The Problem With Beemers….

BMW Cars Deserve Beautiful Sound Systems

Exhibit A above is a BMW original under seat 6.5inch woofer. It is designed to save space and produce as much bass as is possible from its position under the front seats of a BMW car. They also come in 8″ versions dependent on trim levels. They are clearly built to a budget! The plastic chassis is mounted in a plastic enclosure, tuned to reject frequencies above around 180 Hz (band pass) the enclosure ports into the front door sills in order to further enhance the bass. The rest of the speaker system consists of a pair of 4inch mid-range speakers and a pair of tweeters (the latter being an option on some models I believe, although these things change on a fairly regular basis). there are also components peppered around for the purposes of sending restricted frequencies to ensure the speakers operate within their meagre capabilities.

Because of the adopted bass strategy, many customers speak well of the audio when demonstrated in the showroom however, once they have taken delivery of their car, they soon tire of the scrambled mess produced by the sound system. Common complaints are a lack of bass when moving at speed, a lack of clarity at the top end and distortion. No one really mentions stereo image as there really isn’t one worth speaking about. The speaker placement is poor with the mid-range in the doors often partially obscured by the door handle. Tweeters sit in the wing mirror pad – a triangular piece of plastic that covers the workings of the mirror on the inside of the car. The tweeters fire across the car which is fairly standard but not ideal unless the tweeters are very good or some sound processing is employed to add time alignment and fine balance adjustment. The head units are nicely integrated into the car and BMW owners love the “iDrive” controls as they are easy to reach and use while on the move however, sonically, there is more jiggery pokery going on in order to keep the speakers within operating parameters. Many tricks are used in order to do this including reducing the bass when the volume is turned up. In fact much of the equalisation is level dependent which means the sound is different  when the volume control is adjusted.

Rainbow BMW replacement speakers

The result of all this mucking about with the sound presents a challenge to anyone wishing to upgrade. Of course you could choose to simply upgrade the speakers. There are many drop-in replacements available. Our favourites are the kits available from German manufacturer Rainbow. This will certainly improve things however, a far greater improvement can be achieved by adding an amplifier and signal processor. One of our favourite upgrades is to use an Audison Prima AP8.9 bit. £699.99 looks like a high ticket price until we reveal that the amplifier has an Audison bit processor built into it.

The compact footprint of the amplifier enables it to be easily hidden away either behind a panel in the boot or even under the front passenger seat. This 8-channel amplifier allows for versatile configuration. We like to bridge two pairs of channels to feed the under seat speakers. The rainbow woofers are rugged and highly specified and enjoy being driven quite hard. As we are feeding extremely clean power to far better speakers we are able to reduce the highest frequencies sent to the under seats which helps to raise the stereo image. We compensate for this be giving the very capable mid range speakers more work to do by setting the crossover point between them and the woofers as low as we can.  This is done by the bit processor in the amplifier which is equipped with a 10-band parametric equaliser on each of its 8 channels as well as time alignment and on-board Linkwitz-Riley and Butterworth filters to work with.

The extensive equalisation is used to flatten out the head units falsely set equalisation curve and by adding an Audison DRC remote controller, there is no need to adjust the volume control via the BMW controls thus ensuring the equalisation remains stable. A liberal application of Skinz sound treatment to the doors completes our upgrade offering the benefits of reduced road noise and a more solid setting for the speakers.

Audison Prima 8.9bit amplifier

Anyone lucky enough to have visited Driving Sounds/FOUR MASTERS at a recent show may have got to hear the results of our labours. Despite the extremely sophisticated solution, the excellent results achieved in BMW 1 and 2-series in particular, always impress and we often struggle to bring demonstrations to an end as the sound is so engaging. Every one from young children to grandparents are consistently impressed by our work (take a trip to and hear what some had to say following a demonstration)and everyone exposed has to agree that a visit to a FOUR MASTER will net far better performance to pound ratio than any “upgrade” offered by your BMW dealer so please visit your local FOUR MASTER before you tick the box at the showroom.


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