Seas W26FX-001 port help

[Cousin Billy]

My boxes are already built, so there is no turning back. The face plates are not attached, so adding ports is not a problem.

The dual Seas woofers are in a sealed box, 130 liters. The base is nice and tight, nothing lacking.

Unfortunately when it comes time to rock, we don't have that house shaking base. I have read that ports can be stuffed when not needed?.

I get figures of 4" diameter port, by 75 cm long?. I must be doing something wrong.

Vas per driver; 162L, therefore 324 total
Usable cone area; 330cm2 per driver, 660 for two
Box volume; 130 L, no changing this
xmax is 14mm. Only by fooling the computer with a smaller number, say 10mm, can I get a port to fit. I have 32inches to play with.

Any help or suggestions would be appreciated.

[DrDyna]

Seas has a couple of different things on their site for this woofer:

THE ART OF SOUND PERFECTION BY SEAS - E0026-08S W26FX001

According to them, you only need 88L with a 7cm diameter 25.7cm length port to tune to for an f3 of 27hz.

Maybe it's time to saw your box almost in half!

Edit: Didn't notice you said you had 2 in there, I'm not sure what that would do to the port requirement.

[Paul W]

I have pairs of the W26FX in just over 100L sealed and think, even stuffed, that is the bare minimum volume for those drivers. What you have should sound clean and tight...130L ported may sound flabby by comparison. For house shaking bass, consider building a nice sealed sub and work on smooth integration.

[sreten]

Hi, Is Xmax specified in your tool one way or both way ? Might be 7mm for 14mm. rgds, sreten.

Not a huge change in bass going vented around 20Hz with that box volume, ~ 4" dia is ~ 15" long.

[bjorno]

Hi,

Agree with Paul W,

b

[Thomas Schmidt]

AJHorn also tells me that you need 16" of a 4" diameter port - Result is a nice straight SPL curve rolling of at about 38 Hertz, maybe shorten it a bit for more punch around 35 Hertz...

Regards

Thomas

[Cousin Billy]

Thank you all.

Sreten and Thomas, am I safe in assuming if p-p max excursion is 14mm, than 7mm is the right figure to use?. If so then you are right, 15-16" length.

DrDyna, with 2 woofers, that gives me 176L needed space. What I am hoping is 130L stops boomy base. Time to experiment.

[vacuphile]

I think you are putting the question upside down. The first question would be to ask which box tuning you consider optimal for these speakers. Your enclosures are too small for an optimally flat response in a BR, so there will always be a bump. I would suggest that you tune the box at 26 Hz for a F3 of 30 Hz. The bump will be about 2 dB. Don't worry too much about it. With this much of bass power you will need room equalization to get things right anyways.

So then you know the optimal box tuning, and now you can calculate a pipe that would bring it up to that frequency. But, and here is the rub, these calculations don't work, generally. Air outside the openings work to virtually lengthen the pipe. You really need to measure if you have reached that frequency or not. Fortunately, there is a way to do this with only a tone generator. When you sweep, Fb is the point where the cone of the driver moves the least. With speakers with a closed dust cap, you can varify this with the speaker on its back and just a couple of grains of riced placed on the cone. With this speaker it would be a bad idea, because the airgap between VC and pole piece is not covered. The effect is pretty strong though, so you can also use your sense of touch.

Another way of solving the problem of too little bass, one I would prefer, is to equalize a Linkwitz transform into the bottom end. Which is a complicated way of saying that below 40 Hz or so you give a 6dB boost per octave. This should do the trick in a much cleaner and predictable way. Your drivers should be able to handle the additional thermal load.

[sreten]

Originally Posted by Cousin Billy

Thank you all.

Sreten and Thomas, am I safe in assuming if p-p max excursion is 14mm, than 7mm is the right figure to use?. If so then you are right, 15-16" length.

DrDyna, with 2 woofers, that gives me 176L needed space. What I am hoping is 130L stops boomy base. Time to experiment.

Hi, max excursion only affects the required diameter, re max air velocity, not the length, somethings amiss. rgds, sreten.

[vacuphile]

One last note: pipe diameter is not such a major issue by itself. A correct proportion between length and diameter is way more important.

What you want is a pipe diameter that is large enough to 1) not generate too much pipe noise and 2) keep the Q of Helmholz resonance tight enough. The generally accepted rule of thumb that pipe volume should equal displacement volume of the driver is not based on any kind of theoretical foundation, or even on a profound understanding of the process at work. With an appropriate pipe geometry (optimized flares on both ends), the pipe noise can be greatly reduced, as well as the kind of turbulance that would throttle the BR-resonance at high volume. In short, you may need a somewhat smaller pipe than you calculated, given you do the other things right.