As I'm learning about this and been modelling several 10" and 12" drivers in sealed boxes in UniBox, I've noticed the impedance peak varies with Qtc of the box.
The box under consideration will house a driver to run between 80Hz and 400/500Hz. While the free air impedance curves shown on the manufacturer's datasheets display that peak well below 80Hz, UniBox shows them within the operating range once the box is accounted for. How should I take that into the design considerations?
Examples with Beyma drivers:
Example: 12LX60V2 in a 30 liter box would have Qtc=0.53 and the peak at 72Hz. At the crossover frequency, 80Hz, impedance would be past the peak so relatively "smooth" and high...needing less current from the amp to achieve a given SPL? But designing with Qtc of 0.707 seems like a Holy Grail from what I read...a tradeoff?
Sorry for the rambling. As I am into selecting the midbass driver I am wondering if this should be taken into consideration.
Looking forward to learning!
The box under consideration will house a driver to run between 80Hz and 400/500Hz. While the free air impedance curves shown on the manufacturer's datasheets display that peak well below 80Hz, UniBox shows them within the operating range once the box is accounted for. How should I take that into the design considerations?
Examples with Beyma drivers:
- 12P80Fe: impedance peak at 209Hz, in a 3.2liter sealed box with Qtc=0.707.
- 12LX60V2: peak at 102Hz, in a 10.5 liter / Qtc=0.707
- 10G40: peak at 121Hz in a 6.4 liter / Qtc=0.707
Example: 12LX60V2 in a 30 liter box would have Qtc=0.53 and the peak at 72Hz. At the crossover frequency, 80Hz, impedance would be past the peak so relatively "smooth" and high...needing less current from the amp to achieve a given SPL? But designing with Qtc of 0.707 seems like a Holy Grail from what I read...a tradeoff?
Sorry for the rambling. As I am into selecting the midbass driver I am wondering if this should be taken into consideration.
Looking forward to learning!
If the amplifier produces a low impedance output, lower than the lowest load, then it doesn't matter.
Some manufacturers use positive feedback to increase the output of the amplifier when the impedance is lower. That gives a modified sound, compensating in part, for varying impedances of the loudspeaker.
Some manufacturers use positive feedback to increase the output of the amplifier when the impedance is lower. That gives a modified sound, compensating in part, for varying impedances of the loudspeaker.
Hi,
The peak in boxes indicated Fbox, higher than the free air which is Fs.
For Qbox =0.71, Fbox also = -3B, a Butterworth alignment.
You are quite correct in that with an Fbox of 72Hz or 102Hz you have
no hope of using a passive x/o at 80Hz, the x/o must be active.*
Fortunately active x/o's ignore any impedance peaks.
rgds, sreten.
FWIW for the 12LX60V2 in 10.5L. Acoustic high pass is 100Hz
2nd order Butterworth. Add another active 2nd order 100Hz
Butterworth to turn it into 4th order Linkwitz/Riley @ 100Hz.
Then low pass the sub active 4th order Linkwitz/Riley @ 100Hz.
Result : 4th order L/R acoustic @ 100Hz, drivers in phase.
Also note box = 10.5L + the volume taken up by the driver.
The peak in boxes indicated Fbox, higher than the free air which is Fs.
For Qbox =0.71, Fbox also = -3B, a Butterworth alignment.
You are quite correct in that with an Fbox of 72Hz or 102Hz you have
no hope of using a passive x/o at 80Hz, the x/o must be active.*
Fortunately active x/o's ignore any impedance peaks.
rgds, sreten.
FWIW for the 12LX60V2 in 10.5L. Acoustic high pass is 100Hz
2nd order Butterworth. Add another active 2nd order 100Hz
Butterworth to turn it into 4th order Linkwitz/Riley @ 100Hz.
Then low pass the sub active 4th order Linkwitz/Riley @ 100Hz.
Result : 4th order L/R acoustic @ 100Hz, drivers in phase.
Also note box = 10.5L + the volume taken up by the driver.
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Thanks Jon.
I'm considering a Hypex UcD700HG for this, that is reported to stay at 19mOhm in this frequency range. So the impedance peak doesn't matter for my design?
Yes, I plan to use active, digital, crossover. So the amp will be directly connected to this driver and will only reproduce 80 to 400/500Hz
Curious: how did you arrive at this?
Hi,
All boxes tuned to Qbox = 0.71 are acoustic
2nd order Butterworth high pass, with the
-3dB point and impedance peak at Fbox.
rgds, sreten.
Of the passive methods, you could use a series RLC across the driver to eliminate the peak. Otherwise, a shunt crossover would give partial rejection of the peak and is simpler but less efficient. A second order crossover might be fashioned to work instead.
One good approach would be to modify an amp by reducing the size of the input coupling capacitor.
If this is to be crossed to a sub, you might leave it un-crossed.
One good approach would be to modify an amp by reducing the size of the input coupling capacitor.
If this is to be crossed to a sub, you might leave it un-crossed.
Thank you! He said high pass but I was thinking low pass...so I was confused.
Building on that, if the sealed box was to be 21 liter, then Fb=80Hz, and that would be the crossover point from the subs which is the highest I'm confident the subs will play well. But at 21 liter Qtc drops to 0.579, while impedance peaks at 80Hz. Maybe I should consider this larger box despite the low Qtc? Do you think it would sound anemic?
FWIW, my sealed subs have Qtc of 0.48.
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