Gary Tayman

Power Ratings, Speaker Suggestions:

Classic carSpeakers play a huge part in the quality of sound from any car stereo.  You want them to sound great, but your antique car can be quite the challenge -- after all, they should be invisible or at least look the part, in a vehicle that wasn't made for it.  We can make recommendations in some instances, but for the most part it's up to you to decide.  What we CAN do is provide some information to help you out -- no myths, no sales pressure, no technobabble, just some facts and suggestions so you can make an informed decision.  Read on.

 

The basics -- what is sound?

Sound is physical vibrations that get passed through the air.  These vibrations are made up of several frequencies -- bass, treble, and midrange.  Your hearing range is approximately 30-17,000 cycles per second (Hertz, or Hz).  Most sounds are in the 100-3,000 Hz range.

SoundRadios and media players are machines that process sounds in the form of electrical signals.  A typical AM radio reproduces about 50-4,500 Hz.  High fidelity FM radio reproduces 30-15,000 Hz, three times the bandwidth of AM, and nearly the entire hearing range.  A CD or digital sound source can reproduce even more --essentially everything you and your dog would ever want to hear.  A speaker's job is to convert these electrical signals back into physical sound. 

High-fidelity is harder to reproduce for two reasons.  First, it takes more power to reproduce hi-fi at the same listening level as an AM set.  Second, no single speaker can handle the entire spectrum.  Big speakers are better with bass, while small speakers are best with treble.  This is why hi-fi sets have woofers and tweeters.  Most car stereo speakers come as an assembly that contains a woofer, tweeter, and sometimes a midrange.  Of course stereo itself is an added measure; the concept of two channels recreates the ability to hear sounds from different locations, as in real life.  Most modern car stereos have FOUR amps, but they still reproduce only two channels.  The 1970's saw a short-lived system called quadraphonic, using four discreet channels, but the concept never became popular.  Although most modern car stereos have four channels, only two stereo signals are actually reproduced.

 

Now some basics on power!

Power is a measurement of energy.  Did you know that 746 watts equals one horsepower?  You do now.  They're measurements of the same thing.  Your car's motor may offer 300 horsepower, but typical highway driving only requires about 10-12 hp.  In the same manner your stereo might offer 100 watts, but normal listening level is less than a watt for an AM radio, and a couple watts for high fidelity..  A higher-powered stereo allows you to turn the volume up louder.  It's good to have that extra power in reserve so it can reproduce that instantaneous bass drum or cymbal.  By the way, power usage is a log scale.  Doubling the power does not double the volume level -- it makes it only slightly louder.  So a 200 watt stereo offers slightly more volume than a 100 watt; in other words it's better, but not by a lot.  If your stereo provides adequate volume, you're good.  Don't nit pick over the numbers.

Now for a factoid that I bet you didn't know.  Older car radios only offer about 3 watts into an 8 ohm speaker.  That's all you get!  Why?  It has nothing to do with being cheap, and everything to do with your 12 volt DC battery.  Turn the volume up to the limit of 12 volts peak-to-peak, do the math, and you get about 3 watts.  You can double the power to a whopping 6 watts by using 4 ohm speakers -- and now you know why the standard for car stereos is 4 ohms.  But 6 watts still isn't that much when it comes to high fidelity, so those early FM car radios intentionally limited the audio fidelity for that reason.  That's why, for years, the stereo in your car didn't sound nearly as good as the one at home.  Of course stereo has two amps, offering 12 watts, and a 4-channel stereo provides 24 watts -- an improvement, but still inadequate for a good high fidelity system.

Fast forward to today.  How do you get 100, 200, or 50,000 watts in a car?  Two methods.  The first is basically to "bridge" two or more amps together in such a way that each amp works with a portion of the sound wave.  All nice and neatly tucked away in a single audio IC, it's compact and works really well.  But it comes with a warning:  don't go tying speaker wires together, or ground them to the car, like grandpa did in the olden days.  These wires actually have a DC bias voltage on them, and creative wiring could give your stereo a bad smoking habit.  Two wires to each speaker, and be happy.

The second method is used in those huge honkin' trunk-mounted amps that rock your neighborhood.  A power supply converts DC into AC, and a big power transformer gives you a boost of 75-80 volts or more.  Now you can make lots of noise, impress your girlfriend, and make everyone else deaf.

