A two-way with Scan-Speak 8542-05 and Vifa D25AG 35-06

By Lars Mytting
31 Dec 1996

Box Coloration

This was tested by subjective listening, and by playing spot frequencies and tone bursts from 20-20.000 hz. One box with MDF/pine was compared with a similar box of MDF alone.

One quick'n dirty way of testing enclosure vibrations without measuring equipment, is to play different frequencies (signal generator or test CD's) and increase and decrease volume. Hold your hand to the box. Does it vibrate? Does the tone change charachter when played loud? If so, it is probably the "tones" added by the enclosure that you hear. With this, you will get a good indication on how much, and at which frequencies, the enclosure vibration adds to total output.

Back to my two pair of boxes: The differences between MDF/pine and MDF alone were NOT so significant, and I believe that better results may be achieved using another sandwiching method. Subjectively, the MDF/pine box did not sound any different than the MDF box.

The MDF/pine was generally a little bit more dead than MDF alone, and was brought into resonance in a bit smaller frequency range, but I believe this just was a result of added mass and weight to the box. Its heaviest resonances were at 180-200 hz and 400-500 hz, while the box of MDF alone had its heaviest resonances at 300-600 hz. At approx. 200 hz, the MDF/pine had a peak where it vibrated more than the heaviest vibration of the MDF box, but generally, MDF/pine was slightly more dead.

One surprising difference was at exactly 315 hz (You can find that freq. on the Sheffield/XLO Test CD). The MDF box went into heavy vibration, but the MDF/pine box was absolutely dead, no matter how loud the tone was played. All other enclosures that I have tried this on, has started to vibrate at this frequency.

The major reason for not recommending the described sandwiching method is because it is a bit unpredictable, not at least because the 200 hz peak. Maybe it was just because the pine boards went into resonance there, and transplanted the vibration into the MDF. Sandwhiching is no good if the second material used starts to vibrate and sends its vibration into the MDF!

My next experiment will be to fasten the second material with a thick, elastic adeshive, like a thick layer of silicone, to isolate the MDF from it. I don't know which material I will use yet, but it should be something with different density from MDF. Some attention should be sought to keep the sandwiching material from acting like a loose part in the box. This might cause buzzing and severe trouble.

I will share the results on Roy's web page if I end up with something useful. Right now, I'm gonna pop a beer and sit on the porch, playing Lynyrd Skynyrd, and then keep on popping beers until I am sitting in a convertible with Cindy C. Or Helena Christensen, I don't know yet.

Lars

About the
author

Print this
article

Email this
article