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Old 22nd May 2006, 03:16 PM   #1
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Default Tuning Question (Sealed)

Complete newbie question here. I tested my first speaker yesterday to get the t/s values. I am primarily using Winisd for modeling. What does the fb of the box correlate to on the modeling program? I was thinking it might be f3 but I am not sure.
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Old 22nd May 2006, 05:31 PM   #2
sreten is offline sreten  United Kingdom
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Hi,

For a sealed box Fb = change of Fs (free air) by Vbox to Fb.
Fb only equals F-3dB for Q=0.707, for Q=0.5, Fb = F-6dB.

In fact Fb and F-?dB are related by Qtc.

Fb is determined by Fs, Vas and Vbox only.

/sreten.
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Old 22nd May 2006, 08:00 PM   #3
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I'm sorry I still have not grasped the concept yet. Let me try my question again. I have created the alignment I want using Winisd. If I build the box to the size given and then I test for the resonating frequency of the box, what frequency would I look for to know my tuning is correct? In trying to understand what sreten stated that would depend on the Q of the box. If the q on the modeling program states I am using a .707 alignment I would look for the freqency shown at f3. If it shows a Q of .5 I would look for the frequency at f6. If this the case is there a chart or something that shows the f_s at different Q amounts? One more question. Does winisd's or other programs alignments assume any kind of dampening material is being used in the enclosure?
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Old 23rd May 2006, 03:56 AM   #4
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Never mind, I finally got there by myself.

It is really surprising to me that these basics are difficult to find explained on a simple level for beginners like myself to understand. IMHO these instructions should be made available as a sticky at the top of all diy enclosure forums. They should be explained in plain English and assume no understanding by the reader.

Please everyone, help out the newbies, we all have to start somewhere.
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Old 23rd May 2006, 08:45 AM   #5
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thing is kio is that with anything in life, ppl tend to be protective of elements that contistute as being somewhat proprietary to an individual design.

taking all basic "rules" in building that personal goal in a loudspeaker is the first step in allowing everybody get closer to an acheivement done by one person.


this is a diy forum (and everyother diy i've been too) there are no beginning rules to start from because, well, this is diy. the pride you can take in accomplishing something on your own is immense and probably account to 90% of why those that do diy, do it.


take that away... and diy is diy anymore.



Ask around. and learn some, eventually you'll get exactly to where you want and perhaps learn a few tricks yourself.
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Old 23rd May 2006, 09:02 AM   #6
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Basically whern building a sealed box, to check it you would measure the new resonance frequency of the system (Fb you call it, I prefer to call it Fc to denote closed box, and use Fb for vented boxes) and the total Q (Qtc). Then you would compare these two values to what you predicted, and you can work out the -3dB point (F3).
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Old 23rd May 2006, 10:34 AM   #7
sreten is offline sreten  United Kingdom
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Hi,

if you use win ISD Pro (alpha) you can tell Fb by the impedance peak.

/sreten.
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Old 23rd May 2006, 11:28 AM   #8
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I think what you are calling Fb is Fsc, and is shown on the Box tab in WinISD.

It is the resonance freq of the cone on the combined stiffness of the driver suspension and the air of the box.

Fb is the portPR tuning in a vented/PR system.

Dickason's Loudspeaker Design Cookbook is a good place to get the basics.
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Old 23rd May 2006, 05:08 PM   #9
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Sorry for the flame. I have been giving myself a crash course in audio for the last couple of weeks and that one issue alluded me for a while. A book would be a great idea, I really should get one.
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Old 23rd May 2006, 08:47 PM   #10
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Dickason is excellent, but you might find Weems 'Designing, Building & Testing' easier to get into if you are new to it all.
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