Thin and tall VS wide and short enclosure

[limono]

Hi there
After 8 years I was able to buy a pair of Audax HM170ZO woofers and complete a kit I started collecting parts for many years ago (kit origins from 94'). My tastes changed a lot and it won't be my main speaker (I'm into horns and triode amps now). I have an enclosure of required volume (30L ) but the original design calls for slim tall tower enclosure 206mm wide and 1000mm tall with port on the back .What I have is solid vintage JBL cab 325mm wide and 600mm tall with front port (accidentally the diameter of port is almost there -1mm) I could fairly easy use the back of enclosure as a front and even move the alnico ribbon on the top of the cab (but would rather keep it in for practicality purpose)
My main question is how the characteristics of the speaker will change due to baffle difference and if it's predictable at all.
Crossover is 12dB on both slopes at 3khz.
Thanks & regards, L

[Wayne Parham]

One difference is how the internal standing waves line up. In a vented cabinet, there are two mechanisms that cause acoustic resonance: Helmholtz resonance and standing wave resonance. Standing wave modes can sometimes be ignored in small cabinets with small ports because the internal standing waves are high in frequency and easy to damp with internal stuffing. But in a larger box, these pipe modes become significant. They line up at bass, midbass and low midrange frequencies that aren't easily damped with acoustic insulation lining the walls. Sometimes more filler is enough, or possibly a sheet or two spanning the cross-section. Often times, driver and port placement can be used to good effect. It is important to know where the standing waves line up to know for sure.

The bottom line is a tall thin cabinet acts as both a transmission line and a bass-reflex cabinet. It has Helmholtz resonance and pipe mode resonance. You'll see both with an impedance sweep. You can also model both effects, and Martin King's spreadsheets do that very well. Grab a copy of his spreadsheets and play with them a bit and you'll see what I mean.

[limono]

Thank You Wayne
Access to Martins spreadsheet is restricted. I have original kit literature publisched in German "Klang & Ton" with impedance graph (very small unfortunately) Impedance graph has two steep peaks at ~20-25hz and 60Hz.
My German is very very rusty but seems like the tuning (Q=1.4) is right at woofer FS which is 32Hz. The project was launched in 94' when slim tower designs became very fashionable .Also port on the back (dia 70mm with 230mm length) is in the middle of the cab hight so it doesn't work quite like MLTL.
Regards, L