Building a Box

im going to attempt to make a custom box for my friend. im thinking of laying wood down for the inner layer, and fiberglass on the outer, and wrap it in some soft material like every box has. any tips on making it? does it matter where the port air holes are? shape? size?:confused:

When building a box, theres lots to consder, the overall size for a start, the design (shape) you want it, the material, and the most important, the internal volume. Do you have the spec of the sub in question? Post up the make and model number, so i can have a look for you. Maybe i could design one for you, but i'll need info such as recommended internal volume(s), sub displacement, available height, width, depth oh and port length and diameter.

Heres a picture of mine that i built over 3 years ago and its still going strong. It houses a JL Audio 12W6 and is 2.0 CuFt and has a port length of 9 inches dia of 3 inches. The design of it is based on the MTX V80, a 8 inch sub which packs a hell of a punch and rated at 400 watts, particially to do with the design of the box. It has no side which have the same length, therefore the sound does not bounce and cancel itself out.

what did you make the box out of? im thinking of building it with wood and fiberglass/bondo to fill in the edges so no air will escape. im going to make one for my friend that will get 2 12"s. ill tell you what kind and what kind of frequency to do when he gets them. doesnt the frequency decide what kind of box is better: ported, bandpass, sealed?

Most people build boxes out of MDF, including mine which I think is 3/4" thick .. Then possibly pad the inside of it and carpet the outside.. Mine turned out pretty nice I'll take pics when I get my camera.

MDF? that would be wood am i right?

Yep, wood.. Medium Density Fiberboard I think..

Make sure you get the specs for the subs and build the box around those specs. I must agree totally with P11GT....he really knows his stuff...I am new to this but its exactly what I learned when I built my box....

MDF = medium density fibreboard, like frogg said, 3/4 inch or 18mm is best, then you need some self taping screws, 1.5 inch does fine, wood glue, silicone sealer, port, if required, and temrinal. You can fill the inside with what i call, wadding, especially in sealed boxes, this fools the sub making it think that the internal volume is larger than it is. And to finish the outside, you need some strong spray glue, contact adhesive and some backless accoustic carpet of your choice.

Get the spec, i'll have a go. Did i say i needed the sub displacement aswell???

i built a box back in my day for 2 rf 15s. i made the box using fiberboard, then used some kind of bondo to seal it. i thought fiberglass was cool so i put that over the subs. then i covered it all w/ some heavy duty carpet. the only things i would repeat from this experience was the board and carpet. i disregarded specs for the subs and the subs sounded shitty (maybe it was also because i had a pyramid amp:( ). i've since learned from my mistakes.
take p11gt's advice. from what i know, i know that he knows a lot more than me, and it seems most of us when it comes to this subject.

http://www.mtx.com/caraudio/education/ :D

good site to learn how big box needs to be and all that. self-taping screws, are those the ones that are just jagged on the sides so it sticks really well? what did you use for "wadding" the sealed box. where can i get the terminal and port? :confused:

oh ya i forgot, how did you cut out the hole where the subs are seated? i dont have one of those machines to cut perfect holes for the subs. also, do you seal the sub to the box so they cant be taken out, but no air can go inside?

To cut the whole I use a jigsaw and take my time. If you take your time you'll do fine just make sure your circle is right, look how deep the inside subs walls are and thats how big the circle is. Don't make the mistake I did the first time I made a box and think "hey, twelve inch sub twelve inch hole." forgot i had to screw it in, but i've gotten a lot better since then. You can get all the stuff you need from either Crutchfield or your local car audio shop. Make sure the subs sound good ported, i prefer sealed boxes but thats just my taste (it has a tighter/ higher bass compared to ported). If you're not sure about the screws just got to the hardware shop and look for self-taping screws, it's written on the box

Yep, all that Kickercarg20 said.

Wheres the model and spec for this sub anyway?????

