scooby_si

Just wondered wot woz needed when making yer own box or wotever?
I c on chiarks site he has a pikky of twin subs & amp mounted on a flat carpet type board against the rear seats & this does look pucker but sadly no instructions on how 2 do such a thing on the FAQ as yet I'm thinking about getting a sub but i'm not too keen on just a box jobby
Anyway so basically wana no how 2 mount amp & possibly also sub on mdf etc & wot it takes 2 make it pucker. I've got shed loads of sound deadening if that's any use?
Cheers then peaps
Si

chiark

The pic is of my box that took a week or so to build, although that was an hour a day or so...

It's impossible to give instructions how to make it, as I sort of made 'em up as I went along, but...

Make a template for the front.
Make a template for the base.
Measure the angle of the back of the seats. Make a back.
Work out how much volume you need to give the subs, and adjust your base accordingly.
Make some sides (4 of, as each sub has its own chamber) and a top.
Glue and screw it all together.

I made mine out of 12mm mdf with shedloads of fibreglass to reinforce it. The idea was it would be lighter than 18mm mdf but stronger. It's stronger, but no idea if it ended up lighter

I know this ain't much help, but let me know what trouble you're having and I'll try to help

scooby_si

OK cheers m8, i'm still currently looking at a few options so with a bit of luck i wont need 2 do anything too major Whats the story with the needs of mounting an amp wherever then?
Ta
Si

chiark

My amp is mounted in the box. It's a three chamber stylee box, with the middle chamber being used for amps.

For mounting amps, make sure the surface is solid, and make sure cables couldn't get trapped. That's about it really. Oh, and some amps don't like being mounted touching metal of the chassis so may need isolating from that.

scooby_si

Cheers m8 i think that just about covers it Although will probably need 2 do seperate but 4 amp if i get sub(s) already boxed. Am i safe in thinking the amp wont actually need a box thou just sumin 2 screw it onto like? That said how'd u actually secure yer box etc 2 the boot floor then? Staple gun at ready lol
Out of interest wot's the crack with flattening the battery & as mentionned on yer fine site setting up a seperate battery 4 all the sound goodies?
Cheers
Si

[Edited by scooby_si - 8/22/2002 11:49:50 AM]

chiark

No worries Si.

You can mount your amp to the sub box. There's two schools of thought on this tho - some believe the vibration isn't the best thing for the amp, some don't bother about it. (I'm not worried personally, as the box should be solid...)

For mounting the sub box, put a piece of MDF under your carpet that covers the width of the boot and screw from underneath into the box. So you've got the carpet sandwiched in the middle if you see what I mean. Only downside is that it's a bugger to get at your spare wheel now. Perhaps bolting with wingnuts would be better?

And yep, you don't need a box for the amp. Just a solid base.

scooby_si

Cheers m8 round 52
So how's about the hole extra battery malarky how easy or otherwise is that 2 set up as i'm bad enuff leaving my lights on with radio on but engine off flattening battery so dread 2 think wot i'll b like with amp, subs etc
Si

chiark

Very easy - you just need a big 'koff relay. Maplins sell 180A relays for 15 quid, made by autoleads.

I haven't bothered with another battery myself tho...

scooby_si

So out of interest, since i have no chance of being able 2 work it out in me head given that i flattened battery by having bog standard radio on with lights & also having put the windows down in a half hour diner break without engine being on, how long wood it take if it was just radio with set of subs amp etc. I guess it depends largely on how healthy yer battery is & how big da amps etc r but just wondered how cunning it is 2 b using a half meaty system with engine off is?
Si
PS am i draining yer energy yet? lol

chiark

Si,

Assuming standard current draw of x, and average output of Y, the answer is "quite quickly".

