Late C4 Bose vs non-Bose CDM frequency response
Thread Starter
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Late C4 Bose vs non-Bose CDM frequency response
I finally got around to putting a scope on these things.
Based on what I've read here about using the Bose CDM output into aftermarket amps, as well as the difference I can hear between the two, I was expecting to see some ugly equalization in the Bose CDM.
This is what I found:
('MaxV' is at the highest volume setting that doesn't clip. For Bose this is at 100% volume. For non-Bose at about 75%. 'LowV' is a lower volume setting, around 50% of MaxV. All are with tone controls at neutral.)
So, based on frequency response, the Bose is a much better signal source.
However, I also found that the signal out of my non-Bose CDM is perfectly clean, while the signal from my Bose CDM is an ugly ****. I see both periodic amplitude variance (with low frequency input tones it looks like an AM signal) and also a settling of the amplitude over time.
Based on this, I have to assume that my Bose CDM is bad, but on the other hand, since people have reported since the beginning of time that the signal out of the Bose CDM is crap, and since it clearly isn't the frequency response, maybe what I'm seeing is the problem.
If anybody has a Bose CDM they don't need I'd be interested in checking another one to see if it performs the same as mine.
Another interesting discovery - with the Bose CDM, when you turn the bass control up, it cuts the mid frequencies. With the **** up all the way it boosts 30Hz by 30% and cuts 1kHz by 30%.
The non-Bose behaves in a normal fashion, just boosting low frequencies.
Based on what I've read here about using the Bose CDM output into aftermarket amps, as well as the difference I can hear between the two, I was expecting to see some ugly equalization in the Bose CDM.
This is what I found:
('MaxV' is at the highest volume setting that doesn't clip. For Bose this is at 100% volume. For non-Bose at about 75%. 'LowV' is a lower volume setting, around 50% of MaxV. All are with tone controls at neutral.)
So, based on frequency response, the Bose is a much better signal source.
However, I also found that the signal out of my non-Bose CDM is perfectly clean, while the signal from my Bose CDM is an ugly ****. I see both periodic amplitude variance (with low frequency input tones it looks like an AM signal) and also a settling of the amplitude over time.
Based on this, I have to assume that my Bose CDM is bad, but on the other hand, since people have reported since the beginning of time that the signal out of the Bose CDM is crap, and since it clearly isn't the frequency response, maybe what I'm seeing is the problem.
If anybody has a Bose CDM they don't need I'd be interested in checking another one to see if it performs the same as mine.
Another interesting discovery - with the Bose CDM, when you turn the bass control up, it cuts the mid frequencies. With the **** up all the way it boosts 30Hz by 30% and cuts 1kHz by 30%.
The non-Bose behaves in a normal fashion, just boosting low frequencies.
Last edited by VenkmanP; Apr 16, 2012 at 10:37 PM.
