Sure it's not the noise floor of the DSP?Most of the hiss in low cost active speakers is due to poorly performing power amplification. "Proper gain staging" has nothing to do with it.
Sure it's not the noise floor of the DSP?Most of the hiss in low cost active speakers is due to poorly performing power amplification. "Proper gain staging" has nothing to do with it.
Let's say for argument sake the source is the HF amp channels. There's probably at least a 6db efficiency difference between the mid woofer and the horns. Put 6db of attenuation on the output of the HF amp channels and boost the input signal by 6db. Now the audible noise floor is 6db lower with just a change in the gain of the system.Most of the hiss in low cost active speakers is due to poorly performing power amplification. "Proper gain staging" has nothing to do with it.
That's how Ray Dolby got startedLet's say for argument sake the source is the HF amp channels. There's probably at least a 6db efficiency difference between the mid woofer and the horns. Put 6db of attenuation on the output of the HF amp channels and boost the input signal by 6db. Now the audible noise floor is 6db lower with just a change in the gain of the system.
"Unfortunately the tweeters produce audible hiss in a quiet room. Looking at the back side of the board reveals at least one problem - there is a large ground plane that transfers the 400 kHz parasitics from the power amp to the analog input, including the ADC. JBL should have used the standard in audio star topology to isolate the power section from the analog section. The electric noise fed into the tweeter is a lot stronger than appears to the ear - I measured 1 VPP on the speaker terminal in respect to ground with an oscilloscope. The majority of the noise power is in the inaudible range."
Sure it's not the noise floor of the DSP?
I bought the JBL 305P Mkii about a month ago and recently, the Dayton Audio UMM-6 measurement microphone.
I used the "Real Time Analysis" function of REW to get these graphs.
Here's my results of measuring the 305p Mkii *hiss* issue people are discussing.
I measured in 2 rooms, since I wanted to verify the results in a different environment.
Room 1:
View attachment 45667
Room 2:
View attachment 45668
Notes:
1. Measurement microphone was measured at tweeter level in all tests.
2. Measurement microphone was pointed up towards the ceiling (not towards the speaker).
3. 1/6th smoothing was applied to all measurements.
4. Nothing except the power cord was plugged into the speaker during my tests. Again, I didn't plug in the XLR/RCA cables.
5. Regardless of the volume level of the knob at the back of the speaker, the *hiss* is the same volume.
6. Nothing else was plugged into the wall outlet where speaker's power cord was plugged into.
7. Calibration file for my measurement microphone was loaded into REW.
8. C-weighting was used.
Results of measurements in 2 rooms:
1. Measurement 1 (RED) shows just the room noise.
Very quiet at around 20-25dB SPL.
Speaker wasn't plugged in.
This is a baseline measurement.
2. Measurement 2 (GREEN) shows that the measurement microphone measured at 0.5m (1.64ft) away from the tweeter.
The measurement microphone can't detect the *hiss* at this distance.
Personally, I can barely hear *hiss* from the speaker at this distance.
3. Measurement 3 (BLUE) shows that the measurement microphone measured at 0.5in (as close as I could get it) away from the tweeter.
The measurement microphone shows that the *hiss* is peaking at 2khz.
Personally, by putting my ear against the tweeter, i can clearly hear the *hiss*.
My Use Case:
After I completed these tests, i took the speaker back to my listening room, next to a computer tower, and realized that computer's fans are much louder than the *hiss*.
When music is playing, the *hiss* is masked completely.
Overall, I enjoy listening to the JBL 305P MKii speakers, as the *hiss* doesn't affect me.
Your experience may vary.
Only power cord was connected. Not inputs.Inputs not connected or shorted-out?
Yes.Are future distortion measurements planned?
Only power cord was connected. Not inputs.
I bought the JBL 305P Mkii about a month ago and recently, the Dayton Audio UMM-6 measurement microphone.
I used the "Real Time Analysis" function of REW to get these graphs.
Here's my results of measuring the 305p Mkii *hiss* issue people are discussing.
I measured in 2 rooms, since I wanted to verify the results in a different environment.
Room 1:
View attachment 45667
Room 2:
View attachment 45668
Notes:
1. Measurement microphone was measured at tweeter level in all tests.
2. Measurement microphone was pointed up towards the ceiling (not towards the speaker).
3. 1/6th smoothing was applied to all measurements.
4. Nothing except the power cord was plugged into the speaker during my tests. Again, I didn't plug in the XLR/RCA cables.
5. Regardless of the volume level of the knob at the back of the speaker, the *hiss* is the same volume.
6. Nothing else was plugged into the wall outlet where speaker's power cord was plugged into.
7. Calibration file for my measurement microphone was loaded into REW.
8. C-weighting was used.
Results of measurements in 2 rooms:
1. Measurement 1 (RED) shows just the room noise.
Very quiet at around 20-25dB SPL.
Speaker wasn't plugged in.
This is a baseline measurement.
2. Measurement 2 (GREEN) shows that the measurement microphone measured at 0.5m (1.64ft) away from the tweeter.
The measurement microphone can't detect the *hiss* at this distance.
Personally, I can barely hear *hiss* from the speaker at this distance.
3. Measurement 3 (BLUE) shows that the measurement microphone measured at 0.5in (as close as I could get it) away from the tweeter.
The measurement microphone shows that the *hiss* is peaking at 2khz.
Personally, by putting my ear against the tweeter, i can clearly hear the *hiss*.
My Use Case:
After I completed these tests, i took the speaker back to my listening room, next to a computer tower, and realized that computer's fans are much louder than the *hiss*.
When music is playing, the *hiss* is masked completely.
Overall, I enjoy listening to the JBL 305P MKii speakers, as the *hiss* doesn't affect me.
Your experience may vary.
65dB seems like a very low level to me. But you are right that at that level, distortion will probably not be audible on even the crappiest speakers.That is actually yet another proof of Toole's conculsion that THD is not really an improtant metric with speakers. Let's say you listen at some "normal" level, say at 65 dB. You can expect that by spectrum of some random song would show that 2kHz level is at least 20dB lower than level at say 80Hz, so this woud mean that 2kHz signal is played at app 45dB and hiss is addingn 7dB of distortion which translates to -38dB of THD whcih is app 1.25%. Yet, I fully believe that you don't hear it at all..
65dB seems like a very low level to me. But you are right that at that level, distortion will probably not be audible on even the crappiest speakers.
It depends what kind of music you consider.55-65dB is a level of normal human speech. Listening music at 65dB is not "very low level".
That is actually yet another proof of Toole's conculsion that THD is not really an improtant metric with speakers.
Not sure how you could come up with that conclusion from a residual noise discussion.
Introduce a controlled level of THD into a pure tone and play it into your speakers. Tell us what you hear. Anything over 0.1% in the midband is obvious in my experience. With complicated music, it's almost impossible to hear, but who cares? If pure tones are being wrecked, why bother - you may as well lie down with soundbars and bluetooth street walkers.