J-Test

[TimWellens]

Been playing around with REW for the last couple of days doing alot of measurements and love it! Unbelievable REW is still free
Yesterday I made a stupid mistake,while playing various test tones I accidently played the J-Test tone. It was only after 5-6 seconds playing it at mid/high volume I saw the red letters saying NOT TO BE PLAYED THRU SPEAKERS,high level and high frequency!
O boy,did I just wore out my Neumann KH310A tweeters?
I know there is protective circuitry inside these monitors but should I worry now?

thnx

 

[John Mulcahy]

Probably OK if it wasn't loud enough to be uncomfortable, but best not repeated.

 

[TimWellens]

Thnx for your reply!
What test can I do with REW and a Umik-1 to see the tweeters are ok?

 

[John Mulcahy]

Just do normal frequency response measurements and see how they compare with previous measurements. To test the tweeters specifically you would need the mic to be quite close and on axis with the tweeter, with a lower test signal level to allow for the much shorter distance to the mic to avoid clipping the input.

 

[TimWellens]

Thanks you so much,will test this later this evening.Will do the normal frequency swipe on both monitors so I can compare with previous results.Will test the tweeters separately too but alas I don’t have previous measurements of the tweeters alone so can’t compare that.
To make sure I also contacted Neumann to hear if I should be worried.(Will post here their response when they get back to me).
The Neumann KH310a’s have circuitry protection : (Quote from SOS magazine) The driver protection circuitry is quite elaborate, with independent thermal limiters for each driver, as well as soft-clipping and excursion-limiting for the woofer.(end quote)
Do you think these independent thermal limiters would protect a tweeter from a 5-6 second J-test signal on semi loud level?
Cheers and thanks again for your time.

 

[John Mulcahy]

Yes, all should be OK. The main risk is playing the signal at a volume setting that would be used for normal content, since it is a full scale signal and so would be a lot louder than might be expected.

 

[TimWellens]

Just do normal frequency response measurements and see how they compare with previous measurements. To test the tweeters specifically you would need the mic to be quite close and on axis with the tweeter, with a lower test signal level to allow for the much shorter distance to the mic to avoid clipping the input.

Just did a frequency response measurement after the J-test debacle.
In my eyes it’s looking good,I mean there is not much difference between the measurement before the j-test (green) and the measurement after the j-test (purple).
See the screenshots,also the combined graph is included.
Just checked,the J-test spit out a 11,025 hz signal so I zoomed in on 11,025hz on both graphs to see if any damage occured. Before the j-test I measure 69,5 spl db at 11,025 and after the j-test it reads 73,7….Mind you the mic was not 100% in the same spot.
If you look at the graphs,can you conclude that the j-test didn’t do harm to the tweeters?
Find the graphs below.
Thank you so much,donation to REW incoming
(And how is the measurement looking in general? Still acoustic noob here)

 

[John Mulcahy]

The scale of the graph is quite extreme, normally a span of about 60 dB gives a good view rather than 400 dB or so you have currently! You can change the top and bottom SPL values of the graph using the Limits button at the top right of the graph, 100 dB at the top and 40 dB at the bottom should be fine.

There is no obvious sign of any harm having been done.

 

[TimWellens]

Thank you so much for your help,I attached the .mdat file, Im sure a pro eye sees more than my noob eye :-)
Testing was done with a SE x1s MIC , handheld and uncalibrated, an UA Apollo interface and Neumann KH310a monitors....I know really amateurish but my UMIK-1 will arrive in 2 days.
If you have the time it would be awesome if you would give it a quick look,especially the tweeter side.
Support for room acoustics will be for later when I have the UMIK-1 and all is calibrated well.
Thank you so much for your time,couldnt sleep from the stupidity I did with this J-test.

 

[John Mulcahy]

Looks fine, Tim.

 

[dotnet]

When I had a damaged tweeter the uneven SPL plot (compared to the other speaker) was a first hint, but the distortion plot left no doubt. Distortion was through the roof on the damaged one.

 

[TimWellens]

When I had a damaged tweeter the uneven SPL plot (compared to the other speaker) was a first hint, but the distortion plot left no doubt. Distortion was through the roof on the damaged one.

I had this signal coming thru the 2 speakers so if the tweeters are damaged they would be both damaged so I can’t compare the left to the right speaker… I’m not good yet at reading the measurements,what do you think about the distortion in my measurement? (it’s a L+R test in listening position,green is before the disaster and purple is the measurement thereafter).
Thanks!

 

[dotnet]

I’m no expert, but the distortion seems a bit higher almost across the entire frequency range in the after measurement, probably for unrelated reasons. If anything, the tweeter behaviour seems smoother in the second graph. I don’t think there is any damage.

When one of my tweeters was damaged, THD was about 0.3% max on the good speaker, and varying wildly between 0.5% and 25% on the bad one.

 

[TimWellens]

I’m no expert, but the distortion seems a bit higher almost across the entire frequency range in the after measurement, probably for unrelated reasons. If anything, the tweeter behaviour seems smoother in the second graph. I don’t think there is any damage.

When one of my tweeters was damaged, THD was about 0.3% max on the good speaker, and varying wildly between 0.5% and 25% on the bad one.

Thanx I emailed Neumann and explained the case,see what their opinion is.I’m sure they will get back to me soon,will post their reply here

 

[jschwender]

That does not look like a damaged tweeter. Also, most professional speakers are robust, and i doubt that you can destroy this one within 5 seconds on mid level, no matter what signal you use. The only tweeter that i ever damaged so far with a test signal was a cell phone speaker. Some of them are incredibly sensitive to overload, unlike professional drivers.

 

[TimWellens]

That does not look like a damaged tweeter. Also, most professional speakers are robust, and i doubt that you can destroy this one within 5 seconds on mid level, no matter what signal you use. The only tweeter that i ever damaged so far with a test signal was a cell phone speaker. Some of them are incredibly sensitive to overload, unlike professional drivers.

Thank you so much! I really am so depressed making a stupid mistake like this.I love them so much and don’t have the money to buy another pair. (Money is very tight atm don’t have shame to share this).If you lose the trust in your monitors it’s hard to enjoy producing music,I know you understand I was thinking sending them to Neumann (Sennheiser) but as they are sealed monitors I’m not sure if it loses quality once opened to replace the tweeters.

I have 2 monitors and REW was on my small monitor,I’m a bit color blind so I think that’s why I saw the red warning letters for the J-test so late.Maybe it wouldn’t hurt in the next update provide it with an extra pop-up ‘Are you sure? Not meant for loudspeakers!’
Anyway thank you so much for your response,maybe I can sleep more easy tonight