It ain't a good idea to run a half meaty system off the battery as it'll drain the battery, plus you'll be running at 12v rather than the 14V supply that amps like to give their best.

scooby_si

So basically only have it booming when engines running it wood seem?
Der mode continues can u just turn the subs &/or amps off if u were guna just want radio or sumin on with engine off?
Cheers 4 continual help with the care in the (subaru) community retard lol
Si

chiark

I wouldn't run the radio even, but that's just after a particularly bad experience when my Dad flattened his car battery by leaving the radio just switched on (silently - d'oh) whilst parked in a car park. That was 2 weeks tho

Amps are normally wired up to turn on and off with the stereo using the remote turn-on output of the stereo. You could put a switch in this - I did in my first install. However, if you're not using any of the head unit's speaker outputs then you won't hear anything if the amps aren't on

If you do want to run the system with the engine off, don't crank it and don't run it for > 1 hour and you're laughing. Hopefully

scooby_si

Hmm oops i no leaving the engine for a few hours after my dinner break ment mine did start ok but i woodn't wana keep trying my luck with that
So if u aint bored of being the daddy of answering dumb questions yet then i'll proceed
I was thinking about getting a 4 channel amp to do front infinity speakers & possibly pair of subs wired in series as u may c in a thread not soo far from here & doing rear original speakers from the headunit. 1) does that sound about right in terms of being able do the subs off 2channels or duz "one bridged channel" mean i need 2 b looking 4 sumin specific from any amp as well as running the front infinites. 2) Is it possible 2 do this sorta set up but also use the headunit amp 2 do the front speakers if i did wana just run with engine off & not use sub & amp? 3) wood 2 sets of 2 channel amps b more cunning where 1 powers sub & thus can b turned off when not needed & other for the front, wood that b more efficient use of da leky, just a fort (probably a dumb un)?
Cheers
The ever inquiring Si

chiark

AAAAAAARRRRGHHHFHFFH!! (not you, I just wrote a reply and the bbs told me "oops, you didn't end your quote with /quote" and lost the contents of the 'kin reply)

Anyhow, to summarise..

Bridging takes two channels of an amp and makes one more powerful channel. It normally delivers more power than the sum of the two independent channels...

If you put two subs in series, you'll drop the impedance that the amp sees. (You'll double it). If you run 'em in parallel, you'll halve it.

Running an amp on a lower impedance load gives you more power output. However, there are catches: your amp gets hotter, the distortion level goes up but for subs this ain't an issue really, and the biggie is your amp must be stable at the impedance you plan to run.

So, if you have 2 4 ohm subs, your amp will see a 2 ohm bridged load. For reasons beyond me, this is equivalent to a 1 ohm stereo load. Most amps can cope with 2 ohm stereo loads, but not 2 ohm mono. Check the label.

It might be more sensible to either just run one 4 ohm sub bridged off channels 3+4, or have two separate amps (a nice one for the front and something that could drive the impedance of a nail for the subs). Disadvantages are that they take more space, complicate wiring more, more to go wrong, ... But I would think it may be worth it.

You can't have your head unit and an amp powering the same speakers without relays and all sorts of messing about. Don't do it

This answer ended up being better than the first one

scooby_si

yer a gem Chiark most informative
Cheers m8,
Bring on da bangin toons
Si

[Edited by scooby_si - 8/23/2002 6:29:49 PM]

hades

For what it's worth, the reason 2 ohm bridged is equivalent to 1 ohm not bridged is fairly simple:

The effect of lower impedance is higher current for a given output voltage. When an amplifier is bridged, one half helps the other half drive the current through the speakers. Therefore, you get twice the current for the same gain (or output volts per "half" of the amplifier). This is the same thing as halfing the impedance. Can explain in more detail, if anyone really wants.

chiark

Cheers Hades, that sorta makes sense - I guess each channel is being driven in the opposite direction, and hence is sharing the impedance...

scooby_si

I was lost way back so i shant comment on how much sense that makes lol.
Oh while i'm here, no please go i hear them shout, u no u said about screwing the sub box etc 2 MDF under carpet from below? Well if it's right at the back how do u get underneath? Maybe missing sumin as i must confess i aint tried removing the carpet or owt but was a fort that occured 2 me (yep my brain duz occasionally have em)
Si

mikey f

I've asked this on another thread but how do you calculate the sioze of the box comaired to the sub your using?