darms

iTrader: (5)

Thinking of removing my spare wheel and having a custom sub enclosure built.

Maybe a fiber class mould of the area.

Any one interesting/view on this. (Group buy??)

ptholt

I quite fancy a bit of this.

been looking at doing it for a while, but never heard or seen any results.

Kingsize K2

My car is going in, in a couple of weeks, to have two 12"s fitted in the boot. One either side facing eachother. I am getting boxes made between the rear of the car and the wheel arch on both sides.

Not sure that if I get a flat I will be able to drive home on a 12" Sub

necromax

Won't you get phase issues with them facing each other?

Kingsize K2

Now this, is something I have not yet thought about

Tell me more!

necromax

Well, I'm no expert, but my understanding is you shouldn't let subs face each other. I had the same idea of placing them nice and neatly at each side, but was advised that they would either cancel each other out, or possibly even destroy each other if enough power was passed through them. All to do with compression waves I believe, and of course the frequency of them being as they will all be bass tones under 120Hz. Speak to either Chiark, John Banks or you may even see my mate, Globbits who has recently joined the ranks of Subaru ownership with his aquisition of a Legacy. Either of these guys will provide are far better explanation

nom

Well, it's a little more complicated than that, as it usually is with noise. Depending on a load of different variables (including the actual sub used), firing them at each other can actually increase the sound level. Although usually only at a minimum range of frequencies, so unless you like one-note boomings...

It's a good idea on the whole to get the two subs firing in the same plane, preferably in their own seperate boxes (makes the maths much easier & so the result much more predictable). But obviously feel free to make life as complicated as you feel like

necromax

Cheers Nom, I knew one of the in house experts would jump in

Kingsize K2

SO,

Based on Nom's advise it certainly wouldn't damage the speaker and could even provide more bass

Firing in the "same plane" though? Does having them opposite eachother equate to this

nom

Start thinking about waves & cancellations.

If the two speakers are firing at each other, at one frequency the waves will entirely cancel each other out, giving no bass at all but using a lot of power to produce it. At another frequency, they will get to the same place at the same time and add, making a vast amount of noise, but only at the one frequency (and harmonics of it). Generally speaking, unless you are going for SPL competitions or like your ears to bleed, this isn't a good thing. Music typically doesn't sound too good if you like to hear what's going on as bass tends to be all be on the same note.

If the two speakers are firing in the same plane (as in pointing in the same direction and with the front of the speakers at the same level), they will always add together (although not quite as noticeably) and will have no additional increases/drop-outs in sound level at frequencies other than those dictated by the speaker, the box it is housed in and those of the boot.

There are quite enough complications with subwoofers before pointing them at each other IMHO! If you want to get as much SPL as possible but be pretty sure of a good result, place each sub in it's own enclosure (or both subs in one which is split into two with a board or something) with both in the same plane and vent the things (bass reflex style). There are programs out there that allow you to enter all of the details of the sub that you are going to use and then give you an internal volume for the box to be made - you can specify what sort of box (sealed, bass-reflex, etc) & usually then have a graph produced that will show you the expected frequency response. Then, you can start fiddling with either high SPL with an uneven frequency response (for loud booming noises) or a quiter, flat response which would sound more musical, but may not have the required power...

Of course you could always buy a well-made box & have done with it. One company out there (I've forgotten who they are again but they're somewhere in Surrey(?)) makes a box - apparently well-made - which fits to the side of the boot in the scoob. I think they do one for a single sub, and one for two. They give the enclosure size, so then you just need to find a sub which is suitable for that enclosure size.

Hope I've muddled everyone now

CallumW

I little caution flag though...If you are planning to dump a lot of power though a couple of mid-range subs, then porting the box is probably a bad idea as it may tear the sub diaphrams due to excessive speaker excursion (i.e. it may make them flap about too much).

For the original post, the only thing you really have to worry about when installing a sub in the spare wheelwell, make sure all drainplugs or screw holes are sealed to ensure no moisture gets near the sub.

You can always carry around TyreWeld. If you get a flat, say from a nail, you leave the nail in, inject the foam, drive slow for 5 miles (allows it to coat the entire tyre inside) then pump up your tyre to normal pressure and you should be good for a few days until you get it repaired/replaced.

Kingsize K2

Cheers for all the info re: subs facing eachother - sorry if I have hijacked the thread a little

I am now either sticking two subs in one rear facing box, or looking at getting a custom box on one side of the car that fits them both. Any opinions as to whether two speakers facing sideways in the boot will sound less effective then two sittig directly behind the rear seat??

globbits

From experience, sideways isn't quite as good. I've tried firing them backwards, forwards, upwards, and sideways and, to be honest, sideways is the least good for punchy bass. If you like musical bass, then that's fine - they play nicely and will give some push to the music. But, if you like a good solid thump, either face 'em upwards, or towards the back of the car.