Self taping screws are those which have a pointed end and dont necessaraly need a pilot hole, but my advice, when screwing into MDF, its always best to drill a pilot hole as MDF can split and often does, especially if you over-tighten the screw, be warned!!!
The port and terminal can be bought from most car audio shop. If your having a real hard time grasping all this, you should be able to buy a nice pre-built box, ready carpeted and all you need do is to screw in the sub.
To find the right diameter hole required, just turn the sub over and look at the inner lip, judge what the diameter is and make sure you leave enough room for it to sit on the surface of the MDF. Use a piece of latt (strip of wood) halve the diameter to find the radius, and bang in a couple of nails in the latt for that radius. Then centre one nail and use the other to score a circle (like a geometry compass) on the MDF for the hole to be cut.
The wadding can be bought from most fabric shops. Its what they use in some cushions or like what they use in padded jacket. Its not too disimilar to cotton wool, but obviously made from a man made fabric and comes off the roll. There are many thicknesses but any will do as you need lots for a sealed enclosure. All you need to do is then pack it into the box really solidly, so you just leave enough room for the sub to fit into.
Sealed enclosure give tight accurate bass which requires a lot of power to drive it. Ported enclosure gives harder to control bass, but more rumble and SPL. When porting, its best to fit the port on the same side as the sub, dispite what diagrams may show, as the port is the main reason as to why theres more SPL.

P11GT,

Is there any specific type of carpet that you recommend? Also, if I went to a fabric shop, is there a specific name for the padding you mentioned?

Thanks alot !

Originally posted by frogg
? Also, if I went to a fabric shop, is there a specific name for the padding you mentioned?

It's called PolyFil. Spelling might be wrong, but they sell it in clear see-through bags and/or by bulk depending on which fabric store you go to.

About how much would be needed for a sealed box w/ 2 12's?

The general idea is to pack the box full of the wadding, its hard to say how much, but basically, right to the top. It seems like your taking up any air space with this stuff, but beleive me, thats what youre supposed to do. What i was told was to fill it, then try it, possibly try different amounts aswell. Basically, trial and error.

For lack of sleep and lack of more technical detail, the PolyFil actually makes the woofer think that it is in a larger sized box, therefore creating a cleaner, more defined bass response.

Almost like a resonator on an exhaust. Almost. Best comparison I could come up with. Without one, the exhaust has a buzzing sound, like a large ass bee buzzing around your head. With the resonator, the exhaust note is deep, mellow, and to some, me included, soothing to the ear.

There are others who could explain this in more detail, but I thought that would be a good start.

The polyfil actually slows down the sound waves, so that, what NismoPC said, makes it think there's a bigger box. Also, talking about what to make enclosures out of, I saw this picture in Sound Domain. its a box made out of plexi-glass. Check it out.

Here's the rear view. oh, and for the polyfil, you should use about 1 to 1 1/2 pounds of polyfil per cubic foot of box volume

Wow thats a cool box.
Only reason I wouldnt use Plexi is because it scratches too easy and costs too much.

Pexiglass boxes are near impossible to get right. They vibrate like bitch even if you do it right. And you're right they are expensive and hard to cut.

yeah, it is more flash than funtion, but it does look really cool.

im getting 2 sony xplod 10"s...

http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1288338321

THE DETAILS
10" High-rigidity compound Polypropylene cone
600W Maximum Input Power
Single 4-layer 4-ohm voice coils
Durable Santoprene rubber surround
Stroke Stabilizer
Double damper suspension
Gold-plated binding posts
Optimized for small enclosures

PRODUCT SPECIFICATION
Maximum Input Power -- 600 watts
Rated Input Power -- 150 watts
Impedance -- 4 ohms
Sensitivity -- 88 dB/W/m
Frequency Response -- 25 - 2,800 Hz

DIMENSIONS
Thiele/Small Parameters
Fs 26.6 Hz
Qts 0.43
Vas 1.75 ft.
Xmax 0.17 in.
Recommended enclosure size 0.7 ft. sealed


for the recommended enclosure size, does that mean for both or just one? isnt that kind of small? 0.7 foot? and so i should just buy a 300 watt amp that is bridged twice? im planning to make a wedge box for the subs.

