An XXcontroversial Way to Compare the Output of Class D Amps.

[Bill Fitzmaurice]

56 minutes ago, agedhorse said:

 The old way of defining Xmax would often result in THD numbers even greater.

In the case of under-hung voice coils the calculated xmax was zero. That caused more than a bit of consternation for loudspeaker designers.

Eminence was one of the first to adopt Klippel. Circa 2004 they had to switch voice coil former suppliers, as DuPont stopped supplying Kapton to the industry. Changing the formers changed the driver specs, so they had to measure them all with the new formers to update their data sheets. They had recently acquired a Klippel analysis rig, so from that point used it to measure xmax dynamically. Most manufacturers have since followed suit. 

[nekomatic]

On 23/07/2022 at 12:10, itu said:

dB(A)-meter is a good thing to have at hand while measuring loudness. It is probably one of the simplest piece of equipment to own. Cheap ones are not very accurate, but give a good hint where the level is at the moment.

There are plenty of dB meter phone apps. I assume the numbers they give you are nonsense in absolute terms, but would be worth something as a relative comparison i.e. when measured with the same phone and app, is the SPL in situation A louder than the SPL in situation B. 

[Stub Mandrel]

On 23/07/2022 at 12:10, itu said:

dB(A)-meter is a good thing to have at hand while measuring loudness. It is probably one of the simplest piece of equipment to own. Cheap ones are not very accurate, but give a good hint where the level is at the moment.

 

I have used Brüel & Kjær and similar units earlier (prices were sky high). Now that I have changed company, I decided to buy a simple and cheap meter of my own. Saves ears, if the band starts a volume war.

 

I have a Lidl one(!) it works and if it is anywhere near the specs printed in the booklet (it probably is) more than good enough for my needs.

[Stub Mandrel]

On 23/07/2022 at 12:10, itu said:

dB(A)-meter is a good thing to have at hand while measuring loudness. It is probably one of the simplest piece of equipment to own. Cheap ones are not very accurate, but give a good hint where the level is at the moment.

 

I have used Brüel & Kjær and similar units earlier (prices were sky high). Now that I have changed company, I decided to buy a simple and cheap meter of my own. Saves ears, if the band starts a volume war.

 

I have a Lidl one(!) it works and if it is anywhere near the specs printed in the booklet (it probably is) more than good enough for my needs.

[Bill Fitzmaurice]

On 23/07/2022 at 07:10, itu said:

dB(A)-meter is a good thing to have at hand while measuring loudness..

dB (A) is useless for music, it doesn't measure bass. You must have a dB (C) meter at the minimum, dB (Z) being preferred. https://www.noisemeters.com/help/faq/frequency-weighting/

[itu]

1 hour ago, Bill Fitzmaurice said:

dB (A) is useless for music, it doesn't measure bass. You must have a dB (C) meter at the minimum...

True. But the level measurement gives me a hint, of what's going on. Wattage is far less accurate, as you well know. Besides, in band context even dB(A) is pretty relevant.

 

I would say, that a simple and lightweight meter is functional. Comparable data is hard to measure in changing environment outside laboratory. After all, commercial advertisements are far more inaccurate. And yes, I have done acoustical analysis in anechoic chambers (microphones, speakers, etc.; B&K has nice equipment). Meter is a cheap and easy to carry solution. The best alternative so far.

 

Measuring the whole frequency bandwidth needs quite a system. I think the 3160 from B&K was the latest I worked with. The system and the microphone were impressive. And extremely complicated.

[dmccombe7]

2 hours ago, Stub Mandrel said:

 

I have a Lidl one(!) it works and if it is anywhere near the specs printed in the booklet (it probably is) more than good enough for my needs.

Do you have two of them 

 

Sorry couldn't help it, your post has shown twice ?

Dave

[Bill Fitzmaurice]

1 hour ago, itu said:

Measuring the whole frequency bandwidth needs quite a system.

Not really. You can get by with a C weighted meter, for instance:  https://www.amazon.com/Professional-Backlight-Accuracy-Measuring-30dB-130dB/dp/B01MZ0IUGY/ref=asc_df_B01MZ0IUGY/?tag=hyprod-20&linkCode=df0&hvadid=312357852128&hvpos=&hvnetw=g&hvrand=7748314164138405611&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9002322&hvtargid=pla-348660547600&psc=1&tag=&ref=&adgrpid=62539486699&hvpone=&hvptwo=&hvadid=312357852128&hvpos=&hvnetw=g&hvrand=7748314164138405611&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9002322&hvtargid=pla-348660547600

 

I was hired by a major outdoor concert venue that was being threatened with imminent shutdown because of noise complaints from the neighbors, despite having already paid a 'professional' sound control company $50k for a sound metering system. The complaints were about excessive bass up to two miles away. It took me all of five minutes to see what their problem was. The system was 'A' weighted. According to it the levels off-site never exceeded 75dB. But it didn't measure bass, so the actual off-site levels were routinely hitting 105dB and more below 100Hz. I wrote a new sound control protocol for them, then attended their concerts for three years to ensure compliance. It paid me better than playing, so I had no complaint. The noise complaints went away as well.

 

 

Edited July 26, 2022 by Bill Fitzmaurice

[itu]

You are right, measuring lowest bass is a bit like measuring an airplane with an A-weighted unit. Nice results! Maybe I could "invest" to that, or save some more and just buy a pro multi curve unit. Let's see...

[Bill Fitzmaurice]

Even at 125Hz 'A' weighting is 20dB off from actual. To bring that into a more meaningful context 20dB is the difference between 10 watts and 1,000 watts. 😳

[agedhorse]

1 hour ago, Bill Fitzmaurice said:

Even at 125Hz 'A' weighting is 20dB off from actual. To bring that into a more meaningful context 20dB is the difference between 10 watts and 1,000 watts. 😳

Yup, and assuming that the comparison results using A weighting are "good enough" can result in incorrect, inaccurate (by a mile) conclusions. When somebody bases their opinions as "fact" because of meaningless data, yet they believe with all their hearts that it's uncontroversially true, that's getting awfully close to the definition of blind faith IME.

[LukeFRC]

See - this is what’s nice around here… every so often we get a thread where people passionately throwing around misunderstood “facts” go away … and we get to learn from experts like @agedhorse and @Bill Fitzmaurice

[Stub Mandrel]

9 hours ago, dmccombe7 said:

Do you have two of them 

 

Sorry couldn't help it, your post has shown twice ?

Dave

Bug in the forum, if you are not on the last page, sometimes it appears not to register the post so you click again...

[Stub Mandrel]

7 hours ago, Bill Fitzmaurice said:

Even at 125Hz 'A' weighting is 20dB off from actual. To bring that into a more meaningful context 20dB is the difference between 10 watts and 1,000 watts. 😳

 

So my 'a' weighted device is ideal for proving to pub landlords thst we aren't too loud 😁

[Downunderwonder]

I think for the purpose of waving a dB meter in front of a guitard to get him to stop with the godforsaken racket, an A weighted meter is useful.

[agedhorse]

51 minutes ago, Downunderwonder said:

I think for the purpose of waving a dB meter in front of a guitard to get him to stop with the godforsaken racket, an A weighted meter is useful.

Heavily weighted with lead perhaps?

[chyc]

7 hours ago, agedhorse said:

Heavily weighted with lead perhaps?

Only for heavy metal guitarists.