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Monday, November 12, 2007

Great car speakers deserve a little TLC, too

Lot’s of people make them when choosing speakers. Read this first.


When you walk into your local, friendly car audio sales emporium, the smiling pleased-ta-meetcha sales professional is going to lob a bunch of questions your way. You're first thought is: "Why should I share all this personal information with this stranger?" And that's a good reaction. But it's just a car stereo, man. The salesperson is there to help you pick the best system for your needs. They can take your end of the equation and add to it their own experience and knowledge of the products they sell, and help you come up with the perfect system for your budget and your car. So relax. Answer the questions. Now.

Question #1: How much do you want to spend?

The smiling sales professional is not asking this question so he can decide how big a sucker you are, he's asking it so that he can help you budget your money in the most economical way. Your answer to this question helps determine where your money should be spent to build a system that's right for you. He'll probably suggest budgeting your money in the order of component importance: speakers, amplifier, and then head unit.

Question #2: What changes are you willing to make to your car?

He's grinning when he asks this. Maybe he's salivating, too. You've got visions of a bunch of installers completely gutting your car just for the fun of it. You couldn't be more wrong. Answer this question, and establish boundaries for the extent of your installation. It will affect the type of system you buy, and the type of installation the expert suggests.

Question #3: How long are you going to keep your car?

You agree to the most extensive and complicated installation of the most expensive system in the hemisphere. And when you get home you remember that you planned to sell your lemon at the end of the month. The answer to this question can help you avoid that.

Question #4: What is the primary function of your car?

Do you use your car to drive to and from work everyday? Is it a 10 minute jaunt, or an hour commute? Do you travel to distant destinations in your car? Does your car just sit in your driveway until you're forced to go to the grocery store? Answering this question helps an expert decide how much of a system you really need. If you simply drive from home to work, you probably don't need the same kind of extreme GPS navigation and DVD surround sound that you would want if you were traveling long distances on a regular basis. But then again…

Some simple, though very important, things to do when you clean up your act.


RCA and other connectors

Corrosion, moisture, dirt. They all can be present, and they’re all easy to deal with. Check your RCA connectors once a year. A simple unplugging usually is enough to clean them out, but if they’re looking grungy, denatured alcohol (98% Isopropyl) and some cotton swab will do the trick.

Speakers

Dust buildup over time will affect a speaker’s performance, though this applies more to tweeters than woofers. In any case it looks sloppy, so here are two options. Best would be compressed air in a spray can, the same kind used to clean computers and practically every other piece of electronic equipment. The low pressure spurt of air is enough to remove surface accumulation, gently. You could use a compressor, but only if you can reduce the air pressure to a gentle summer’s breeze. Too high a pressure, and you could be saying adios to a diaphragm. A dust cloth is another option to use on woofers.

Amps

The venerable cotton swab and alcohol (98% Isopropyl), or contact cleaner, will get the job done nicely on amp terminals. Painted amps can be cleaned using a mild cleaner that is sprayed onto a cloth. Under no circumstances spray anything directly onto an amp. Under no circumstances spray anything directly onto an amp. That was not a typo. Yes, we repeated ourselves. The same procedure also applies to raw metal amps, but you can apply a little metal polish to make them sparkle. Finally, if you run bare wire into terminals and it becomes corroded, you can cut off the corrosion and re-strip the wire, but make sure you have enough length to work with before you start hacking away.

Head Unit

Any dust is easily removed with your handy dandy spray can of compressed air. But what about all of those grimy little fingerprints. We know they’re not yours. Here’s what to not to do first. No solvent. No alcohol. You don’t want anything in that circuit board, but you can use electronic switch cleaner that is plastic safe sprayed directly if the buttons are sticky.

Vacuum Cleaner

To our knowledge, the vacuum cleaner is not part of a car’s audio system, but we give it a separate heading for a good reason. Don’t use one on your speakers. It’s not worth risking a ruptured diaphragm.

Follow these few simple procedures, take your time, and your car’s audio system will shine the way it was designed to.


Some simple, though very important, things to do when you clean up your act.


RCA and other connectors

Corrosion, moisture, dirt. They all can be present, and they’re all easy to deal with. Check your RCA connectors once a year. A simple unplugging usually is enough to clean them out, but if they’re looking grungy, denatured alcohol (98% Isopropyl) and some cotton swab will do the trick.

Speakers

Dust buildup over time will affect a speaker’s performance, though this applies more to tweeters than woofers. In any case it looks sloppy, so here are two options. Best would be compressed air in a spray can, the same kind used to clean computers and practically every other piece of electronic equipment. The low pressure spurt of air is enough to remove surface accumulation, gently. You could use a compressor, but only if you can reduce the air pressure to a gentle summer’s breeze. Too high a pressure, and you could be saying adios to a diaphragm. A dust cloth is another option to use on woofers.

