This is a review and detailed measurements of the Greenwave Broadband EMI Meter. It was kindly drop shipped to me by a member and costs US $135.
The device is simple: you plug in the AC cord (see on the bottom) into an AC outlet which both powers the unit and shows/sounds a couple of values and buzzes through the small speaker. They are quite popular at audio shows to demonstrate the before and after effect of power filters. The unit attempts to show both before and after levels in blue LED above but it is subject to failure as you see above. It seems to sample the noise level and if there is a change, it shows a new value. This works sometimes if you plug it in just right. Otherwise, the mere act of plugging in the unit causes it to read differing measurements, making it think a filter has been added to the circuit.
Company provides scant specification for the unit:
But what is there should be an alarm to audio users as the lowest measured frequency is 3 kHz. And the highest 10 MHz. In other words, bulk of what it measures is above audible band.
I was originally hope to try to find its frequency response and linearity but sweeping an input tone through it. Alas, since it combines AC power with source of noise measurement, this was not easily feasible (I would have to build a high-voltage noise injection interface). So I resorted to just some spot checks as you see below.
Greenwave EMI Meter Measurements
As always, I start my measurements with the noise and spectrum of my "raw" AC mains power strip which has a number of devices plugged into it:
We see that the bulk of the harmonic noise and distortion is under 1 kHz. Therefore measuring from 3 kHz as the Greenwave meter performs, is of little value. Still, I plugged the unit in, only to have it overflow (it shows 1---).
So I went the other extreme and tested it with my B&K 9801 Lab AC generator. This is its spectrum:
We see far cleaner output with second harmonic at -74 dB. Total noise+distortion has dropped from 2.5% to 0.05%. Here is what the meter shows now:
On one hand it is correctly showing lower value. On the other hand, the buzzing noise it made was much louder than when fed from my "dirty" Raw mains! I don't know what it is using to source that noise. I briefly "powered" the unit with my analyzer and the pitch increased with the input frequency. So it seems to be just be feeding AC into that speaker but then I don't know how it would make noise in response to ultrasonics. I would think that it would need to demodulate the input waveform. Regardless of what it does, I would ignore the noise. Alas, it is quite annoying so I wished it had an on off switch for that.
That's all I have for you.
Conclusions
Directionally, the testing shows that the meter in there is showing something proportion to level of input noise. How correct it is, is hard to say. The fact that company documents it to work from 3 kHz and up, should automatically disqualify it from usage for audio. I know some audiophiles think any radiation is bad but remember, your equipment internally performs massive filtering of such high frequencies. Yes, there are rare cases of AM radio leaking into circuit but unless that is what you are facing, do not confuse noise over AC line with noise level inside the power circuits of your audio gear!
I can't recommend the Greenwave Broadband EMI meter. I think it easily misleads people to spend money on power tweaks which have no value as far as improving your audio gear.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The device is simple: you plug in the AC cord (see on the bottom) into an AC outlet which both powers the unit and shows/sounds a couple of values and buzzes through the small speaker. They are quite popular at audio shows to demonstrate the before and after effect of power filters. The unit attempts to show both before and after levels in blue LED above but it is subject to failure as you see above. It seems to sample the noise level and if there is a change, it shows a new value. This works sometimes if you plug it in just right. Otherwise, the mere act of plugging in the unit causes it to read differing measurements, making it think a filter has been added to the circuit.
Company provides scant specification for the unit:
But what is there should be an alarm to audio users as the lowest measured frequency is 3 kHz. And the highest 10 MHz. In other words, bulk of what it measures is above audible band.
I was originally hope to try to find its frequency response and linearity but sweeping an input tone through it. Alas, since it combines AC power with source of noise measurement, this was not easily feasible (I would have to build a high-voltage noise injection interface). So I resorted to just some spot checks as you see below.
Greenwave EMI Meter Measurements
As always, I start my measurements with the noise and spectrum of my "raw" AC mains power strip which has a number of devices plugged into it:
We see that the bulk of the harmonic noise and distortion is under 1 kHz. Therefore measuring from 3 kHz as the Greenwave meter performs, is of little value. Still, I plugged the unit in, only to have it overflow (it shows 1---).
So I went the other extreme and tested it with my B&K 9801 Lab AC generator. This is its spectrum:
We see far cleaner output with second harmonic at -74 dB. Total noise+distortion has dropped from 2.5% to 0.05%. Here is what the meter shows now:
On one hand it is correctly showing lower value. On the other hand, the buzzing noise it made was much louder than when fed from my "dirty" Raw mains! I don't know what it is using to source that noise. I briefly "powered" the unit with my analyzer and the pitch increased with the input frequency. So it seems to be just be feeding AC into that speaker but then I don't know how it would make noise in response to ultrasonics. I would think that it would need to demodulate the input waveform. Regardless of what it does, I would ignore the noise. Alas, it is quite annoying so I wished it had an on off switch for that.
That's all I have for you.
Conclusions
Directionally, the testing shows that the meter in there is showing something proportion to level of input noise. How correct it is, is hard to say. The fact that company documents it to work from 3 kHz and up, should automatically disqualify it from usage for audio. I know some audiophiles think any radiation is bad but remember, your equipment internally performs massive filtering of such high frequencies. Yes, there are rare cases of AM radio leaking into circuit but unless that is what you are facing, do not confuse noise over AC line with noise level inside the power circuits of your audio gear!
I can't recommend the Greenwave Broadband EMI meter. I think it easily misleads people to spend money on power tweaks which have no value as far as improving your audio gear.
------------
As always, questions, comments, recommendations, etc. are welcome.
Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
