Sub Woofer Installs For Ba's

[81CJH]

Guys I have an XR6T w/ premium, and I've installed a 10" Peerless XLS Sub into the factory 8" location. It's 100% on the original unit, and it does the job nicely, despite being in the "free air" position. I should mention that the sub isn't designed to be free air, it's actually designed for a very tiny 21L enclosure!

I'll send in some photos soon, but if you'd like a look at the sub I'm using, check out this: Peerless 830514

For the record, I'm using a run of the mill passive line converter from Jaycar into a Rockford P3001 2ch amp.

There's no muddiness issues with the back seats up, as it goes straight through to the cabin.

[edit] a couple more things, the line converter is getting signal straight from the factory sub amp, NOT the rear speakers, and if you're planning on using one of these, you'll be needing a 2ohm stable amp if you haven't got one. (see Zmin spec of 2.4 ohms)

Edited 19/10/05 07:22 AM by 81CJH

[veczar]

that's means its going thru 3 amps doesn't it... Head unit, fact amp, your amp. that's one more than needed? The spec sheet of that sub says 2.4ohm but up the top in the heading it says 4ohm. Odd.

Also the Rockford P3001 is a monoblock (1 chan) amp. But you are right it is stable at 2ohm.

Im glad it sounds good may be an option for me as a 2nd sub. How hard was it to mount? And when it is pumping does the reflex of the sub get anywhere near hitting?

[IH8TOADS]

Good job 81CJH. I wouldnt mind some more details of how you used the factory amp wiring as the signal to my amp is corrupted by electrial aliens. Cheers.

[81CJH]

Ok then, sorry about that first post, it was a bit rushed.

veczar:

That is correct, My P3001 is running off a line level converter attached to the speakeer connector from the factory amp. I did this for ease of integration and to maintain the sound of any DSP effects etc. This way, my P3001 runs on AP (everything thru, no LP filter) and my sub reproduces what the factory one did, just louder.

With regards impedance, the Sub is indeed advertised as 4 ohm, but if you look at the blue trace on the graph at the bottom of that page, you'll see that the impedance is at its lowest between 100 and 200Hz. They give you the exact figure in the table as being 2.4 Ohms @ 133Hz. Impedance is different to resistance. If you look at the DC resistance of the voice coil (Put a multimeter on ohms accross the speaker terminals) it's listed as just 1.8 Ohms! I don't know all the ins and outs of it, but it's pretty obvious looking at the graph that the impedance of a speaker isn't the same the whole way through it's frequency range.

The P3001 is actually a 2CH amp, but it can be operated in mono mode down to 2 Ohm stable, and for some reason they only quote the bridged (300Wx1) output in the specs. Buggers me why, but I can assure you it is actually a 2CH amp.

IH8PORK:

Dude I know what you mean. I haven't been able to decipher it myself yet, all I've found so far is that there's no conventional 12V remote power wire amongst it. There's 2x12V constant power and 2xGND (probably because they didn't want to run bigger cable to power the thing), and there's probably the equivalent of line level RCA's in there somewhere too, but I haven't gotten in there with an oscilliscope to find out for sure. It seems at this stage that the amp is always on!

Unless it has an RS485 data line back to the ICC to tell it when to switch or something, I'm buggered if I know. Anyone else?

[Paradoxx]

With regards impedance, the Sub is indeed advertised as 4 ohm, but if you look at the blue trace on the graph at the bottom of that page, you'll see that the impedance is at its lowest between 100 and 200Hz. They give you the exact figure in the table as being 2.4 Ohms @ 133Hz. Impedance is different to resistance. If you look at the DC resistance of the voice coil (Put a multimeter on ohms accross the speaker terminals) it's listed as just 1.8 Ohms! I don't know all the ins and outs of it, but it's pretty obvious looking at the graph that the impedance of a speaker isn't the same the whole way through it's frequency range.

That's correct, with any inductor (coil) you have different impedance at varying frequencies. The closer to DC the signal is (ie 0Hz) the more the coil will conduct. The varying magnetic field in the coil is what impedes the flow of current so if that magnetic field is slower or smaller there is less impedance. They quote speakers with an impedance based on the nominal impedance created at normal listening frequencies. It kinda flat-lines at 4 or 8 ohms depending on the number of turns.

More useless trivia... but it may answer someone's question!

[81CJH]

you might be able to answer a trivial one of mine...

Why is it (once again referring to the graph) that at resonance the impedance goes through the roof? I would have thought it'd be the other way around. When I think of a speaker's resonant frequency, I take that to mean the frequency that it can best reporduce with the least effort, much like humming in a confined space, changing pitch until you find the frequency that really resonates around you. Maybe I'm just weird for doing that, but it's interesting. Try it in the shower or the bathroom sometime.

Anyhoo.... If the resonant frequency is the one that stands out as the loudest & proudest, wouldn't that frequency produce a downward dip in the impedance?

Trivial.

I also notice that (altough it's probably unrelated), the highest point in the dB ouput plot (in the normal subwoofer freq range anyway) is at approx. double the resonant frequency at a smidge over 80Hz.

