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REW + UMIK-1strange SPL response behaviour 8 years 5 months ago #15423

  • giuliodido
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Hi,
some months ago I bought an UMIK-1 microphone and a nanoDIGI: I used them with REW and I found everything very nice and simple.
A few days ago I used again the UMIK-1 just to measure my new Magneplanar, and I found something really strange: the SPL response has dips at 2kHz (-30dB, 1.5 octave wide), 6kHz (-15dB), 10kHz (-10dB), etc.
I tried both near field and far field, always the same result. Also left and right speaker.
I then tried another loudspeaker, and same result as well, with the same dips at same frequencies (while in the past the response was almost flat).

Soon I will post a screenshot.

What could be the cause?

Thank you

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Last edit: by giuliodido.

REW + UMIK-1strange SPL response behaviour 8 years 5 months ago #15430

  • john.reekie
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One giveaway if REW is having a problem is to look at the impulse response (set to %FS). If it doesn't look like an impulse response then REW is upset about something.

Is it possible you have REW set to 44.1 kHz?

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REW + UMIK-1strange SPL response behaviour 8 years 5 months ago #15441

  • giuliodido
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Hi,
thanks for the reply. Below the SPL response and the impulse response.
REW is set to 48kHz
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REW + UMIK-1strange SPL response behaviour 8 years 5 months ago #15443

  • john.reekie
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Oh, the dips are at odd multiples of 2 kHz, so that suggests interaction between two sources, one delayed by .25 ms. If it's acoustic, that corresponds to a path length difference of 8.5 cm. (Hope I worked that out right...) Is the microphone away from any reflecting surface?

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REW + UMIK-1strange SPL response behaviour 8 years 5 months ago #15447

  • giuliodido
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Purple response is far field (listening position at ~2m), blue response is near field (right in front of the grill cloth, 3cm from the planar source). Front panel is ~55cm wide, so it isn't diffraction.
Also, microphone and loudspeaker were right in the middle of the room, without reflecting surfaces near them.

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REW + UMIK-1strange SPL response behaviour 8 years 5 months ago #15547

  • JohnPM
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Could be a feedback/monitoring path. If you are on Windows make sure "Listen to this device" is not selected in the audio properties for the UMIK-1. If you are using multiple sweeps to measure could also be timing misalignment between sweeps, in that case you would see multiple peaks (same as number of sweeps) separated by the timing misalignment, use a single sweep to avoid that.

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Last edit: by JohnPM.
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