Home Theater Forum and Systems banner

1 - 20 of 88 Posts

·
Registered
Joined
·
162 Posts
Discussion Starter #1 (Edited)
I am starting this thread to highlight some of my new build. The driver will be a Mach 5 MJ-18m.
The enclosure is being constructed with 3/4 fir plywood. It has 3 - 4" ports, two in the front and one in the back. The glue blocks are approximately 1" x1" oak stringers. The front baffle is coupled to the rear baffle with 1" x 1.5" oak stringers. The glue being used is yellow carpenters. You can see I'm not done yet.

Net volume is 12.28 cu. ft.
Tuning frequency is 18.27 Hz

http://www.hometheatershack.com/gallery/index.php?n=1271













 

·
Registered
Joined
·
154 Posts
That looks nice so far! Finally, another box made of plywood and using glue blocks! :) That's a very interesting port configuration you have. Do you plan to put another brace from side to side? Looks like it wouldn't interfere with anything.
 

·
Registered
Joined
·
162 Posts
Discussion Starter #3
Do you plan to put another brace from side to side? Looks like it wouldn't interfere with anything.
It is doable. I had planned on it. There are still 3 pipes at 22 inches to install.

The design changed as I got building. I should have drawn it out to scale on graph paper, but I got ahead of myself. Braces in all 3 dimensions were also going to be holding the pipes in place. I had to move the pipes so that design became inefficient to build. I decided to make the bottom removable. This negated a glued brace for it, although I could have used screws. Somewhere along the line I figured, why not try it with a minimum of braces and see if I notice anything happening?

With 3 large ports the box will not be holding even 1 psi, will it? Then the braces, if installed, would only be preventing panel flop. I have never had a subwoofer before so I suppose my first worry is the whole unit may vibrate or shake, not just individual components.

I think I will try it without too much bracing and add more if I need to. I don't really have that much front to back bracing either, so I'll be watching for problems there too.
 

·
Registered
Joined
·
46 Posts
I'm very interested in this build. I too will be bitting the bullet and constructing a MJ18-M build.

Good luck and things are looking good!

What size AMP did you decide on, 550?
 

·
Registered
Joined
·
162 Posts
Discussion Starter #5
What size AMP did you decide on, 550?
The amp will be a Tapco Juice J800.
It is 800 watts bridged mono into 4 ohms. It is all that I can afford and I do not expect to use it's full power. I will be the guinea pig if it sucks. :jiggy:
 

·
Registered
Joined
·
154 Posts
It is doable. I had planned on it. There are still 3 pipes at 22 inches to install.

The design changed as I got building. I should have drawn it out to scale on graph paper, but I got ahead of myself. Braces in all 3 dimensions were also going to be holding the pipes in place. I had to move the pipes so that design became inefficient to build. I decided to make the bottom removable. This negated a glued brace for it, although I could have used screws. Somewhere along the line I figured, why not try it with a minimum of braces and see if I notice anything happening?

With 3 large ports the box will not be holding even 1 psi, will it? Then the braces, if installed, would only be preventing panel flop. I have never had a subwoofer before so I suppose my first worry is the whole unit may vibrate or shake, not just individual components.

I think I will try it without too much bracing and add more if I need to. I don't really have that much front to back bracing either, so I'll be watching for problems there too.
Experimentation is fun. 90% of the time I don't draw my designs up either, everything is just in my head. I even did the same for a 300 sqare foot deck my wife and I built last spring. Occasionally I will take the time to draw things out on graph paper, if it's got some weird angle.

So if you're not supporting the pipes with braces, how are you supporting them? At 22" long, they will want to come away from the panel to which they're mounted, unless you just use gobs of wood filler or caulk or bondo, or something. True, the air pressure in the box won't be as high as a sealed box. However, remember that the vents are only at their most active right at the tuning frequency, and air movement drops off significantly above and below that point. So at, say, 40Hz, the box will act almost entirely like a sealed box, and at a high enough output level, can resonate just the same as one. You have some mighty large panels there upon which the interior air pressure is acting.

All that said, is not to say that it will sound horrible or even bad. It just may not sound quite so accurate or clean as it might, if you have a lot of panel flex.
 

·
Registered
Joined
·
3,251 Posts
So if you're not supporting the pipes with braces, how are you supporting them? At 22" long, they will want to come away from the panel to which they're mounted, unless you just use gobs of wood filler or caulk or bondo, or something.
If I'm not mistaken (look at picture #5 & 6) ...he's using those brackets :yes:
 

·
Banned
Joined
·
22,577 Posts
Looking forward to seeing the finished build and some measurements.

I don't see that term "EBS" used too often.
 