Edited 21/10/05 02:35 PM by 81CJH

[Paradoxx]

Ok with the impedance, I dont know for sure but I think it has something to do with the fact that because it is at it's natural frequency it is creating the largest back-EMF (electro-motive force) which is what impedes the current in the first place. The free-est movement of the coil at resonance probably means that this back EMF is at its maximum. At other frequencies it doesn't move as freely and hence less EMF produced.

With the output at twice the resonant frequency, if you look at a plot of a sound wave and plot another one at twice the frequency you have a multiple of the original, so it creates a bunch of harmonics and it just so happens that with that model sub it is its loudest at that point. Dunno if this makes sense or not... but I understand it in my head!! Hehe.

[81CJH]

Ok with the impedance, I dont know for sure but I think it has something to do with the fact that because it is at it's natural frequency it is creating the largest back-EMF (electro-motive force) which is what impedes the current in the first place. The free-est movement of the coil at resonance probably means that this back EMF is at its maximum. At other frequencies it doesn't move as freely and hence less EMF produced.

With the output at twice the resonant frequency, if you look at a plot of a sound wave and plot another one at twice the frequency you have a multiple of the original, so it creates a bunch of harmonics and it just so happens that with that model sub it is its loudest at that point. Dunno if this makes sense or not... but I understand it in my head!! Hehe.

<{POST_SNAPBACK}>

Ok I've done a lot of reading about this today and I'm still none the wiser, except now my brain hurts.

I think you're off track with the back-emf thing, purely because of ohm's law. The frequency at which the EM field would be at its largest would be the frequency that the loudspeaker impedes the least (electrically), therefore the most current will flow, creating the biggest magnetic field around the voice coil. So of course it also stands to reason that the biggest em field around the voice coil will produce the most back EMF when it collapses. I'm pretty sure that's right, given that on the data sheet their 1W@1m sensitivity measurement was done at 133Hz which is, surprise surprise; right where the impedance is lowest. I think THAT, is the frequency that makes the speaker "flap" the most, which all makes pretty good sense when you consider the fundamental operation of the loudspeaker. Current through suspended voice coil attracts/repels with respect to the permanent magnet producing movement. Therefore the biggest EM field = most movement from said magnet.

...which is all very well and good, but has gotten me -all closer to answering my original question.

On that note, about the best I can come up with is that the resonant frequency must be the frequency that the physical construction of the cone+suspension assembly resonates at. That is, if the frequency you're feeding in is the same as the frequency the cone naturally wants to move at, then there will be minimal (approching none whatsoever) mechanical impedance to the reaction between the permanent magnet and the electromagnet.

If the frequency was below that, then you would be using current trying to hold the cone in or out longer than it would naturally. Above it, and you're using current trying to pull the cone back when it's still wanting to go out and vice versa. If you're right on the money, you don't need near as much current to move the cone.

Efficiency! that's the word I'm looking for. So maybe it's not that the impedance suddenly goes way up at that frequency, maybe it's that everywhere else in the frequency band you're making the whole thing work harder to push this bloody great cone around.

Does that sound reasonable? I won't be surprised if it doesn't. I'm so over this I can't believe I asked this question in the first place. If any audiophiles want to chip in here please enlighten us. Here's the link again; I know I'm sick of scrolling back up trying to find it:

Peerless 830514

[XR06T]

just a q,

found the rubber thing on the passenger side footwell to run the power cable through, but how did you guys put the +ve wire onto the battery??

did you get a whole new battery connector terminal thing and put the other wires into it too or go for the factory look and connect the wire into the factory terminal?

I also noticed that there is a red 4 gauge lookin wire coming off the battery running all the way to the trans, would it be possible to tap into this and run my power from there? anyone done this or should I stay well away from this wire. I checked it out and could not see a fuse in it or anything. it seems to run directly from the battery to the trans..

cheers guys, very informative thread!!

[81CJH]

I actually ran my power cable through the drivers side footwell. I'm not familiar with the one you're referring to, but I know mine turned out really well. It's a bit of work though, you have to jack the car up and take the front right wheel off, then remove the inner plastic guard lining. Once you've done that though, it's smooth sailing. The rubber grommet is very large (it's where the main wiring loom goes through into the cabin so it's pretty big), and you basically just follow the main loom up through the guard and it pops out right next to the battery. Neat as!

Access to the grommet from inside is pretty easy too, just take off the kick panel in the footwell and lift the carpet, it's right there.

As for the red wire you found that's unfused, that would be the one going to the starter motor. Technically you could tap off this, but personally I wouldn't. This is because if you cut and join it with anything less than a good solid crimp connection like what's on the battery terminal, you'll get massive voltage drop going to the starter motor. Remember that that wire isn't fused because when you crank the engine over that starter motor will draw an enormous amount of current, albeit only for a second or two. So it wouldn't matter how big a fuse you put in there, it would blow. That gives you some idea of the current involved, and the need for the best possible electrical connection between it and the battery. It might be a bit more work, but I'd definitely recommend the driver's side option, and run straight to the battery.

As for the connection to the battery, Head on down to your local battery shop. Preferrably a battery specialist, not just a servo or tyre shop. They should be able to hook you up with some decent connecting hardware, and can probably hook it up for you there and then if you have your wiring already run.

Hope this helps