someone please explain all the Q's to me please

Discussion in 'Archived Threads 2001-2004' started by Mike Dr, Jan 9, 2002.

  1. Mike Dr

    Mike Dr Stunt Coordinator

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    Qts, Qms, Q of the box ... and so it goes on ... will someone please explain the significance of the various Q's we encounter in speaker design? I am about to build a Tempest sonosub and this whole "well do you want a high or low Q design" subject is giving me a headache.. from what I understand, lower overall Q means "tighter" bass .. this whole Q thing is a pain when it comes to finalizing the dimensions and tuning frequency for the upcoming sub..
     
  2. Travis G

    Travis G Stunt Coordinator

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    Mike

    Q is basicly a measure of damping. It's an indication of how well a speakers movement is controlled. The important thing to remember is this...

    A lower Q indicates a more controlled speaker. A high Q indicates loudspeaker that likes to misbehave.

    Qts - Represents the total damping of a driver.

    Qms - Represents the mechanical damping of a driver(the ammount of damping provided by the suspension.)

    Qes - Represents the electrical damping of a driver (the ammount of damping provided by the magnet and voice coil.)

    A high Q means the speaker has a tendancy to resonate which means the speaker will sound louder at the expense of a smooth frequency response and transient response.

    A lower Q means the speaker is more damped and will not sound as loud but will have better transient and frequency response.

    Too low of a Q may not allow the speaker to play very loud before reaching it's power limits. This is known as being overdamped.

    Too high of a Q will not sound very natural and will not provide deep bass. This is known as being underdamped.

    Most people tend to aim for an overall Q somewhere between .7 and 1
     
  3. Mike Dr

    Mike Dr Stunt Coordinator

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    Ok .. makes sense.. I hear .5 .577 and .7 as commonly referred to Q numbers.. is there any reason for this? Also you say most people try .7 to 1 .. doesn't this depend on the type of speaker you're making also? how exactly is this Q value defined (math formula?)
     
  4. Ron Shaw

    Ron Shaw Stunt Coordinator

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    In my opinion, when designing a loudspeaker, you should aim for flat response out of the loudspeaker (Q=.707). A loudspeaker with a Q of 1 will have a hump at Fb. A loudspeaker with a Q of .5 will be about 6db down at Fb, and is usually intended to be used with equalization to restore flat response. A Q over .707 can cause response problems that can be difficult to tame later, and should be avoided. Keep in mind I am talking about Loudspeaker system Q, not the driver Q. The various Qs of a driver are of importance when designing the enclosure, but of no importance after that (aside from the fact that they all contribute to final system response). For a phase inverter enclosure (bass reflex, or ported), usually a raw driver with a lowish Qts is better. High Qts drivers are usually better suited for sealed systems.
     
  5. Patrick Sun

    Patrick Sun Moderator
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    Mike, if you are really interested in speaker design and terminology, you should really go buy Vance Dickason's "Loudspeaker Design Cookbook", which is on its 6th edition. It's available at Amazon and Barnes & Noble, I believe.
     
  6. Mike Dr

    Mike Dr Stunt Coordinator

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    Ron - I will be using equalization regardless since I have a BFD, but a very high Q box will probably be too large for my taste anyway.. so far it's looking like i'm gonna make something between Q .5 and .7
     
  7. Ryan T

    Ryan T Second Unit

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    Hi, I'm building a 230L sealed tempest and it has a Q of .5

    does this mean that i'm going to have to use equalization with it? Thanks

    Ryan
     
  8. ThomasW

    ThomasW Cinematographer

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  9. Mike Dr

    Mike Dr Stunt Coordinator

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    How dow one calculate the Q anyway? [​IMG]
     

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