Almighty Subwoofers
By Stig Erik Tangen
01 Jan 1997
Impedance correction
Impedance correction of the speaker is important to the amplifier. No amplifier sound better with a strongly reactive load than with a less reactive load. The point in impedance correction is to flatten both the impedance phase angle and magnitude. This is usually done with L-R-C filters connected parallell to the input terminals. It is possible to achieve a perfectly flat impedance this way, but the drawback is the need for extremely large value capacitors and inductors. There is no way out of using electrolytic capacitors and cored, thin-wire inductors. Using components of such quality is disasterous to sound quality, even in impedance correcting filters.
I simply use a resistor in parallel! This solution will not flatten the impedance as much, but will provide an enjoyable improvement. By selecting a proper resistor quality, the resistor in it self will not detoriate the sound quality. I use a 10 ohm "Kool-Pak" (Caddock MP930), which is a thick-film resistor in a TO-220 housing. The power capacity of the Kool-Pak is 30 W when mounted on a proper heat sink, sufficient for most applications. The audible result of impedance correction is a tighter bass that also sounds deeper and better defined.
Amplifier requirements
The good efficiency of the JBL 2226 driver will not make calls for high-power amplifiers. In fact, the system's efficiency in the bass-range (40-100 Hz) is higher that most speakers, who rarely exceeds 90 dB. Crossing at 100 Hz will also leave nearly 90% of the power in music to the main system.
My own main system has a sensitivity of ca. 92 dB. Measurements with real music on this system show that the power requirement for the sub is only 1/10 of the main system. I use 80W/4ohm amps for the main systems, and a 2x20W/4ohm amp for the subs. I don't have any records that make the sub's amp clip before the main systems' amps. 20W on these subs are in fact enough power to knock your socks off!
Sound
The first listening tests were quite a shock to me. I had certain ideas of how it would sound compared to my previous system, but the result was very different from what I had expected. It took me some time to get used to it, and realize how great an improvement it really was. Their sound quality is absolutely outstanding compared to all other subwoofers I have heard, even compared to high-end headphones. They reproduce every sound in a recording without any sign of loosing control or definition. Powerfull transients can really pound on your chest, but there is no car-fi-boom-box rumble, only ultra-tight punch.Virtually no speakers can reproduce a continous low frequency signal, like a church organ pedal, without loosing the grip after 100-200 ms. The tone starts like a soft transient, and then dies a little in intensity. This does not happen with these subwoofers, they never run tired. At first it was also very surprising to discover the huge differences that really exists between different recordings in the low frequency ranges. The subwoofers have very good definition, and display these differences with all possible clarity.
Stig Erik Tangen
|
Top
