Sound Quality

Your car can be a great place for music listening. Many commuters suffer for hours each day with inferior sound quality that they'd never tolerate from their systems at home. Others assemble sophisticated sound systems in their cars that don't reach their full potential because of some common mistakes.
I've put together suggestions on how to improve the sound in your vehicle, with some tips for simple factory systems and some ideas for more sophisticated setups. Don't live with bad sound — even the simplest improvements to your system can yield great results.

Tip #1: Replace your car's speakers.

Boston Acoustics S65 speakers

In most cases, speakers are just about the last thing a manufacturer thinks about when building your car. Factory systems have improved in the last few years, but many so-called "premium" systems still use relatively inexpensive amps and speakers that don't deliver top-notch sound. You can make a big difference in your system's sound quality by installing a nice set of speakers. You'll hear tighter bass and more overall clarity, and you'll most likely notice little details in familiar songs that you've never caught before. Replacement speakers give you maximum bang for your buck, so they're a good first step on the road to better sound.

Learn more about car speakers.

Apple's iPod® touch®

Tip #2: Select a lower level of compression for your music files.
Yes, you can store more music files in your MP3 player with more compression, and they'll sound OK when you're listening through earbuds. But you lose some high- and low-frequency information when you compress your music, along with some of the details that make your music interesting. And, on a good car audio system, you can really tell that something's missing. Don't settle for the default setting when creating your files. If you want to use your iPod or MP3 player in your car, try using as little compression as possible. The higher the bit rate, the better your music will sound through your car's system.

Learn more about MP3 and other formats.

The Alpine iDA-X305S uses its high-quality DAC to bring out the details in your music

Tip #3: Bypass your iPod's built-in digital-to-analog converter.
A digital-to-analog converter, or DAC, has the job of converting digital information — 0's and 1's — into analog music signals. The iPod's built-in DAC usually does a good enough job for casual listening with earbud headphones, but it doesn't deliver the same level of performance you can get from the more advanced DACs found in many of today's better car stereos. Fortunately, if you can connect your iPod to your aftermarket stereo via a USB cable, you might be able bypass your iPod's DAC. It depends on the individual stereo, so be sure to check the stereo's "Hands-on Research" info on the Crutchfield website for confirmation.

Learn more about getting the best sound from your iPod.


Tip #4: Use Dynamat or another sound deadening material.

This Dynamat door kit will treat all four doors in your vehicle.

Dynamat does two things to make your system sound better. First, the thin metal in your door panel does not make a good home for a speaker — it vibrates as your speaker plays, affecting accuracy. When you attach Dynamat to your door panel, it deadens those vibrations and rattles, creating a more stable platform for your speaker, more like the wooden baffle on a home speaker.
Second, have you ever noticed how your system sounds really good at 25 mph, but gets a little harsh when you hit 60? Road noise tends to mask the lower frequencies first, so your system sounds overly bright when you turn it up at highway speeds. Dynamat lowers interior noise levels in your car, so you don't have to turn your music up as loud when you're driving. You'll hear more musical detail, and your amps won't have to work as hard. And that's all good.

Watch our video on installing Dynamat.

Tip #5: Add an amplifier.

Alpine's PDX-F6 amplifier

You may be saying "My factory stereo puts out 200 watts, and that's plenty of power." But there's a huge difference between 50 watts peak power per channel produced by your car stereo and 50 watts RMS from an outboard amplifier. A separate amplifier will provide more clean power than any car stereo, and that'll make a night-and-day difference in sound quality. Your system will sound better, whether you listen to Mahler at a conversational level or Megadeth turned up to 11. An amplifier is essential to getting great sound in your car.
Learn more about car amplifiers.

Tip #6: Add a signal processor or an equalizer.
A car interior presents some serious problems when it comes to sound quality. Glass and plastic surfaces reflect sound like crazy, while carpet, seat covers, and other absorbent materials soak it up. Add poorly-placed speakers to the mix, and you'll find significant peaks in frequency response in most car interiors. These peaks make your music boomy in the bass or shrill in the upper frequencies, causing "ear fatigue."

AudioControl's EQL equalizer features 13 bands of equalization, and its level matching controls deliver maximum voltage to your amplifiers.

