To recess or not to recess

[AntM]

Can anyone give an explanation of the advantages of recessing the tweeter to that there is not step at the edge of the faceplate. I read somewhere that diffractions set up standing waves that can cause response ripple.

I have a morel MDT32S tweeter and it is just screwed onto the baffle (no recess). I have been pretty disappointed with the sound as there appears to be a resonance. I wondered if this was related to not recessing the driver (I noticed a similar problem with my old seas tweeter, and have so replaced the tweeter, amp an loudspeaker cables in an attempt to find the source of the problem!!)

I guess I could test the theory by placing some cardboard around the faceplate to reduce the step.

Regards

 

[simon5]

There's two schools on this issue.

One is you recess tweeter to have a phase/time accurate speaker.

Second is :

Aim for a reasonably smooth frequency and impulse response, and take steps to eliminate any reflections from the front of the cabinet or from the interior surfaces. Reflections are much more audible, and much more unpleasant, than you’d imagine from looking at the little wiggles they make in the frequency response curves. On the inside of the cabinet, intelligent use of felt (85% wool) and Deflex pads can usefully damp reflections. On the outside, never put the driver in any kind of cavity, since even the best felt absorber has only a modest absorption capability. It’s far better to mount the faceplate precisely flush with the front panel and radius the cabinet edges if at all possible.

http://www.nutshellhifi.com/library/speaker-design1.html

 

[AntM]

Is there any software that can model edge effects? I'm already using the Passive Crossover Designer excell spreadsheet, which tells me the effects of the time-alignment, but it does not include the edge effect.

given the faceplate radius is, say 5cm, this wavelength corresponding to a frequency of 6.4kHz, would I expect a peak at around this frequency?


Any help gratefully received.

 

[morbo]

You recess both drivers to avoid diffraction, unless they are designed to be surface mounted. Have a look at this:

http://www.zaphaudio.com/mtg-surface.html

 

[AntM]

Great link!
Looks like an additional thick cardboard faceplace is the solution (at least to test the theory) as my scissor skills are great, but my woodworking skills didn't develop since the age of 3!