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Re: Yes, I think that concept's full of holes ... :-))

Hi lne937s,

Great post ... thanks! :-))

I'm now at the stage with my IIIas that "improving" the frame is about all that's left to me! :-)) So I was very interested in your comments about vibration and how to deal with it.

However, I think that the key point wrt vibration in Maggie frames is not whether this vibration is causing the frame to emit noise of some frequency (like vibrating box speaker sides can) but, rather, does the Maggie frame material help to damp the vibrations which are occurring in the panel driver assembly (and generated by the mylar flapping)?

As you probably know, the IIIa (and its successors) have a bass/mid driver assembly which sits in a big rectangular rebated hole in the MDF frame and then a long ribbon "cage" which sits in a ribbon slot, between the mid side of the panel and the edge of the frame. Consequently, there is a thin strip of MDF between the ribbon "cage" and the bass/mid driver assembly.

Now, re. MDF ... are you sure that MDF has "a fairly random fibre structure" and so is actually quite well damped? I thought MDF was mostly sawdust in a glue matrix ... so something made of particles/'chunks' of wood (like flooring-grade particle board) would be a much more damped material, due to the sizeable chunks of wood in the glue matrix??

Or am I confused here?

I suspect there are slightly different problems to be solved in a 2-way Maggie (which consists of a single sheet of mylar with two separate drivers on it, surrounded by the frame) and a 3-way Maggie which has 2 physically separate drivers and a narrow strip of frame between the bass/mid driver assembly and the ribbon "cage".

In a 3-way Maggie, the important thing IMO is to reduce the vibrational effect which the bass/mid driver has on the ribbon "cage".

The inside edge of bass/mid driver assembly vibrates ... this causes the thin strip of frame to vibrate and this causes the ribbon cage to vibrate. Which is not good ... if I sit and listen in the almost-dark, I can see the ribbon "shimmer" when loud bass transients occur.

In other words, it's not the "sound" which this vibrating MDF frame makes which is important (you commented about whether the MDF vibrations "sounded" natural?) ... the issue is, is the frame transferring vibrations from one driver to another!!?? :-))

The only way I can see to minimise this transfer of vibration from the bass/mid driver assembly to the ribbon cage is to make a long vertical sawcut along the inside edge of the inner ribbon cage flange ... to physically separate most of the length of MDF which supports the ribbon cage, from the MDF which surrounds the bass/mid driver assembly. This IMO *must* be more effective than changing the frame material?

Do you agree ... or again, am I confused? :-))

However, wrt the frame material, can you comment on what is likely to be the more vibrationally inert material?

1. MDF vs. flooring-grade chipboard (aka "particle board") ... due to the sizeable particles of wood which are in the flooring, compared to the "dust" in MDF?

2. MDF (or flooring-grade chipboard ... whichever is the one you specify in 1. above) with a CF skin bonded either side vs. the same core but having CF on one side with lead sheet on the other side? This adds weight but sacrifies stiffness!

Regards,

Andy



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