0.7 CuFt sounds about right.

If you want to use one box, then i suggest you partition it so that each sub has it own air space. Have a look at some of these designs, and if you want, i can supply you with the full details, better diagrams and measurements for you to build it yourself.

I still need the sub displacement to calculate accurately, the correct CuFt for each sub.

i want to build a wedge box, like diagram 2, except i want the subs on the angled part of the box. how would i find the sub displacement? i check the sony xplod site and it didnt say anything about sub displacement. can you give me the measurements of each side? thanks. :D

what kind of amp should i get? should i strictly get an amp that puts out 300 watts? how do i know how much power each sub will get? is there a way to give more/less power to a sub or speaker from the amp? or is it divided evenly? what is the difference between 2 channel/4 channel? and whats the difference between 2 OHMS or 4 OHMS? sorry for all the questions... but dont want to blow my subs? oh ya, and do you think overheating will become a problem?

Right, first things first, worry about the amp later.

Ive no problems designing the box and getting all the sizes for you, hell, i can even tell you how big to cut each bit of wood and put it together like a jigsaw, but the main thing you gotta remember is, it may look really small in your boot. This is because of them being only 10 inch and also with the box only being 0.7 CuFt for each sub. The only way to find the displacement is to have a look at the spec sheet found in the box. I dont know if you could ask the retailer to have a look for you, or wait till you buy them. But it should be in there. Get me the exact model number..... theres no guarentee, but i could ask around here and try to find out for you. If all else fails, then i could use an estimate, which wont effect the performance, not that you could hear anyway, but its best to include some sort of figure.

Right, about the amp, i would suggest you join the subs in series, i.e. daisy chain, so you drop the impedence down to 2 ohms, then buy a 2CH amp that can handle 2 ohms and puts out around 100 watts RMS at 2 ohms Bridged. That'll be plenty of power for them. Dont just take my advice on this, ask around, suggest what ive said, and let me know what feedback you get. Never go for amps that claim 200, or 400, or 600 watts max, cos theyre just bullshit figures, go for the RMS value, it a true rating of power.

Lastly, i need some dimensions of your boot/trunk, where its gonna sit. I take it that i'll sit directly behind the rear seats, in the middle of your boot/trunk. Also, is it a hatch or saloon? Make sure you take into consideration, any parcel shelf mounted speakers which will come down when the boot/trunk is closed, therefore reducing the available height. Ive drawn a quick sketch of the measurements i'll need.

Originally posted by P11GT
Right, first things first, worry about the amp later.

Ive no problems designing the box and getting all the sizes for you, hell, i can even tell you how big to cut each bit of wood and put it together like a jigsaw, but the main thing you gotta remember is, it may look really small in your boot. This is because of them being only 10 inch and also with the box only being 0.7 CuFt for each sub. The only way to find the displacement is to have a look at the spec sheet found in the box. I dont know if you could ask the retailer to have a look for you, or wait till you buy them. But it should be in there. Get me the exact model number..... theres no guarentee, but i could ask around here and try to find out for you. If all else fails, then i could use an estimate, which wont effect the performance, not that you could hear anyway, but its best to include some sort of figure.

Right, about the amp, i would suggest you join the subs in series, i.e. daisy chain, so you drop the impedence down to 2 ohms, then buy a 2CH amp that can handle 2 ohms and puts out around 100 watts RMS at 2 ohms Bridged. That'll be plenty of power for them. Dont just take my advice on this, ask around, suggest what ive said, and let me know what feedback you get. Never go for amps that claim 200, or 400, or 600 watts max, cos theyre just bullshit figures, go for the RMS value, it a true rating of power.

