I have tried to search a lot on this topic. But still could not find any answers to the following simple questions...
1) I am trying to measure and generate FRD files for few tweeters using an Omnimic V2. Usually a short sine wave sweep signal( 20Hz to 20Khz) is what is generated by the OmniMic V2 Test Track CD. But if I connect the tweeters directly from an amplifier without any series capacitors, and run the track(which someone else told me, what he is doing), there will be a real chance of damaging the tweeters right? There will be over-excursion as the sine-wave sweep signal, goes all the way down to 20Hz, while most of the tweeters have a Fs in 1000s to 2KHz or more?
2) What about making a first order filter by adding a series capacitor? I know that will protect the tweeter, but won't it affect the frequency and phase response too?
3) What distance shall I be measuring them? 1m? since 1m is used for specifying SPL figures.
4) Should the mic be directly/straight pointed at the tweeter? I am asking because I have seen youtube videos with measurements taken, while microphone is pointing down; away from speaker, if I am not wrong. What's the correct way to position the measurement microphone?
I have both Omnimic and REW setup with two EMM-6 microphones.
So far I used Omnimic for measuring the frequency response of the entire multi-way speaker, where the above points are not an issue(because I have been measuring speakers with crossover network)
1) I am trying to measure and generate FRD files for few tweeters using an Omnimic V2. Usually a short sine wave sweep signal( 20Hz to 20Khz) is what is generated by the OmniMic V2 Test Track CD. But if I connect the tweeters directly from an amplifier without any series capacitors, and run the track(which someone else told me, what he is doing), there will be a real chance of damaging the tweeters right? There will be over-excursion as the sine-wave sweep signal, goes all the way down to 20Hz, while most of the tweeters have a Fs in 1000s to 2KHz or more?
2) What about making a first order filter by adding a series capacitor? I know that will protect the tweeter, but won't it affect the frequency and phase response too?
3) What distance shall I be measuring them? 1m? since 1m is used for specifying SPL figures.
4) Should the mic be directly/straight pointed at the tweeter? I am asking because I have seen youtube videos with measurements taken, while microphone is pointing down; away from speaker, if I am not wrong. What's the correct way to position the measurement microphone?
I have both Omnimic and REW setup with two EMM-6 microphones.
So far I used Omnimic for measuring the frequency response of the entire multi-way speaker, where the above points are not an issue(because I have been measuring speakers with crossover network)
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Hi Ronj,
The OmniMic test signals have versions that say "Bass Removed" and "Bass and Midrange removed" which you can use if you are skittish. Bass removed is safe enough for most tweeters. If you really have a delicate super tweeter (5kHz or higher) maybe bass and midrange removed are the better version.
I typically use "Bass removed" but I'm not using very delicate tweeters. Your own mileage may vary. Yes, you can use a cap in series if it is large enough. 🙂
Yes, use 1m but make sure you have set the amp output correctly. There is a 50 or 60Hz test signal for this. Any multimeter will work at this Hz. Disconnect any speakers, and measure the output of your amp. Should be 2.83 Volts.
Yes, measure pointing straight at your tweeter, but the OmniMic is fairly omnidirectional.
Your measurements for crossover design need to be int he same direction as you are planning to listen. So if you plan on listening on tweeter axis that is how you should keep your microphone for all other drivers as well.
Best,
E
The OmniMic test signals have versions that say "Bass Removed" and "Bass and Midrange removed" which you can use if you are skittish. Bass removed is safe enough for most tweeters. If you really have a delicate super tweeter (5kHz or higher) maybe bass and midrange removed are the better version.
I typically use "Bass removed" but I'm not using very delicate tweeters. Your own mileage may vary. Yes, you can use a cap in series if it is large enough. 🙂
Yes, use 1m but make sure you have set the amp output correctly. There is a 50 or 60Hz test signal for this. Any multimeter will work at this Hz. Disconnect any speakers, and measure the output of your amp. Should be 2.83 Volts.
Yes, measure pointing straight at your tweeter, but the OmniMic is fairly omnidirectional.
Your measurements for crossover design need to be int he same direction as you are planning to listen. So if you plan on listening on tweeter axis that is how you should keep your microphone for all other drivers as well.
Best,
E
Thanks a lot for your input. I have been always using track 12. I will check out the others now. And I am so sorry about the previous post. While I was writing it, I got overcome with a very nasty daytime sleepiness spell. I just spell checked, grammar corrected and punctuated the first post to a good extent. I am still sleepy though.
