Guys - I need to measure the sensitivity of the Heil AMT tweeters, and the only reference I have off hand is the ARTA manual. Is there an easier way to measure 2.83V and maybe use Omnimic? Should I measure closer and scale to 1 meter? Just want to do this right.
If you have an Omnimic, that's the way to do it. Look in the help file, there's an instruction there.
You can measure closer than 1m and calculate sensitivity at 1m, but be real accurate with your distance measurement, at 1/4 m a small error in distance is multiplied by 4.
Dang it! I'm such a dumbo! I did a Google search and found your post on PE TT, which is perfect for me, since I have OM Thanks twice, dude. Owe you a beer.
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
Dang it! I'm such a dumbo! I did a Google search and found your post on PE TT, which is perfect for me, since I have OM Thanks twice, dude. Owe you a beer.
Guys - I need to measure the sensitivity of the Heil AMT tweeters, and the only reference I have off hand is the ARTA manual. Is there an easier way to measure 2.83V and maybe use Omnimic? Should I measure closer and scale to 1 meter? Just want to do this right.
If you have an Omnimic, that's the way to do it. Look in the help file, there's an instruction there.
You can measure closer than 1m and calculate sensitivity at 1m, but be real accurate with your distance measurement, at 1/4 m a small error in distance is multiplied by 4.
Dang it! I'm such a dumbo! I did a Google search and found your post on PE TT, which is perfect for me, since I have OM Thanks twice, dude. Owe you a beer.
Glad I could help, I don't know the post, but RTFM is always a good answer
Just another thought as I'm sure these tweeters are quite sensitive. 95dB at 1m is very loud, so you could also measure at a lower voltage and do some math to determine sensitivity at 2.83V
The blurb from the "how to" section of the Omnimic manual:
Loudspeaker sensitivity is normally expressed as the SPL level that is sensed at 1 meter from the loudspeaker when it is driven from a voltage of 2.83Vrms. When you are using a CD as the signal source with OmniMic, the nominal level of the swept sine signals can be determined (or set) by use of the 50Hz reference tones that are at the end of the Version 3 OmniMic Test Signal CD or DVD.
To use these, you may want to disconnect the speaker of the channel being tested (the output voltage of quality amplifier should not be affected by whether a speaker is being driven). Then attach a Digital Voltmeter (also known as a "DVM") to read AC Voltage across the amplifier terminals. Be sure to configure the voltmeter for AC Volts and that the probes connect to the meter's Voltage (and not its Current!) reading terminals.
Turn any equalizer or tone controls off. You can then play the 50Hz reference tone tracks and measure or set the voltage level from the amplifier. Next, reconnect the loudspeaker, set OmniMic at the 1 meter distance from the loudspeaker and play the desired sweep track of the test CD. Use the OmniMic software in its Frequency Response measurement mode for Sine Sweep, and the plot should then be a reading of SPL sensitivity.
The reason 50Hz tone is used is because 50-60Hz is where a multimeter will be most accurate. One of the great benefits the Omnimic has over the competition is that it is calibrated for SPL so you can measure absolute SPL with it.
Working on it! Initial problem, I had V2 of the OM test tracks, and I wasn't about to wait for 3 days for PE to send me a new disc. Went into OM and checked for update, and there was the new SW (5.02) and Test Tracks with the 50Hz test tone references. Now for some measurements!
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
Hmmm, setup was pretty easy, but I was getting about 120dB for 2.83 AC Volts. Read the notes, ok need use 2.00 ACV for a 4 ohm driver. So I recalibrated to that voltage. Switched to Track 2. Getting the characteristic 5-7 dB shelf from 2k to 10K, but the main part of the shelf is at about 115 dB one meter. Using some cheap 20 uF caps to protect the Heil. Pretty sure the meter is accurate, the amp I'm driving shows about 1W peaks for the sweeps. (Head scratcher)
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
If you want sensitivity at 2.83V, use 2.83V regardless of impedance, but just realize that this is about 2W for a 4 ohm load.
120dB is uhh, a bit much. What are you using for an amp? And for a meter while were at it? Do you have a 5-10W resistor in the 4-20 ohm range you can attach to the amp when setting the voltage, just to be sure the amp isn't doing weird things when there is no load.
You can do this test backwards as well. Instead of setting the amp at 2.83V and measuring the driver, just measure the driver as you normally would, adjust the amp gain for 85-90dB or whatever you're comfortable with. Then play the 50Hz tone and measure the amp output voltage. From here you can do some math to figure out how many dB to shift your measurement for a 2.83V result.
