Phase Distortion In Car Audio Systems – Timing is everything
Phase Distortion In Car Audio Systems – Timing is everything
We have stated many times that music and sound is a very complex amalgamation of art and physics. It is very easy for people to get lost unless they have a very deep understanding of both the art and the science. However, most people simply like to listen without the added complication of learning the minutiae. In these blogs we try to keep things simple. The danger here is that we reduce the art and science into overly dumbed down, anomalistic rhetoric with no value. However, there is listening and listening. We encounter many people who fundamentally believe that they don’t know the difference between good sound and poor sound. Once we sit them in a demonstration vehicle, they realise that they absolutely do, it is simply that they are not exposed to good sound on a regular basis. An iPhone docking station sounds very similar to a Bluetooth speaker and actually neither sounds very good! Cars are just the same. You may experience different sound from manufacturer to manufacturer but actually, none sound that great when compared to a car with an aftermarket upgrade!
As well as covering off the very obvious issues such as bandwidth (highest and lowest frequency reproduced) and frequency response (amplitude differences across that bandwidth) there are many more factors that can seriously affect a listeners perception of sound .
Phase is the position of a point in time (an instant) on a waveform cycle. A complete cycle is defined as the interval required for the waveform to return to its arbitrary initial value. (Wikipedia)
If you play a simple pure tone (sine wave) from two separate sources the phase relationship between the two outputs is critical in order to hear what is being produced accurately. If you shift one very slightly in time, the two sounds will add and subtract from the final output. This phenomena has been harnessed by music producers since the early 60’s when allegedly, a clumsy “tape op” in a studio brushed against one of two tape machines which were playing the same thing. The resultant “wooshing” sound marked the start of time modulation effects which were added to the pallet of sounds available to musician and music recordists alike. These are now many and varied and include little boxes with names like; Chorus, Flanger and Phaser – All of these thing work on a similar principle that being; the delay of one or more versions of a single wave form played against the original.
However, although it is great fun to play with phase when creating sound, it is a completely different matter when reproducing music with integrity. Here, any phase or time differentials must be guarded against as they will adversely affect the final reproduction of the music you are listening to.
Phase distortion is relatively easy to detect at low frequencies. Even the untrained ear can detect the lack of bass that results from two low frequency signals being output out of phase. The result will lack Oomph and if the phase is 180 degrees out of phase then these frequencies will cancel out completely and you will hear nothing – This is however, as difficult to achieve as avoiding phase cancellation all together.
It is in the middle and high reaches where the phenomena becomes more difficult to identify especially in the automotive environment. FOUR MASTERS have instruments at their disposal (Audison bit Tune) to identify phase irregularities. Those without such sophisticated equipment at their disposal however have to rely on their ears and experience. Now and again we come across car owners who have upgraded and are not totally convinced by the result. One such customer, recently came to us directly for help. As he was using all of our equipment (Hertz speakers, amplifiers and processor) we were pleased to help out. He was almost embarrassed as he felt that the issue, although a source of disappointment, was so subtle it would not be a fault but a case of not having invested enough money in his system in the first place.
The customer was unhappy that whatever he did with his processor (the very excellent Hertz H8 pictured above), he could not get a solid stereo image to sit in front of him. Most of the sound was good and in fact the system sounded great apart from this anomaly. It was vocal placement in particular that perturbed him most. We looked at his settings and it was obvious that he had made adjustments with the time alignment and balance to try and rectify the issue. Our top engineer spent a good deal of time doing the same thing – Massaging settings in an attempt to get the image in the desired place and stable! – He works with the equipment fitted all of the time and as well as the image issue he began to mutter about the sound being a little hollow in the high-mid range. Having applied all of his knowledge and expertise for almost an hour and getting nowhere, he made the smart decision to step back and look at the wiring and hey presto, the woofers were wired out of phase! This is a simple mistake to make and a good argument for getting a specialist expert like a FOUR MASTER to carry out complex installations rather than having a go yourself. It is often not enough to be able to solder and remove door cards from a car, there is no substitute for knowledge and experience which can only be gained through many years of working with and learning about audio equipment. Our own engineer was fooled too as there was no lack of bass due to a 10″ subwoofer set at significant levels.
On correcting this, the image set up easily and he was able to establish a solid sound stage to the customers requirement. The customer went away with a renewed enthusiasm for car audio and a system that sounded loads better even though, the full effects of the phase discrepancy seemed small and trivial to begin with!
Make sure you get a full phase check carried out by a FOUR MASTER to be certain you are getting the very best from your equipment!
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