From time to time there has been some discussions of the JAMO dipoldesign R 909 (now there is also a R 907 along the same line):
http://www.jamo.dk/Default.aspx?ID=5966&M=Shop&PID=17139&ProductID=17649. In particularl I remember one thread here from spring 2007 where MJK and myself were contributing:
http://www.audiocircle.com/index.php?topic=41297.msg368661#msg368661 . I think this was the first time that MJK was hinting at what is now his famous passive OB-design with the Eminence Alpha 15s and the Fostex FE 103 E:
http://www.audiocircle.com/index.php?topic=41297.msg368661#msg368661 , which he published in September the same year:
http://www.quarter-wave.com/OBs/OB_Design.pdf . I went on designing the 'Volks-OB' put forward also inte automn 2007:
http://www.audiocircle.com/index.php?topic=46951.0 .
However the thought of a 3-way passive OB-design along the JAMO lines never left my head, so here I now present one. I would like to see how far one could come with a JAMO like 3-way dipole speaker although on a budget. The choice should be made from units possibly performing at a high level but not taken from the most prestigous and expensive brands.
First I would like to introduce my partner 'Grizzla' to you. She pointed me to the anagramatical subject line by voicing her 'mjao' every day when something is at issue or just for company. She has contributed also with the letter 'G' in the name. Here you see her carefully examining some of the crossover components:
The beginning was of course with simulation with MJK's Math Cad software. In this case with 2 Alpha 15s and the Monacor MS-100CHQ on a baffle with the same measures as the prototype presented below. Crossover were set with 12 dB/octave with LR characteristics at 200 Hz and 280 Hz. result was like this:
This seemed promising enough to go further with a test baffle, which looks like this:
It is an MDF baffle which measures 110/120 cm x 40 cm (44"/48" x 16"). Lowest Eminence Alpha15 is placed centered 22.5 cm (9") up from the bottom to give place for the small legs (shelf holders, two of the same at the back). The upper woofer is then placed as close as possible to the lower bass unit. Then the MS-100CHQ is placed 92.5 cms (37") up and 12.5 cm (5") in from the smallest side. Finally the tweeter is put on the baffle close to the midrange unit. The picture is of the left hand speaker , the right hand one is a mirror copy.
Units:
For bass produced by a narrow baffle I would consider the Eminenca Alpha15s as mandatory given the current market supply. They will give powerful, tight and transient true response to you. Those who describe the Alphas as sloppy and too high Qts speakers are simply wrong.
The midrange is supplied by the Monacor MS-100CHQ. My first encounter with this speaker was in a thread of German Audiodiskussion late 2005 titled (in translation) 'Fullranger bis 13 cms if you were free to choose'. Frank Kuhl of Monacor there put forward both the MS-100CHQ and the SP-130X/8 as possible alternatives. Later I bought a pair of both. The MS-100HQS were no fullrangers, so they were laying around til now. But the SP-130X/8 were put to good use in the 'Volks-OB'. For this design I however remembered the Monacor claims, so I decided to give it a try. I didn't regret. The link to Monacor is here:
http://www.monacor.de/typo3/index.php?id=56&L=1&act=8&act_sub=23&artid=5258&spr=EN&typ=u . By some puzzeling thoughts these speakers are placed in the Monacor Carpower range. Given their response and build quality they should also be among the Hi-Fi units. MS-100CHQ is built in Germany by the same factory that also build the well known ETON speakers.
Among tweeters I chosed between Monacor units RBT-95 and DT-28N. RBT-95 is a magnetostat ribbon speaker (
http://www.monacor.de/typo3/index.php?id=75&L=1&act=8&act_sub=25&artid=6467&spr=EN&typ=u ) and DT-28N is an neodymium tweeter (
http://www.monacor.de/typo3/index.php?id=75&L=1&act=8&act_sub=25&artid=3573&spr=EN&typ=u ). My final desicion was in favour of the DT-28N which I thought presented the most pleasent sound. The square cut out you see in the baffle was for the RBT-95 units.
Crossover:
I had difficulties getting a balanced crossover between the bass and midrange using a 12 dB/octave filter.I was a bit puzzeld by that. So I decided along the KISS guidelines and tested 6 dB/octave crossover slopes. I stayed with them. All bits suddenly seem to fall in place, this is the filter:
which resulted in this (in my livingroom) frequency response:
All in all you see here a +- 3.5 dB difference over all the frequency range.
Sound:
This by a margin is the best OB-speaker I have constructed so far. It outperforms the 'Volks-OB' in direct comparison. The B200s will not touch this mid-tweeter combo in performance. I have in fact stopped listening for faults in this speaker, just enjoying it. By the way it runs Lynn Olsen's speaker teaser: Mussorgsky's Picures at an Exhibition, orchestral version, with the Minneapolis Symphony Orchestra in full colours. Diana Krall's 'Live in Paris' comes over more 'live' than I ever heard it yet portraying the band beautifully ambient and my constant meter Manger's: 'Musik wir von einem anderen Stern' sounds like never before.
/Erling
