Physics Questions About Speakers

Discussion in 'Speakers' started by Matthew Will, Mar 10, 2004.

  1. Matthew Will

    Matthew Will Stunt Coordinator

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    Here are some questions that bug me

    1. What restricts xmax? Surround and spider or the way the voice coil is designed around the magnets?

    2. How do companies determine all the mathematical quantities of speakers? Basically how do they determine the recommended box sizes?

    3. What is the difference between a free air speaker and all others when comparing build designs?

    4. Does the angle of the cone determine sound qualities at all? Would a flat cone produce weird tones? I would think a flat cone would be best.

    Follow up to question 4 - If a cone is angled in it has more surface area than a flat cone in the same diameter circle correct? So the angled cones could possibly have a higher spl than a flat cone sort of like how a 15" moves more air than a 12". Is this correct?

    5. Why are some speakers said to be harder to get moving than others? Or why do some speakers require more power to really sing? Is that determined in voice coil design?

    6. Is the spider used only for stablizing the bottom of the cone?

    7. Force = mass X acceleration. So if you have a cone that weighs 5 grams and a cone that weighs 10 grams and got them to move at the same acceleration/velocity would the cone that weighs 10 grams produce more force/SPL? Or is it simply the mass of the air that needs to be moved and therefore the perfect cone would be a lightweight but extremely rigid surface?

    Matt
     
  2. ken nomimashita

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    1. the suspensions limit is XSUS and that is how far it goes linearly (basically) the magnets limit is XMAG and that is how far it goes while still retaining 71% of the BL(magnet strength). XMAX is the smaller of these numbers.

    2.they use a dumax machine (usually) and they test box sizes after they guess them using the TS parameters.

    3.by free air,you probably mean infinite baffle and thats when the speaker isnt enclosed but it has something that seperates the front and rear waves. this sounds good with certain speakers but reduces powerhandeling.

    4. no. anyhow,the radiating diameter is what you base the displacement off of. curvature does not add cone area. elemental designs and some other companys use flat cones and (i have heard them) they sound exactly the same as "normal" cones.

    5. speakers that are "harder to move" are less sensitive (see sensitivity rating, ([email protected]) and have stiffer suspensions (usually). the voice coil is merely suspended by the suspension and doesnt affect sensitivity, but powerhandeling and some other things.

    6. it maintains the linear motion of the voice coil.

    7. the mass of the cone usually determines what it sounds like at certain frequencies and has nothing to do with the SPL is produces (within reason).

    hopwfully this helps.
     
  3. Matthew Will

    Matthew Will Stunt Coordinator

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    1. What usually determines if a speaker is good for infinite baffle? My guess is that it is so light and sensitive that it needs no compression force behind it.

    2. So is SPL simply a factor of the XMAX and diameter of the speaker? (Excluding the frequency being played)

    3. How does the mass of the cone determine what it sounds like at certain frequencies? I'd like you to think about this though. I still think that having an extremely rigid cone would produce higher SPL ratings simply because it transfers the energy more efficiently. A "mushier" cone would have more give to it. Does this make some sense?

    4. Is a spider absolutely needed? If the speaker was designed very precisely I imagine that the voice coil could stay aligned in the magnets. I'm sure you've seen those globes that elevate themselves between two magnets. I'm sure the voice coil could do the same. Ideas? Matt
     
  4. ken nomimashita

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    1. im not exactly sure what to look for because i have never actually tried an IB setup.

    2. no. the port resonance(if applicable) and room gain (in the house) or cabin gain(in the car) are very important too. many of the loudest speakers in existance have quite small xmax.

    3. it makes a difference in the Fs and mostly the low end extension (heavier can help it play lower). a lighter cone wont be louder in most cases. there are too many other things going on. having a cone with "give" would just reduce the efficiency that the voice coil moves the cone with and it would sound like shit.

    4. that may work but speakers are normally used in more positions than just laying flat on the magnet so having the spider there is a nice extra.
     
  5. Robert_J

    Robert_J Lead Actor

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    1. Taken from the IB FAQ:
    6)How do I choose a driver?

    Chose a driver preferably with a 1/2 roll rubber or foam surround. Accordion surrounds are limited in their usefulness and are usually noisy when driven hard. Look for a woofer with a Qts that is in keeping with the sonic characteristics you want. We DO NOT recommend using prosound drivers. Most have too small an Xmax for use in an IB. Also we DO NOT recommend using drivers designed by car audio manufacturers. A few car audio woofers are ok; but by and large, most aren't appropriate for IB use.

    7)Which Qts/Qtc should I chose?

    For an IB, the Qtc of the system is the Qts of the driver. If you like very tight bass, chose a lower Qts driver. If you like the "HT" sound, then chose a driver with a higher Qts. Dual voice coil woofers can be used with a variable resistor in series with the inputs of an unused VC. This allows the "Q" to be adjusted to the listener's wants/needs. One drawback of this is that the power handling is cut by at least 25%. Here's a LINK to the Adire Audio article on RDO (resistively damped operation).

    NOTE: using RDO or leaving one VC open will decrease the output of each driver -3dB.

    -Robert
     
  6. DanielKellmii

    DanielKellmii Supporting Actor

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    Good questions. Now go get your engineering degree if you are not doing so already.
    Underpaid and Underlaid. But it is a decent job.
     

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