Audio 102

zakimak

A while back there were some issues between posters about audio which inspired me to start this thread to give some insight of what I’ve learned throughout my studies. This is a general post and is meant to give in general terms. It is not meant to be completely scientific with all the jargon and terms that most would not care to understand or in such details that would be difficult to follow. Hopefully there is enough aspects within to provide people with some insight and knowledge so they can make informed and aware future decisions. Please feel free to make any corrections but more importantly add to the discussion if warranted. Some background before we proceed.

Sound Reproduction

Music reproduction is not limited to car audio. With that, the premise is no different from other forms; be it a home system and its’ many variants or any amplified concerts. The goal is to reproduce “music” or more appropriately, ‘sound’, as faithfully as possible to its’ original source. There really is no perfect system but a more or less a subjective one. This will always going to be contentious issue but nonetheless it is still a system that comprised usually of a source, some form of amplification and a driver/speaker. Debates between each system will vary but in a well designed and executed one, it would be very much evident and satisfying.

The first thing that must be addressed when designing an audio system is that - the only perfect system is the original instrument in which the sound was created; be it a guitar, cymbals, horns, vocalist or even digitally synthesized sounds with some caveat. Another acceptance we must make is; the environment in which we listen to will always be a compromise and will add it’s character to the sound produced. Unless we are listening to live music in the original environment in which it was played, everything is simply a reproduction. Any reproduction in any form will never be as faithful as the original and colourization must be accepted. The best we can do is minimized the effect.

Once we accept that notion, we can accept every system’s limitations and not spending time arguing whether the Mark Levinson Monoblocks are any better than the cira ‘95 Krell’s and simply just enjoy the sweet sound it produces. That said, there are bad gears and good gears and the mythological belief in the ‘best and cheapest’ are left to the uninformed and biased. With all things in life, ‘diminishing returns’ applies and choosing an audio system is no different. The trick is to get the best gears one can afford, be it $1000 or $100 000. On that note, a system is only as good as its’ weakest link so we must choose wisely in order to get the best return for any given budget.

Before we decide on a gear to form our system, we need to understand how sound are reproduced, how we perceive it, what specifications are important and why it is relevant. This knowledge will allow us to understand why manufacturer place importance on certain specifications and how it applies to our purchasing decision.

Continue to Part 2

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Part 2

The Sound

When soundwave are produced, it create a pressure wave that are “heard” by the ears. In audio reproduction, this wave is reproduced by the ‘speaker(s) or ‘drivers’. There are 3 basic sound elements that are important to human interpretation of sound.

Frequencies - measured in Hz.
Levels - measured in decibels.
Localization - measure in time and space - In this case, degree and milliseconds

All 3 aspects intertwine - meaning each element must also be in consideration when dealing with another. One might have more influence on another but they are not isolated onto themselves. There are subsets of each aspect and I will limit it as much as possible to facilitate easier reading and understanding.

Frequency:
Frequencies are ripples or cycles which causes air pressure/vibrations at a given time. For example, when something is vibrating at 20 cycles per second, it translate to 20 Hertz (Hz). These cycles are measurable in term of size or often referred to as acoustic wavelength. Imagine an acoustic wavelength as generated by a pebble hitting on a calm pond. The amount of ripples from one to the next indicate its’ frequency if one can measure the time it takes from one cycle to the next. Not only is the wavelength size discernible but also the cycle. The lower the frequency, the bigger the wavelength. For example, a 20 Hz wavelength is more than 58 feet long. This phenomenon plays to huge advantage in car audio which are addressed later.

The human ears are capable of “hearing” frequencies between 20Hz to 20 KHz. Some believe to have the ability to hear beyond 20khz but generally, the accepted norm is between the noted frequencies. ‘The lower the Hertz the lower the sound‘. Anything below 20Hz are ‘felt rather than heard’. Keep this frequency band in mind when viewing specification data. When apply to our ears, we are most sensitive to the frequency between 500hz and 2Khz in terms of volume/level or localization. Typically, anything below 85Hz is very difficult to locate. As stated above, the interaction between these 3 basic elements from one to the next cannot be avoided.

