally functioning brain. We all have them, it’s nothing to be ashamed about, but it is something that affects our objective evaluation of reality. 

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6 hours ago, bluesman said:

1. The fact that there's no input attenuation on the power amp does not mean that it's "always" dissipating 50W at the speakers.  It will do so if (and only if) its input signal reaches the voltage at which it achieves its rated output.

 

Hi - I don't think anything was saying that. However, the 50W (30W) implies a gain. And the gain is 20 (I can tell you). Now "mV" of noise as such, will surely blast through closed doors if only the efficiency is good enough.

Try to set your volume wide open, and now listen to your speaker (tweeter). Hear something (more or less faint) ? good. Hear nothing then no dice today. But if you do, next up is the efficiency. Is it 94 ? (very good already) then add 24dB to reach what we have here. And I tell you: if you hear the faintest of noise already, increase that with 24dB will imply fairly blasting noise.

And this was for 94dB of efficiency. This can be way less just the same ...

 

Thanks for that chart; nice.

 

6 hours ago, bluesman said:

noise at 40 db will only be clearly and directly audible if and when the SPL of the program is below 50 dB.

 

Although it will be off topic, these matters are not really about "clearly and directly" (however, you may be right on it) because it is about distortion. Thus no matter you won't be able to hear it "directly", it easily shows on an analyser  (even a scope when the differences are low enough) and therefore are always important. But anyway, this is a different subject. How the ambient noise floor would be able to make the background more black and such, is on topic and this we could wonder. Mighty difficult to check / compare.

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7 hours ago, STC said:

You have 6dB loss for every doubling of the distance. Not every 1 meter.

 

Oops, I surely wrote that wrongly. Thanks for the correction. But point is, it is not about that (hence the easy mistake - blurp). It is about the directivity and how that makes the rule fail. Try a tube ... (of 100m long if you want).

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Background noise of a room is very different at various frequencies. Some noise is external noise, but a lot of the background noise is actually generated by technical installations such as refrigerator, routers, computers and ventilation systems etc in our homes. They can be removed or turned off (at least temporarily) if you put some effort to it. 

 

In a normal room the background noise is almost always loudest in the lower frequencies. It is not correct IMO to assume that because the background noise is 40 dB that we can’t hear below that. Some low frequencies will be masked yes, but far from all sound. Like in math we should never rounding off decimals until the summary.

 

How about hum? Hum is 50/60 Hz, but also has harmonics at 120 and 180 Hz. The reason that the background noise in a room normally is highest around those frequencies, is not surprising when we think about all the electrical gear, Mains noise, transformers and ventilation systems we have on standby in our homes.  

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2 hours ago, PeterSt said:

 

Oops, I surely wrote that wrongly. Thanks for the correction. But point is, it is not about that (hence the easy mistake - blurp). It is about the directivity and how that makes the rule fail. Try a tube ... (of 100m long if you want).

 

Be it line array or waveguide horn, the best it could do is 3dB attenuation. So at 7 meter and a 4dB lower NF, it cannot be the reason as you suggested in the earlier post. 

 

It is possible the system at your customer’s place could be picking other noise that get amplified. 

 

I have nothing further to add. 

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17 minutes ago, STC said:

So at 7 meter and a 4dB lower NF

 

Nobody said that was at 7m at the customer.

 

18 minutes ago, STC said:

I have nothing further to add. 

 

Then try that tube. Don't you believe that or what ?

 

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1 hour ago, PeterSt said:

 

Nobody said that was at 7m at the customer.

 

My mistake. I was guessing since you are not giving the distance. 

 

 

1 hour ago, PeterSt said:

 

 

Then try that tube. Don't you believe that or what ?

 

 

I have two eight feet tubes to do such experiment. None of the sounded like a good horn speaker when heard in the other end of the tube. :)  

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7 hours ago, PeterSt said:

the 50W (30W) implies a gain. And the gain is 20 (I can tell you). Now "mV" of noise as such, will surely blast through closed doors if only the efficiency is good enough.

Try to set your volume wide open, and now listen to your speaker (tweeter). Hear something (more or less faint) ? good. Hear nothing then no dice today. But if you do, next up is the efficiency. Is it 94 ? (very good already) then add 24dB to reach what we have here. And I tell you: if you hear the faintest of noise already, increase that with 24dB will imply fairly blasting noise.

