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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Audio Measurement and Testing => Topic started by: Miguel Dahl on January 10, 2020, 02:25:38 PM
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Just some quick traces I grabbed on the stage yesterday. There are spikes and dips somewhat due to conditions when I took the measurments. But look at 6k and above.
These are Radian Microwedges 12". Active powered. Oooold. We use an RCF DSP and I just tuned them by ear. But, I know we have "pairs" of even matching speakers. This trace is the with two "ok" ones and two "dull" ones.
Can this indicate a busted or bad "some" component within the speaker?
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Try swapping hi freq drivers to see if anything changes.
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How do they sound with sine wave sweeps ? Stage monitor high frequency drivers ( any driver that faces up at the world ) require routine cleaning. When was the last time you pulled the diaphragms, cleaned out the voice coil gaps and vacuumed out the phase plugs?
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How do they sound with sine wave sweeps ? Stage monitor high frequency drivers ( any driver that faces up at the world ) require routine cleaning. When was the last time you pulled the diaphragms, cleaned out the voice coil gaps and vacuumed out the phase plugs?
I have no idea if or when that was last done. I've never done it during my three years there so far. There's some slight distortion-ish on at least one of them.
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Distortion could easily be caused by crud rattling around on the diagram which when facing up acts like a catch basket. Once a year cleaning at a minimum would be my recommendation. Also switch your analyzer to log display. Much more useful.
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Distortion could easily be caused by crud rattling around on the diagram which when facing up acts like a catch basket. Once a year cleaning at a minimum would be my recommendation. Also switch your analyzer to log display. Much more useful.
I'll pop those grilles when they come back from the current job and have a look. Why/how is log more useful?
Reason I started the thread was that my colleague said it "looks" like something fishy with a resistor or something. My thought is that the HF drivers are just past their prime, as the speakers are very old.
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If it turns out the HF drivers are shot. Would it be possible to recone everything with new coaxial drivers from RCF? Like this one https://www.bluearan.co.uk/index.php?product=RCF_CX12N351_-_12_inch_450W_8_Ohm&id=RCFCX12N351. We have a good price from our RCF dealer, that why RCF..
Since we already are not on factory DSP tunings, a different driver would just leave the cab itself as "Microwedge". But is this possible? We have been thinking of getting rid of them, bit if one can give them a second life with this, then I guess it's worth keeping them.
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Determine the actual problem first, then look for a solution.
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I'll pop those grilles when they come back from the current job and have a look. Why/how is log more useful?
Reason I started the thread was that my colleague said it "looks" like something fishy with a resistor or something. My thought is that the HF drivers are just past their prime, as the speakers are very old.
"Log" gives equal space to each octave, making it easier to see the "big picture".
Assuming the same drive source was used for each, cabinet and mics were in exactly the same place, the deviation between each is within 2 dB to 6kHz. I've seen plenty of brand new drivers that don't match any better.
The high frequency loss above that could easily be caused by "dust bunnies" accumulating in the horn, take a picture when you pop the grilles, my bet is grill foam rot accumulation glued in with some sticky goo in the "dull pair".
Assuming these are active cabinets, there should be no resistors in the cabinets.
If they are using the Radian Microwedge passive crossovers, loss of the HF bypass capacitor could account for the reduced HF output above 6 kHz.
Diaphragm replacements that don't match original specs could also account for the HF differences.
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"Log" gives equal space to each octave, making it easier to see the "big picture".
Assuming the same drive source was used for each, cabinet and mics were in exactly the same place, the deviation between each is within 2 dB to 6kHz. I've seen plenty of brand new drivers that don't match any better.
The high frequency loss above that could easily be caused by "dust bunnies" accumulating in the horn, take a picture when you pop the grilles, my bet is grill foam rot accumulation glued in with some sticky goo in the "dull pair".
Assuming these are active cabinets, there should be no resistors in the cabinets.
If they are using the Radian Microwedge passive crossovers, loss of the HF bypass capacitor could account for the reduced HF output above 6 kHz.
