TQWL diy speakers

Discussion in 'DIY Discussion' started by eggzy43, Sep 17, 2005.

  1. eggzy43

    eggzy43

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    Hi guys,
    I'm new to ZeroGain so please be gentle with me. I'm currently building a pair of TQWL speakers in a workshop in Huyton, Liverpool.
    The bass/mid units are taken from my old Eltax speakers [6 ohms]. I connected them to a rubbish stack system amp [my Cyrus 1 is being repaired] just to test them and they sounded....well, pretty poor in my opinion, very inefficient, but I put it all down to the "amplification" and the drive units. i.e. the cabinets are okay, there was certainly plenty of low bass and the cabinets [not fully glued up yet] showed no signs of resonating due to their thick walls I assume. My plan is to get some full-range drive units, I wonder if anybody known of any *affordable* units I could try? are any of those in-car speakers worth a go?

    Thanks for your time
    Cheers
    Eric
     

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    eggzy43, Sep 17, 2005
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  2. eggzy43

    zanash

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    Get in contact with wilmslow audio they do a range of good drivers to suit all pockets. I'd be very suprised if they could not help you.
     
    zanash, Sep 17, 2005
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  3. eggzy43

    LiloLee Blah, Blah, Blah.........

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    Not that I want to dampen your fire, but doesn't TQWL stand for Tuned Quarter Wave Loading? Why I ask this aren't you supposed to build the cabinet based on the specifications of the speaker unit? So how did you arrive at the size of the cabinet? Martin King is 'The Man' for this whose web site is here http://www.quarter-wave.com/
     
    LiloLee, Sep 18, 2005
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  4. eggzy43

    eggzy43

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    yes

    TAPERED QUARTER WAVE TUBE AKA VOIGT PIPE
    Yes they are made to a specific plan I got off the web, I think its a Martin King variation its pretty flexible re. drive units. I went for high-mass and extra rigidity in order to minimise internal damping, internal bracing struts were a no-no...I must confess the maths behind all this has me truly scuppered but I'm trying to be intuitive about it all - my instinct tells me that a good quality pair of drive units coupled with a good amp, some prudent damping and the cabinets fully secured [plus spikes!] & a good sprinkling of pixie dust? Will give me a pair of great sounding speakers. :confused:
    My aim is to achieve a rich subterranean layer of bass rather than the one-note thumpers so prevalent in the high street shops.
     

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    eggzy43, Sep 18, 2005
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  5. eggzy43

    zanash

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    I'd go for a nice rub down with some snake oil too!

    Your refference to damping,in this context it's not raelly nessesary as ththe sound pressure wave travels parallel to the cabinet. Only speakers were the sound wave is reflected by the rear wall of the speakers should need panel damping. As to stuffing the pipe, this is to effectivly lengthen the pipe, ie to get a low frequency responce from it, this of course is offset by the energy lost in the extra stuffing.

    I've built three simple folded horns and three transmission lines to my own designs, both of which are close relatives of the TQWT.
     
    zanash, Sep 18, 2005
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  6. eggzy43

    3DSonics away working hard on "it"

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    Hi,

    First, the design you show is quite old and was designed for drivers with a fairly low Q, to "fatten up" the bass of these. They actually do not go all that low at all, they rather balance the out the often shelved down bass of higher efficiency drivers.

    Consider a driver with an Fs in the 40-50Hz and a Qt around 0.3.

    Seas has a nice XP cone 6.5" coax driver that would likely be a good fit, the tweeter can be crossed over with a single capacitor and resistor.

    Secondly, Martin King popularised the rigid mathematical analysis of the TQWT/TQWL et al and provided tools to do so. This led him to develop a bass-reflex/tqwt hybrid often called MLTQWT.

    I hope that helps.

