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.
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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
Crossover
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 contact@jantzen-audio.com
Cabinet
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.
Measurements
 
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
  
 
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