The Defiants - InDIYana 2019 Build

[PWR RYD]

My post was "unapproved"? I guess facts hurt.

[KEtheredge87]

My post was "unapproved"? I guess facts hurt.

Hey Craig, not sure if the forums are playing games with us... I didn't see anything from you except the quote above. What were you trying to share with me?

[johnnyrichards]

He was trying to share that there was a batch of the RS28 that are bad, and a lot of them made it into the wild. There is some data collected at another forum demonstrating it. PE seems to be addressing it

[KEtheredge87]

Thanks johnnyrichards , I saw those other posts too. While quality control issues are never fun, there is a happy end to this little emergency. I started a post on the Facebook group that many here frequent to see if more folks had some knowledge that could help. The guys at PE noticed and contacted me to give me some details and offer a solution. They said an official post from PE is supposed to come tomorrow to explain in more detail, but the gist of the issue is this:

The manufacturing house that makes the RST28F and RST28A tweeters started putting the wrong foam down inside the RST28F tweeters without telling PE there was a change. Unfortunately... in the engineering world, these things happen, and nobody likes it! The design of the motor does not allow us to replace that foam without damaging the motor, so there's no way to fix those incorrectly made motors. PE is having new stock sent via air freight... but they won't be available in time for InDIYana.

Lucky for me / us... While the motor design is the same between both versions of the tweeter, only the RST28F's seem to have been incorrectly made. PE is going to assemble a good motor from the Al tweeter with a fabric dome, and send it my way. They're even going as far to closely match the impedance signature of this replacement to the ZMA file I have of my good tweeter outside of the waveguide.

I'm glad to see PE is taking care of their customer base. Quality spills suck... there's no debating that. But I find that what a company does in the wake of a spill is infinitely more important, and Parts Express went out of their way to help me today. I don't expect any special treatment... and I didn't ask for any... but they were there all the same. Thank you very much, PE!

[jhollander]

Are custom made tweeters allowed? Actually that's pretty amazing service. Lots of good stuff (and people) coming to Indy.

[KEtheredge87]

Are custom made tweeters allowed? Actually that's pretty amazing service. Lots of good stuff (and people) coming to Indy.

Ya know John, I sure hope so! Although Ben's rules say a competitor must list the cost of all modifications that were made to the driver... I'm not quite sure how to tally this one up!

[KEtheredge87]

Quick update and question Gents... XO measurement and testing is finally underway. So far I've got something that sounds passable, but will still get some attention and attempts to better the result. One odd result I am seeing and I don't quite understand is an apparent suckout on my tweeter right around 1kHz. The blue line in the OmniMic data is my good RST28F with Visaton WG148R waveguide with no crossover applied. The red line is my XO measurement for the HF section as shown in the Xsim screenshot. I've never used a waveguide before... but that missing 10 dB doesn't feel right to me.

Anyone ever seen that before?

[jhollander]

Might try tightening up the gating. It looks like there's a blip at 4.2 ms and your gating is at 5.? ms.

[KEtheredge87]

Might try tightening up the gating. It looks like there's a blip at 4.2 ms and your gating is at 5.? ms.

Thanks John, I'll give that a go. Jeff B suggested I was having a room reflection over on facebook. I guess the bit I still don't understand is if that dip is truly a room reflection, I don't get why it's only in the filtered response, not the raw driver response... quite curious.

[Wolf]

1k = 13" That's where I'd start.

Next, since you have a 1st order, I'd drop the parallel resistor and go second order. It may be the Fs of the driver and the interaction of the 1st order rolloff.

Later,
Wolf

[KEtheredge87]

1k = 13" That's where I'd start.

Next, since you have a 1st order, I'd drop the parallel resistor and go second order. It may be the Fs of the driver and the interaction of the 1st order rolloff.

Later,
Wolf

Thanks Ben, going 2nd order is on my docket for tonight's measurement and experiment session. I was hoping I could get away with just a cap and a single resistor on the tweeter, as the woofer starts to give me a pronounced hump at the knee if i increase that parallel capacitor in value. Having a shaping resistor there would be quite helpful... oh well... maybe I'll save that idea for XO version 2 for MWAF!

[rpb]

Thanks John, I'll give that a go. Jeff B suggested I was having a room reflection over on facebook. I guess the bit I still don't understand is if that dip is truly a room reflection, I don't get why it's only in the filtered response, not the raw driver response... quite curious.

Looks like a second driver might be causing a cancellation, or you wired the x-over wrong. When you measured the tweeter, where did you disconnect the woofer? Should be disconnected before the woofer filter, not after. L2 and C2 might be creating a notch filter?????

If you measure again, and get the same result, move the mic location, and see if the dip frequency changes. If it does, disconnect the tweeter, and run a sweep ro see if you hear a second source..

[KEtheredge87]

Looks like a second driver might be causing a cancellation, or you wired the x-over wrong. When you measured the tweeter, where did you disconnect the woofer? Should be disconnected before the woofer filter, not after. L2 and C2 might be creating a notch filter?????

If you measure again, and get the same result, move the mic location, and see if the dip frequency changes. If it does, disconnect the tweeter, and run a sweep ro see if you hear a second source..

I think you win bud! Last night I just disconnected the woofer AFTER the filter, not before it. Today I went to a 2nd order XO before I read your suggestion and tried a frequency measurement with the woofer disconnected before the filters and the 2nd order tweeter network left as-is. No more odd notch. Must have been my extra parts in the network causing chaos.

[Wolf]

I just assumed that was tweeter and its filter. Good call, RPB!
Wolf

[KEtheredge87]

Alright guys - I'm having some issues with Z-offset, one of the very basics of XO simulation. I'm simulating designs that appear to have good reverse nulls in PCD and/or Xsim, but have a non-existent reverse null in Omnimic when I measure. That tells me that my Z-offset calculation within PCD alone is incorrect, so I've tried using the OmniMic GUI as well as some guestimations based on Fusion360 X-section views. As expected... I get a few different results.

Here's my PCD setup, and some result files with Z-offsets being compared in PCD.

Measurement setup:
24.25" away on tweeter axis. (0.61585m)
woofer located -6.75 inches down / 0 inches over from the tweeter axis (-0.17145m)

Measurement FRDs Recorded:
1) Woofer alone
2) Tweeter alone
3) Woofer and tweeter together.

Measurements of FRDs loaded into PCD without ZMA files (OmniMic FRDs contain phase info already):
1) PCD's woofer FRD slot gets the RS180P-4 alone file
2) PCD's tweeter FRD slot gets the RST28F-4 alone file
3) Import overlay on graph gets the RS180P + RST28F file
4) Offsets for listening distance and driver locations set appropriately with tweeter axis being the origin


My observation is that my PCD-based results aren't lining up as nicely as Jeff's how-to instructions would indicate. Calculating Z-offset within the OmniMic GUI results in a value that I believe more... but PCD seems to disagree with it. This uncertainty makes me suspicious of everything...

Without getting this Z-offset thing nailed down, none of my simulated crossover results are translating to actual measurements.

Surely someone else has run into these issues before. Does anyone have some suggestions?
Thanks in advance!