can somebody help i'm feeling a little dumb

Discussion in 'Archived Threads 2001-2004' started by Billy Posey, Jul 11, 2001.

  1. Billy Posey

    Billy Posey Second Unit

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    I currently a electrical engineering student, I been envolved in electronics since the beginning of high school, and have been an audio enthusiast since I can remember and I have spent the last couple of years researching diy speaker kits and plans. But there is that I am embarrased to admit that don't comepletely understand what is meant when one tunes an enclosure to a certain frequency. Can some one help me on this? Thanks
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  2. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    I'm by no means an expert, but I'll take a stab. Only ported enclosures are "tuned". This refers to the resonant frequency of the port. Like the tone made when you blow over a coke bottle, ports have a resonant frequency depending on their diameter and legnth. This resonance helps the driver extend lower than it would in a sealed box.
     
  3. Dustin B

    Dustin B Producer

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    The way I think of it is that driver excursion goes up as the frequency goes down. With a ported enclosure as you get closer to the tuning frequency the driver's excursion begins to go down again. This is because the driver is starting to unload on the port (or passiver radiators). As you get closer to the tuning frequency the driver is unloading more on the port. Until you get to the tuning frequency of the port at which point the driver has completely unloaded on the port (at this point in a passive radiator system the driver is hardly moving and the passive radiator is flailing away). Then as you go below the tuning frequency driver excursion rises at a significantly faster rate than a sealed box would.
    The point then of using a ported or passive radiator system is to allow the driver to play louder lower to a certain point. Past that point your output drops rapidly and your excursion goes way up, really fast. While in a sealed system with the same driver, you can't go as low as loud, but the drop of in output and the rise in excursion is much slower. So depending on what you want, you choose between a ported or sealed system.
    That's my understanding, I've yet to get through my head what unloading onto the port or passiver radiator actually is or why it happens. I just accept it as decree of the audio gods and use it to my advantage. Gotta love what a low tuning, a large enclosure and a tempest can do [​IMG]
     
  4. Mark Seaton

    Mark Seaton Supporting Actor

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    Mark Seaton
    Billy,
    I had to go through the same bit of fact-finding that you are now experiencing. Remember that most of what you need to understand a loudspeaker has been, or will be taught to you soon. The problem is that you get this in the form of "tools" and not direct applications. The key is to do some head scratching (I preffer while listening to music [​IMG] ) and get some texts to help you along in making the connections. If you are game, I suggest you start by heading to the library, and checking out a book which I believe is called "High Performance Loudspeakers," by Martin Colloms. Just go to the library and do a search on Loudspeakers and you will find some good information. Colloms's book will also give you some more understanding of how a driver's Q, fs, and compliance are dependent on components of the driver. Understanding this makes understanding simulation results a bit more clear IMO. The book has a lot of info, and depending on how far you are in your degree, some will make sense, and some may only make conceptual sense. Push through it, as later more of it will begin to make sense, so scrape from the text whatever you can. Fortunately, loudspeakers as a generalization can be useful examples in describing systems and phenomena, so many professors will use them as examples.
    Mark Seaton
     
  5. Billy Posey

    Billy Posey Second Unit

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    Thanks all for the information as always I am sure that I will many more questions and will be going to the library
    and checking out that book and many more if possible
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  6. Isaac C

    Isaac C Stunt Coordinator

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    While you're in the library, look for all those useful papers from the Journal of the Audio Engineering Society (http://www.aes.org One of the best books to learn about the specifics of this hobby is by reading the book, "Acoustics" by L.L. Beranek. Any reference you can find... it's all good [​IMG]
    have fun!
    isaac
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    SPICE simulations
    My Subwoofer Simulator
    Nelson Pass: Descriptions of push-pull often illustrate this type of operation with a picture of two men sawing a tree by hand, one on each side of the saw. Certainly this is an efficient way to cut down trees, but can you imagine two men playing a violin?
    [Edited last by Isaac C on July 13, 2001 at 01:35 PM]
     

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