A Bit of Bass for Betty the Bentley

I will admit it isn't very Bentley like but it will be living in the boot where it will be out of sight. The other unit needs to go in, each one will be driven from a separate channel on the amp and will be bridged to 2 ohms. It's probably overkill but it should sound excellent and that's what matters.

Things have changed over the years, I seem to recall that the Cortina Mark 2 that my parents bought in the early 1970's didn't have a radio. You could buy one, it was an option, from what I remember it was AM only and had an output of about 3 Watts. Mum had a portable radio that sat on the passenger seat, hardly ideal. When Japanese cars started coming in they had a radio as standard, usually AM/FM but still only a few Watts per channel.

You could buy after market stuff - 8 tracks were popular back then and the cassette tape was invented back in about 1963 but it took a very long time before the likes of Ford and Vauxhall bothered with such new fangled devices. Except for the Japanese stuff very few cars were designed with sound in mind, most came out the factory without speakers or anywhere specific to put them, those ugly add on rear shelf pod things were the norm back then. God they were shit.

It's only really in fairly recent years that manufacturers have started fitting decent sound systems and designed the cars with acoustics in mind. Most of the premium brands now work with high end audio suppliers to produce systems of outstanding quality - Bentley now use Naim (at an extra cost of about 7 grand), Audi fit Bang and Olufsen, Porsche used to use Bose, don't know what options they offer now. Doors are usually much deeper and often pods are moulded in to allow for deeper more powerful bass. Tweeters are fitted high up so the passengers and driver get more direct high frequencies directed to where they are needed. The number of speakers has gone up massively, 2 used to be the norm, then 4 but these days 14 is not unheard of. Everything has a sub too, nobody wants a car without a fairly decent system and they definitely want bluetooth and CarPlay and all those sorts of things.

By the mid 1980's chips had come out that gave high power amps in a tiny package, 20 or 25 Watts per channel  was common, my Capri had a very cool little after market Clarion cassette only player with that sort of power driving 2 6.5 inch speakers, I thought it was the mutt's nuts. i sunk the speakers in to the rear parcel shelf so the boot acted as the speaker cabinet - I was Jack the biscuit, the thing had power and bass. My Last Jag had a factory system by Bowers and Wilkins, it was 1200 Watts from memory, had a sub and 8 or 10 other speakers, it sounded fantastic.

Betty - being from 1998 originally had an Alpine system which had been removed long ago and a later head unit fitted. When I get her the front left speaker was damaged and was making a horrible noise so I changed the front pair - I kept with Alpine and used the closest modern equivalent of what was in there. It sounds ok but there is no real bass - nothing much below about 60 or 70 Hz and it has no thump to it. Being mad on music it just doesn't do it to me, it's all flat and very 1980s rather than 2020's. I don't spend much time in there and I'm not looking to turn it in to a mobile disco but I would like something better. As the car is not really designed with sound in mind the doors are pretty shallow. I don't want to modify them so my only real option is to add a sub woofer into the boot area. you can get ones that go under the seat but they are rubbish, not worth the trouble.

I am at the limits of my Wife's patience and tolerance at the moment, so a big spend isn't going to get authorised so a bit of creativity is required.

Designing a sub woofer is pretty easy, there is a ton of info out there, calculators on line and even software that gives you a cutting list for the bits of wood or MDF to make your own. My initial idea was a Temu 10 inch driver built in to an MDF cabinet with a large slot type reflex port driven from an amp of about 500 Watts. The Alpine head unit has a subwoofer output and the level can be controlled from the menu, I can run an RCA cable down the car to the boot area, the remote switch wire is already there for the electric aerial, the hotel battery is right there too. The Arnage has two batteries - the starter battery and the hotel battery that powers everything apart from the starter. there is a load sharing controller so it's a bit more complex than that bu I will wore to the hotel battery. Between them they can provide over 1400 amps, which should be adequate. These days you can buy high power amps for very little money but you need to be aware that a lot of them advertised with massive power are a massive con. In my search I saw one claiming to deliver a massive 7600 Watts but looking at an on line test it was more like 100 Watts per channel RMS. It's been going on for years and it's really annoying but stick to the principle that power costs money and you won't go far wrong.

