[Wireman54304]

I am building a sub to look like this end table pictured, and I have an 18” sonic brand sub I am using to rob the parts from.
When I look at the cabinet the driver was originally built with, the enclosure size is really small in comparison to the size of the port.
The port starts out 2” high x the width of the cabinet travels across the top, then gets wider down the side and then wider still on the bottom.
Basically like a tuba.
The dimensions of the cabinet I want to build are going to be 2’x2’x2’
I found a really cool video on the build it’s very simple and very strong.

It looks like who ever made this video really knows there stuff.
The specs they show are [email protected] / corner port @38Hz [Frei zum Nachbau] Thomann the box Speaker 18-500/8-A Pläne & Konstrukte | Lautsprecherforum.eu
The sub I’m building is for home theater and I obviously want the deepest base possible.
I was hoping for around 20hz if that’s possible.
I am surprised that the ports are only 12” long, about half the length of the cabinet.
What would happen if I were to lengthen the ports?
I am planning have the driver firing at the ground, what should that distance be?
I have a Crown XLS 402 amp I plan to use to power it.
Any advice is most appreciated.

 

[Da Wiz]

You can get a 12-inch subwoofer from Hsu Research that is "flat" down to 12 Hz... under $1000 (it is flat to 10 Hz in my room, but that's the lowest test tone I have, it might do 8 Hz. There is NO SOUND from the subwoofer at 10 Hz, it feels like somebody turned-on a fan when reproducing 10 Hz though---lots of WIND created. 16 Hz is easily audible though--and room shaking. The 15-inch Hsu subwoofer is also flat to well below 16 Hz with better power and control than the 12-inch model (slightly over $1000 as I recall). Both of these subs have 2 ports and they come with solid-rubber port plugs. You can leave 2 ports open, close 1 port with a plug and leave 1 open (my favorite for deep bass and low-ish distortion). Or plug both ports that limits deep bass but also lowers distortion and sounds best when listening to music.

20 Hz is not much of a stretch for an 18-inch driver unless it is not a particularly suitable driver for a subwoofer. And looking at the 2 drivers shown in the "still" image for the video... those are SHORT EXCURSION bass drivers not well-suited for a "modern" subwoofer for home theater. So if your 18-inch driver(s) really have surrounds around the edge of the cone that limit travel as much as the surrounds in the image before the video starts, you are barking up the wrong woofer. 18-inch drivers with short throws like that are designed to be horn loaded in high-efficiency enclosures (like 95- to 100-dB per 1 watt of power). They are NOT designed produce low frequencies below 40 Hz or so--at least not as part of their design-intent. If your woofer(s) has a large radiused and flexible surround that allows an inch of "inward" travel and another inch of "outward" travel, then you have an appropriate woofer for a modern subwoofer design that requires a "long throw" woofer to produce low frequencies with though air moved to be suitable for frequencies well below 20 Hz.

The opening of The Edge of Tomorrow (Tom Cruise, Emily Blunt) has a sub-bass effect that starts at around 40 Hz and descends all the way down to 10 Hz. So yes, there is low bass lower than 20 Hz on movie soundtracks.

Another way to be sure your 18-inch subwoofer WILL NOT do 20 Hz or lower (besides not having a long-throw driver), is to put the 18-inch driver in an enclosure that is too small to support 20 Hz and lower frequencies. Porting can overcome some of the limits of a too-small enclosure, but porting raises distortion (unavoidable) in the process of supporting deeper bass.

 

[BP1Fanatic]

The wife and I watched Edge Of Tomorrow a couple of days ago. That opening bass is off the hook!

 

[NBPk402]

The wife and I watched Edge Of Tomorrow a couple of days ago. That opening bass is off the hook!

Be careful, I have heard of people frying their subs with the intro.