Level:
In general, the larger the atmospheric pressure that are generated, the higher the perceived loudness levels or Sound Pressure Level (spl). The spl level as measured in decibels (db) also to some degree, give clues to our brains to interpret its’ direction due to localization impression via psychoacoustic. We tend to perceive something is closer if it is louder than something less so. A note about levels, the louder the sound, the less sensitive our ears becomes at the extremes of our frequency detection. An odd phenomenon also applies when the levels are low. Manufacturers often uses “loudness” equalization to address this phenomenon. What this means is our sensitivity to higher and lower frequencies are diminished as pressure (loudness) rises or lower. Part of this is due to our ears inability to transfer the pressure waves effectively at the extreme. This phenomenon should be considered when tuning a system for various loudness levels. Also note that at certain extreme levels, our ears will introduce distortion as well.

Keep in mind that the amount of air moved in terms of volumes is different from the size of the wavelength. What we are referring to here is the volume (amount) of the waves at any given time. Not the size in duration as it pertain to frequency. To use the same pond analogy as above, imagine that the distance of the wavelength is the same but the height from top to bottom of each ripple is larger. This will equate to a perceived level given the same frequency.

A subset of Level is something that is crucial in quality music reproduction: Dynamic. Dynamic or Dynamic Response or Headroom, also measurement in decibels, is the db difference between silence and full volume in a timed event. For instance a gunshot is heard in the middle of the a field. The db difference between silence and the bang in that short duration is what is considered to be the dynamic response. This translate into the system’s ability to reproduce sounds that are faithful, true and natural. If a system has poor dynamic, it would sound “compressed or monotone”. Keep in mind every recording is compressed to some degree. The majority of music recordings are purposely compressed to prevent overloading the process or system which when occurs would create distortion which we would find much more objectionable than compression.

Localization:

Probably one of the most important and least appreciated aspect of great sound is how our ears interpret localization. In other words, where the sound is coming from. Localization is subtle but very important to great sound. We perceive localization using our stereophonic ability to judge distance, depth and above all it’s location within our environment. Our brains mainly uses time delay to interpret direction with levels being second. Frequency plays a part but timing, measured typically in milliseconds (ms) is what matters in location. Delays, levels and frequency also provide what our brain interpret as depth which translate to the size and type of our environment. Localization is greatly diminished the lower the frequency or level due to the brain’s inability to decipher sound masking and our sensitivity to very narrow bands (between 500hz and 2Khz)

To illustrate, if one were to hear a sound with a frequency that has no bearing between the distance of our ears was generated from our left side, the left ear will pick up the sound several milliseconds faster than the right thus our brain will interpret it to have come from the left. This lateral detection provide us with a sense of horizontal tracking. We are less sensitive vertically since 3D detection rely on the third factor; reflection. Until we develop a third ear above our head or below our chin, we are limited to only two receptors along with reflected sound to determine vertical localization. If one were to be in an Anechoic chamber which all reflected sound are absorbed by the room, vertical detection is virtually impossible. Fortunately, we don’t live in an Anechoic chamber so our environment will assist us with vertical detection. That being said, low frequency or frequency with wavelengths larger than the distance between our ears are much more difficult to detect if the initial sound are generated within the immediate range. That means that sound 20hz wave having some 57 ft in length would be impossible to locate if one were within the 57th range of the source. Beyond that range, our localization rely more heavily on levels.

Why is this important? Localization give us depth and proper soundstage and illustrate why stereo sounds ‘better’ than mono.

Bare in mind the above 3 major elements assume that the source producing the sound is from a source that is capable of producing the required frequency and levels. This get complicated when we encounter real world limitations thus the importance of the above and will be redress below.

Continue to Part 3

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Part 3

The Car Environment

As most of us will listen to music the majority of the time in the car or at home, I will limit the discussion to these two environment. Music Hall, concerts, natural reproduction can be discuss another time in a more esoteric thread.

