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GLM Measurement: Body in or out the room?

avantmidi, modified 5 Years ago.

GLM Measurement: Body in or out the room?

Youngling Posts: 15 Join Date: 5/28/15 Recent Posts
Hi Ilkka,

Question 1:

It seems logical to mee that the measurement must be done with myself sitting in the chair / in the sweetspot
Holding the mic just before my head. After all we are sort of biological absorbers / diffusers and are part of the room = response.

Am I correct about this statement? I'm sure your guys cracked this one out of the matter in your development process?
Thanks allot!

Question 2:

The measurement is being done with the mic and a sweep at a certain volume. Once calibrated and set the actual volume of the music being played will vary in db when the user changes the volume of the audio interface. Does this effect the response curve? Did you guys take account for this in the algorythm?

Enjoying my 8351,s very much every day. Great products!
ilkka-rissanen, modified 5 Years ago.

Re: GLM Measurement: Body in or out the room?

Yoda Posts: 2564 Join Date: 3/23/09 Recent Posts
Hi,

Answer 1:

You are being correct that our body does act as an absorber/diffuser while we are in the listening room. There are many studies done on this subject for example regarding designing of a concert hall. The amount of audience in the hall will change the acoustics of the space significantly. It does require certain ratio of people vs. volume before the effect becomes measurable. A single person in a normally sized listening room does not yet change the acoustic properties of the room so much that one would need to account for it.

When it comes to holding a microphone near your head, it must not be done. Any obstacles near the microphone will cause strong reflections which will distort the measurement. Preferably there should be at least 1 meter of free space at all directions from the microphone. You should use a microphone stand for good results. You can be in the room but you should stand clearly away from the microphone, preferably towards the back of the room, away from the area between the loudspeakers and the microphone.

Answer 2:

The frequency response of a good loudspeaker is linear up to the point when it starts to compress and distort its output. Maximum SPL value in the datasheet describes this level. Depending on the loudspeaker design, this level is more or less frequency dependant, typically the extreme ends of the response starting to compress earlier than the mid range. Another variable is that our hearing is non-linear too. Our hearing is less sensitive to low frequencies at low listening levels. Some devices include some sort of loudness compensation to overcome this issue but the results are debatable. Our loudspeakers or software does not employ any level based frequency response equalization.

https://en.wikipedia.org/wiki/Equal-loudness_contour
https://en.wikipedia.org/wiki/Loudness_compensation
avantmidi, modified 5 Years ago.

Re: GLM Measurement: Body in or out the room?

Youngling Posts: 15 Join Date: 5/28/15 Recent Posts
Dear Ilkka,

Thank you very much for your clear explanation. Once again great service.
Will be ordering a mic stand for calibrations now.

All the best,

Chris