This is one of those things I thought I knew then suddenly find myself unsure of. I'm trying to figure out my power requirements for a set of tower speakers I'm building. The main driver I need 30w in to a 6.93Ω load to drive to xMAx, it's single voice coil.
P(w) = v² / R
v²=P(w) * R
207v²=30 * 6.93Ω
sqrt 207v²=~14.4v
i = v / r
14.4V / 6.93Ω = 2.077922A
~14.4V @ ~2amp is the power requirement for the main driver to drive to xMax
That part I have down. Where I start getting lost in my own lack of math skills is when it come to the low fs drivers. There dual voice coil, each coil is 3.25ohm, the plan is to wire them in two parallel sets of three coils.
WinISD tells me I need 135w (29.6v) for each driver with 2 coils in series (6.49Ω) for one driver. What WinISD does not tell me is if that voltage requirement is RMS or P2P. Does anyone know?
I'll have three coils in series 9.73Ω across 1.5 drivers in two sets parallel 4.87Ω.
My bad at math brain tells me;
v²=P(w)*r
v²=135*9.74Ω
1315v²
36.25v
i = v / r
36.25v / 4.87Ω = 7.44A
So if I've done that right, I need ~36v @ 7.5A to drive all three drivers to xMax. So am amplifier with 300VA+ power supply @36v should provide the current. So something rated 330w @ 4Ω.
Again, I'm bad at math and prone to making simple mistakes. Have I done the math right?
P(w) = v² / R
v²=P(w) * R
207v²=30 * 6.93Ω
sqrt 207v²=~14.4v
i = v / r
14.4V / 6.93Ω = 2.077922A
~14.4V @ ~2amp is the power requirement for the main driver to drive to xMax
That part I have down. Where I start getting lost in my own lack of math skills is when it come to the low fs drivers. There dual voice coil, each coil is 3.25ohm, the plan is to wire them in two parallel sets of three coils.
WinISD tells me I need 135w (29.6v) for each driver with 2 coils in series (6.49Ω) for one driver. What WinISD does not tell me is if that voltage requirement is RMS or P2P. Does anyone know?
I'll have three coils in series 9.73Ω across 1.5 drivers in two sets parallel 4.87Ω.
My bad at math brain tells me;
v²=P(w)*r
v²=135*9.74Ω
1315v²
36.25v
i = v / r
36.25v / 4.87Ω = 7.44A
So if I've done that right, I need ~36v @ 7.5A to drive all three drivers to xMax. So am amplifier with 300VA+ power supply @36v should provide the current. So something rated 330w @ 4Ω.
Again, I'm bad at math and prone to making simple mistakes. Have I done the math right?
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Not sure i Get this. Do you have three dual coil drivers each side? I would in that case serial connect three and thee coils in two parallels resulting in a 6 ohm speaker. Next step think about system sensitivity. Assume they are 90dB and 100 watt giving 110dB max SPL. Next ohms laws U=RxI and P=UxI -> I=root(P/R) = ~4A and 24V @100 watt. It would be easier if you let us know which driver it is. 6 coils could very much give a 1000 watt heat tolerance but the xmax would be the system mechanical limit anyway.
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Xmax would be peak, but most drivers can cross that line without issue so the extra few dB wouldn't go astray. You might appreciate the headroom.
It’s rates 8 ohm 200 watt.
I assume that’s a combo of both coils and each is 4 ohm and 100 watt then. Looking at the curves for this thing it’s Fs is around 40Hz and over that point it’s more like 8-10 ohms.
Would you consider a 4th driver in your design? That would allow a simpler connectivity serial/parallel everything at 8 ohm 800 watt which may be feasible if you place an active HPF at 40Hz. Much easier to calculate too!
Root (800 watt / 8 ohm) = 10A and further 8 ohm x 10A = 80 V.
Sensitivity of the system is 83+3+3 assuming 4 drivers= 89dB.
800 watt is 10+10+3+3+3dB = ~+29dB.
Confirmed with 80V/2,83V = +28,2dB (not sure about this one…)
Max SPL 89+29=118dB at 100Hz theoretically. This is peak.
With music 10-20dB headroom practically more like 100dB RMS but again xmax would probably be your system limit, not power.
In any case a 1000 watt amp would be smart here.
What’s your crossover plans for the above midrange? 200Hz? Active?
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Upper Range
Mark Audio Alpair 12p
Vented 13.5L tuned to 58hz
24db high pass @ 45hz (excursion control)
Sub Section
50L tuned to 24hz, 5" folded round port ~49.3"lg
24db low pass @ 70hz
IIR +2db @ 31hz Q 1.2
FIR Subsonic filter brick wall filter @ 20hz.
Crossover/DSP will be mixed FIR & IIR
Projected is 106db peak from the 12P, peak system power projected 12P 30W (20.8v) P-P, listening level would be about 2W RMS (3.7v) 95db.
I really don't want a 4th driver, that would require 66.6 liters in just the lower portion of the cabinet along with a 6" vent 53"lg entire cabinet would be 80 liters. With 3 Drivers I still have 3-6db of headroom above the 12P's practical output for music.
I also have a 15" Ultimax in the fireplace if I feel the need to **** off my better half.
I hoping for slim towers, not a Monolith from Clarke's Space Odyssey series.
Talking with a friend yesterday evening he thinks it's as simple as 14.8v per coil or 44.4v or about 500W into 4Ω @ 10amp PEAK to xMax. Real world I think is more like 7.7v RMS/11v PEAK for listening levels.
But I'm also not sure that's right either. I guess I will just build a test enclosure and take measurements as the real world often varies from the theoretical.
One simple way to think about it is that the sub driver and the full range driver have a delta of 10dB sensitivity which means you would need 10x the power on the sub. 30 watt on the full range, 300 watt on the sub (single sub but then again at 100Hz). Adding two more drivers should increase the sensitivity of +6dB which you need at lower frequency. You probably need some eq here. Also I’d cross between them at 80Hz or higher to get a cleaner mid but the you need a smoother roll off than 24dB or lots of eq. I guess it will work just fine what you have in mind. Depending on room size and placement of course.
Your friend is correct, 135(watts) x3=405 watts, which at 4.87ohms requires 44.4volts (which are measured RMS, not peak to peak) to achieve. To deliver 500 watts into 4 ohms also requires 44.4volts.
As the voice coil DCR of 4.87ohms (or higher) would only be around Fb (box tuning), an amp that delivers more voltage may be required to push the drivers to Xmax if your simulation shows a higher impedance at Fb than the DCR.
Maybe I’m slow. You plan to use three of these drivers right? Your most likely system impedance is 6 ohms and total 600 watt -> 10A, 60V. This based on 3 and 3 serial connected coils in parallel. Other connections results in 2,66 ohm or 24 ohm which I don’t see any practical at all.
Max SPL:
83 (1watt single driver two coils serial 8 ohm as per spec)
+20 (100 watt)
+~7 (600 watt)
+~5 (3 drivers)
= 115dB peak ~ 100dB RMS music.
Max SPL:
83 (1watt single driver two coils serial 8 ohm as per spec)
+20 (100 watt)
+~7 (600 watt)
+~5 (3 drivers)
= 115dB peak ~ 100dB RMS music.
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