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How's that done ? You disconnect two speakers and point the mic to the speaker ? Does the disconnected speaker output need to be "terminated" with an 8 Ω resistor or so ? Or you just isolate the path ?
The mic would be on axys to the speaker only when vertical and horizontal deviation from perpendicular are zero 😛
No, I was measuring the response of the entire multiway system. Not measuring individual drivers.
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I did that today... was a scray proposition...
I played 50Hz tone and jacked up to read A/C voltage on my DMM until 2.8V (with out having any speakers connected) then I used the same Amplifier setting to play track 14, Right channel Sine wave sweep without bass without midr-ange; yet it sounds so loud I am so scared.
I was measuring a pair of NS1000M Beryllium tweeters and they are infamous for being very easily damaged and extremely expensive and difficult to find another pair 🙁 One tweeter had gone muffled, that is why I needed to measure. I had my heart in my mouth all the time through the measurement. Hope everything is still fine.
Ronj,
2.83 V is the equivalent of 1w at 8 Ohms, very standard measurement. I think with bass removed you should be fine.
Best,
E
2.83 V is the equivalent of 1w at 8 Ohms, very standard measurement. I think with bass removed you should be fine.
Best,
E
Yeah I understand that, but how about 4Ohm Speakers? Then it should be half of that voltage right?
No, 1/(squareroot of 2) of that voltage. Power is voltage squared.
But most drivers these days aren't spec'd for efficiency (dB at 1W), the spec is usually sensitivity (dB at 2.83V) because that's easier to deal with and measure since speaker driver impedance isn't really constant.
Ronj,
Amplifiers are voltage sources. 🙂 The question you want to know when designing a speaker isn't how much power it uses, but how loud it is at a reference voltage, and assume the amp will provide.
Best,
E
Amplifiers are voltage sources. 🙂 The question you want to know when designing a speaker isn't how much power it uses, but how loud it is at a reference voltage, and assume the amp will provide.
Best,
E
Going back to the original questions.
IMHO, the only reason to measure at 2.83V and 1m is to have an absolute level, but you need to calibrate all the setup. If you want a relative level it is absolutely fine to measure at a different distance and voltage.
Measuring at 1m is usually tricky in avoiding room reflections and often requires a short gate, leading to artificial smoothing. A tweeter can be measured at short distances, see here in the infinite baffle section: Zaph|Audio
The mic should be pointed straight at the driver, except if you want to measure off axis.
I usually measure in box, all the drivers, pointing at the tweeter, between 60 and 80 cm away. The level is what makes me not worry about damage, if you want to add a cap on the tweeter choose the value wisely not to modify the FR in the place you want to put the crossover.
Ralf
IMHO, the only reason to measure at 2.83V and 1m is to have an absolute level, but you need to calibrate all the setup. If you want a relative level it is absolutely fine to measure at a different distance and voltage.
Measuring at 1m is usually tricky in avoiding room reflections and often requires a short gate, leading to artificial smoothing. A tweeter can be measured at short distances, see here in the infinite baffle section: Zaph|Audio
The mic should be pointed straight at the driver, except if you want to measure off axis.
I usually measure in box, all the drivers, pointing at the tweeter, between 60 and 80 cm away. The level is what makes me not worry about damage, if you want to add a cap on the tweeter choose the value wisely not to modify the FR in the place you want to put the crossover.
Ralf
Thanks a lot I got the all the answers I was looking for. You guys are wonderful!
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Yeah, you don't HAVE to measure at 2.83V. However it is convenient as it puts your measurements in the same absolute scale as the spec sheets.
1V will also work, but in a tool like XSim, the absolute output wont be correct.
Just make sure you measure all of your drivers at the same voltage before designing a crossover. 🙂 So, if that is 1V or 0.5V, keep it consistent as you measure your woofer, tweeter, etc.
I have pretty good luck at 1M doing gated tweeter measurements by the way. Most tweeters don't like a crossover below 2.5kHz anyway, so my gating is usually able to go down low enough for me.
I also super cheat when measuring 2-ways and use 1M exclusively.
Best,
E
1V will also work, but in a tool like XSim, the absolute output wont be correct.
Just make sure you measure all of your drivers at the same voltage before designing a crossover. 🙂 So, if that is 1V or 0.5V, keep it consistent as you measure your woofer, tweeter, etc.
I have pretty good luck at 1M doing gated tweeter measurements by the way. Most tweeters don't like a crossover below 2.5kHz anyway, so my gating is usually able to go down low enough for me.
I also super cheat when measuring 2-ways and use 1M exclusively.
Best,
E
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