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How to get your car stereo really LOUD!


Here we’ll examine the basics of how to get your car stereo really loud.

First of all, if you want to go win in car stereo DB drag at a big event, you have a long row to hoe. The real car audio professionals spend months in building, testing, rebuilding, and re-testing to come up with the staggering volume levels they post in the high profile events. You will need a car that probably won’t be street legal, will weigh a couple tons, and will be all but useless for listening to music. Competition car stereo DB drag systems are designed around a “resonant frequency” of the car; the box is tuned precisely to the note that naturally is the loudest in the particular vehicle due to the internal acoustics. Easy in theory, in practice it is the Holy Grail! The basic car audio principals are the same for that and your average street beater, but if you want to seriously compete, I’d highly suggest you join a competition organization and get involved with a group or team.

If you just want to impress your friends, blow out a Zippo lighter, anger your neighbors, and pick up noise ordinance tickets read on!

First of all, we need to discuss what “loud” is. Car audio sound energy is measured in decibels. This is simply a logarithmic scale that measures acoustic energy. About the lowers part of the scale you’d experience outside of a specially sound deadened laboratory is a whisper at 40 db, your average stock radio is 100 db, and 135 is the air horn on a large train. At about 194 db sound waves become “shockwaves” the crest of the wave is 2 atmospheres of pressure, and the trough is vacuum. Richter scale zero is approximatly190 db. 300+ db events include catastrophic meteor strikes and volcanic explosions. (Just to give you guys something to shoot for!)

To simplify 10 db increase is an increase of 10 times more “intense”. To avoid higher math, and further confusion, for practical purposes in the audio world, a 3-db gain is considered “noticeably louder” and generally requires either doubling power, or doubling radiating area.

OK, enough with the technical stuff, how do we get our chest to itch and our doors to flex. Well, if you caught any of the above, you’ll notice you need power and radiating area, and generally speaking, the more the better. But before we go there, I’ll touch on sound deadening.

Yes, it will sound really stupid to talk about sound dampening in a thread about being loud but bear with me here. First of all, flex is actually the enemy of loud. If your speakers are working to flex your windows and panels they are NOT compressing the air inside the car. You will notice many ultra high powered show cars use multiple layers of sound dampening and often even over inch thick bullet proof glass and some go as far as to fill doors with cement.

There’s also some psychology involved. We perceive sound intensity largely based on what is called “noise floor” that’s simply how quiet the listening environment is. In a very quiet library, a normal voice seems loud while at a concert; you’ll need to shout to stand a chance of being heard. By the same token, a well sound deadened car will be perceived as much louder inside that one that is poorly deadened. Many luxury cars are very well dampened right from the factory, if you have the budget and ability, consider doing some deadening yourself. There are many products designed for this, and most are comparable. Also with this “flexing” idea in mind, be sure to build a solid box and brace internally as needed. If the walls of your box are flexing in and out, you’re wasting power. Some folks use multiple layers of MDF, Fiberglass, or whatever box material to build box walls up to 1.5″ or even thicker. This is nice, but at high power levels even 1.5″ MDF board will flex a LOT without some bracing.

OK, so power. You’ll need lots of it. Class D amps will get you there. They’re efficient and relatively inexpensive. As I’ve discussed in previous articles, many manufacturers are less than honest in power ratings, but if you stick to reputable brands, you’ll likely get close to what they advertize. Most cars have adequate charging system to keep up with about 1000-1500 watts of output power. Beyond that you should plan to upgrade your electrical system. The best and most effective upgrade is a “high output alternator”, next is additional batteries. Most high-end competition cars use combinations of the two both multiple heavy-duty alternators, and rows of batteries.

Next radiating area. This breaks down into two categories, the obvious…your speakers, and the often-overlooked ports. All things being equal, bigger speakers are louder. X-max can also be important, but only at low frequencies. At the frequencies most DB drag competitions work with, woofers with low mass are a bit more important (complex law of physics stuff). If you?re really competing, low mass/efficiency, and high thermal power handling is key. For a daily driver that will rattle your teeth on the ultra low notes in your test CDs high x-max is nice.

Before deciding on woofer and box design, you should figure out how low frequencies really are. Most people have no idea what 30hz feels like and try to tune their box down to 20hz when what they’re really after is closer to 40. Go out and invest 15$ in a “bass mechanic” cod with the “test tone” section. Listen to it on a good woofer or woofers and get a feel for what frequencies you really want to get loud. You may decide that most of your music never even needs anything below 35hz and you can plan your shopping and box build accordingly.

