100 dB peak from a toy!! That sounds like a reason to complain to some
governing body somewhere.
Armchair audio engineer here with a few tips (and I wasn't in the
meeting, so forgive me if I'm repeating things that have already been said).
A capacitor's impedance is inversely proportional to frequency. A
single cap in series will attenuate low frequencies more than high
frequencies. Your grown-up ears may not be able to tell the difference,
but the toy probably uses PCM to generate sound and likely has little to
no output filtering of its own, so that sound is going to have an
above-average amount of high-frequency energy.
The "common" way to peel back the power going to a speaker is with an
arrangement of resistors known as an L-pad. This is the combination of
a series resistance and a parallel resistance that keeps the total
impedance seen by the output circuit constant, while reducing the
current flowing in the speaker.
There are calculators available on the web where you punch in the
speaker impedance and the desired reduction in decibels, and it tells
you the resistor values to use.
Note: Audio circuit impedances (including speakers) are nominally
measured at 1 kHz. A speaker, being an inductor, will measure a bit
higher at 1 kHz than at DC. All of that said, given it's being directly
driven by IC pins, the impedance probably isn't as critical.
HTH!
-B
On 2/14/24 15:53, The MacDougals via TriEmbed wrote:
The Problem Of The Month this month was how to lower the volume on a
childs toy.
The speaker is driven from two pins of the processor. The DC resistance
of the speaker is 9.3 Ohms.
Several suggestions were made on how to reduce the volume. I will
report here on the first few things I tried.
I downloaded an app on my iPhone to measure loudness.
The app was very specific in stating that the values measured were
approximate.
LAeq
Max
LCPeak
TWA
unmodified
85.90
91.20
102.40
52.00
22 ohm in series
80.00
86.60
96.60
46.20
47 ohm in series
74.00
80.70
90.80
xxx
47 uf in series
87.70
93.50
104.20
55.30
1 uf in series
76.30
83.10
95.40
xxx
To my untrained ear, I found the 1 uf to be a good result. I did not
notice a change in the tonal qualities, but I am untrained and old (so I
don’t hear high frequencies).
---> Paul
_______________________________________________
Triangle, NC Embedded Interest Group mailing list
To post message: [email protected]
List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
TriEmbed web site: https://TriEmbed.org
To unsubscribe, click link and send a blank message:
mailto:[email protected]?subject=unsubscribe
Searchable email archive available at
https://www.mail-archive.com/[email protected]/
_______________________________________________
Triangle, NC Embedded Interest Group mailing list
To post message: [email protected]
List info: http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
TriEmbed web site: https://TriEmbed.org
To unsubscribe, click link and send a blank message:
mailto:[email protected]?subject=unsubscribe
Searchable email archive available at
https://www.mail-archive.com/[email protected]/
