One of the greatest tools in the audiophile toolbox is math. What? Math sucks you say. Well I say get your calculators out and start working your brain. This will be fun, honest.
In retail, chat forums and lunch rooms across the country the single most common questions are "How do I get my system louder?" or "How loud will these subs be?" I can personally guarantee you that you ask ten people this question, including the guys at the stereo shop, you will get 13 different answers and none of them will be basing their answers on facts. They simply do not know how it works. There are some basic physics at work here.
Volume, which is measured in decibels ( by dB), is a function of power, cone area, enclosure design, and transfer function. Oh, you knew that already? Ok, sure that last statement might seem a little obvious, but understanding how they interact together is critical to calculating volume. That's right, you can calculate exactly how loud you system will be. Enough BS, here is the worksheet. You won't find this anywhere else, send your friends.
You will need to fill in this basic info:
- How many subwoofers do you have?
- How much RMS Power does your amplifier make?
- What is your subwoofer/s sensitivity rating?
- What type of box are you using?
- What type of vehicle are you installing this in?
The enclosure will make a big difference, if it is a crappy home-built box with lots of leaks, held together with carpet and liquid nails, it probably won't function as well as a professionally-built enclosure (like the Q-Logic pre-fab enclosures- shameless plug).
Every time the cone area doubles, the output of the system theoretically increases by 3 dB, which is relative to a doubling of volume.
- One sub: +0 DB
- Two Subs: +3 DB
- Four Subs: +6 DB
- Eight Subs: +9 DB
Let's consider sub sensitivity, with 3 dB per sub added and calculate the SPL. Each time the output power (wattage) of the amplifier doubles, the SPL increases by 3 dB. To figure this, use the following figures.
This represent 3 dB added per doubling of power starting at 1 watt/meter SPL.
Next we add in Transfer Function, which is also called cabin gain. It is a theoretical gain you get from the inside of the vehicle.
- add 12 dB for a standard car/truck
- add 16 dB for a hatchback car
Now we figure in box type
- For a sealed box, 0 dB, sealed offers no dB gain.
- For a ported box, 3-9 dB depending on tuning frequency and air ripple. The higher the ripple, the more gain but at a cost of sound quality.
- For a bandpass box, 6-12 dB again depending on the tune freq. and ripple.
For example, a 12" Rockford subwoofer has a sensitivity of 86 db at 1 watt/1 meter, and is capable of handling 300 watts.The sub is installed in a ported enclosure, in a hatchback vehicle.
- Base DB is 86
- Ported Box +6 DB
- 300 Watts +24 DB
- Hatchback Vehicle +16 DB
- Total: 86+6+24+16= 132 DB
Again all of these numbers are theoretical but a great way to be able to understand what you need to do next in your car. If you have any questions post them below and we will be glad to help you figure it out.
Thank you for reading and go and enjoy your music!