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Signal generators and frequency analyzers

Discussion in 'General Electronics Chat' started by tommy, Jan 10, 2003.

  1. tommy

    tommy New Member

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    i seem to be getting inacurate reading .....frequency roll off at 92 cycles per seconds ..............I am using a sure sm57 mic to get freuency sweep sample...............could this be the problem.........or could it be room conditions ........oh..............for you die hards...... i have successfully rewrapped a voice coil in a vintage cerwin vega tweeter ..this was a big challange..... I was very careful to match the serface aera of the magnet wire ... oh once you get halfway done you cannot put it down you get the nest effect.....vintage stuff is way better than anything you can buy now days
     
  2. pebe

    pebe Member

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    If you can get the response of a tweeter down to 92Hz, you're doing very well. What did you expect to get down to?
     
  3. kinjalgp

    kinjalgp Active Member

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    92Hz from Tweeter? Sounds strange!!! :roll:
    Normally tweeters are designed for High frequency reproduction above 1000 Hz.
     
  4. dave

    Dave New Member

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  5. tommy

    tommy New Member

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    i am testing roll off of an inductor.........the tweeter i was proud of because all the speaker repair guys said it couldnt be fixed..........
     
  6. pebe

    pebe Member

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    You hadn't mentioned an inductor so I thought you were testing the tweeter! I thought it a bit strange to be doing it at that frequency.

    So you were testing the roll off of an inductor? And it rolls off at 92Hz? You cannot test frequency responce of the inductor as a single entity - you must have it tuned with capacitor or as part of an R/L combination.

    Could you provide a bit more info?
     
  7. tommy

    tommy New Member

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    i want the roll off to be around 92 cycles per second my thinking is i want smooth cross for this speaker .....i want a lot of bass for this channel or close the reason for the steep roll off .....i have a 15 inch cerwin vega to is being used in as center in pro dolby digital application...............i have a .9mh inductor the capasitor is 176 microferads
     
  8. herbymcduff

    herbymcduff New Member

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    What I'm not understanding is that you want a 15 in Cerwin Vega(assuming 4 ohm load), with an inductor and cap in series with it. Thus making a bandpass. A wide range of frequencies.

    Now, you only want to let through any thing below 92 hz. Why. Subs are generally good at 250 hz to get good bass. And you only need to place an inductor in series with it.

    At your frequency of 92 hz, I calculate a 6.9mH inductor. At 250 hz, I calculate 2.5mH.

    Hope I didn't confuse anyone. Let alone myself.
     
  9. tommy

    tommy New Member

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    its 8 ohm the calculation is 3500 khz.. I dont want to use a port because i can nver seem to get them right .what i am talking about is the pitch of the roll off........disapating the overall frequencies... a sound that is at a specific frequency lets say 250 hz -250 cycles per second that 250 cycle per second can disapate at or go away at a 90 to 100 cycles per second meaning.....how fast the sound goes away....once the bass frequency has sounded i want the sound to difuse but want the wave pressure to still be in the room....maybe i am looking at this wrong the enclosure is sealed i am trying not let the cone rumble when its not needed. now if this was a 20,000 square ft hoot theater i would cross it anywhere and call it good I want a lot of sound but i dont want it to travel very fare ....in otherwords i now am thinking that i need to raise and lower the roof i am realizing since i have no control over wave pressure.
     
  10. herbymcduff

    herbymcduff New Member

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    You could try Bass Box 5.1 or X-Over 2.03 from Harris Tech. You can make your boxes pound at certain freqencies and such. Try to search for them on the net.
     
  11. pebe

    pebe Member

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    [/quote] its 8 ohm the calculation is 3500 khz.. I dont want to use a port because i can nver seem to get them right .what i am talking about is the pitch of the roll off........disapating the overall frequencies... a sound that is at a specific frequency lets say 250 hz -250 cycles per second that 250 cycle per second can disapate at or go away at a 90 to 100 cycles per second meaning.....how fast the sound goes away....once the bass frequency has sounded i want the sound to difuse but want the wave pressure to still be in the room....maybe i am looking at this wrong the enclosure is sealed i am trying not let the cone rumble when its not needed. now if this was a 20,000 square ft hoot theater i would cross it anywhere and call it good I want a lot of sound but i dont want it to travel very fare ....in otherwords i now am thinking that i need to raise and lower the roof i am realizing since i have no control over wave pressure.[/quote]
    I'm not sure just what you mean -or say! - in your posting.

    "what i am talking about is the pitch of the roll off........disapating the overall frequencies... a sound that is at a specific frequency lets say 250 hz -250 cycles per second that 250 cycle per second can disapate at or go away at a 90 to 100 cycles per second meaning.....how fast the sound goes away...."

    If you are talking about the rate of decay of the sound, then this is a function of room acoustics - not loudspeaker response. Sound in a room with lots of absorbant surfaces will decay much faster than one with reflective walls.

    "once the bass frequency has sounded i want the sound to difuse but want the wave pressure to still be in the room...."

    Whatever do you mean?

    "....maybe i am looking at this wrong the enclosure is sealed i am trying not let the cone rumble when its not needed."

    If you mean you want to stop the cone resonating and giving vibrations after the energising force is removed, then you need better damping on the unit. AS your loudspeaker resonates it generates power which is dissipated by the output impedance of your amplifier. For good damping this should be as low as possible. Your amplifier should normally have a low output impedance but you should make sure you use thick (low resistance) cables to your loudspeaker.

    I don't know what crossover you are using for your tweeter, but there are plenty of designs on various sites, and details of design enclosures.
     

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