25 replies to this topic

[mitch233]

So i have a 15" MTX audio subwoofer with no box at the moment, i want to make my own box out of mdf but i have no idea of good measurements for a subwoofer box.

I was wondering if anyone has any measurements that work well for a 15" subwoofer box lol. I could just buy a pre-made one but i've been told making my own would sound better.

[Matty_Lib]

You'll have to get the specs of the woofer and then work from there. There's a lot of variables affecting how it'll sound (overall volume, port size/length/location etc). Then you can work out what kind of box you want to make.

[mitch233]

Rightio, i'll have to get around to finding those out soon.

[psynthetic]

Worth noting when you decide if you wanna port or not.

Porting is DISTORTION. It also only reinforces a particular frequency at maximum efficiency and can even reduce energy in other frequencies. In a professionally designed system they generally try to use the ports to reinforce things in the range that the speaker starts to loose efficiency.
The length of the port creates a time delay on the out of phase energy from the rear of the sub, the goal being to release it at just the right moment to sum with the energy out the front. The improvement is subjective..

Lots of people are happy with their ported subs and I'm happy for them, but to me it doesn't make sense when you have a dedicated bass speaker to use extra tricks to try and bring out even more. 
For me porting makes sense on an 8" home stereo speaker that doesn't have the low end frequency extension it needs for a satisfactory "thud"
The whole point of (to me) of getting a sub is so you can stop using tricks like porting and go to a sealed system. Considering you've probably spent some good money on your sub + amp if you're running a 15" it seems a shame to possibly compromise it with porting.

 

The plus side of porting is you can get away with a more compact box also, you don't have to worry about the air pressure inside the box creating resistance that will make your gear have to work harder to get the same output. (Some manufacturers actually use this air pressure to provide "braking" for their subs to save money in the amp department)
So, if you do go a sealed box, make sure you have one big enough to handle the displacement. If you go ported, make sure you start with a longer port length than you need and then "tune" it by adjusting the length, you'll just have to listen to what sounds best to you.

 

 

 

[Samwise]

Lots of people are happy with their ported subs and I'm happy for them, but to me it doesn't make sense when you have a dedicated bass speaker to use extra tricks to try and bring out even more. 
For me porting makes sense on an 8" home stereo speaker that doesn't have the low end frequency extension it needs for a satisfactory "thud"
The whole point of (to me) of getting a sub is so you can stop using tricks like porting and go to a sealed system. Considering you've probably spent some good money on your sub + amp if you're running a 15" it seems a shame to possibly compromise it with porting.
 
The plus side of porting is you can get away with a more compact box
 

JL Audio defied this. My 12" came in a huge ported box and it really punches.

[psynthetic]

JL Audio defied this. My 12" came in a huge ported box and it really punches.

I'm not sure I follow? I'm not saying you can't use a big box? Or that porting can't produce a subjectively pleasing result (just that it uses distortion to do it)

Infact, depending on the frequency you want to reinforce you'll be forced into using a certain time delay on your port, which means either a longer/deeper box, OR something called a "folded horn" or "J Bin designs etc, where it's forced to turn corners to achieve an even greater time delay...

[Liberty]

I just replied to your private message mate. I've provided all the links you need so you should be all good. In order for other people to reference and benefit from this topic, here is what the private message included.

 

Sure thing man. I am unsure EXACTLY which one it is as the pics they provide for the sub are from the US (hence it could differ slightly in style and where the logo is placed) but the measurements for the boxes are almost the same. If you have enough time and resources to muck around, make both styles and see which sounds better with the sub in it. You can sell the other one or give it to a mate that might have a similar sub.

 

Anyway, here they are.

 

This one is the one I am pretty sure it is, however it is a slightly smaller box and isn't branded as Thunder, which is what the sub you have is (5515-44) - http://files.mitekus...119347239f3.pdf

 

This one is the other one, it has slightly larger measurements but nothing drastic. I'd make this one first and compare as mentioned (TR5515-44) - http://files.mitekus...620564379b0.pdf

 

Oh, and I'd definitely be going for the vented enclosure over the sealed enclosure. That is if you have enough boot space. You get a much better sound and the sub performs a lot better.

 

Let me know how you go and if you need anything else mate.

[mitch233]

I'll have to get help off some of my friends a little bit as i'm completely new to this haha but i'll look into what you're saying psynthetic.

[allpaw4]

First of all, I have to disagree, a sealed box will always have a smaller size (if the design is any good), which is why most car setups have a sealed box.

There are also 2 main different sorts of ported boxes out there. One is the tuned length port, with a set length of tube placed in the box (and its placement is also key), and the other being some form of bandpass. The idea behind porting is to flatten the frequency line. Tune it so the low points are enhanced, and the high points are lowered. I have seen speaker boxes that have twin ports (and they sounded amazing), but the bloke who built them was a sound engineer, so I figure thats probably out of our range here.

The general rule with a sub box, is the bigger the volume, the better it will sound. But volume is a premium in a vehicle. So bear in mind how much of your boot needs to remain 'usable'.

 

Do a little research and figure out which way you want to go. I would stick with a sealed box for a car personally, but it is purely a personal choice (I like having a boot I can use).

