The excellent Mark Audio CHR-70 drivers in these transmission line speakers retail for $28 each. Yet the easy to build enclosures with the same driver retails for $2000. There are no crossovers as these are single driver speakers.

The Mark Audio Alpar 10 as used in the $4500 SMA4 single driver transmission lines cost a little more at $110 each.

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Now if you consider that in quantity these drivers could probably be had for 50% retail you can easily see that one would be paying thousands for a simple cabinet. There are no R&D costs as these plans are available to anyone and free of charge.

Do you see why folks are attracted to DIY? Even if you're not these enclosures could be built for a couple of hundred at any local cabinet shop.