XT25TG30 Testing with Waveguides

[davepellegrene]

I'm using the plexiglass waveguides I'm making. This style is designed to fit my baffle that has the sides sloping in at the top 7 Degrees and the bottom is designed to cut out to fit the RS150.

I made three versions basically all the same except for the throat. After looking at the Raal tweeters with the way they have the face plate toothed I thought I'd see if I could figure out what that did.

Here are my guides. I put a strip of weather stripping on the back side to help with balancing them on the tweeter without having to attach them.

Guide P


Guide Q. The guide sits down into the face plate as it does on WG P except I cut teeth into the guide.


Guide Q1. This sits on top of the face plate holding the teeth about an 1/8" above the surround.


Guide Q1 with teeth filed deeper into throat.


This is the flat baffle

Flat baffle 0,30,45


WG P 0,30,45


WG Q 0,30,45 Look how flat the top end is on axis from the teeth.


WG Q1


Looks like P and Q are the better of the three with Q loosing a little on the bottom end but smoother on the top end.

Flat Blue
P Red
Q Green
On axis


30 degrees


45 degrees


I'm liking Q the best. Seems the teeth help lift and flatten the top end out.

Dave

[[email protected]]

Re: XT25TG30 Testing with Waveguides

interesting dave.

[dlneubec]

Re: XT25TG30 Testing with Waveguides

Nice job, Dave. I like the Q looks and how it flattens the top end on and off axis.

BTW, I got the WG's you sent, but have not had a chance to do any measurements to date.

[edlafontaine]

Re: XT25TG30 Testing with Waveguides

Dave, I take your work to be very interesting. What is the ~spacing between the saw teeth?

I gather the Raal spacing to be ~6/inch

[TN Allen]

Re: XT25TG30 Testing with Waveguides

Would it be advantageous to continue the teeth out along the guide surface in a radial pattern? These could blend into the surface toward the mouth. This would increase the surface area without increasing the overall size and extend the effect of the teeth. I don't know if this would be advantageous but perhaps.

[cjd]

Re: XT25TG30 Testing with Waveguides

Would it be advantageous to continue the teeth out along the guide surface in a radial pattern? These could blend into the surface toward the mouth. This would increase the surface area without increasing the overall size and extend the effect of the teeth. I don't know if this would be advantageous but perhaps.

Almost all the impact seems to be near the interface between the tweeter (dome in this case) and the waveguide, from what I have found. I would surmise this is because they affect high frequencies specifically, and the narrowest part of the throat is where the most reflections end up causing trouble.

C

[davepellegrene]

Re: XT25TG30 Testing with Waveguides

Hey Dan, I wondered why I hadn't heard anything.

Ed,
On the Q guide I just took a file and gut grooves in the guide randomly. They very in spacing but average about every 1/8". This is the same guide as the P guide. After I saw that it had descent results I made the Q1 guide. On this one I made the hole smaller so the teeth would be in the path similar to what the Raal is. I also spaced them out just over an 1/8" and was more precise on making them even. I made a couple of rings varying from a 1/16" up to 3/8" thick and put them between the guide and the tweeter. The larger the spacer the larger the dip was in the upper octaves. The best result was putting the guide up against the face plate. Since the face plate is about an 1/8" thick with about a 45 degree bevel it still puts it an 1/8" away from the tweeter face. So it appears just putting the grooves in the side of the guide seems to work the best. I'm thinking it may be stopping reflections which in turn stops cancellation. This is just a guess. I also tried making a sprocket to press into the guide but it did not leave very deep ripples and did not have much effect.
TN,
Grooves up the sides may be an option but you need to be careful because it seems to effect the bottom end. I also tried a spiral tip to see what it would do. I think it just gave an effect that the surface wasn't smooth and caused a not so smooth response.

Dave

[ryanbouma]

Re: XT25TG30 Testing with Waveguides

Interesting you had postive results. I tried this just recently:



The changes were very mild and slightly worse. Having said that, I got a few comments that the notches were likely to small. The shape you have chosen is different also (teeth). I stopped there. Nice to see someone else try this and get results that appear to be an improvement.

