Fiberglass Resin used in Sub Enclosures

[holdenater]

I am doing a build for a single 18" sub. The box will be slot ported and tuned to 28hz. I have herd that applying fiberglass resin to the interior of the box is a good idea to help bounce the sound waves off the walls. Is this true? If so how do you apply it to MDF wood? How much will a 8 cubic feet box take? How many coats? Will I need to use the fiberglass cloth?

[Hugh G. Rection]

I am doing a build for a single 18" sub. The box will be slot ported and tuned to 28hz. I have herd that applying fiberglass resin to the interior of the box is a good idea to help bounce the sound waves off the walls. Is this true? If so how do you apply it to MDF wood? How much will a 8 cubic feet box take? How many coats? Will I need to use the fiberglass cloth?

interesting. i would use it with impedance rise in mind, more than making sound bounce off walls.

[holdenater]

what do u mean by impedance rise?

interesting. i would use it with impedance rise in mind, more than making sound bounce off walls.

[byers319]

Go to the top right, use the search feature.

[Hotdog]

What is impedance rise (box rise)?

-The impedance is the resistance of the coil when AC is applied. Since the coil acts like an inductor, the impednace changes with frequency.

What people call impedance rise is due to the woofer being put in a box. If you look at the impedance plot of a woofer in free air, the impedance rises at the resonant frequency of the driver. Once in the box, the cone has a different reaction with pressure behind it, which can change the impedance plot. You also have new impedance spikes due to the box size, port tuning, etc.

Impedance rise may in fact not even be a higher impedance at all frequencies (more than likely will be an increase in the overall average, but the spike at the driver's resonant frequency may still be the highest impedance). Many times it is just additional humps/spikes in the impedance plot, or even changing of the impedance spike seen with the woofer in free air. For someone playing music, the additional humps/spikes will increase the average impedance seen while playing music. For someone burping at a single frequency, they need to know the impedance at their frequency to match the amp to the sub. There is a good chance the impedance will be higher near the frequency they burp at, since it not far above port tuning.

For the average person, ignore "impedance rise". The hardcore competitor uses the actual true impedance to his advantage to get all the power he can from the amps

Found here

http://www.stevemeadedesigns.com/board/topic/83029-everything-you-need-to-know-about-car-audio/