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MG1.6 electrically-flat crossover

Posted by EdG (A) on March 16, 2002 at 16:18:03

MG1.6 electrically-flat crossover

One thing that perplexes me about the stock 1.6 crossover is the gap between the electrical response of the woofer and tweeter sections. This gap is shown below (green=woofer, red=tweeter, blue=sum amplitude, yellow=sum phase). At the crossover frequency, the response is almost 4dB down.

While the dip is an intentional part of the MG1.6 design, I was curious what the MG1.6 would sound like with a electrically flat crossover. I designed the following resistor network to accomplish this:

I built the resistor network into a pair of DIY speaker cables. It requires no modifications to the stock crossover. I used 5%, 10W resistors. 25W resistors would be better.

The resulting electrical response is as follows:

The speaker's output level is reduced by 5dB, making it even less efficient.

The woofer section's -3dB point is raised from 200Hz to 400Hz.

The tweeter section's -3dB point is lowered from 1.6KHz to 860Hz.

The electrical response is flat to within 1dB. I gave the response a slight downward tilt which may be eliminated by increasing the woofer resistors to 6.8 ohms. I know others have measured the tweeter's acoustic response and it is not flat (which is one reason for the dip in the crossover).

The crossover frequency remains unchanged.

How does it sound?

Quite different, as though the MG1.6 had sprouted a midrange. Vocals went from good to amazing. Timbres seem more accurate. The slight treble emphasis is gone (I believe the dip in the stock crossover created the perception of an emphasis in the 2K-5K range). The speaker now sounds dark - perhaps a little too dark. There are no apparent anomolies around the crossover frequency, no QR tweeter resonances, no driver integration problems, and no problems due to loss of damping.

Also there's no longer as great a difference between the Maggie sound and the sound of the box speakers I have.

Downsides? First, the loss of efficiency. Secondly, there's more horizontal lobing. I added phase shifts of -45, -30, -15, 0, 15, 30, and 45 degrees in the below figure to compute the lobing. There's a 4dB variation from -45 to +45 degrees, roughly double that of the stock crossover. I could detect the lobing walking around the room and playing a test CD. I couldn't detect lobing on music. The output-of-phase tweeter is essential.

I thought I'd share the results of my experiment with the group. I'm going to try the electrically-flat crossover for a week. Going back to the stock form is simply a matter of changing speaker cables.

Comments?

Ed

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