2-Way closed box speaker with Scan-speak units. This speaker system is designed for near field monitoring in small room("M" for M1 means Monitor) and for reproducing clear images. I selected closed box system. Though "M1" has restricted bass, It can deliver more articulate bass response than any other base-reflex system. In my room(about 20 square meter), It can play chamber music, jazz, pop with satisfaction.
It's amazing mid-bass unit from Scan-speak. It has a sufficiently low bass response and makes me possible to make a closed box system. It's sound is very clear and wide in midrange but need some network technique to control some gentle bump (300-1000 Hz) in the midrange. This unit and some revised versions are used in many well known commercial speaker systems (Wilson WATT5, ProAc 2.5, etc.). The Thiele-Small parameter of specification and test results are listed in List 1.
The driver units. Click for a larger version (99Kb).
List 1. Thiele-Small parameter of woofer
It's another amazing tweeter from Scan-speak. And It's updated version of the legendary D2905/9000. Though not cheap, I can say it has very high cost performance. It's dynamic range is beyond expectation for soft dome and well match with 18W/8545.
Cabinet drawing showing the front and side. Click for the whole drawing (12Kb)
I wished system Qtc around 0.577 (Bessel Alignment). This low Qtc can give very detailed response what I like. The optimum volume was 16 liter but I designed internal volume 20 liter and Qtc is measured 0.53. The network will raise Qtc somewhat.
The crossover network
Here are some criteria for network design:
Picture of the crossover. Click for a larger version (81Kb).
Sensitivity is around 84dB/2.83V and -6dB point in bass is about 47Hz. It is very satisfactory result for small speaker. It's bass roll-off is about -8dB/Oct. With room enforcement in bass, this speaker can reach down to 40Hz.
Minimum impedance is 7 Ohm and it's a very kind load for amp. No wrinkle in graph shows good restriction of cabinet vibration.
Well designed crossover must show steep dip at crossover point and M1 also shows steep dip.
For my experience, It need more than 2 weeks of burn-in. And It's bass improves dramatically during burn-in. It's sound is well balanced. It make me feel comfortable and I can't hear any booming sound in bass. Finishing my project, I sold my $2,000 speaker system.
|System:||Closed box 2-Units 2-Way system|
|Drivers:||28mm soft dome tweeter (Scan-speak D2905-9300)|
7" Paper cone with carbon fiber (Scan-speak 18W/8545)
|Crossover Frequency:||1800 Hz|
|Sensitivity:||84 dB (1m/2.83V)|
|Impedance:||8 Ohm (Minimum 7 Ohm)|
|System Resonance:||47 Hz|
|Frequency range:||47 Hz - 20 KHz|
|Size:||470 x 230 x 350 mm (H x W x D)|