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Sorry for the late reply...
yesterday
I totally open my speaker box then i saw the following:
Woofer (no sticker attached to it that could determined its rating or wattage)
Tweeter(titanium, 700watts, 4-8Ω)x2
(Woofer and tweeter are in parallel)
and there is 12w10ΩJ Resistor in series with 100v 4.7μF Capacitor in series with the tweeter.
I dont know if that is the work of our hired technician or it is by default.
and this is my drawing about what I've seen on the connection of tweeters and the cap. and the res.
yesterday
I totally open my speaker box then i saw the following:
Woofer (no sticker attached to it that could determined its rating or wattage)
Tweeter(titanium, 700watts, 4-8Ω)x2
(Woofer and tweeter are in parallel)
and there is 12w10ΩJ Resistor in series with 100v 4.7μF Capacitor in series with the tweeter.
I dont know if that is the work of our hired technician or it is by default.
and this is my drawing about what I've seen on the connection of tweeters and the cap. and the res.
The drawing puts all components in series!
But from the sounds of it, there is a high-pass filter in series with the Tweeter which is great.
Please do yourself a favour though and measure the resistance of the capacitor.
When measuring the resistance of a capacitor, expect the meter to read 0Ω, then start climbing until it eventually shows infinity (or 'Open' or 0L... or any method it uses to show a very high number)
This is normal. If the Capacitor shows 0Ω and does not change, it's a 'short-circuit' and could be the cause of the blown tweater. This component is responsible for blocking the heavy bass notes from hitting that poor little tweeter.
** Special note when measuring Capacitors!
They can 'hold' electricity, some uses of capacitors may result in them holding 100s of volts, and freely measuring or touching them can cause serious personal harm.
However, the capacitor used as a 'filter' like this usually has 0V, but it's never too early to practice being safe. Don't touch the metal wires on the capacitor until you have set your meter to read 2000V to measure the capacitor. If it shows 0V, set the meter to 200 or 20V and try again. Once you have confirmed there is no voltage present, then you can measure the resistance of the capacitor.
But from the sounds of it, there is a high-pass filter in series with the Tweeter which is great.
Please do yourself a favour though and measure the resistance of the capacitor.
When measuring the resistance of a capacitor, expect the meter to read 0Ω, then start climbing until it eventually shows infinity (or 'Open' or 0L... or any method it uses to show a very high number)
This is normal. If the Capacitor shows 0Ω and does not change, it's a 'short-circuit' and could be the cause of the blown tweater. This component is responsible for blocking the heavy bass notes from hitting that poor little tweeter.
** Special note when measuring Capacitors!
They can 'hold' electricity, some uses of capacitors may result in them holding 100s of volts, and freely measuring or touching them can cause serious personal harm.
However, the capacitor used as a 'filter' like this usually has 0V, but it's never too early to practice being safe. Don't touch the metal wires on the capacitor until you have set your meter to read 2000V to measure the capacitor. If it shows 0V, set the meter to 200 or 20V and try again. Once you have confirmed there is no voltage present, then you can measure the resistance of the capacitor.
hevans1944
Hop - AC8NS
Your drawing shows two horn tweeters wired in series and also connected in series with a 12 Ω, 10 W, resistor and a 4.7 μF, 100 V, capacitor. Is this correct?
At 1000 Hz (the typical minimum frequency for a "tweeter") the RC network presents an impedance of about 36 Ω. At 20,000 Hz the network impedance drops to 12 Ω. The total impedance at 1 kHz would then be 44 Ω to 56 Ω, falling to 20 Ω to 28 Ω at 20 kHz. How can a single horn tweeter have an impedance of both 4 Ω and 8 Ω that sums to either 8 Ω or 16Ω when two are connected in series? Answer: it can't.
Who knows what the "actual" speaker impedance is? All that label means is the tweeter can be driven from an amplifier providing either 4 Ω or 8 Ω source impedance to a level of 750 watts without total destruction (titanium is wonderful stuff, right?). What does than even mean? Is that 750 watts for-real rms power or some hokey marketing hype "music power" inflated over rms power by a factor of two or four or whatever the market will bear?
Let's be conservative and assume it means real rms power. And let's assume the amp has 4 Ω source driving impedance. Then to drive that tweeter with 750 watts requires P = I²Z, or I = √(750/4) A = 13.7 A. Hmm. If that much current must flow through a 12 Ω resistor to reach the tweeter, then the amp must produce E = I R = (13.7) (12) = 164 V (rms) across the resistor alone and E = I Z = (13.7) (4) = 54 V (rms) across the speaker terminals or a total of 218 V (rms) at the amp output terminals. I don't think there are too many modern solid state amps that will output that kind of voltage. Maybe 54 V directly to the tweeter is possible, but without a BA output transformer and a kilowatt or two of power, I don't think the higher voltages will be obtained. Could be wrong, of course. Haven't played around with audio power amplifiers since the 1970s and then only at hundred watt or so power levels.
The effect of the RC network is to reduce the power available to drive the tweeter at low frequencies by increasing the impedance in series with the tweeter. This is a good idea. You can "play around" with the numbers using an online RC impedance calculator at this web site. Note that the 4.7 μF capacitor has a reactance of about 33.9 Ω at 1 kHz, so if it was passing 13.7 amperes to drive the tweeter to 750 watts at that frequency, it would have about 464 V rms dropped across it. Not a good idea with the capacitor rated for only 100 V. Probably a good idea not to drive the tweeter with 750 watts at 1 kHz.
Is this speaker system for use on a performance stage to impinge loud sounds on an audience? They make speakers just for that.
