[Bumpy]

If I tap my baffles with my knuckles I can hear a corresponding 'echo' from the diaphragm of the midrange driver. Dont like this, but what is it indicating.

[richidoo]

The diaphragm is intended to move, so no biggie. It just displays a lack of mechanical damping in the driver suspension. That can be a good thing, translating to more detail if the amp can make up for the lesser mechanical damping with electrical damping. The driver's Qm spec will be higher than other drivers with more mechanical damping.

It should move much less when you have the amp powered on with no signal. The amp will provide electrical damping to control the cone. Since suspension loading is at a minimum with no signal, damping should be at maximum with no signal.

Lots of series resistors in the crossover filter will reduce the amp's ability to control the driver.

[Bumpy]

The diaphragm is intended to move, so no biggie. It just displays a lack of mechanical damping in the driver suspension. That can be a good thing, translating to more detail if the amp can make up for the lesser mechanical damping with electrical damping. The driver's Qm spec will be higher than other drivers with more mechanical damping.

It should move much less when you have the amp powered on with no signal. The amp will provide electrical damping to control the cone. Since suspension loading is at a minimum with no signal, damping should be at maximum with no signal.

Lots of series resistors in the crossover filter will reduce the amp's ability to control the driver.

Thanks, that’s an angle I had not considered. My test was certainly with the amp off, and I will try later with it on 👍

[sfdoddsy]

It's indicating that your baffles and driver are resonating at that frequency.

Whether that resonation is audible will depend on whether the mid-range driver is playing at that frequency, and whether it excites the baffle as much as your knuckle.

I suspect not.

If you have measurement equipment, just do a sweep as is, and then another one with your hand gripping the baffle (flesh is a great dampener).

If there is no difference, don't worry.

If there is a measurable difference, see if you can hear it.

I spent years trying different dampening techniques on my OBs, only to discover that when I put it to the test I couldn't hear or measure a difference .

[Bumpy]

I’ve stood the whole speaker on a shock absorbing mat and the knuckle effect is reduced considerably. I guess this has changed the resonance of the baffle. Sounds better too. 

I’m thinking of isolating the mid driver from the panel. The aim is not to screw it to the baffle, but to either hang it by its magnet on a sound isolated blacket or by four springs as seen in the old microphones.


https://www.audiochocolate.com.au/wp-content/uploads/2014/07/Ear-Trumpet-Labs-Louise-Mic.jpg

[Tyson]

I like to use a combo of very strong baffle and then cover the back side with NoRez. 

[JLM]

You are witnessing conservation of momentum.  The baffle being unbraced will behave like a springboard (cantilever) when tapped and the mass of the driver diaphragm plus air next to the baffle will naturally counter react to try conserving the momentum.  When playing music the baffle is likewise moving to counter the momentum of the driver(s).  Note that this goes against the whole concept of the baffle being completely inert, which open baffles are inherently poor at.

Deadening the baffle (by increasing mass, changing materials, or as you did by dampening the support) would reduce this effect.  But dampening the support could also lead to further dampening the physical performance of the driver(s) beyond what the springboard effect of the open baffle already does.  Again it's conservation of momentum.  With a spring loaded driver it would be matter of the diaphragm mass versus the driver frame/magnet mass.  Note that use of gasket material is used to acoustically seal or seat the driver to the baffle, not dampen it per se.

[gab]

I’m thinking of isolating the mid driver from the panel. The aim is not to screw it to the baffle, but to either hang it by its magnet on a sound isolated blacket or by four springs as seen in the old microphones.

one solution here:

http://www.linkwitzlab.com/orion-rev1.htm

[HAL]

Another option to the NoRez if you do not need the foam. is something like Dynamat or CAE VB-2 or other constrained layer damping material. 

Does not have to be very thick to damp the baffle vibration to a lower level. 

[Bumpy]

I found this innovative company Art Audio in Canada that mounts its drivers conventionally, then tunes any baffle resonances by applying pressure with thumbscrews to the rear of the drivers. Any comments?

https://www.youtube.com/watch?v=Z0Hd39GMdg0