Matching Car Speakers to Your Mobile A/V System
A look behind the specs
Todd Cabell is the Senior Director of E-Commerce at Crutchfield. He drives a 2000 Ford F-150 with an Alpine stereo in the dash, Polk/MOMO speakers, a Rockford Fosgate amplifier, and an MTX Thunderform under the rear seat. He hopes to one day outfit his 1962 Mercury Comet with a worthy sound system as well.
More from Todd Cabell
Let's face it — despite manufacturers' best attempts, car speakers are not cool, flashy products. They don't come with multicolor displays or fold-down faceplates, and they do not offer you the satisfaction of pushing a button to make something happen. In fact, in most applications, car speakers are not even visible, but hidden away behind factory grilles. But car speakers are perhaps the single most crucial element of your mobile A/V system. For no matter how sophisticated the electronics in your setup, it's your speakers that determine how your music sounds.
If you think it's hard trying to decide which in-dash receiver to buy, try shopping for car speakers!
This spread from the Summer 2003 Crutchfield catalog shows 20 different 6"x9" speakers.
A typical full-size Crutchfield catalog lists about 120 different car head units, and about 150 different car speakers (including components and separates; excluding subs). Once you determine what size speaker will fit in your factory speaker openings, you've still got to choose from 10 - 30 speakers in any given size category.
Plus, the relative lack of specialty features makes car speakers all that much more difficult to distinguish from one another. Aside from adding more drivers (2-, 3-, 4-, or 5-way?) or including an external crossover, car speakers are all designed in largely the same way.
As Richard Clark has noted in Car Audio & Electronics, "Every [speaker] manufacturer has access to pretty much the same materials, and until some company starts using 'unobtanium' to build speakers, this is not going to change." 1
<img src="//a248.e.akamai.net/pix.crutchfield.com/ca/reviews/20030722http://pix.crutchfield.com/ca/ca_div.gif%20vspace=10%3E%0A%3Cbr%3E%0A%3C/span%3E%3Cspan%20class=" panel1"="" height="3" width="380"><a data-cke-saved-name="footnote1" name="footnote1"></a><sup><b>1</b></sup> Richard Clark, <a data-cke-saved-href=" http://www.carsound.com/columns/clark/clrk0005.shtml" href="%20http://www.carsound.com/columns/clark/clrk0005.shtml" target="_blank">"Speaking Out On Speakers,"</a> <span class="italicText">Car Audio & Electronics</span>, September/October 2000</span><span class="TextTiny"></span></p>
Listen before you buy! While listening to different models at a car A/V retail store is a good idea, the best way to shop for car speakers is to install them in your car and try them.
Car speaker shopping fallacy #1: The best way to shop for a car speaker is to go to the store and listen to a bunch of different models.
Reality: While listening to different speaker models is a good way to get a feel for how different speakers perform, it does not give you the most realistic experience of how a speaker will sound in your system. Why? Because each vehicle presents its own, specific acoustic challenges.
Think back to your experience shopping for home speakers. You can listen to a pair of home speakers that completely rock your world in the retail store listening room, but take them home and squeeze them between the barcalounger and the fern plant in your den and they will sound quite different.
The same is true for your car. Unless your retail store's got a weather machine and can simulate a semi passing you on the right, it's not going to give you the most accurate assessment of how the speaker will sound in your vehicle. Speakers that sound especially bright and full in the retail store may sound boomy and brash when you crank them up in your ride, while speakers that were dull-sounding and flat in the store might really shine in comparison. The only way to really understand how a certain pair of speakers will sound in your car is to, well, install them.
The best way to evaluate any speakers car or home is to install them where you plan to use them and test out some of your music. Retailers that offer a money-back guarantee make shopping for speakers a whole lot less stressful.
Car speaker shopping fallacy #2: Specs tell you the whole story on how a speaker will sound.
Reality: There are 2 reasons why you can't rely on speaker specs to evaluate a speaker's potential performance: the lack of specification standardization, and your own personal tastes.
First, there is no industry-wide, standard testing procedure for measuring car speaker performance; different manufacturers use different methods to arrive at their figures for specs like frequency response and sensitivity.
Second, how a speaker sounds is a subjective judgement it's not something you can quantify. Maybe you're a "low-end" fan who wants to feel the bass bouncing off your chest; or maybe you listen for crisp detail and clarity on the high-end. Whatever your tastes, it's your music, how loud you crank it, and what type of vehicle you drive, that are the biggest factors in how a speaker will sound to you.
