Port Question

ridr4lif · Post by **ridr4lif** » Sun Jan 16, 2005 5:29 pm

Now having a few days with my new box, ive noticed i want some more low end bass. My box is tuned to 38 hz. I believe the port is 18" long.
Will a longer or shorter port lower my tuning frequency?
Also, by lowering the tuning frequency, will i lose higher frequencies?
TEDD

Jonathan · Post by **Jonathan** » Sun Jan 16, 2005 6:11 pm

You won't lose higher frequencies by tuning lower. You'll need to lengthen the port to tune lower, but remember that increasing port length will also decrease net box volume, you'll have to find a happy medium. I use the calculator on http://www.bcae1.com for situations such as yours since it calculates then re-calculates to compensate for the length and box it's in. I don't know how low you want to go or what size your box is, but around 32 hz offers a good balance of depth and SPL. If you want even deeper, 28-30 works well and usually gives great sound quality. Depends on the subwoofer you're using as well, you don't want to tune at or below it's resonant frequency.

71buickfreak · Post by **71buickfreak** » Sun Jan 16, 2005 6:15 pm

You will need a longer port. you won't lose any hgiher frquency bass, you will gain lower frequency bass. I would need your current port sizes as well as your box size. you can also use WinISD to calculate it yourself

Justin from Detroit1 · Sun Jan 16, 2005 6:32 pm

I hope you are running a subwsonic filter on those subs. Currently, they are being damaged playing all tones below 38 hz.

Mercedesbends69 · Post by **Mercedesbends69** » Sun Jan 16, 2005 7:21 pm

I have my enclosure tuned to 28hz. Sounds good. I'm suprised by how much SQ I actually get out of them but I don't notice it "missing" any frequencies at all.

bigbassman · Post by **bigbassman** » Tue Jan 18, 2005 1:46 pm

port tuning is a trade off..

by design, a port reinforces frequency output. The mass of air inside the phyiscal deminsions of the port resonates in response to pressure changes inside the box. This mass of air is only acoustically in phase with the driver for a small frequency band... move the tuning frequency, and that reinforcement band shifts as well..

so while it will affect the upper frequency performance.. most systems are too loud in that range anyhow, and the user will not have any complaints.. :)

Justin from Detroit wrote:I hope you are running a subwsonic filter on those subs. Currently, they are being damaged playing all tones below 38 hz.

that's incorrect.. excursion octuples (or more) below tuning for every octave.. if the driver is only moving at 6 mm (one way) at a 40hz tuning, and has an xmech of 30mm (one way), that driver could reproduce content @ 30hz, which is 1/2 octave lower, without reaching xmech.. it would however, sound worse, due to the distortion that increases below tuning, due to the physical nature of the box...

no woofer, regardless of install, will magically be damaged just because its playing 1-2hz below the tuning frequency... doesn't work that way :)

I currently run with a 14.5 cuft wall, 170sq inches of vent, and a 33hz tuning.. I have usuable response down to nearly 24hz with my 8's...

and no.. they don't magically break or suffer from it

Loyd L.

NDMstang65 · Post by **NDMstang65** » Tue Jan 18, 2005 2:00 pm

Yep...Loyd hit the nail on the head..

Your not going to unload a woofer playing 1-2Hz under 'tuning' :) - in most circumstances, woofers in ported design can play 1/2 octave under tuning safely...

ridr4lif · Post by **ridr4lif** » Tue Jan 18, 2005 2:07 pm

thanx for all the responses guys. Yes i do have a subsonic filter and i think its set around 35hz. I just want lower bass extension w/o having to worry about anything breaking (even tho it sounds like i wont hurt anything...). Anywayz, i guess ill check out bcae1.com and see what i can come up w/ for a new box...THANX A LOT GUYS
TEDD

ridr4lif · Post by **ridr4lif** » Thu Jan 20, 2005 5:24 pm

3dB Down Point (f3) 21.4301 Hertz
Resonant Frequency (fb) 24.497 Hertz
Enclosure Volume (Vb) 3.6373 Ft3
Proper Port Length 6.2973 Inches

ok...so i went to bcae1.com and this is the numbers it came up with for me. This is way off of the box volume, port length, and frequency that kicker supplied. i dont kno if the port is round or slot tho. Can anyone help? Thanx
TEDD

Justin from Detroit1 · Thu Jan 20, 2005 6:51 pm

I wasn't saying the subs "magically" start getting damaged when playing frequencies belowing the tuning of the enclosure. I could have gone into great detail about it but 99% of people don't care about the details. It is ALWAYS a good idea to have a working subsonic filter on any ported setup.