Axis 15" prototype box build

[emilimo701 10+ year member]

I've never built a box before. Building a box for a $400 driver should be done nice, so building a prototype seemed like a good idea -- especially if I wanted to construct the final product with some nice birch (black/"onyx" stain) that could run up to $200, or possibly more.

I'm building the first run out of particle board. Why particle board? Why not use MDF when the first run could possibly come out good enough to keep? Well, besides the obvious factor of cost, I was not particularly sold on MDF over particleboard. I know. it's common knowledge that MDF is the better material. All the big boys use it. But where's the proof? The flooring grade particleboard I got felt stiffer than the MDF, and was lighter. Sure particle board doesn't like water, but neither does fiberboard. Finally, I was very turned off by the MDF at both Lowe's and Home Depot. Many of the sheets had frayed ends that gave it an effect of cardboard. STILL, I did not want to fall victim to my own perceptions. So I went on the internet for about an hour trying to glean as much dirt as I could on particleboard, and found nothing more than anecdotal evidence and unsupported arguments. So particleboard it is for the prototype; if something goes wrong then I guess I will have learned my lesson.

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After hours upon hours of obsessive deliberating, I settled on 4.2 cubic feet, tuned to 22 Hz. That volume was the max recommended by Audiopulse (who I'd actually trust more than other manufacturer's suggestions), while 22 Hz is the driver's resonant frequency. It's natural to tune at the driver's Fs because it has the perfect QTC of .40 for a butterworth alignment (4.2 cubes is slightly larger than what butterworth alignment calls for, however).

What I'm looking to get out of the finished product is a system for tailgating with a fairly flat frequency response (IN OPEN AIR) to 30 Hz, and −3db extension into the mid- to low-20s. If I do everything right, this goal should definitely be satisfied.

Not many drivers have such a low Fs, and even then people still tend not to tune so low. I realized I had to do a lot of research and thinking on my own.

For modeling, I used WinISD Pro Alpha extensively. I did some checking with calculators from websites such as cerstereo.com, bcae1.com, ajdesigner, and a couple others that I may have forgotten. Luckily, most calculators agreed within about 1 inch of low long the port should be. Convinced, I drew up a design, starting over a few times until settling on the one captured above.

My only restriction was that this had to fit into a FUTURE car. I therefore did not have any exact dimensions. But at 38" wide, it should be able to fit into 95% of SUVs and station wagons. at 25.5" deep, it should be able to fit into most cargo areas, save for compact hatchbacks or small SUVs like the Tucson.

I really did not want the port to span more than three edges. Because of the restriction in width, I realized that the more square I made the design, the more "edge" the port needed. I quit trying to work a miracle and reluctantly added the last 180-degree turn behind the front baffle. I'm hoping it is not too close to the driver. For aesthetic purposes, I'd like not to move Miss Axis any further to the left.

People don't often post the specs of their boxes. I figured I would anyway.

Dimensions:

height: 17.5"

width: 38"

depth: 25.5"

net volume, after displacement: ~4.2 ft^3

port height: 16"

port width: 3.5"

physical port length: 68.2"

effective port length: ~70"

estimated tuning frequency: 21.8 Hz

Going to start piecing the box together tonight/tomorrow.

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[FarrisAudio 10+ year member]

lighter wood means less dense. less dense=more flex. Flexin is cool, but not on your speaker box.

 

[RAM_Designs 5,000+ posts]

lighter wood means less dense. less dense=more flex. Flexin is cool, but not on your speaker box.

Density has nothing to do with flex. Quality plywood is much more rigid and less dense than MDF, and will naturally flex less.

 

[RAM_Designs 5,000+ posts]

As far as the box looks, I'd be weary of that internal port opening being so close to the speaker. I'd slide it over as far to the left as you can.

 

[emilimo701 10+ year member]

As far as the box looks, I'd be weary of that internal port opening being so close to the speaker. I'd slide it over as far to the left as you can.

Okay thanks; I think I will do just that. I have not cut the opening yet. Would 4 inches over be enough?

 

[emilimo701 10+ year member]

lighter wood means less dense. less dense=more flex. Flexin is cool, but not on your speaker box.

In my reading over the past few weeks, this is how I have come to understand it: you don't want the box to flex (resonate). Stiffening the material raises its resonant frequency, and increasing the density of flexible material lowers it. For subwoofers, it is much more practical to get the resonant frequency of the box material above the the woofer's play band than get it below it. Therefore, the stiffer and less dense the material, the better. I'm not saying that particle board is superior to MDF, I just wanted to try it before I knocked it

 

[emilimo701 10+ year member]

Ah shet. Where should I put the wire terminal? Didn't think of this in my sketch.

 

[supermaxx123 10+ year member]

just make sure your enclosure is braced and you won't have a problem, seeing as this is a pretty big enclosure you would need bracing. With a port that long i'd also be worried of resonating in the port so i would brace the port as well. The terminal can go anywhere you'd like, preferably on the side closest to the sub. make sure it's airtight. Double up on your front baffle won't hurt either.

 

[supermaxx123 10+ year member]

Also don't expect a flat response from your enclosure as the programs you used to model them will not take into consideration the cabin gain which will make a big difference, it might work to your advantage though and it's not something a nice eq can't fix //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

My enclosure is tuned to 37hz yet is loudest at 32hz, and i had very weak bass at around 60hz all due to the cabin.

Overall I'm sure you'll be impressed with your enclosure, I can't stress bracing enough!

 

[RAM_Designs 5,000+ posts]

Also don't expect a flat response from your enclosure as the programs you used to model them will not take into consideration the cabin gain which will make a big difference, it might work to your advantage though and it's not something a nice eq can't fix //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gifMy enclosure is tuned to 37hz yet is loudest at 32hz, and i had very weak bass at around 60hz all due to the cabin.

Overall I'm sure you'll be impressed with your enclosure, I can't stress bracing enough!

And it changes a bunch from one vehicle to another. I was tuned at 32hz in my Dodge 4-door truck and peaked at 57hz on the meter. Granted, I was only 3db down at 35hz which actually sounded pretty smooth to the ear.

 

[emilimo701 10+ year member]

just make sure your enclosure is braced and you won't have a problem, seeing as this is a pretty big enclosure you would need bracing. With a port that long i'd also be worried of resonating in the port so i would brace the port as well. The terminal can go anywhere you'd like, preferably on the side closest to the sub. make sure it's airtight. Double up on your front baffle won't hurt either.

Yeah, I am not going to glue-seal the box immediately. One of my goals was to not use bracing, then open it back up and install bracing and see if I notice any difference in response/noise/flex/box-integrity/whatever. Oh and the front baffle will be doubled at 1.5 inches total.

 

[emilimo701 10+ year member]

Also don't expect a flat response from your enclosure as the programs you used to model them will not take into consideration the cabin gain which will make a big difference, it might work to your advantage though and it's not something a nice eq can't fix //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gifMy enclosure is tuned to 37hz yet is loudest at 32hz, and i had very weak bass at around 60hz all due to the cabin.

Overall I'm sure you'll be impressed with your enclosure, I can't stress bracing enough!

This box won't really be listened to in a car -- for tailgating only!

 

[supermaxx123 10+ year member]

Yeah, I am not going to glue-seal the box immediately. One of my goals was to not use bracing, then open it back up and install bracing and see if I notice any difference in response/noise/flex/box-integrity/whatever. Oh and the front baffle will be doubled at 1.5 inches total.

If you have that much time haha. the bracing helps a lot.