Vented box acoustic parameters??
I am about to add a constrained layer damped aluminium plate to the baffle of my woofer & sub enclosure.
That will make it impractical to modify the boxes so I decided to check they were tuned correctly, before I did any irreversible work.
At that frequency it's most practical to determine the resonance with an impedance test rather than use a mic.
So the result is that I have restudied the way the acoustic parameters are reflected (or transformed) into the impedance curve of the speaker.
I did the calculations for the speaker years back, by hand but must admit I didn't have a real intuition for the acoustic parameters.
The "acoustic mass" of the port is in kg/m^4, not just a mass.
Similarly the acoustic compliance is m^5/N.
I understand they are multiplied by Sd^2 to become mechanical units but these are not intuitively obvious units to me.
Anyone here have an explanation of this?
I read Olson and Beranek back when I did the calculations, now a quick check with Vituix* showed I did pretty well.
But I never had a real feel for the work.
Now I have a copy of Marshall Leach but I don't find the presentation very clear.
I also have LSDC by Dickason but the focus is on how to use software.
Software wizards means almost anyone can achieve a reasonable result but it is not very educational just to copy the recommendations of a black box process.
Anyone know books, articles or websites that explain this better?
I can do the maths and physics but I want to understand more.
David
*Excellent piece of work, my compliments to the author.
I am about to add a constrained layer damped aluminium plate to the baffle of my woofer & sub enclosure.
That will make it impractical to modify the boxes so I decided to check they were tuned correctly, before I did any irreversible work.
At that frequency it's most practical to determine the resonance with an impedance test rather than use a mic.
So the result is that I have restudied the way the acoustic parameters are reflected (or transformed) into the impedance curve of the speaker.
I did the calculations for the speaker years back, by hand but must admit I didn't have a real intuition for the acoustic parameters.
The "acoustic mass" of the port is in kg/m^4, not just a mass.
Similarly the acoustic compliance is m^5/N.
I understand they are multiplied by Sd^2 to become mechanical units but these are not intuitively obvious units to me.
Anyone here have an explanation of this?
I read Olson and Beranek back when I did the calculations, now a quick check with Vituix* showed I did pretty well.
But I never had a real feel for the work.
Now I have a copy of Marshall Leach but I don't find the presentation very clear.
I also have LSDC by Dickason but the focus is on how to use software.
Software wizards means almost anyone can achieve a reasonable result but it is not very educational just to copy the recommendations of a black box process.
Anyone know books, articles or websites that explain this better?
I can do the maths and physics but I want to understand more.
David
*Excellent piece of work, my compliments to the author.
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The original A.N. Thiele and Richard Small papers published in AES are a good place to start. Their published work on loudspeaker low frequency analysis went from approximately 1970 to 1980 if I recall... Two papers you should read in particular are "loudspeakers in vented boxes" part 1 and part 2... I don't have a link, the copies I have were photocopied from my university library in 1987.
It is, of course, important and good to seek an ever deeper understanding of a subject. This should not stand in the way of progress however. If you measure the impedance of your woofer/box system, the tuning frequency is the frequency of minimum impedance between the two peaks... i.e. the valley. Make your measurement, and be confident about moving forward.
It is, of course, important and good to seek an ever deeper understanding of a subject. This should not stand in the way of progress however. If you measure the impedance of your woofer/box system, the tuning frequency is the frequency of minimum impedance between the two peaks... i.e. the valley. Make your measurement, and be confident about moving forward.
As an Aussie I must point out that the A.N Thiele papers were first published in the Australian IRE, 10 years before the JAES.😉
I do have those papers and they are excellent, as you say.
But intended for the Elec.E. audience, assume some familiarity with the work of Novak and others.
You are correct that I can take the measurements and move forward.
And I am now confident that the results are fine.
It's just that the need to look back at the old work has reminded me of some questions I had at the time.
I only feel that I really understand the maths when I have some physical intuition, for me that is the fun part.
The second question was the relationship of the two peaks on either side of the impedance minimum that occurs at resonance.
I know they will be equal maximum and reciprocally spaced in frequency if the box is tuned to the same frequency as the speaker.
Is there a rule of thumb for their frequency?
I have played with this in Spice simulation and see the trend there but haven't tied it to the acoustic parameters yet.
In fact my first question was a lead-in to this one.
Best wishes
David
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