Getting true audiophile sound fidelity out of a car hi-fi (PART 1)

[WarrenM]

WHAT IS AUDIOPHILE SOUND?

The usual definition of Audiophile sound is sound which has been reproduced to recreate the original performance as closely as possible. The aim of an audiophile system is to reproduce music with such accuracy that it is audibly indistinguishable from the original performance. Of course, even if price is no object, it is highly unlikely that you will ever hear such a perfect reproduction, in which it is impossible to tell whether you are hearing the players live or a recording of them reproduced.

The more you are willing to spend on a sound system the more compromises you can eliminate in it and the closer you can come to fidelity. But, of course, spending oodles of money is no guarantee of positive results, and judicious use of limited resources can give you better sound than spending vast amounts of money on the wrong things.

HOME HI-FI vs CAR HI-FI

A bit of background may be valuable. My home hi-fi sounds very good. It has been built up over many years, primarily from 2nd-hand components, to listen to high quality classical, jazz, folk and rock music. Over time it has cost many thousands of dollars, but sounds like it should have cost many times its actual cost. Additionally it meets a critical secondary criterion known as WAF (wife acceptance factor), which means that my wife does not threaten to divorce me every time she tries to squeeze past a pair of 8' high room-dominating speakers. It is far from perfect, but you would find few home systems which sound significantly more realistic, especially considering it is relatively unobtrusive. Sitting in a central position between the two front speakers (the "sweet spot"), you can listen to well-recorded music on a vinyl record or CD or a good FM radio station, hearing the position of each singer or instrumentalist not only in his/her position from left to right, but even getting a sense of a three-dimensional sound stage and where each instrument and singer is in their specific place on the stage. There is much more to it than that, but the result is that you can almost imagine yourself in the audience of the live performance!

Why bother telling you this? It is not to brag about my home system - when you walk into my home you are unlikely to even notice the sound system (if it is not playing) as it most certainly does not physically dominate the room - it is NOT imposing which is a significant part of its appeal - I am telling you this to point out how different a good home hi-fi is, compared to a supposedly "great" car hi-fi. Most "great" car hi-fi systems are great by virtue of how imposing they are - not by virtue of how true-to-life they are. They are devised (certainly not designed) to dominate your (and the neighbours') auditory environment often with no regard whatsoever for the essence of the music they are supposed to reproduce.

A typical home listening room might be 4 metres by 5 metres (6.4m diagonally) or larger. There are lots of things in the room which reflect sound, but the vast majority of the sound hits you directly from the speakers in front of you, with all frequencies reaching you at the same time. That's why a convincing stereo sound stage can be reproduced in front of you.

In stark contrast, a car is a very small compact unit, with lots of reflective surfaces, many of them closer to your ears than the speakers themselves. So sound reaches your ears from the sides, back, above, below and in front, in no particular order. Any frequency which happens to have the same wavelength as an internal dimension of the car, will be amplified by the reflections of that frequency over and over again resulting in many frequencies which sound unrealistically loud or soft compared to the rest of the music.

The sound from the speakers on your left (in a right hand drive) reach your ears long after the sound from the speakers on your right. The reflections from the left speaker may reach your right ear at almost exactly the same time as the original sound. All this destroys any sense of sound stage, or at best results in a soundstage which partially sits outside the left door!) High frequency notes are very directional and of small wavelength, so it would be possible to create a convincing stereo sound stage based on careful positioning of your tweeters (or full-range speakers), so that you are sitting halfway between the left and right speakers. Unfortunately, your car is not shaped in a way to make that possible, and anyway, it would mean you need a separate pair of speakers for each listener in the car!

MY HONDA SHOOK ME INTO ACTION

When I bought my 2nd-hand Accord Euro Luxury CU2 last month, I was confronted by a totally unexpected shock: The sound system sounded awful. This was unexpected for two reasons: Firstly I had traded a Mazda 6 Luxury Sports which had a Bose system which sounded OK enough that I never felt it necessary to replace it; Secondly, the Euro felt so luxurious that it seemed incomprehensible that Honda could do such a crappy job of the hi-fi. But they did even worse than I realised (more on that later).

Until my last car, I always upgraded my car sound system to get it to a minimal level of competence for replaying music. My last car's Bose system more-or-less met that minimal level. I never went further than that because you can't get real hi-fi in a car anyway, so why commit a lot of money to a hopeless enterprise.

At least that is how it used to be.

A REVOLUTION IN CAR HI-FI

One thing has changed which I would never have chanced upon, had I not been knocked out of my comfort zone by the unexpectedly crappy sound system Honda had dumped on me.

That thing is Digital Sound Processing (DSP). DSP does two essential things in a car:-

1. It adjusts the volume of every audible frequency in the car so that each note is at the correct volume.
2. It delays the electrical signal from reaching each speaker by a different amount of time, so the sound reaches your ears from all speakers at exactly the same time.

The result is that an amazingly convincing sound stage can be created. Suddenly, the biggest traditional problems with music in a car have been overcome.

Of course the issue of just how deep a bass note you can play in your car is still a problem, but some of that is overcome by the DSP as well. By equalising the response of your sub-woofer, it will extend the useful bass to the limit of the car's capability.

THE PROBLEM DOES NOT STOP THERE THOUGH

Back to my Honda Accord Euro Luxury CU2. The head unit in this car and most other cars these days, especially higher end models, is fully integrated with the dashboard and all its functions, including functions on the steering wheel. Which means that replacing the head unit with something better or different means losing all that integration.

But keeping the head unit and changing speakers is also a problem! The existing speakers are not very good (that is being incredibly generous). To cope with them, the inbuilt equalisation of the head unit has been set to compensate for hopeless high frequency responses, dips and spikes in response curves, midbass standing waves, etc. When you put in really good speakers, all of these compensations turn your new expensive smooth-response speaker into an ugly harsh hissy monster.

Thankfully, your DSP comes to the rescue again. There are DSPs manufactured by Alpine, Rockford Fosgate, and JBL (maybe others too), which compensate for the pre-equalisation set in the head unit, so that the playing field is set to normal before it does all its equalisation and time-alignment of the new speakers.

WHAT DO THESE DSPs COST?

More than I wanted to spend, but less than I was prepared to. The JBL unit retails for about $1400 in Australia, but can be found for below $1200 (OUCH!). It is possible to find it for less on US sites, which I did.

Which brings me to a significant issue. If you are going to spend considerable money on a DSP, it makes sense to spend considerable money on your speakers and amplifiers and other components of your car hi-fi systems. It is also worth making sure that the job is done properly. If you are feeling your way and installing your first car hi-fi, maybe you should bite the bullet and get a professional to install it for you, or at least with you.

And take advice from the professionals. If Fred from across the road says you should use U-Beaut Speaker Cable on all your speaker leads, I'd be sceptical. If a car hi-fi installer with several years' experience tells you that your corroded connection to the battery needs to be replaced with at least 8-gauge wire, believe him - he is not trying to scrape an extra $15 profit from you.


Next:
WHAT TO DO ABOUT NOISE



Regards
Warren