this thread was inspired by another member stating that it would be good to have a general guide to loudspeakers, so here's all i know. every member is welcome to add or change anything i say to correct terms. this is to clear up the misconceptions and confusions in loudspeaker design.
Let's start on speaker drivers themselves, and with that, a little on sound.
The audible range of sound is roughly 20hz-20khz. This means that anything below 20hz is subsonic (infrasonic) and i am not aware of the term for above 20khz. This means, speakers that try to sell you on frequency responses up to 25khz are not worth the extra money unless you are a dog. Now, this does not hold the same for infrasonic waves. These waves while inaudible, are rather felt. Because of the wavelength of the sound, they fluctuate less and thus travel through barriers. An easy way to think of this is by taking a sword. Drive that sword (soundwave) into the ground. It goes into the ground. Crumple the sword, and try it again. It just bounces off (this is similar to high frequencies).
Within the audible range of sound, there are different regions. We shall start from the bottom and go up. We start with infrasonic bass (1hz-19hz). Now, from 20hz to around 60-80 hz is called subbass. The drivers used for this are subwoofers. More on the word later. From around 80-500 can be considered the bass to midbass region. The drivers used for these are woofers. Now from there up to around 2khz is the bandpass or midrange region. These drivers are obviously midrange cones. These most often are paper coned speakers anywhere from 3"-6.5" in diameter and are generally in typical cone shapes, domes or planar. From about 2.5khz to 20khz are the high frequencies. These drivers are tweeters and most generally range from 3" to 1/2". Planar or ribbon tweeters are very popular for this sound range.
Most subbass drivers are very large, because to make large sound, you must move large air. This concept also makes sense if you think about Jurassic Park. Who wants to listen to dinosaur steps that sound like you are tapping a dixie cup? These diameters are generally 18" up to multiples of 5"-8" drivers. Most commonly, 12" subwoofers are used, and most HTIB setups are either a few 6.5" speakers in bandpass boxes.
When selecting a speaker to use in a cabinet, it is most often useful to know the specs of the speaker. More importantly, it is useful to know what those specs mean
I'll give you a run down on some basic terms, and suggestions on clarification and correction are very welcome.
A - Attenuation, loss of db
B - Magnetic flux density in gap
Bl - Electro-magnetic force factor
BL - Driver motor strength
Cab - Acoustic compliance of air in the enclosure
Cas - Acoustical equivalent of Cms
Cmes - The electrical capacitive equivalent of Mms
Cms - The driver's mechanical compliance (reciprocal of stiffness)
D - Effective diameter of driver
F3 - -3 dB cutoff frequency
Fb - Enclosure resonance (usually for reflex systems)
Fc - System resonance (usually for sealed box systems)
Fs - Driver free air resonance. This is the point at which driver impedance is maximum
Lces - The electrical inductive equivalent of Cms
Le - Driver inductance (voice coil, mainly)
Levc - Driver voice coil inductance
Mas - Acoustical equivalent of Mms
Mms - The driver's effective mechanical mass (including air load)
n0 - The reference efficiency of the system
p - Density of air at STP 1.18 kg/m^3 (rho)
Pa - Acoustical power)
Pe - Electrical power)
Vd - Venerial disease No, but for real. It is the volume of air displaced by the speaker. A word on this: DO NOT TAKE THIS NUMBER AS DEFINITE. Many people assume that more Vd = louder sound. Most cones are rather the same size (same diameter cones i'm talking about) and those with a similar xmax will have a similar Vd. But why are some of these tailored to SPL and some to SQ? If you don't believe me, here is an example. My dayton 15" has 21mm of xmax. My DD 9515 has 13mm of xmax. THe dd walks on the dayton in spl, even though technically they have a similar Vd. Reason Vd doesn't account for pure, all out SPL is because Vd takes distortion and linear output into account. For musical listening, we only want our subwoofers to function in a linear, relatively low-distortion manor. For SPL, distortion and linear output goes out the window. All we care about is moving as much air as possible, so they can push the subwoofer well beyond it's linear limitations and out to it's mechanical limitations (Xmech) Vd is calculated by multiplying the xmax by the Sd.
Ras - Acoustical equivalent of Rms
Re - Driver DC resistance (voice coil, mainly)
Revc - DC resistance of the voice coil only
Rg - Amplifier source resistance (includes leads, crossover, etc.)
