Mordaunt-Short 500 Series THX Subwoofer Tuning For Optimum Sound Quality, Equipment required

SUBWOOFER TUNING FOR OPTIMUM SOUND QUALITY

Your MS500 system incorporates subwoofers built into the left and right front speakers to generate substantial amounts of low-frequency energy for a satisfying bass response. In addition the M500 system has been designed to give a substantially flat frequency response.

However, the dimensions of some rooms and the positioning and nature of furniture can cause the bass response to be uneven. Typically rooms with this problem exhibit a ‘room mode’ where the room dimensions cause reinforcement of a narrow band of frequencies. This leads to a slightly ‘boomy’ sound where a small band of frequencies appear louder than normal.

If you experience this problem, we advise that you first experiment with speaker placement. Begin by adjusting the distance between the speakers and the distance from the speakers to the back wall etc. until a satisfactory response is obtained. Remember to always use your ears as the ultimate guide. Remember what sounds right to you, IS the optimum solution regardless of measurements etc. that you may take.

If speaker placement alone is insufficient to solve these problems we have incorporated a sophisticated notch filter that allows you to attenuate a small range of frequencies for a more even, flatter bass. See instructions below:

Equipment required

•EQ Test CD (supplied) containing eight test tones that will highlight any low frequency ‘room mode’ resonances.

•Sound Pressure Level (SPL) meter (not supplied): This gives an accurate measure of the volume level of the tones emitted from the test CD. SPL meters are available from Radio Shack (US), Maplin (UK) and all good electrical shops. If you are unable to locate one ask your dealer for advice.

Instructions

1.Start by placing your loudspeakers in their intended locations (positioning is discussed on page 5), ensuring that the notch filter is set to the OFF position on both units.

2.Set the levels of the whole speaker system as required for optimum response (fixed in THX mode).

3.Sitting in the listening position (as per fig.5) set the SPL meter range to 75 dB, it’s weighting to C, and set the response to slow if it has a slow/ fast response setting.

4.The supplied test CD includes eight tracks, each one a specially recorded tone at 1/6 octave spacing (in addition, each tone corresponds to a value on the supplied table).

5.Play each track on the CD in turn. Sitting in the listening position and using the table provided, record the reading shown on your SPL meter for each track played on the table provided. Should any one frequency be 6dB-12dB above the average of the others, then use of the Notch filter may be beneficial. Proceed as follows.

6.Go to the rear of each MS502 and switch the notch filter to its –6dB setting and adjust the notch filter frequency knob to the approximate frequency of the highest reading taken as above. Always adjust both notch filters (one for each speaker) together in tandem.

7.Play the test CD again and record a second set of SPL readings in the table to verify the improved flatness of response.

8.Repeat steps 5 and 6 until a satisfactory fairly flat response is obtained.

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