ported or bandpass box

Status
Not open for further replies.
Jump to Latest
#5
Vented Fo Shizzle

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?
 
#6
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
 
#7
Brace yourself for this!

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
 
#8
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).
 
#11
I don’t completely agree that an 18 is obsolete. Although I love horns, I think they are not always the best choice for most people in a domestic environment. I am a big advocate of 6th order alignments (not band pass). This is an assisted alignment, which uses a 6db boost at a certain calculated frequency. This is especially useful with efficient woofers where the 6db boost will not cause excessive power demands. A 6th order alignment generally gives a smaller box size than a 4th order, and with a lower F3 as well. The Selenium 18SW2P will give a 26Hz f3 in a 4.5 cu. ft. box, which is smaller than any horn design. For home, a 15 is probably more than enough. The Selenium WPU1505 will give about 27Hz f3 in about 3.5 cubic ft. That is a very high quality woofer that meets the price point. Check out the H.E.L. site for information on 6th order alignments. See the article on Alignment Calculations.

http://www.highefficiencyloudspeakers.com/Downloads.html
 
#12
The Selenium 18SW2P will give a 26Hz f3 in a 4.5 cu. ft. box, which is smaller than any horn design. For home, a 15 is probably more than enough. The Selenium WPU1505 will give about 27Hz f3 in about 3.5 cubic ft
Click to expand...

Guess you haven't seen my AutoTuba at 3.7 cu ft., which delivers 90dB/watt at 20 Hz in room. While there may be some usefulness still for 15s I think the 18 is a dead horse unless you absolutely positively can't go with a horn, which means you're either a DIYer who'se all thumbs or a manufacturer trying to put out a profitable product for less than $2k retail. Direct radiators and bandpass boxes held a size advantage over horns until quite recently, but with today's drivers and the horn geometries that they allow it's no longer the case.
 
#13
Well, maybe at 4.5 ft3 it isnt smaller than any horn design, but I still prefer the 6th order alignment for the smooth response. While I admire the Autotuba design, I dont feel its the right solution for every application. Just my opinion, of course.
 
#14
While I admire the Autotuba design, I dont feel its the right solution for every application
Click to expand...

Of course not. It's too powerful for my car, for instance, and I use an even smaller Tuba 18 for my own HT.

Even though they've been told by Tuba 24 owners that they can't use all the power that it offers I've got guys at my forum who want to build a version of Tuba large enough for an eighteen; if anyone ever built one it would provide a fine acoustic substitute for a 3 ton wrecking ball.
 
#17
Horns can be made smaller now thanks to long throw high Bl drivers. The long throw makes it possible to use smaller drivers, 8s instead of 12s, 10s instead of 15s, etc, to minimize the rear chamber and throat sizes. The high Bl allows the use of smaller pathway cross-sections. Smaller cross-sections result in higher throat impedances, and that can cause a loss of motor control over the cone in high power/low frequency/long excursion usage, but with Bl of 12 and higher available now on small diameter long excursion drivers the problem has been overcome.
 
#20
Hi Bill, I'm really interested in the autotuba. It looks really cool but I don't have a woodshop available to me to build one. (appt living in North Jersey) Are there any guys with licensing to build them for resale? I'd sure like to get my hands on one. The autotuba, not the guys. Thanks,
Ricky
 
Status
Not open for further replies.
Top Bottom