waveguide for dome tweeter?

hi guys. I know this has probably been asked in some form or another before, but ill ask anyway.

to start at the beginning, i am planning to make a 'waveguide' for a dome tweeter im using with a 5" driver i have a few of.

The waveguide will, as closely as my manual skills allow, follow the diameter and cone profile of the woofer. The aim being to align the acoustic centres of both drivers, in the depth dimension, and also hopefully as a result of the cone profile, shape the polar response of the dome tweeter to be more akin to that of the woofer.

this may be a simplistic way of viewing things but it is only as yet an experiment. dims will be: dia = 90-100mm and depth 10-15mm with a roughly conical profile as the woofer cone, although curved is very close to conical. Alternatively, a rectangular guide may tried too, similar dims, but with a more horn like curved profile.

can anyone advise if there are any glaring omissions here, or any problems/difficulties with what im planning?
 
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cnclld

Member
2005-01-21 1:03 pm
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Soft domes may cause problems with waveguides but I don't think it is caused by pressure on the dome. Soft domes have always bending modes in their pass band, so their movement is not fully pistonic. Different areas of the dome radiating not in phase with each other can cause problems with coupling to the waveguide. Soft domes have also typically much higher shape than metal domes, which could be a problem as well.

A waveguide with the same diameter as the woofer is close to optimum at low frequencies. The profile of a curved cone might work fine as a waveguide, but does not offer any essential benefits. The optimum cone profile is not likely to be the optimum waveguide profile and vice versa. Most important things would be to make smooth transitions from tweeter to the waveguide and from the waveguide to the front baffle to avoid diffraction.
 
Actually, a 5" driver is about 12,7 cm so that would be about 344/0.13 = 2 646 Hz.

Take a look at this tutorial:

Practical DIY Waveguide

well i took the cone diameter measurement, not the total including surround, perhaps my mistake there. good link though.

Zaph|Audio

Hi, worth reading for general and c/o details, rgds, sreten.

AHHHHHH i forgot about Zaphs page! I knew id seen something like this SOMEWHERE before...thanks for the pointer in the right direction.

I took a stab at this some time back. Visit here and download my report. There's links to Zaph's effort as well as others included in the document.

Revitalizing the AR 3/4 inch tweeter using a waveguide - The Classic Speaker Pages Discussion Forums

again, thanks for the link

Soft domes may cause problems with waveguides but I don't think it is caused by pressure on the dome. Soft domes have always bending modes in their pass band, so their movement is not fully pistonic. Different areas of the dome radiating not in phase with each other can cause problems with coupling to the waveguide. Soft domes have also typically much higher shape than metal domes, which could be a problem as well.

A waveguide with the same diameter as the woofer is close to optimum at low frequencies. The profile of a curved cone might work fine as a waveguide, but does not offer any essential benefits. The optimum cone profile is not likely to be the optimum waveguide profile and vice versa. Most important things would be to make smooth transitions from tweeter to the waveguide and from the waveguide to the front baffle to avoid diffraction.

Thats great, lots of useful info facts and opinions here. |I didnt think i d get such a great response. Thanks guys!
 
following the advice of many, a cheap experiment ensued

having ten minutes to spare the other day, and having found a large lump of plasticine, i mostly out of boredom, made a small doughnut. inside diameter roughly matching the dome and surround diameter of the tweeter i have lying around, and the doughnut thickness of about 1". I pressed this onto the faceplate of the dome tweeter, and using a flat surface, compressed the doughnut ring a little.

making a small plasticine waveguide of sorts.

I have to confess that im completely thrown by the change to the tweeter. There is some gain around 3-6k i reckon, due to a slight emphasis on 'ch' sounds, but the integration of woofer tweeter seems better, and more coherent. At this point the depth offset is unchanged from the un-wave-guided tweeter, so it is not better time alignment per se, maybe phase is better, or the dome tweeter polar response is matched better to that of the woofer?

any opinions?

at this point im sure theyres a positive effect, especially when the gain is compensated for in the xover, but im struggling to pin point what else has changed :confused:

can my poor attempt at a waveguide really IMPROVE a tweeter???
 
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