Common Car Audio Myths Debunked

Common Car Audio Myths Debunked

Time to lay down the law  -  O.S. style!

Car audio holds a special place in my tech life. It can be blamed for pointing me on the road to pursuing the truth in the mysterious world of electronics, physics, and life in general. Nothing's worse than living a lie, especially when it was sold to you so cheaply by ignorant or greedy peeps. As I learned early on, there were many misconceptions flying in from all sides about nearly all aspects of car audio. A few brave pioneers blazed shiny trails to direct us to get to the bottom of the way things really are. Allowing for a more enjoyable sonic experience. In particular I'd like to personally thank Tom Nousaine who tirelessly explored all things audio. JL Audio also deserves some recognition as they provide fantastic documentation and tutorials for all (even during times when the industry was full of highway thievery). Without further ado, here is my attempt to debunk a few annoying myths. I have also provided many links just in case you don't want to simply take me at my word.

SPL levels - "My friend's car hits like 200dB" - Any mention of super large numbers in the decibel range and you should already have a number of red flags popping up in your mind. Even though you might hear of some vehicle hitting over 160dB (we'll use the 160dB mark for examples in this section), the misconception remains that hitting another 10 decibels more shouldn't be too hard (you know, toss in a few more amps and subs). In reality it is EXTREMELY difficult. The myths surrounding how loud a system can reach has to do with the fact that very few people know how the decibel scale functions. So lets get down n dirty and and see why pushing past 160dB is so hard. *First things first, the decibel scale is a logarithmic scale NOT a linear scale. (think of the Richter scale, and if you're still confused, then keep reading)* In other words every increase on the scale is not equal. In air (earth's atmosphere) the theoretical scale is 0-194dB. Now there is A LOT more information needed to completely explain it, but for this post as it pertains to subwoofers reaching extreme SPL, I'm gonna over simplify it a bit (hit up the links to teach yourself something). In an a very rough sense, in order to increase by 6dB ~ 10dB you need to double your output. So, to go from 150dB to 160dB you're gonna need twice the watts & twice subs, etc. The higher you get up in the dB scale the more difficult it becomes. Most dB drag racers use the golden rule that every time you double your watts you get about +3dB, all else being equal. And if you're wondering what happens if you could get enough power to punch through the 194dB ceiling? Well the 'sound' would become so distorted that it would be difficult to classify it as sound and would behave like a shockwave, leaving the sound scale behind. So, whats is the current SPL record for dB drag racing? At the time of this article, an astounding 181.8dB!
References:
Explanation of SPL with charts
dB Drag Racing current leaderboard

"It's easier to blow a sub with too few watts than too many" - This myth is like a never ending onslaught of zombies, you just have to keep on killing them (but then again whats the point? Can you actually bring death to something that's not really alive? anyways...) More often than not the key part of this myth is ignored when debates begin to rage. The key word is: easier. Is it possible to destroy a sub with too few watts? Maybe, but in any universe I've ever been to, it's never easier. There are two types of woofer failure; mechanical and thermal. In mechanical failures the woofer ends up destroying itself by extending too far, causing the cone, surround, or spider to rip or separate from one another. There is also the ever painful "bottoming out" when the voice coil slams into the magnet. In thermal failures, the voice coil receives enough current to cause it to heat up beyond its designed maximum, and burns itself out, sometimes in spectacular fashion. Without enough electrical current, the subwoofer simply will continue to soldier on. So in what circumstances could you accomplish in dealing a death blow to a sub with too few watts? Well, this ought to sum it up: user error. It could be that the user/owner doesn't know about RMS and MAX ratings, or perhaps the woofer is either free-air or in an overly large enclosure (in case you don't know having any sub in or behaving like its in free air, with no help from a properly built enclosure, is very very bad) A free air sub can be destroyed well before hitting its max watt rating. Also the quality of the products being used could play a role, as in a high quality amp powering a Uberfunktronix 78,000W 10" sub. As you can see in the preceding conditions the real failure is the dufus that put it all together, NOT the fact that there are too few watts. Some argue about amplifier clipping being the cause, but amp clipping is just pushing an amp too far where the signal coming out is full of distortion, and usually ends up sending out more power than its stated rating. Keep that up long enough for the woofer to over extend itself OR slowly heat the coil without giving it a chance to cool off, and you might, might destroy the sub. If it really was easier, YouTube would be full of titles like this: "1000W premium sub destroyed by my Uberfunktronix 100W amp!!! rofl ftw lolz..." When in this world governed by actual physics you see these:
Vid1  Vid2   Vid3   Vid4
Manufacturer Power Chart - notice the 'Green (minimum)' explanation.