Before moving on, there is one more aspect of power you should know about.  The stereo makers use different methods of measuring power, usually to inflate the numbers so as to impress the potential buyer.  There used to be peak, average, and others, but lately they've settled on RMS (Root Mean Square, a formula for calculating real energy).  The FTC mandated an RMS measuring standard for home stereos, but unfortunately it doesn't apply to car stereos.  So they cheat by using a square wave to give a higher reading.  The good news is most car stereos use the same standard, so comparison is easy -- but you'll need to cut that figure in half to get close to the real FTC measurement.

 

Now let's choose our speaker locations!

"Why can't I use the original dash speaker?"  Maybe you can, if you don't need high fidelity, or in a situation where nothing else will fit.  But two things must be checked.  First, it's really old; is it warped, torn, or eaten by mice?  If it looks good, there's another hurdle -- and it's a big one.  Some original speakers have one terminal connected to ground.  Remember my earlier comment about the bad smoking habit?  New stereos have bridged amps with a DC voltage on the speaker wires.  Grounded terminal means dead short.  Be careful!

Dual Voice CoilIf at all possible, use new speakers.  The dash LOCATION is fine, assuming a new speaker fits.  Most 1950's-60's cars use standard sizes, but you should check to ensure there's not an A/C duct or windshield wiper snuggling up next to it.  Expect your new speaker to be physically larger in the back.  Something else -- if you only use one speaker, you don't have stereo.  The Aurora FMR Conversion will automatically switch to mono if a single speaker is connected, but most stereos don't do this.  You get either a left or a right channel only.  Custom Autosound Dual Voice Coil (DVC) speakers help with that -- electrically two speakers, you can feed a left and right channel to it and get the full program.  There are also "dual speakers" that can be used in a pinch; these are essentially two very small speakers mounted next to each other on a single board.  Their advantage is that they'll fit in places where a DVC won't, but that's the only advantage.  The small cone size is a disadvantage, as I'll explain shortly.

Some cars have a location for a rear speaker -- voila!  Stereo!  Is there a rule somewhere that says stereo must be left and right?  Actually, many GM cars of the 1960's did this -- left channel front, right channel rear.  Many sedans and coupes have rear package trays that allow for two 6x9 speakers to fit.  Some Mopars have package trays pre-perforated for this -- cool!  A dual voice coil in front, stereo pair in the back, not a bad choice!

One more idea if you like the Dual Voice Coil concept:  If your car has a single dash location and a single rear location, Use TWO DVC speakers.  If you connect both left channels to the front speaker, and both right channels to the rear, you'll have the full stereo effect AND the full power of the 4-channel stereo, all without punching holes in other places.

If you want to get creative with speaker locations, there are three things you need to consider:  cone size, baffle, and compression area.  Cone size:  bigger is better if you want bass.  Smaller allows more locations, if you don't mind the sound quality of a pocket transistor radio.  Best location is one that allows for decent sized speakers.  Baffle:  a fancy name for a wall.  Sound comes from the front of the speaker, and also the back.  If they cancel each other out, it sounds crappy.  A baffle masks the back of the speaker.  Compression area:  in a small enclosure, the air compressing behind the speaker can limit its movement.  Your car's trunk -- huge; doors or kicks -- not so much.  A small enclosure restricts the bass.

UndercoverNow for some creativity.  Many years ago some genius invented a really cool speaker enclosure.  It's called a ported enclosure, or a bass-reflex.  Essentially it's a small speaker enclosure with a hole in it.  The hole -- fitted with a mailing tube or molded plastic tunnel, is a precise size and shape.  The sound coming from the back of the speaker, particularly the bass, gets inverted inside that tube, and ADDS to the sound coming out the front.  Yes, it works great.  Ported speaker enclosures are available that fit on the package tray or under the seat -- not a bad choice.

Another idea that's neat is the satellite system.  You might already have this on your home computer or TV set.  This works on the principle that your ears determine the direction of sound by the treble notes, not the bass.  If you place two small tweeters on the desk or TV stand, and stick a subwoofer under the sofa or some other hidden location, you can hear the entire spectrum and it all appears to come from those little tweeters.  For the car, there are not many matched systems out there, but there are subwoofers available with lots of crossover adjustments so you can match them with existing speakers.  Suddenly the cone size no longer matters -- you can place any size speakers anywhere, and the sub will make up the difference.  The biggest issues here are, where to mount the sub (probably under the seat), and is it powered -- if so, you need additional wiring to power it.

