Supra Install

Having got my hands on a new toy (1990 Supra 3.0 Turbo) I feel the need to install even more toys inside of it! I haven't done a serious install before so I decided to do this one myself (since it won't be the end of the world if I make some mistakes on an old car).

Comments, suggestions and general advice about my choices would be well received.

I decided to go with a Kicker 405 amp, since Hugo has one in his Beetle and recommended it. It has 4 x 55W and 1 x 290W @ 12.5V, rising to 4 x 75W and 1 x 390W at 14.4V.

The '90 Supra is fitted with 4" components front and rear, and having taken a look at the enclosures I am very nervous about modifying them for larger drivers. The enclosures are very well made and you get a lot more sound out of them than you would expect from a stock system. Therefore I have gone for a pair of Diamond M341 4" drivers for the front. If these sound good (they sound incredible for their size in the showroom) then I'll keep them up front and add some coaxials in the rear, otherwise I'll move the Diamonds to the rear and find some way of fitting 6.5" Infinity Kappa Masters in the front.

The Diamonds come with a crossover which has an additional connection that isn't documented - it's labelled RAF. Any ideas?

The sub is going to be a custom build, which is being designed by our resident experts John & John. It will be based around a 6th order band pass design with either 2 x 10" or 2 x 12" drivers. It's going to be a very odd shape to fit the trunk (which I'm totally sacrificing to the cause) with the drivers mounted vertically and each enclosure ported upwards. I haven't chosen drivers yet as they will be dependent upon the cabinet calculations.

I have a 1F capacitor on order, but I'm not sure if it will really be necessary for this relatively small system.

I've ordered 2.5mm oxygen free cable for the cabin drivers and 4mm for the sub. The line cables are oxygen free 6mm double shield with moulded gold connectors.

I have some ideas for a fun install, involving lots of MDF, some brushed aluminium and a couple of neon tubes. I didn't do any of that stuff when I was a kid so I feel I have to go for it now

So - apart from the neon tubes - what huge mistakes am I about to make?

Rob

Nifty! Congrats on the new wheels.

My only question is: Why bandpass? If you're already consigned to giving up trunk space, why not go with some really decent sealed enclosures for smoother, more accurate bass?

___________
Tony Fabris

I think the cap will not be necessary, but I may be wrong. Well, Tanstaafl could answer that one better.
Gods, 4 in. speakers for such a terrific car? What were the designers thinking? Typical of a development phase not enough centered on target public but on other goals.

I'll second that, especially if you are going with a two driver enclosure; you will get enough bass out of a sealed one, and when you'll need some more accuracy and refinement (cymbals sound awful in bandpass enclosures, for example), you will have that too. Or maybe a compromise between both, a ported enclosure?

Any idea what head unit you are going to use?

I believe the '91 model had 6.5" speakers. The strange thing is, the designers DID put a lot of thought into the sound system - the speakers mount into sealed enclosures in each door, and different enclosures in the rear pillars. They fitted components front and rear as standard. Apparantly this was one of the best sounding stock installs of the time (I can't tell because the stock head unit is knackered).

It does seem odd to go to all that effort and then fit 4" speakers. Luckily the 4" Diamond M3's sounded incredible in the showroom so I'm crossing my fingers.

Rob

Rob would give up more trunk space when having a bandpass than having a sealed box. The sealed boxes can have pretty small enclosures to sound good!
But a sealed enclosure is what I'd suggest if you want a really nice and high quality sound..

TeeMcBee
Got my Mk2! # 080000143

How about retro fitting the 91 door enclosures to your new chariot and i think the supra be a hatchback could you fit stuff in the rear shelve

The answer to that involves hours and hours of intense mathematical argument with John. The proof is in the pudding, though. John's sub is incredibly loud and very musical for its size - I haven't heard the other John's sub yet but apparantly it is much louder and has an even wider dynamic range, so I'm confident I'll get something good.

Rob

Read the original post one more time, 5 channel amp 4 channels to the speakers in front and back and one channel left over for two subs does this work. Or am i being electrically challenged.

Two drivers, one "sub"

Dooh

Yeah it'll have to be a Mk.3 empeg with satellite internet streaming, 50 band EQ and 12" TFT colour display.

