Dayton ND25FN-4 Flat baffle and waveguides

[davepellegrene]

Re: Dayton ND25FN-4 Flat baffle and waveguides

I added results from testing today with an 8" guide in post #2

Dave

[davepellegrene]

Re: Dayton ND25FN-4 Flat baffle and waveguides

After a discussion in another thread I did a test comparing the ND25 on a flat baffle vs an 8" guide and a 165mm x 115mm guide. I EQ'd the flat baffle FR down to flat with my Mini DSP. I then matched the guide FR to it and took measurements.

Here are the results

Flat baffle Impedance sweep


Waveguide Impedance sweep


The guide raised the Impedance by a couple hundred hurts and also lowered it by two 1.5 Ohms.

Flat baffle polar


8" round guide Polar 0-90 degrees axis


165x115 Elliptical guide polar 0-90 degrees horizontal


Cut off of both guides seem to be hire then the flat baffle. Interesting.

Flat baffle distortion 80 dbs


8" guide distortion 80 dbs


165mm x 115mm Elliptical guide distortion 80 dbs






Flat baffle distortion at 90 dbs


8" guide distortion at 90 dbs


165mm x 115mm distortion 90 dbs


Looks like the flat baffle with this tweeter will play lower then both guides. The guides have a cut off around 2 kHz and have better distortion above but have worse distortion below.
I wonder if the rise in impedance with the reduction in Ohms changes the resonance to effect this.

[davepellegrene]

Re: Dayton ND25FN-4 Flat baffle and waveguides

Flat baffle CSD


8" guide CSD


165mm x 115mm guide





Flat baffle Tone burst


8" guide Tone burst


165mm x 115mm guide




Flat baffle Wavelet Spectrogram of Impulse Response


8" guide Wavelet Spectrogram of Impulse Response


165mm x 115mm Wavelet Spectrogram of Impulse Response



Dave

[Pete Schumacher]

Re: Dayton ND25FN-4 Flat baffle and waveguides

That's very interesting Dave, the fact that the impedance changes so much.

I've done comparisons of the RS28 impedance in the guide and outside of the guide and saw nowhere near the change you just displayed.

But then the RS28 guide offers only a continuation of the flange opening, transitioning smoothly onto the guide walls.

[cjd]

Re: Dayton ND25FN-4 Flat baffle and waveguides

Your scale is different but I suspect something else may be happening here. Distortion looks worse on the guides down low. The change in Fs and the loss in response are likely pointing the way but darned if I know where to start -as is the peaking distortion in the guide between 1-2k. Probably throat size and interface at the tweeter.

Nice work as always.

[davepellegrene]

Re: Dayton ND25FN-4 Flat baffle and waveguides

That's very interesting Dave, the fact that the impedance changes so much.

I've done comparisons of the RS28 impedance in the guide and outside of the guide and saw nowhere near the change you just displayed.

But then the RS28 guide offers only a continuation of the flange opening, transitioning smoothly onto the guide walls.

I usually don't see a change in the Impedance. It is kind of a surprise. I checked it several times and had the same results.

[davepellegrene]

Re: Dayton ND25FN-4 Flat baffle and waveguides

Your scale is different but I suspect something else may be happening here. Distortion looks worse on the guides down low. The change in Fs and the loss in response are likely pointing the way but darned if I know where to start -as is the peaking distortion in the guide between 1-2k. Probably throat size and interface at the tweeter.

Nice work as always.

I think what is going on with the distortion down low is the guides cut off is around 2 kHz or above with these tweeters so I have applying less reduced EQ with the DSP with the guides which is translating to more distortion. You can see from 2-8 kHz the distortion is lower with the guides because I reduced the EQ more from the guide boost. If I where to roll the tweeter off on the flat baffle at 2 kHz and match the guides to that the distortion would be about the same below 2 kHz. Not sure there is a good answer for the comparison.

I hadn't noticed the scale change until you said that. Not sure why that happens. It does make it harder to compare.

Dave

[mzisserson]

Re: Dayton ND25FN-4 Flat baffle and waveguides

After a discussion in another thread I did a test comparing the ND25 on a flat baffle vs an 8" guide and a 165mm x 115mm guide. I EQ'd the flat baffle FR down to flat with my Mini DSP. I then matched the guide FR to it and took measurements.

Here are the results


Looks like the flat baffle with this tweeter will play lower then both guides. The guides have a cut off around 2 kHz and have better distortion above but have worse distortion below.
I wonder if the rise in impedance with the reduction in Ohms changes the resonance to effect this.

That's very interesting Dave, the fact that the impedance changes so much.

I've done comparisons of the RS28 impedance in the guide and outside of the guide and saw nowhere near the change you just displayed.

But then the RS28 guide offers only a continuation of the flange opening, transitioning smoothly onto the guide walls.

Dave,
Thank you very much for your work. I think this is good information. It shows that for this tweeter it is *likely* to play nicer on a flat baffle like you stated. There are no giant sweeping conclusions off one tweeter, however I like the methodology that was employed where you EQ'd by lowering, not raising. I think this resembles a crossover fairly well, and in some ways what I expected to see. The goal is always a flat on-axis response, weather surface mounted or WG loaded.

If you are ever willing to go through the process again on other tweeter I am certainly interested in the data. To Pete's point: There may be tweeters that work better specially if the guide is meant specifically for the tweeter, but a flat vs. WG on it using the method you have would be very interesting as well. If nothing else I think this gives some consideration into a way to work on the WG's and do some experimentation using these test methods to work on geometries that may be more universal? I guess more data is needed at this point though if you wanted to continue down this rabbit hole.

In context of what started this all, there are advantages and disadvantages to all design formats. I think the more we try to universally assign a therom to speaker design and the more data that becomes available it shows that each speaker or driver is more and more a unique snowflake that needs to be treated as such and the key to ultimately making an exceptional speaker lies in the understanding of what attributes work in what format.... Sort of like box alignments only with many, many more parameters... When to use a WG and why, when not to and why.... I still think Pete is spot-on with his design and a prime example of when a WG is of very good use. Thanks again, I really do appreciate all the work.

[davepellegrene]

Re: Dayton ND25FN-4 Flat baffle and waveguides

I have been using EQ for a while to choose the slope of the bottom end using the distortion plot. Basically it tells how low you can go at a given spl.
I'm going to look into the throat iteration a little closer. Seems when there is an impedance issue something is not right. One thing I realized is the dome is 28 mm not 25 like I had thought. The surround color wraps up onto the dome making it appear 25mm. I'll see if opening up the throat changes anything.

This same guide on other tweeters extends quite a bit lower.
Dave