Break-in "Subwoofers sound so much better after you break them in." - Oh the mysterious art of breaking in subwoofers, elusive as a certain cereal to a silly rabbit. In all fairness, there actually is a very short mechanical break-in period for some subs, especially if they are built for extreme excursion and power. The spider is usually the one in need of a little pre-game stretch. With all the exotic materials and checmicals used today, the fresh off the production line sub might need to run through some flexing before settling in. Most manufactures accomplish this when performing final quality assurance, especially for subs in a powered enclosure. Some raw subs might not receive this flexing and so it will happen in the first few seconds or minutes of use. I could keep going on in detail but this article by the fine folks at Audioholics does the heavy lifting for me. To sum it up, the break in is very short and makes almost no audible difference. So what's really happening is more human in nature. Most people after installing a system will dedicate many hours to fine tuning and tweaking all the dials until satisfied. Combine that with simply getting familiar with your new sounding setup, and it accounts for nearly all the break-in period.

Polyfill - The stuff of miracles, or just a bunch of fluff? - Polyfill is no miracle substance. It's the stuff in the stuffing of your pillows, and stuffed animals. It's cheap and well...fluffy. Some claim its divine in nature as it makes their subs much louder and more powerful, while others claim its nothing but snake oil for sub enclosures, and actually hinders subwoofer performance. Here is a great example, read the product reviews here and see the division, one star or five, no middle ground. The one star reviewer claims to have done extensive testing and proves the uselessness of polyfill (notice no actual hard numbers were provided). So what is this fluff all about? Polyfill is stuffed into a box at about 1.5 lbs (24oz) per cubic foot of internal space. It does not act like spinach to Popeye nor is it like kryptonite to Superman. It does not affect the subwoofer directly, but changes the behavior of the enclosure or more accurately the air inside the enclosure. Your subwoofer will vibrate and move the air behind it, cause all those molecules to move around and 'echo/bounce' off of the sides of the enclosure (NOT a standing wave, more on that in another section) creating friction etc. Polyfill will reduce that effect by converting that friction or sound energy to moving or vibrating the fibers, in turn 'slowing/reducing' the vibes, just as if the enclosure where in fact much larger than it really is. This changes the overall sound, causing people to use such descriptions as: smoother, deeper, richer, etc. The one star reviewer measured (if he did at all) the sub output itself, neglecting that the change is in the enclosure, not the physical properties of the sub itself. I personally feel that using polyfill is subjective and NOT a substitute for a properly built enclosure. Don't believe you can overcome a poorly (especially too small) crafted enclosure with miracle fluffiness of any kind. I do generally stuff enclosure as it does help fight any rough around the edges in the sound. Enough of my stuff follow this link for hard data..

Standing Long Waves - "Never build a square sub box" - People do amazingly stupid things to avoid these standing long waves, just like all those crazies that go out of their way to not get whatever scary disease pops up each year (I'm looking at you bird flu & mad cow diseases). A standing long wave happens when the distance between parallel boundaries are 1/2 the wavelength of the frequency at which the standing wave exists. (for math nerds, read this) Sub-bass waves vary from 56.4 feet (20 Hz) to 11.28 feet (100 Hz), the possibility of generating a standing wave would be almost impossible in car. Distortion created by upper frequencies or the fact that the enclosure itself is vibrating or resonating due to poor construction can be overcome by adding polyfill and building the enclosure out of heavy duty materials and ample bracing. And that's the short of it ;-)

Amps, Watts, and Reality -  There are too many quotes and myths concerning electrical current and how it relates to watt ratings of car audio components to list here, and I'm lazy. So here is a run down on some car audio electrical basics. 

*Years ago nearly every manufacturer was touting their MAX watts and how awesome they were. Zeus himself must have been quaking in his boots at the sheer power of these ILS watts (If Lightning Strikes). Recently however there has been a drastic shift, now most respectable companies give you the RMS watts as the main numbers of concern. A big thanks to the CEA2006 standard. Basically the RMS watts are the averaged output of the amp, since this is what happens most of the time during listening, those are the numbers you need. Keep in mind also that your cars 12V system varies between 11 & 15 volts. Most of the time amplifiers are tested at 14.4V. Keep Ohm' s Law in mind at all times. 

*"Class D amplifiers will never sound as good as A/B amplifiers since they are digital and not analog". At the astonishment of most people the D in this case does NOT stand for digital. The class type has to do with HOW the amplifier does its job (adding more electrons to the flow) and not with its sound processing. The reason you see more and more class D amps is because they run cooler, therefore smaller and have a theoretical efficiency of 100%. But its greatest strength is it's biggest weakness in that a constant switching is taking place and needs to happen quickly enough with out adding or taking away from the original signal. So the better the quality of the design the better the amp (as with anything in this life). Class D  Class A/B

We took a brief journey through audio mythology and came out all the better. This was not an all inclusive list and one day I hope to do a part II of other common myths. So please leave comments and suggestions below and we'll give those myths the same O.S. treatment!