Now you guys have me worried

Discussion in 'Archived Threads 2001-2004' started by Mark_E_Smith, Jun 29, 2002.

  1. Mark_E_Smith

    Mark_E_Smith Second Unit

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    Ok I dove off and decided to build my own MTM center channel speaker. I could not find a design that I thought would match my main speakers, ESS monitors which have a ribbon tweeter. So the first thing I did was to buy a few books on speaker building and the Bass Box and Xover Box software. After looking at several speaker/tweeter combos I sellected the Audax HM170C0 and the HI-VI RT2C-A. The box is 8.5" X 10" X 24". This is a ported inclosure. I have yet to finalize the port. But it looks like about 3" X 2" X 5" for a target tuning of 61 Hz,I chose this becaust this driver has a 6 db sag below 500 Hz to Fs. It does seam to have a nasty 4 db peak at 600 Hz and a cliff at 5k. So the crossover is a 2nd order L-R at 2400 Hz for the woofer and a 2nd order L-R at 2700 Hz for the tweeter. Acording to the model this should be fairly flat. I use the measured speaker from Audax in a 15 L ported enclosue and Hi-Vi's web spec and compared to some other measurements I found at various places. I built the crossover with theta capacitors for the RT2C, as Wayne recomended in his Veritas design. I also opted for flat wire 16 guage inductors. After I built the crosover I made a cardboard box and installed the speakers/crossover and listened to them, they had incredable midrange detail and crystal clear highs, the botom end was lacking but hey this was a cardboard box. I am about to finish the box
    Am I just ignorant or am I missing something? I am planning on buying a clio lite system latter this year maybe then I will see something, but so far I am a happy camper and it was not that scarry to build the crossovers. Is ignorance bliss? What is baffle step?[​IMG]
     
  2. Patrick Sun

    Patrick Sun Studio Mogul

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  3. Mark_E_Smith

    Mark_E_Smith Second Unit

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    Thanks very interesting, I hope tuning the enclosure to a 61 Hz might help the baffle step that I see in the response curves. May be I will also mount the crossover out side the box so I can make adjustments later. [​IMG]
     
  4. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    "May be I will also mount the crossover out side the box so I can make adjustments later."

    Excellent idea.
     
  5. Patrick Sun

    Patrick Sun Studio Mogul

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    The tune of the enclosure won't really help out in the baffle step compensation because the baffle step is a rise from low frequencies up to around 500Hz, up to 6dB difference between the extremes. It all depends on placement of the speaker in a room that determines how much BCS is needed (putting the speaker near walls would lessen the amount of BCS needed, but then you would compromise on midrange/tweeter sound quality due to reflections).
    Here's my idea of keeping the XO on the outside of the enclosure: [​IMG]
    Photo of my current center channel XO that sits outside of the box for the interim until I finalize the XO (one of these days).
     
  6. Hank Frankenberg

    Hank Frankenberg Cinematographer

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    Patrick, please post your crossover board exotic hardwood source [​IMG]
     
  7. Dave Poehlman

    Dave Poehlman Producer

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  8. Patrick Sun

    Patrick Sun Studio Mogul

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    Hank, Shhhh! I had that stuff imported especially for my speaker project. Nothing but the best! No siree, Bob!
     
  9. Greg Monfort

    Greg Monfort Supporting Actor

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    >Am I just ignorant or am I missing something?
    ====
    Both I imagine. [​IMG]
    ====
    > I am planning on buying a clio lite system latter this year maybe then I will see something, but so far I am a happy camper and it was not that scarry to build the crossovers.
    ====
    They are straightforward in concept, but they assume a resistive load so it's necessary to either use impedance compensation for them to work properly or XO them well away from their Fs and the inductive rising portion of its BW.
    ====
    > Is ignorance bliss?
    ====
    For many folks, just look at the crap they buy from Best Buys, etc., and are very happy with. Heck, some of the expensive offerings suck IMO. Then there's the initial 'I built it so it sounds great' feeling of pride that most DIYers go through. [​IMG] You may have gotten lucky/done fine though, I'm not familiar with these drivers or the design software you used.
    WRT XOs, Wayne Parham wrote a good XO treatise to use as a guideline to compare/fine tune yours if need be. http://www.pispeakers.com/Speaker_Crossover.doc
    Bottom line though is if it sounds good to you/others and blends well with the mains, then the rest is just nit picking fine tuning.
    GM
     