Amps

The venerable cotton swab and alcohol (98% Isopropyl), or contact cleaner, will get the job done nicely on amp terminals. Painted amps can be cleaned using a mild cleaner that is sprayed onto a cloth. Under no circumstances spray anything directly onto an amp. Under no circumstances spray anything directly onto an amp. That was not a typo. Yes, we repeated ourselves. The same procedure also applies to raw metal amps, but you can apply a little metal polish to make them sparkle. Finally, if you run bare wire into terminals and it becomes corroded, you can cut off the corrosion and re-strip the wire, but make sure you have enough length to work with before you start hacking away.

Head Unit

Any dust is easily removed with your handy dandy spray can of compressed air. But what about all of those grimy little fingerprints. We know they’re not yours. Here’s what to not to do first. No solvent. No alcohol. You don’t want anything in that circuit board, but you can use electronic switch cleaner that is plastic safe sprayed directly if the buttons are sticky.

Vacuum Cleaner

To our knowledge, the vacuum cleaner is not part of a car’s audio system, but we give it a separate heading for a good reason. Don’t use one on your speakers. It’s not worth risking a ruptured diaphragm.

Follow these few simple procedures, take your time, and your car’s audio system will shine the way it was designed to.


ive tweeters the respect they deserve, really.



In another "Advice" article 12 volter Paul Seredynski talked about some causes of automotive loudspeaker failure. Now we'll look specifically at tweeters-why they fail, and how keep them healthy longer.

Tweeters reproduce the very highest frequencies (treble). High frequencies require that the speaker move back and forth very fast, up to 20 thousand times per second! To move that fast, the moving parts (voice coil wire, former and cone) must be lightweight. Music is delivered to the tweeter in the form of electrical current. As current flows through the tiny voice coil wire in the tweeter, the coil gets hot and may burn out if fed too much current. A crossover network filters out the lower frequencies so the tweeter is only asked to reproduce frequencies and amounts of current that it can safely handle. Most tweeters should be crossed over at 3000Hz or higher. The lower the crossover point you choose, the greater the chance the tweeter will fail.

About Crossovers
In coaxial speakers the "crossover" is usually a single capacitor. A capacitor reduces the level of low frequencies at a rate of 6dB per octave. That means that if the capacitor's filter value is 3000Hz, the current will be reduced by 6 dB one octave below 3000Hz or 1500Hz and by 12dB two octaves below at 750Hz (Fig. 1). More sophisticated crossovers use a capacitor with an inductor (coil) to make a "second order crossover" (Fig. 2) that rolls off the lower frequencies at a rate of 12dB per octave. To use our previous example, with a 12dB per octave cross-over, the signal is down 12dB at 1500Hz and 24dB at 750Hz. You can see by looking at the graph in Fig. 3 that there is far less low frequency energy getting to the tweeter with a second order crossover than a first order. A tweeter with a second order crossover will play louder and last longer than one with a first order filter. At the lower, more dangerous frequencies, much less energy gets to the tweeter, and thus much less heat.

Rule Number One

NEVER EVER RUN A TWEETER WITHOUT A CROSSOVER NETWORK!

Electronic Crossovers
In more sophisticated installations the passive crossover network supplied with the tweeter or component system is replaced with an external, electronic crossover. In this case the low frequencies are filtered out before a dedicated tweeter amplifier (Fig. 4). While this method has multiple performance advantages, there are potential dangers.

The crossover point is usually adjustable on an electronic crossover and the possibility for setting it incorrectly goes up exponentially. If you set the crossover "by ear" at low levels, it'll sound great at crossover frequencies as low as 1000Hz, but as soon as you turn up the volume, Poof! Bye, bye tweeter.

The calibration settings on an electronic crossover are rough at best, just because the knob says it's at 5000Hz doesn't mean it is exactly. To be absolutely certain that you have chosen a safe and appropriate hi-pass filter setting, use a signal generator and Volt meter to measure the filter characteristics of your crossover. Many professional car stereo installers have equipment capable of confirming cross-over filter characteristics.

Rule Number Two

NEVER SET A HI-PASS TWEETER CROSSOVER LOWER THAN 3000Hz.

Equalizers
Equalizers (or EQs) are electronic devices that can adjust the frequency range to achieve "flat" response. When misused, they are notorious tweeter killers. Many people adjust the EQ to yield flat response as measured by a RTA meter. But meters don't "hear" like people, and "flat" response is often too bright. Over adjusting an EQ for measured flat response is a sure-fire way to fry your tweeters. If your system isn't "bright" enough for you, don't compensate by turning the treble control or EQ all the way up. Either move the tweeters so they are more in line with your ears, or add another set of tweeters.

Rule Number Three

BE CAREFUL WHEN USING EQUALIZERS OR TONE CONTROLS. NEVER TURN THEM UP TO, OR EVEN NEAR, THE MAXIMUM SETTING.

Loud Vs. Distortion
We understand if you want to play your car system REAL LOUD. We also understand that if you want to play it that loud you'd better have plenty of speakers and amplifier power. Asking your one set of itty-bitty tweeters to keep up with the eight 12" woofers in your trunk is unrealistic. As soon as you hear any distortion, it's a sign that some part(s) of your system is operating at or beyond its limits.

Rule Number 4

WHEN THE SYSTEM DISTORTS-TURN IT DOWN! THEN BUY MORE STUFF!


Source: http://www.polkaudio.com/education/advice.php


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