If you want sensitivity at 2.83V, use 2.83V regardless of impedance, but just realize that this is about 2W for a 4 ohm load.
120dB is uhh, a bit much. What are you using for an amp? And for a meter while were at it? Do you have a 5-10W resistor in the 4-20 ohm range you can attach to the amp when setting the voltage, just to be sure the amp isn't doing weird things when there is no load.
You can do this test backwards as well. Instead of setting the amp at 2.83V and measuring the driver, just measure the driver as you normally would, adjust the amp gain for 85-90dB or whatever you're comfortable with. Then play the 50Hz tone and measure the amp output voltage. From here you can do some math to figure out how many dB to shift your measurement for a 2.83V result.
Good suggestions - I'll give that a try tomorrow along with a couple of tests at 2.83v with other speakers I've got with pretty much known sensitivity. Also, find my Oscope and check the voltage with that.
Amp is vintage Kenwood KM-208. Pretty clean, extended and powerful. Tones played from Volumio on a RasPi with PiFi DAC. The real unknown in this is the new meter (Surpeer AV4 autorange, 4 1/2 digit, true RMS, reads Frequency.)
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
If you want to determine if there's any change on your amp output with or without a load, just lower the voltage and use a driver that will be fine with a 50Hz tone, so not a tweeter.
FWIW I haven't used the test tone CD in years. The software will generate the tones, so I just run a cable from my computer. Under the config menu, the first item is "play from soundcard". When you are in the SPL/Spectrum Tab, there is a tone generator available in the config menu for the 50-60Hz tone.
Here's a calculator for working out change in SPL over distance. Note that this doesn't account for boundary reinforcement, so for indoor measurements this calculation is accurate for gated reflection free measurements. I wouldn't use this for a subwoofer.
For S&Gs I wanted to see if I could determine the sensitivity of a speaker using Omnimic and an arbitrary distance and voltage. So I took a speaker, set up the mic at 60cm, and set the gain on the amp until the frequency response was about 70dB. I used the calculator linked above to determine that 70dB@60cm is equal to 65.56dB@1m. To confirm this math, I backed my mic up to 1m, and sure enough we were at about 65.5dB.
I then played a 55Hz test tone from the Omnimic tone generator, and measured a whopping 0.338V at the amp output, with the speaker connected, and to be sure, I disconnected the speaker and measured the same voltage exactly.
So 65.56dB@0.338V@1m is where we are at now. Math is hard, so we'll just use another website calculator to sort this out as well. From the same site:
We determine that 2.83V is a 18.45dB gain from 0.338V, so my speaker sensitivity then becomes 84dB@2.83V@1m. I expected 84.5-85dB, so we're pretty darn close.
In any case, another fun piece of information, is that the 120dB measurement you took above, using the online calculator, is more like a 50V measurement if we expect a 95dB sensitive tweeter, so your meter would have to be off by miles to get that sort of output, and probably fry the diaphragm in the process (and melt your ears). The only think I can think to add is to make sure your cal file is loaded. I have an old V1 omnimic that uses a code instead of a cal file, but if I don't enter the code when I install the software, I'm off by about 5dB for SPL.
@dcibel -- great tips, and good links, I'll dive into it tomorrow. Dug out my (little CN) scope, and hooked it up while the source and amp were setup to deliver 2.00 ACV with a 50 Hz sine wave. I hadn't used this scope very much, so I diddled with it until I had a stable waveform covering 3/4 of the vertical screen. At .1v per division, it was about .56 v PtoP, in fact that's what the display read. So then I look at the probe, and sure enough, it's a 10x probe, so I've actually got 5.6ACV peak to peak, which means about 2.00 v RMS. I've got a couple of other speakers to test, I'm using some RS125Ps in 4 L boxes as stands. Hopefully, the SPL delivered by them at 2.00v will be more in line with the desired results.
Thanks again for your assistance.
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
I take it you are using 2V to match up with the sensitivity @1W used in the ESS specs? If that's the case, keeping in mind that these have a pretty much flat line impedance at about 3.5 Ohms (going off of Nicholas' measurement), you'd be looking at 1.87V for 1W. Not that it matters much, as long as you record the voltage used and mic distance we can get a fairly accurate calculation of SPL for any voltage.
