Something I am curious about...

Squall Leonhart

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Nov 21, 2016
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This is something I have been curious about for awhile but I have been unsuccesful in finding the answer using google.

So a typical stereo amplifier like for example the Denon 720AE will reproduce frequncies down to 20hz. Then you have a speaker like the Q Acoustics 3020 that only go down to 64hz. I assumed the cross over would filter out anything below 64hz but this doesnt appear to be the case because if you set up a turntable without a subsonic filter you will see woofer excursion on the speakers which leads me to believe the frequencies lower then 64hz are not being filtered out by cross over as the speaker is attempting to reproduce them. Albeit unsuccessfully.

Can anyone explain why this is the case and if a cross over dosen't filter out low frequencies it cannot reproduce then wouldn't it be unsafe for the speaker even when you play a typical CD which still supports frequencies down to 20hz like amplifiers?

Also with home cinema amplifiers you can set a frequecy cut off which you cannot do on a stereo amp. So how do stereo amps become compatible with a wide range of speakers if you cannot set a cut off point?
 
Speakers do not have a crossover or filter at low frequencies. The crossover is usually to prevent bass entering the tweeter and sometimes to roll off the upper range of the woofer. The speaker still moves at, say, 40Hz, even though you cannot hear it due to the small cone. In your example, 64Hz is not a brick wall cutoff, just a realistic lower level, probably about 6 to 10dB lower than the midrange level.

The subsonic wobble you see from a warped LP is better filtered out in the phono stage, leaving a range down to 20Hz available for sources like CD.

Home cinema amps often have a setting that defeats any roll off to a sub woofer, in case you are using it full range in stereo. A 'speaker size' setting can affect this too, but only to protect small satellite speakers, and help balance the sound.

I hope that helps.
 

stereoman

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nopiano said:
Speakers do not have a crossover or filter at low frequencies.

Almost true. In fact not so many , but regarding my new post about "Canton" LSs.

"As their names imply, the woofer sections of the 780 DC and 790 DC incorporate Canton’s Displacement Control (DC) technology, trickled down from the Reference and Vento lines. Displacement Control involves including a high-pass filter in the woofer section to reduce a driver’s extreme low-end output, something that a small driver can’t and therefore shouldn’t be asked to reproduce, as it’s likely to generate lots of distortion. Canton’s claim that DC cleans up the bottom end appears to be true -- our measurements of the SLS 780 DC revealed very high output capability and extremely low distortion for a speaker of this size and price."
 
Squall Leonhart said:
Thanks for reply. So that means that if a CD has loads of recorded 20hz or 30hz content it will have no negative effect on the driver? It just wont reproduce the sound that low?
Yes, as major has already said. The only point I'd add is that this is why caution has to be exercised if you have a bass tone control, as turning that up, along with a high volume could damage the woofer. Although you get virtually no useful output, the voice coil could overheat and warp, either catching or stopping moving altogether!
 

drummerman

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stereoman said:
nopiano said:
Speakers do not have a crossover or filter at low frequencies.

 

Almost true. In fact not so many , but regarding my new post about "Canton" LSs.

"As their names imply, the woofer sections of the 780 DC and 790 DC incorporate Canton’s Displacement Control (DC) technology, trickled down from the Reference and Vento lines. Displacement Control involves including a high-pass filter in the woofer section to reduce a driver’s extreme low-end output, something that a small driver can’t and therefore shouldn’t be asked to reproduce, as it’s likely to generate lots of distortion. Canton’s claim that DC cleans up the bottom end appears to be true -- our measurements of the SLS 780 DC revealed very high output capability and extremely low distortion for a speaker of this size and price."

Kef used to do that until a while ago.
 

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