Hi all,

I was having a look at two pairs of headphones, and noticed their sound
pressure level ratings. The two sennheiser pairs were px100 with 114
dB, and the cx300 was 112 dB.

Firstly, in relatively simple terms - what IS the sound pressure level
? I have read so many definitions, but none make it very clear cut and
easy to understand. I know it is measured in decibels, which is a
logarithmic scale. I know it is referenced to close to 0 db (right ?),
threshold of hearing. So does it refer to the maximum sound level (in
dB) the headphone/whatever can attain ?

With the two examples above, how could you compare them? I.e. one 114,
the other 112 - does it mean the cx300 probably couldnt go "as" loud as
the px100???

Sorry if that sounds newbie ... i know it depends on the impedance etc
etc too......

In article .com,
"andrew_h" wrote:

Hi all,

I was having a look at two pairs of headphones, and noticed their sound
pressure level ratings. The two sennheiser pairs were px100 with 114
dB, and the cx300 was 112 dB.

Firstly, in relatively simple terms - what IS the sound pressure level
? I have read so many definitions, but none make it very clear cut and
easy to understand. I know it is measured in decibels, which is a
logarithmic scale. I know it is referenced to close to 0 db (right ?),
threshold of hearing. So does it refer to the maximum sound level (in
dB) the headphone/whatever can attain ?

With the two examples above, how could you compare them? I.e. one 114,
the other 112 - does it mean the cx300 probably couldnt go "as" loud as
the px100???

Sorry if that sounds newbie ... i know it depends on the impedance etc
etc too......


In most cases, 3db in these terms is about a click on the volume knob.
The next level up or down of perceived volume.

I say listen to them both and choose which sounds better, don't rely on
the numbers.

--
Cyrus

*coughcasaucedoprodigynetcough*

andrew_h wrote:
I was having a look at two pairs of headphones, and noticed their sound
pressure level ratings. The two sennheiser pairs were px100 with 114
dB, and the cx300 was 112 dB.

Firstly, in relatively simple terms - what IS the sound pressure level
? I have read so many definitions, but none make it very clear cut and
easy to understand. I know it is measured in decibels, which is a
logarithmic scale. I know it is referenced to close to 0 db (right ?),
threshold of hearing.

Sound itself is the result of rapid variations in air pressure
sufficient to cause movement of your eardrums due to the
difference in air pressure between your outer ear and your
middle ear. When those pressure variations are of a sufficient
level and within a certain range of frequencies, the movement
of your eardrum causes, through a series of mechanisms,
nerve impulses to be sent on to your brain.

So, "sound pressure level" is what it seems to be: the level of
pressure variations in the sound. It is an objective measure
of the amplitude of the pressure variations, refered to a very
small level of pressure variations referred to as the "threshold
of hearing." This level, corresponding to a pressure difference
of 0.0002 dynes per square centimeter (corresp0nding to about
a trillionth, 10^-12, of a watt per square meter), was determined
early in the previous century through a statistical analysis of a
number of subjects' ability to detect very low level sounds at
specific frequencies. That threshold does vary from individual
to individual and within an individual, varies widely with
frequency (though the frequency dependence has very similar
properties acros the population as a whole), varies with age and
with the amount of exposure to loud sounds (older people
who ran jackhammers or played in rock bands have significantly
elevated thresholds compared to young children, especially at
higher frequencies).

So does it refer to the maximum sound level (in
dB) the headphone/whatever can attain ?

No, it usually refers to the sound pressure, under some
possibly unspecified conditions, generated by the untis when
a "standard" electrical signal level is applied.

I.e. one 114,
the other 112 - does it mean the cx300 probably couldnt go "as" loud as
the px100???

No, if you read the Sennhesier spec sheet on these headphones,
it will tell you exactly what it means. From their spec sheet for the
PX100, for example, it states quite explcitly:

SPL (1 kHz, 1 Vrms) 114 dB

That means when they applied a 1 volt, 1 kHz sine wave to the
headphone, under their test conditions, it produced an SPL
of 114 dB (which, by the way, is EXTREMELY loud). To put this
in perspective, 114 dB is more than 10,000 more sound power
than the noise level in an average automobile traveling at
highway speeds in traffic.

Basically, these specs are a measure of the voltage sensitivity
of then unit. They are not a measure of maximum output.

With the two examples above, how could you compare them?

I would listen to both and pick the one I think sounds best, is
most comfortable on my head, and which works best when
connected to the equipment I'll be using it with.

Sorry if that sounds newbie ... i know it depends on the
impedance etc etc too......

Actually, it doesn't, since it's stated quite clearly as a voltage
sensitivity. It is only marginally an issue if you're going to be
using it on a portable player with VERY limited output voltage.
The one with 114 dB sensitivity will play 2 dB louder at any
given volume setting than one with 112 dB sensitivity, but
2 dB is small enough not to make a substantial difference.

And, to repeat, 111-114 dB is VERY loud, enough that pushing
your ears to that level is likely to result in long-term damage.

Whatever you get, TURN IT DOWN and save your hearing, please.

Thanks for your excellent reply.

So, in real terms - the SPL of headphones is something of a useless
stat?

Can the SPL of headphones be compared (assuming they've taken all at
1V, 1kHZ?)? Would comparing them only tell you that one will be
slightly louder than another (i.e. if one was 114, and one 111, then
like you say the 114 would play 2db louder at any given volume.)?