Baffle construction question

[Christof]

I'm playing around with different baffle construction methods and would like to ask the pros/cons of this method:

Given 1.25" total thickness comprised of 0.75" mdf + 0.5"mdf. with bitumen layer between. What effect will there be if I sink the driver 0.5" deep into the baffle with a roundover going from the face of the driver frame to the baffle face. For example if the rebate needed to flush mount is 1/4" deep what happens if I cut it 3/4" deep and roundover the upper 1/2"?

Make any sense?

thanks C.

[caratje]

Hi Christof,

Talking about constructions without pictures is pretty difficult, but I am not going to make pictures either way...

To start with, I don't have that much theoretical nor experimental experience, but I read a lot and with my physics background, I think I can answer your question pretty well. So it is up to you to make up your mind!!!

First of all, I am not going to talk about the phase off-set you might introduce, because this is totally depending on your filter. And then you can use this as an additional parameter to tune or be further away from what you modelled.

Next to that, my impression is that there is a significant difference between tweeters and woofers with respect to your question. Basically it is related to the actual wave length the unit is going to make (but also the construction, for most woofers the moving parts are very close to the other edge of the unit).

So let me dive into the worst case situation, waves with the size in the range as large as the unit / width of the baffle!!! At this frequency range the speaker is acting in between a point-source and a flat-surface wave source. I don't know how to explain it in details, but the rolling off behaviour (radiation like the sun shining throught a big window versus a point source like the traditional lightbulb in my old bike) is very important. What is best? My feeling says (and most physics rules too) it has to be smooth over the frequency domain, so try to avoid turbulencies due to unflatness. Therefor I think it is best to build in woofers units with a depth equal to thickness of the front plate of the unit.

About how to make the hole look like from the back side? It should be stiff, but also smooth and open. Somewhere I saw a nice design based on 45 Degrees, but he also adjusted the bracing.

But to be totally open and fair to you, I don't know how much you will hear any of the ideas I descripted above. So depending on the time, balance looks/sound, wood-skills, I would pick something that best fits your needs!!!

Good luck,

Joep

[wintermute]

Hi Christof,

I tried this with my tweeter. The result was a very broad dip in response (of about 4-5db) centered around 5Khz.

It may not be an issue with the lower frequencies of a woofer, but I would guess that time delays between your woofer and tweeter would be more of an issue.

The reason I was recessing my tweeter was to compensate for time delay, however the anomaly in the response has made me reconsider doing that.

In General you will want your woofer further forward than your tweeter, pulling it back will only make time alignment harder (unless you come so far back that the tweeter and woofer are 180 deg out of phase, in which case you could just reverse the polarity of your tweeter

Tony.

edit: the recess for this tweeter was made off published diameter, which as you can see is actually not the true diameter