OT: Calibrating a sound level pressure meter

[N_Cook]

Just for my own purposes so relative rather than absolute but if possible to
calibrate then all the better. No access to a calibrated one to
cross-calibrate, falling ball calibrator etc.
An old Dawe 1405D that sems to have little info out there. Mic and
electronics works and I've now repaired the suspension on the meter but fsd
is now .586V but is marked as 1.45V .
As the replacement phosphor bronze is probably more stiff than the original
, if any thing , I would expect greater fsd . It may be .45V marked and a
type number 1 or something ahead of the .45, there is quite a gap.
Anyone experinece of the ipod app, toy? or worth borrowing someone's ipod
and obtaining the app if any absolute use for cross-calibration

[N_Cook]

Other than the B battery test mark on the scale for running off the 1960s
B122
type 22.5V battery . But of course no standard for what the B equates to for
light load and less than 22.5V , seems to work adequately on 15V , I intend
using 2xPP3 , 18V

[nesesu]

With nominal batery voltage [22.5V] applied from a bench supply, where
does the meter pointer fall relative to the 'battery' markings on the
scale?
If the pointer is in the 'good' area just above the minimum battery
mark then the meter deflection is in the right ball park, not as far
out as your first post would suggest.
My B&K came with a calibrator source that fits over the mic and emits
a tone of about 1kHz to tweak the calibration if needed.

Neil S.

[spamtrap1888]

Do you own a loudspeaker?

Most speakers are rated for so many dBSPL with one watt input, at one
meter. You will need as anechoic a room as possible, or just set it up
outside at night (or whenever the ambient noise is minimum). I would
use a pink noise source (constant energy per octave) -- .wav files
seem to be on the web.

[isw]

In article
<d22b3c03-3705-4202...@z19g2000vby.googlegroups.com>,

That's not even wrong.

Isaac

[N_Cook]

spamtrap1888 <spamtr...@gmail.com> wrote in message
news:d22b3c03-3705-4202...@z19g2000vby.googlegroups.com...

+++++

I can see that being as accurate as a calibrator that hasn't been calibrated
for 20 years say or manufacturing variabilities of ipod microphones.
Assuming the chosen speaker magnet does not decrease in power too much over
time.
I assume that is for speaker driver on its own, in free space as, I assume
the sound from the rear of the cone ,in theory ,will never reach the SPL
meter.

[N_Cook]

Mulling it over I assume you mean using a complete production speaker
cabinet with bass+mid+tweeter and cross-overs etc, of known make and model
and spec

[spamtrap1888]

On Sep 29, 12:26 am, "N_Cook" <dive...@tcp.co.uk> wrote:
> spamtrap1888 <spamtrap1...@gmail.com> wrote in message

I meant an array in an enclosure, sorry.

[N_Cook]

nesesu <neil_su...@telus.net> wrote in message
news:ba2271f0-894f-44c9...@dm9g2000vbb.googlegroups.com...

++++++

I'll go with your suggestion and leave as I found ignoring the new
suspension ribbon and a replaced intermittant B-E transistor
Looks as though Dawe bought in these Sifam ribbon suspension meters , the
original label saying 1.45V and mention of an external pcb. I suspect Dawe
removed that pcb and the movement itself is 100mV. Battery test is simple
chain of resistors , protect diode and rest switched out. So if 100mV fsd
then for a new B122 battery 100 percent fsd would correxpond to 24.5V and
the B marker correspond to 15.5V which seems reasonable. As the mic is
capacitive , about 300 to 3KHz 3dB bandwidth , not electret, not worth
going to any effort calibrating this SPL.
B mark is 64 degrees of 90 degree arc of meter swing, 71 percent fsd

[spamtrap1888]

On Oct 1, 9:17 am, "N_Cook" <dive...@tcp.co.uk> wrote:
> nesesu <neil_sutcli...@telus.net> wrote in message

To measure SPL, A-weighted, it would have to cover 200 to 20000 Hz. No
acoustical standard covers 300 to 3000 Hz.

http://en.wikipedia.org/wiki/A-weighting

[N_Cook]

spamtrap1888 <spamtr...@gmail.com> wrote in message

news:7259f8e1-9d93-44d8...@g29g2000yqh.googlegroups.com...

+++

It is very basic one probably intended for schools use, no A or C wightings
just 40 to 120 dB att sw and slow/fast response sw (470uF across the meter)
and battery sw, but there is a calibration pot externally accessible.
I will use the calibrator preset via ps variation and the B mark to reset
the meter to deemed 15.5V and 24.5V B and 100 percent of the meter

[josephkk]

I am not all that comfortable with your declaration of NO standard covers
300 to 3000 Hz as that range is very commonly used in radio and telephony
measurement.

?-(

[spamtrap1888]

If the only sound sources were telephone receivers, then a sound level
meter that covered only the voice channel range (originally limited by
the frequency response of the carbon granule "transmitter") would have
some value. But real sound sources cover more of the 20-20000 Hz audio
range.

[N_Cook]

If I get back to this meter. I cannot make sense of the B indicator , the
resistor chain suggests 100mV fsd but reassembled and largely functioning
meter fsd is more of order 1V.
2 db ranges 60 and 70dB are stuck together . But for good posistions
switching between ranges for differing 1KHz sine signal in, consistent "0"
dB and +6.7 dB switching betweeen adjascent ranges. Don't know if that 6.7
instead of 10 is due to sine rather than noise source, will have to try
again with an attenuateable noise signal

[josephkk]

Whoosh much? No other cases ever occurred, and were measured?

?-)

[spamtrap1888]

Troll much?

>  No other cases ever occurred, and were measured?
>
> ?-)

Start here:

http://en.wikipedia.org/wiki/Sound_level_meter