Snake oil! (part 3, speakers)

Among musicians and pro-audio people there is a lot of confusion about the power handling and frequency range of speakers and speaker cabinets.  Part of this confusion comes from not quite understanding how to interpret the ratings, and part of it comes from the fact that a lot of the published ratings are terribly misleading, and some are outright lies!

The power handling of a speaker is usually determined by feeding “pink noise” (a wide spectrum of frequencies all at once, with lower frequencies having higher power) through a power amp into the speaker.  The amplitude of the pink noise signal is gradually increased, proportionally raising the wattage output of the power amp, until the speaker burns out.  The manufacturer then picks a nice round number (like 300 or 1000) of wattage just below the point where it burned out, and publishes that as the power handling of the speaker.  It’s technically “true”—but the reality is that actual music has drastically spiky peaks in amplitude (very different from a stable sine wave) that are focused in narrow frequency ranges.  A test tone or pink noise causes very steady, smooth speaker motion, with one level of wattage; while the intense transient spikes from instruments and music can produce a huge range of wattage peaks and valleys, and can make the speaker work much harder.  This essentially renders the pink noise rating meaningless, or at best excessively optimistic.

Speakers have more meaningful specific technical attributes, such as Xmax or Xlim, that describe their actual handling of the physical work of producing sound waves; these attributes paint a much more accurate picture of the amount of abuse a speaker can take, in real-world applications.  Unfortunately many speaker retailers don’t publish these specs, and even when they do, you almost have to have a college degree in speaker design in order to understand and interpret those specs correctly.  This is where it’s good to make friends with somebody who actually does have that type of education and knowledge.  My point here is not that you should look at Xmax and Xlim specs, but rather to show how little it helps to even bother with the wattage ratings the manufacturers publish.  With not-so-great mechanical handling specs, the speaker will “fart out” and distort long before it reaches the max wattage it’s rated for.

To compound matters, the physical performance of a speaker is heavily dependent on the cabinet it’s installed in.  The physical structure of the box, its porting, and interior baffles and shelves, have a huge impact on the efficiency and useful frequency range of the speaker.  So a speaker that is rated for 20 Hz to 20 KHz may only be able to usefully project from 80 Hz to 10 KHz (for example) when installed in a non-optimal cabinet.  And the design of the cabinet also hugely impacts the volume various frequencies can reach without speaker distortion, so again you’re looking at a situation where the wattage rating of the speaker has pretty much nothing to do with how loud the speaker cab can get before breaking up.

The sad thing is that speaker cab manufacturers intentionally take advantage of what the general public doesn’t know.  For example they publish that their cab is rated down to 35 Hz, even though the tuning of the box means the true 3 dB down point is more like 50 Hz.  The cab maker will fudge these numbers by testing at different distances, different volumes, and in rooms that reinforce those low frequencies; and they get away with it because they are not obliged to follow any official standard for testing.  Even “good” brands do this, and they excuse it by saying that’s the only way they can compete in the market against the other dishonest brands.  After all, if a typical consumer wants a wide frequency range, and if they don’t know the science behind acoustic design, they will just read the specs provided by the manufacturer—and that’s perfectly normal and reasonable to expect!  But then the consumer will read specs saying one cab has a range of 20 Hz to 20 KHz (a lie), and another cab has a range of 60 hz to 10 KHz (the truth), and which one do you think they’ll buy?  So even good brands are essentially forced to lie, in order to compete.  This has resulted in a very unhealthy market where almost none of the specs can be trusted.

Really there are only two practical solutions to this dilemma: either get yourself deeply educated on the science of speaker design and acoustics, or identify some reliable people who are in fact educated in these fields, and ask their advice.  Don’t just take the word of your neighborhood amp tech, or a guitarist buddy, without checking up on their claims.  There’s a lot of people out there reciting old myths, bad science, and falsehoods, and proclaiming them as indisputable facts.  Even the speaker, amp, and cab manufacturers do this!  So ask around, and get as many responses to your questions as you can, even if the question is as simple as “how much power can this speaker handle”.

Social Share Toolbar

2 Comments »

  1. john said,

    April 14, 2010 @ 6:50 am

    another great article, thanks Cyrus.

  2. Wackadoodle said,

    April 19, 2010 @ 1:29 pm

    I’ve appreciated all the Snake Oil posts, really great stuff. I was in the market for a giggin cab recently, I needed something loud, but also compact and lightweight. I scoured the internet and forums and poured over stats. It became clear that the only useful stats manufacturers published were the one relating to weight and dimension (and sometimes it seemed they lowballed the weight). The most useful resources for me were customer reviews, youtube videos and the occasional soundclip. Not ideal, but much easier to grasp that SPLs.

RSS feed for comments on this post · TrackBack URI

Leave a Comment