Sd - Effective piston radiating (surface) area of driver
Vab - The volume of air having the same acoustic compliance as the enclosures
Vas - The volume of air having the same acoustic compliance as the driver suspension: Cms
Vb - Net internal volume of enclosure
Xmax - Maximum peak linear excursion of driver
Z - Total driver impedance
Q (es) (ts) (ms) (tc) - Q stands for "Quality Factor", which describes the ratio of energy stored to the energy dissipated. These are very useful tools when designing a cabinet. For the sake of time and people not liking to read, Qts is generally the only useful tool in PRELIMINARY cabinet construction (Qtc, someone else can explain that because i'm not too sure). Qts it the total Q of a speaker, thus Qes and Qms. A lower Qts driver is generally suited for a ported enclosure (.3>), higher values (.7<) are suited for sealed enclosures. The median values can either be used for other enclosure types. Qtc describes the total "Q" of the "system" (driver in the enclosure). Qts is used to indicate the low frequency behavior of the subwoofer. Qtc is used to indicate the low frequency behavior of the system; ringing/overshoot/decay, frequency response, low frequency extension, group delay, etc. How does this tie into the stored/dissipated energy ratio? Well, the higher the Q(tc), the higher the ratio of energy storage compared enery dissipated....resulting in "ringing" and slow decay, and an underdamped response. The lower the Q(tc), the opposite, less ringing and faster decay, and an overdamped response. A Qtc of .707 is said to have maximally flat requency response and lowest F3, with a transient response (ringing, overshoot, etc) that is "not too bad". Good graphical representation here: http://www.carstereo.com/help/Articles.cfm?id=29 I SHOULD ALSO MENTION THAT THIS IS THE TIP OF THE TIP OF THE ICEBERG ON PARAMETERS
Let me see, where to start.
Vented (ported) are very common enclosures at they most usually are used in subwoofers, which people seem to take the most notice to. The port on these enclosures is used to enhance or bring out a sound around a certain frequency that the enclosure is tuned to. Using damping materials in these enclosures can also smooth out the sound much like in sealed boxes.
Sealed are very common because they are simple. 6 pieces of wood, some glue and maybe a bit of alcohol and u have yourself a sealed box. While these may seem to be easy and not very difficult to design, this is not the case. These have the tendency to be "peaky" in higher frequency ranges. They also have a tendency to require smoothing in certain response ranges. This is where the use of damping materials comes into play. Eggcrate foam, fiberglass, Dacron, pillow stuffing or Polyfill is very popular to use to dampen these waves.
Bandpass enclosures are also common because they are easy to **** up and be loud no, but really these are probably THE most commonly used speaker designs in the commericial budget subwoofer market. Nearly, actually i'd venture to say that EVERY HTIB has a bandpass subwoofer. All bose subwoofers are actually bandpass as well. They are very tedious to design and generally do not perform well on paper or in the physical. I have heard one good bandpass, and that is unfortunately a bose. The enclosure consists of a variation of one half of the driver firing into a sealed enclosure, and the other half firing into a ported enclosure. These are VERY hard, mine you VERY VERY hard to get correct, but they are the best for sheer output when other options are either impractical or undesirable.
Horns: Here is a brief overview of how horns work via Dan Wiggins: Horns operate on the principle of a lever and dispersion control. A high pressure, low velocity end (the throat) is connected via an air-load to a low pressure, high velocity end (the flare end). SPL is the integral of velocity, meaning that if we can double the velocity at the end of the horn, we can increase the effective SPL by a corresponding amount. Longer, slower flare rates tend to amplify the effect, and is why high SPL horns are quite long with slow flare rates. Radiation angle is also affected by the flare shape, meaning that dispersion is reduced, so the output from the off-axis angles is reduced, and that energy is redirected into the on-axis (in the flare angle) of the horn, further increasing output. This is why you can find horns that will have outputs beyond 112 dB SPL in their beam angle - a theoretically "impossible" number, since 100% efficiency is 112 dB SPL! Of course, that is for a full-space radiation pattern; cutting down the radiation angle means one can reach levels higher than 112 dB SPL over a narrowed dispersion range.
There are alot of other types that are less popular such as transmission line, DBR (double bass reflex) and passive radiator, infinite baffle and isobaric.
That is all for now, i'll probably update it later with more stuff when i get home, probably a general overview on filters.
Single spaced parameters courtesy of Michael Lalena