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Level meter for home theatre systems

Having trouble adjusting the levels in your home theatre system? This simple project makes the job easy.

By John Clarke

Main Features
  • 10 LED dot bargraph display
  • -13dB to +6dB display range
  • Level control
  • Attack and decay rate follows VU standard
  • Portable battery powered unit
Click for larger image
Fig.1: the LM3914 LED display driver IC includes 10 comparators, a 1.25V voltage reference and a signal-input buffer stage.

You might think it is a straightforward matter to set up the levels in your home theatre system but depending on your room layout and the physical positioning of the various speakers, it can be surprisingly tricky. This is especially the case when you are trying to get an overall good balance at a number of listening positions.

Without the correct balance, the surround effect will not be the best it can be. Balance between the centre speaker and the left and right channels is critical since they present the front sound-scape. And as is often the case in many home theatre systems, if the centre loudspeaker is too dominant, it will detract from the imaging.

With the Loudspeaker Level meter, you can set up the levels accurately and quickly. It is just a small box with a 10-LED bargraph display on the front. Controls include the power switch and a level adjustment. On the base is a small electret microphone for monitoring the sound level from the loudspeaker.

In use, each loudspeaker is driven with a noise signal in turn and the Loudspeaker Level Meter is placed at the listening position and aimed at the speaker. The LED bargraph meter level adjustment is set so that it reads 0dB for one loudspeaker. Then the noise level of each of the other loudspeakers is adjusted at the amplifier so that they are all the same. Generally, they can be adjusted to within 1dB of each other.

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