Outer Limits 4x4 Board

Bought some Precision Response gear from Jaycar today:

- 6.5" splits (60W RMS, Kevlar cones, soft cone tweeters)
- 12" sub (300W RMS)
- 4x100W RMS amp (although amp/manual says 4x130W RMS @ 4 ohm)

Now my question is re the sub. I went in with the intention of buying a 10" Precision Response sub, Vas = 29.8L, as the sub enclosure needs to fit between my rear shelves and the back of my seat. Which in a Sierra, isn't much room.

Anyway, the Jaycar 'audio guru' convinced me that if I could stretch the sealed enclosure volume to 35L I would be far off better going the 12" sub. I can stretch the sealed enclosure volume to 35L so bought the 12".

I have just noticed on Jaycar's website though that Vas = 72.5L for the 12" - much, much more than I can achieve.

Should I be returning the 12" for the 10" (Vas 35L) that I had my eye on originally? I'm somewhat doubtful that their audio guy knew what he was on about.....

Am looking for a smooth bottom end extension of bass, not doof-doof bass, if that helps.

you will find most subs have specs for a ported and a sealed box and im sure a sealed box requires a smaller volume

i built 2 sub boxes using the 12 inch response subs and they are about 115 ltrs ea. , they are ported and run off a 350 watt amp , they shake the house , anyway when building them the sealed box option was less than 1/2 the size but also had a reduced frequency response or something like that

if you look on google you should be able to find formulas to build speaker boxes and it will show you the frequency response as you adjust the size of the box , but you need all the vas ,ve etc of your sub you intend to use

sooo much easier fitting a 10" for that reason. But, would you consider a sealed enclosure. The 72L is for a ported enclosure isnt it? You will lose a bit of the soft bottom end, but its in a sierra!

Ported enclosure requires a larger volume to recieve identical cone excursion at the subwoofers resonant frequency.

If you don't have the volume to make a sealed enclosure to suit the vas spec's for the 12", return it for a 10.
You could always make an enclosure to suit the available space and then 'fudge' it by using accoustic wadding, but it's a compromise at best.

By the sound of it, your audio tastes will be better suited to the tenner anyway.

Subwoofa's mate. Hektik. Not the stuff you see on OL every day.
Once upon a time I held a NSW dbdrag title for SM1-2 and had trophies from major events all over the country. Still have the car I competed in, but it barely has a stereo fitted.
Now my zook doesn't even have a headunit. Who needs music when you have the lumpy growl of a 1.6 and squeaky suspension bushes.
Can't say I miss my ricer ways in the slightest.

Thanks guys. I was under the impression that you should shoot for Vb = Vas. So I was thinking Vb = 72.5L optimal. I was wrong

There sub has the following characteristics:

Qts = 0.42 (total dampening of the speaker)
Vas = 72.5L (air volume that has the same compliance as the speaker's suspension)
Fs = 25.8Hz (free air resonance)

Found a calculator that relates Qts, Vas, Fs and Wb to find the 'Qtc', which is the total dampening of the speaker including all system resistances.

The 'optimal' (or balanced) Qtc is 0.707. For a given speaker, Qtc increases as box volume decreases, and Qtc decreases as box volume increases.

- Qtc around 0.6 will give lots of driver dampening, hence lower SPL (sound pressure levels) but good transient performance.
- Qtc around 0.7 is often considered 'optimum' as it gives a good balance between driver dampening, SPL, transient response, low bass runoff and a flat response curve.
- Qtc around 1 is a much smaller box than optimum, fair transient response and low bass performance, but noticeable bass peaking mid-range.
- Qtc around 2 is very boomy and muddy with poor transient response and low bass performance, but has a tiny enclosure

(Source: http://diyaudiocorner.tripod.com/dilemma.htm)



My 35L box will come in at Qtc = 0.735 which ain't far off 'optimum'. May peak a little more in the midrange than the ideal 40L box (Qtc = 0.707) but should be okay.

Mnemonix, this ain't a ricer! But it is daily driven, so it's nice to have a decent stereo. 6.5 drivers fit into stock kick panel locations without any spacing; I've installed the tweeters flush into the door panel between the window winder and where the door meets the dash; and the amp/sub will be built into my shelves.

The only telltale looking through the windows will be the tweeters, but being black on black lining they're not easy to spot.

The head unit's only a base level Kenwood MP3/WAV player ($99) that shouldn't scream *STEAL ME* either

......al powered by a stock Zook alternator????

Potential for 500 watts power, realistically driven to 80 watts total would still need 10+ amps due to inefficiencies of the amplifiers (Bucking supply voltage to output stages usually to 40-50 volts, and inefficiencies of class C output stage).

Methinks a new alternator will soon be on the menu, if not, then several new batteries

DAMKIA wrote:.....al powered by a stock Zook alternator????

Nope. 110A EL Fairmont alternator. Pushing into a 550CCA 95RC battery currently; second Optima battery on the cards running a Traxide isolator and second fuse box internally for fridge, lights, etc. Will likely leave the stereo off the main battery.

My camping trailer will get its own CD player and speakers running off the Ultima for camping.

The amp is definitely overkill for my needs but the 4 x 50W RMS Precision Response amp is no longer available in stores, and a bit of headroom never hurt. Will adjust the amp gain to compensate.

Actually the sub won't have any overhead. I can have 4 x 130W or (2 x 130W + 1 x 380W) into 4 ohms, but my sub has 2 x 4 ohm voice coils. Soi I'll either run each voice coil on a separate channel for 2 x 130W @ 4 ohms, or bridge two channels and run the coils in series for 1 x 230Wish (?) @ 8 ohms.

Amps not 2 ohm stable in bridged mode unfortunately, although the Jaycar bloke said it was fine to run it that way