Hi guys!
First of all, I apologize for my ignorance and for my continuos newbie questions
Well I explain my project: I've an 8 ohm full-range driver that I want use without any filter.
I would to add a 4 ohm tweeter filtering it by a 2,3 uF or 2,7 (at max) uF capacitor.
So the general contribution of the tweeters is very minimal.
So guys, do you consider this union of two different impedance drivers doable?
Thank you for your precious help and for thepatience, guys!
Regards
First of all, I apologize for my ignorance and for my continuos newbie questions
Well I explain my project: I've an 8 ohm full-range driver that I want use without any filter.
I would to add a 4 ohm tweeter filtering it by a 2,3 uF or 2,7 (at max) uF capacitor.
So the general contribution of the tweeters is very minimal.
So guys, do you consider this union of two different impedance drivers doable?
Thank you for your precious help and for thepatience, guys!
Regards
do you consider this union of two different impedance drivers doable?
Sure, usually the tweeter needs a series resistor to match the woofer's level anyway.
Adjust the capacitor's value smaller accordingly. Which drivers are you using?
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Yes, except add the series resistor (probably a few ohms) in line with the tweeter if you need
to attenuate the high treble. Even if the drivers happen to match well in levels, and so no
resistor is necessary, all that happens is that the impedance of the system drops at the top end.
The tweeter's inductance may raise that high end impedance upward anyway.
So what you are really asking is: can I mix a fullrange speaker without crossover to a high passed tweeter?
The short answer is yes but be aware that:
1) the impedance at high frequencies will be low. The reason is that there your amp needs to drive both drivers in parallel.
2) this configuration creates lobing and interferences, because you get HF sound from 2 different and distant sources.
Both problems can be eliminated with an appropriate LP filter to the fullrange. But without at least datasheets containing FR and impedance graphs for both drivers I wouldn't attempt to design a crossover, as the outcome could be easily far worse than driving the fullrange alone.
Ralf
The short answer is yes but be aware that:
1) the impedance at high frequencies will be low. The reason is that there your amp needs to drive both drivers in parallel.
2) this configuration creates lobing and interferences, because you get HF sound from 2 different and distant sources.
Both problems can be eliminated with an appropriate LP filter to the fullrange. But without at least datasheets containing FR and impedance graphs for both drivers I wouldn't attempt to design a crossover, as the outcome could be easily far worse than driving the fullrange alone.
Ralf
Thinking in nominal terms (8 vs 4 Ohms) , the ideal situation would be to take a 8 Ohm tweeter with the same sensitivity like the fullrange and as said by giralfino, filter both: lowpass for the fullrange and highpass for the tweeter at the same xo freq.
Question is: if using a tweeter at 4 Ohms (still thinking in nominal levels) it has half the "resistance" (impedance) compared to its imaginary 8 Ohm sibling so it is more efficient when converted into 8 Ohm terminology, by +3dB (2x power).
I think you can combine a 4 Ohm tweeter with a 8 Ohm fullrange with a proper crossover as long as you "convert" your 4-ohm data onto 8 ohms data and calculate with increased SPL for the tweeter, hence if you don't have the drivers yet you might select a ~3dB less efficient tweeter than the 8 Ohm fullrange and then you'll be fine.
Somebody pls confirm this, I'm not an electric engineer just thinking loud, this Q has always interested me too.
Thanks.
Question is: if using a tweeter at 4 Ohms (still thinking in nominal levels) it has half the "resistance" (impedance) compared to its imaginary 8 Ohm sibling so it is more efficient when converted into 8 Ohm terminology, by +3dB (2x power).
I think you can combine a 4 Ohm tweeter with a 8 Ohm fullrange with a proper crossover as long as you "convert" your 4-ohm data onto 8 ohms data and calculate with increased SPL for the tweeter, hence if you don't have the drivers yet you might select a ~3dB less efficient tweeter than the 8 Ohm fullrange and then you'll be fine.
Somebody pls confirm this, I'm not an electric engineer just thinking loud, this Q has always interested me too.
Thanks.
Crossover calculation has also to be taken with precaution: 8 Ohm formulas for the fullrange part and 4 Ohms (or 8 Ohms with a series resistor) for the tweeter part. The series resistor burns some energy away from the tweeter so again, according to my brainstorming now, a tweeter with +3dB sensitivity would be just equal to the fullrange when "dampened" by a series resistor (which lowers its efficiency).
The full range has inductance in the voice coil so its impedance will be higher at the frequency the tweeter starts to be active.
So here you have an example - a 8 Ohm Peerless midbass driven fullrange (red line), with a 6 Ohm Seas tweeter with a single 2.2uF cap as a HP filter (yellow line). The combined impedance is the blue line.
With a nominal 4 Ohm tweeter the impedance will be even lower. Surely nothing too critical.
Ralf
With a nominal 4 Ohm tweeter the impedance will be even lower. Surely nothing too critical.
Ralf
Attachments
From Audioholics:
Comparing the Sensitivity of Speakers with Different Impedances
If the amplifier is set to 2.83V, the 4 ohm speaker will draw 2 watts of power from the amplifier while an 8 ohm speaker draws 1 watt. (Power = Voltage2/resistance. So, 2.832 = 8. 8/8ohms = 1 watt.) This potentially gives the 4 ohm speaker a +3dB SPL advantage over the 8 ohm speaker for a given input level. This seems to be unfair.
So when using a 4 Ohm tweeter with a 8 Ohm woofer
- the tweeter's sensitivity is (should be) stated in 4 Ohms
- if that's the case, 4 Ohm sensitivity <=> 8 OHm sensitivity +3dB
- hence you shall choose a 4 Ohm tweeter for your 8 Ohms woofer with 3dB less sensitivity to get the same SPL (in theory) - no series resistor needed
- OR you use for the 4 Ohm tweeter the same sensitivity like for the 8 Ohm woofer AND add a series resistor to it (4 Ohms) to lift overall impedance to 8 Ohms while "eating away" 3dB SPL from the tweeter
Comparing the Sensitivity of Speakers with Different Impedances
If the amplifier is set to 2.83V, the 4 ohm speaker will draw 2 watts of power from the amplifier while an 8 ohm speaker draws 1 watt. (Power = Voltage2/resistance. So, 2.832 = 8. 8/8ohms = 1 watt.) This potentially gives the 4 ohm speaker a +3dB SPL advantage over the 8 ohm speaker for a given input level. This seems to be unfair.
So when using a 4 Ohm tweeter with a 8 Ohm woofer
- the tweeter's sensitivity is (should be) stated in 4 Ohms
- if that's the case, 4 Ohm sensitivity <=> 8 OHm sensitivity +3dB
- hence you shall choose a 4 Ohm tweeter for your 8 Ohms woofer with 3dB less sensitivity to get the same SPL (in theory) - no series resistor needed
- OR you use for the 4 Ohm tweeter the same sensitivity like for the 8 Ohm woofer AND add a series resistor to it (4 Ohms) to lift overall impedance to 8 Ohms while "eating away" 3dB SPL from the tweeter
That seems wrong, when adding a 4Ohm resistor the SPL will be 6dB down because voltage available to the tweeter will be halved to 1.415 , while for 1Watt power the voltage available to the tweeter should be 2Volt , so in case of identical sensitivity expressed in dB/Watt/m , the units should receive the voltage that matches the 1Watt , so the 4Ohm tweeter should have a series resistor of 1.6 Ohm , provided the impedance of the tweeter is indeed 4Ohm at the choosen crossover frequency , otherwise adapt to real-world impedance of the wteeter
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