Copyright 2009 © Troels Gravesen


The bass drivers have been discontinued by ScanSpeak. Possible substitutes are Peerless HDS-P830869.

Cabinets constructed by Anders Mark/Denmark
ScanSpeak 21W/8554-00 + ScanSpeak 15M/4531-K00 + XT25BG-60-04

Download pdf data files:
21W/8554-00 - 15M/4531-K00 - XT25BG-60-04

For tweeter, use ScanSpeak R2604/833000

17-06-2009: Having had a few responses already on the Mark21, I feel compelled to add a few words to the overall construction and sound, although I do everything I can to avoid describing sound, because it really doesn't make sense. What I hear is not what you or anyone else will hear.

The Mark21 is a speaker delivering a significant soundstage thanks to the twin eight inch drivers. Sensitivity is high and even small (solid state) amps can drive this speaker although some 100+ watts will hold better grip on the low-Fs bass drivers.

The 15M middriver is a revealing unit and due to the overall flat tuning, good source material and decent amps/CD-players/turntables + cartridges are given the opportunity to deliver their best. If available, the Mark21 will deliver lots of detail and magnificient transparency. And it can be played loud, really loud without significant distortion.

Go to construction pics at bottom of page

Mark's comments in Danish:

Hej Troels.   Her er nogle billeder af den færdige højtaler. Har siddet hele formiddagen og nydt cd-en (Nat & Dag/jazz) og kunne blive siddende mange timer endnu, hvis ikke jeg skulle møde på arbejde om lidt:)   Det var en god ide justere basportene langt ned, ca. 30 hz, da de bestemt ikke mangler bas. Endvidere har jeg købt nogle basfælder, som rydder godt op. Lige pt. er der propper i portene og bassen er meget passende til min ikke så store stue. Oppe i køkkenet hvor der er mere plads fungerede det godt uden propper. Lækker bas de kan spille. En ting er sikkert, det er ikke den sidste højtaler jeg bygger, det har været lærerigt og iøvrigt fantastisk at skabe et resultat jeg er så glad for lydmæssigt. Ses sikkert engang til vinter når der skal bygges igen. vh. Anders


For ruler flat response: R2011 = 0 ohm, R1011 = 1 ohm.
If you use XT25TG-30-04 tweeter: R1011 = 0.47 ohm and C1041 = 22 uF. Other components the same.

Crossover components

Crossover kit available from Jantzen Audio. Mail at


Click image to view large.

No further details will be given. What's impotant here is reach a final 68 liter net volume for the bass drivers and maintain front panel dimensions and driver placement. Make front panel from 2 x 16 mm MDF and chamfer down to 20 mm depth as shown on drawing.
Rather than making a cabinet with curved side panels, a standard rectangular cabinet will do just as well. Insure proper bracing. Mark's cabinets are made from multible layers of thin MDF to reach an overall thickness of ~22 mm + bitumen pads. Mid driver cab. net. volume = 6 litres and do not forget to chamfer driver hole. Ensure mid cab is absolutely air tight. The are two ports on the rear panel, 65 mm (ID) x 200 mm providing a vent tuning of 28 Hz. Place ports symmetrical to bass drivers.


Left: SPL/1m/2.8V for all drivers. All these drivers are easy when it comes to crossovers. Both bass and middriver have an overall
flat response throughout the midrange and both have smooth roll-off characteristics. Also here the XT25TG delivers a smooth response.
Right: SPL/1m/2.8V for the finished system. Sensitivity = 91-92 dB/2.8 volts.

Left: Point of crossover between bass and mid = 400-450 Hz.
Right: Point of crossover between mid and tweeter = 2800 Hz.

Left: Impedance of final system. Minimum impedance = 2.5 ohms, however at modest phase angles.
Right: Step response showing negative polarity of mid and tweeter.

Mark's construction pics