Challenger - Compact 2.5 way silver flute/SB build.

Challenger - This thing is meant to challeng the high output monkey coffins so popular on this forum. I don't expect it to match them, but give them a run for their money, while remaining higher WAF.

Design Goals

Budget friendly
Compact / high WAF / hifi looking
90db/w/m with generous BSC
Hi power handling (with sub use)

I ended up with the SB29 tweeter loaded in a Dayton 8" waveguide. This is the real soul of this design I think. And silver flute W20RC38-08 woofers.

Here is some building so far. This is more a test cab than anything. Targeting 25L sealed.

Got some free plywood. But it's not very good. Free is good though.



Baffle and cut outs.



To do the cut outs I used a poor man's jig.



Wow, that worked good. Extremely tight fit. One woofer really didn't wanna fit.



Trimmed the waveguide to 42mm opening. Was supposed to be 41mm.



EDIT - Got a good fit, eventually.



Time to measure.

Ok, so I took measurements outdoors to get as low a FR as possible. I actually am not a fan of 2.5 ways. Not the main reason, but a part of why, is because I've seen very few 2.5 builds where the designer actually measures the baffle step. They usually just model it. That irks me.

So here are the results of my testing. I should mention that my start frequency was 100hz iirc. Measured pretty loud and wanted to keep the bass out. Not sure if that's good or bad.



Those are offset for clarity, so they're not at all indicative of level. First thing I notice is the silver flutes are actually pretty close to their spec sheet. But the breakup is higher q. The other variations are likely baffle step and diffraction.

The tweeter though... hmm. This is what zaph got (where I got the idea to use this combo).



What could be happening here? I'd appreciate some help with the following:

Why doesn't my tweeter response look right (it's close)?
Why did the IR show reflections way earlier than the woofers?
Any suggestions on target XO point? I was thinking 1500hz because that where directivity starts and seemed a natural spot for the woofers.
I don't know much about CD design. What am I looking for? Is it ok to push the tweeter lower and sacrifice directivity?

Thanks for any help.

Completed pics:

You think it's close eh? Hmm. I see a similarity, but zaph is getting more loading around 1500-2500hz. Also that top end... Yuck. I think I'll remove the baffle and work on fitment between the throat and tweeter more. I'm suspicious I messed that up. I'll take some pictures of it.

The silver flutes are a nice surprise but don't look like they lend well to a 2.5 way. What ya think about that?

That does help, thanks!

Ya, more loading where it matters. I think I might have a sloppy fit around the throat and that region is omnidirectional and not loading into the waveguide properly. Does that make sense?

Addicted, cool! Are those the same drivers? You just used the manufacturer's sheet from silver flute and then summed the baffle step/diffraction? Can you show me the raw simmed results before filters? Also maybe the XO components you got.

Are you working on a similar project, or just modeled it for fun.

Thanks! I thought it looked like a triple 8 as well. A little construction perk I found was the woofer frames and waveguide were identical diameters. Visually very pleasing I think. That and one router jig setting did all three holes perfectly. Fluke they were so perfect.

I've read that as well, and have some thoughts on that. I use my impedance jig to get T/S parameters, but I don't put much weight on them. IME, the manufacture's are pretty decent and DIY kits don't have a high drive voltage. T/S parameters change with drive level afaik.

Here is a screen shot of 2 woofers in parallel with 100watts. High passed with the receiver set to small speakers with drastically reduce excusion I believe.



That uses manufacture specs. I've also modelled using others' specs, just to see. Sealed they're not too far off, but I did over size the box just a bit to make sure.

More measurements coming hopefully after the weekend. I'll measure the acoustic center offset and the re-installed tweeter. Perhaps the woofers again as well.

Any suggestions out there about controlled directivity? Suggested XO point? Etc.

BTW, how did you get the transfer function to tilt down in your model Addicted? Am I missing something here? Thanks for the baseline as well. Chances are the AC offset will screw around with it, but we'll see

The tweeter is back about 80mm on the baffle. I figure 50mm will be close. Like you thought, 30 for the woofer. So 80 minus 30 should be a good guess.

Kbgl!!!!! Nice to see you. You've never steered me wrong. I gotta ask though, if anything I thought maybe lower than 1500hz. The CTC spacing is up there, and the tweeter should be able to take it. Fs is 500hz, and with the WG it'll be well protected once flattened.

