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The past year or so I have been spending gradually more time in the office. There is no one close to disturb, so the standard computer speakers was exchanged for a micro stereo during the winter. A huge upgrade, but of course they fell very short...
A month or so ago a friend donated a pair of potato mashers (2410's with 2301). In storage I had a pair of 2215A's.
Here's a shot of the result.
Obviously the footprint needed to be very small, so the inside of the box leaves less than 1 cm on each side of the drivers and between them. The box is only 28 cm deep.
It is designed as a modified U baffle. The last year or so I have been reading up on open baffles and wanted to try out a variation of a concept Nelson Pass wrote http://www.enjoythemusic.com/diy/091...le_speaker.htm with the accompanying diyaudio thread http://www.diyaudio.com/forums/multi...e-project.html
The baffle is actually 22mm chipboard, with 20mm pine glued onto it. The sides and top are also pine.
The cutout in the baffle for the 2215 is approximately 1/3 of the area of the 2215.
Here's a shot of my work desk.
The design started with building the raw U baffle without the slot.
Actually the design started with some rather anxious measurements of the 2410/2301 combo. The slot loaded ob does not have much hf extention, so the crossover point would have to be a stretch for both drivers.
Attachment 56426
Equipped with that measurement there was time to build a U frame and mount a 2215. First a measurement on the ob.
Attachment 56427
Then the 2215 was covered leaving a vertical 10cm wide slot.
Attachment 56428
Finally I covered the 2215 with a circular opening with d=21cm.
Attachment 56429
Given these results I went for the latter.
It was time to look at crossovers. Given the measurements I aimed at 650Hz, 12dB/octave, passive.
First the high-pass showed this impedance curve:
Attachment 56430
I didn't particularly like the impedance peaks in and around the crossover region. Since the 2410/2301 needed to be padded I placed a 15 Ohm resistor in parallell with the driver and measured the impedance again:
Attachment 56431
Which was much more pleasing...
Speaker workshop suggested this high-pass filter:
Attachment 56432
I had a 3mH inductor lying around, so the network ended up like this:
Attachment 56433
Then I run an impedance plot on the the 2215 in the baffle with the circular slot:
Attachment 56434
The low pass network with compensation network ended up like this:
Attachment 56435
First in place measurements:
Attachment 56437
There's way too little in the bottom. Which led me to add the following passive circuit between the preamp and poweramp:
Attachment 56438
The low frequency improved, but not enough. As a bonus the 2410's now got far too much low frequencies... Due to this I decided to redo the passive circuit. Routing the HF outside the low frequency compensation. The HF leg was built with a 10K pot for easy adjustments. Meaning I needed another poweramp for the HF. The low frequency compensation have also been made steeper.
Attachment 56439
No measurements of this setup yet.
Nice build, with up to 10dB boost from the slot loading! Albeit it forces you to cross the woofer lower...
Can we have a picture of the rear?
Here's a picture of the rear.Attachment 56476
Nice project, indeed. :cool:
Do you know the trick to CC without a batterie?
___________
Peter
Thank you. Sounds quite nice too. The OB bass is quite intriguing.Quote:
Originally Posted by Hoerninger
I know about the diode CC, but I got a bag of 50 battery clips for this purpose, so why not use them...
Computer speakers? :D
Very interesting indeed... thanks for sharing, and for sharing all of the details!
Widget
+!Quote:
Originally Posted by Mr. Widget
Yes!
Thanks for sharing. This is a great educational thread.
(and I now have computer speaker envy) :)
Steike!