Most car receivers give you treble, midrange, and bass controls — useful for global fixes but not for zeroing in on problem areas. You'll need a sophisticated equalizer to kill these peaks, whether it's built into your receiver or in a processor that you mount in your dash or near your amplifiers.
An outboard equalizer gives you multiple points for adjusting frequency response, so you can iron out the peaks in your system. A parametric equalizer allows you to vary the centerpoint and width of each EQ band, so you can really zero in on a problem area. Sound processors can help you eliminate frequency response peaks and increase bass response, and some even include a microphone for analyzing your car's acoustics.

Learn about equalizers.

Tip #7: Build a better sub box. Or buy one.

Sound Ordnance sealed 12" sub enclosure

If you're building a sealed box, make sure it's sealed properly. Air leaks can really hurt your sub's performance. If you're using a ported box, make sure you've got the right sub in there. You can destroy a sub that's designed for sealed box use by driving it hard in a ported enclosure. Also, it's important to build a box with the correct interior volume for the sub you've picked out. A mismatch can result in poor performance or a sub fatality. You can also avoid all of these issues by buying a premade enclosure that'll work with your subwoofer.

Learn all about box building.

Tip #8: Your crossover can really improve the sound of your system.
Many in-dash receivers now include frequency filters that'll work with your preamp and speaker outputs. If you've got a sub, use the high-pass filter to remove the low bass from your car's full-range speakers. You'll get more clean volume out of them, particularly if you're driving them with the receiver's built-in power. Or maybe your sub sounds really strong, but the bass sounds like it's coming from behind you. Experiment with raising or lowering the crossover point on your low-pass filter, and you'll be able to bring the bass up forward with the rest of the music.

This JL Audio Slash v2 Series amplifier features front and rear frequency filters.

Many amplifiers feature subsonic filters that remove super-low bass below the range of human hearing. Go ahead and turn it on — your amp and sub will run cleaner without that subsonic sludge. Also, the compression you use to create your music files can cause a low-frequency sputtering sound in your subs. Your subsonic filter can remove or minimize this noise.

Common questions about crossovers.

Tip #9: Set your amp gains properly.
Our Tech Support people field calls every day from customers who can't understand why their new car audio system sounds so bad. The #1 problem? Most people think the gain control on their new amplifier controls the volume level. Naturally, they turn it all the way up and then bad things happen. The gain control actually adjusts the amount of input signal coming into the amplifier. Crank it up too high, you'll hear some nasty distortion.

Set the gain control on this Sound Ordnance amplifier properly, and you'll keep distortion out of your system.

The general idea is to turn your receiver's volume control roughly 3/4 of the way up to maximum volume, then turn up your amp gain until you hear distortion. Back it off a little, and you're all set. Every amp manufacturer will have specific suggestions, so you'll want to check out your manual for the best way to set the gain on your new amplifier.

Learn more about setting up your new amp.

Tip #10: Don't max out your tone controls.

This JVC navigation receiver offers a 7-band EQ and plenty of user presets.

Boosting your factory radio's tone controls up to 11 might make your system sound better sitting in your driveway, but it just creates distortion when you turn it up on the highway. A heavy low-frequency boost, in particular, will put a big strain on your factory system. If you want to fatten up your sound, try using a smaller boost in the bass, lower the highs and mids a touch, and then turn up your overall level a little more. But maybe you've replaced your factory radio with an aftermarket stereo that features a multi-band equalizer. The rule still holds true — you should avoid excessive tone boosts or cuts if possible. A bad EQ setting can make a good system sound terrible, while an intelligent tone curve can make a good system sound great.
It's a bad idea to fool with your EQ on the road. If you can, program a few different EQ presets into your receiver, so you can see what works best in your car without having to adjust settings while you're driving. Or cycle through your receiver's preset curves to see if one of them sounds particularly good at highway speed, then customize that setting in your driveway.

What to look for in a car stereo.

Tip #11: Add a sub and hear what you've been missing.

JL Audio ProWedge™ enclosure

I've installed a lot of car audio systems, and I still love to see that "Wow" moment when somebody hears a sub in their car for the first time. A good subwoofer will bring the bottom octave of your music back into proper balance, so you'll hear familiar tunes in a whole new light. It'll take a load off your full-range speakers too, since you'll be playing your tunes with the bass control set at "0" instead of "+5". Some people get turned off by subs throbbing next to them at traffic lights, but it's not just about the boom — you can adjust any subwoofer to fit your tastes and your vehicle. And once you drive with a subwoofer, you can never go back to living without one. Or two.

Watch our video on adding a powered sub.

Tip #12: Use a capacitor if you're going to push your subs hard.