As a rule of thumb, big woofers need big boxes. And big woofers in big boxes need big ports. Hands down, ported boxes will get a LOT more output since the port effectively doubles the volume of air the speaker moves around tuning frequency. Of course the tradeoff is you need a LOT of space for the box. Ported boxes are always bigger than sealed for the same woofer and the port itself eats up a lot of volume. Also, bigger boxes will play louder (due to acoustics of speaker/box systems), big boxes with ports and powerful speakers require a lot of port area for the port to function effectively, and big area ports must be longer, and thus take up even more space.

Carefully consider the space you have to work with and the power you plan to use before shopping for speakers. Stick to reliable brands and if you want to use a ported box, make sure you buy a woofer that is designed to function well in a ported box. All other factors equal, a good 12″ driver in a big-ported box will outperform an 18″ woofer in a box that’s poorly designed or too small.

Just some basics in tuning a ported box. Download box design software of your choice. I use winISD, but there are a few others that are freeware or shareware (use Google). Plug in some woofers and play around. For music listening, you?ll want to keep the response graph relatively flat (no big camel humps), and it should roll off somewhat smoothly hopefully down around 40hz or lower. Some high-end drivers will graph rather oddly due to their design, those manufacturers usually mention it in their advertizing and recommend box designs that will perform well real world. In general, higher tuning = louder peaks, but this may not be very musical, and tuning too high risks damaging speakers and losing output in the useable low frequencies that you want. I’ll also mention here that many of the top quality woofers these days have some great technology to really outperform the entry-level stuff (that still uses 20 y ear old technology). I personally recommend American made woofers that use “constant BL” technology. There are a few different types, but it really makes a difference in efficiency at high power levels. Simply put, a speaker that can mechanically travel 28mm 1 way is pretty useless if the motor begins losing strength after 10mm. I can tell you from experience that a single high quality woofer at 1000W will outperform 2 inferior woofers of the same size running 1000W each. If your budget doesn’t allow for that, consider running multiple lesser quality drivers at much lower power levels. Say 4 cheap woofers running 250W each could probably keep up with the one premium at 1KWif you have more space than money.

Next, we?ll discuss location and car acoustics. Small cars take a lot less equipment to get the same results. A small hatchback or pickup will get loud with a lot less equipment than a 70’s Cadillac. Also, a pickup or hatchback, or SUV has a single cabin area. Often a LOT of sound is lost between a trunk and cabin of a sedan. This can be improved by removing extra padding, metal, or other “stuff” between the trunk and cabin area, building a custom box that ports up through the rear deck, or even ripping out the back seats entirely and building a “wall”. Also worth noting that woofer boxes and ports generally work best at the rear of the trunk facing the rear. This isn’t always true, and there’s no exact science. It’s mostly guess and test. Play around with different locations for your box and aiming different directions, you may be surprised at the difference in output.

Lastly we’ll talk about diminishing returns. As stated earlier, a 3db gain involves doubling either power or radiating area, so let’s say you have a pair of good 15″ woofers in a ported box running 1KW each and you’re hovering around 148 db. Now you want to break 150. You’ll now need to either cram in 2 more 15’s plus their port volume, or double the power (if your woofers can even handle 2kw without smoking). Now you see the dilemma. Either way you slice it, you’re looking at a sizeable investment in space and money. Even if you just want to add another 2KW amp, you’re looking at additional battery(s), alternator upgrade, wiring, amps, and possibly upgrading woofers to some with higher power handling. Now picture doubling that again if you want to hit 154, you’ll need 15’s that can handle 4kw each (not many out there), plus total of 8kw of power. DEFINITELY a monster alternator (or two) and 3-4 an additional batteries. Or 8 15″ woofers with adequate port space.

The moral of that story is not to worry too much about whether you should get a 1000W or 1200W amp. The audible difference is minimal. Also, again, don’t try to cram too many woofers or too large a woofer into too small a space, your gains will be minimal, and your performance will suffer.

So remember the basics. Big power, big woofers, big box, big ports. Bracing and sound deadening as needed. Electrical system upgrades as needed to keep up with the aforementioned big power. Buy woofers that can handle the power you plan to give them and will perform well in a size box that you can fit in your application. And keep it safe! Prolonged or even brief exposure to extremely loud noises can and will cause permanent hearing loss.


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