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Thread: A Study on Hilt Sound Resonance

  1. #1

    Default A Study on Hilt Sound Resonance

    This is a thread to condense the information I have discovered in testing of sound resonance in saber hilts.

    First I will explain resonance and sound waves, then describe an optimized single speaker setup, then a two speaker solution. Then I will list detailed information and data. Hopefully someone will sticky this so it can be found easily.

    What is resonance?

    For our purposes it is the ability of the hilt cylinder to amplify speaker output by physical connection to the speaker much like a horn. With only a mouthpiece of a horn there is no resonance. With mouthpiece plus horn we have resonance and sound is louder.

    Here is a diagram that shows how different wavelengths propagate differently in the same space.



    Of course the main limitation with our sabers is the small size. It's difficult to propagate low tones.

    The length of a 60hz wave (which is about the frequency of a saber idle hum) is 19 feet. The length of a 15khz wave (which is about the highest frequency of a saber sound) is 9 inches.

    Fortunately we don't need that much length to get good results.

    Single speaker resonance chamber rule of thumb is 1.5 times as long as the width of the speaker.

    Because the different frequencies we hear are of different wavelengths or differ in size this makes it difficult for a single speaker setup to perform well at all frequencies.

    When the speaker is pointed straight out the pommel vent. There is good upper frequency resonance but the lower is lost due to not enough length for the lower longer waves.

    When the speaker is pointed inside the hilt. This is often referred to as reverse sound. The lower frequencies perform better but the upper range is easily baffled by internal components. One way to improve the upper frequencies with this setup is make holes along the length of the hilt to release upper tones before they are attenuated by stuff inside.

    A major limitation to a single speaker setup is one speaker has a hard time making a wide range of sounds at the same time. This is why we see professional speakers with 2,3, and 4 different size speakers in one box. Sound quality is improved by dividing the different ranges of sound between speakers.

    To overcome some of these limitations here is an example of a two speaker setup. The sound quality of this setup was the best found during testing.

    Two speaker module







    module installed in pommel






    The speakers point in opposite directions. The bigger one points to the inside of the hilt from the pommel. The smaller one points out the vent in the pommel. This gives the bigger speaker a longer chamber for lower tones and a small chamber is big enough for higher tones.

    A 4.7uf ceramic capacitor is soldered on the positive leg of the bigger speaker then connected to the tweeter. This is needed to only pass higher frequencies to the smaller speaker. Making it only produce higher frequencies. I used a surface mount 0805 size part .

    A ceramic cap will pass only higher frequencies to the smaller speaker.

    An inductor will pass only lower frequencies to a speaker.

    This in turn improves the performance of the speakers.

    Here is a good site that will elaborate and let you play around with numbers. Depending on speaker specs you can tailor a setup to your needs.

    http://www.bcae1.com/passxovr.htm

    It is important that air can flow from the speaker area to vent holes some where down the hilt. The further down the holes along the hilt the better. Only a small path is needed for enough air flow but the better the flow, and the longer the path, the better the low tones will be.

    So what this gives you is optimized sound from both ends. A long chamber for low tones and a small chamber is enough for the tweeter. Also more audio input can be applied without distortion.

    It is important to mount the speaker firmly and seal the seam around the big speaker for best performance.

    Many hours went into testing different configurations. What you see are a 36mm 2w speaker with shielded magnet and a 16mm sony mp3 cell phone speaker JB welded to the back.
    Note: this pommel has larger I.D. than mhs parts.

    The smaller speaker has a small box around it with a port on the side so it is better protected from the bigger speaker pressures nearby.

    The magnets from the different speakers should be separated by non magnetic material. I used a small aluminum square.

    The two speaker setup is probably not worth doing unless you are using a high end sound board mostly due to the quality of the sound samples from the low end boards. Also this does not necessarily make a saber louder but more of an improvement on sound quality.

    I would make a movie but it would not convey how it sounds.

    I will tell you that during testing of 7 different small speakers with ESB I heard stuff that I normally don't.



    Here is a link to the thread that the initial round of testing was done. If you want detailed information on how much a resonance chamber can amplify sound from a speaker there is lots of info in there.


    http://forums.thecustomsabershop.com...ead.php?t=9608


    Hopefully this will give some insight on resonance in sabers.

    If there is some thing more to add or explore or questions let me know.

    SR
    Last edited by Sunrider; 10-13-2010 at 09:51 AM.

  2. #2
    Board Lurker Andro's Avatar
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    Man, you've got me sold. But hey, it's me.

    If I ever manage to get a hold of some buttered toast in my lifetime, I won't have to consider another sound setup (or when Tim has the TCSS sound board...). Great job, mate!
    Last edited by Andro; 09-02-2010 at 05:45 PM.

  3. #3
    Council Member Novastar's Avatar
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    As always, your posts ROCK, Sunrider!!

    That is some EXTENSIVE work you did, and I just (really, REALLY) want to say thanks!!!!

    I was pretty much of the brethren that a dual-speaker setup was (fairly?) hopeless overall... but I think I see what you're saying--really separating the highs from the lows.

    Just a quick question... given these examples (let's say):

    * 28mm "big/low" and a 16mm "small/high"
    * 36-40mm "big/low" and a 16-20mm "small/high"

    ...would you say these would be the "close to correct" chambers needed?

    * for the 28mm ... ~2.2 inches of res space...
    ...for the 16mm ... ~1.25 inches of res space...

    * for the 36-40mm... ~2.5 inches of res space...
    ...for the 16-20mm... ~1.3 inches of res space...

    ... so you'd need around 3 to 4 inches total (not including space for actual speakers + separating the speakers with non-magnetic buffer)?

