Coaxially 'mounting' a tweeter in front of a midrange

[ErinH]

I'm currently running 3-way fronts in my car (midbass in kicks, midrange in pillar, tweeter in stock locations at far corners of dash).

Last year I had mounted a tweeter above a 3.5" midrange in the pillars and had excellent results. I wound up wanting to try a 4" "fullrange" driver and while it's nice... it's just not as 'fullrange' as I had hoped so I put a tweeter in the car to help the top a bit.

Now I'm doing a new install and am going back to pairing the tweeter with the mid for a multitude of reasons; namely less comb filtering and better physical alignment. I'll be going on axis to some large degree; at most the drivers will be 15* off axis.

The problem is space in the pillar.
I'm not sure if I'll be able to get the tweeter physically above the midrange I use, as the midranges I'm considering are a tad bit larger than the one I used last year. I'm in no rush to do the install just yet, but I am trying to get some ideas going on what I can do.

The tweeter will be a 3/4" dome; possibly this vifa ox20. It might be another 3/4" dome from scan that I have filed the flange down on.
The midrange is undecided just yet but I'm down to 3 and all are in the ~ 4" OD range.

I'm considering trying to coaxially mount a tweeter in front of the midrange. As it stands, the midrange will be crossed NO higher than 4khz due to falling polar response above this point. I'm thinking if I cross at 4khz, and keep the tweeter close to the cone, I should be fine regarding reflections off the tweeter and back in to the cone... I think. If I mount the tweeter 0.25" off the cone that gives me a frequency of 27khz before the first reflection comes back... or no? I'm trying to envision this, so I'd appreciate help with this.
The midrange I use should still be under beaming at this frequency. I would think this would help keep the tweeter from mucking things up.

The only real drawbacks I can see to mounting a tweeter like this is the fact that the sound physically comes from the tweeter in front of the midrange, but I'll have DSP available to phase align the tweeter and level match it to the mid.

As far as how I'm going to mount the tweeter coaxially, should I go this route, I'll figure something out. A coat hanger wire just may be the trick.


I hope that helps give you guys an inkling as to what I'm wanting to do and the answers I'm trying to resolve. Any input would be appreciated.

Thanks,
Erin

[ErinH]

Any input?

[carlspeak]

KEF's been doing that for some time now with their Uni-Q designs. Some pics would help of what you had in mind. KEF buries the tweeter at the base of the mid. Hanging a tweeter in front of a mid should create all kinds of issues with the mid's response, shouldn't it?