Not all high-end audio show cars are built with an in-your-face extreme mentality. As a matter of fact, some of the most of impressive cars maintain a very low-key image; that is until you hear them. The JBL 2006 BMW 325i is one of those vehicles. Built by one Gary Biggs, considered by many to be the single best fabricator and audio system designer in the world, this car is flat-out flawless. The best thing about the 325i is its simplicity, utilizing JBL audio gear and processing to create an amazing audio system.
Lots of ported boxes are on the market. Many look great, but they don't always sound good. The engineers at Harman/Kardon came up with a solution, the SlipStream port, which eliminates port noise (that annoying "whooshing" sound that comes from most ported enclosures). Ports make noise when they can't pass enough air or when the air in the port is moving so fast that the air outside of the box can't keep up. When ports can't pass enough air, the enclosure and the woofer operate almost like a sealed box. The result is increased speaker excursion, less bass output and a better chance of damaging the speaker.
The SlipStream port works so well due to the flares, which are calculated to reduce turbulence inside the port as well as the ends. Too much or too little flare doesn't work. The air inside the port should move back and forth just like a speaker's cone, causing the air outside of the box to transfer the sound. To do this effectively, the air at the end of the port needs to stay "connected" to the air outside of the port. If the port is too small and if the air moves back and forth too quickly, discontinuities occur, and we hear that as port noise.
When looking at a standard straight-sided port, the airflow through the port is not uniform. There are areas of high turbulence. When those areas occur at the end of the port, they are forced into the listening space, causing that "whooshing" sound we call port noise.
In the SlipStream port, the areas with the highest turbulence are contained within the port and never make it to the outside. The air inside the port acts like a piston and transfers the energy to the air outside of the box uniformly. Therefore, there is no port noise!
The area of the SlipStream port is calculated differently than a conventional straight-sided port. This means a SlipStream port can easily tune an enclosure to lower frequencies than a straight-sided port with the same cross section. This means much better woofer reliability and more low bass.
An Interview With Gary BiggsHow did you get started in the car audio industry?I graduated high school in 1987. My first car was a 1979 Ford Mustang; it was a retired Texas Highway Patrol car. A friend of mine, Pat Cunningham, got me started into car audio. He competed in local TOW contests, and so I started hanging out at a local stereo shop "The HiFi Shop" in Lawton, OK. My first system was made up of used gear that I bought. Soon I entered my first contest and won my class. The local shop offered me a sales job. I have worked for four retailers and two manufacturers in the past 20 years.
Where do you get your ideas for setting up acoustic environments?I have learned the most from our research and test labs that Harman has in Northridge, CA. Observing and visiting with the engineers in the recording and sound rooms has taught me a lot.
Where did you learn to install? A school or were you a DIYer?One-hundred-percent DIYer! My first upgrade to the Mustang was the addition of a Clarion EQ underdash booster. I spent about four hours hooking up those 12 wires, but it worked the first time I turned it on!