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Question about sound below an amps frequency specs

if an amps frequency response are spec'd out to be between 20hz to 20khz, will it pass information above and below those numbers?For instance will it pass a 15hz tone or will any information below 20 hz be cut off by some internal filters. If an A/v receiver has the same frequency specs in their manual, will it also cut off info above or below its stated specs? Could info going through its LFE be cut off below 20hz as well. The reason I ask is when I was playing a Realtraps bass test CD I downloaded, my speakers had no info below 20hz, though the disc starts with 10hz tones. Just for fun I played the same disc using my tube amp and had significant bass through my mains well below 20hz. Which made me wonder.
shiva

Showing 2 responses by ar_t

ar_t
165 posts
 
NO...........

Filters are spec'ed for "-3 dB point". Using a straightline approximation, the response at the "-3 dB point" is really 0 dB.

We do things like that to confuse the non-technical crowd. Devious nerds, us engineer types are.

Back to the topic at hand......

FR specs that don't give a +/- X dB number, are assumed to be -3 dB points. Amp FR spec's usually give a value of the 20 Hz and 20 kHz points.

There is no way a typical amp has a -3 dB point of 20 kHz on the top end. Typical amp has -3 dB point on the top of between 100 and 200 kHz. At a point 5 times lower than the "-3 dB point", the response is down only 0.2 dB. Which would be around 20-40 kHz in this example.
ar_t
165 posts
 
Will it pass info outside of those ranges?

Yes. How much........figure that each one represents a first order filter in the amp.

IOW........those numbers are 3 dB down, and one octave away would be 6 dB down. Two octaves would be 12 dB down.

Playing low frequency tones usually results in tons of distortion, and that is very likely what you heard.
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