Car audio has advantages and disadvantages over conventional home system. The biggest disadvantage and also its’ biggest advantage is the environment in which sound are reproduced. The main disadvantage is where the listener is sitting. Either to the left or to the right of the optimum spot of a typical speakers set-up. There is really no truly cost effective way to correct this problem although new DSP technology has limited this issue. I will not go into the various acoustic properties problem associated with the various materials found in a typical car as it is beyond this thread.

To truly understand this importance, one has to understand how music are recorded. The majority of music recordings are done via a studio with the engineer placing each musical instrument or voice in a precise area to create depth and proper soundstage. This is not a physical placement but rather the use of panning, ambience/delay and level control.

Another method of recording and are mainly used in classical music is binaural recording. These recordings utilizes a dummy head with two microphones either embedded into the ear canals or on the side of the dummy’s head to capture live recordings. The dummy is placed in the optimum (center) position in the amphitheatre to capture all the nuances heard as if a live person was sitting in that very seat thus capturing not only the main sound but also the natural ambient sound from the environment, the same ambience/delay and level typically artificially created in the studio as stated above. This method will also recreate the proper soundstage that engineers strive for and in my opinion, the purest form of recording. Of course this type of recording is only effective for Classical or Operatic performances or in an environment as envisioned by the artist.. Either scenario requires that the listener of these recordings be placed in the center of the two speakers which as stated above, is not feasible in a car.

The problem is distance differences caused by where the listener is in relation to each speaker located in a typical car. Differences in distance create levels and time delays variations and if not angled correctly to the listener, deviances in frequency reproduction as well causing localization issues.

To elaborate, frequency and levels changes dramatically at off-center. For tweeters, there is typically a drastic drop-off at the high end. Occasionally the drop off are not uniform thus creating coloured sound at off-angle. Some designs are better than others when dealing with this issue but we’ll limit our discussion to basic linear drivers and not exotic eletrostatics or ribbons. Thus if you taylor the set up to the driver, it cannot be done for the passenger. Unless you’re the driver in the Mclaren F1, compromise must be accepted.

Some novel ideas has been tried to solve this problem in the past by utilizing a center speaker and Digital Signal Processing (DSP). Its’ effectiveness especially DSP is largely due to our psychoacoustic responses but by no means optimum. In my opinion, there is no way to correct this natural phenomenon to achieve absolute proper soundstage. Thus, the only feasible way is to minimize the effect is by proper placement of speakers, angles of each drivers and at the longest possible distance from speakers to listener as possible as the ratio difference would be lessen.

As such, issue relating to timing and frequency between drivers from each channel must also be taken into consideration. For example when dealing with component setup (Tweeter and woofer), it should always have the same facing angle and distance. Optimally from the same point. Due to the short distance from the drivers to the listener in a typical car installation, poor soundstage would result and at worst, the illusion of musical chairs would result. This phenomenon can be illustrated when an instrument is playing at a lower octave thus a lower frequency then as it move to a higher octave, movement of the instrument is noticed. Sound originally played by the woofer at the door for example, would creeps toward the tweeter on the dash. If both drivers are close to each other this creeping would be minimized.

Fortunately, this creeping is very difficult to detect since crossover frequency between tweeter and woofer are in the frequency range that the brain tends to have difficulty in localization and the majority of all recordings contain many complex notes that masks this movement. Some system mask this phenomenon by overlapping the x-over frequency to make the transition less evident to cover the deficiency in placement.

With the above, we also have to keep in mind that no speakers/driver can produce all the frequencies in the desirable range and at an acceptable level. Now our problems are two folds. Multiple speakers in multiple locations. Concentric design speakers will limit the creeping issue but will still have issues with time delay in a stereophonic setup if not place with diligence. Again, angle and distance must be well researched, something that a home system would not much of an issue, all else being equal. Fortunately localization is of a non issue when we are dealing with low frequencies as it is quite difficult to locate the source with any accuracy below 85Hz hence, subwoofers can placed in the back without the sense bass coming from the back.