Diaphragm replacements that don't match original specs could also account for the HF differences.
Ah, yes the big picture. Indeed.
There are active cabs.
Here's all of them. I guess that the one blue guy in there was fed a higher level. "pairs". But i'll pop the hood and take a look at how it looks under the grille.
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I wasn't aware that Radian ever made an active version of the MicroWedge. Are these stock units or some sort of add on power amp? If these are something with purpose tuned DSP they could probably use another pass at the tuning. Thats the kind of response I'd expect from a passive crossover even on the good traces..
Ah, yes the big picture. Indeed.
There are active cabs.
Here's all of them. I guess that the one blue guy in there was fed a higher level. "pairs". But i'll pop the hood and take a look at how it looks under the grille.
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I wasn't aware that Radian ever made an active version of the MicroWedge. Are these stock units or some sort of add on power amp? If these are something with purpose tuned DSP they could probably use another pass at the tuning. Thats the kind of response I'd expect from a passive crossover even on the good traces..
I was unclear. They are being driven active, like using external amps :)
I believe it was two summers ago when I tuned them, the traces looked pretty much the same then as now.
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I was unclear. They are being driven active, like using external amps :)
I believe it was two summers ago when I tuned them, the traces looked pretty much the same then as now.
Looking at the phase trace can also be helpful when trying when troubleshooting and give some clues as to what's going on. A sine wave sweep can also be revealing for distortion in ways that pink noise or music will not. Looking at the traces is interesting but won't tell you the whole story, they're telling you that further investigation is required. I've seen all kinds of HF driver problems that are sometimes easily resolved but you never really know until things are taken apart and inspected.
Just off the top of my head here's some possible sources of the roll off shown in the trace:
-dirt/debris blocking phase plug and/or voice coil gap
-liquid spill with residue in phase plug and/or voice coil gap
-Shattered diaphragm
-Shifted pole piece
-cracked magnet
-missing/damaged/broken passive X-over network (I don't recall if these Radians had the switchable passive network and if they did, do the passive components remain in the circuit when switched to active)
-Wrong impedance diaphragm installed.
It can be a bit of a detective story to get to the bottom of some of the more challenging issues especially if someone has monkeyed with things when they really shouldn't. One tip if you're trying to compare traces it's really important to not change the testing drive level when making critical comparisons to known good units.
(I'm not one to brag but I did once earn myself the nickname "Diaphragm Hunter" in a dogged pursuit to ensure that even the most well used loudspeakers played well with each other)
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Aight.
Just to follow up. Our shop is pretty small. I know I can't do very precise measurments in there, it's hard surfaces and stuff everywhere. And I don't want to take it outside because 1) our shop is in the middle of a residential area 2) It's cold up here.
I have a feeling that I should build some sort of box or something which blocks out at least some mid/HF reflections. How would you guys deal with this?
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Aight.
Just to follow up. Our shop is pretty small. I know I can't do very precise measurments in there, it's hard surfaces and stuff everywhere. And I don't want to take it outside because 1) our shop is in the middle of a residential area 2) It's cold up here.
I have a feeling that I should build some sort of box or something which blocks out at least some mid/HF reflections. How would you guys deal with this?
To find out whats causing the differences between loudspeakers it's not absolutely critical to measure in a perfect environment. It's much more important to make the same measurement of each loudspeaker each time in order to compare the defective units to the ones that you think are good. The position of the loudspeaker in the room, the position of the microphone relative to the speaker, the drive level, the mic preamp settings. If you have any pipe and drape or a backdrop you could put up can help with the MF/HF reflections. Any box you could build would only create other problems with the measurement.
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To find out whats causing the differences between loudspeakers it's not absolutely critical to measure in a perfect environment. It's much more important to make the same measurement of each loudspeaker each time in order to compare the defective units to the ones that you think are good. The position of the loudspeaker in the room, the position of the microphone relative to the speaker, the drive level, the mic preamp settings. If you have any pipe and drape or a backdrop you could put up can help with the MF/HF reflections. Any box you could build would only create other problems with the measurement.
