What is Your Signal to Room Noise?

[bluesman]

I'm sitting at my workstation with the window wide open and a circulating fan running in the next room. With the music off, the ambient SPL averages 37.2 dBA.  I just put Wes Montgomery back on (West Coast Blues, from what's probably my all time favorite album - The Incredible Jazz Guitar of Wes Montgomery) and am listening at an average level of 52 dBA at about 1 meter from the speaker plane while I work.  For casual listening in the same room, I'll average about 60 db. And when I practice on guitar, I'll be at about 65-68 db.

 

The occasional bird will harsh my sonic mellow, but they're pretty quiet around here - it's not a cheep neighborhood.....

 Ka ching!

[bluesman]

 

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:

 

 

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.  

[bluesman]

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.

[bluesman]

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.

[bluesman]

20 hours ago, daverich4 said:

 

Can I ask you what app this is? Is it for Android? I can’t find it in the Apple App Store. 

 

I’ve been using the NIOSH SPL meter on my iPhone for a while now. It’s free from the App Store and is almost as accurate in the 40-100 dB range as the units our audiologists use, once calibrated to match (an easy task in the Settings panel). It’s far better than Radio Shack & similar.