Sure it's not the noise floor of the DSP?
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JBL LSR305P MKii and Control 1 Pro Monitors Review
- Thread starter amirm
- Start date
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.
Although this is assuming there's active crossovers, which is possibly not the case at this price point.
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mhardy6647
Grand Contributor
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That's how Ray Dolby got started
OK, actually he got started (well, his initial claim to fame... I think... was) with the epochal Ampex VRX-1000 rotating head video tape recorder
https://www.historyofrecording.com/ampexvrx1000aniv.html
This Ampex Mark IV was the star of the 1956 NARTB Show. Here Phil Gundy, Ampex vice president, (far left) looks on as VTR design team members, (L-R) Shelby Henderson, Alex Maxey, Fred Pfost, Ray Dolby, Charlie Ginsburg and Charlie Anderson admire their creation. (PHOTO CR[E]DIT: Fred Pfost)
https://www.tvtechnology.com/show-news/plan-to-display-early-vtr-at-nab-show-stalls
As an odd, ego-centric aside, I was privileged to work, for a while, for the son of one of the other Ampex engineers on that team, Fred Pfost. I actually got to meet and chat with Fred Pfost at his home in Los Gatos, CA, once... many years ago. He was a charming and eccentric fellow.
restorer-john
Grand Contributor
As I said, most of the hiss. Not all of the hiss.
Noise is noise. It's unwelcome at any price and releasing products into the marketplace with excessive residual noise is just part and parcel of the second rate design that goes into a lot of gear these days. Find powered speakers that are silent and buy them- don't make excuses for average performers because they are cheap.
And attenuating the output of a noisy HF driver amplifier is not the solution. Using better quality (less residual noise) amplification, processing and front ends is the best way.
PS. I had a pair of powered "near field monitors" recently given to me for "parts" as the musician owner had been told the hiss was normal. I ended up donating them to a local OpShop- and they were a brand that should know a lot better.
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On hiss...
Please tell me the frequency spectrum of hiss. If that is stated somewhere in the previous 21 pages, I apologize because I missed it.
My hearing is gone above 10K, primarily due to complete lack of hearing protection during Army basic training and advanced age. I cannot hear a basket of asps hissing at me, much less high frequency hiss from a tweeter.
Please tell me the frequency spectrum of hiss. If that is stated somewhere in the previous 21 pages, I apologize because I missed it.
My hearing is gone above 10K, primarily due to complete lack of hearing protection during Army basic training and advanced age. I cannot hear a basket of asps hissing at me, much less high frequency hiss from a tweeter.
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:
Room 2:
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.
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:
Room 2:
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.
OP
- Thread Starter
- #411
Yes.
Try shorting-out the inputs and see if there is a difference. Plug in an input cable(s) and short between the hot pin and shield at the far end.
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restorer-john
Grand Contributor
As Wombat mentioned, standard residual noise testing requires a shorted input. The inputs are high impedance, so if left un-terminated, noise can easily intrude and skew observations.
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..
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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..
55-65dB is a level of normal human speech. Listening music at 65dB is not "very low level".
DarthVince
Member
G'day to all. First post. Great site. Thanks Amir!
I'm in the process of downsizing our accomodation and our living room can't accommodate multiple components and conventional speakers.
I've looked at a number of in-wall and on-wall speaker systems but haven't been bowled over. These are bulkier than I would like for on-wall use but the compromise may be worthwhile. I would appreciate advice/feedback on how they might perform when wall-mounted and in close proximity to the rear wall.
I'm in the process of downsizing our accomodation and our living room can't accommodate multiple components and conventional speakers.
I've looked at a number of in-wall and on-wall speaker systems but haven't been bowled over. These are bulkier than I would like for on-wall use but the compromise may be worthwhile. I would appreciate advice/feedback on how they might perform when wall-mounted and in close proximity to the rear wall.
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It depends what kind of music you consider.
This morning I was listening to Schubert piano pieces while eating breakfast. The forte were above human speech levels, at 75dB I guess, only because I set volume so that I could hear the pianissimo.
restorer-john
Grand Contributor
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.
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.
What is the difference between -38dB hiss coming from JLB at 2kHz and harmonic distortion component generated by speaker? Both are artificial and not part of music, so, as long as the music is playing if one is not audible neither is the other.
I merely expressed that hiss in a THD metric.
P.S. I am in no way justifying the existence of the hiss - it shouldn't be there.
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