X-Authentication-Warning: delorie.com: mail set sender to geda-user-bounces using -f X-Recipient: geda-user AT delorie DOT com Message-ID: <4FCBC2DB.80004@plastitar.com> Date: Sun, 03 Jun 2012 13:02:35 -0700 From: Phil Taylor User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:9.0) Gecko/20111222 Thunderbird/9.0.1 MIME-Version: 1.0 To: geda-user AT delorie DOT com Subject: Re: [geda-user] Power to a speaker OT References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-HR-Scan-Signature: d451904ff5be65ee52378d3778426101 X-HR-ClamAV-Scan: Clear X-HR-SA-Score: 0.0 (/) X-HR-Status: Normal-(phil AT plastitar DOT com/66.147.237.116) Reply-To: geda-user AT delorie DOT com 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