As stated, although the space in which the listener is placed in a car is the biggest problem, it is also the biggest advantage since the confined space of the vehicle will allow phenomenal amount of low frequency to be not only heard but felt. The obstacle to achieve desirable bass notes in most listening environment is a non issue in a typical car. When we are dealing with low frequencies the listener is within the space of the wavelength itself. The confined space also allow higher levels with ease.

With the above basic knowledge, let set out each individual component in a typical cars system. Begin in the order of the typical audio chain;

Continue to Part 4

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zakimak

Part 4

Head Unit.
The head unit or radio is typically referred to as a device that has the capability to receive, decypher and convert various signals into a low level analog or digital signal so that it may be used by the device down the line - typically some sort of amplification or frequency division network/DSP.

For instance, it may receive radio or satellite signal, convert various compression formats (mp3, mp4, WMA, WMV, Ogg, FLAC, etc) or playback CDA or HD Audio, DTS Audio or DVD Audio data. There’s a vast number of features that may be brand or model specific but essentially they all do the same thing, providing an audio signal to the next device. Some will have built in amplification which can be use to power speakers but are typically very limited. DSP are typically limited to simple effects (stadium, hall, bathroom, karaoke, etc)

Location in chain: Beginning

What to look for:
Essentially most modern brand name head units are features specific. Whether it be navigation, Video, Bluetooth voice or streaming, Iphone integration, format support, etc. The differences and will usually reflect in the price are the features. It is best however, to spend sometime testing the GUI and look at the display carefully. Not all display/touch surfaces are the same as cheaper one tend to use resistive screens rather than capacitive ones which are better in the majority of cases as they have better visibility in sunlight and sensitivity. An alternative and gaining popularity are computer based systems which requires customizations and component sourcing. If you decide to go this route, I suggest doing a lot of research into it as the technology availability changes daily. Personally, I would prefer using something simple like and Ipad, playbook, Nexus, etc. One caveat, give some serious listening to the output stage of these units as any of their deficiencies will be very relevant when amplified which didn't seem to be objectionable when heard through the earbuds before.

In the Z34:

Base Audio: Plays CD and radio but no decompression (mp3/wma) capability nor satellite radio. Onboard amplification. 4 Speakers (tweeter and woofer)

Bose system: Plays CD, mp3, wmv, satellite. 6 speakers and 2 subwoofers, outboard amplification

NAV: Same as bose plus navigation with USB and HD system with 9 GIG data built in


Division Network/Etc

These devices do not generate signal themselves but rather take the signal from the head unit and process them according to their function.

Line Driver
Importance: output level and frequency response.

This is a device that performs like a simple amplifier that boost a low level signal from the head unit to a level that is much higher (typically 10v<) to keep the noise floor down. Some design would include a gating function which would shut off any signal being pass down the line if no signal is present at the input stage.

What to look for:
There really isn't much to look for here with the exception to the signal to noise ratio and output voltage. Measured in db and volt, the higher the value, the better. Signal to noise ratio measure the background noise a component makes when there are no signal. Since this is a mini-amplifier, be aware as to how this rating was achieved. At maximum rated output or at standard 2V. Although less significant, it does have some effect as the higher the output, the differences will be more pronounce. Always compare apple to apple.

In terms of output, the higher the voltage, the cleaner the signal can be used to drive multiple devices while keeping the noise floor low.

Location in chain: Usually before the amplifier

Digital Signal Processing (DSP)
Importance: Type, number of effects, adjustment level, output level

Famously first use in the studio by Lexicon then made popular on the consumer level by Yamaha, this is a device that incorporate signal delays/division/equalization and mix it back into the chain or alternative path for further processing. Famous for the stadium, hall and bathroom effects and are highly effective in movie production where individual signals can be manipulated to simulate a helicopter fly-over. In car audio, it is pretty limited since I have yet heard an unit that can process full HD/DVD/ audio effectively. One aspect that can be effectively use is timing of individual drivers. As stated above in localization, individual driver timing can be accomplish to ensure the sound from each individual driver will arrive at the same point at the same time. This greatly reduce delays variations.