Rob

(Nah, just kidding!)

But Rob, I thought you said in Amersfoort that the Mk 3 would... Ooops. Sorry, shouldn't have said that.

No, you are right, I realise now you were just kidding

One of the few remaining Mk1 owners... #00015

I was under the impression that Rob was planning on giving up all of the trunk space, anyway....


Roger - not necessarily speaking for empeg

The answer to that involves hours and hours of intense mathematical argument with John. The proof is in the pudding, though. John's sub is incredibly loud and very musical for its size - I haven't heard the other John's sub yet but apparantly it is much louder and has an even wider dynamic range, so I'm confident I'll get something good.

Well, the figures speak for themselves:

6th order bandpass (2 chamber, driver in middle, chambers individually ported).
91 litre box (split 75/16).
Single Eminence Kappa Pro 12" driver (400w, only cost £100!)
Dimensions approx 60cm x 37cm x 42cm. Weight 20kg.
Materials: 1/2" plywood, 1" on top panel (weak point), 8x1/2" cross bracings, 3x2.5" (top) and 1x4" (bottom) drainpipes for ports.

And it manages: -3dB 32-120Hz, -20dB 23Hz.
Free air efficiency: 92dB/w/m (cars give you about 10-20dB more)
Free air max SPL: 118dB.
Free air response: 35-110Hz +/- 1dB.
In-room max SPL: >126dB at 36Hz (actually off the scale of my SPL meter)
In-room response: +/- 10dB :) (bloody rooms)
In-car max SPL: untested, my guess is 20dB in-car gain at 35Hz, around 135dB.

It's not hugely efficient, but I did design it for very low frequency response. This is a trade-off with any subwoofer. The lower frequency bass you want, the less efficiency you'll get, unless you make it much bigger. The other John (who's joining empeg soon btw) designed his sub around a higher -3dB (about 45Hz) and a larger enclosure of 120 litres, giving an efficiency of around 96-98dB/w/m in free air.

The enclosure cavity sizes, driver parameters, and port sizes are all tightly linked in bandpass designs. I used a combination of a few utilities to find the right design ("Dosbox", "WinISD" and one of two of my own). The most important and most often ignored parameter when tweaking is excursion. In my design, excursion is within 1% distortion xMax for pass-band at 250 watts, by which time it's reached about 115dB. A similarly designed sealed enclosure would probably be hitting end stops at <110dB at around 40Hz.

Before sealing the box completely, I wrote a little utility to measure the impedence magnitude and phase response. In vented enclosures, the impedence phase crosses 0 degrees at the port frequency. This gives a good measure of how far off your port lengths are compared to ideal. I started off with long ports and gradually sawed them down to the right size after several measurements. After sticking the box together, I measured the ports as being within 1Hz of the intended tunings.

As for that "tight" sound... what this actually means is having a low group delay, or at least a smooth, similar group delay. It is true that almost any bandpass or vented design will have a higher group delay than a sealed enclosure. However, this only holds true from around 70-100Hz in my design, and even then it's only around 3-5ms. This happens to be faster than the ear can measure at such frequencies. Below 70Hz, it rises to around 10ms, and a peak of 20ms at 35Hz. At such low frequencies however, the human ear is very poor at recognising group delay. Also consider that the sealed enclosure would have stopped outputting appreciable amounts of audio below 40Hz.

There's only two things I would have done differently had I designed it now:
1) Make it bigger, up to 120 litres. The parameters were fairly critical at 90 litres for the intended response curve.
2) Flare the ports, or make them wider. It "puffs" when it's near max wattage. This wouldn't be audible if my treble system could match the SPL of the sub :) (but I'd mess my ears up)

If anyone else is considering building a subwoofer, try out various designs in an appropriate program, and see for yourself the advantages of a vented or bandpass enclosure.


- John (from empeg)

(The above may not represent the views of empeg :)

RAF = rear ambient fill

It's basically a load balanced output for rear speakers, ie. you can run 2 sets of speakers off the same 2 channel amp output, and get an attenuated rear speaker output for rear fill without changing the impedance at the amp. Tends to work quite well in smaller interiors, so it might be worth trying in the Supra.

Dominic

Cambridge Car Audio
http://www.cambscaraudio.co.uk