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General speaker questions for audio and home theater.

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Original Message

You don't even need a filter for that trick

Posted by Presto on August 24, 2009 at 12:38:05:
Richard Bass Nut's "near perfect" full range speaker has a built-in 2nd order high-pass filter also known as natural rolloff. The effects of the resulting phase distortion are seen well into the midband. A mangled square wave at 50hz admist rolloff would cause distortion in the midband at up to 500hz.

Most "1st order designers" do not mention their designs are only TRUE acoustic 1st order where the drivers are not rolling off. Once the drivers roll off, you get all kinds of mayhem going on. Running a mid or midbass "full range" with no low pass filter, for example, means the driver is allowed to pass it's natural rolloff which is 12db/octave - not the 6db/octave required.

What would be better, in my mind, is WILLFULLY coming up with a 4th order acoustic response and just removing the phase roll with forward-reverse digital signal processing. It does work. If you're listening to CD or PCM you've already got a filter in your DAC. What's a bit more DSP to achieve transient perfect reproduction? Might be a worthwhile trade if you ask me.

I tested the Thuneau Allocator and with phase correction enabled, the crossover (by itself) is truly transient perfect with the Arbitrator properly dialed in - aka reproduces square waves at ALL frequencies. The trick is to get the electrical transfer functions to combine with the drivers natural rolloffs / response to yield the 4th order acoustic transfer function.

1st order speakers and full range cone-type speakers are (IMHO) over-rated and are only truly transient perfect for portions of their bandwidth where drivers are in the linear (non-rolloff) region of their respective bandwidths. They are moreso "just another way to skin the cat" with their own set of limitations and exceptions - just like every other design out there.

Cheers,
Presto