 

You're doing it again.  SPLs in dB are not additive. What you describe simply does not happen - adding 24 dB of noise to a 94 dB signal will result in an SPL of exactly 94 dB.  This is true whether the noise is ambient or coming from the speaker. And this thread is about ambient noise in the listening environment - the OP does not mention electronic noise at all.

 

Gain is simply boost in signal between input and output - it has nothing at all to do with the rated output power of the amplifier.  It is measured and expressed without units as the ratio of the output parameter to the input parameter ( voltage, current, or power).  The formulae for audio amplifier gain in dB are 20 x log (base 10) of voltage or current gain, and 10 x log (base 10) of power gain.  But decibels are also a ratio, specifically the ratio of measured SPL to a reference pressure (which, by convention, is 0.02 mPa).

 

The wattage of an amplifier has nothing at all to do with the gain of its circuitry - the designer sets the gain based on the intended parameters of use (input voltage, speaker impedance, and desired output power being the 3 most important).  The gain of an amplifier is the ratio of output voltage / current / power to the same parameter at the input when the output into its rated load is at its rated levels of power and performance (e.g. distortion). A 1 volt 1 kHz sine wave may drive one "50W" amplifier to 50 WRMS into 8 ohms at 0.001% THD and another to 50 WRMS into 8 ohms at 10% THD.  The former might be capable of 500 watts onto 8 ohms at 10% THD and could therefore be sold as either a 50 watt or a 500 watt unit, depending on the fine print.

 

With 0 input attenuation, background noise at the speakers from most amplifiers in properly functioning systems (regardless of the output power rating of the amplifier) is barely audible and comes from a few sources.  Some is external noise in the input signal from upstream components, and some is introduced into the amplifier's circuitry at various points from the environment (e.g. RFI) and via the power line.  You're also hearing internal noise generated by the amplifier itself - and some wonderful and classic amps are noticeably noisy.  But none of it drives an amplifier to more than a few milliwatts unless something is wrong with a component or the way the system is set up and interconnected.

 

"A piano (open wing - just measured at 1m) is 90dBSPL. This is doable as a piano does not come across as too loud in a random home's room. But now put a trumpet player next to it.  No. A drumkit is 110dBSL on the splash cymbals when used in rock fashion. No."

 

Either your observations on SPL of live instruments are a bit off or you're really banging away on your instruments.  Checked 10 minutes ago, my Yamaha grand piano hits about 85 dB in our apartment's living room with my meter sitting on the lyre and pointed at the open top when playing Brubeck's "The Duke" (at the same level I used Saturday night on a similar piano at a trio gig in the Grant Room of Philadelphia's Union League).  I check SLPs on gigs because some of the venues we play are volume sensitive, and my jazz quartet (electric guitar, piano, bass, full drum kit) rarely tops 90 dB with the meter on one of the stage mic stands, even when playing high energy fusion tunes.  In fact, my blues band (guitar, organ, amplified harmonica, bass, drums) rarely hits 95 db in the front row.  I'm playing through a Vibrolux and a Blues Deluxe together, and our bass player's rig is 1200 watts with a ceiling high stack based on a 21" bass bin.

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5 hours ago, bluesman said:

You're doing it again.  SPLs in dB are not additive. What you describe simply does not happen - adding 24 dB of noise to a 94 dB signal will result in an SPL of exactly 94 dB.

 

You know what ? I understand what you are talking about but I have no clue of the why of it. You seem to be thinking (if I get that right) that I say or claim that noise "blasts" on top of music. I say nothing of the kind. Let's agree that you don't have the slightest idea of what *I* am talking about. And if we don't agree, that's what I'm thinking anyway.

 

There is no signal. Did you get at least that ?

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My listening room is very quiet, around 25 dBA during the daytime, slightly lower at night.  I live in the country.  I listen almost exclusively to classical music.  I generally listen so that musical peaks reach around 85 dB.  When I listen to popular music (Mariah Carey or Chris Isaak or Ella Fitzgerald or Patti Page), I keep it below 75 dB.

请教别人一次是5分钟的傻子,从不请教别人是一辈子的傻子

 

 

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14 hours ago, PeterSt said:

Is it 94 ? (very good already) then add 24dB to reach what we have here.

 

So what are you trying to do in the quoted sentence if you're not trying to add 24 dB to 94 dB? 

 

In prior posts in this thread, you've stated several other things that suggest you're trying to add dB, e.g.

