Car Audio: SPEAKER AND SOUND SYSTEM 101

Occasionally, I come across incidents where car audio systems are being damaged without any clue to the owner, whether by over-driving components, maladjustments of the equipment or simply a combination of crappy equipment and stupidity. I’m going to review some common issues and offer some “guidance” if I may in the hopes that I might be able to save some gear- and ears in the process.

WHY DO SPEAKERS FRY?

Speakers can be damaged mechanically by driving them beyond what they can handle. Generally, speakers have certain limits as to what their motor structure can handle. Mechanical damage is generally caused by driving the speaker with too much power but it can also be done when a speaker is in a ported enclosure and is driven with frequencies below the port tuning frequency. This damage is common in many of the “garage built money saving” enclosures I’ve come across here.

SPEAKER FLAMBE’:

When a woofer is driven with a high powered amp to high levels, there’s always a larger amount of current flowing through the voice coil. Since the voice coil has resistance, there is a voltage drop across the speaker's voice coil. This means that there may be a great amount of power being dissipated (in the form of heat). When a speaker is driven with lots of clean power, the cone moves a lot. (Excursion) Tweeters and Midranges move less but the results can be the same.

For speakers with” vented pole pieces”, this forces a lot of air to flow in the magnetic gap (area where the voice coil moves up and down). When over-driving the amplifier results in clipping, the voice coil is still able to move as far as it should for the power that's being delivered to it but is likely not being cooled enough. This can cause the voice coil to overheat. This excess heat may cause the voice coil former to be physically distorted and/or melt the insulation off of the voice coil wire and/or cause the adhesives to fail (especially if the speaker is rated to handle no more than the power that the amp can produce cleanly). If your speakers are rated to handle the maximum 'clean' power that your amplifier can produce, slight clipping isn't generally a problem. Severe clipping is more likely to cause a problem.

CLIPPING IS NOT A HAIR-STYLE:

What exactly is clipping? Well, if you ask most folks, you don’t get a correct response. (Usually a blank stare) Clipping put simply is when the amplifier can no longer provide a clean output signal. Turn your factory radio up all the way and you can get a pretty good example of clipping on a small scale. Heck, you can even sit at any given intersection, roll down the window and take in a good helping of clipping from probably 80 percent of the audio systems in the cars next to you! Regardless of whether you do this on a set of Honda door speakers off the factory deck or a set of JL’s running off a 4 channel 100 watt amplifier, the results are the same- meaning you can end up damaging your speakers because they are unable to dissipate the amount of heat generated they receive.

Example of a clipped audio signal- the FLAT areas are clipping.

CROSSOVERS AND MAKING IT ALL WORK:

When designing any audio system, it is important- CRUCIAL actually- to make sure you have proper crossover settings. Having properly set crossover points will result in higher power handling, better separation and overall improved sound quality.

A crossover is a filter. Passive crossovers use capacitors and/or inductors in between the amp and the speakers to block/pass different ranges or frequencies such as blocking bass from the tweeters and highs from the woofers, etc. There are two types of crossovers in use which are Passive and Active or Electronic. Passive crossovers allow tweeters, mids and woofers to be driven from a single full range amplifier. They allow the proper frequencies to go to each individual speaker, while Active crossovers use op-amps to divide up the frequencies.

All crossovers have different roll-offs or slopes that can be changed to further “fine tune” the system. This is the rate which the audio level increases/decreases per octave as the frequency increases/decreases. It is usually given as a number (6, 12, 18, 24...) of dB per octave. Electronic crossovers commonly have a 12dB/octave slope. This means that every time the frequency of the audio signal is changed by a factor of 2 (one octave), the level of the audio signal will change by 12dB.

As with any audio system, it’s always better to have your installation and tuning performed by a professional installer at a reputable shop. I’ve had my share of customers who came in to have us handle their installation because the “other shop they were at didn’t feel comfortable about taking on their system installation”. Now that’s scary!