    Ciao T
     
    3DSonics, Sep 18, 2005
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  7. eggzy43

    zanash

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    Thats good advice .....I didn't feel it was my place to critisise your drive units, which aren't ideal for the TQWT....but will let you get a feel of the possible performance that the speakers are capable of.
     
    zanash, Sep 18, 2005
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  8. eggzy43

    eggzy43

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    Thanks for the good advice guys...yeah them Eltax units were totally wrong, as for stuffing the cabinets I've read a lot of pro and anti stuffing columns over the years [ I think it was Jimmy Hughes in The Hi-Fi Review who advised us all to remove the stuffing from our speakers for a clearer, more open sound...imagine next months mail box?]and it just leaves the humble DIY'er like myself somewhat confused but do you agreeI should emulate the damping shown on the B&W pic which seems like quite modest damping? A friend of mine is bringing in a tone generator shortly that should help. I have a practically unhindered access to professional tools and materials and as you can see an extremely limited knowledge of acoustic theory...talk about a recipe for disaster :eek:

    "Seas has a nice XP cone 6.5" coax driver that would likely be a good fit, the tweeter can be crossed over with a single capacitor and resistor." thanks 3D I'll check that out.
     
    eggzy43, Sep 18, 2005
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  9. eggzy43

    zanash

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    Removeing the stuffing on sealed or reflex boxes yes been there and done that..... but on pipe speakers , as previously stated the stuffing does another job entirely, don't confude the two !

    You should use BAF wadding or the next best thing ....keep away from glass or rock wool , its horid stuff and posses a health hazard.

    The stuffing should be used to tune the bass responce and you should start with a density of 1lb /cubic foot sorry can't convert to real money as my makes my brain hurts! This is in the area above the drive units , the pointy bit. you then need to look for the 1/3 nodes and place wadding at theses points of about the same density , the areas between can be thinned out. Its as much a suck it and see exercise as any other DIY project. Its down to you anyway ......we can only offer advice, if you choose not to use it .....well as long as the cabinet is only screwed together you can go in and out of it to re stuff.
     
    zanash, Sep 19, 2005
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  10. eggzy43

    T-bone Sanchez

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    Check out www.madisound.com before you buy any drivers, bout the same price as UK based suppliers only their price is in $$$$'s ;0)
     
    T-bone Sanchez, Sep 19, 2005
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  11. eggzy43

    Yellow

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    Hi Eggzy43

    You can't just shove a pair of drivers into a quarter-wave cabinet and expect good results. The mechanical and electrical properties of the driver have to work with the cabinet.
    Forget car speakers...can't believe you are even considering this, when you have a quarter-wave system on the go.

    Get some good info in TL designs. The main criterium to look for is the fundamental free-air resonant frequency. This has to match EXACTLY with the length of the TL, or else the whole system will fail with alarmingly catastrophic consequenses.
    Yes, it'll make some sound....but NO....it won't be a good sound in the bass department. Be careful.

    Regards,

    Neil.
     
    Yellow, Sep 20, 2005
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  12. eggzy43

    zanash

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    Yellow....true but not the whole picture

    By altering the stuffing density you can make the driver think its in a longer pipe, an therefore adjust the bass to suit the cabinet. This is called the accustic length as opposed to the actual length. This is normally done to adjust the length to get the 3/4 wave in phase....ie to reinforce the bass at the driver.

    1/4 wavelenght = [speed of sound/driver resonance[free air]]/4

    times this by 3 to get the pipe length of the 3/4 [ in phase]

    you can then compare your pipe length to that of the driver's theoretical pipe


    all information taken from LD Sharp's...Q & E transmission line design.


    some refferences
    http://members.optusnet.com.au/~audiosoft/spkdesref.html
     
    zanash, Sep 21, 2005
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  13. eggzy43

    eggzy43

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    thanks...

    ...for all that i'll take it all on board. You guys certainly know your onions. If it does all go pear-shaped I'll turn them on their backs and they'll make some lovely flower boxes! :)
     
    eggzy43, Sep 21, 2005
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