What to look for:

Adjustability and flexibility. Aside from the gimmicky sound effects, the main use is time delay. Look for ones that has tine tuning (small increments) and total number of channels available. This would allow individual adjustment to individual drivers. Be aware, that expert tuning with proper measurement tools will be necessary to fully use this effectively. As much as some who hates OEM systems, this area is where they truly excel. Tuning for specific trim levels due to different textures are completely possible but is prohibitively expensive aftermarket.

Location in chain: Usually after the head unit

Equalizer
Importance: Type, number of bands (20Hzto20KHZ), adjustment level, Q curve.

Dependent on the head unit, most are limited in the number of bands available for adjustment. Usually you can expect a Bass and Treble (typically at 100hz and 10KHZ). A dedicated EQ will allow more frequency bands for finer adjustment. The more you have the more adjustability to shape the sound.

There are essentially two types commonly use. Parametric and Graphic. Parametric EQ allow you to sweep between a predetermined set of frequencies and then have the ability to increase or decrease the level of the selected frequency. This is very desirable since the flexibility would allow pinpointing the exact frequency you would want to adjust. Graphic equalizer contain predetermine frequencies and would only allow level adjustment. A word on Q. This term is refer to the effect or the curve of the band adjacent to either side of the frequency that is being adjusted. The higher the Q the less effect. Think V verses U. Q can sometimes be adjust but are typically found only in Parametric EQ. Usually the greater the number of bands, the lower the Q in order to have a more precise adjustment of said frequency. In general, Graphic EQ are often use to shape the sound where as Parametric EQ is to fix certain undesirable frequency within the system.

What to look for:

The more you bands you have the more adjustability. That said, the ability to increase that particular band is meaningless if you can't increase or decrease it sufficiently. Expect any decent unit to have the capability to do it with +/- 12db. Anything above 18db or more acts like a filter and when having the ability to adjust the Q to very narrow band, can act like a frequency kill.

Location in chain: Usually after the head unit


Continue to Part 5

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zakimak

Part 5

X-Over
Importance: Type, number of X-over frequencies, frequency cut-off, adjustment level-roll off.

Since no linear driver/speaker is capable of reproducing all (20HZ to 20KHZ) frequency flatly and at a desirable level, any decent system will require 2 or more drivers to achieve the desired frequency range and level. In theory, simply hooking up these speakers would work. However, if a driver is designed for a specific range, using a full spectrum signal to power the speaker outside that range can both be damaging and inefficient.

For instance, if a tweeter is only capable of producing frequency from 1.5Khz and up and anything below would cause excessive travel by the voice coil and thus damage, powering it beyond this capability will surely damage the tweeter. To prevent this from happening, a X-over limit frequency outside the designed range from passing through. In practical terms, the linear drivers being the norm and as such, variations on the design are used to produce specific region of the musical frequency. Typically, tweeters for high frequencies (2.5khz to 20khz) midrange/woofers (80hz to 5khz) and subwoofers (20hz to 200hz). To divide these signal to the specific speakers, two methods are used; Active and Passive.

Active X-overs are electronic unit that divide the full spectrum signal into sets of signals and pass it to the designated amplifier while passive X-over are made up of diodes, capacitors, resistors and are designed to allow specific frequency from the amplifier to pass to specific speaker/driver.

Active X-over an efficient way to utilize amplification power as specifically dedicated amplifiers can be use. This provides more flexibility since variable x-over ranges are not fixed and can typically be overlap and level adjustments. With the flexibility comes the cost is more as dedicated amplification must be use.

Passive X-over usually are included separately with the speaker in a typical 2/3 way component set or are already built into 2/3 way system. Rarely would you one find one that come with a subwoofer. Typically, the amplifier that drive the subwoofer would have the necessary frequency removed ahead of the chain. Some don’t but the only harm is higher frequency entering the subwoofer and effecting the soundstage. Levels to individual drivers are set within the Passive network but the adjustability is very limited.