As John Atkinson explained in a November 1998 article in Stereophile:
- Anyone who looks at published measurements should never assume that one measurement a frequency response, or an impedance curve, or a dispersion pattern fully or even partially describes the sound they will hear. It's only the totality of all possible measurements that will give the [shopper] any idea of what's going on. What you hear always depends on more than one measurement. Ergo, no one measurement can tell the whole story. 2
2 "Measuring Loudspeakers, Part I," Stereophile, November 1998
That's a good question. For the purposes of the average shopper, there are three specifications (aside from size and price) that you should pay attention to when shopping for car speakers sensitivity, frequency response, and minimum power handling.
A speaker's sensitivity denotes how loud a speaker plays for a given voltage level from an amplifier.
Stay with me now.
Think of a speaker's sensitivity like this it tells you how effectively the speaker converts power into sound. The higher a speaker's sensitivity rating, the louder it will play on the input power it receives. A speaker rated 3 dB higher than another, for example, requires much less power to produce the same output, or volume.
Sensitivity or efficiency?
Now, here's the tricky part due to the lack of an accepted standard for measuring speaker sensitivity, different manufacturers have different ways of determining a speaker's sensitivity.
- 1 watt/1 meter: The manufacturer measures the sound pressure level (SPL) that a speaker produces with one watt of power at a distance of one meter. But this measurement is actually a measure of a speaker's efficiency, and not its sensitivity. That's because what determines the value of 1 watt of power depends on the frequency of the signal and the speaker's impedance. A speaker requires much more power to produce low frequencies (200 Hz and lower) than high frequencies (1 kHz and up), so an efficiency rating based on the SPL at 1 watt/1 meter depends on the frequency used in the test.
"Efficiency is strictly defined as how much acoustic power the loudspeaker puts out for how much electrical power it is being driven with. If you feed a loudspeaker with 100 electrical watts, how many acoustic watts of sound does it produce? The answer is 'not many,' a typical moving-coil loudspeaker being about 1% efficient." 3
- 2.83 volts: The manufacturer measures the SPL a speaker produces at 1 meter on 2.83V of input power. Today's solid-state amps do a pretty good job of maintaining their output voltage in comparison to older, tube-style amps. So the measurement of a speaker's voltage sensitivity is considered a more accurate measurement.
Now, a voltage of 2.83V will produce 1 watt from an 8-ohm speaker (the impedance of a typical home speaker), but car speakers are almost universally 4-ohm designs. So using 2.83V to measure a car speaker actually gives you the speaker sensitivity rating of 2 watts input power measured at 1 meter that's an effective 3 dB gain in sensitivity from an actual 1 watt/1 meter SPL measurement!!
For a truly accurate measurement of a 4-ohm car speaker's voltage sensitivity, you'd need to measure the SPL of the speaker at 1 meter, on 2 volts.
Tom Breithaupt, Amp and Speaker Engineer and Product Manager for Blaupunkt, explains:
- Computing power (watts) from an amplifier (the voltage device) to a speaker (the resistor) is simple math P=(V x V)/R. Thus, running 1 volt into 4 ohm speaker, this computes to (1 x 1)/4 = 0.25 watts. Now, for 2.83volts/4 ohms, this equates to (2.83 x 2.83)/4 = 2 watts. As for 1 W/1 m, this requires 2V of drive voltage, which is (2 x 2)/4 ohms. Now for an 8 ohm speaker, for 2.83volts/8ohm, THIS NOW is 1 watt!! What is the difference? It is simply a 3 dB higher value when you reference 2.83V over 2V for a 4 ohm speaker as 99% of car audio is.
3 "Measuring Loudspeakers, Part I," Stereophile, November 1998
Detailed charts that list the most important speaker specifications are helpful tools for the car speaker shopper.
Why is speaker sensitivity important?
If you're confused by all the different methods speaker manufacturers use to determine speaker sensitivity ratings, don't worry you're not alone. The important point to understand is that there are several ways to measure this spec. So how do you (the average shopper) use sensitivity specs to decide which speaker to buy?
- Speakers with high sensitivity ratings (90 dB and up) require less power to play loudly, so they make good choices for pairing with a low-powered factory head unit. Even if you plan on using amplifiers in your sound system, a sensitive speaker will require less amplifier power to get the kind of volume and depth you want.
- If you try to drive speakers with low sensitivity ratings (87 dB and below) with a factory head unit, your music may not play as loud as you'd like without distortion.
- High-performance speakers are "overbuilt" to handle high power, so they tend to be inefficient. If you're buying outboard amplifiers for your system, don't be turned off by speakers with low efficiency ratings! See Ken Nail's discussion of "Receiver Power vs. Amp Power A difference you can hear" for more information.