This StreetWires Power Station capacitor acts as a buffer between your bass setup and your car's electrical system.

They didn't have subwoofers in mind when they built your vehicle. Big bass sucks up a lot of power, and most car electrical systems aren't equipped to deal with it. A capacitor acts as a buffer between your amps and your car's battery. You connect the cap inline on the power cable from your battery, as close to the amp location as possible. It stores up power from your battery, then releases it instantly to satisfy your amp's demand for the power needed to reproduce a big bass hit. Maybe you notice a big drop in performance after you run your subs loud for a minute or two? Or do you see your headlights dimming in time to the music at night? A cap cures these problems by taking the brunt of those demand peaks from your amp, so your amp sees a more consistent supply of power.

Frequently asked questions about installing a car amplifier.

Bonus Tip: Use high-quality cables for your amplifiers.

These StreetWires ZeroNoise® 9 Series patch cables offer excellent signal transfer with minimal noise.

Electricity's like running water. You wouldn't run a garden hose from your well to your house, because not enough water would get through to keep up with demand. That's why you don't want to use cheap, undersized power cable to get power to your amplifiers — the amp will be starved for power when you start pushing up the volume control. Good power cable allows current to flow freely so your amp gets the juice it needs during peak demand. High-quality patch cables promote better signal flow from your receiver to your amps, so you hear a more focused, detailed sound. And good patch cables will also reject noise caused by your car's electrical system. Don't believe it? Ask any guitar player about the importance of good cables.

Watch our amplifier installation video.

How about your home system?

Learn about ways to get great sound in your home, too — from simple things like placing your speakers properly, to more sophisticated improvements like power conditioners and high-quality cables.

Sound pressure Level

From Wikipedia, the free encyclopedia

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Sound measurements
Sound pressure p, SPL
Particle velocity v, SVL
Particle displacement ξ
Sound intensity I, SIL
Sound power Pac
Sound power level SWL
Sound energy
Sound energy density E
Sound energy flux q
Acoustic impedance Z
Speed of sound c
Audio frequency AF v t e

This article is about the measurement of audible sound. For the music album, see Sound Pressure Level.

Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure caused by a sound wave. Sound pressure in air can be measured using a microphone, and in water using a hydrophone. The SI unit for sound pressure p is the pascal (symbol: Pa).

Sound pressure diagram: 1. silence, 2. audible sound, 3. atmospheric pressure, 4. instantaneous sound pressure

Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level. The commonly used "zero" reference sound pressure in air is 20 µPa RMS, which is usually considered the threshold of human hearing (at 1 kHz).

Contents  [hide]  1 Instantaneous sound pressure 1.1 Intensity 1.2 Acoustic impedance 1.3 Particle displacement 1.4 Distance law 2 Sound pressure level 2.1 Multiple sources 2.2 Examples of sound pressure and sound pressure levels 3 See also 4 Notes 5 References 6 External links

[edit] Instantaneous sound pressure

The instantaneous sound pressure is the deviation from the local ambient pressure caused by a sound wave at a given location and given instant in time.
The effective sound pressure is the root mean square of the instantaneous sound pressure over a given interval of time (or space).
Total pressure is given by:

where:

= local ambient atmospheric (air) pressure,

= sound pressure deviation.

[edit] Intensity

In a sound wave, the complementary variable to sound pressure is the acoustic particle velocity. Together they determine the acoustic intensity of the wave. The local instantaneous sound intensity is the product of the sound pressure and the acoustic particle velocity.

[edit] Acoustic impedance

For small amplitudes, sound pressure and particle velocity are linearly related and their ratio is the acoustic impedance. The acoustic impedance depends on both the characteristics of the wave and the transmission medium.
The acoustic impedance is given by^[1]

where

Z is acoustic impedance or sound impedance

p is sound pressure

U is particle velocity

[edit] Particle displacement

Sound pressure p is connected to particle displacement (or particle amplitude) ξ by

.

Sound pressure p is

,

normally in units of N/m² = Pa.
where:

Symbol	SI Unit	Meaning
p	pascals	sound pressure
f	hertz	frequency
ρ	kg/m³	density of air
c	m/s	speed of sound
v	m/s	particle velocity
= 2 · · f	radians/s	angular frequency
ξ	meters	particle displacement
Z = c • ρ	N·s/m³	acoustic impedance
a	m/s²	particle acceleration
I	W/m²	sound intensity
E	W·s/m³	sound energy density
Pac	watts	sound power or acoustic power
A	m²	Area

[edit] Distance law

When measuring the sound created by an object, it is important to measure the distance from the object as well, since the sound pressure decreases with distance from a point source with a 1/r relationship (and not 1/r², like sound intensity).
The distance law for the sound pressure p in 3D is inverse-proportional to the distance r of a punctual sound source.

