Ported speaker ??

[dallaire]

Hello all, I have a question about the tuning of a six inch peerless driver. I have the SW2 software/hardware setup hooked up to my laptop. As best I try to pre measure speaker parameters and use a box allignment program, the tuning of the box seems to be a few HZ off the mark... So my question is while trying to design the "ideal" ported enclouser, should the two impeadance peaks be the same in "hight" of resistance. My goal is to have a finished Q of 707, which I think most consider ideal? Anyway is that the goal in designiing a ported cabinet? to make the two impeadance peaks equal in value???
Thanks,
Dallaire

[sreten]

Hi,

Not really though it is a possibility. Often the best alignment is
take the maximally flat box and detune the port by 0.8 to 0.7.

/sreten.

[JLC7]

Are you tuning by changing the port length or box volume?

Cabinet volume and port length calculators usually just get you close. It might help instead to change the amount of stuffing/dampening in the cabinet to get exactly the tuning you want.

[dallaire]

Sreten, I'm not sure what you mean when you say detune the enclouser? you mean play with port length? I would assume that using "WinISD beta" it tells me to tune the box to 52Hz when I input the data from my SW2 program/hardware setup. So then after retesting and I don't hit the 52Hz mark, I would assume to be ideal allignment would be to adjust until I get 52Hz?? I didn't know that stuffing or in my case one inch insulation board, could make a difference in the tuning frequency! I wanted to use the board material because its a ported cabinet. I am also using one inch MDF nicely braced and flaring the ports
When you say detune to .7 or .8 what would that look like on the impeadence graph? port hump higher than speaker lower? I want to understand you correctly....
Thanks,
Dallaire
Also -- The valley, not the first peak is the tuning freq. correct??

[JLC7]

The tuning is the valley.

Programs like winISD, are highly idealized models of what should happen with your speaker. Needless to say, you'll very rarely see exactly what it tells you. It's still a good starting point though.

The drivers and crossover all take up volume in the cabinet, volume that isn't accounted for in the ideal winISD model. The dampening material also has the effect of changing the apparent volume of the box.

[sreten]

Hi,

WinISD and the like suggest a maximally flat vented box, often
reducing the port frequency ~(increasing length) somewhat works
well, which lowers the lower impedance peak in frequency and in level.
How much lower depends on the driver.
Yes the port frequency is the bottom of the dip between the peaks.

You do not get a Q of 0.707 for ported speakers, only sealed.
Vented volume is usually near x 2 sealed volume for Qtc=0.7.

/sreten.

[dallaire]

Thanks guys, I have in fact oversized the box a couple of hundred cubic inches for bracing and driver displacement, as for crossovers I have the Marchand 24db per octave setup with attenuator 12 position pots. I have been looking at the Behringer DCX unit that has all the digital processing and crossover selectable bells and whistles, but have heard it is only so so. I do like the 48 db rolloff instead of the 24 I am currently using, also the ability to delay one channel or another for time arrival purposses.
Thanks,
Dallaire