Speaker sensitivity is not a very good guide as to how a speaker will sound. Some highly sensitive speakers (horn-loaded PA speakers, for example) offer high output, but relatively poor sound quality. Studio monitors, on the other hand, are designed to play with a flat, extremely accurate sound, but typically have very low sensitivity ratings.
A speaker's frequency response spec refers to the range of frequencies a speaker can reproduce without distorting. Theoretically, the human ear can detect frequencies between 20 Hz and 20,000 Hz, though a more realistic range might be something like 30 Hz to 15 kHz. So if a speaker claims to have a frequency response range of 60 Hz - 20 kHz, you can expect it to play across that spectrum of frequencies with equal accuracy, right?
This diagram shows you where different instruments fall within the audible frequencry spectrum.
Well, theoretically but as we've already seen, theory and reality rarely coincide in terms of actual A/V products. Different speakers are designed to reproduce different frequencies. A subwoofer will not give you much in the way of high frequency response, and a 4" car speaker is not going to give you much bass response. But aside from the physical limitations associated with the size and driver configuration of a speaker, speakers tend to overemphasize certain frequencies and neglect other frequencies as a necessary byproduct of converting electrical energy into acoustic energy. For this reason, frequency response ratings are often described in terms of a +/-3 dB range.
Michael Riggs, author of Understanding Audio and Video, puts it like this: "Clearly, the ideal [frequency response] would be something like +/-0 dB from 30 Hz to 15 kHz, corresponding to a straight horizontal line across the response chart (that is, 'flat' frequency response). In practice, however, most audio components fall short of perfection. This is especially true of devices such as microphones...loudspeakers, which convert mechanical energy to electrical, or vice versa." 4
As with determining a speaker's sensitivity rating, a speaker's stated frequency response specs are only as good as the method used to determine them. They can give you an idea of the potential bass extension or high frequency coverage of a particular speaker, but they do not describe how neutral, or "flat," the speaker's timbre is. For that kind of judgement, you need to listen to the speaker.
4 Michael Riggs, Understanding Audio and Video, Pioneer Electronics, 1989, p. 42.
All car speakers, especially components, will perform better and produce richer sound when powered with an external amplifier.
Minimum power handling (Watts RMS)
Note that we're talking about minimum power handling here not the RMS power range, and certainly not the Peak Power rating. Many manufacturers overemphasize peak power ratings to make their speakers sound tough and rugged.
- The peak power rating refers to how much power a speaker can handle during a brief musical burst. This figure has almost no meaning in terms of how a speaker performs. Peak power ratings only give you the vaguest idea of how much headroom, or power handling, a speaker might have. In my opinion, you should ignore peak power ratings altogether.
- RMS power ratings are the more realistic specs, but even here there's ground for caution. RMS power refers to continuous power output the amount of power you'd use to drive your speakers for hours at a time. But as with all other specs, there is no agreed upon standard for measuring speaker power ratings. Many companies adhere to the Electronic Industries Association (EIA) standard for loudspeaker power testing called RS-426B. This test consists of passing a test signal through the speaker with a flat response from 40 Hz to 1 kHz, with a three decibel per octave roll-off from 1 kHz to 10 kHz, and with a rapid roll-off above 10 kHz and below 40 Hz. This is a good test of speaker performance, but it is not a full-bandwidth (20 Hz to 20 kHz) test.
- Minimum RMS power ratings can be useful, however, when matching speakers to an amplifier. If you're driving your speakers with power from your factory head unit, it's probably a good idea to steer clear of speakers that have higher minimum RMS ratings (8 watts and above). Though you can almost certainly use these speakers with your factory head unit, you won't be able to drive them to their peak performance, as most stock factory head units will top out somewhere around 10 watts. As you push the receiver's internal amp harder, you risk distorting the signal and possibly damaging the speakers as the voice coil heats up.
Higher-powered aftermarket receivers and external amplifiers can easily drive the vast majority of car speakers. As Ken Nail's Powering Your Subwoofer for Peak Performance article makes clear, underpowering your speakers is just as, if not more dangerous, than overpowering them.
Make an informed buying decision
As we've learned, speaker specifications tend to create more confusion than clarity for the average car speaker shopper. This is in large part due to the absence of industry-wide standards for testing and measuring speaker performance. But, as important as establishing rigorous testing standards is, there is no substitute for testing speakers in your car. Hopefully, you've now learned enough about how to use speaker specifications to your advantage when deciding which models to try out in your vehicle.
Good luck speaker shopping and happy listening!