I double checked everything, and all was correct, so the only thing left was to install OM on a different computer. Results were at least pretty close to what was expected. Drive was 2.00ACV RMS, monophonic short sine sweep. Ran 2 tests, dipole and monopole FR was bit different for each. Not seeing the stated 95 dB sensitivity. Used a 20uF cap inline to protect the tweeter.
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
Excellent, glad you got it sorted out. If they mislabelled the 95dB@1w and actually meant 95dB@2.83V, that would be pretty on the money for peak sensitivity. The downside of that sensitivity rating is that it's not useful information if you intend on a normal crossover in 1-2kHz range.
Just another thing to add, that I found when measuring my AMTPRO drivers was the lack of vertical directivity actually made measuring them indoors very easy, since there was next to no reflection from the floor/ceiling. Looking at your measurement, I think you could increase the gate to a bit more than 5ms without much artifacts in the response.
It's a very usable response anyway, there's some info linked in the thread about these tweeters over at DIYAudio from a German site that claims to have found the cause of the peak at 5kHz and some added felt/foam to strategic locations to fix it.
I'll look into those links, maybe try some things and post results if anyone is interested. Looks like the Heil ESS tweeters are going to be $160 / pair long term.
But Chahly - Stahkist don't want speakers that look good, Stahkist wants speakers that sound good!
Hah- You're looking at a lot of money there. $600 for the ATD, if you can find it. ~$200 for the LCY (thanks, Leon!)), about $700 for the NOS Eton hexacone woofer, plus whatever you get the Heils for. I'm guessing that is easily $3.5k in drivers alone.
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Thanks twice, dude. Owe you a beer.
Can't wait to see what you guys do with these. Inquiring minds need to know.
The 12'' AMT Series with a good woofer would be nice.
To use these, you may want to disconnect the speaker of the channel being tested (the output voltage of quality amplifier should not be affected by whether a speaker is being driven). Then attach a Digital Voltmeter (also known as a "DVM") to read AC Voltage across the amplifier terminals. Be sure to configure the voltmeter for AC Volts and that the probes connect to the meter's Voltage (and not its Current!) reading terminals.
Turn any equalizer or tone controls off. You can then play the 50Hz reference tone tracks and measure or set the voltage level from the amplifier. Next, reconnect the loudspeaker, set OmniMic at the 1 meter distance from the loudspeaker and play the desired sweep track of the test CD. Use the OmniMic software in its Frequency Response measurement mode for Sine Sweep, and the plot should then be a reading of SPL sensitivity.
3 days for PE to send me a new disc. Went into OM and checked for update, and there was
the new SW (5.02) and Test Tracks with the 50Hz test tone references.
Now for some measurements!
Read the notes, ok need use 2.00 ACV for a 4 ohm driver.
So I recalibrated to that voltage. Switched to Track 2.
Getting the characteristic 5-7 dB shelf from 2k to 10K, but the main part of the shelf is
at about 115 dB one meter. Using some cheap 20 uF caps to protect the Heil.
Pretty sure the meter is accurate, the amp I'm driving shows about 1W peaks for the sweeps.
(Head scratcher)
Amp is vintage Kenwood KM-208. Pretty clean, extended and powerful. Tones played from Volumio on a RasPi with PiFi DAC.
The real unknown in this is the new meter (Surpeer AV4 autorange, 4 1/2 digit, true RMS, reads Frequency.)
-- great tips, and good links, I'll dive into it tomorrow.
Dug out my (little CN) scope, and hooked it up while the source and amp were setup to deliver 2.00 ACV with a 50 Hz sine wave. I hadn't used this scope very much, so I diddled with it until I had a stable waveform covering 3/4 of the vertical screen. At .1v per division, it was about .56 v PtoP, in fact that's what the display read. So then I look at the probe, and sure enough, it's a 10x probe, so I've actually got 5.6ACV peak to peak, which means about 2.00 v RMS.
I've got a couple of other speakers to test, I'm using some RS125Ps in 4 L boxes as stands.
Hopefully, the SPL delivered by them at 2.00v will be more in line with the desired results.
Thanks again for your assistance.
Results were at least pretty close to what was expected. Drive was 2.00ACV RMS, monophonic short sine sweep.
Ran 2 tests, dipole and monopole FR was bit different for each. Not seeing the stated 95 dB sensitivity.
Used a 20uF cap inline to protect the tweeter.
Looks like the Heil ESS tweeters are going to be $160 / pair long term.
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