Location in chain:
Active: Usually before an amplifier or line driver.
Passive: After amplifier and before speakers/driver
High Pass: indicate a frequency range from which signal above is allow to pass through - High
Low Pass indicate a frequency range from which signal below is allow to pass through - Mid/Mid Bass
Band Pass indicate a frequency range between two specific frequencies which signal above is allow to pass through - Mid/Bass/Mid Bass/Subwoofer

Amplifiers:
Importance: Number of Channels, Power within the frequency (20Hzto20KHZ) produce, power at different resistive value (power at different Ohms), Current rating, Damping factors, Slew rate, Frequency cut off

When it comes to Amplifiers, the first thing most people look at is the wattage. True, power rating will give you an idea what the amplifier is capable of but be aware of how this specification was achieved. Some rating are measure using a sine wave only at 1KHZ and not full audio spectrum and in short burst. This would be unrealistically favoured to show a rating that is not real world. Music in not a single frequency so this reading without reference is very misleading. Additionally, any rating must also include the percentage of Total Harmonic Distortion (THD) value for leaving it out can have an amplifier whose rating originally is 20W (20hz-20khz with .1%THD) to an rating of 2000W (20hz-20khz with 100%THD) because it is CLIPPING. It is also worth noting to observer what input voltage was use to achieved the rated output. Sometimes manufacturer rate their output using a 14.4 volt rating rather than 12volt. A 14.4 volt rating is typical for all car alternator when the car is running and @around 12 volt when not. Using 14.4 volt as oppose to 12 volt will obviously yield higher wattage output. Most high current, well designed amplifier will rate their output at 12 volts. Remember again to compare same specs at the same variables.

Impedance and Ohms

Giving the above, we must also look at what resistive value that this wattage was achieved and at what duration. Because speaker/drivers are directly driven by an amplifier and have resistive values consider as ‘loads’, the amplifier must be able to provide this power in this context. Car audio nominal ratings are typically rated at a resistive value of 4 ohms. Mindful that this rating is not linear across the frequency spectrum there are typical peaks and valleys. So a 4 ohms speakers might have frequency in which it there are 3 or 6 or 2 ohms area. On average that speaker is 4 ohms and is rated as such. If the amplifier is incapable of producing power at lower resistive rating, it may overheat or clip (produce distorted signal). Either scenario will cause damage. Clipping is the leading cause of speaker damage not overpowering. A high current amplifier often can be stable down to .5 ohm. Remember every time the impedance is half, power demand are doubled and the amp must be able to supply this power effectively otherwise clipping will result (assuming at full volume) or overheat. Often in a badly designed system where the amps are clipping but not completely obvious, the result is “ringing” in the ear of the listener. Most times it is caused by extreme decibels but clipping can also have this affect.

Damping Factors/Slew rate

When a signal is sent to the speaker, its’ movement is based on what that signal is asking it to do. Without sufficient damping factor, the speaker would continue to move because of inertia. As the it bottoms from one end to another base on the design of the drive, this ‘ringing’ effect would make the sound very “muddy or sloppy”. An amplifier with high damping factor rating would minimize this effect thus give it a much tighter control/sound.

Slew rate is a measure of an amplifier's ability to follow its input signal change in comparison to its’ output voltage which relates to an amplifier’s ability to pass complex waveforms without clipping them. This is not typically advertise but if one exist, look for the lowest number as it translate the ability of amplifier that is stable.

Signal to Noise Ratio

We touched briefly above regarding S/N ratio noting that it is a measurement of background noise generated by the unit. As noted, be aware that how this was measure be it at full volume of at 1 watt or full volume. The higher the number the quieter the amplifier all else being equal.

Channel Separation

Channel Separation measured in db is the mount of difference between 2 channels. Mono having 0db separation as both channels share the exact same signal, the higher the number the less likely signal from one channel is heard through another.


