A weird tweeter - the Motus UH25CT1

dcibel

I splurged on a pair of these that were recently available on the PETT classifieds. A rare find and I decided to jump on them simply due to what I've seen of Motus Woofers - their measurements in AudioXpress show them to be of the best available at any price IMO.

These tweeters have a large 5" flange instead of the usual 4", and the plate is very clean, no extra screws holding the tweeter in place through the front of the flange which I really like. The first thing I noticed when I got them is how light they were, much lighter than anticipated, but then I remembered they were advertised as a neodymium motor, not ferrite.

Why so big if it's a neo tweeter? My curiosity got the best of me, so I cracked open the case. The flange and rear chamber by the way are very nice cast aluminum peices. Inside I found some very soft feathery material, and lots of it. A small and very well ventilated neo motor was inside. Essentially this tweeter could very well be a small flange neo, but Motus opted to give it a huge damped chamber instead. I guess I can't complain about that.

For those interested, heres the datasheet:
http://nedlab.com/wp/wp-content/uploads/2014/06/UH25CT1-tweeter.pdf

And here's a Google Photo album with some shots of it. I really should have dusted off the dome before taking pictures. The dome looks similar to my HDS tweeters, almost transparent.
https://photos.app.goo.gl/rwe4MYSyXFyebCPl1

dcibel

The way these are constructed should make it very easy to replace the nice cast aluminum plate with a waveguide...gives me something to think about.

Wolf

I have to admit I was elated when I saw the ad, and then disappointed when I saw they were gone already.

A waveguide would likely flatten the curve, but I don't know how much. I see an impedance ripple at just below 2K, but the HD is -40dB at 1k/1W, and the response is smooth and the Fs well damped.

dcibel

I was glad to find that the seller was Canadian as well, so the price was very good since shipping was dirt cheap. I just thought I'd share some detail of their unconventional construction. I'd like to see more manufacturers make them like this, using a thicker face plate so you can screw the tweeter in from behind and hide the screws.

I found some old issue of Voice Coil (Dec 2012) where these were tested. Unfortunately the distortion test resolution is very poor, not like their recent measurements. They tested quite well, not the best dome in the world but I don't think I'll have any problems using them as low as the frequency response permits.

Wolf

The Old TB 25-1743 and the textile sibling both screwed together from behind. The 1743 is a nice unit!

dcibel

It just looks so much cleaner. I looked up that TB tweeter, looks like the faceplate has a bulge outwards, so it is not a flat face and requires no more of a counterbore than most other tweeters. This Motus unit has a 6mm face which is pretty bulky.

dcibel

This tweeter is a bit small for the 38mm throat of the Visaton WG148, but I think it might work pretty well anyway. Since the faceplate is flat, I just held the waveguide on with clamps. The round edge of the faceplate comes right up to the edge of the waveguide, so it doesn't look super out of place visually.