ScanSpeaker

scanspeakerI designed the ScanSpaker as a mid-sized but high-end two-way speaker using Scan-Speak drivers. This floorstanding speaker uses the Scan-Speak D2905/990000, a 1″ soft-dome tweeter, and the Scan-Speak 18W/8545-00 mid-woofer, which has a 17-cm diaphragm made out of carbon fibre and paper.

1. Drivers

As the ScanSpeaker name suggests, all the drivers are made by ScanSpeak. I used the 8545 woofer (17cm diameter) and the 9900 tweeter (aka «The Revelator», 28mm dome). These are very good, but expensive drivers. The 8545 midwoofer has the reputation of very smooth reproduction of voices. This wasn’t true in my speakers at all until I added impedance-compensation for the impedance-rise caused by the voice-coil. The 8545 has a strange “bump” at about 600–700 Hz. It doesen’t look like a membrane-resonance at the waterfall-diagrams so it can be corrected with an LCR-network. The 9900 tweeter has a special frontplate which is supposed to improve lobing behaviour. I heard and read rumors suggesting that this special frontplate design causes a slight resonance somewhere between 10–20 kHz, but I couldn’t see it on my measurements. The dome diameter is 28mm and the resonance-frequency is at 530 Hz, so the Revelator goes lower than most other tweeters. The 9900 has a reputation to acts a bit like a «diva» when designing the crossover, which I attribute to the very pronounced impedance peak at resonance.

2. Enclosure

case

Drawing of the ScanSpeaker enclosure

I used a bass-reflex construction for the ScanSpeaker. I put two bass-reflex channels in the bottom of the case, «aiming» at the floor. This works because the speaker stands on spikes at about 2 cm above the floor. The internal volume of the case is about 18 liters. The front is 18.8 cm wide which is about the minimum possible with the 8545 woofer. An ideal case does not vibrate at all – the driver’s membranes are the only thing that should move. To get a «dead» case I built the case from 18 mm particle-board (inside) and 10 mm MDF (outside). Enclosure vibrations are further dampened by a layer of ceramic «bathroom» tiles and a layer of «Hawaphon» on the insides of the enclosure walls. A layer 10 mm felt and some wool  dampen internal sound resonances and eflections in the case. In addition, I installed a piece of cardboard at the top of the case with some foam glued to it. The cardboard is angled at about 30° relative to the face plate, which helps to avoid standing waves along the long axis of the enclosure.

3. Crossover network

The final crossover filter networks for the midwoofer and the tweeter are shown in the figures below. The initial design started out by calculating theoretical parts values, which were then optimized by acoustic measurements and by ear. As mentioned above, the 8545 woofer frequency response shows a slight «bump» at about 600–700 Hz. This is compensated using an LCR network. Also, for proper operation of the tweeter filter, the impedance peak of the 9900 needs to be compensated. This is achived by an L-pad in between the tweeter and the filter network. The L-pad is also matches the tweeter SPL to that of the woofer.

ss_xover_woofer

Midwoofer crossover filter network

ss_xover_tweeter

Tweeter crossover filter network

The parts values for the midwoofer filter are:

  • L1 = 1.8 mH
  • L2 = 15 mH
  • C1 = 10 µF
  • C2 = 15 µF
  • C3 = 3.9 µF
  • R1 = 5.6 Ohm
  • R2 = 4.4 Ohm (tot. resistance of LCR including L2)
  • R3 = 1 Ohm

The parts values for the tweeter filter are:

  • C4 = 3.9 µF
  • L3 = 0.82 mH
  • R5 = 10 Ohm
  • R6 = 8.9 Oh

2 thoughts on “ScanSpeaker

  1. Michael wrote on 28. February 2015:

    Hallo Matthias,
    i^ve done this crossover and was very happy, but build it with the SS-9700 and and 2x 8545, second with a 6,8mH coil.
    Now i have this combination with the 9900 and will try it with your crossover again.
    Are or has there been any update. The original Crossover in the box (Audiodata elance) make it sound a little dull to my ears.
    Kind regards, Michael

  2. matthias wrote on 01. March 2015:

    Hi Michael

    I have toyed around quite a bit with the crossover design, but I always came back to the one published here. The only (better) alternative was an active filter using DSPs. But please make sure you take into account the facts that (a) you have TWO woofers and (b) your baffle geometry (width, driver placement) is most likely different from my design. These differences will almost certainly require some changes in the crossover filters. Also, do you have the 8545 or 8545K mid-woofers? The 8545 has a slightly different frequency response than the 8545K (which I used here). To make a long story short: just give it a try and make some changes to see if things get better or worse. Also, you will probably not end up with an optimal result without the help of measurements of the actual results. Good luck!

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