[TriEmbed] P.O.T.M. preliminary report

[Brian]

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: TriEmbed at triembed.org
> 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:unsubscribe-TriEmbed at bitser.net?subject=unsubscribe
> Searchable email archive available at https://www.mail-archive.com/triembed@triembed.org/
>