    I mean... that sounds about right, FO SHOOOOOWW... Problem is... what a bloody space hog, huh?
    ~~ GREYTALE NOVASTAR (Writer, Director, Choreographer, Sound Designer, Actor, Saber Designer, Vocal Artist)
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  4. #4

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    Your post rocks....sound res is always a prblm maybe you have found a solution for that 2 speaker setup sounds like it would work...yes a high end soundboard would be the only way

  5. #5

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    Just a quick question... given these examples (let's say):

    * 28mm "big/low" and a 16mm "small/high"
    * 36-40mm "big/low" and a 16-20mm "small/high"

    ...would you say these would be the "close to correct" chambers needed?

    * for the 28mm ... ~2.2 inches of res space...
    ...for the 16mm ... ~1.25 inches of res space...

    * for the 36-40mm... ~2.5 inches of res space...
    ...for the 16-20mm... ~1.3 inches of res space...

    ... so you'd need around 3 to 4 inches total (not including space for actual speakers + separating the speakers with non-magnetic buffer)?

    I mean... that sounds about right, FO SHOOOOOWW... Problem is... what a bloody space hog, huh?
    Thanks guys

    It is not as complicated as that. With the two speaker setup as shown 1.5 x 16mm = 24mm from speaker to pommel vent.

    For the big speaker obstructions don't matter as long as air can work its way to holes at the emitter end of the hilt.

    Two inches of space is the maximum needed for this type of setup.

    Low tones will not be baffled by internal components as long as there are gaps for the air to go through.

    Simply keep in mind air needs to flow through the hilt and make ports inside if needed.

    You can just blow through it to check.

  6. #6

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    Info also needed, before perhaps worrying about "sealed enclosures" for "low driver":

    For each varying board, economy, Hasbro FX, UltraSound, CF, what is the low freq of the actual sound samples? Nova may know answer to this for CF, but what about Hasbro, etc? Anyone recorded and checked freq. analysis of the differing sounds?

    The speaker itself is going to roll over very sharply below, perhaps, 400hz, so many "rumbling" wouldn't be reproduced even it it was present.

    I put a sealed enclosure on my first two sabers, but the entire time, I was wondering, am I wasting my time, given the size of the driver, its low-frequency response, and the audio sample low freq content?

    We may scavenge some low-frequency harmonics that arent' there, given resonance chamber, body of hilt etc, similar to "bass boost" in small devices, but is the meaty rumble even there to be heard?

    Perhaps output to line levels on decent stereo system, and then analysis of audio to see what is truly there. Nova probably has good low end in his samples, but even then, if speaker cannot reproduce, he's wasting space and dynamic range.

    Questions to ponder.

    AK-47s and Lightsabers, both so fun to build

  7. #7

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    The original saber hum was modeled after 60hz power line buzz. So idle hum should be around there. It is hard to get good sound in this range but can be done.

    When I mention sealing I mean not letting air pass by the main speaker. By no means should any chamber be sealed. They must be well vented.

    Nova has mentioned that he reduces the sample level below 80hz. Maybe he could explain more. I'm guessing a two speaker setup could candle this frequency range better than the single speaker.

    I don't think we will ever get meaty rumble which is below 50hz. But the idle hum is right on the edge of what we can improve.

    This is the difference between a speakers with & without resonance chambers.



    Then I took off the tubes woah . difference?
    data



    I is important to note that while the specs on these speakers drop off at 400hz we can still see a huge change at 250hz of 15db.

    The frequencies below 250hz would also improve by sealing the speaker against the end of the tubes and making the tubes longer.

    A waste of time is it? If never you try, never know will you.
    Last edited by Sunrider; 09-03-2010 at 11:49 AM.

  8. #8

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    Didn't mean to imply "waste of time", just that I said to myself "is it a waste of time"

    the boost at 250Hz is very meaningful. The lack of boost below that is probably to be expected.

    who can argue with a 15db+ boost from a 1Watt speaker.

    You would have to have much larger speaker and much more power to equal that boost in a non-resonated environment.


    The sealed enclosure for the speaker is to help ensure that the long wavelength bass sounds do not cancel each other out. But, given the levels at "bass frequencies" are very low DB, seems like more to gain by putting resonance on front, rather than enclosure on back.

    Too bad no room for a 12" sub in my saber.

    AK-47s and Lightsabers, both so fun to build

  9. #9
    Council Member
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    Rhyen Skytracker's Avatar
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    Well done my friend. Thanks for taking so much time researching this for us. This was a HUGE help.

    Live long and...I mean May the force be with you. http://saberconcepts.50.forumer.com/index.php

  10. #10

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    Thanks Rhyen

    Didn't mean to imply "waste of time", just that I said to myself "is it a waste of time"
    No worries. I was only implying that it is indeed a matter of opinion weather or not it is worth the time & effort to implement these things in your own design.

    I would say that one would defiantly have to appreciate good sound quality.

    The sealed enclosure for the speaker is to help ensure that the long wavelength bass sounds do not cancel each other out.
    Waves canceling each other out is defiantly something to think about when a speaker is pointed toward the inside of the hilt. If you look at the insides of automotive mufflers you can see baffles strategically placed to cancel out sound waves. These types of flat surfaces that stand in the way of air flow are to be avoided. More round surfaces and a single path to the vent holes is better to avoid cancellation.


    But, given the levels at "bass frequencies" are very low DB, seems like more to gain by putting resonance on front, rather than enclosure on back.
    I agree. For our purposes a sealed chamber behind the speaker/s is useless. It is the chamber space in front of the speaker that is important to utilize.

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