Replacing driver screws with brass screws

In a properly designed speaker, the drivers will not be fixed to the cabinet with wood screws.  Obviously these will work loose very quickly because of the vibrations of the driver.
They should be fixed with bolts running right through the cabinet wall and held in place by locked nuts that cannot unscrew.
They should be torqued up very tightly to ensure that the cabinet wall and gasket material are compressed as far as possible to minimise any looseness that may be caused by future compression.
Gasket should be as thin as possible to minimise variable compression.
Not rocket science, just sensible and simple engineering.

MC, yes for our purpose, call it "rattle". If it's tight, (driver to cabinet) it is as ONE... If you listen with a scope say 2" from the screwface, note that tone and THAT SPOT (need to mark your measurement spots)
Torque, and listen.. If there is a "Rattle", that's real bad. The two pieces are NOT bound one to the other. Torqued properly...Recheck for TONE. Kinda see the difference?

We don't want a "given amount of movement" between the two pieces.
EX: Head to block, they move....

"No movement torque"...different kind of torque spec. This is the engineers job.... Not the mechanic... BUT, we'll fix it anyway. 

I'm not trying to come off as a "SQUINT" OK!!! Get to "squinty"
I can't keep up. :-)
  
We are looking to TUNE each securement to the same tone, via ear.
I suppose you could measure it pretty easy, if you need to, (for the measurement crowd). Then move your scope (pickup) over the securement. I TRY to get them all the same (tone) 2-4-6" away.
I try to TUNE/Torque so I don't have to do it again.

The above method will show you how BAD Big Box store 11-15 plywood really is..  HUGE voids... (internal wood rattle).  It will DRIVE you nuts, kind of noise. HARD to fix outside and look good, kind of NUTS... :-(

If you have a breakin (tone gen) for say 24-36 hours, recheck your securements. I've done it so many times, I can still hand torque to within 10 inch lbs of torque. Then see if it holds. It always does NOW..
If they come loose (never have), they NEVER come loose again. Silicone/thread locker/JB weld/binding head SS lock washers/nylock nuts/pinch nuts!!!

I use a (2-3) stage CROSS pattern torque too. 

OR Torque to tone if YOU want to. You know, learn something. :-)

MDF is easy to OVER torque... If it's too tight, it will warp the speaker rim and or pull the threads... If it's to loose, it will come loose again and pull the threads. When it's torqued RIGHT, and the screw HEAD is bound, it CAN'T move. If you can't get it tight enough, Half moon hardwood backers for the bass drivers. 3/8" thick 1-2" wide. Oak or Apatong. 60-160.00 usd PER driver.

Load 20 BASS drivers, gets spendy. You can make your own.  20.00 for 8", 30.00 for a 12", 1/2 red oak. few tools..

Regards

Another word of caution against over-tightening of drive units.  

Don't do it.

As mentioned earlier it alters the tone, but it does more than that, it alters the amount of resonance pumped into the baffle. Since the baffle due to the cutouts is normally the weakest part of the cabinet, you certainly don't want more resonances there. 

With large drivers the issue becomes paramount.

Some, like Harbeth only recommend finger tight, and I tend to agree.

Over-tightening in my experience often results in an uptight and dynamically constrained sound. 

For sure there are better ways of attaching drive units to the baffle, but they are all more time consuming and more expensive to implement than simple wood screws.

Here's what Siegfried Linkwitz had to say on the subject.


Mounting a driver to a baffle

'Typically a loudspeaker driver has screw holes in its basket for mounting it to a baffle. Usually a sealing gasket is placed between the driver basket rim and the baffle. The driver becomes in effect stiffly clamped to the baffle.

This method sets up a mechanically resonant structure which is formed by the compliance of the basket and the mass of the magnet...

A) Drivers with a stamped metal baskets are prone to exhibit a high Q resonance when tightly clamped to the baffle. The magnet moves relative to the voice coil at the resonance frequency. Energy is stored and also readily transmitted from the moving mass of the cone into the cabinet.

B) Soft mounting the driver basket to the baffle using rubber grommets reduces the resonance frequency. A 2nd order lowpass filter is formed that reduces the transmission of vibration energy from the moving cone to the baffle and cabinet. The resonance must occur below the operating range of the driver.

C) If the driver is mounted from the magnet and the basket rim touches the baffle only softly, then the magnet-basket resonance cannot occur and the transmission of vibration energy into the baffle is minimized. The basket-magnet resonance can be measured with an accelerometer that is mounted to the magnet.

The drive signal is optimally a shaped toneburst.

Its energy is concentrated in a narrow frequency band. When tuned to the right frequency a long decay tail becomes visible on an oscilloscope. Often the resonance can be seen as a small bump in the driver's impedance curve in the few hundred Hz range. It should not be confused with the higher frequency bump due to cone breakup.

An early example of a box loudspeaker where a KEF B110 midrange/woofer driver magnet is clamped to a support structure. The clamp can be tightened from the outside of the box. The basket rim is floating.

Often the effects due to driver mounting are deemed to be of secondary importance to the overall sound quality of a loudspeaker. They are usually costly to remedy. They cannot be ignored when the goal is to design a loudspeaker of the highest accuracy.

http://www.linkwitzlab.com/frontiers_2.htm#N

I read this discussion with great interest. So I just checked my Revel Salon 2's. Yep, little black screws! What a cheap way to finish off a pretty good speaker.