From: blockedofcourse@foo.invalid   
      
   On 12/11/2025 2:30 AM, Martin Brown wrote:   
   > I suspect a bit of specsmanship here with them stating power in dB as if the   
   > thing generated white noise when it is at a single frequency.   
   >   
   > Shades of "peak music power" and other consumer conning metrics.   
   >   
   > You have to be very careful testing loudspeakers with sine waves - it is   
   > surprising how bad a mechanical resonance can be even at low powers.   
      
   [Most sirens are tuned to a particular resonance to get some free "gain";   
   the horn dimensioned to exploit that resonance.]   
      
   Of course specsmanship comes into play.  But, relying on an SPL expressed   
   /solely in dB/ is silliness -- and should be recognized as such!   
      
   At what *distance* was it measured??   
      
   My smoke detector *claims* an SPL of 85 dB -- /at 10 feet/!  Presumably,   
   someone (at the manufacturer or in the industry) decided "at 10 feet"   
   was a good place to determine its "loudness".   
      
   Yet, when I take out my meter, I get a bit over 100 dB (at a foot)   
   and 125 dB "near" the device itself!  Gee, wouldn't specsmanship   
   coerce them into using THESE numbers, instead?  Sure *seems* better   
   than an 85 dB device!   
      
   The siren I'm using in the house produces a comparable SPL (87 dB)   
   but /at 30 feet/ -- as I want to know what I can expect from it   
   at the extremes of the house, not "10 ft", "5 ft" or even "50 ft"   
   away!  *At* the phase plug, my meter is pegged (~140 dB).   
      
   Thinking of SPL without concern for distance is like specifying   
   a resistor without noting the power dissipation.  Or, a diode   
   without its PRV.   
      
   I've located our siren in the center of the house in the underside   
   of a lintel (because that is "guaranteed" to be above the level of   
   our heads yet not so high to risk losing signal from a ceiling mount).   
      
   So, if you happen to be IN that doorway when it sounds, it is likely   
   just 12 inches from your ears.  Hence the desire NOT to have it kick   
   full on at 116 dB (measured 12 inches from the horn).   
      
   OTOH, you wouldn't want to LIMIT its output because of that possible   
   condition -- it would be ineffective at either end of the house,   
   behind closed doors, over ambient sounds, etc.   
      
   "Settling" for 87 dB at those limits on the assumption that the   
   occupants can avoid the device with an "early warning" seems   
   like a good *design* decision.   
      
   OTOH, if you are trying to get consumers to buy a device based   
   on *one* number (because you don't want them to have to understand   
   a graph of SPL vs distance), you would likely opt for the highest   
   number you could claim (e.g., AT the phase plug).   
      
   And, fudge that based on how your competitors fudge theirs.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)