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Old 07-14-2002, 07:48 PM   #1
Lee

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Are large magnets always better? ..

Quote:
4.12 Are large magnets always better than small magnets? [ST]
Magnet size is meaningless!

Every speaker will have an optimal BL (See section 4.1 What are "Thiele/Small parameters?" [CD, RDP],) product, the field strength in the air gap multiplied by the length of the voice coil wire in the field.

If the BL product is too low, the speaker is electrically not very well damped (which will result in a woofer with a high Qts). A bump in frequency response and a level drop in midband efficiency may be the result. If the BL product is too high, the speaker is electrically overdamped (Low Qts woofer). A very high midband efficiency, but the driver starts to roll of early.

An high BL product can be achieved in a number of ways: increase field strength; or increase wire length in magnetic gap.

The increase in field strength is limited; so some manufacturers use very thin wire for the voice coil, as such they can achieve a high BL product with a low field strength (cheap magnet). Or they use an 8 layer voice coil... needless to say that electrical power handling will decrease enormously.

Long stroke woofers, having only a part of the voice coil in the air gap, need a very high field strength to achieve a high BL product. Often this means a big magnet as well...

Use magnet size as an indication, but as nothing more than that.
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