Here’s a strange phenomena?

[JBL 4645]

This evening I was conducting an alignment test with 100Hz sine wave all-channels with individual testing of JBL control 5 LCR as well as LCR sub bass extension and JBL 4645 LFE.1 with same frequency.

Needing something to sit on while in front of the DCX2496 I moved an speaker that isn’t even connected or even in any use what so ever and while looking at the display outputs on the Alesis RA300 my hand just wondered down to the bass mid driver on the AWIA speaker and while I pressed gently on the driver I noticed the 100Hz sine wave pitch rising?

I did a few more test by placing the SPL db meter close to the driver on the AWIA set the SPL for 0db doesn’t matter what the level was it was 80db okay, but that is neither here or there. Pressing down on the driver again I noticed a +3db rise now that is weird, I could feel the vibration on the AWIA bass mid driver while resting my fingertips on the driver.

So what does this mean because I’m totally baffled LOL.

[hjames]

Bingo - its the harmonic resonance of that speaker cabinet ...
you are near the sweet spot that cabinet is tuned for and it hummed back atcha! When you damp the cone with your fingertips it changes the airspace/cabinet size and you better hit the tuned frequency ...
So - is the AIWA a sealed cabinet or tuned port? I'm guessing sealed ...

Its like a tank circuit in a transmitter - setting the resonance improves the efficiency and your output goes way up!


Packing the cabinet with some fiberglass would also change the resonant frequency.



This evening I was conducting an alignment test with 100Hz sine wave all-channels with individual testing of JBL control 5 LCR as well as LCR sub bass extension and JBL 4645 LFE.1 with same frequency.

Needing something to sit on while in front of the DCX2496 I moved an speaker that isn’t even connected or even in any use what so ever and while looking at the display outputs on the Alesis RA300 my hand just wondered down to the bass mid driver on the AWIA speaker and while I pressed gently on the driver I noticed the 100Hz sine wave pitch rising?

I did a few more test by placing the SPL db meter close to the driver on the AWIA set the SPL for 0db doesn’t matter what the level was it was 80db okay, but that is neither here or there. Pressing down on the driver again I noticed a +3db rise now that is weird, I could feel the vibration on the AWIA bass mid driver while resting my fingertips on the driver.

So what does this mean because I’m totally baffled LOL.

[JBL 4645]

Oh, evening Heather

No its open just laying on the floor. I hope you didn’t misunderstand me, it’s not connected up its just something to sit on while I face the unit DCX2496 the sound is only coming from the JBL LCR and I did a few tests. I removed the grill to each one of the left and right and only the centre was playing the 100Hz size wave. I pressed gently on the right and I noticed the pitched again went up?

It’s has if the sound is bouncing around the room, (obviously) and since something is its way and little tiny bit of fingertip pressure applied simply changed the SPL db level, weird LOL??

I’m allergic to fibreglass one due to be skin conduction, something other maybe?

So the AWIA is neither hare or there I even tried the large sub bass while only the centre channel was outputting the 100Hz, anyway I’m not going to worry about it too much, just find it strange that’s all?

[Andyoz]

I suspect the new kitten may have something to do with this.

I don't trust the look of him/her....

:)

[JBL 4645]

I suspect the new kitten may have something to do with this.

I don't trust the look of him/her....

:)

Evening Andyoz

LOL well it does have a slight tendency to bite when playing with it. But I’m afraid kitten, wasn't present in the room this evening its been playing in the hallway and bedroom.

I’m just puzzled as to why? I have a theory maybe its like how Heather put it, the sound is passing though the enclosure and pressing down on the bass mid driver somehow shifts the tone upwards by a few db in close proximity.

Anyway I’m not going to dwell on it too much, unless someone else has a theory? Or maybe someone else could try this out and see what you make it.

[boputnam]

Bingo - its the harmonic resonance of that speaker cabinet ... Actually, the undriven cabinet was acting as a passive radiator. The woof would naturally respond to whatever frequency was being generated, irrespective of cabinet tuning.

[JBL 4645]

Actually, the undriven cabinet was acting as a passive radiator. The woof would naturally respond to whatever frequency was being generated, irrespective of cabinet tuning.

bop hello there

I see passive because there is no active power going though it. Does this have some advantages for practical use?