I meant that with line level devices the subjective can be checked against the objective electronic measurements. With a power amp the electronic output doesn’t tell you the whole story. Listening tests with speakers are the only way to thoroughly test them.
1/5 of a dB difference
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Opinions vary and that is pretty much the problem with depending solely on subjective listening tests.
Design engineers depend on objective measurements to refine/improve designs. If the listening tests don't agree with the objective measurements you are measuring the wrong stuff.
JR
PS; I killed a lot of brain cells working on design of dynamic processors (like compressors and/or noise reductions). Not easily but even that can be dealt with objectively, but I had to roll some of my own custom test equipment.
user 37518
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There is some research on speaker load simulation (some of this is discussed in Doug Self's book). I agree that just adding an 8 ohm resistor and measuring THD is not as representative as when a complex load is presented. But I think that a speaker equivalent electrical circuit model could do wonders in terms of simulating a real load.
This is a little inside baseball but when trying to measure extremely low distortion on high power amps we used special (read expensive) non-inductive power resistors.
Distortion specs with multiple zeros after the decimal point are mostly about marketing.
JR
There are some well known speaker brands with very difficult loads to drive. Top on the list is B&W. They can destroy power amp sonics. The N801 is a torture test. I’ve only ever heard one amp that made them sound right to me. The N801 would be a good one to measure and simulate.
user 37518
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Yes, non-inductive power resistors are pretty common these days when people try to measure amps. They are sold on e-bay for a relatively low price.
user 37518
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I think I have already mentioned it before, but in the RF/MW world it is pretty common to try to model power transistors very accurately, in order to use such models in simulators; the fancy name for this is "behavioral modeling" and it has nothing to do with Psychology.
These days, RF/MW power amp design is 80%-90% (or more) simulation and 10%-20% real prototype testing, because it is so complicated to achieve high-efficiency, large bandwidth, etc.; without mentioning that it is extremely expensive to build many prototypes: the PCB material is no regular material (expensive and not sold commercially to your average Joe), the cost of a single low power transistor starts from around $70 USD, with high power transistors costing several hundreds or even in excess of a thousand dollars (for example); high frequency capacitors and resistors can also be very expensive. So accurate models and simulators are essential for RF/MW power amplifier design.
Anyway, I won't bore you with more of that, but a colleague and friend of mine is very much into modelling these transistors. It is a very complicated process of measuring experimental data and then proposing some electrical equivalent models combined with numerical methods, like neural networks or numerical optimization, to try and achieve the same response of the real transistor, but in a simulator. I guess that something similar could be done with speakers, and, in fact, it should be quite easier: they work at much lower frequencies, no distributed effects are present, the effects due to temperature variations are not as fast as in a transistor, and so on. Perhaps proposing an LCR circuit/electrical equivalent model (which should involve several components) and then using optimization or neural networks for the component values, in order to try and mimic experimental data of certain speaker, is one possibility to create a suitable simulated speaker load. Then it is just a matter of building it.
I mean, this probably has already been done before—perhaps by someone in this forum. I guess I should take a look at some papers out there. It sounds like an interesting topic to look into.
P.S. I am aware that the thread just de-railed from 'are 0.2 dB audible?' to RF transistors, neural networks, speaker modeling, and power amp testing. Sorry for that.
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When I worked for SSL and was filling in for the NY support staff I got an early evening call from Frank Filipetti at Right Track explaining that the Mini Monitors were left-heavy.
I came in and measured them and sure enough the Left output at that control position was about 1/10th a dB hot due to mistracking.
Frank was concerned that it might be right-heavy at a different position so we elected to cross-patch the Main monitor outputs into the Mini amp. That control used an Alps Black Beauty and tracked well.
I'm not sure how it was ultimately resolved other than finding a better pot for the Mini Speakers but after that I never doubted anything the man said he heard.
pucho812
Well-known member
It’s a tough call, I don’t like to doubt what people claim to hear. But if I happen to be in a space where I notice other issues related to Sonics and acoustics, it calls into question what they are hearing.
I don't know. While I still believe 0,2 dB can't be heard, the last week has shown some people do have golden ears.
My car failed. Miserably. The garage I go to, is an old style place. No sales, just maintenance and repair. It's manned by a father and his two sons. The father has been doing this for over half a century, his sons for twenty years. They know about cars.
One of the sons can spot failures before they happen, just by listening to the engine, or driving the car if it's suspension, or a rattling something somewhere. Neither his father, nor his brother have this gift. Is it in the ears, as it clearly isn't in the genes?
My car failed. Miserably. The garage I go to, is an old style place. No sales, just maintenance and repair. It's manned by a father and his two sons. The father has been doing this for over half a century, his sons for twenty years. They know about cars.