Did you just hear a new term?  Crossover.  This is a circuit that sorta directs traffic.  It essentially directs the high frequencies toward the tweeters and the low frequencies to the woofers.  Without a crossover, a lot of energy would be wasted sending sounds to speakers that can't reproduce them.  Since different speakers have different characteristics, it's nice to have a crossover that's adjustable.

 

Choosing speakers:

Armored with all the above information, it's time to start shopping for the speakers themselves.  What to look for?

The one spec that's boldly imprinted on the box is the wattage -- "140 Peak Watts!"  Big fat hairy deal; it means very little.  For starters, the speakers don't produce any watts -- the stereo itself provides the power, speakers convert it to sound.  That wattage number is an estimate of how much power it is guaranteed to handle -- and it is a bit misleading.  There are two speakers in the box, meaning 70 watts apiece.  The number is "peak" -- remember what I just said about different standards of measurement?  In the real world, RMS is about 70% of peak, so now we're looking at 45 watts.  But if the stereo is rated at 45 watts, remember this is only 24 real watts anyway, so the speakers are adequate.  Are you still following me?  Bottom line, most all decent car stereo speakers will handle your car stereo, even at full volume, which I hope you don't do.

Car Stereo SpeakersThere's another number that means quite a bit more, and I bet you have to really search to find it.  It's called efficiency, or SPL (sound pressure level).  This is a numerical rating of how loud the speaker is per given watt.  Good home speakers have an SPL rating of 120 or so.  Car speakers, if good quality, are in the 91-95 range.  Small or cheap speakers may have an SPL in the 80's.  Now for a marketing trick:  since the challenge of smaller speakers is to give you adequate bass, some speakers are "loaded" in such a way as to make the bass seem better by cutting the treble and midrange.  In other words, deliberately reducing the efficiency.  The salesman will blab, "These speakers are SO good that you need at least 200 watts to drive them!"  Translation:  they are so badly loaded that you need to feed them 200 watts to hear the dadblamed things!  This is NOT a spec to brag about; go find some more efficient speakers.

Then there's that spec called Frequency Response.  This is the spread of frequencies that the speaker will reproduce, plus or minus 3 dB.  If the response is 30-18,000 Hz, it means the speaker will reproduce any frequency between those numbers at the same volume level.  It can reproduce lower and higher, but not quite as loud.  The bass is worth looking at, but a lot of stereo guys seem to go hogwild over the treble -- 22,000, 25,000, 30,000!  Why?  Your ears can't hear over 17,000, and remember FM stops at 15,000 (FCC rules).  Anything above this is a waste of time and money.

Finally, there's impedance.  The short answer, the standard for car stereos and speakers is 4 ohms, not much else to say.  But what does it mean?  In simple terms, resistance is a load.  Feed current through a light bulb, and this resistive load converts power into light.  If you have coils and capacitors, they also enter into the mix -- and a speaker has coils.  The total load measurement is impedance; that's why the term is used..  If the speaker is "matched" to the 4-ohm stereo, you get the best performance.  If you use 8 ohms instead, it'll still work but you have less power available. If 2 ohms, same thing plus it draws more current than called for.  Bottom line, stick with 4 ohm speakers.

After reading and understanding all of this, the best way to compare (if you can) is to go to your local car stereo store and listen to them.  Many such stores have a wall of speakers, and a rotary switch that lets you compare them.  Do you like the sound of a certain pair?  Go with them.  All the specs in the world boil down to one thing -- sounding good.  If you like them, that's what really matters.

 

Summary:

Hopefully this page has helped you understand a little more about power and speakers.  I've tried to cover all the bases without boring you to death, or going way over your head.  Let me tell you, it was not easy to write this, but I really want to educate everyone -- the more informed you are, the better decisions you can make.  If you have questions let me know -- I'll do my best.  What I CAN'T answer are questions like, "Are Pioneers better than Kenwoods?" or "Do you like Infinitys?"  If you like shopping by brand name, great -- but the comments I've made above are your best source for comparison.

 

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