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Thread: A new pair of computer speakers for the heavy user

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    Super Moderator yggdrasil's Avatar
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    A new pair of computer speakers for the heavy user

    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.
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    Johnny Haugen Sørgård

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    Super Moderator yggdrasil's Avatar
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    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.
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    Johnny Haugen Sørgård

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    Super Moderator yggdrasil's Avatar
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    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.
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    Equipped with that measurement there was time to build a U frame and mount a 2215. First a measurement on the ob.
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    Then the 2215 was covered leaving a vertical 10cm wide slot.
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    Finally I covered the 2215 with a circular opening with d=21cm.
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    Given these results I went for the latter.
    Johnny Haugen Sørgård

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    Super Moderator yggdrasil's Avatar
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    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:
    Name:  2410_driver_and_horn_impedance.jpg
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    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:
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    Which was much more pleasing...

    Speaker workshop suggested this high-pass filter:
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    I had a 3mH inductor lying around, so the network ended up like this:
    Name:  highpass_v2.png
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    Johnny Haugen Sørgård

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    Super Moderator yggdrasil's Avatar
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    Then I run an impedance plot on the the 2215 in the baffle with the circular slot:
    Name:  2215_driver_impedance.jpg
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    The low pass network with compensation network ended up like this:
    Name:  lowpass_with_compensation.png
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    Johnny Haugen Sørgård

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    Super Moderator yggdrasil's Avatar
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    First in place measurements:
    Name:  frequency_response_left_and_right.png
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    There's way too little in the bottom. Which led me to add the following passive circuit between the preamp and poweramp:
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    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.
    Name:  compensation_v2.png
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    No measurements of this setup yet.
    Johnny Haugen Sørgård

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    Senior Member pos's Avatar
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    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?

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    Super Moderator yggdrasil's Avatar
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    Here's a picture of the rear.Name:  IMG_8087_CR2-2.jpg
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    Johnny Haugen Sørgård

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    Nice project, indeed.
    Do you know the trick to CC without a batterie?
    ___________
    Peter

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    Super Moderator yggdrasil's Avatar
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    Quote Originally Posted by Hoerninger View Post
    Nice project, indeed.
    Do you know the trick to CC without a batterie?
    ___________
    Peter
    Thank you. Sounds quite nice too. The OB bass is quite intriguing.

    I know about the diode CC, but I got a bag of 50 battery clips for this purpose, so why not use them...
    Johnny Haugen Sørgård

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    Administrator Mr. Widget's Avatar
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    Computer speakers?

    Very interesting indeed... thanks for sharing, and for sharing all of the details!


    Widget

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    Quote Originally Posted by Mr. Widget View Post
    Computer speakers?

    Very interesting indeed... thanks for sharing, and for sharing all of the details!


    Widget
    +!
    Yes!
    Thanks for sharing. This is a great educational thread.

    (and I now have computer speaker envy)

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    Steike!

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