Accuton C25-6-012 in a waveguide

[davepellegrene]

I've been working on a guide for this tweeter. Pretty interesting being it has what I would call a reverse dome or dished. Won't mention who's it is unless he wants to chime in.
He wanted an ovoid shaped guide or elliptical. After running it through a few different ones I ended up with the one I call L2. Real similar to the one Dan N. is using with the N26A. I was able to reduce the throat size to 1" and also was able to design a phase plug that works quite well with it. The biggest challenge was this tweeter has a peak around 15 kHz and the guide would magnify it. I was able to push it up in frequency and also reduce it by half with the phase plug. I also got about a five db boost around 12 kHz from the phase plug at one point but it enlarged the dip at 60 degrees off axis at 12 kHz. I split the difference and got about a 3 db boost and cut the dip back.
All measurement were taken with the driver about 1' off the floor pointing up with the mic half way to the ceiling. It's about 33" away from the driver on axis. Click on one of the pics in the link and you can go forward and back.

This is Flat baffle vs WG L2 with a base plate to reduce to 1" and a phase plug.


This is Flat baffle 0 20 30 40 50 60. It's basically a 2'x4' board with a 3" thick piece of 703 on top with the driver set down in flush.


This is WG L2 with 1" base plate and phase plug.


This is my prototype


Here is a link you can toggle back and forth between flat baffle and WG2 with plug and WG 2 with and without plug.

Dave

[xavier]

Re: Accuton C25-6-012 in a waveguide

I guess that's my cue to "chime in." When I saw how great the off axis response was with the waveguide in Maestro Neubec's "Echelon," I thought this was something I should pursue. Looks fantastic, Dave! I've read that waveguides can be problematic with inverted domes: http://www.positive-feedback.com/Iss...diomachina.htm. I know Gryphon uses one in one of their speakers using an Accuton tweeter.

Is the picasaweb link at the end of Dave's post not working for anybody else?

[davepellegrene]

Re: Accuton C25-6-012 in a waveguide

Should be working now.

Dave

[carlspeak]

Re: Accuton C25-6-012 in a waveguide

I've admired the work you're doing here with fab'd WG's. But in this case, I don't see any advantage of the WG over the flat baffle measurements.

[davepellegrene]

Re: Accuton C25-6-012 in a waveguide

I've admired the work you're doing here with fab'd WG's. But in this case, I don't see any advantage of the WG over the flat baffle measurements.

You don't consider the 10db boost from 1.5kHz on up to about 3kHz. Then a 5db boost on up to 8kHz and then another 2-3kHz all the way to 15kHz an advantage? Isn't that the main idea of the waveguide along with better directivity? Let's not forget about acoustical centers.

Dave

[carlspeak]

Re: Accuton C25-6-012 in a waveguide

You don't consider the 10db boost from 1.5kHz on up to about 3kHz. Then a 5db boost on up to 8kHz and then another 2-3kHz all the way to 15kHz an advantage? Isn't that the main idea of the waveguide along with better directivity? Let's not forget about acoustical centers.

Dave

Only if you can flatten the BBC dip that results from the WG.
Off axis response is clearly better with the flat baffle.

[ryanbouma]

Re: Accuton C25-6-012 in a waveguide

Only if you can flatten the BBC dip that results from the WG.
Off axis response is clearly better with the flat baffle.

I don't understand? What BBC dip. And, although the flush off axis looks unusual for a flush dome, it's not better than the waveguide. imo.

[carlspeak]

Re: Accuton C25-6-012 in a waveguide

[quote=ryanbouma;1837142]I don't understand? What BBC dip. quote]

The WG variance from 1K bottoming around 12K is about 10 dB. The flat baffle variance is only about 5 dB.

[jonasz]

Re: Accuton C25-6-012 in a waveguide

IMO the wg off axis looks better without the blooming around 6-7kHz. I'm sure the added directivity down low will also match a midwoofer better.

[davepellegrene]

Re: Accuton C25-6-012 in a waveguide

If I'm not mistaken and i'll check when i am home the 30 degree off axis with the guide is better then the on axis without. I thought that out weighed the dip at 12kHz. I do remember Mark stressing the flat/ straight off axis on the flat CSS tweeter.
Remember the flat baffle measurement is on a 2'x4'x3" thick piece of rigid fiberglass. I wonder if this is giving it any boost. I just set the guide on top of the tweeter and set a 12"x8" piece of fiberglass with a hole cut out to fit the guide when measuring it. I have a 10"x20" baffle I can fit them to to test. I just find I get Difraction off the baffle from 4kHz to about 8kHz that effects my measurements.

Dave

[ryanbouma]

Re: Accuton C25-6-012 in a waveguide

[QUOTE=carlspeak;1837148]

I don't understand? What BBC dip. quote]

The WG variance from 1K bottoming around 12K is about 10 dB. The flat baffle variance is only about 5 dB.

Ya, but anyone who would use this, would flatten the response in the cross over.

Like this:



Or this:



Or this:



Just to name a few.

PS, that middle one is the CSS LD25x waveguide Dave P did. That's on a 10x26 baffle with woofers below it. I owe you an email with my measurements Dave. I have a few questions also. TTYL.

[carlspeak]

Re: Accuton C25-6-012 in a waveguide

Nice flattening job, but at what sacrifice? More xo complexity I suspect.

I'm all for improving directivity, if that is a design goal (though not everyone's cup of tea) and for having a convenient way to move the tweeter's acoustic center back into the cab and lowering its xo point.

Maybe someday I'll get a chance to hear an example or two of Dave's WG work which, as I mentioned earlier,is commendable from the perspective of someone who's a Sigma Xi member.

[ryanbouma]

Re: Accuton C25-6-012 in a waveguide

Nice flattening job, but at what sacrifice? More xo complexity I suspect.

Each one of those used a single capacitor. That's it. Just one small cap.

[Sidi]

Re: Accuton C25-6-012 in a waveguide

take a closer look at those pictures. the flattening is a single series cap. a first order HP filter to combat the 10db/decade rise from the waveguide.

A decent explanation of the benefit is given here:

http://www.zaphaudio.com/hornconversion.html

[carlspeak]

Re: Accuton C25-6-012 in a waveguide

take a closer look at those pictures. the flattening is a single series cap. a first order HP filter to combat the 10db/decade rise from the waveguide.

A decent explanation of the benefit is given here:

http://www.zaphaudio.com/hornconversion.html

Let me see if I get this right. The WG gives you a 10 dB rise in a nice place on the Freq. curve then you proceed to knock it back down with a cap? What's been gained besides the directivity and backing of the AS?