Visaton WG 148 R waveguide and the Dayton RS-28A issues

[fjhuerta]

Hello all, I think I'm having some issues with my RS-28A tweeters and a Visaton W 148 R....

I installed the waveguide on the tweeter without much issues. I then added some foam between the waveguide and the faceplate, since there was a gap between them.




It looks good, so I didn't expect any issues. But, on axis, I have this weird FR. Look at the major drop at 4KHz.



Both tweeters measure exactly the same.

With a very weird crossover, I can make the RS-28 behave on a 2 KHz, 2nd order L-R crossover. This is at about 50 deg, with the crossover filter.



On axis, though, I obviously get that strange artifact at 4 KHz.



I have no clue as to how to fix this artifact, or if it is a result of the waveguide + tweeter's geometry, and something that can't be avoided.

Any help or ideas on how to fix this (or whether not to care about it!) would be appreciated!

[DeZZar]

How do they measure without the wave guide?

[fjhuerta]

How do they measure without the wave guide?

Pretty much as the PDF states they should.

I just did something irreversible. I disassembled the entire tweeter, and took out the mesh. It seems it was hitting the border of the waveguide, and there was a gap I couldn't fix with putty, silicone, etc.

So, I took out the faceplate, removed the mesh and glued with epoxy the plate that holds the dome and the terminals to the magnet. Then I glued the entire assembly to the waveguide. Everything now sits perfectly flush.

The change is permanent, so this should better fix my issue.. or else I just wasted a pair of waveguides and new old stock RS28s.

I'll wait until tomorrow to let the epoxy set and measure everything again.

[Billet]

If it sounds good, it is good! If not, well then back to the drawing board...

[DeZZar]

What was the waveguide intended for here? Just curious because the tweeter should already be happy to cross fairly low and appears to be pretty well behaved through to 45 off axis and sufficiently sensitive? Something to do with diffraction?

[fjhuerta]

What was the waveguide intended for here? Just curious because the tweeter should already be happy to cross fairly low and appears to be pretty well behaved through to 45 off axis and sufficiently sensitive? Something to do with diffraction?

Diffraction, and I wanted to experiment with a way to get a better power response while combined with common 7" / 8" woofers. My latest comercial speakers were a set of Revels with waveguides. I want to get as close to their sound as possible.

[DeZZar]

The Revels use a much less aggressive looking waveguide. Based purely on your images the waveguide you have has a fairly distinct short "throat" with a much steeper angle that then transitions aggressively to a wider flatter surround - which in this case significantly exaggerates the 1-3K response. The revels appear to have a far more linear gentle shape.

In any case I personally wouldn't consider the waveguide to provide any benefit here. You end up with nearly 10db difference between the output at 3K and 5K - that's double the volume from a perception point of view - if I saw a tweeter like that I'd avoid and move on to another candidate. It had a good smooth response without the waveguide - but with it you need a bunch of crossover parts to wrangle it back to reasonable - that has to lead you to asking why?

Revel is likely using their waveguides because it actually benefits their tweeter and its integration with the rest of the system...

[fjhuerta]

When using the waveguide, and re-contouring the curve, I'll drop the response by 10 dB in the lower end, and thus, distortion. That's the first benefit. The second one I want to explore is off-axis response, I'd like to find out if waveguides can help me with directivity. The third one is diffraction. I've had some major issues with it and my cabinets.

I've only used the Seas DXT waveguide before and I liked it. I'd definitely like to explore this waveguide thing more... every speaker I've built doesn't have one. I want to understand why people like them so much.

And anyway, it's impossible for me to return the RS28s to normal now. I'll have to measure It tomorrow. I hope response is back to something sane.

[jhollander]

Did you have the waveguide mounted in the a baffle when you measured? If you have a piece of cardboard flush mount the driver in the cardboard and use packing tape on the front to hold it flush.

[fjhuerta]

Did you have the waveguide mounted in the a baffle when you measured? If you have a piece of cardboard flush mount the driver in the cardboard and use packing tape on the front to hold it flush.

No.. I didn't. I assumed since the waveguide rendered diffraction moot, baffles were unnecessary. I'll try this again - with a baffle. Thanks for your thoughts!

[rpb]

No.. I didn't. I assumed since the waveguide rendered diffraction moot, baffles were unnecessary. I'll try this again - with a baffle. Thanks for your thoughts!

Likely a reflection from whatever is behind the wave-guide is cancelling part of the frequencies. For a quick test you could get someone to hold it from behind at arms length, and remeasure. As John suggested, it will change a little when placed on a baffle.

[JamesTan]

And anyway, it's impossible for me to return the RS28s to normal now. I'll have to measure It tomorrow. I hope response is back to something sane.

I understand this thread was started more than 1 year ago but really interested to know what is the outcome from your new measurements.