Lastly, i need some dimensions of your boot/trunk, where its gonna sit. I take it that i'll sit directly behind the rear seats, in the middle of your boot/trunk. Also, is it a hatch or saloon? Make sure you take into consideration, any parcel shelf mounted speakers which will come down when the boot/trunk is closed, therefore reducing the available height. Ive drawn a quick sketch of the measurements i'll need.

ill tell you the exact sub displacement when i get the subs and the exact model # and all that when i get them. what do you mean join the sub in series? do you mean i should get a Sony Xplod amp? what is impedence? RMS is how much power is sent on a constant basis right? bridged means how many subs/speakers the amp can be hooked up to? it is a 2 door 200sx and ill get you the dimensions when i get it back, its in the shop right now. parcel mounted speakers are what?

oh and btw, can you redo the picture? the words are blurry and cant read what they say. thanks. :D

when you say "2 OHMS BRIDGED", does that mean that both subs combined puts out only 100 watts RMS? so 50 for each sub? Channels means how many different sub/speakers they can split the power to?


would something like this be ok for an amp?

http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=1289678061

That Kenwood amp will do nicely:D Good choice. The RMS value is what power the amp is capable of producing. You can use any amp on any speaker as long as the speakers can handle what the amps can give.

That is 2 Channel, so what you do is follow the instructions given and use it bridged, i.e. it could be that you use the left channel positive and the right channel negative to achieve this. It will show you on the amp.

To lower the ohms to 2, you will need to connect one positive of one sub to the negative of the other sub, thus leaving you with one positive, and one negative at each end. So the power goes from the amp (+)into sub1(+), then sub1 (-) into sub2 (+) and sub2 (-) back to the amp (-). This is what you call "Series" (i'll do another diagram for this)

Parcel shelf (rear deck) mounted speaker are what you would class as rear speakers. Basically, i need to know if they stick into your boot space especially when its closed, thus reducing the available height, thats all. All these things have to be considered when making a box, so you know its gonna fit.

heres how to connect in Series. Dont use the exact terminals as ive stated, the terminals used to bridge the amp will be mark clearly on the amp, just follow how ive wired the subs, then you'll be left with one positive and one negative at each side which connect to the corresponding amp terminals.

ill get the specs of my trunk back to you when i get the car back, but just wondering, does it really matter? cause i want to put the subs into my future G20. will i have to make a new box for that car? thanks for all the help so far, youve been a great help :D

I think the box will be fairly small anyway, so if it'll fit into the 200sx, it should go into the G20 no problem, dont worry about it. When ive designed it, i'll give you an overall size, so you can judge for yourself.

There are however, serveral tools, you'll need. This is what i have and would use.

Wood saw
Cordless drill/screw driver
Sander, flat bed or orbital
Jigsaw
and if possible, a power plainer.

The power plainer helps you get the correct angles when joining the sloping side to the box.

and dont forget a good pencil, ruler and tape measure.;)

Originally posted by P11GT
I think the box will be fairly small anyway, so if it'll fit into the 200sx, it should go into the G20 no problem, dont worry about it. When ive designed it, i'll give you an overall size, so you can judge for yourself.

There are however, serveral tools, you'll need. This is what i have and would use.

Wood saw
Cordless drill/screw driver
Sander, flat bed or orbital
Jigsaw
and if possible, a power plainer.

The power plainer helps you get the correct angles when joining the sloping side to the box.

and dont forget a good pencil, ruler and tape measure.;)

i have a wood saw, drill (not cordless though), jigsaw, and what is a power plainer?

A plainer is used to take thin slices of wood off, similar to what a shaver does, so a power plainer is just mains powered and therefore easier to use.

heres another

so i this picture, the guys putting an angle on the edge of the wood, this is what you'll need to do for some parts of the box, so find or lend a tool to do what he's doing.

i will need the sander for smoothening out the edges right? i dont have a sander, but i can sand by hand.

yeah, sure thing, you'll need several grades though, from rough to smooth. Help you build up your forearms.;)

Thiele/Small Parameters
Fs 26.6 Hz
Qts 0.43
Vas 1.75 ft.
Xmax 0.17 in.
Recommended enclosure size 0.7 ft. sealed

for the specifications, what does all of them mean? Fs, Qts, Vas, Xmax. and for the recommended enclosure size, do they mean the entire volume of the box? thats damn small.

