Phil please don't answer I know you know this one... A theoretical situation: A sub is at the back of a hatch to move back wave and front wave in time. Its in a ported box and a port is usually delayed 90 deg out of phase= 1/4 wave length. So in placing port opening forward at a distance of 1/4 wave length of tuned frequency, will this put the port back in phase with front and back wave response from the sub (back waves-meaning sound waves from the top of cone moving backwards in car, not sound waves from the back of subs cone). Who knows the answer?

Hmmmmm... If the port was made to be 90 out of phase then that would make it 270 deg out of phase with the original wave (at tuning freq) created by the front of the woofer (side of the woofer facing out of the enclosure).

This being the result of the sub box internal wave from the back of the woofer (180 deg out of phase) plus the 90 deg created by the port.

If the port was brought forward a 1/4 wave length it would be in front by 90 deg, making it again 180 deg out of phase with the original wave. So... the port would be perfectly out of phase with the woofer?

If you put the woofer 1/4 wave in front of the port, it would be 360 degrees out of phase with the back of the woofer, making it in phase with the back of the woofer, and out of phase with the original wave.

Am I correct?

Hmmm... :huh:

All of this would only occur at the tuning frequency, and at any other frequency, the waveforms would be hideously more or less out of phase. If the wave were to hit over 150db slightly above the tuning freq with the handbrake off and out of gear, the car would start to shake forward, and vice versa if it was under the tuning frequency. Also, if a small child was to be put in between the port and the woofer, at the tuning freq they could be sheared apart.

I think I may have to put this theory to the test.... Come here son, I wanna try something...

I know the answer, its called Use The Search Function and find the article I posted from Harman-Karden USA about the 1/4 wave theory and doing front/rear wave alignment.

Yeah because its talked about all the time...

Well... I have yet to try out another project along the same lines...

It would consist of a subwoofer inside a folded box to give a 1/4 wavelength to another woofer mounted beside it. In theory just like a passive radiator, with the second woofer acting as the port, being 90 deg out of phase... nuthin new.

But, what if I were to put a non-polarized cap on the terminals of the passive woofer, set at a -6dB rolloff at the box resonant freq.

At the resonant freq, it would act as a normal passive radiator, but as the freq increased, could the cap be used to start to induce the coil, making it stiff like a short circiut? Could this also start to help shift the phase of the woofer (start to lag towards another 90 deg of shift due to the capacitor) and help keep it in phase above the resonant freq?

Hmmm.. maybe I need a diagram...

hey, we use the same theory for calculating dipoles and element spacing for radio antennas
hhaha

HA!! really? I thought I'd get away with it being my idea We use a similar setup to control internal vibrations on helicopters. The main rotor blades (due to centrifugal force) act into the mainframe at a relative torque 90 degrees to the rotation of the blades. This would shear the airframe apart unless it was dampened by a slab of weight opposing the force at a vibe node, with a capacitor/coil tank circuit to change the vibe automatically according to changes in freqs. The freqs are usually around 200-300 rpm, so I thought I could maybe use the same theory somehow in a sub box.... Dunno

well, you could add weight to the sub cone to 'tune' the woofer to the resonance of the car.... hmmmmmm

It is, i rarely have a day in my life where in one form or another it doesnt get discussed.

woosh!!!straight over my head.makes for an interesting read though