ported or bandpass box

[lXxAndyxXl]

I was wondering what would u guys go with a ported or a bandpass box for djing. (using 2 18's in seperate boxs)

[ChesterFuzzin']

i used to have that same dilemma except it was sealed vs. vented....

the answer:

use both...

i got 2 12" sealed, another 2 12" vented...

in your case..

put one in a bandpass and another in a vented..

best of both worlds...

[Bill Fitzpatrick]

Both vented. Forget the bandpass.

[lXxAndyxXl]

is there a big difference between the 2.

[BassAwdyO]

Personally, I would go with vented straight up.

Advantages:
easier to design and build
better group delay
more efficient per total enclosure volume
you can easily tell when driver gets to xmax and could be damaged

Disadvantages:
24db/octave rolloff on the low end compared to 12db/octave of a 4th order bandpass, no disadvantage to 6th order bandpass on the rolloff
Sometimes less efficient at higher bass frequencys.


Unless you're going for the loudest boomiest bass you can get, go with the bass reflex. You wont even be able to see those pretty woofers movin in a bandpass unless you have a plexi window. You'll still need the same low pass filter because above the rolloff of the bandpass the sub doesnt "see" ports in the box and the panels rattle to hell. You might have your sub playing too loud for too long and not even hear the sub reaching xmax and beyond when distortion becomes easily audible in a vented enclosure. Vented is also the deepest bass per enclosure volume. you need 2 chambers in a bandpass whereas you only need 1 in a vented system. the volume you waste making 2 chambers could be used to make a single chamber of the same size that could be tuned even lower to achieve the same flat response curve.

What kind of subs?

[lXxAndyxXl]

Driver Properties
Name: 55-1875
Type: Standard one-way driver
Company: MCM Electronics
No. of Drivers = 1
Fs = 31 Hz
Qms = 2.193
Vas = 404.9 liters
Cms = 0.171 mm/N
Mms = 154.2 g
Rms = 13.7 kg/s
Xmax = 4.4 mm
Xmech = 6.6 mm
P-Dia = 405.5 mm
Sd = 1292 sq.cm
P-Vd = 0.568 liters
Qes = 0.46
Re = 6.8 ohms
Z = 8 ohms
BL = 21.07 Tm
Pe = 400 watts
Qts = 0.38
no = 2.528 %
1-W SPL = 96.18 dB
2.83-V SPL = 98 dB

[BassAwdyO]

Alright, well your 18's they looked funky on winISD. the crazyiest rolloff eva! I wouldnt have bought drivers like yours myself. They modeled up with extremely high SPL in the region above 50hz. These seem like PA drivers more than HT drivers. You could use about 11 cubic feet tuned to 32hz to get a nice loud box that would go low enough to quake 117db @30hz anechoic. You got to see those response curves to believe them. Low Qms high Vas NO XMAX High Fs Its amazing what they do with home theatron subs today. I want my sub to go down to 10hz with a 3db/octave rolloff on it. Adire audio tumult baby. You know how I do it. It dont need some 20 cube enclosure, just six

[BillFitzmaurice]

As stated by both myself in your last thread, and by others in this, the driver you chose unfortunately doesn't model up particularly well in any alignment. Chalk this up as a learning experience. The way to go about designing a speaker it is to decide on the application requirements, choose the box alignment that will best achieve the goal, and then find a driver that works in the cabinet. What you've done is akin to buying an engine and then trying to find a car that it will fit into, when the way to do it is to pick the car first and then choose which of the offered engines to go with.

For DJ or live pro-sound use eighteens in vented boxes used to be the sub of choice, but today's folded horns loaded with smaller high excursion drivers have rendered the eighteen inch driver a dinosaur. A single ten inch driver in a 24 inch cubed folded horn with 300 watts input will give the same output as two eighteens in a direct radiator alignment driven by 1000 watts.

As for what to do with the MCM 18s I'd dump them and start the process from scratch. No offense intended, but it shouldn't be too hard to find someone willing to buy those 18s based on the fact that they're big and look good (even though they aren't particulary useful).

[lXxAndyxXl]

what would u recomend for around $170.

[BillFitzmaurice]

For $139 (at Parts Express) the Eminence HL10a is a high excursion ten optimized for horn-loaded sub wooofer applications. This is a new state of the art driver, and as such not many designs have yet been created for it. Here's a link to one of mine that works quite well with it:
http://www.billfitzmaurice.com/plans.../products_id/5