Does Speaker Grill Cloth affect port behaviour?

[stv]

The lower peak is reduced as you add more grille cloth.

That could actually be a good thing

yes - but unfortunately the cloth also raises the bottom of the "valley" between the two peaks which shows the reduction of Q of the resonator.
So the efficiency of the resonator is reduced by the cloth.

I quickly replicated the impedance change in hornresp ...



resulting response change:



reduction of port output by ~ 2 dB in simulation.
I would need to confirm this by response measurements - but not today!

EDIT:
.... and cone displacement simulation:

 

[weltersys]

This is the impedance measurement taken at 0.5 V rms and with 8 Ohm series resistance.
without cloth, with one sheet and (for confirmation of its effect) two and four sheets of speaker grille cloth:

The cloth appears to reduce the lower impedance peak by 2 ohms at 0.5V.

When driving the speaker at Fb and slightly higher levels (4 V in my case) the cloth is moving quite a lot and starts to slap against the baffle.

What is the impedance change at 4V?

This happened because I simply wrapped the cloth around the speaker. Anyhow, the cloth moves A LOT with the air of the port. The cloth did not create any audible hiss/noise, as I would have expected. Not at lower levels before the slapping noise was predominant, at least. At higher levels the air flow is affected and I would generally not advise to use grille cloth near the opening of a port - let alone inside the port!

I'll admit I've never left less than 18mm clearance between the port and grill cloth, nor used that tight of a cloth weave when testing with and without grill.
Haven't seen the grills moving much at all until the driver's surround slapped into it, indicating Xmax had been exceeded by a few mm 😉

I quickly replicated the impedance change in hornresp ...

Looks more like 3 ohm difference than 2 ohms.

reduction of port output by ~ 2 dB in simulation.

Or perhaps 1.33dB if the impedance change were equal.
I wonder if a flat alignment (equal impedance peaks either side of Fb) would exhibit the same "Q" damping.

I would need to confirm this by response measurements - but not today!

When you get around to response measurements, I'd find it interesting to determine if the reductions are linear with drive level, and how they vary with the proximity of the cloth to the port, and if a more open weave like Acoustone FR410 would change the results.

Thanks for the tests!

Art