Help with speaker porting

[Drummer 35]

Hi all,


Im working on a prototype but Im having problems regarding porting.


It will be a floor stander with dual 8" woofers and a 1" comp. driver for highs.


For the alignment I want, the cabinet has to be 60 liters. (woofer Vas 25 liters) and tuned to 50hz (driver fs 53Hz)


The problem is that tunning the box to 50hz needs a big port diameter to avoid port chuffing I think, but, I´ll have port resonances at freqs where the woofer is still working.


My doubt is what would be less harmful, a "small" diameter noisy and low linear port or a big and long port, with its resonances. Are those resonances really audible at all?


Thanks for your help.


David

 

[giralfino]

To simulate a reflex box you need Vas Fs and Qts. What Qts has your driver?
I’m not on a PC where I have Unibox, so can’t check, but you shouldn’t have any problem in tuning at 50Hz a 60L box with a large enough port, as 50Hz is a relatively high tuning. Chuffing depends on port diameter and power used. Download Unibox and see yourself.
I suspect you are using pro drivers with high power specs, and think you need to drive them at specs. At home you’ll only need a couple of watts.
Chuffing and resonance are two different effects.

Ralf

 

[Drummer 35]

Hey Ralf,


Thanks for your response.


Yes, you are right, these are pro drivers, with high power specs. (Qts=0,31, Qms=14,3 Fs=53Hz Vas=24,8 Xmax=6mm)


I am aware that chuffing and resonance are two different effects, but from simulations it seems that I have to decide between those two.



The problem is that using a smaller in diameter port (2" or 3"), I´ll get chuffing, but using a proper 4 or 5 inches port I´ll get port resonances (or that´s what the sim says) and don´t know how to avoid that.


Any ideas?


Thanks!

 

[giralfino]

IMHO you are using a too large box and too low tuning for that driver. For two of them I'd aim for a 30L box tuned to 60Hz. Anyway below tuning excursion increases a lot, and you'll run out of excursion quickly before reaching your maximum rated power. For example wiring the drivers in parallel at 64W excursion exceeds xmax below 35Hz, but vent velocity is below noise level with a 10cm port. For the same input power and same port diameter, the smaller box has lower port air speed.

Ralf

 

[Drummer 35]

Thanks Ralf.


Anyway, I think its a matter of taste. I like the sound of big boxes tuned a bit down fs. I think 30 liters is too small for two ot these drivers and 60 hz would a bit shy on bass, dont you think?


Those drivers have 94dB/1W/1m sensivity, so I doubt I´ll use them with so much power.



What software are you using Ralf?

 

[giralfino]

Unibox, and it’s free.