Edit, assuming I can get the tweeter looking like zaph's measurements that is. Hopefully I'll have time this weekend to work on that.

Ah I see. True, I did say high power handling is a requirement

Thanks.

Ok, I've investigated this tweeter issue. Seems the fitment is tight:



But it's not perfectly centered. Forgot to take a picture. Off a couple mm. Also, like I said previously, I did cut the waveguide to 42mm instead of 41mm. I have 2 spare Dayton 8" horns so I may trim another to illiminate that as a possible problem. Anybody know if those errors would affect things? Also, I may not have had my mic calibration enabled Not sure, but will remeasure after I align the tweeter better and see what happens.

While I had the baffle off, I took this picture:



You can see how the tweeter is placed against the waveguide. The the plain jane rears of the woofers.

Ok, I've got some better results from the tweeter.



This is looking pretty good. Getting quite similar to Zaph's results. There were a few things:

1. My mic cal may have been turned off. Not sure why it would have been turned off. I plan to remeasure the woofers because of this, and a couple other concerns I have;
2. I did tighten the fit to seal it better. That may have loaded it better;
3. I centered it better, but still not perfect.

I'm going to re-mount the tweeter altogether. I'll get it as perfectly centered and tight as possible. I think the majority of the issue was the cal file. Otherwise I'd say this combo is extremely sensitive to fitment. I'm talking millimeters here. I didn't even notice until I had problems and started to get really picky trying to find any issues.

Stay tuned for complete measurements results. From those, the modelling can begin (once I measure impedance too).

Got the files addicted! Thanks! That'll help get this a baseline.

I had a bit of a delay

It was just me. A pick up towing a boat hit me. I'm fine, just rattled and sore. But the biggest annoyance is it has set me back getting measurements

Hopefully this weekend.

Buffed right out!



Ok, lots of info here. Could use some feedback aswell.

I mucked around with the tweeter to waveguide fitment, and I've convinced myself I didn't do anything wrong. The only difference between Zaph and me, is the throat diameter on mine is 42mm. I never did change the waveguide (lazy), but I believe this is right, and it's what I'm going with.

First off, I'm impressed by this right here.



That is the raw tweeter, also with a series 6.8uF cap, and with the cap just off axis. See how the 5khz and top octave anomolies smooth right out off axis I'm pretty excited about this, cause that is a nearly perfect LR4 at 900hz!!! That's awesomely low for a dome. It probably wouldn't play too loud, but the sweeps were darn clean. Also, with an LCR on the Fs, it turned into a perfect LR4 at 1100hz which is still really good and the transfer function is over 20db down at Fs. I'd really like to see this paired with a bass friendly woofer. Someone should. I would, but I'm building this

Here is the raw tweeter measurement really zoomed in. I wanted to highlight that area in blue to show the strange diffraction I was struggling with not shown on Zaph's plot. As shown above, it goes away off axis, and I will ignore this diffraction for the most part. I really can't explain where it comes from. 5khz relates to an approximate 68mm wavelength. That's in the middle of the waveguide



Ok, now the fun stuff!

I'm using AddictedtoHT's impedance zma files cause I'm lazy. I have checked my drivers with Arta, and they're bang on. Thanks Addicted!!

In PCD I came up with a LR4 at 1250hz XO that I like. Here it is.



A few things to point out here.

1. I zoom in lots. This might not look as smooth as some people's models, but note the scale.
2. That dip marked with green isn't really there I believe. Even if it was, it wouldn't be audible.
3. That hump is the diffraction I pointed out above. It is there, but ignore it I say

Here's a more commonly used scale.



That top octave peak marked with yellow is real. It does smooth off, off axis, and it is in the top octave where I can bearly hear. Addicted had a great circuit in his initial models that snipped that off a bit, but for now I'm going to leave it alone. My avr has PEQ that I could use if need be.

So this is the basic schematic of this model.



Now, what do people think?

7 components, but 4 are inductors. Basically needed to smash the extention of the silver flutes into place.

If it would help, I can show distortion plots, but I've checked and that tweeter is solid down to 1000hz.

Is any of my logic off? I'd still love some feedback on controlled directivity. I know it's a small waveguide, so directivity won't be astounding.

Oh, I meant to note that all the woofer measurements are pretty much no good below about 150hz. When the project is done, I plan to get nearfield/Ground plan measurements, and proper outdoor measurements again.