damping material for midrange glare

[PreSapian]

heres the story. i have a pair of Jim Holtz's Statement Monitors that is of open back dipole design. i was tweaking with the midrange tunnel yesterday by taking out the acoustic foam and layering in cork sheets. this killed the high frequency ringing and opened up the tunnels enough to make the speakers sound almost like a open baffle. but the midrange glare was becoming too obvious after several songs to be fatiguing. adding back in the acoustic foam tames the midrange glare but this subsequently reduces the dipole effect. i spent all day yesterday trying to find the right amount of foam to maintain a balance between tamed midrange and the 'wow' factor of the dipole. ended up going to sleep at 1 a.m. , groggy eyed and unsatisfied. i think the solution could be with a new damping material that i could try from your suggestions. please let me know. cheers.

[CLS]

Don't know that speaker, but I saw 'tunnel' and 'foam', is that transmission line instead?

[Mike Gergen]

I've been going to Goodwill and purchasing old wool sweaters. Cut them into pieces and use for filler.

[ScottG]

Originally Posted by PreSapian

heres the story. i have a pair of Jim Holtz's Statement Monitors that is of open back dipole design. i was tweaking with the midrange tunnel yesterday by taking out the acoustic foam and layering in cork sheets. this killed the high frequency ringing and opened up the tunnels enough to make the speakers sound almost like a open baffle. but the midrange glare was becoming too obvious after several songs to be fatiguing. adding back in the acoustic foam tames the midrange glare but this subsequently reduces the dipole effect. i spent all day yesterday trying to find the right amount of foam to maintain a balance between tamed midrange and the 'wow' factor of the dipole. ended up going to sleep at 1 a.m. , groggy eyed and unsatisfied. i think the solution could be with a new damping material that i could try from your suggestions. please let me know. cheers.

Is the "glare" a pipe resonance (rear of the speaker) or is it a reflection/and/or resonance (transmitting through the cone)?

If its the former then consider damping just the exit of the "pipe".

If its the latter consider making the pipe into an expansion line.

[John_E_Janowitz]

Midrange "glare" is also often a function of flux modulation and non-linear inductance in the driver. If it becomes more evident at higher output levels, this is generally a good indication it is in the driver. If this is the case, nothing you can do to the cabinet will fix it. Also a lot of what you will hear can be seen as something irregular in an impedance curve. Measure a curve with the driver both in and out of the cabinet. You can tell a lot by comparing those 2 curves.

John

[PreSapian]

haha. sorry. transmission line is what i forgot to say. the glare turned out to be from the vinyl damping sheets that i had layered over the chinese birch. taking that off got rid the glare and made the sound overly warm (which i liked) but also killed off detail and imaging. at 2 a.m. this morning i found the best compromise between half vinyl and half cork sheet, cut into 8 pieces and layered in alternating pattern. listening to them then, i thought, yes, these will be the speakers that i pass down to my grandkids. cheers.