Few days ago, my old friend called. “Hey, I’m playing with new toys here. Multi full-range driver. I need some help to tune-up the sound.”
Today, I visit him after I return from the office. Below is his speaker (taken with my camera phone – sorry – poor quality).
He uses 12 pcs of 2,5″ full range driver for each speaker combined with one 1″ tweeter. (light brown box on top). I listen this speaker with Single Ended Class A amplifie (I don’t remember the tube), runs at around 3 Watts RMS and consumer class DVD Player (without pre-amp).
The overall sound is a little bit “light”. I think we have more treble here. The tweeter is too dominant. Then I start to tune up the speaker. First, I try to add a Zobel. We have around 12uF capacitor on hand and around 4R resistor. Hm… no good. I lower the resistor to 2R9. Still no good.
Then I decide to reduce the tweeter. I add a resistor in serial with the tweeter. My first guess, 2R9 should be ok. We examine the sound. Great! Now the high is no longer too dominant. But I’m not yet satisfied with it. The box is transmission line. I add a piece of cartoon behind the driver to minimize the “echo” effect (yes I hear some echo from the port in some tone). I also add some damping material inside the labyrinth.
Now we have problem with lower region. Those 12 pcs of 2.5″ full range simply can’t reach too low. I think only around 100-150 Hz and simply don’t have punchy low. I suggest him to add a subwoofer. I see a bookshelf with 6.5″ woofer (see picture above, bookshelf with dark brown color, it looks like a two way but the tweeter is disabled). Why don’t we try it as subwoofer? We use car amplifier to power the 6.5″ “subwoofer”. After some listening test, we adjust the high pass filter for the subwoofer at 40 Hz @ 18dB. We also adjust the gain to match with the main speaker. Voila, the speaker sounds superb. The “subwoofer” blends perfectly with the main speaker. The vocal is great, the low extension also amazing. We finish the Stimela (Hugh Masakela), Black Magic Woman (Patricia Barber), Smile (Eriko Ishihara), Poems of Chinese Drums (Yim Hok Man), and some Chinese track like Chai Chin, Chen Lily, etc all with smile full of satisfaction.
Picture above show the system. Single Ended Class A tube, consumer class DVD Player as source, a car amplifier to drive the bookshelf “subwoofer”, some power supply to power the car amplifier, a scissor, cable, etc 🙂
Photo above shows the speaker system. The top is main speaker (12 pcs of 2.5″ full range driver and a 1″ tweeter) and below is a 6.5″ bookshelf “subwoofer”. The tweeter is disabled.