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July 23rd, 2019, 04:43 AM  #1 
Newbie Joined: Jul 2019 From: uk Posts: 1 Thanks: 0  How do I rearrange to find X with this equation?
Hi, I have been using the below equation to calculate Watts required to reach a reference level Sound Pressure Level (SPL), however I cannot seem to successfully rearrange equation to find required Lsens. Can anyone help and show me how to rearrange this so that X (or in this case Lsens) is the subject? Equations used to calculate the Watts: dBW = Lreq  Lsens + 20 * Log (D2/Dref) + HR W = 10 to the power of (dBW / 10) Where: Lreq = 105 SPL (required SPL at listener) Lsens = 89dB (loudspeaker sensitivity (1W/1m)) D2 = 2.5m (loudspeakertolistener distance) Dref = 1.0m (reference distance) HR = 0dB (desired amplifier headroom) dBW = (ratio of power referenced to 1 watt) W = 249W (power required) 
July 23rd, 2019, 06:04 AM  #2 
Senior Member Joined: Apr 2014 From: UK Posts: 963 Thanks: 342 
OK, starting with: dBW = Lreq  Lsens + 20 * Log (D2/Dref) + HR Add Lsens to both sides: dBW + Lsens = Lreq + 20 * Log (D2/Dref) + HR Subtract dBW from both sides: Lsens = Lreq  dBW + 20 * Log (D2/Dref) + HR 

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