Subwoofer question

[linuxonly]

Hi,

These are graphs from a Logitech Z906 AVR. I can't imagine those 3 or 4 inches main speakers are linear from 30 Hz to 12 kHz, exception made of the room boost between 70 and 90 Hz. Is it safe to assume the device never turns the 8 inches subwoofer off even thouh I address each speaker individually with REW measure function?

 

[JStewart]

Is it safe to assume the device never turns the 8 inches subwoofer off even thouh I address each speaker individually with REW measure function?

Pretty safe and if correct it would mean there is a crossover in place routing low frequencies sent to the speakers you are measuring, over to the sub. In a AVR there is usually a setting to designate speakers as “small” or “large”. If the setting is on large then the AVR will not route low frequencies to the sub.
In the absence of having this setting, you could verify by turning the sub off or unplugging it when taking a measurement.
I wouldn’t think a 4” driver to have much output at all below 100Hz.

 

[linuxonly]

there is a crossover in place routing low frequencies sent to the speakers you are measuring

Interesting. The fact that the FR, FL, FC, RR, and RL traces are all superimposed below 100 Hz and LFE has an identical trace 6dB louder, which L+R would also do is a strong indicator of the same speaker being mesured below 100 Hz. I wonder how I missed that in https://www.avnirvana.com/attachments/capture-d’écran-du-2024-08-20-12-05-33-png.73034/

Thanks for the confirmation and your input. Makes perfect sense for stereo mode or quadraphonic in order to cover all the audible range.

Unfortunately the Z906 is a black box and it's configuration is fixed -

Back to the drawing board then.

 

[linuxonly]

STEREO
1 - What would be the proper approach to design filters for this system in stereo mode? So far I treated the L and R channels as if they were full range speakers and got good IR filters resulting even though the subwoofer is handling all the frequencies below 80 Hz. The L and R channels just don't have the bandwidth inherently to be full range and must rely on the subwoofer to add the bass response. Therefore I'm not sure the 2 lower octaves are time/phase aligned with the physical L/R speakers, if you see what I mean.

Impossible to turn the subwoofer off. As a consequence all the speakers responses contain also bass coming exclusively from the subwoofer.

The difficulty here is I use SPDIF output and unless I take special measures, the AVR is seen as a stereo system with 5.1 passthrough.

6 CHANNELS
2 - I also made IR filters for this system in 5.1 mode. The target curve for LFE ranges from 20 to 80 Hz and the target for the speakers, from 80Hz up. Not really tested because I only have access to a stereo convolver. Will eventually study the filter chain plugin in pipewire. Needless to say, those filters are unfit for stereo mode.