To be honest, i dont know what all that means, the only figures you need be concerned with are:

sensitivity, it could be 89% or 90% or 91%, this gives you the efficiency of the sub, the higher the value the better.

power handling, Watts RMS/Max but then again, you cant always rely on Maximum value cos some manufacturers do state false values.

and Xmax, which is the ammount of excursion of the woofer, giving an idea of how much it moves. Note, the more it moves, the more power required to drive it, generally speaking.

If you look beyond these values, then thats when you cross into Pro Competition equipment, where subs will cost a hell of a lot more than most people would spend, and the sound produced would be used for competitions and sound different to your everyday listening habbits.

I just need the boot sizes and the displacement when you get them, and thats all i need. With a little help using my maths skills, i can calculate the exact box size, then break down the volume into areas which will give me the sizes of each panel of wood used to put it together. Its simple when you know how, but this is something ive learnt over the space of 5 years building boxes for myself, friends and clients.

i have the spec of my trunk, here they are...

available height between trunk floor and parcel speaker = 18 inches

distance between seat and speaker = 12 inches

available width clearing struts and hindges = 40 inches

do you want me to go ahead and design the box with an estimated value for displacement or wait till you get the proper value?? I can take an average displacement of a ten inch and use that. I think there will be very little in it, and there'll be no difference in quality.

hm, let me wait until i get the subs, probably a week or so. not too long :D

ok, i'll start to draw up some diagrams, ready for the measurement figures, this should save some time.

Here you go Aznvirus, the first part of your box.

wait wait, i wanted a wedge box, something like this, sorry for the confusion... hope its not TOO much trouble to redesign it :D

http://www.mtx.com/caraudio/images/wedgeHWWD.gif

thats what it is man!!!!

heh, that is a wedged box :)

Originally posted by frogg
heh, that is a wedged box :)

Thanks Frogg, thats what i intended it to be. It just could be that i havent exagerated the slope enough on the diagram, but it is a wedged box, with the subs mounted on the sloping side as requested.

oh ok, just checking, it looks like its wedged on both sides :p

Originally posted by P11GT
Here you go Aznvirus, the first part of your box.

where is sides E,F,G?

see diagram:D

Originally posted by P11GT
see diagram:D

oh i get it, so both subs are going to have their own air space, didnt know there was a piece hidden inside the box. :D

yep, gotta keep things right.:D

cool, im sending the check for the subs, so ill receive it within 3-5 days. :D

btw, why is bridging better then just normal? and can you tell the difference between 2 ohms and 4 ohms? :confused:

in theory, by going down in ohmage, you can gain dB, i.e. 8 ohm sub would produce, say, 140 dB but if you then run it at 4 ohms, it will be 143 dB, twice as loud as before!! this is what ive been told, thats why i wire the subs in series and bridge the amp providing it is a 2ch amp. After experimenting with the wiring in subs, ive found that series gives the best result, but it does depend on the equipment.

BTW, check to see if you can purchase your MDF board in 18mm (3/4 inch) and what size the sheet comes in. Its best to buy a full 8 x 4 Ft sheet, cos it works out cheaper. You wont need all of it, but it'll do for spare. The reason i ask, is so that i can give you a plan of the wood, and how to cut each panel, so you get the most out of the MDF sheet.

ok ill go check the hardware store for 3/4 in. MDF. btw, why do i need the contact adhesive, those are just strips of adhesive tape right? is it for extra "stickyness" of the accoustic carpet?

nope, contact adhesive is a glue, but what you do is, you cover both surfaces, allow it to go tacky, then press them together. Its the same stuff they use on self sealing envelopes, and is really strong when done correctly. It doesnt absorb into the acoustic carpet like some glues can, so it wont effect the finish, thats why people use it.

Hey, P11GT, I was reading that the optimal design for a sub box is spherical. Something about standing waves or somethin? Anyway, you ever think of takin it on as a project?

Hey, anythings possible. Making a spherical sub shouldnt be too hard, i think the idea is that the sound waves just bounce around and dont cause them to cancel waves coming from the sub. Good idea. I'll think about it:D