Right. I guess I'll start by checking the speakers for something physical which looks odd. Then I'll swap drivers and cabs to see if a "poor" driver performs better in a "good" drivers cab.
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+1 to what Matthew said. You're not really looking for an accurate measurement of the speaker. You're looking to see what is causing that one to behave differently than the rest. Keeping your setup identical, and then simply swapping speakers out should give you the accuracy you desire. Realize though, that in a small room with reflections, even very subtle changes could make a difference in the result.
As an experiment, start with one speaker, and shift the position a couple degrees each way and re-test to see how much of a difference you see in your lines. Sometimes things in the room can offer weird, very specific reflections that will change the results dramatically. Even where you stand in the room can make a difference!
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This came out a bit wrong from my part. I know I don't need perfect measurments to try to solve this particular issue. It was more "overall". For general tuning. We are already off "stock-setup" for the MW's so tuning needs to be done by ear and what I can see from frequency and phase response traces. It's also to have an environment which is adequate enough for looking through the scope for the rest of the speakers we have. This is probably Off Topic though.
But I'll start with what I wrote in my previous post. Looking for stuff, then swap drivers around.
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For this kind of testing you can measure a meter from the front of the cabinet and learn all you need to know to move forward. The first step really should be removing the diaphgrams and cleaning out the drivers. After that you have some thing to measure, without that you have too many unknown variables. Any speaker that faces up toward the band should be assumed to be compromised so some degree after a couple dozen shows. After a couple years it should be assumed to be beyond usability without service.
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Found this in one of the really bad ones:
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Metal fatigue plus over excursion. Life's rough on poor little stage wedge diaphragms
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Found this in one of the really bad ones:
Now we are getting somewhere!
It's all fine to try to figure out what the problem "might" be but opening up the drivers will tell the story.
So, now put a "good" driver on the horn in the "bad" cabinet and re-test.
Post results.
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Now we are getting somewhere!
It's all fine to try to figure out what the problem "might" be but opening up the drivers will tell the story.
So, now put a "good" driver on the horn in the "bad" cabinet and re-test.
Post results.
That's my next move tomorrow, if I have time.
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Anyone know if just the diaphragm is available on the after-merket from Radian?
I've googlet but did not find the diaphragm.
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Anyone know if just the diaphragm is available on the after-merket from Radian?
I've googlet but did not find the diaphragm.
The diaphragm you posted before looks like the Radian 1750PB-8, Parts Express shows two in stock today at $96.98. You did not mention the driver type, so just a guess as to if it that is the correct unit, the 1750PB-8 is used in these Radian drivers: 636PB, 651PB, 745PB, 760PB, 835PB & 850PB.
Radian also makes after-market diaphragms that fit many other manufacturer's drivers, so pretty good chance they will continue to make diaphragms to fit their own drivers.
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The diaphragm you posted before looks like the Radian 1750PB-8, Parts Express shows two in stock today at $96.98. You did not mention the driver type, so just a guess as to if it that is the correct unit, the 1750PB-8 is used in these Radian drivers: 636PB, 651PB, 745PB, 760PB, 835PB & 850PB.
Radian also makes after-market diaphragms that fit many other manufacturer's drivers, so pretty good chance they will continue to make diaphragms to fit their own drivers.
Thanks. We'll prolly go through our distributor, but I was curious if this part exists (anymore) as it's an old speaker.
It's the 5312 (-16) from Radian which sits in these.
This might be a retarded question. But terms in english is not my strongpoint.. What's the difference between a diaphragm and a driver? To me in English it's diaphragm, cone, or driver. Diaphragm and cone I understand, but the driver?
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In common US English usage a driver is an entire speaker motor including the magnet, voice coil and diaphragm or cone. Low frequency drivers refer to woofers, high frequency drivers most often refer to compression drivers operating above 500 hz.