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Date: Sun, 3 Jun 2012 17:06:29 -0400
Message-ID: <CALSZ9gq=_09w2Ve_YVB40jWs+VeF7fH4pMsm-XRPN+PPMJPH4A@mail.gmail.com>
Subject: Re: [geda-user] Power to a speaker OT
From: Rob Butts <r DOT butts2 AT gmail DOT com>
To: geda-user AT delorie DOT com
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The audio is a short sound similar to a duck quack.

On Sun, Jun 3, 2012 at 4:02 PM, Phil Taylor <phil AT plastitar DOT com> wrote:

> On 6/3/2012 12:26 PM, Rob Butts wrote:
>
>> I am using a microchip microcontroller to read in a 8ks 16 bit .wav file
>> and output it through the dac.  I have a small 109 dB speaker 32 ohm
>> impedance, nominal input power of 12mW and max input power of 20mW for 1
>> minute.
>>
>
> 12mW = Vrms^2 / zspkr
>
> so ... that's 1.8 Vpp continuous or 2.3Vpp for shorter times.  The dac
> rails are high enough to hit the power level most likely (even on 3V). The
> current provided by the DAC is probably not high enough though to drive the
> speaker directly.  you'd need 30mA before output current limiting kicks in,
> a power op amp, or some discretes inside an opamp feedback loop to drive
> that speaker.  (compute max current at waveform peaks, not with average or
> rms voltages.)
>
> we need to know what kind of audio you are playing back.  if it's a sine
> wave, you won't need any gain ... to hit your power level.  But if it's
> music you will need some gain to get it loud.
>
> As for other ways to limit the power it would be possible to pre-process
> your sound file, design a limiter circuit, or clip the analog going into
> the speaker.  Each of these options would have its own tradeoffs.
>
> Some compression may be needed to get the audio to feel loud, as will some
> gain, though it sounds counterintuitive.
>
> Phil
>

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The audio is a short sound similar to a duck quack.<br><br><div class=3D"gm=
ail_quote">On Sun, Jun 3, 2012 at 4:02 PM, Phil Taylor <span dir=3D"ltr">&l=
t;<a href=3D"mailto:phil AT plastitar DOT com" target=3D"_blank">phil AT plastitar DOT co=
m</a>&gt;</span> wrote:<br>
<blockquote style=3D"margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-=
color:rgb(204,204,204);border-left-width:1px;border-left-style:solid" class=
=3D"gmail_quote">On 6/3/2012 12:26 PM, Rob Butts wrote:<br>
<blockquote style=3D"margin:0px 0px 0px 0.8ex;padding-left:1ex;border-left-=
color:rgb(204,204,204);border-left-width:1px;border-left-style:solid" class=
=3D"gmail_quote">
I am using a microchip microcontroller to read in a 8ks 16 bit .wav file<br=
>
and output it through the dac. =A0I have a small 109 dB speaker 32 ohm<br>
impedance, nominal input power of 12mW and max input power of 20mW for 1<br=
>
minute.<br>
</blockquote>
<br>
12mW =3D Vrms^2 / zspkr<br>
<br>
so ... that&#39;s 1.8 Vpp continuous or 2.3Vpp for shorter times. =A0The da=
c rails are high enough to hit the power level most likely (even on 3V). Th=
e current provided by the DAC is probably not high enough though to drive t=
he speaker directly. =A0you&#39;d need 30mA before output current limiting =
kicks in, a power op amp, or some discretes inside an opamp feedback loop t=
o drive that speaker. =A0(compute max current at waveform peaks, not with a=
verage or rms voltages.)<br>

<br>
we need to know what kind of audio you are playing back. =A0if it&#39;s a s=
ine wave, you won&#39;t need any gain ... to hit your power level. =A0But i=
f it&#39;s music you will need some gain to get it loud.<br>
<br>
As for other ways to limit the power it would be possible to pre-process yo=
ur sound file, design a limiter circuit, or clip the analog going into the =
speaker. =A0Each of these options would have its own tradeoffs.<br>
<br>
Some compression may be needed to get the audio to feel loud, as will some =
gain, though it sounds counterintuitive.<span class=3D"HOEnZb"><font color=
=3D"#888888"><br>
<br>
Phil<br>
</font></span></blockquote></div><br>

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