 

There are various computer programs out there that will allow you to input all the data from the subs datasheet (which would have come with it in the box if it was new, or get the model number of the sub and go searching for them on the net). Its worth mentioning that if you get the specs wrong, the design will be wrong, and will not sound as good as it could.

It will then take that data and spit out the optimum box size. There should also be a set of parameters you can change to give it maximum dimensions in the case of a restricted measurement (like the height of the box when it is in the boot). With those measurements, it will likely make one larger than optimal, in exchange for making another smaller.

 

You will more than likely find that you will not get the optimum size box to fit for a 15" sub, and keep anything resembling a usable boot. Expect most of the forward part of your boot to be dedicated sub storage.

 

Looking at those spec sheets, make sure you get a 2 ohm stable amp (preferable 1 ohm stable even, being the sub is only 1.67 ohm). You'll cook the internals of the amp after a while if you dont. Note the max input power on the sub too - 400Wrms. You can feed it with more, but you'll cook the voice coil of the sub over time if you over-power it (ever had a speaker thats scratchy when you push it in and out? thats the varnish flaking off the coil due to excessive heat and scratching on the side of the magnet).

 

I know this sounds like heaps of info to take in, but if you look at the spec sheets and design your audio system by whats written rather than what the sales person is trying to sell you, you will end up with a nice sounding, well balanced system that doesnt give you problems in the future like dead amps and dead speakers.

[psynthetic]

First of all, I have to disagree, a sealed box will always have a smaller size (if the design is any good), which is why most car setups have a sealed box.

 

I reckon all those small box car setups are putting practical sizing ahead of fidelity or using air pressure to make up for poor braking, not because it's "better". It either has sufficient volume for the air that will be displaced or it doesn't. But that's entering into the subjective area of individual setups.

The majority of everything else you said is quite true (or at least true enough for our purposes here today) 

 

- EDIT: I probably shouldn't of made an "absolute" statement like "ported boxes are smaller: as some porting enclosures are quite elaborate and require depth to do their thing rather than just a bit of venting. Fair call.

 

However I just not keen on using tricks like porting. Given the choice (and budget) i'd rather get a full range speaker setup that does the job precisely than a ported setup in ANY home/car application. Big PA systems you don't really get the option of a sealed rig..

 

 

 

 

 

[mitch233]

Haha, lots of information to try learn. Thanks for all this.

Boot space isn't too much of a worry as i don't use it much at all so in that area i'm not too fussed.

For the amp, something like this lhttp://www.alpine.com.au/showItem.php?item_id=269 would do?

i currently have this http://www.alpine.co...php?item_id=272 amp for my speakers.

[Liberty]

The links I gave in my post are from the MTX website. They'd be the ones I follow through and through. Once you start going out of these parameters and measurements, things get complicated and unless you know what you're doing, you could negatively affect the sound.

[CRUISN]

Sealed FTW. I like tight, punchy bass.

 

Theres so many sub box caclulators on the net its ridiculous. Google.

[cre8ive]

I have 3x 12inch subs in the back of my Lib, I have a sealed box made of 16mm MDF and carpeted, very simple to make. the beautiful thing about it is I can crank the crap out of my stereo and it doesnt make to much noise outside of the car. I also have my subs pointing away from me just because cosmetically they look awesome as they flash blue with the bass but would sound much deeper if pointed towards me. But nothing sh!ts me more when tossers pull up next to you and their car is vibrating like crap,   so you can't actually tell how loud my car is because Subaru build brilliant cars because they seal really well. Hope this helps

Cheers Sandy

[psynthetic]

It's not a "brilliant" amplifier.. but it's got the right power ratings and frequency response to do what you want.

It's a little hard to to tell more than the basics because the sub's documentation is super abbreviated and the link to the PDF for the amp you mentioned is in 3 languages and none of them are english so I can't see the amps damping factor, slew rate or anything else.. although i think there is a formula to work out the damping factor of an amp from the impedance values..

Make sure you run it in 2ohms not 4ohms for your sub. (regardless of what one of the two links it was in the end..)  

At 2ohms the RMS output of that amp is more than double the rated RMS input of your sub (almost triple..), this is good because it means you wont send your amp into clipping (which is bad) easily.
It's a bad thing in that if you're reckless and turn your amp up too much it'll trash your sub. (Keep your levels are nominal gain or less)

[mitch233]

Righto, i'm assuming for a brilliant amplifier i'd be looking at more money? lol or just better brand/choice.

Well at least i have a fair bit of stuff to get started with now. Just need some time off work now lol. Thank you heaps.

 

I'll definitely make sure to not blow the amp or the sub haha.

[Liberty]

You will pay more for something better as always. You just gotta find the fine line between what you want in your car and what that amplifier is capable of dealing with. If yours isn't enough, find the best one that suits your budget.

[psynthetic]

Liberty hit the mark, you can get better, but it's all about $$$, also, once you get past a certain point in quality you start paying more for smaller gains.
Alpine is just as good as any other mainstream brand you'll put in there for the most part.

The thing is, if your Subaru has a decent rumble to it i doubt you'll hear any improvement in your sub bass with a "brilliant" amp unless the car is off. ;-)

[mitch233]

Hahaha, makes sense. Yeah money is a little bit of an issue at the moment but i should get there eventually

I'll take some shots as i go with the progress of the box too.

[psynthetic]

That'd be cool.