The other thing I can recommend doing is reversing the phase to the subs. Rather than connecting the +'ve on the amp to the +'ve on the sub(s), connect the -'ve on the amp to the +'ve on the subs, and the +'ve on the amp to the -'ve on the subs. This 180' phase-inversion is a poor-man's time-alignment, and will effectively delay the sound to the subs. What you end up with is subs which are kicking in beat with the front speakers, rather than a little delayed 'coz of the distance the bass needs to travel.

Give it a go - you'll be surprised. Necromax will probably agree - if he's ever online! (Why ain'tcha ever on ICQ any more?!)

[Edited by globbits - 1/14/2002 1:18:11 PM]

Kingsize K2

Cheers Globbits! Rear facing, single box w/ two subs, firing out of phase it is to be!

I'll let you know the results

CallumW

Definately agree with globbits on that one.
Facing the sub to the rear of the car makes the boot space act like a bigger box for the subs and gives them a bit of room to "breath" properly....try not to face subs towards a solid object (like the back of the seat)

Most new headunits with subwoofer control can reverse the sub phase with the push of a button.
It may be worth fiddling about with the subs so that one is in phase and the other out. In theory they should cancel each other out, but y'never know.....worth tweaking to see if it works

Callum

[Edited by CallumW - 1/14/2002 5:53:21 PM]

chiark

Callum has hit the nail on the head with car stereo sometimes - forget what "should" and "shouldn't" work, and get tweaking.

Change phases, even when it makes no sense to do so. Sometimes you'll find surprising results. Like when I got the passenger side midbass driver out of phase with respect to the rest of my component system, it sounded better. Checked it twice, and it was definitely out of phase. But I preferred it...

My subs are firing backward and are in-phase. The theory for pointing backwards is that it gives them the most free air to play into...

CallumW

ooh...Just had a thought (it happens...rarely)
If you are having a custom twin sub-box put in, here's an idea for you.
If you're having them rear facing, you can have it so that it has 2 ports at the top of the boxes. (Hold on it get's worse)
What you can then do is cut 2 holes in the rear shelf and have the ports slot through and down into the box. (cover with wire mesh to stop people using them as ashtrays)

You'll need smaller ports (2-2.5") though as it'll be pulling the air from inside the car cabin.

Set it up right though and you'll be knockin' out the eyeballs of anyone sitting in the car


Callum

Kingsize K2

Callum m8,

You make me laugh! I intend on causing eye problems for my back seat passengers as soon as poss

Question is, what exactly has to be cut on the back shelf as I don't want to go cutting holes around the place? And do I join the holes in the box to the holes in the rear shelf by plastic tubing?

Other than that my car it standard. Bar the two amps under the front seats. OK, maybe the exhaust system. And the induction kit. Oops, the in-car phone holder and the wheels...

CallumW

You have several options.
From what I remember from doing a mates speakers in his RB5 rear shelf (I drive not a scoob) the chassis shelf under the cardboard shelf is metal.
Either punch 2 holes in them both so the ports line up and are a tight fit.
Either that or remove the shelf an put in an MDF replacement (should be able to get one from most car hi-fi shops).

The ports can go straight into the box and should cause temporary blindness.

Another option is to remove the rear speakers totally (lets face it, the only time they really get used is when your with the missus in a car park ) and tidy up the holes by using cloth to cover. You can leave it at that as the sound will emminate through the holes or you could set the ports using the speaker holes and into the box.

Either way you can laugh at the people in the car shouting *turn it down*...but not hear what they are saying....from 3 feet away

globbits

I'm with nom (and necromax, since he plugged me on this. You _can_ get away with having subs facing each other, but you'll suffer with flat spots in the bass. If you're looking for thumpy bass, then you might be lucky if you face 'em together. But, you're more likely to have a very weird sound. If you're looking for melodic bass then forget facing the subs together - it'll just be a disappointment.

If you want a lot of heavy bass, build one box, for both speakers, where the enclosure size is the minimum recommended by the manufacturer. (Well, twice the minimum, since you've got two subs!) Make sure all the joins are sealed with silicone sealant and then really fill it with loft insulation, to stop resonance. The small enclosure size and well-sealed enclosure will let the subs really kick.

Oh, and if you want ridiculous bass, try putting a bass port into that enclosure. I can't promise how the sound will go after that, 'coz porting boxes is a bit of a black art. But, if you're lucky, the boom will be heard in the next town

[Edited by globbits - 1/10/2002 12:06:23 PM]