Headroom

Music is dynamic in nature and good amplifiers will allow quick bursts of power that is over the rated RMS/Nominal rating. Standard is 3db which equal doubling the power. A amplifier that has high headroom generally sound more dynamic since it can produce more power at a given time.

How much power?

How much money is enough? Keep in mind what your speakers are capable of but more importantly the power ratio when apply to a balance system. I favour the 1-2-4 factors approach in which the mid get twice the amount of power while the bass four times that of the high. This is on the basis on an active system. Many good system utilized a single amplifier while using an EQ and passive x-over network to achieve balance. The rule of thumb is get as much good clean power as you can afford.


Continue to Part 6

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zakimak

Part 6

Speakers:
Importance: Frequency response. Efficiency, Impedance, Power handling; Rolloff; Q (subwoofer); Size

Without a doubt this is singularly the most important aspect within the system. This is what makes or break a good system. As I’ve indicate in the preface of how sounds are produce, many specifications company champion are not really that important. The most important are frequency response and efficiency. Tweeter cannot produce thumping bass nor midbass produce decent cymbals. With that in mind, most company will provide the frequency response specification with a +/-3 DB deviation. That specification is absolutely useless without a graph. A swing of 2 db all over the place can be worst than one with a single 6 db difference which is still with the +/- 3DB spec . What’s more difficult to determine is the response off center. Variations of responses are typical on mid to high frequency drivers and are more pronounced. Some have cliff like roll off that only sound good if faced directly at the listener. Knowing this deviation would allow some predictions as how it will respond given the mounting location and angle.

Often when people think about speaker they’d ask “how much power can it take” which they perceive it to be how loud it can play. This is half correct, the determination of “loudness” apply to how efficient the speaker can produce in terms of db given 1 watt of power measured at a distance of one meter. This is standard measurement in terms of speaker efficiency. Some don’t follow this rule but all reputable company will. Given that any 3 db drop will require doubling the power to achieve the same level of loudness and it takes ten times the power to double the volume (6db), one can see how efficiency is so important. Bare in mind the human ear and how we perceive volume is not linear, “perceived loudness” ratio is even worst as the volume increases.

Power rating is meant as a guide to determine what the speaker can safely handle in term of clean wattage. This does not mean that a 50 watt amplifier cannot fry a 500w rating speaker. As noted above, the worst thing can happen to a speaker is when an amplifier clip. When an amplifier is driven past it’s maximum a sine wave become a distorted square-wave-type waveform causing the speaker to overheat.

What to look for:
Selecting your speakers really comes down to 4 things with one being above all else and that cannot be measured with specifications. The first being physical size of the speaker given the space available. The majority mid/midbass speakers are mounted in the doors and as such the depth and physical size available dictate what can go in there. The rule of thumb is that you try to put the biggest drivers since bigger driver usually means the ability to produce a lower frequency given the same volume. This is not absolute but general rule. The theory is always put as much frequency bands in front rather relying on the sub to fill in the sound. Rear fill and reasoning can be discuss later but any good system would put as much as possible up front. You don't go to a concert facing backwards do you?

Which leads to frequency response. For the front one look for roll off in the low end. This determine where x-over frequency would need to be set. For example if the speaker begins to roll off around 100HZ, your X-over would be set around this band to start and your subwoofer would have the low pass point around this point as well. Tuning will be done later but this will give you a general guideline. In general, if a graph is provided, look for a smooth and linear line with as little deviations as possible. Again industry standard typically quote +/- 3db. Without one, I would suspect it's validity.

Impedance is something to consider since most car amps are designed to work with a 4 ohms load. Keep in mind that should you run any speakers with a different load, make sure the amp is capable of delivering the power cleanly. Not all amps are rated nor designed to power speakers below 4 ohms nominal. A word on efficiency, as stated above, it determine 'how loud' the speaker can play given a set power so selecting a efficient speaker allow your amp to be more efficient.

