Speekerz wot I maid

Discussion in 'DIY Discussion' started by Tenson, Apr 13, 2007.

  1. Tenson

    Roy Lewis

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    Hello

    Your coaxial design looks very interesting. I put your box parmeters into MJKing's Ported Box worksheet and it came out very well. The long narrow port does not seem to cause any anomalies, so you have succeeded with the above !

    But its the crossover confuses me. Using cookbook formulas, a 1.3uF cap into an, ( with 1.33 resistor ) 8 ohm comes out around 15Khz ? Or am I missing something here. Can you help with a bit more explanation

    Thanks

    Roy
     
    Roy Lewis, Apr 28, 2007
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  2. Tenson

    Tenson Moderator

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    Hi Chris,

    The only thing I wish I did in mine was to not bother with the rear tweeter and slopeing back so the driver could have a little more breathing space behind it - and I have changed that in the plans already.

    For resonance control I find bracing from opposite panels works well as drawn. The vibrations in each panel are 180 degrees out of phase so when connected together they cancel almost perfectly. I have been using a 3 layer box construction on another pair of speakers that uses MDF, Silicon and then lead. But I think that would be impractical for this speaker as you wouldn't be able to lift the thing! Plus that much lead is very expensive.

    Basically I think the plans pretty much cover all that is needed.
     
    Tenson, Apr 28, 2007
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  3. Tenson

    Tenson Moderator

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    Ahh, something to mention, I did stuff the port a small amount with some fluffy stuffing. You know the type. Just a small amount to absorb any higher harmonics.

    The tweeter crossover seems like that because the tweeters level is too high for the woofer after it has had baffle step correction. So by using the filter much higher than a text-book design would for a ~4KHz Xover, you can bring the level of the tweeter down without the need for an L-Pad network. The series resistor then evens out the otherwise upward tilting response.
     
    Tenson, Apr 28, 2007
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  4. Tenson

    Tenson Moderator

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    Here is about how I laid out the stuffing inside the speaker

    [​IMG]

    Here is the type of stuffing I used

    [​IMG]

    and here is the part where the speaker mounts. Note the stuffing on the left and right side of the speaker, this made a big difference so don't forget it. I used Rockwool here but the same stuffing used everywhere else will work fine too.

    [​IMG]
     
    Tenson, Apr 28, 2007
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  5. Tenson

    Tenson Moderator

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    I have been trying a few things with the crossover for these speakers. The original design goal was to make them as simple as possible but they sounded so good I wanted to see what more could be teased out of them!

    The original crossover used the natural roll-off of the woofer with a first order filter on the tweeter. As the woofer naturally has a 2nd order roll-off it was not the ideal way to do it and the crossover is not as perfect as it could be; pushing the tweeter harder than is needed.

    This new crossover has 1 more component – a 330uH inductor in parallel with the tweeter which makes the tweeters roll-off 2nd order to match better with that of the woofer.

    In the original crossover the more gentle slope of the tweeter boosted the upper frequency response higher than ‘flat’ and so I compensated for this rise by using more baffle step correction than was otherwise needed.

    So, this new crossover gives the tweeter an easier ride since it is not asked to reproduce such low frequencies and it also has a more ‘ideal’ crossover between the woofer and tweeter. Interestingly, when I built the crossover to have a pretty much flat response, as I have done with most other speakers (I use in-room measurements, a few meters away from boundaries) the sound was rather full bodied and lacking presence. In my experience this is not normal for a speaker with a flat response from the lower midrange up.

    Here is the woofers response with the BSC to give a flat response.

    [​IMG]

    I found that I had to give the whole response a slight tilt to the high end to get the more open sound that I am used to from a flatter response with most speakers.

    [​IMG]

    I believe this must be because the tweeter is mounted in the woofer cone that acts as a wave-guide thus limiting dispersion. So while the high frequency response in front of the speaker is flat, the amount of energy in the room is still not as much as from a speaker with a wider treble dispersion. So to get a similar amount of total energy in the room (power response) the whole response needs tilting up a little bit.

    This is the end response of the whole speaker and new crossover that I found sounded just right.

    [​IMG]

    Here is the final ( I think!) new crossover design. Oh and also please note that the bass goes deeper than 50Hz as the graph seems to think. It might be a room mode suck-out or what I don’t know. But I have heard it reproduce stuff down to around 35Hz when positioned near room corners.

    [​IMG]

    Happy listening everybody!
     
    Last edited by a moderator: Jun 13, 2007
    Tenson, Jun 13, 2007
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