Waveguide for XT25

[pjblakey]

Here's some pics of the XT25 wg with Vifa P21 that I rescued from my Apogee Centaurs.
The first picture shows the mounting arrangement I used for the tweeter.
I've listened to voice, piano and orchestral so far and with the crossover at 1800Hz, 4th order on the tweeter and 2nd order on the woofer, a little EQ via the minidsp, quite satisfied. Nothing is "WOW-that's impressive, but very smooth, musical and, a bonus is that the 8" woofer performs so much better in the 1.2cuft cabinet than over-stuffed in the .7cuft Centaurs.
Vertical dispersion is massively improved over the Centaurs, and there is not a bad seat in the room. More dynamic than the Apogees, too.
I'll keep playing.
Peter

 

[SpinMonster]

Dispersion should be a wow.

What size cap are you using to get the response back to flat? If you arent and are just using EQ, you are missing out on the cap lowering the 300-1500 stimulating frequencies that cause the higher order distortion. That cap keeps lowering distortion far outside its pass band

 

[pjblakey]

The sort of WOW I meant is that nothing about the speakers appears excessive. You know, the sort of thing that can impress in a dealer's showroom or one's own diy project and after a few hours, becomes fatiguing. Dispersion is wonderful, but I usually sit in the same central location when I'm listening, so that doesn't concern me too much. It's certainly a huge improvement over the Centaurs, which have been my reference for 22 years. I have built several speakers over the last few years, and these may displace the Apogees. First impressions is that they are silky smooth yet have oomph when needed.
No cap being used- I wouldn't know where to start. The only measuring tools I have are a Radio Shack spl meter and two ears, and they are no longer effective beyond 10kHz (the ears), so I'm not sure I could hear the distortion you mention?
SpinMonster, thanks for all the posts-they have encouraged me in this previously unknown area, to me.
Peter

 

[SpinMonster]

The wow on your speaker is how beautiful that WG is.

I owned the apogee stage and never had anything better. I had the Krell KSA250 with all top shelf parts in the system. When I sold that speaker it was my intention to upgrade but Jason Bloom died and the company with it. His dad sold the company but they discontinued making ribbon speakers. I thought I'd one day own that transparency again but It became difficult to justify the expense if replacement parts were in question. I'm aware of Graz selling great replacements but I no longer want a system that needs to be listened to in that 12" sweet spot.

My current speakers dont have that ribbon transparency or depth of sound stage but what I have is 95% of the best I've heard.

If I can find a prime example of the Duetta signature I will buy it for a dedicated music system in one of the unused rooms in my home. My home theater needs the dynamics and SPL of the wave guide system which sounds good anywhere in the 21 x 21 foot home theater.

 

[AllenB]

I can turn a knob to vary a cross over freq to test power handling but some how that demonstrates the dark side of active cross overs....flying blind.

I think the case here is that the WG makes the XT25 so much wider in effective band than a bare XT25 that its overlap to the usable RS180 range can land anywhere between the frequencies I tried with the end result sounding fine with any of them. To exaggerate the example, if I was matching the RS180 with an RD50 from BG, the cross over is not limited to one dead on freq because their ranges overlap so much.

Spinmonster, it doesn't. You have an understanding of what you're hearing from your drivers. I was more interested in how you sized up the drivers individually and brought them together, and I probably should have used a () in that post.

 

[SpinMonster]

I had response graphs from both; RS180 builds are all over the net and Dave supplied the curves for the XT25 w/WG. I have a 31 band analyzer and aligned everything based on those elements. The acoustic centers are about as close to perfect as it can get. The DCX2496 fixes a multitude of irregularities.

 

[SpinMonster]

Here's some pics of the XT25 wg with Vifa P21 that I rescued from my Apogee Centaurs.

The Vifa is a perfect match to the WG. Its likely one of the only 8" I would use and I did look into it as a great driver. Its top end was really well behaved.

How tight does the bass sound? The centaurs had nothing great to talk about in the bass dept. Ported would wake it up.

Your WG's are beautiful. Where can I get a pair? I'd love to see them stained and polyurethaned in high gloss. I bet horns and female vocals are magic on them.

 

[454Casull]

Why did the response drop so much after 10 kHz?

 

[SpinMonster]

Wave guides are designed to boost the bottom end. This one boosts up to 12K. I need about 5db EQ to be flat to 20K. I can hear above 16K so its irelevant to me. Also Wave guides aren't about being a flat response, they are about getting back to flat with a cap to kill low end distortion.

