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Originally Posted by guitarbizarre
Before I start, I want everyone to understand where I come from by posting this.
Firstly, a staggering number of people are blissfully unaware of the purpose of Hi-Fi sound reproduction equipment. The aim is NOT to give you a sound that you find pleasing. The aim of Hi-Fi audio is to reproduce a recorded sound exactly as it is recorded, warts and all. The part where 'sound you like' comes into it is the recording studio, where it is the engineers job to produce a final sound that pleases the ear and if at all possible sounds suitably natural.
In all honesty, cars are one of the single WORST musical platforms possible for this, for a number of reasons.
WARNING, BIG SCIENTIFIC EXPLANATION BELOW, IF YOU AREN'T INTERESTED IN THE MECHANICS OF HI-FI SOUND, SKIP THIS POST.
Firstly, lets consider the 'ideal' listening room and a system to compliment it.
The ideal listening room is firstly, very large. Why? Because the speed of sound is constant at a given pressure, but wavelengths INCREASE with lower frequency.
Because of this, we can build this equation.
340.29 m / s = Speed of sound at sea level.
5Hz - Supposed frequency of the cannons in the 1912 overture.
16Hz - Generally accepted lower limit of human hearing. Also, lowest notes on a pedal organ.
So by dividing speed of sound by frequency of sound, we end up with the total distance covered by a sound when it has completed a single full wavelength.
68.05800 meters - Minimum distance for a 5Hz note to complete a wavelength.
21.268125 meters - Minimum distance for a 16hz note.
If those notes are not allowed to complete a full wavelength before being interrupted, then they will double back on themselves from the reflections, and begin to cancel themselves out because they are now out of phase with themselves. This creates dead but vibrating air, and contributes to exciting the Bass Nodes of a room. When this happens, then the room itself and all the air within it begins to vibrate and the bass is not heard but felt. Whatever IS heard is distorted. This is the phenomenon known as 'Standing waves' and is frequently heard in clubs at high volumes. Frequently it is referred to as 'Phat Bass', by the uneducated masses, who sadly see it as a positive thing because it allows them to engage with the music they are listening to physically, regardless of the quality of system used.
Obviously, a car is nowhere near this big. As such, faithful bass reproduction is all but physically impossible (And technically, IS impossible with today's technology)
Secondly, the ideal listening room is NOT RESONANT. The ideal listening room WILL reflect sound to a certain degree to allow good stereo imaging and the illusion of ambience and space, but it will not add its own character to the sound produced. For this reason, recording studios often employ 5 feet thick concrete blocks with additional soundproofing on the rear walls to prevent any trace of resonance but still allow an amount of reflection.
Cars however are constructed of various loosely linked moving parts and resonant metal panels, an engine which produces vibration, inadequate road surfaces that introduce inertia and momentum in all coupled parts independent of each other, which in turn means more active error correction in the CD player (Or other optical media, if you're into SACD or DVD-A), and so on, and so on. Soundproofing such as there is, is grossly inadequate to mask even engine noise in most situations, never mind the vast tonal range of a stereo system.
That is the listening room side of music reproduction somewhat dealt with (I say somewhat, there is always more!).
Now we move on to the speaker itself.
Cars do not produce a vast amount of electricity. Because of this car stereo speakers must be extremely efficient to produce reasonable volume levels. This is a benefit in some situations but requires an equal compromise - For high efficiency, speaker cones must be very light. For light weight they sacrifice stiffness.
To sacrifice stiffness is to move away from the ideal 'perfect piston' of speaker design. (A 'perfect' speaker would have no friction between itself and the surround, would weigh nothing, would be infinitely stiff, and would be perfectly flat. The cone shapes, carbon fibre/kevlar, aluminium domes, and extremely flexible suspending elements of modern speakers are all developments to achieve this with the least possible compromise.)
Secondly, speakers require a surrounding cabinet of some kind.
The very best speaker cabinets contain a large volume of air in a sealed box that has extensive cabinet bracing to reduce resonance, and they also ensure that standing waves do not appear in the cabinets by utilizing curved geometry to deflect them in certain ways. Manufacturers building speakers in a smaller box face two choices. Either utilize a bass reflex port (A hole in the speaker cabinet with a tube attached to the inside, designed to allow the speaker to reproduce lower frequencies more easily, but with a corresponding loss of final control), or use a sealed box construction but lose bass response, at the benefit of the existing bass sounding more natural and tuneful.
Obviously a car cannot accommodate a speaker cabinet of this magnitude or even design in most instances!
This means that in effect most car speakers use the bodywork as an impromptu speaker cabinet, or operate on a free air principle. Neither of these are ideal as bodywork resonates (and bodywork is different on different cars, preventing any matching between speaker and cabinet), and free air speakers run into severe problems with sound reflecting off a rear surface. (A speaker mounted on a flat panel in free air will produce sound. However the sound will be distorted by reflections from the rear. To construct a speaker on this principle without sacrificing performance would require the speaker to be mounted on an infinitely stiff board that extended many feet/meters in each direction from the bass cone!)
I hope this finds at least one person who will read and appreciate it. Few people really appreciate the amount of different factors that go into producing a good sound, and even fewer can tell the difference between a truly detailed sound, or one that has simply been EQ'd to sound that way, without actually being able to reproduce the tiny details that really make music worth listening to.
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08-12-2009, 01:25 PM
Linear Mode
