UMIK-1
I placed the UMIK-1 just about 1 meter from the VM752, The REW said I have clipping in the input. That makes me think that the UMIK has a low dynamic range. Do you have a clue what is happening to my setup ?
Thanks
I placed the UMIK-1 just about 1 meter from the VM752, The REW said I have clipping in the input. That makes me think that the UMIK has a low dynamic range. Do you have a clue what is happening to my setup ?
Thanks
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Dumptruck et al, this dip in responce is roughly at the same point as the exit flange diameter. I would think having a bit more uplift of the baffle to soften this edge would go a long way in reducing this ripple.
Mike
Mike
Alan, first off the devs of REW have said not to pay much attention to the clipping level warning, so there must be a bug. In your case if the cal file is loaded in REW the reference should be set, but... you should ensure proper microphone input level in windows. I'm running 7 (on a laptop using built in sound), set this via Control Panel/Sound/Recording, select the Umik-1 and click on Properties. Select the Levels tab.
What is the reference level set for in REW? -12dB is typical.
What is the reference level set for in REW? -12dB is typical.
The display of the mic said it is at gain 18db. Is that too high ?
I go to sound/recording/level. I am at 100%. Should I turn down this a little say 80% ? Any idea ?
Thanks
In the Preferences page in REW the Sweep Level should be set to -12dB. This compensates for headroom and prevents clipping.
Mine is set for 85%, but have used as low as 20%.
Mine is set for 85%, but have used as low as 20%.
If you cant get rid of it by usual means of putting damping felt or similar,
lower the XO point. Your excellent tweeter would not mind, I suppose.
Correct me if I'm wrong here.
Is it safe to use the REW software to produce a scan between the crossover frequencies and then test the drivers with no crossover.
At this late hour I cannot remember the crossover frequencies of the Platinum but say its 400Hz and 4kHz.
The woofer can be tested from 10Hz to whatever as it wont suffer HF.
The VM752 can be tested from about 300Hz to whatever again as it wont suffer HF.
The ScanSpeak tweeter needs to be carefully fed from only 3kHz and above.
Is it safe to use the REW software to produce a scan between the crossover frequencies and then test the drivers with no crossover.
At this late hour I cannot remember the crossover frequencies of the Platinum but say its 400Hz and 4kHz.
The woofer can be tested from 10Hz to whatever as it wont suffer HF.
The VM752 can be tested from about 300Hz to whatever again as it wont suffer HF.
The ScanSpeak tweeter needs to be carefully fed from only 3kHz and above.
Be very careful when you test it without the crossover.
I first tested the speaker with crossover using the checking function and the REW said the level is OK.
'without switching off anything' I test the VM752 raw driver between 200 and 10,000Hz.
For your tweeter, you can test it with a 10uf capacitor to protect it. I test my between 500Hz to 20,000Hz.
When raw driver is connected to your amp, do not switch off or switch on anything.
If you are unsure, test it with a cheap spare driver first.
Good luck
Tweeters are normally the only concern being as fragile they can be. Agree with the 500 and up test range. The importance of out of band testing is to insure out of band frequency responce does not interfere with slopes chosen function properly. The first order cap is required of most tweeters and it's additive function to the proper acoustic slope, eg a 4th order LR combined with a first order electrical and say a 2nd order acoustic roll off will become a 7th order acoustic network. Must say I don't use a cap with my AMT's (rt4001). They are rather rugged and yes I have Oops'd on occasion. 😉
You are correct. I lowered the listening level under the settings of the mic and the clipping was prevented. I was able to measure the VM752 under 2.83V input and there is no more clipping message.
Thank you.
One evening taking measurements, wife started giving me ugly looks. When the commercials came on I'd hit mute and ask her to be still nicely. The volume level was the issue. So since what I needed could be measured from 1cm I upped the mic gain and dropped the level. Much better looks from the wife.
Tho have to admit doing 3 back to back sweeps on a dozen drivers was a bit much for her. Next day my nieghbor Rob wanted to know how my Star Trek Transporter project was going 😉
Tho have to admit doing 3 back to back sweeps on a dozen drivers was a bit much for her. Next day my nieghbor Rob wanted to know how my Star Trek Transporter project was going 😉
comparing VM752 with other domes
I always wonder how the VM752 compare to other mid range dome. I measured 3 other Dynaudio domes I have got - D76, D54, M560.
I config the input level to about 2.8v on all four drivers and then do a sweep on them. These measurement are done in a living room so they are smooth to 1/3 octive.
Please see the attached overlay. The VM752 is most of the time more sensitive than all 3 dynaudio mid up to around 5KHz. As it is a 3 inch dome, it is expected to roll off much faster after 5K anyway compare to the 2 inch Dynaudio.
To my surprise, the Escotar mid is not as sensitive as the VM752 given it has a more rug magnet compare to other dynas. In fact the D54 seems slightly more sensitve than the Escotar. This is not what I expect either.
The D76 is more or less flat from 500-5000 Hz. In fact, I find D76 very musical and easy to work with.
After these measurements, I really have to try out the D76 again to see how it performs in my 3 way electronic crossover system.
I always wonder how the VM752 compare to other mid range dome. I measured 3 other Dynaudio domes I have got - D76, D54, M560.
I config the input level to about 2.8v on all four drivers and then do a sweep on them. These measurement are done in a living room so they are smooth to 1/3 octive.
Please see the attached overlay. The VM752 is most of the time more sensitive than all 3 dynaudio mid up to around 5KHz. As it is a 3 inch dome, it is expected to roll off much faster after 5K anyway compare to the 2 inch Dynaudio.
To my surprise, the Escotar mid is not as sensitive as the VM752 given it has a more rug magnet compare to other dynas. In fact the D54 seems slightly more sensitve than the Escotar. This is not what I expect either.
The D76 is more or less flat from 500-5000 Hz. In fact, I find D76 very musical and easy to work with.
After these measurements, I really have to try out the D76 again to see how it performs in my 3 way electronic crossover system.
Attachments
Yet another problem
I finally got around to fishing out the laptop and loading the REW files onto it to take some measurements.
When I plug the laptop into the Quad I get and underlying electronic hash noise, a mixture of white noise and a medium frequency whine.
Obviously I can't use this when taking frequency measurements.
The noise is the same on the line-out and headphone out ?
I was hoping to use the laptop rather than drag the PC out of its cubby hole.
I finally got around to fishing out the laptop and loading the REW files onto it to take some measurements.
When I plug the laptop into the Quad I get and underlying electronic hash noise, a mixture of white noise and a medium frequency whine.
Obviously I can't use this when taking frequency measurements.
The noise is the same on the line-out and headphone out ?
I was hoping to use the laptop rather than drag the PC out of its cubby hole.
You might have to get an external soundcard/DAC of some sort. Is the output level all the way up? Does the noise change if you move the cable around?
Try turning off the radio wifi or Bluetooth on the laptop. That adds noise. Also check to see if you are using different grounded outlets to power amp and laptop. Might be ground loop. I have used several laptops with REW and noticed noise from wifi transmissions - not super loud but noticeable. No huge whine or hum.
Can you just play mp3 songs from your laptop to amp? That is a basic test of having system working.
Can you just play mp3 songs from your laptop to amp? That is a basic test of having system working.
The volume of the noise does not vary with the volume of the required signal.
The laptop and the power amp are using the same mains outlet.
I'm at work at the moment but I'll try the suggestion of turning off the wifi in the morning.
The laptop and the power amp are using the same mains outlet.
I'm at work at the moment but I'll try the suggestion of turning off the wifi in the morning.
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