What's wrong with my C-notes?

[Chris_Perez]

Thanks so much Chris. I'm hopeful we can figure it out.

Hello Josh,


I went ahead and took measurements of the ND25FW-4 tweeter and there has been pretty much no significant change between the golden sample (from 2015) and our current stock (manufactured in 2022).
Here is the results of the measurements:
Red = Golden Sample (2015)
Black = Unit from 10-2019 stock
Blue = Unit from current stock


It is doesn't appear that the issue is caused by the tweeter.

[billfitzmaurice]

You don't have to point the mic at the ceiling but it should be aimed 90 degrees off-axis. Aiming at the ceiling does that, as does at the floor or to either side, or any of some 356 other one degree increments of rotation. Just as important is to take measurements outdoors, so that you're only measuring the speaker and not the room.

[joshshetter]

Hey guys, hope everyone has a good weekend, mostly just rain here.

I was about to run a c-note up to PE, wanted to measure again just to make sure they're still wonky. I 'm wondering if my results could be from my measurement process. I noticed I got a big HF tilt when pointing the mix on axis vs. at the ceiling. I'm thinking this might have been my fault all along, whoops.

Orange is pointed at ceiling, teal is pointed at tweeter, taken in room.

[joshshetter]

Apologies DrewsBrews.

Looks like I'll be taking the speakers up to PE office to be analyzed, should be a fun trip.

[DrewsBrews]

Driver break in? Really? Didn't expect to see that here. Respectfully no, that has nothing to do with my issues.

PE support suggest break in and I just rolled my eyes....

Doesn't seem particularly respectful to me. Crap like this only hurts the hobby, and is why I have largely kept to myself until recently. In the future, please just ignore it rather than berating someone for trying to help.

Sometimes it takes thinking outside the box to figure something out... I was merely trying to rule out other things before assuming you did something wrong during construction.

I've heard of woofers getting a slight boost in db/W after loosening up a bit. My thinking was if that is the case, then maybe it will raise it up to the tweeter level a bit. But you are right, probably not enough for what you are seeing.

My second statement was about potential for something mechanically wrong causing the reported distortion. It can come in and out and can be hard to detect audibly, especially if something else is grabbing your attention like the boosted HF. But it seems the distortion has been figured out.

[joshshetter]

Thanks so much Chris. I'm hopeful we can figure it out.

[Chris_Perez]

Hello Josh,

I have been looking over this thread, and the rising response on the tweeter is unexpected. From what I can tell, your crossover looks like it is wired correctly, so I don't believe that is the issue.

If C3 (2 uF in parallel with the tweeter) is open, or removed, then the response will tilt up slightly, but that would only cause about 1.5 dB increase at 15,000 Hz. I can't see any immediate issues or changes that would cause the 4 dB increase that you have measured.

Just to make sure, I will pull one of the ND25FW-4 and measure the response, just to check to see if anything has changed.

In the meantime, I will have one of our customer service reps get in touch with you so we can try to work though this discrepancy.

Thank you,
Chris Perez

[duanebro]

One should go to the ground and the other the woofer?

[joshshetter]

Why 2 wires on the ground side of the crossover?

Look at the layout in the manual for the answer to this.

[duanebro]

Why 2 wires on the ground side of the crossover?

[rpb]

I looked at the xo schematic, and it should work, assuming everything is wired correctly, I used PCD to calculate a notch for the top end.

.1mH 1.5uf 3 ohms (In series with each other, and placed across the tweeter terminals.)

I assume you have confidence in the measurement setup, and that no tone controls or effects have been mixed in by accident.

[billfitzmaurice]

When I first looked at it all I could think was WTF??? With a third order high pass C2 is typically at least twice the value of C1, not less than half. What C3 is doing there I can't imagine. Plugging the FRD and Z into XSim along with the suggested values it looks really odd. Changing C2 to 12uF and deleting C3 looks much better.

[djg]

Have you tried over at DIYaudio forum? They're really smart over there.

[djg]

Sometimes the manual XO diagram is wrong, but you'd think with the C note popularity, that would have been remedied.

[tomzarbo]

In your first graph in the first post, I see the tweeter level rising at 15k maybe 2.5 to 3 dB over the average (1 k) level. That doesn't look ALL that bad to me, although depending on the person, it may sound harsh. I wouldn't plan for a response like that myself.

But your point is I think that it's not the response that is shown in the manuals and resources section of the C-Note product page. And you're right, It looks to have a fairly flat response where yours rises above 5k. There is a difference there.

My guess is that the tweeter is somewhat out of spec. That is the item that is subject to several different procedures when it comes to assembly and uses several different materials. In all the testing I've done of caps, resistors, and coils, (ones that I purchased from PE) none of them was out of spec more than just a little bit.

BTW, I wasn't suggesting that woofer break-in was the cause, just providing a bit of information based on my experience since you seemed to dismiss it pretty quickly.
And since I'm not the best a doing my own crossovers, I'd hate to open my mouth about your crossover layout and get it wrong, so I didn't even attempt a visual.

You may be able to insert a series resistor after the tweeter crossover (after the 2 uF cap) to tilt the response down a bit if you're willing. I don't know if you have spare resistors to mess with, but maybe start with a 4-6 ohm resistor and then work up from there? Not the best solution especially since you bought it as a kit and shouldn't have to customize it as such, but it's an idea. I'm sure others better qualified may be able to offer a more accurate guess on the value of the resistor.

R1 which is placed before the tweeter crossover should not affect the tilt of the tweeter response, mostly just the overall level, so I don't think that would be it if it were off-spec.

Yeah, I'm not much help.

TomZ