·
Registered
Joined
·
203 Posts
I don't see that term "EBS" used too often.
Not here on HTS anyway :daydream: Still see it elsewhere

Half the time people refer to their sub as an LLT it is not and is infact an EBS :rolleyesno:

Good looking box, now we need finished photo's, listening impressions and prehaps even graphs
 

·
Registered
Joined
·
162 Posts
Discussion Starter #11
I don't see that term "EBS" used too often.
I am pretty new to subwoofers, all of Home Theater in fact. EBS and LLT are equally new to me as well. I did not know what either meant 2 weeks ago. I did notice that two of the tuning choices inside WinISD are described as EBS 3db or 6db.

After reading the LLT description a couple of times I came to the conclusion that my chosen design was not aiming low enough to meet LLT criteria.
This has a lot to do with my budget on this project. I was up in the air for a long time choosing drivers. For an extra $100 or so I could have procured a driver more suited to LLT, something lending itself to flatter response below 18 Hz.

So for now I will enjoy all I can with an extended bass shelf design using the MJ-18m. If the cash crunch ever lets up around here I can easily upgrade to an IXL-18.2.2. I think that is a better subwoofer for a large and low tuned box, based on playing around in WinISD for only about 1 week. :daydream:
 

·
Registered
Joined
·
1,001 Posts
Your project is gonna produce some prodigious bottom end. The box will probably need more braces. I built a similar sized ported box using an 18" Pro driver and began with 2x4 braces spanning the center of each panel. It wasn't enough bracing. The panels would vibrate at higher dbls at certain frequencies and it was perceptible. At lower volumes it wasn't. Try yours and see.
The IXL 18 2.2 IS an excellent driver. Others have used it and rave about it.
 

·
Premium Member
Joined
·
3,374 Posts
Build looks great, Have you decided on a finish?
 

·
Registered
Joined
·
162 Posts
Discussion Starter #14
Build looks great, Have you decided on a finish?
Yes, I picked out a green paint yesterday. I am trying for an environmentally friendly sub.

The next pictures are before and after I siliconed the port tubes in. I also squeezed a bit of no nails adhesive into a few gaps to see if that product will stand up to subwoofery. I have heard good things about it from my cabinet maker friend.

http://www.hometheatershack.com/forums/attachment.php?attachmentid=11435&stc=1&d=1231353775
http://www.hometheatershack.com/forums/attachment.php?attachmentid=11436&stc=1&d=1231353775
 

Attachments

·
Registered
Joined
·
162 Posts
Discussion Starter #16
The box will probably need more braces. I built a similar sized ported box using an 18" Pro driver and began with 2x4 braces spanning the center of each panel. It wasn't enough bracing.
Now that I look at it some more, I am hoping the actual tubes and their mounts are going to aid in this problem.

I just love lookin down the throat of that sub and seein all the innards and stuff.
Me too. If something loosens up in there, I will definitely hear a rattle or buzz of some sort. That being said, my cabinet maker friend swears by the strength of glue over mechanical fasteners so I have to give his theory a try. I used his shop and he gave me a hand when 4 hands sped up the process. :ponder:
 

·
Registered
Joined
·
46 Posts
Looking good so far! Have you decided on a batting and/or fill? I am still considering these materials myself.

Just ordered my Driver and Sub...I'm right behind you! :)
 

·
Registered
Joined
·
162 Posts
Discussion Starter #19
Have you decided on a batting and/or fill? I am still considering these materials myself.
I am semi allergic to pink fiberglass insulation, so definitely none of that. I don't want to have light fasteners like staples, detaching inside and gumming up the magnet. The inside will be hollow as you see it.

I just do not think I will be that hard to please. I need a sub do dump off the low frequencies present in home theater, so my other speakers don't over excur. Plus the music these days contains tons of low frequency tones, boom boom boom. My regular speakers make tympany sound like tympany, cello sound like cello, and guitar sound like guitar. I expect the sub to make boom boom boom sound like boom boom boom.

I am not trying to oversimplify the subject or make light of the technical details. I just think I am not that hard to please and batting won't help make it better to me. :hide:
 

·
Registered
Joined
·
1,001 Posts
I am not trying to oversimplify the subject or make light of the technical details. I just think I am not that hard to please and batting won't help make it better to me. :hide:
There are some technical considerations regarding acoustics and physics using batting. But since your box and driver combination wasn't an attempt to use a smaller box than optimum for your driver and desired frequency response then the only reason you need batting is to reduce internal reflection. There is even a debate over whether ANY batting is needed. But since egg crate foam is easy to obtain and it's cheap and it's easy to install, I say cover the inside with some foam. It makes a "box" seem a little bit more complicated for those that "don't know anything" and need to be impressed with your sonic accumen.
 
1 - 20 of 88 Posts
Top