As luck would have it I was on facebook one day and an ad came up from somebody literally 100 yards down the road from me that had a sub woofer box with two 500 Watt 12 inch drivers in it, the ad said he would throw in a couple of amps of unknown functional status and all for just 40 quid. The speakers were ok, the couple of amps turned out to be one amp and of course it was knackered.. I bought one off ebay but the one I got is a hefty beast rated at about 300 Watts x 4 and verified by an on line test I saw some time back. 

These things all work in a similar way and when you open them up they look remarkably similar inside. The tech that allows such high power is quite interesting - it started to come in about 1980ish, and that's the DC to DC converter. It converts the 12volts of a car supply in to anything up to about 120v which can then be stuffed in to the 4 ohms of your speakers to give massive power, my particular one runs at plus and minus 30 volts to give a max of 60 volt in to a 2 ohm load. Many amps are capable of running down to 2 ohms, that's serious power that would almost certainly require a significant power distribution system and an additional or uprated alternator. You can go mad with this stuff, spend a fortune and have way more sound pressure than is sensible or safe. I don't want that, I just want a decent system that will go down to 20hz, up to 20 Khz and will sound at least as good as the system I have in my house. It has to be cost effective and it has to keep the interior original, I don't care about boot space, if we need boot space we take the Insignia.

So I have the massive twin 12 inch ported box, 2 12 inch drivers, a broken amp and a new lower power amp on it's way, I also have a 10 inch 500 Watt driver coming and a pile of MDF in the garage. Much experimenting will happen, I am attempting to fix the amp I have first, some parts are on order, I think I know what's wrong with it but until I fix the first fault I can't test the rest.

I'm sure many folk will be horrified with what I am up to, purists will be accusing me of heresy and will be reporting me to various authorities. I couldn't care less, my car, my rules. Hopefully it will sound fantastic, which will be the cream on the cake because it is the most incredible and rewarding car to drive. I love it to bits, this is the last thing to sort, in my opinion it will make it even more enjoyable than it is now.

Update - I had a few spare hours, I'm waiting for coils and plugs to cure my misfire so I thought an hour or two in the electronics lab would be fun, the amp needed fixing, the stars were aligned, time to get on with it. I had already taken it to pieces and noticed that two of the four large electrolytic capacitors were bulging, always the first thing I look for. I ordered them - 1000 micro farad 50 volt items. They were a sod to get out, it's quite a good quality printed circuit board with through hole plating, notoriously difficult unless you have a really powerful soldering iron, inevitably a couple of tracks lifted so I had to repair them too. I was pretty gobsmacked that the amp burst in to life, I was kind of expecting the power supply part of it to work but not a lot else but all channels worked perfectly. I tested them down to 2 ohms and the amp didn't go in to protect, which is a bonus. It has a switch to select low pass specifically for a sub woofer on channels 3 and 4, the idea being you can run either a pair of single coil subs or a single dual coil sub and a pair of full range drivers from the single amp. I set it up on an old test speaker first in case there was a big DC voltage on one of the outputs, then I tested it on the sub that I intend to use, I am confident it will do the job nicely. Not bad for a freeby. Sadly the two drivers that came with the sub box are both knackered, I have a pair of Pyle 10 inch units to go in instead, I had to make some adapters so they fit in the 12 inch holes, just some MDF I had lying about in the garage.

In the workshop the bass is deep and powerful, just what I was hoping for, there is loads more power than I need, which is great as I can run the whole system well within it's capability and get a really good sound quality as a result. I have bought the RCA leads to go from the front to the back, routing that tidily will be by far the hardest part of the job, I expect it to take best part of a day as I don't want it showing anywhere. The rest is easy but will have to wait now, I have other stuff to do and expect my ignition parts to arrive today or tomorrow, so that will then take priority.

The amp on the the bench Two of the four capacitors in the middle of the board were faulty, I changed all 4.