Simple Passive Harsch XO Using PTT6.5 and RS28F in a Waveguide

[norman bates]

Neat

 

[wilbur-x]

If I should alter the cabinet:
Will the project goal "survive" as long as I keep the original baffle width, the active TL-line's length, face- and outlet opening area?

 

[bwaslo]

I am looking at the data a little more carefully from the RST28 and WG300. Despite having a very good step response, the phase measurement appears to just rise and not have a 55deg bump like a true Harsch XO. Whether or not this makes an audible difference vs the RS28F, I am not sure. I do want to let folks know about this and so they can choose their tweeter accordingly. The RS28F will measure better according to my data.

Here is measured phase for the RST28F-4 in the WG300 integrated with the PTT6.5:

XRK, keep in mind that phase response is affected by absolute delay, it depends on where you define the reference plane to be. The effect on the graph is dramatically stronger as you go higher in frequency. It's like sitting a half inch or so closer or further from the speaker, totally fair. If you "remove" some overall delay from that measurement (see the Tune menu for the Power Amp in Xsim, or the "delay" control in OmniMic, or similar viewing adjustment in other programs) you can bring the curve down to 0degrees or any other value. Bring it to zero in the highest octave and your rise will become a bump.

 

[xrk971]

Hi Bwaslo,
Thanks for pointing that out - so that means that the new RST28F is probably fine from the standpoint of a 55deg Harsch rise bump. Although very top octave from 15kHz on up seems to be falling and not rising like the RS28F.

I was able to get the predicted phase to unwrap and have the 55deg bump by adding a -1.12in delay to the "Amplifier":

 

[xrk971]

I might have some time to make the Pathfinder for this TL using honeycomb cardboard panels. About 1/2in thick so perfect for this. Will use combination of Titebond glue and tack in place with hotmelt.

First thing to do is cut a long uniform strip of 7in wide parallel boards to use for the internal walls.

Long metal straight edge yardstick and sharp utility knife should do the trick.

 

[mainframe99]

Pathfinder = prototype? Please do. I must see measurements... precious...

 

[AdamThorne]

Hey, cool! Someone pointed me at your Harsch stuff at a meetup last Nov and I've been wondering since if it could find a passive implementation. Nice to see an example lay it out.

 

[xrk971]

This Harsch passive XO was really a lucky break. Sometimes these things just fall out of the sky. I tried to do this with budget drivers once and the crossover simulation was hairball complicated with 20 crossover components:

Low-Cost PMC-inspired TL Monitor with DC130A and DC28F

 

[Solve]

@xrk971 any progress in the TL build?
Also planning to build these with WG-300 but dont know what tweeter to choose yet.
Now I just have to convert the plan from inch to mm.

 

[wilbur-x]

@solve: waiting for the Satori BE with wave guide? (no data yet).
Bliesma could also be an option, but decent waveguide have to be confirmed.

 

[Solve]

@solve: waiting for the Satori BE with wave guide? (no data yet).
Bliesma could also be an option, but decent waveguide have to be confirmed.

I have to start with something cheaper than those.

 

[mainframe99]

I am hanging out for measurements of that waveguide satori be

 

[xrk971]

Satori TW29BNWG-4 Beryllium Dome Tweeter with Waveguide

Nice! $860/pair. Aluminum waveguide though. How they put stuff up for sale before the measurements are available is strange. It’s all about the polars if they are offering a WG.

 

[bambadoo]

They are not available yet. Over a year late in fact. Should be ready may 2019...

 

[xrk971]

From Madisound I can click add to cart and do not get an error. I assume it means that they are in stock?

 

[bambadoo]

According to SB acoustics they are not ready for delivery yet.
As of 18 may 2020 they responded to me:

To update you on the TW29BNWG-4 (Beryllium waveguide version) we are still undergoing development. We have come across a technical issue causing delays. I am afraid I do not have a date for release.

 

[xrk971]

Ok, that was over 3 weeks ago - maybe they figured it all out?

 

[bambadoo]

Maybe but it has been listed like that from Madisound since end of january....even if they have not started producing it yet.. Maybe they got some early samples?

 

[dwk123]

I know for certain that a couple people over on HTGuide ordered and received units from Madisound, probably 6-ish weeks ago. So, they existed at one point. I wonder whether there was an initial sample run from which Jeff B got some to complete the Helios design and Madisound had the remainder of that run, but there is now a glitch in ramping up production.

Edit: preliminary measurements here: Driver Evaluations for a new project - Page 9

 

[mainframe99]

Hmm... Might just have to look into waveguides for the t34a I've got here first.