Hello! It's said that it's possible to increase Qts of a woofer, when it's a low Qes/high Qms driver with 2Fs/Qes >= 160 (I'm referring to this post).
I replaced my old woofer, working in 57 litres, with a Beyma 8P300fe because I wanted to experience PA-oriented drivers, and this driver fully matches the features above, having Qts 0.33/Qms 9.54/Fs 61Hz/Re 5.2ohm. Now it's difficult to decrease volume of existing enclosure under 35 litres without hard modifying it, so Beyma is working badly out of its optimal range (10-30 litres).
My question is: can I increase Qts of Beyma inserting a series capacitor instead of a resistor, so its reactance increase Re and so Qts in the extremely low range leaving unchanged Re and Qts for the upper frequencies and so high efficiency in the mid range band?
I've made a simulation with Visaton Boxsim and the result is encouraging, please see the difference between solid line (using 600 uF in series with woofer) and dashed line (without capacitor) in the 40-60 Hz band:
Is it a problem to make the woofer work under its 61Hz resonance frequency? I'm going to try this but I'd like to know if it may be theorycally correct, in which case I may leave woofer in this slightly large enclosure, even improving extension and limiting the 160-180Hz peak.
Thank you very much.
I replaced my old woofer, working in 57 litres, with a Beyma 8P300fe because I wanted to experience PA-oriented drivers, and this driver fully matches the features above, having Qts 0.33/Qms 9.54/Fs 61Hz/Re 5.2ohm. Now it's difficult to decrease volume of existing enclosure under 35 litres without hard modifying it, so Beyma is working badly out of its optimal range (10-30 litres).
My question is: can I increase Qts of Beyma inserting a series capacitor instead of a resistor, so its reactance increase Re and so Qts in the extremely low range leaving unchanged Re and Qts for the upper frequencies and so high efficiency in the mid range band?
I've made a simulation with Visaton Boxsim and the result is encouraging, please see the difference between solid line (using 600 uF in series with woofer) and dashed line (without capacitor) in the 40-60 Hz band:
Is it a problem to make the woofer work under its 61Hz resonance frequency? I'm going to try this but I'd like to know if it may be theorycally correct, in which case I may leave woofer in this slightly large enclosure, even improving extension and limiting the 160-180Hz peak.
Thank you very much.
Hi Andrea,
I think you are wasting your time trying to use a cap to boost bass response.
Try an alternative approach like this. Beyma 8P in 35 litres tuned to 61 Hz
gives slightly humped response but when you install the filter and series RLC
in parallel with the unit, it all appears much more friendly. Simulated impedance
and spl may not be the most correct hence the parts will be off too.
I think you are wasting your time trying to use a cap to boost bass response.
Try an alternative approach like this. Beyma 8P in 35 litres tuned to 61 Hz
gives slightly humped response but when you install the filter and series RLC
in parallel with the unit, it all appears much more friendly. Simulated impedance
and spl may not be the most correct hence the parts will be off too.
Attachments
By inserting a series capacitor you are not increasing apparent driver Qts, you are making a 3rd order (closed box) or 5th order (vented box) system. Both of these have been studied before in some detail and papers have been published in the literature.
For example, published in the JAES:
Closed Box: N Thiele, "Closed-Box Loudspeaker with a Series Capacitor"
Vented Box: T. Mellow, "A New Set of Fifth and Sixth-Order Vented-Box Loudspeaker System Alignments using a Loudspeaker Enclosure Matching Filter: Part II" (see section 8)
Sometimes the added capacitor can result in real benefits. It depends on the particular system in question. I would continue to experiment with your BoxSim modeling and if it looks good, go for it.
Keep in mind that you will need a bipolar capacitor rated to an appropriately high AC voltage in this application.
For example, published in the JAES:
Closed Box: N Thiele, "Closed-Box Loudspeaker with a Series Capacitor"
Vented Box: T. Mellow, "A New Set of Fifth and Sixth-Order Vented-Box Loudspeaker System Alignments using a Loudspeaker Enclosure Matching Filter: Part II" (see section 8)
Sometimes the added capacitor can result in real benefits. It depends on the particular system in question. I would continue to experiment with your BoxSim modeling and if it looks good, go for it.
Keep in mind that you will need a bipolar capacitor rated to an appropriately high AC voltage in this application.
A second (or even third) order electric highpass will give enough correction possibilities by changing the quality factor of the network. The series RLC might be necessary, that's why I'd opt for an active filter, just one opamp and some resistors and capacitors will do fine. Result is a B4, a regulated power supply will be available in most amps. Just a series cap won't do though.
You'll find the needed math on Linkwitz' pages:
fourth image on this page
You'll find the needed math on Linkwitz' pages:
fourth image on this page
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