LinearX LMS, Glitches in Frequency Response at 100, 1,000, and 10,000 Hz

[iLikeMacs]

Hello,

I'm posting here because this forum is one of the few places that the now-defunct LMS (Loudspeaker Measurement System) by LinearX has been mentioned.

I recently noticed glitches in the frequency response at 100, 1,000, and 10,000 Hz.

I ran the external analyzer calibration routine which reported no errors between the oscillator output and line input.

However, when I run a loopback measurement from the oscillator output to the line input, the glitches are visible.

I would greatly appreciate if anyone else has seen this problem and was able to fix it. Thank you very much in advance.

 

[alsinaleandro]

Hi, I were user of this board and used a lot years before. Unfortunately this is a common problem of the LMS board. This happens because the VCO changes its frequency multiplier along the sweep, it spans many orders of magnitude in the full audio frequency spectrum. Many complaints have been posted on the LinearX forums but Chris said this problem has no solution, and the magnitude differences between every step of these glitches are inside the expected +/- 1dB tolerance of the system.

 

[Mark Tillotson]

This is a common issue with any spectrum analyzer, be it audio, RF or microwave. No one oscillator setting can cover the entire spectrum, so you switch between oscillators or harmonics to cover the entire band. Normally a self-calibration would correct for it.

The graph suggests you are seeing the uncalibrated data - or calibration has failed or is not operating? This could be a symptom of the device using battery-backed-up RAM for its calibration data, and the battery going dead?