At 1000 Hz (the typical minimum frequency for a "tweeter") the RC network presents an impedance of about 36 Ω. At 20,000 Hz the network impedance drops to 12 Ω. The total impedance at 1 kHz would then be 44 Ω to 56 Ω, falling to 20 Ω to 28 Ω at 20 kHz. How can a single horn tweeter have an impedance of both 4 Ω and 8 Ω that sums to either 8 Ω or 16Ω when two are connected in series? Answer: it can't.
Who knows what the "actual" speaker impedance is? All that label means is the tweeter can be driven from an amplifier providing either 4 Ω or 8 Ω source impedance to a level of 750 watts without total destruction (titanium is wonderful stuff, right?). What does than even mean? Is that 750 watts for-real rms power or some hokey marketing hype "music power" inflated over rms power by a factor of two or four or whatever the market will bear?
Let's be conservative and assume it means real rms power. And let's assume the amp has 4 Ω source driving impedance. Then to drive that tweeter with 750 watts requires P = I²Z, or I = √(750/4) A = 13.7 A. Hmm. If that much current must flow through a 12 Ω resistor to reach the tweeter, then the amp must produce E = I R = (13.7) (12) = 164 V (rms) across the resistor alone and E = I Z = (13.7) (4) = 54 V (rms) across the speaker terminals or a total of 218 V (rms) at the amp output terminals. I don't think there are too many modern solid state amps that will output that kind of voltage. Maybe 54 V directly to the tweeter is possible, but without a BA output transformer and a kilowatt or two of power, I don't think the higher voltages will be obtained. Could be wrong, of course. Haven't played around with audio power amplifiers since the 1970s and then only at hundred watt or so power levels.
The effect of the RC network is to reduce the power available to drive the tweeter at low frequencies by increasing the impedance in series with the tweeter. This is a good idea. You can "play around" with the numbers using an online RC impedance calculator at this web site. Note that the 4.7 μF capacitor has a reactance of about 33.9 Ω at 1 kHz, so if it was passing 13.7 amperes to drive the tweeter to 750 watts at that frequency, it would have about 464 V rms dropped across it. Not a good idea with the capacitor rated for only 100 V. Probably a good idea not to drive the tweeter with 750 watts at 1 kHz.
Is this speaker system for use on a performance stage to impinge loud sounds on an audience? They make speakers just for that.
@hevans1944 I always enjoy your posts though I don't always fully understand.
Can you explain how you arrived at the rc impedance @1khz? I thought it'd be much higher than that. I get 34k for Xc alone.
Thanks, John
Can you explain how you arrived at the rc impedance @1khz? I thought it'd be much higher than that. I get 34k for Xc alone.
Thanks, John
the speakers are 16 x 17.5 x 29 in inches, yes, it is used to be in stage but since it has no working tweeters we set it aside for the mean time.
hevans1944
Hop - AC8NS
So did you do the test with the 9V battery to see if the horn-tweeters are actually damaged?
hevans1944
Hop - AC8NS
I just used the on-line calculator at this web site. Plugged in 0 for R, 4.7 μF for C, and 1 kHz for frequency. Result was 33.86 Ω for Xc. After reading your post, I used my Windows calculator to compute Xc = 1/(2πfC) using f = 1000, C = 4.7 x 10^(-6). Same answer.
I must admit I did make a few simplifying assumptions, like the tweeter impedance being real and constant, not complex and varying all over the map as a function of frequency. The point I was trying to make, perhaps unsuccessfully, is that it is unlikely this pair (?) of tweeters was even capable of being driven to 750 watts using the RC network that was installed. The 12 Ω, 10 W, resistor is about the same as the tweeter impedance (for two tweeters in series), so it would also have to dissipate about half the power input even if Xc = 0. That's not gonna happen at any frequency, even if the amplifier is capable of providing the 1500 watts necessary to "make it so." Conclusion: the 740 watt rating is manufacturer's hype if the RC network is "original equipment".
@Hop,
1.The op said the tweeter itself has a writing of 700W (post #10),not the entire box.
Since the box may have been build from a collection of speakers of diffrenet brands and put in the box by a "manufacture",
it would be hard to get to a conclusions from the cross over values.
nevertheless, the limitations of the resistor and cap voltage rating still hold.
2. About the voltage the amp needs to put out to the speaker:
using a "bridged PA configuration" (i.e the speaker isn't referenced to GND) that voltage can be halved(from the PA "point of view").
3. I think the Crossover frequency of a 2 way speaker system would be above 2kHz.
4.It is essential that the op perform an ohm test of each of the horn-tweeters and the R and C of the filter,while they are disconnected from each other..
1.The op said the tweeter itself has a writing of 700W (post #10),not the entire box.
Since the box may have been build from a collection of speakers of diffrenet brands and put in the box by a "manufacture",
it would be hard to get to a conclusions from the cross over values.
nevertheless, the limitations of the resistor and cap voltage rating still hold.
2. About the voltage the amp needs to put out to the speaker:
using a "bridged PA configuration" (i.e the speaker isn't referenced to GND) that voltage can be halved(from the PA "point of view").
3. I think the Crossover frequency of a 2 way speaker system would be above 2kHz.
4.It is essential that the op perform an ohm test of each of the horn-tweeters and the R and C of the filter,while they are disconnected from each other..
Last edited:
@hevans1944 Thanks I got it.
I used too many zeros. My second mistake was assuming Z was merely Xc+R.
I used too many zeros. My second mistake was assuming Z was merely Xc+R.
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