604E - 612 Port size?

[TerribleT]

Hi, I have a pair of 612 cabinets with one 604 duplex and one 604E duplex speaker. I will replace the 604 with another E. The question I have is the port size. I checked the literature on the web for the dimensions of the port and they are smaller than what I have, which are 13" by 5.5". Can anyone tell me what the correct port size should be?
Regards,
David

[GM]

The correct size depends on what the desired Fb is and/or how much series resistance there is from amp (if tube), room placement, and wiring. Anyway, the drawing I have shows a 3"h x 7.75"w slot, which will lower the cab's tuning ~a half octave.

GM

[GM]

Fb is the resonant frequency of the cab and should be low enough to play all your music. If vinyl only, then ~40Hz, if you listen to CDs, then as low as you can (FWIW my cabs are tuned to 16Hz and corner loaded for organ/movie special effects) and still have good tonal balance/enough efficiency to have acceptable dynamics.

Not knowing how much output impedance your amp has, etc., about all I can recommend is get a scrap piece of 3/4" thick board (ply, MDF, anything not knotty or split) and clamp it to your vent to close it off as much as possible, then attenuate the horn till it sounds about as good as it's going to listening to a variety of music with lots of low stuff, then open it up some and do the listening thing again with the same music. At some point you should find a cross sectional area that sounds the most tonally balanced to you.

GM

[TerribleT]

Thanks GM for your reply. I do not know what Fb is or what I should want it to be. But my amp is a SE parafeed 45 amp with plain 16 gage speaker wire. The speakers are 6 feet apart and 2 feet away from the wall. Given this information, should I keep my present slot dimensions or should I make them smaller? Any further help would be appreciated. Thanks
David