Can someone explain tuning?

Discussion in 'Archived Threads 2001-2004' started by Casey H, Aug 4, 2002.

  1. Casey H

    Casey H Stunt Coordinator

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    What is the major difference between tuning's? And why would I want one over the other? (Ex. 15Hz vs. 18Hz vs. 21Hz) I had a higher level of explanation from Dr. Hyre of Adire, but would like the low level version. Any help is appreciated!
    Casey [​IMG]
     
  2. rodneyH

    rodneyH Supporting Actor

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    JohnQ, I have a thread that I started tis morning asking a similar question, I haven't received ANY responses yet, would you be so kind to take a look and help a beginner out???
     
  3. Casey H

    Casey H Stunt Coordinator

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    JohnQ,

    Thanks... I am looking at a 226l Sonosub (24") with an Adire Tempest. Would prefer to use a 6" wide port for convenience.

    Casey
     
  4. Patrick Sun

    Patrick Sun Moderator
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    Y'all should really download LspCAD from the Adire website and play around with various tuning points.
    Also read Andrew Low's tutorial on using LspCAD.
    For a 6" wide port
    Fb = 15Hz, port length = 37" (a little too long)
    Fb = 18Hz, port length = 24.5"
    Fb = 21Hz, port length = 17"
    For the Vb = 226 liters, it's flattest at Fb = 21Hz, but I'd rather have the additional protection with Fb = 18Hz over a flat response (plus room gain will help down low as well).
    Once you figure out the volume the port and the driver takes up (simple geometry for the port, assume around 10-15 liters for the driver), just add that to the 226 liters, and solve for height given a cylinder 24" wide.
     
  5. Casey H

    Casey H Stunt Coordinator

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    Thanks Pat!

    I was hoping you would chime in here! I did put all of this in LspCad, I guess it is just a challenge for me to read all of what is going on there! I will go back based on what you said and re-look the stats. Anyway, I think 18Hz is the way to go with this idea.

    Thanks, Casey
     
  6. Casey H

    Casey H Stunt Coordinator

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    Thanks John!
    Does anyone have the Unibox DBase with the Tempest built in that they could email?
    Thanks, Casey [​IMG]
     
  7. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Here's my lame interpretation for tuning so correct me if I'm wrong.

    If you blow into a glass bottle, when you reach the right "tuning" point the air resonates producing the bottles "tune". If you have a small MDF enclosure like that of a car audio sub, you can actually stick your head in it and "HUM" low notes to find the tuning point where a specific tone is amplified.

    Sound is basically moving air, so when the driver is "moving" the air back and forth it creates a tuning point (reinforcement?) in the enclosure.

    The same concept with air moving back and forth inside the bottle except you're blowing air into it with your mouth and not by a driver. When the sound (air) wave cycles inside the bottle is a tuning point.

    So infinite baffles don't have tuning points because there is no way for sound to travel back and forth to complete a cycle.
     
  8. Dustin B

    Dustin B Producer

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    You've sort of got it Chris, at least from my understanding.

    You just have to replace enclosure or box with port. It isn't the box that has the resonance, it is the port (sort of like pipe organs). What the tuning point is, is a function of the ports cross sectional area, length, and the net volume of the enclosure. Change any one of those and the tuning point of the enclosure (Fb) will change.

    So as the port starts to resonate, it can take over the output from the driver (driver doesn't have to move as much). Which allows the sub to play lower louder. That is until you go below the tuning point, then the output drops quickly. That's the trade off. Sealed boxes have a shallower roll off, but it starts sooner. Bass reflex designs don't start to roll off until later, but that roll off is much steeper.
     
  9. Casey H

    Casey H Stunt Coordinator

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    Great information Guys! Thanks!
    So what is the fine line there? When you look at Pat Sun's designs he always tunes to protect the driver. What defines the "optimum tune"?.. Is it driven by how the sub is to be used?
    Later, Casey [​IMG]
     
  10. Patrick Sun

    Patrick Sun Moderator
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    Well, if you want to hit those low 20Hz frequencies that are preferable in a HT setting for DVDs, you are going to select a driver that can be used in a ported enclosure that will allow you to go low (with authority). Use the right driver for the right application.

    Many people come here hoping to re-use a car woofer, but in a HT setting, the driver is ill-suited for being used as a HT sub due to the driver's characteristics (usually high Fs (resonant frequency), and high Qts (driver Q affect how it'll react in either an enclosure or open baffle).

    I port low to give the driver just a bit of protection down low at high SPLs. But some others live for that "smack you in the chest" bass which requires a higher tune (up to in the 30Hz range), but sacrifice that soothing low 20Hz rumbling. It's always some sort of trade-off involved when building a sub. So tailor a sub design to your requirements, and you won't be disappointed.
     
  11. Adam Bluhm

    Adam Bluhm Supporting Actor

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    ... little bit of a beginner question, fellas.
    Is a straight port better than a flaired port? No explanation is necessary. [​IMG]
     
  12. Dustin B

    Dustin B Producer

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    No, a flared port is better (the flare requires the port air speed to be higher before compression and/or port noise occurs). Problem is cost and finding flares for 6" ports.

    Although for a Tempest I'd take a 6" straight port over a 4" flared port.
     
  13. Joe Tilley

    Joe Tilley Supporting Actor

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    Something I'm trying to understand is how the length of the port lowers or rises the tune? Is it the mass of air in the port,or the length allow for a longer or shorter sound wave.
    I know this is probley a pretty stupid question,& I'm sure the answer is right in front of me. But I get lost when you guys start breaking it down into X plus Y times 4 divided by 3 or graphs & such.
     
  14. Dustin B

    Dustin B Producer

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    I'm completely guessing and talking out of my ass here. Engineers correct my guess if wrong.

    From my current understanding of how ports and passive radiators work I think the tune has to do with the mass of the slug of air in the port, and how much resistance there will be to that slug moving into the enclosure.

    Longer tube means more air in the tube which means more mass and a lower tune.

    So smaller enclosures make the movement in more difficult. Requiring the slug to weigh more (longer port) to tune lower. The bigger the enclosure the easier it is, so the lighter the slug can be and the shorter the port needs to be.

    As port diamter increases you get a greater surface area pushing in (more difficult) which would again require more mass so a longer port.

    Again, this is just my guess at what is going on from my current understanding of how the different parameters change Fb.
     

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