  10. Mark_E_Smith

    Mark_E_Smith Second Unit

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    The software I used is a crossover modeling program by Harris Tech I also bought the enclosure design that integrates with the crossover program. The drivers are Audax 6.5 " carbon fiber cone. I chose these because people claim the have great detail and the off axis response is pretty good. The tweeter is a ribbon type that acts like a peizo in resistance but has incredible detail. My main speakers have a version of this type not brand of tweeter and I just love them. My goal was for musical detail for accustic rock and folk music then HT. The woofer has one nasty 3 db spike starting at 500 peaking at 600 and gone by 700 I am just not going to worry about this right now. My uneducated theory is the more you add to a crossover the more it will color the sound. So I tried to match the woofer and tweeter even if it costs a little more and maybe I wouldnt have to jump through hoops with the crossover. Right now I am thinking about adding some angle baffles inside the box to breakup the paralle sides and back as it might be a little to tubeish ( 8.5" X 8.5" X 22.5" inside deminsions) it might have a standing wave at about 280 hz.
     
  11. Greg Monfort

    Greg Monfort Supporting Actor

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    >The software I used is a crossover modeling program by Harris Tech I also bought the enclosure design that integrates with the crossover program.
    ====
    OK, I've heard mixed reviews over the years, but I know David keeps refining it so I imagine it's pretty good by now.
    ====
    > The tweeter is a ribbon type that acts like a peizo in resistance but has incredible detail.
    ====
    So it's very high resistance and basically a capacitor? IOW, a resistor in parallel sets the XO point and a cap if need be to set the level.
    ====
    >My uneducated theory is the more you add to a crossover the more it will color the sound.
    ====
    Good theory!
    ====
    >So I tried to match the woofer and tweeter even if it costs a little more and maybe I wouldnt have to jump through hoops with the crossover.
    ====
    Good planning!
    ====
    > Right now I am thinking about adding some angle baffles inside the box to breakup the paralle sides and back as it might be a little to tubeish ( 8.5" X 8.5" X 22.5" inside deminsions) it might have a standing wave at about 280 hz.
    ====
    Yes, as soon as you deviate from the golden ratio you start getting ripple in the mids and it can get very nasty with increasing aspect ratio.

    GM
     
  12. Mark_E_Smith

    Mark_E_Smith Second Unit

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    The ribbon tweeter has a flat 7.4 ohm resistance from fs to 40KHz it also rolls off below fs at > 12db per oct
     
  13. Greg Monfort

    Greg Monfort Supporting Actor

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    OK then it's not like a piezo electrically, but at least it's an easy component to XO, though a bit pricey.

    GM
     
  14. Dan Wesnor

    Dan Wesnor Second Unit

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    You absolutely have to have a microphone and measuring software to design speakers (you "by-ear" guys, feel free to start the stoning). Using manufacturer's measurements will not show the effect of your box on the frequency response, which can be quite dramatic. The drop in output below 500Hz is baffle step, and the other peaks and dips are more than likely edge diffraction.
     
  15. Mark_E_Smith

    Mark_E_Smith Second Unit

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    Greg,

    you are right and it fits with your signature, 94 db @ 1w/m, 80 power handling although some say they seem alittle bright.

    Dan,
    I understand you are correct, without the tools it is very difficult to get it right esp for the beginer, thats why I intend to get a clio lite system, however I do think you can build something that will blow the doors off most things you can buy at 4 x the price of the parts esp with the software to simulate the x-over and design the box even if you use the factory or someone elses measurement.
     
  16. Dan Wesnor

    Dan Wesnor Second Unit

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    Yu can start off with Speaker Workshop and an uncalibrated mic. SW is free, you can probably get the mic for $20.
    www.audua.com
     
  17. Mark_E_Smith

    Mark_E_Smith Second Unit

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    Thanks, downloaded. I have a Radio Shack spl meter I think it has an output do you think it would work for the mic?
     
  18. Dan Wesnor

    Dan Wesnor Second Unit

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    It would work for the basics, but because of it's response curve, might give you misleading results. Make sure you have a copy of the corrections.
     

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