Curt, please check.

[cole]

First, I want to thank you for helping me out with the VHT,s. The idea for eliminating standing waves is great. I started investigating just what you did so as to apply to future designs when neccassary. Please check it for me.

since the most problematic, or highest aplitude, is 1/2 of a wavelength between two walls, we take half the speed of sound(565ft) and divide it by 3.79(the length of the woofer enclosure). This equals to a standing wave at 149Hz and is obviously inside the woofer cut-off point. Now we have to move the standing wave to a higher freq. and out of the woofer cut-off point. We now introduce a piece of MDF to essentially split the legth in half and shorten the reflection pionts. With the board in place we now have 1.84ft on either side. This translates to a standing wave at 307Hz on both sides and clearly outside the woofer cut-off point. Since the width and depth do not produce standing waves inside the cut-off point of the woofer they will need no attention.

I started to study standing waves and room modes after your help and this kind of helped me to see what your thinking was. Anyway, I hope I got the just of it.

Curt, thanks again. You have moved me right into the world of room response, bass traps, and diffusers.

[curt_c]

http://www.partsexpress.com/projectshowcase/vht/towerdrawings.jpg


OK, lets see if I can answer this one without making any mistakes...

The longest side of the woofer enclosure is only 25”. I think you were calculating the entire height of the enclosure, but the woofers won’t see all of it. This is the mistake I initially made as I didn't note that the crossover enclosure was sealed from the woofer enclosure.

So, (and since I work in inches) 13560 / 25” = 542 Hz and divide by 2 to get the half wavelength frequency of 271 Hz. Adding the shelf will move it back to 542 as the 25” is cut in half, and yes, conveniently out of the passband.

The mid enclosure is another story, as we can’t easily push the fundamental standing wave frequency out of the mid’s pass band. Adding the shelf between the mids only raises the standing wave frequency to roughly 680 Hz, however the stuffing you will be adding should mitigate the issue. The other dimensions 6.5” and 7.5” will provide standing waves of 1043 Hz and 904 Hz respectively, spreading out the phenomena somewhat. Probably the stuffing will be the real hero in the mid enclosure and the shelf will be doing more as a panel brace than a real help to the standing wave issue. A windowpane type brace in its place probably would be just as effective.

> Curt, thanks again. You have moved me right
> into the world of room response, bass traps,
> and diffusers.

There is always something, isn’t there?

C

[cole]

I used 3.79 for some reason. Not sure what I was thinking. I took it a step further this time and added .75in into the length to accomadate the shelf volume. Now we have a box length of 25.75/2.14ft. 565 divided by 2.14 = 264Hz standing wave. With the woofer shelf in place, that leaves .695 on either side (accounting for .75in off the original 2.14 for the shelf. 565 divided by .695 = 813Hz standing wave.

Curt, by chance would you still know roughly at what Hz everthing is crossed at? Using Vince's original design?

[curt_c]

http://www.partsexpress.com/projectshowcase/vht/measurements.jpg


> Curt, by chance would you still know roughly
> at what Hz everthing is crossed at? Using
> Vince's original design?

Looks like 400 Hz and 2.1 kHz. ;^)

C