5Hz - 100Hz

[cerwinmad]

i played a 5-100Hz signal through my setup (Awesome fun!!!!) and predictably my sub rolled off at about 25Hz ie no volume below there and some port noise, but amazinly my VE-12 fronts played the full spectrum, there was no roll off! at the 5Hz point they where moving in and out alot!! with no port noise. the lower freq response is suppose to be 28Hz, anyone care to explain!! i know the sub has a low pass filter of 12dB initial/24dB ultimate, but i thought loud speakers had a natural roll off based on box design and that this would initiate a point where the driver would no longer produce sound.

 

[j_garcia]

Secondary harmonics. They are trying to reproduce those frequencies even though they can't. You get sound, but it is not likely the actual note that is being played.

 

[cerwinmad]

the 12 inch driver was moving in and out very slowly, 5Hz (5 cycles a second) was about right. i ran them with sub off too and it was the same, i could hear it till near the end ( 20Hz i presume) then it was felt through the floor. the pressure waves felt strange-hard to explain. i had it about 3/4 total volume.

 

[j_garcia]

Yep, I can actually hear my sub until about 18Hz and then it is nothing but vibration after that, and that is how it should be.

 

[mtrycrafts]

the 12 inch driver was moving in and out very slowly, 5Hz (5 cycles a second) was about right. i ran them with sub off too and it was the same, i could hear it till near the end ( 20Hz i presume) then it was felt through the floor. the pressure waves felt strange-hard to explain. i had it about 3/4 total volume.

Just because it moves doesn't mean it moves with enough force to matter.
Do you have THX processing by chance? That may roll off the sub.

 

[Loren42]

Yes, they rate it at 28 Hz at probably 3 or 6 dB down from some frequency that represents the highest dB on the frequency curve (usually 1 KHz).

After 28 Hz the roll off will probably be 12 dB per octave.

So, while it appears to produce sound at 5 Hz, the actual output in SPL drops at 12 dB every time the frequency is one octave lower.

No magic.

Since the woofer rolls off at 12 dB per octave you can compensate by adding more power to create a flat response. So, if 20W is needed at 60Hz to give a set SPL, then at 30Hz you will need 320W to get the same sound level, and at 15Hz, you will need over 5kW to achieve the same SPL that you got at 60 Hz when you only used 20 watts!

That should tell you how little actual power is generated below 28 Hz even though you see a lot of cone movement, it is virtually nothing as far as sound pressure level goes.

 

[fredk]

I bet the sub has a highpass filter to keep from bottoming. I am surprised the drivers in your fronts didnt bottom trying to produce a 5Hz tone.

 

[cerwinmad]

I bet the sub has a highpass filter to keep from bottoming. I am surprised the drivers in your fronts didnt bottom trying to produce a 5Hz tone.

yes the sub does, and it has overexcursion protection. I am amazed they didnt bottom out too, thats why i posted!!!! i was impressed that it had solid volume to the point i couldnt hear the bass, and the floor told me it was still working well. the tone started at five Hz and rose up too 100 Hz then down again. i found out my ceiling, walls, oven, bookshelf, fireplace, kitchen cabinets and outside wall all have a resonant frequency fun. oh and my standalone shed does too ha ha