If sound pressure , is measured at a distance , one can calculate the sound pressure at another position ,

The sound pressure may vary in direction from the source, as well, so measurements at different angles may be necessary, depending on the situation. An obvious example of a source that varies in level in different directions is a bullhorn.

[edit] Sound pressure level

Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level.

where is the reference sound pressure and is the rms sound pressure being measured.^{[2][note 1]}
Sometimes variants are used such as dB (SPL), dBSPL, or dB_SPL. These variants are not recognized as units in the SI.^[3] The unit dB (SPL) is sometimes abbreviated to just "dB", which can give the erroneous impression that a dB is an absolute unit by itself.
The commonly used reference sound pressure in air is = 20 µPa (rms), which is usually considered the threshold of human hearing (roughly the sound of a mosquito flying 3 m away). Most sound level measurements will be made relative to this level, meaning 1 pascal will equal SPL of 94 dB. In other media, such as underwater, a reference level of 1 µPa is more often used.^[4] These references are defined in ANSI S1.1-1994.^[5]
The distance of the measuring microphone from a sound source is often omitted when SPL measurements are quoted, making the data useless. In the case of ambient environmental measurements of "background" noise, distance need not be quoted as no single source is present, but when measuring the noise level of a specific piece of equipment the distance should always be stated. A distance of one metre (1 m) from the source is a frequently-used standard distance. Because of the effects of reflected noise within a closed room, the use of an anechoic chamber allows for sound to be comparable to measurements made in a free field environment.
The lower limit of audibility is therefore defined as SPL of 0 dB, but the upper limit is not as clearly defined. While 1 atm (SPL of 194 dB) is the largest pressure variation an undistorted sound wave can have in Earth's atmosphere, larger sound waves can be present in other atmospheres or other media such as under water, or through the Earth.

Equal-loudness contour

Ears detect changes in sound pressure. Human hearing does not have a flat spectral sensitivity (frequency response) relative to frequency versus amplitude. Humans do not perceive low- and high-frequency sounds as well as sounds near 2,000 Hz, as shown in the equal-loudness contour. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring sound pressure: A, B and C. A-weighting applies to sound pressures levels up to 55 dB, B-weighting applies to sound pressures levels between 55 and 85 dB, and C-weighting is for measuring sound pressure levels above 85 dB.^{[citation needed]}
In order to distinguish the different sound measures a suffix is used: A-weighted sound pressure level is written either as dB_A or L_A. B-weighted sound pressure level is written either as dB_B or L_B, and C-weighted sound pressure level is written either as dB_C or L_C. Unweighted sound pressure level is called "linear sound pressure level" and is often written as dB_L or just L. Some sound measuring instruments use the letter "Z" as an indication of linear SPL.

[edit] Multiple sources

The formula for the sum of the sound pressure levels of n incoherent radiating sources is

From the formula of the sound pressure level we find

This inserted in the formula for the sound pressure level to calculate the sum level shows

[edit] Examples of sound pressure and sound pressure levels

Sound pressure in air:

This table needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2009)

