first steps with REW

arivel

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Hello.
when I create a sweeps file, the error in the attached image appears, what is it due to?.
when you want to measure, REW offers two possibilities:
1 use sweep created by REW .
2 use previously created sweep file .
what is the difference between the two choices?
 

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arivel

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this is my first measurement.
I used the default sweeps provided by REW .
I used a small and old poor quality woofer speaker (frequency 20-1500 Hz) and a microphone without calibration because it doesn't need it, it's the OM1.
I placed them on the sofa next to me without positioning them correctly, for now I don't have to make precise measurements but I only need it to learn how to use REW.
Is the sound card calibration shown in the graph correct?
 

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arivel

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after creating the sound card calibration file can I play with the knob that adjusts the outputs and the knobs that adjust the microphone inputs or do I have to touch nothing anymore?.
in the image, main output at top right and mic/H-z/line at bottom left
if there are adjustment errors both on the audio interface and on the amplifier, are there any protection mechanisms to avoid causing damage to the loudspeaker?
 

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Last edited:

John Mulcahy

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You can change anything, but if the gain of the input path is changed SPL calibration would need to be repeated to show meaningful SPL figures.

There are two protection mechanisms on the Measure dialog, but avoiding damage is your responsibility. For most measurement purposes the level should not be higher than you could comfortably listen to.

There are two Protection mechanisms for sweep measurements. Abort if heavy input clipping occurs will abort the measurement if more than 30% of the samples in an input block are clipped. Abort above SPL limit will abort the measurement if the SPL exceeds the limit that has been set. Note that if the limit set is higher than the input can measure before clipping occurs it will not offer any protection, but in that case the first mechanism might be triggered.
 

arivel

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I want to compliment the author of this wonderful software and the patience he has with me.
Is it possible to compare the measurement I make with my instruments with the graph made available by the loudspeaker manufacturer to find out if I've made a state-of-the-art measurement or if I've done something wrong instead?
 

John Mulcahy

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You can certainly compare them, but the comparison will have less to do with the state of the art than the different measurement environments and presentations. Manufacturer measurements may be made in an anechoic chamber, or in an environment or using equipment that minimises the influence of reflections from room surfaces. You can get closer to that by measuring in the largest space you have available (or outside in suitable climates), with speaker and mic as far as possible from all surfaces including the floor and ceiling, and by applying windowing to the measurement impulse response to exclude reflections. Manufacturer measurements are always smoothed, some much more than others, so that also needs to be taken into account.
 

arivel

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because in preferences it does not appear to me in the same way as in fig. 1 ?
only the entry e-mu 0404 appears in the driver box
 

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John Mulcahy

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The layout has changed a little since that old help image. The names of the inputs and outputs depend on what the ASIO driver decides to call them.
 

arivel

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one thing is not clear to me. to find out if the sound pressure is 75 decibels do I have to use a sound level meter or can I use my OM1 microphone combined with the SPL meter application which is already integrated in REW ?.
 

John Mulcahy

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REW needs to know how the voltages from the mic relate to SPL, it can't work that out itself with an analog mic. Some USB mics include sensitivity information in their cal file, REW can use that and knowledge of how the OS input volume setting affects level from the mic to determine the SPL. For an analog mic if you have a figure for the mic sensitivity in mV/Pa and a multimeter to measure voltage you could use this process. Otherwise you need an external SPL meter or you can just make a guess of the SPL and use that guess. SPL calibraton only affects the level at which the graphs are drawn, it doesn't change their shape.
 

arivel

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Hi, I have two questions to ask.
as is done with the sound card, is it possible to create a calibration file tailored to the loudspeaker in order to have a graph in which only the frequency response of the cabinet is seen instead of that of the cabinet together with that of the loudspeaker?.
I would like to make a comparison between the frequency response of the speaker without cabinet and speaker with cabinet to see the differences, in which conditions should I measure the speaker?
 

John Mulcahy

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The cabinet doesn't have a response (bar some potential for surface vibrations), but being in an enclosure will change the response of the driver.
 

arivel

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Is it possible to see the phase difference between woofer and tweeter?
 

arivel

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what does this error mean?

REW V5.20.13 running Azul Systems, Inc. JRE 1.8.0_345 64-bit on Windows 7 Locale: language it, keyboard IT, windows-1252 at 96 DPI


Message:
java.lang.NullPointerException
Stack Trace:
roomeqwizard._E.A(y:213)
roomeqwizard._E.A(y:2253)
roomeqwizard.JC$10.run(y:924)
java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
java.awt.EventQueue.access$500(EventQueue.java:97)
java.awt.EventQueue$3.run(EventQueue.java:709)
java.awt.EventQueue$3.run(EventQueue.java:703)
java.security.AccessController.doPrivileged(Native Method)
java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
 

arivel

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lately I can no longer make measurements with emu0404 sound card and OM1 microphone.
if i start to turn up the volume of my marantz 510 i get a strong audio feedback between speaker and microphone so i have to turn everything off.
 

arivel

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after creating the sound card calibration file (mine is an e-mu 0404 usb), can I put my hand on the preamplifier and output knob or do I no longer have to touch anything?
 
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