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dzseki 14th March 2012 10:54 PM

Grundig Aktiv-box 40/50 modification
Not sure if this is the right section for this thread since the speaker is active powered but let give it a go...
Perhaps not me the only one who owns a grundig aktiv-box, I have the 50 model. I really liked the sound of it until I heard my friend's JMlab speakers, the bass was far better on the grundig, maybe too much, but the vocals were so dull on the grundig compared to the JMlab, so I diged myself into the circuitry.
With simulating the crossover circuit, and with some test measurements I found that there is a hole around 300Hz in the grundig's frequency response. This is because of poorly phase aligned crossover sections at the bottom for the sake of extra sub response (which is too much anyway) I've found a really easy way to greatly advance the sound of these speakers: swap two resistors in the crossover R43 and R56 so R43 should be 3,9k and R56 should be 15k, with this simple mod the sound really brights up, and you get a very wide, and open stage, and this is approved by the owner of the JMlab speakers too :)
This modification is only suitable for the aktiv-box 40/50 (4way) crossovers, the later models using slightly different filter topology, so I don't know if they have this problem too, but if there is interrest about that I can look for that too.

turk 182 4th December 2012 02:40 AM

seeing as how your a grundig fan i'm trying to find info on an older passive model :
Hi-Fi Lautsprecher BOX 40 25 Watt 5 Ohm
if you have have an info or can refer me to anyone who does i would really appreciate it.

from a canadian grundig fan
turk 182

p.s. what kind of amp/x-over is in the activ box 40

dzseki 4th December 2012 07:19 AM

I don't know that specific model, but you should take a look at this page:
Grundig Kataloge und Anleitungen
In the '66-'67 catalog there is a Hi-Fi lautsprecher box 40a, but I guess it is newer than what you look for

turk 182 4th December 2012 11:33 AM

this does help me get a better idea of their age/date of manufacture.
which makes me wonder if the boxes i have where maybe made for export i've found lots of info about domestic models but the 40 seems to be a mystery

many thanks

p.s. if you come across anything else please let me know

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