One of the sons can spot failures before they happen, just by listening to the engine, or driving the car if it's suspension, or a rattling something somewhere. Neither his father, nor his brother have this gift. Is it in the ears, as it clearly isn't in the genes?
user 37518
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I had a similar gift in my young days, I could go to the bathroom at a party with the lights out, just by ear....
user 37518
Well-known member
Perhaps I didn't express myself correctly, but I am sure you've entered a bathroom with no lights in a party.I've never been to a party with no lights. Did I miss out on something?
user 37518
Well-known member
Don't know what that means, but okI'm usually in the kitchen...
not worth arguing about
It's a combination of experience and talent. I grew up with two older brothers who were motor heads so I learned about automotive tech by osmosis. As a young puke I would pedal my bicycle around the neighborhood and help older kids get their cars started after they messed up a tuneup or repair. Later I had a part time job pumping gas in a gas station and would occasionally fix car repairs that the full time day mechanic mishandled.
A couple anecdotes from that part time gas pump jockey stint. One easy repair was a car that pulled in with the engine missing badly. I popped the hood and found the spark plug wires loose, not seated down onto the spark plugs... 5 minutes later the car owner drove away happy.
My favorite story from that time period was fixing a friend's car. he worked in that gas station and wasn't a good mechanic, so paid to have them tune up his engine. After that work the car wouldn't start again. While I was working at night, some friends would come and hang out with me. One night I decided.... I can start anything so I said, "let's start Jack's car."
After cranking away with no luck, I decided to push it with the station tow truck to jump start it at speed. Curiously even this did not work... The car had fuel and spark, but no love. On the side of road a couple miles from the gas station I asked for a 1/2" wrench. I unbolted the distributer popped it out and reinstalled it one tooth over. I apparently guessed right because after that it started right up with the keys.
Jack's car had been sitting in the station dead for weeks.===
Another car repair story.... One night I was pumping gas and a customer pulls in with one front wheel locked up. I diagnosed his problem as a bad brake master cylinder. When really worn the piston can get cocked inside the brake cylinder and lock up. I cleared it by loosening the brake line at the master cylinder to release the pressure and it started working again. I told the customer to park the car at the station and I wrote a note to the day mechanic to replace the brake master cylinder.
The next day, the day mechanic took the car for a test ride and said the car was OK, and gave it back to the owner. The next night I am pumping gas and I get a desperate phone call from that same car owner. This time his car has the same front wheel locked up again but he is halfway across the state. He begged me to tell the guy at the station he was stuck in, how I fixed it last time. I think the day mechanic believed me this time around.
===
A trick that we used to help diagnose obscure engine noises was to get a old wood handle straw broom. Hold the straw end up to your ear, and probe around the motor with the wood handle. Sound will conduct up the wood handle making it easier to isolate water pump, alternator, etc noises.
I am not a big fan of auto dealership mechanics. About 15 years ago I started hearing what I thought might be a bad wheel bearing. I took my car to the dealer I bought it from and shared my concern. Their mechanic took it for a test ride and said no problemo...
It turns out I had a bad bearing inside the differential. When I took to a shop that specialized in rebuilding rear end chunks, I learned that he had to tear it completely down... I figured as long as it was going to be completely torn down I ordered some different ratio gears.JR
Jona Lewie. That's why you'll always find me in the kitchen at parties. Don't remember the song?
In my case, it's often because I'm the cook
user 37518
Well-known member
Never heard it, also before my time. Will take a listen though.Jona Lewie. That's why you'll always find me in the kitchen at parties. Don't remember the song?
In my case, it's often because I'm the cook
When I used to throw parties in my house with live bands, the kitchen was where the cold beer and food was. I would cook a big batch of chili and barbecue chicken on my grill outside, not to mention gallons of my home brew beer on ice. I would start serving food and beer at noon, for all my friends who were working musicians so couldn't party that night. The chili was pretty popular and would often run out by 6PM.
There would be multiple local bands that would show up to jam (most of Peavey's amp design engineers also gigged in local bands). Just about anybody could get up to jam at my parties. I recall one party when I noticed that there were way too many party goers hanging outside in my driveway. When I went back inside I figured out why. There was one guy who apparently was just learning how to play bass and he only knew one riff, barely. The other kind souls playing with him had no way to politely stop the pain. I didn't have to be polite so I gonged him (anybody remember the gong show?). Everybody but him thanked me for cutting the music (?), and party goers filed back inside.
We would typically have some seriously good music, most of the time.
JR
There would be multiple local bands that would show up to jam (most of Peavey's amp design engineers also gigged in local bands). Just about anybody could get up to jam at my parties. I recall one party when I noticed that there were way too many party goers hanging outside in my driveway.
When I went back inside I figured out why. There was one guy who apparently was just learning how to play bass and he only knew one riff, barely. The other kind souls playing with him had no way to politely stop the pain. I didn't have to be polite so I gonged him (anybody remember the gong show?). Everybody but him thanked me for cutting the music (?), and party goers filed back inside.We would typically have some seriously good music, most of the time.
JR
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