[iyonix-support] Re: Frequency response of Iyonix

On 6 Jul 2007, Paul Vigay wrote:
> Following a discussion on the ZFC mailing list, I thought I'd do some
> research into these 'Mosquito' yoof dispersion systems, and found some
> ringtones of various frequencies.
> 
> However, some don't appear to play on the Iyonix, which led me to wonder
> what frequencies the Iyonix sound system can actually play, and which ones
> I can't hear - ie. which is capable of discerning the higher frequency, the
> Iyonix sound system or the human ear.
> 
> A selection of MP3 format samples can be found at
> http://www.freemosquitoringtones.org/ but I was wondering if anyone know
> the actual technical spec of the Iyonix sound system?
> 
> I can hear them all up to the 21.2KHz tone, but the 22.4KHz tone is
> completely silent, so I wonder if it's my hearing or the Iyonix can't go
> that high.
> 

No doubt others will render a fuller reply regarding actual 
measurements of the frequency response of the Iyos sound system.
I think I once measured it, but have lost all the frequency response 
graphs I produced. I remember not being very impressed :-(

There are some things to bear in mind however:

1) The frequency response of the Iyos internal speakers will be much 
worse than the frequency response (in voltage terms) of the output 
jack.

2) The possible frequency response of MP3s vary with bit rate. I can't 
off hand remember actual figures, but I think at a bit rate of 128kb/s 
then the max frequency an MP3s can output is something like 14kHz 
(-3dB down). For 320kb/s bit rates, it will go up as far as 20kHz and 
maybe just a tidgy-widgy teensy-weensy bit more than that, but not, I 
think, up to more than half of 44.1kHz (i.e. 22.05kHz). [Sorry, I 
haven't looked at the bit rate of the ones you are using].

3) Measuring the maximum frequency you can hear by using either MP3s 
or an Iyonix is a bit iffy. A lot will depend upon how loud the tone 
is. The louder it is, the higher frequency limit you will be able to 
hear. Hearing is also usually measured at threshold of hearing sound 
levels, not at, say, 90dB SPL. Even some deaf people can hear tones if 
they are loud enough.

4) I strongly suspect the reason you can't hear the 22.4kHz tone 
because that is more than half of 44.1kHz (assuming you have set 
44.1Ks/s bit rates)

5) Also, not many people over 20 years of age can even hear up to 
20kHz, let alone above it. I would be very surprised if you could 
actually hear a pure tone at 22.2kHz, unless you are playing it at 
90dB SPL or so, when it might even be audibly by me with my ears 
(which at threshold levels cut off at 3kHz!). Also, at high loudness 
levels, your ears may also be introducing some distortion and it might 
be that which you can hear.

6 At 21.2kHz (or any other frequency, for that matter) you may be 
hearing sub-harmonics or, more likely, intermodulation distortion of 
one kind or another, particularly on an Iyonix. This kind of 
distortion folds back high frequencies to lower frequencies, making 
them easier to hear. You might just be hearing the distortion.






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