Source of sound	Sound pressure	Sound pressure level
Sound in air	pascal RMS	dB re 20 μPa
Shockwave (distorted sound waves > 1 atm; waveform valleys are clipped at zero pressure)	>101,325 Pa	>194 dB
Theoretical limit for undistorted sound at 1 atmosphere environmental pressure	101,325 Pa	~194.094 dB
Stun grenades	6,000–20,000 Pa	170–180 dB
Rocket launch equipment acoustic tests	~4000 Pa	~165 dB
Simple open-ended thermoacoustic device[6]	12,619 Pa	176 dB
.30-06 rifle being fired 1 m to shooter's side	7,265 Pa	171 dB (peak)
M1 Garand rifle being fired at 1 m	5,023 Pa	168 dB
Jet engine at 30 m	632 Pa	150 dB
Threshold of pain	63.2 Pa	130 dB
Vuvuzela horn at 1 m	20 Pa	120 dB(A)[7]
Hearing damage (possible)	20 Pa	approx. 120 dB
Jet engine at 100 m	6.32 – 200 Pa	110 – 140 dB
Chainsaw at 1 m	6.3 Pa	110 dB[8]
Jack hammer at 1 m	2 Pa	approx. 100 dB
Traffic on a busy roadway at 10 m	2×10−1 – 6.32×10−1 Pa	80 – 90 dB
Hearing damage (over long-term exposure, need not be continuous)	0.356 Pa	85 dB[9]
Passenger car at 10 m	2×10−2 – 2×10−1 Pa	60 – 80 dB
EPA-identified maximum to protect against hearing loss and other disruptive effects from noise, such as sleep disturbance, stress, learning detriment, etc.		70 dB[10]
Handheld electric mixer		65 dB
TV (set at home level) at 1 m	2×10−2 Pa	approx. 60 dB
Washing machine, dishwasher		42-53 dB[11]
Normal conversation at 1 m	2×10−3 – 2×10−2 Pa	40 – 60 dB
Very calm room	2×10−4 – 6.32×10−4 Pa	20 – 30 dB
Light leaf rustling, calm breathing	6.32×10−5 Pa	10 dB
Auditory threshold at 1 kHz	2×10−5 Pa	0 dB[9]

[edit] See also

• Acoustics
• Amplitude
• Decibel, especially the Acoustics section
• Phon (unit)
• Loudness
• Sone (unit)
• Sound level meter
• Sound power level
• Stevens' power law
• Weber–Fechner law, especially The case of sound

[edit] Notes

1. ^ Sometimes reference sound pressure is denoted p₀, not to be confused with the (much higher) ambient pressure.

[edit] References

1. ^ "What is acoustic impedance and why is it important?". http://www.phys.unsw.edu.au/jw/z.html. Retrieved 2011-08-11. 
2. ^ Bies, David A., and Hansen, Colin. (2003). Engineering Noise Control.
3. ^ Taylor 1995, Guide for the Use of the International System of Units (SI), NIST Special Publication SP811
4. ^ C. L. Morfey, Dictionary of Acoustics (Academic Press, San Diego, 2001).
5. ^ Glossary of Noise Terms — Sound pressure level definition
6. ^ Hatazawa, M., Sugita, H., Ogawa, T. & Seo, Y. (Jan. 2004), ‘Performance of a thermoacoustic sound wave generator driven with waste heat of automobile gasoline engine,’ Transactions of the Japan Society of Mechanical Engineers (Part B) Vol. 16, No. 1, 292–299. [1]
7. ^ Swanepoel, De Wet; Hall III, James W; Koekemoer, Dirk (February 2010). "Vuvuzela – good for your team, bad for your ears" (PDF). South African Medical Journal 100 (4): 99–100. PMID 20459912. http://www.scielo.org.za/pdf/samj/v100n2/v100n2a15.pdf. 
8. ^ "Decibel Table - SPL - Loudness Comparison Chart". "sengpielaudio". http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm. Retrieved 5 Mar 2012. 
9. ^ ^{a b} William Hamby. "Ultimate Sound Pressure Level Decibel Table". Archived from the original on 2010-07-27. http://www.webcitation.org/5rXlLRYsP. 
10. ^ EPA Identifies Noise Levels Affecting Health and Welfare, 1974-04-02, http://www.epa.gov/aboutepa/history/topics/noise/01.html, retrieved 2010-11-01 
11. ^ "Active Water". Bosch. p. 17. http://www.boschappliances.com.au/Files/Bosch/Au/au_en/ProductAnnouncement/Images/Bosch_Active_Water.pdf. Retrieved 4 March 2012. 

• Beranek, Leo L, "Acoustics" (1993) Acoustical Society of America. ISBN 0-88318-494-X
• Morfey, Christopher L, "Dictionary of Acoustics" (2001) Academic Press, San Diego.

[edit] External links

• Sound pressure and Sound power – Effect and Cause
• Conversion of sound pressure to sound pressure level and vice versa
• Table of Sound Levels - Corresponding Sound Pressure and Sound Intensity
• Ohm's law as acoustic equivalent - calculations
• Definition of sound pressure level
• A table of SPL values
• Relationships of acoustic quantities associated with a plane progressive acoustic sound wave - pdf
• Sound pressure and sound power - two commonly confused characteristics of sound
• How many decibels is twice as loud? Sound level change and the respective factor of sound pressure or sound intensity
• Decibel (loudness) comparison chart