Uros

Sealed box guitar cabinet help needed
« on: January 15, 2018, 05:30:20 PM »
Hi,

I am working on a guitar amplifier project and I need a help regarding the speaker cabinet design. I am going for a sealed box design and I am going to use a Jensen P10Q.  Here's the catch: Jensen P10Q has an unusually large Qts value of 1.88, especially compared to the targeted Qtc of 0.577. Using equations for calculating a box volume I get a Vb of negative value (obviously, since Qts>Qtc).               

This raises a few questions: Should I use this Vb value regardless of the minus sign, or is there a different set of equations that should be used when Qts>Qtc? Should closed box designs with a low Qtc be avoided when drivers with a much larger Qts are to be used?

Thanks in advance.

Cheers,

Uroš


JMFahey

Re: Sealed box guitar cabinet help needed
« Reply #1 on: August 26, 2018, 11:19:21 AM »
Although very late, I answer because same or very similar problem may be found by somebody else; in fact it´s a very common problem: making a custom Guitar cabinet.

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I am working on a guitar amplifier project and I need a help regarding the speaker cabinet design. I am going for a sealed box design and I am going to use a Jensen P10Q.
 
Ok, fine classic Guitar speaker.
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Here's the catch: Jensen P10Q has an unusually large Qts value of 1.88,
typical of relatively small magnet, **stiff** thin cone undamped Guitar speakers.
What you mention is the norm and not the exception.
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especially compared to the targeted Qtc of 0.577.

Targeted by whom;)
Low Q is desirable to get a well damped flat response **HI FI* type cabinet; but we are talking *Guitar*  here .
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Using equations for calculating a box volume I get a Vb of negative value (obviously, since Qts>Qtc).   
     
So you can´t build a Hi Fi cabinet with a Jensen P10Q .     

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This raises a few questions: Should I use this Vb value regardless of the minus sign, or is there a different set of equations that should be used when Qts>Qtc? Should closed box designs with a low Qtc be avoided when drivers with a much larger Qts are to be used?

You are building a Guitar cabinet, you have 3 options:

1) build a closed cabinet.
It will be excellent for guitar, fat and warm, and *will*  have a bump at the resonant frequency.
IF the box is too small and said bump appears >150Hz , sound will be "boxy" (too much low mids) ; if lower it will be considered "fat" .

2) make an open back one: is the classic solution, used even today, not as "fat"  but sound will be "open"  and of course "not boxy".
What most Guitar combos use today.

3) IF you want to make that cabinet usable to listen to Music (you might want to add a Tweeter)  you can opt for the 40´s to 70´s solution in cheaper "Radio Gramophone players" and early Home Audio stuff: an "aperiodic damped cabinet".

You have seen them at Pawnshops and Salvation Army shops: a regular looking cabinet but with a Masonite or chipboard back full of little holes, pencil sized or smaller: air can pass through them but flow is restricted, it acts as an Acoustic resistor which damps the annoying Bass bump , end result is ..... acceptable ..........

 
« Last Edit: August 26, 2018, 11:23:34 AM by JMFahey »
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