[davepellegrene]

Re: XT25TG30 Testing with Waveguides

Interesting you had postive results. I tried this just recently:



The changes were very mild and slightly worse. Having said that, I got a few comments that the notches were likely to small. The shape you have chosen is different also (teeth). I stopped there. Nice to see someone else try this and get results that appear to be an improvement.

Once I realized the Q guide worked better I took my triangle file to the Q1 guide. It's hard to tell in the pick but the teeth in the Q1 guide are above the surround. In the Q guide the teeth are tight to the face plate of the tweeter. I filed the teeth deeper on the Q1 guide. By doing this it cut grooves into the throat and set the teeth back. In other words it made the opening larger so the teeth were not over top of the surround but more around it. I kept testing it as I went deeper and it slowly removed the dip in the upper octaves. It actually looks a little better then the Q guide on the axis measurement. The Q1 guide doesn't have the Knee at 10KHz that the Q guide has. I also noticed as I deepened the notches the lower end dropped over a db.
The measurements are on my other laptop. I'll post the results tonight when I get a chance.

Dave

[cjd]

Re: XT25TG30 Testing with Waveguides

Interesting you had postive results. I tried this just recently:

< image removed to keep post size down... look up >

The changes were very mild and slightly worse. Having said that, I got a few comments that the notches were likely to small. The shape you have chosen is different also (teeth). I stopped there. Nice to see someone else try this and get results that appear to be an improvement.

The interface between the tweeter and the waveguide start is very poor in this pic. Get some (wool, though even synthetic works) felt and make a gasket at the very least.

That aside, the reflections in yours are still going to be dictated primarily by the core throat diameter. I think I'm agreeing that your notches are too small, but also perhaps shape is playing a big role here still.

[ryanbouma]

Re: XT25TG30 Testing with Waveguides

That is probably just the photo. I might have only had the tweeter loosely attached even. I can't remember. The fit is fine. I also tried silicone for a seal and nothing changed at all. TNA also made some that had a custom ring to absolutely perfectly seal around the surround, again, barely any change. This waveguide also performs very well, without the notches. I may try bigger notches in the future. This was just and try and see without much thought. For now, there's to many waveguides to test, and not enough time.

You can see the background info here: http://techtalk.parts-express.com/sh...d.php?t=229031

Sorry for the highjack Dave. Nice waveguides by the way. I'm happy to see the XT25 does well. I had a hunch it did. Almost ordered one to find out.

[cjd]

Re: XT25TG30 Testing with Waveguides

I also noticed as I deepened the notches the lower end dropped over a db.

I'm also noticing that the notch in the upper frequencies also moves down - perhaps to 11k-14k or so, rather than 14k-18k (guessing at all these numbers...)

A 1/4" difference in diameter would do that, so some of this is probably not the notches, but the diameter change of the interface.

[davepellegrene]

Re: XT25TG30 Testing with Waveguides

A 1/4" difference in diameter would do that, so some of this is probably not the notches, but the diameter change of the interface.

That makes sense.
I hope to get to a point that I can look at the response and know what to do to the waveguide to manipulate it.

Dave

[davepellegrene]

Re: XT25TG30 Testing with Waveguides

I posted the Q1 waveguide filed up in my first post right under the pic of it not filed so you can see what I have done to it.

Here is a pic of it as well.


This is a comparison of it before and after filing. I took measurements a couple times as I was filing it and could see the response changing as I went along.
Original in red
Filed in green

On axis.


30 degrees. Notice how the bottom end has dropped a little.


45 Degrees. I'm assuming this is also better since the hump has been flattened out.


Dave

[davepellegrene]

Re: XT25TG30 Testing with Waveguides

This is WG Q red vs WG Q1 filed green on axis.


These were all taken yesterday with the same set up. I'll run another test section tonight to verify.
I have noticed that it is very critical to make sure the guides are placed exactly the same as a couple degrees makes a difference the farther off axis I get. There seems to be a point the dip in the upper octaves shows up right around 45 degrees. By looking at the tweeter from just behind the mic position it seems to be right around the point I can't see the tweeter because of the depth of the guide. Makes me wonder if the off axis would get better if the guide were shallower. Could be at the expense of the lower end though.

Dave