  • Thus, supposed my ambient noise would be a constant 50dBSPL for some reason, could I suddenly bear 100dBSPL easily ?
  • if my ambient noise would be 38dBSPL, would I be able to bear 108 dBSPL ? well, "bear" maybe yes, but would it be required to perceive everything which is in there ?  Or would 90dBSPL be OK because I can hear 18dB into my 38dB ambient noise ?
  • For me too the dynamic range "we" can perceive is something like 70dB maximum. This does not mean that we can utilize it, never mind we can also hear into the noise. Thus, it is hard for me to imagine that we can utilize that 70dB of range when music plays at 70dBSPL and we would be able to hear right into the noise up to 0dBSPL.
  • Or would 90dBSPL be OK because I can hear 18dB into my 38dB ambient noise ?

Your math doesn't work and your concepts of sound pressure levels are incorrect because dB are not additive once the difference between the two signals is greater than 10 dB - and they're only partially additive below that delta, as shown in the table I posted above.  Your SPL won't be 108 dB just because you have 38 dB of ambient noise and a 70 dB signal - it will be 70 dB.  Even if you have a 60 dB ambient noise background, a 108 dB SPL signal will still measure 108 dB.

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6 hours ago, bluesman said:

 

So what are you trying to do in the quoted sentence if you're not trying to add 24 dB to 94 dB?

 

I don't know. I am not aware of it despite what you quoted from my text. I'm afraid you missed the crux of this thread ?

 

Otherwise I live in an other universe. Shall we keep it at that ?

Again, I will state that there's nothing wrong with what you say, hence we agree. So you must be reading different things in my posts. Like adding dB's (looks to be your hobby horse).

 

Stop this loop.

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I took some measurements again today, and realistically I am hitting peaks on my meter in the mid to high 80dBA area when I turn up the volume.  I'm certain with the right song and mood, I could see readings into the 90dBA range.  Using Roon to provide a lossless signal path, and listening to several different formats from various masters, a song that is more compressed might sound loud enough at a lower perceived volume level, while others might require a bit more power to make it sound loud to my ears.

 

Generally speaking, I mostly listen for extended periods of times under 60dBA according to my meter.

 

Full path:

Laptop as Roon core streaming Tidal or Qobuz using the highest quality versions.>

ASIO drivers provided by RME to connect via USB to an RME ADI-2 DAC with subtractive PEQ settings to lower dB of frequencies around 2500-8500 Hz gently, peaking at -3.5dB centered around 5500 Hz.>>  

The analog output level of the DAC is set to Auto reference with balanced XLR that has always been +1dBu, but can automatically switch to a higher output level of +7, +13, or +19dBu if necessary (though I have never seen this happen).  According to the specifications, +1dBu makes the signal-to-noise 115.4dB RMS or unweighted 118.9 dBA.>>>

My amp is a 2-channel Marantz MM7025.  Using the balanced inputs, the input sensitivity is 2.4V with the input impedance at 30 kΩ, a signal-to-noise ratio of 105 dB (IHF-A according to the specification sheet, but not sure if this means A-weighted or some other standard as it is a bit vague) and a damping factor of 100.  The rated power output is 140W/channel 8Ω.  The amp seems to handle peaks fairly well in my application.  It is a good quality amp, but nothing special about it, and it is affordable.>>>>

The speakers are Klipsch RP-280F tower speakers.  Sensitivity is rated at 98dB @ 2.83V/1m.  The nominal impedance is 8Ω  and they handle 150W RMS and 600W peaks.

 

The speakers are positioned 6.5 ft (2 m) apart and I sit centered between them about 7.5 ft (2.25 m) from each to form a triangle.  The speakers have a toe-in of only 1°-2°, or about .5 inch (13 mm) when measuring from the wall to the outside edge of the front and back of the speaker cabinet. 

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4 minutes ago, AudioDoctor said:

This is at roughly the listening point

 

Hi - Although it would inherently compare all of our figures, this is not how SPL is measured. This is at 1 meter distance from the speaker (some make that 2, but that is an other standard). So if I say I play at 85dBSPL, this was measured at this 1 meter distance. I know ... this makes it incomparable for room sizes and such.

Now what ...

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Just now, PeterSt said:

 

Hi - Although it would inherently compare all of our figures, this is not how SPL is measured. This is at 1 meter distance from the speaker (some make that 2, but that is an other standard). So if I say I play at 85dBSPL, this was measured at this 1 meter distance. I know ... this makes it incomparable for room sizes and such.

Now what ...

 

Do you sit 1 meter from your speakers?

 

 

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As I suggested, it would inherently compare our figures (if it were about that in the first place). But it is just not how it is done. Nobody would expect it either. At least not me ...

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