The last and most important things to look for in any speaker is...using your ears. No specifications can determine what truly sound good except your own ears. Keeping in mind that what you hear in the typical booth would sound slightly different in your car. That may be but you can't start with a bad ingredient and make it into a gourmet meal. So whatever sounds good to you will likely to sound good to you in the car as well. Trust your ears and don't rely on what people TELL you what sounds good and what doesn't. Everything else being equal, it is you that must live with it. I would often start when someone asks me for advice is to first ask what type of music they listen to, how loud and then give suggestions as some type of speaker tend to perform better than others. I would recommend that you visit your dealers and ask them for their recommendations base on your music types and just listens to each recommendation and come to your own conclusions


In the Z34 (pre-2012):

Base Audio/Nismo: 4 Speakers system
2”x2 tweeter - on dash
6.5x2 woofers - doors

Bose and NAV system: 8 Speakers system
2”x2 tweeter - on dash
6x9x2 woofers - doors
3.5x2 - at the back fill
3.5X2 Subwoofers for coupe; 6x9x2 Subwoofers for Roadster


I have no affinity for brands of gear as everyone has their own preference. One can however be assured that typically brand name will likely carry a longer warranty have better features and likely quality which will unlikely to be inexpensive. One thing that one needs to remember is that this is a system and like any system, it is only as good as the weakest link. It would be like planning a track session with a GTM TT and have balding snow tires. My suggestion is to set your budget and plan accordingly. Avoid putting excessive budget in one area while neglecting others.

Installation has a huge effect both cosmetically and sound quality and in particularly on higher end systems, sometimes as much as 70% of the total cost. That said, the majority do not need to spend that percentage on a typical instal to get great sound as there are many great companies out there that produce great gears.. What’s important is to select ones that fits your budgetary needs and ones that will reproduce the music that you listen to in ways that sounds good to YOU unless you want to do it to satisfy someone else’s tastes.

Again, this is not a comprehensive thread dedicated to every little detail. It is an overview with some background information that hopefully will give you some perspective and knowledge when dealing with car audio. In the future with time permitting, I will add to this with related posts and updates as necessary and the practical side of things. I hope to discuss further in the future on other aspects including; accessories; cabling, power distribution, alternator, grounding and installation.

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bigaudiofanat

Looks good from the parts I read, I will have to take an evening and read over all of it. Looks like you went in more detail about sound reproduction. Glad to see that. Let me know if you want my tips about ground and cable routing that I have come across in the multiple z's i've worked on. Keep it up.

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Navster

What ohm are the speakers on the Bose with Nav system? I want to keep my factory HU but would like to change just the speakers in the car. I have read a lot about new speakers and amps and rewiring but I do not want to install a new amp. If I could find aftermarket speakers with the same ohms I should be fine correct?


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RonRizz

bose speakers are typically 1 or 2 ohms. Can you replace them with regular aftermarket speakers? yes. But you will lose a TON of volume.

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P99rs Head Unit--- Amps- 2 Pioneer Prs800d --- Zapco ST1000MX---Zapco ST-4XSQ---- SI BM mk5 Subs---SI TM65v2 Midbass--- SI M3 mids--- SI M25 xbl2 tweeters ----- 2016 MECA street class 3rd place at world finals

Navster

http://www.clearwateraudio.com/cwc8b.html
Has anyone heard of Clearwater? They make speakers for Bose amps

RonRizz

Good info. I never heard of them before.

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P99rs Head Unit--- Amps- 2 Pioneer Prs800d --- Zapco ST1000MX---Zapco ST-4XSQ---- SI BM mk5 Subs---SI TM65v2 Midbass--- SI M3 mids--- SI M25 xbl2 tweeters ----- 2016 MECA street class 3rd place at world finals

Navster

why not just do a simple transformer based impedance matching with after market speakers? I mean, it should not really change the load on the amplifier.


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Navster

Or just 2 ohm speakers I guess


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Navster

Hey does anyone know what the voltage level for RCA input is on the mrp 2000 alpine

YzGyz

Good info but way way over the top for most people. I skimmed some of it. Good stuff anyways.

YzGyz

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YzGyz