I've been running a sealed box for the last two years or so 1.25 cu ft per chamber. I've always wanted to try a ported box tuned low and finally got to work on one. This is for two Brahma 12" Mk1, 2.5 cu ft @ 30 hz per chamber. I haven't hooked up the subs yet, I plan to do that this weekend, I still need to put the finishing touches on it.

A pic of one of the subs and the old sealed box.



New box construction 1







Carpeting this thing was a pain, my first time doing this, lots of rookie mistakes but in the end I think it turned out ok.




T bolts premounted...


Just thought I'd share.

 

That is a huge box!!!! Look good though. Are you going to get a trailer to keep it in?

 

Yeah really, that thing is massive.

 

I got a JL system in my 4Runner. If your putting it in a ride that has back glass and not a trunk I say it should pound.

 

It is huge!!! I'm gonna break my back getting it in the ride. I have a 97 4runner limited with a 130 lb box in it right now.... I imagine this thing would weigh close to 160ish. All in fun though.

 

Oh yes. Especially at traffic lights.

 

you may want a higher tuning freq after you get it installed. I would tell you to play with tuning a bit but your kinda stuck on the tuning thing all you can do is change internal volume with wood blocks or something now.

out of the last 4 or 5 enclosures I have built I ended up raising the tuning frequency a little on all of them. Whats really interesting is building the thing using computer modeling and then hooking a freq generator to it to check the tuning after its built. Computers do a good job but nature and physics always have the last laugh.

There is nothing quiet harassing a big sub with a mackie 1400i and a freq generator

 

ok i've always wondered, can somebody explain the difference in sound between a ported and sealed box for me?

 

Sealed means it is pretty much air tight, no openings for the air to move in an out of the box. This usually translates to a tight bass response but can take some power to move the speaker at higher volumes because essentially the speaker is moving out and pulling against a vaccum. I like them because they can be smaller and it is a little harder to blow a sub. My opinion.

Ported boxes have some type of opening to allow the bass sound waves to escape from behind the speaker. They are more energy efficient and can produces lower bass notes. BUT, there is a science to tuning them so they sound good. You usually have to design the box for a certain frequency range. You will notice in the pictures above that he has a L-shaped slot that goes from the back of the box to the front. This is part of the design. He probably used a computer program to plug in the speaker characteristics, ie frequency, volume required, etc. and then put in the desired response range and it told him what the box will need to look like to produce that desired performance. All bare woofers include a spec sheet that has the factors that both sealed and ported boxes will need to produce the desired response range. Usually the speaker builder will recommend certain box sizes to get the most out of the driver.

Hope that helps. It is much more technical than my explanation above, but I hope you get the idea.

 

thats perfect. i'll stick with my sealed boxes.
oh yeah, but are there any pros to running 2 subs in the same sealed box, vs separate sealed boxes?

 

The primary disadvantage is if you blow one speaker then it begins to reduce the performance of the single remaining driver. That is the only real problem I can see. Other than that as long as they are both performing well then you are ok because they act in unison.

 

Stoutshady - good looking box!

To expound upon what DavidA said, those driver characteristics are also known as Theile-Small parameters and describe what the sub should do as it operates. There are a TON of box calculators out there and mostly what you do is enter in every TS parameter you can find, look at the EBP to determine box type and volume, then let the puter come up with something, then modify the box to get the appropriate response curve.

Ported boxes have tuning frequencies. The box volume, port area, and port length all influence a box's tuning frequency. Most ported boxes tend to be tuned to about 30hz. What this means is that from about 28hz up (varies with the sub's cms,) the sub box will load the cone of the sub, and you get a good deal of output. However from about 28hz down the port unloads and the sub acts as if in free air. And if you have the volume up and the material being played drops below 28hz, you are going to damage the subs as they over excurt. This is why if you run ported you either need to have a keen ear to listen to the subs or a sub sonic filter.

Across the usable bandwith, ported has a lower power handling than sealed. However at the tuning of the port, the ported box can mechanically increase a subs power handling. This is how Im able to utilize a FULL 8.8kW on 4 L7 12s and not make their cones tear loose from the surround/spider. My box is tuned to 40hz and I burp at 42hz. With the system running wide open, I can play to about 38hz and up to about 85hz. The cool thing is I can do 150s legal on the TL sensor from all frequencies from 39hz to 57hz - ungodly flat for an spl box.

sound of ported Aside from being MUCH louder than their conventional sealed counterparts, a vented box is FAR more effiecient and will play the lower notes louder than a sealed as long as you stay above the vented's tuning. A vented can be made to sound every bit as good as a sealed and then some, its all in the box.

With subs, it's best to divide the subs. This is something I really noticed on the meter. Up to 1dB can be gained by isolating the subs from one another even when there is only one power source and the material is exactly the same!! Also dividing the subs allows you to run multiple amps and not worry as much about the subs fighting each other. Again something you wont hear but a meter most definately will.

Anyone quadding out at a traffic light (unprovoked mind you) should be shot.

 

Nice box work!! Your first looks like a real master piece and your second looks like the monster that's going to eat the master.

Along with the other invaluable information already given, might I suggest lining the boxes' chambers with fiber batting (like that which pillows are made of) applied with some spray/brushed on adhesive to help tune/smooth/clean out your subs' sound ?!?

 

ive never heard of adhering polyfil to the sides of the box before, sounddeadening sure, but usually polyfil is put in loose inside the box.

 

My bad, I meant the cotton-like fiber batting found in low cost pillows.

I got the idea after having to replace a mid range in one of my home speakers after a little party mishap and saw that that was, essentially, what they used.

If gluing it in place is a bit much for you, try stapling it to the insides.

 

Typically you use polyfil to slow down air movement and "fool" the woofer into reacting like it is in a larger box. You two are talking about the same stuff, batting/polyfil, same use. I use polyfil in sealed boxes when they are usually on the small side of what the specs call for. It works well for making them perform and sound better in the smaller boxes.

 

...and use the DynaMat foil sheets on the interior of the port style boxes to eliminate distortion, structural inconsistences and get a crisper response, right ?

p.s. Don't forget to use a good silicone based caulk along all of the joints (as is not evident in pics of either box stoutshady ) to insure a good seal and reduce potential structural vibration.

 

I did, where it was needed... the glue acts as a good sealant where there are no gaps.. but here is another pic



I finally threw it in the trunk this yesterday, first impressions are... it's loud. BUT not that accurate.. I need to listen some more and make some adjustments on HU. It has promise though.

 

Oh and the first box is a prefab.. I wish I can make a box that nice!!! It was made by subzero -- excellent build quality.

 

I was reading somewhere the other day NOT to use silicone based adhesives because some vapor they put off can degrade and destroy foam surrounds on some speakers. I will have to look that up. They recommend Liquid Nails to assemble boxes now. Never heard that before. Weird.