The drop off up top has to do with throat size. You cant maximize everything. What is improved outweighs the extreme top end. It isnt something noticed even without EQ.

 

[AllenB]

I had response graphs from both; RS180 builds are all over the net and Dave supplied the curves for the XT25 w/WG. I have a 31 band analyzer and aligned everything based on those elements. The acoustic centers are about as close to perfect as it can get. The DCX2496 fixes a multitude of irregularities.

I guess you're correcting for group delay in the waveguide, how much does doing this extend the usable bandwidth?

 

[pjblakey]

How tight does the bass sound? The centaurs had nothing great to talk about in the bass dept. Ported would wake it up.
SpinMonster.....Ditto to all the things you say about Apogees.
With my new creation, there is surprisingly little "room bloom" except at 40hz. The minidsp helps me flatten that and the bass and is down 5db at 31hz. Relaxed(BR) bass is oodles better than when the 8" drivers was in the Centaurs, which by the way, I have modded to create a 6.5" bass reflex cabinet with excellent results.
When I have a little spare time, I'll turn a couple more pairs of waveguides..........
Peter

 

[AndrewT]

Do these waveguides need some throat structure to become accurate?
Or are they good enough with nothing in the throat.
Does the bullet have some effect?
Can the bullet be dispensed with?

 

[ra7]

Here's some pics of the XT25 wg with Vifa P21 that I rescued from my Apogee Centaurs.

Peter

That is gorgeous. Make some for us too, man. We'll pay you

Nice work, btw. Try toeing in the speakers a little. You might perceive more depth in the sound-stage. And yes, it should not be wow... nothing should stand out and grab your attention. Just smooth, easy sound. I think you got the crossover and overall balance right.

 

[SpinMonster]

The WG boosts to 1500hz by 10db. Lowering the XT25's electrical contribution at that freq with the WG is increasing a non-powered mechanical contribution, is thus lowering power requirement to hit the same spl by about 85%. Using the XT25 under 2K LR4 was formerly not advised. The use of a cap to get the response back to flat lowers output from the tweeter 30db at the resonant frequency and lowers distortion in the 1500hz range by 20+db. Excursion at 1500 is less than a 1/4 of what the bare tweeter is. The RS180 obviously benefits from not being crossed as high as the is less beaming, less distortion, and you are further from its break up. The twin peaks are then down by >40db at 6000 and >50db at 9000 with a LR4

 

[SpinMonster]

Do these waveguides need some throat structure to become accurate?
Or are they good enough with nothing in the throat.
Does the bullet have some effect?
Can the bullet be dispensed with?

Dave designed them by building multiple version before settling on what worked. The phase plug is why the XT25 works so well in a WG. You wont want it removed, nor can you. At some point people should stop trying to reinvent the wheel and trust that the resulting tests indicate it already works well.

 

[SpinMonster]

When I have a little spare time, I'll turn a couple more pairs of waveguides..........
Peter

What did you use as a model to form the proper profile of the guide?

 

[AndrewT]

Dave designed them by building multiple version before settling on what worked. The phase plug is why the XT25 works so well in a WG. You wont want it removed, nor can you. At some point people should stop trying to reinvent the wheel and trust that the resulting tests indicate it already works well.[/QUOTE)Is this answer telling me that the bullet is what allows the XT to work with a waveguide?

And is this also saying that if the speaker does not have a bullet there is no point in fitting a waveguide?

 

[pjblakey]

Quote:
What did you use as a model to form the proper profile of the guide?

Zaph has a TMM waveguide speaker on his website and provides the co-ordinate to shape the profile. Troels has a detail of the throat/faceplate interface for this driver. I combined both.
By the way, what value capacitor would you suggest for the xt25?
Peter

 

[pjblakey]

Quote:
That is gorgeous. Make some for us too, man. We'll pay you

I'm not into making money from a hobby, but........I would consider a trade or partial trade for another pair of XT25 tweeters or something similar. The ones I used for this project are the only ones I have, and I would sometime like to build some 2.5 towers using my Peerless
Nomex woofers.
Peter

 

[SpinMonster]

Quote:
What did you use as a model to form the proper profile of the guide?

Zaph has a TMM waveguide speaker on his website and provides the co-ordinate to shape the profile. Troels has a detail of the throat/faceplate interface for this driver. I combined both.
By the way, what value capacitor would you suggest for the xt25?
Peter

That depends on the lift given to the low end of your guide.