ZD3C w/ DQ25SC16 Tweeter Build

[rsbonini]

So, as discussed in the ZDT3-5-sort-of-Duelund-crossover-design-I-hope thread, I was looking to build the Zaph ZDT3.5/ZD3C speakers but with the same tweeter Zaph used on his ZA5 series designs. Since I was in need of a decent centre channel, I chose to start with that.

I went a different route with construction, however the cabinet dimensions are exactly as specified. The baffle is not removable and was attached to the box with wood glue and dowels so that a 1" radius could be routed into the top and bottom edges. The finish is a walnut-ish formica. While this is my first speaker build, I've had the invaluable guidance and help of an experienced speaker DIYer. Below are some photos of the progress to date.

Internal cabinet braces:




Cabinet assembly:






Adding roundovers:








Formica wrap:




Modifying midrange mounting plate:






Cuttin driver and port holes:

[rsbonini]

With respect to the tweeter substitution, my hope/plan at this point is to leave the woofer and midrage crossovers unchanged, and modify only the tweeter section. Here's the original design from Zaph:



R4 will have to be increased to deal with the increase in sensivity (about +4 dB over the original). My thinking is to keep the 3rd order topology, but add the Fs resonance parallel filter that fjhuerta gives in his thread.

Does this seem like a practicable approach? Any other suggestions for successfully integrating this tweeter?

[Bear]

Depending upon the total effect on phase, you may need to convert R4 from a straight pad to an L-Pad (add a parallel resistor, as well). After that, you are playing with the filter values to adjust generally to align the overall shape of the response curve to your target, as well as the all-important phase alignment.

Keep an eye on Zaph's ZA5-series filters to ensure that you're not heading down a rabbit hole on some tweaks.

[rsbonini]

How does a series pad vs an L-pad affect phase?

[rsbonini]

First testing and evaluation this week. The woofer and mid crossovers are as per Zaph's original design. Several concepts were attempted for the tweeter crossover, including some really detailed and welcome suggestions from another forum member. Ultimately the local speaker DIYer made a suggestion based on the original Zaph crossover, which seemed to provide the best starting point. After some iteration it seems to be at a usable point that sounds pretty good.

Meaurement setup:


Response curve (old X-over):


Final X-over circuit:


I'm not too sure about the measurements lower down, and ultimately I'm just going to trust that Zaph's design is doing what it's supposed to down there. I am wondering if the upper response can be improved. The DQ25 does have a rising response that was expected.

I am wondering though, is it possible to reduce the dip from about 3.5KHz out to 9KHz? Any suggestions for how to do so? I'm wondering if adjusting R15, and using a pair of RC/RL shunts in place of R16 would be the best approach.

[Evil Twin]

Do you have raw driver data measurements and FRD files generated from them? If so, then it would be straightforward to model the crossover and system response and update the design. While I have RS52's, and am working on a few new project concepts with them, I don't have any DQ25's, though that would be an easy problem to fix.

As I have used the RS52 in Duelund like crossovers, and am working on new ones, this is interesting to follow up on.

I will look into the original Zaph design and perhaps I can come up with some useful suggestions for you in the reasonably near future.

BTW, nice work on the cabinet built- this is overall like a grown up version of Jonmarsh's NeoD CC, which is also a quasi-Duelund design, using the RS52AN, but with now obsolete woofers and tweeter.

Expect a follow up soon.

[Evil Twin]

Look at the detailed "factory" information

A pair of DQ25SC16-04 has been obtained and a test baffle will be constructed soon, to measure and prepare minimum phase FRD files.

Whether the difficulty is due to differences in the basic tweeter amplitude responses or some other factor cannot be determined from speculation.

However, the detailed Peerless measurement shows a dip in this area, and that is likely the fundamental cause.





The tweeter originally used in the design, the Dayton ND20FB, appears to be much flatter.





This part is currently out of stock at PE, but due to return to availability around Jan 20.

It is understandable due to the delivery issue why you have this self inflicted problem-

After I generate measurement data I will investigate whether there is a crossover remedy to be had, compensating for the tweeter behavior.

[bbe22]

ND20 and DQ25 ( nude) responses in a small (but not the same) baffle for comparison

[rsbonini]

To have the dark lord himself deign to provide feedback on this little project of mine is most humbling. The NeoD CC would probably have been my preferred option, but driver supply issues and a lack of updates from Johnmarsh (understandably, as he seems to be a very busy guy) on a proposed new driver/xover configuration scuttled that.

The dip does seem to be characteristic of the tweeter itself and may be irresolvable. That being said, setting R15 @ 2R, and R16 @ 4R7 gives the following response (gated @ 1.8ms):



Which, unless someone tells me is subpar with respect to the inherent potential of the design and drivers, I think I could be quite happy with.

Learning to setup and take (accurate) FRD measurements is something I would certainly like to do, but haven't gotten to yet. Unfortunately, getting this project completed prior to other (some might say more important) priorities coming into play, was also a consideration.

Thanks to everyone for all the excellent input so far!!

[rsbonini]

I've been listening to the centre for a little while and am very pleased with the ability of this speaker to keep up with the tower speakers (Monitor Audio Bronze 6s). The previous centre was shallow and anemic, as though something were missing. No such worries with this speaker. Dialogue is clear, detailed, and precise, even way off-axis. Effects have real heft and presence, as though they are being propery rendered to scale.

If anyone thinks there are any obvious improvements to the x-over please do let me know. Thanks all for your interest in this project.

Here are a few more additional photos from the build.

Mid-range X-over:


Tweeter x-over:


Bass X-over inside cabinet:


Mid-Range X-over inside cabinet:


Speaker rear:


Speaker front:


Speaker perspective: