got subs? pt ll
Hi gang,
I think one of the things I'm most passionate about is when a person, product, or company, sets out to exploit the hard working, innocent shopper that's trying to take care of their family while managing a budget; t'is the reason that I started my own comm'l/indus'l h.v.a.c. service company a while back; just tired of seeing my "X-Bosses" get rich on the lack of understanding of their loyal customers!
And the same applies wrt buying speakers, or anything else for that matter. There are just
sooo many tricks (loop holes and semantics) around marketing their products that the general public won't pick up on because of dishonest sales people, industry brotherhood or... SHHHHH, hush hush! So I wanted to shed some light on a subject where I believe part of the problem lies: people not understanding...
The Spec Sheet, "I live by them"!
Probably 7 out of ten speaker manufacturers are (for the most part) honest companies trying to make an honest buck. But it's the other three that we're talking about here so there are a few things that you should know so you won't be so vulnerable. When buying a speaker or an amp, most people do the very same thing when choosing a product... they look to the
wattage! And the reason is because they really aren't familiar with too much else about speakers, but that's probably the
LEAST important factor regarding it's build.
So the exploitative manufacturers have picked up on this as a weakness among the general public and has capitalized on that to the fullest. Here's a classic example: You go to an auto parts store, let's say... Pepboys (a very fine company). A speaker in a fancy package has the words "bass-o-matic 7500" on the box. The '7500' really has nothing to do with the product, it's wattage or power handling, it's just there to grab your attention. A glance at the back of the box reveals
a list of features, still with no real information about the speaker in the box; just a bunch of
'weasel words (phrases that the company made up themselves) like, "This component driver features
"APOS technology"!, which in reality stands for: "A Pile of S%#T"!
But you buy it anyway because you think that, that 'APOS' means something highly technical, above your head, so rather than research the acronyms, you ask the goofy kid behind the counter what this means, who tells you that "it's just the way the speaker's made"... and adds... "my cousin's buyin' four of them when he gets paid on Friday"; because he don't know what it means either! Okay, below is a typical spec sheet from one of the drivers that I use for my 'concert stage' bass rig (not the "Thiele Small parameters", which I won't go into now); just keeping it simple here.
SPECS
The first thing is usually it's size (diameter) shown in mm and/or inches. Next, the speaker's operating impedance expressed in ohms which I won't discuss now either; I'm planning to go into that
in depth in my next initiation to this thread. Okay, looking at the spec sheet above, the next four lines describe the power handling data. It says: 1000 watts
continuous pink noise A.E.S. (Audio Engineering Society). What this is, is the result of a 'Real World' (mimicking an actual music program) scenario, meaning that the amplified signal is 1000 watts using a random pink noise filter with an equal amount of energy in all frequency bands. It specifies a 6 decibel crest factor over a 10 decade bandwidth e.g., 50-500 hz. The driver is placed in a "Free air" environment (no speaker box). The pink noise signal is not constant in time but has a dynamic element, inherent in it's structure. This type of stress test has a continuous duration of 2 Hrs and is designed to try the speaker's thermal
and mechanical attributes w/o any appreciable damage to it's moving suspension, it's voicecoil, or bobbin (former).
The next figure listed below is the I.E.S. (International Electrotechnical Society) and reads, 700 watts "Continuous power". This is a different kind of test baring an IES pink noise program filter and tries to approximate a frequency content of a real music like signal with a high and low frequency reduction, having a 6 decibel crest factor (A 6 db crest means there is four times the energy than that of an average music signal; 3 db is only twice the energy of the average signal). This test is run continuously for 100 hours w/o signs of any appreciable damage to the driver.
Using the same amount of power (700 watts) as in the IES stress test, a speaker manufacturer may choose to use another standard method to validate it's driver's capabilities, with a test protocol known as the "E.I.A. (Electronic Industries Association) 426A". This test places the subject (driver) in a "worst case scenario" environment and tests the speaker's thermal attributes first and foremost. The generated pink noise signal is saturated with a frequency bandwidth that reaches from 500 Hertz/cycles per sec (HZ / cps) all the way down to 50 HZ/cps (10 decade frequency bandwidth). This is a standard test and is run 'continuously' for a full period of 8 full hrs. It allows a dynamic range of a 6 db crest factor, but has a far more saturated content than it's 100 hr cousin; the IES, and, must cause no appreciable damage to the driver.
The next power spec below
(Continuous Program) says 1400 watts (a 3 db increase). Now this program test is not as punishing as the EIA 426A, but more represents a "real world" performance situation. 1400 watts is double that of the 700 watts continuous sinewave test because they use a very different program signal, also called 'pink noise' which has a lot of
'rests or holes' in it's signal (remember disco... thump, thump, thump...), which enables the driver to cool between pulses. It is primarily designed to test the driver's ability to excurse (move in and out), so it's mechanical limitations are pushed to it's boundaries. This figure is the a 'middle ground' specification, and is the one that you and I should use when choosing a new driver. It's also the one to match power with the amplifier that will be used!
And then the last standard power rating is p/p or peak to peak. The spec sheet says: 7000 watts peak. What this reveals is how much power a driver can handle for a split second
BTW: this is a 10 decibel crest factor (700 to 7,000 and considered extraordinary); someone drops a mic during a performance or suddenly disconnects a microphone... ever hear that LOUD buzzzzzz!? So the driver must be able to withstand that kind of torture even for a second or two.
Note: If you're very careful, you should use an amp that is more than capable of destroying a low frequency driver or sub, BUT must prevent the amp from doing so. Using an amplifier that is under powered is more likely to blow a speaker than an amp that's over powered because when an amp is turned all the way up and runs out of power, it starts to generate what's known as square waves; a signal cycle pattern that has it's curved tops/bottoms cut-off (hence the term, square wave). A driver cannot reproduce sq waves efficiently (un-natural wave pattern) so becomes distorted and disfigured in it's effort to reproduce them, and is usually damaged as a result!
Now that I've tried to explain what some of the power rating specs mean, you can glance at a typical data sheet and know how to compare "Apples to Apples", so
BEWARE! Some manufacturers will list the p/p (peak to peak) rating as the
Power handling. A mere play on words but negates the standard order, making their product appear to be superior or equal to the competition when in fact, it's not even close. Imagine... you buy a speaker rated at 700 watts (in a fancy box) believing it's just as capable as the one described above; but in reality this is the speaker's p/p rating. It's true rms rating is only 175 watts rms. Remember 175 watts x 2 (or 3 db's) = 350 which is their program rating, and then x 2 (or 6 db's) = 700 watts which they'd have you believe is their continuous sinewave rating. So be careful, buy smart, and most of all... HAVE FUN! Happy trails!
rigtec, cheers
anyways, great work man! Lovin this thread. Lots of good quality info.
ray:
