A 3 way design study

[tmuikku]

Perhaps except there seems to be some wiggle in frequency response still especially if the edge is circular and diffraction magnifies, at least I remember seen messurements of some dome tweeter in waveguide (lip height) and not flushmounted done tweeters that showed difference, and lower in frequency than 20k. Perhaps it is not too meaningful and audible, but if one wanted to play safe better make it 1/10th wavelength

 

[vineethkumar01]

I think about it this way: the wavelength of 20 kHz is 17 mm, and thus 1/4 wavelength is 4.3 mm. Any gap or bump which is less than 4.3 mm will be insignificant.

Really cool waveguide, BTW...

j.

Thank you.. So it may not cause issues i guess.. those minute gaps are much less than a millimetre i think..
Probably knowing that it is there is just triggering my OCD..

 

[vineethkumar01]

Perhaps except there seems to be some wiggle in frequency response still especially if the edge is circular and diffraction magnifies, at least I remember seen messurements of some dome tweeter in waveguide (lip height) and not flushmounted done tweeters that showed difference, and lower in frequency than 20k. Perhaps it is not too meaningful and audible, but if one wanted to play safe better make it 1/10th wavelength

Thanks tmuikku.. I will try to use some filler material if possible.. The gaps are so tiny that something smooth flowing like super glue itslef finds it hard to seep into that gap.. Probably i should have used a gel type superglue which might have filled up those minute holes..
Let me explore what i can do about this..

 

[fluid]

You can see a COMSOL analysis of a similar type of phenomenon here
https://www.audiosciencereview.com/...imulation-analysis-screws-in-waveguide.22985/

Often it is difficult to know what "sound" will consider to be the effective size and it does not always agree with your eyes

I don't think in most cases for a waveguide you would want the actual 3D printed plastic to be the final surface unless you have used an SLS nylon or other UV stable material, as if your waveguide sees the sun for long enough it will start to degrade. Spray fillers, sanding and paint are a good way to cover up many small imperfections and get a nice looking more finished product.

 

[vineethkumar01]

Thanks a lot fluid..
Right now i dont know which product to use to finish this product.. I am in the process of exploring this aspect..
I see commercial products like XTC-3D being used, some using wood filler etc to cover up gaps etc.. I dont know what is there that it is available in India.. Hence the survey...
I will study what I can do regarding this..

 

[fluid]

Have a look at the hardware store, car body repair or auto stores if you have them near you. Pretty much any sort of filler can be used but some will be much harder to remove by sanding which is not something you want.

 

[jcga]

Excellent, I dare so see some real measurements on that one

 

[Juhazi]

So I 3D printed my first waveguide.
It is the ATH generated ST260 KVAR with 1inch throat. This was a real learning experience in 3D printing even though i would have probably wasted about 250+ gm of PLA+ filament material.
---

Excuse me, but isn't that a horn for a compression driver?

So many variations and sidelines in this thread that I feel like too old to follow... But still one of the most interesting and sane threads! Thank you Vineeth!

 

[vineethkumar01]

Thanks a lot Juhazi.. None of this would have been possible for me without help from you all.

Yes I should have called this ST260 a horn instead of waveguide. My mistake. Honestly, these days, I don't know the difference between horn and waveguide as in most cases, in a home environment, the purpose for which they are being used is for directivity control to different extents..

In fact I only had one speaker project to build when I started this thread. But as O keep learning more and more, I just become fascinated with all the variations and concepts out there that makes me want to try out a good subset of them.. I am just so fascinated with this hobby that i cant get it out of my head..

Believe it or not, all these experiments and concepts learnt helps me a little bit at my job too even though there I have to play around with devices radiating in the 2.4, 5 and 6GHz bands in thr electromagnetic spectrum.. Studying the depth of concepts involved in science/art of speaker building and acoustics and the visualizations of it in softwares like VituixCAD helps me a lot too.. Anyway I diverge..

My plan, at the moment, with these parallel smaller builds that are going on are the following. Common to all is the Satori woofer box which works upto around 300 Hz. The top modules for this are as follows:

1) 2 way with SB15CAC30 + SB26CDC tweeter in a small waveguide designed by augerpro. I am 3D printing a baffle for this box as I write this.

2) Sica 5 inch Coax top. Drivers will hopefully arrive soon.

3) A horn top for the Satori box. This ST260 horn is an experiment in this series.. It seems like it needs to be high passed around 1500Hz or so, which is a region where probably my Satori woofers are not much comfortable. So I will definitely need a much bigger sized horn, if this concept is to work reasonably well, i guess..

There are some other plans too in background like putting that 15PR400 driver that i have in an open baffle configuration along with some with something else on top.. But for now I have promised myself that i wont think about new concepts until i finish and understand the capabilities of the above mentioned 3 concepts..

Thanks and Regards
Vineeth

 

[vineethkumar01]

Excellent, I dare so see some real measurements on that one

Thank you.. I will definitely take measurements and post here once i get my drivers next week..

 

[augerpro]

I wonder what a good seal coat would be for the SLS nylon waveguide? I know the nylon absorbs moisture, maybe that was why it discolored?

 

[vineethkumar01]

I wonder what a good seal coat would be for the SLS nylon waveguide? I know the nylon absorbs moisture, maybe that was why it discolored?

I too dont know about this.. As you said, I guess in my case, moisture might have caused the yellowing since the waveguides have been stored inside a zip pouch in a shelf for a year now

 

[vineethkumar01]

I got the Peerless DFM 2544R00 8 compression drivers today. Since one of the horns was printed out, i couldn't wait to see some measurements.. So i took an impedance sweep and horizontal polars upto 60degrees of one driver. I was going to do the full sweep but the overall rotating setup came crashing down to the floor due to the flimsiness of the base (an xps foam box) that i had kept on the turntable to raise height of the horn+driver up from the floor and due to my attempts to ensure that the horn mouth is at ths centre of the turntable.

Fortunately, it looks like the driver has survived. But the horn broke off from the base. It could be stuck together with sugerglue, I have to try or print another one.

Anyway here is what i got till now.

Setup

Impedance measurements of both drivers without horn

Horizontal polar upto 60 degrees with 4.06ms gate

To my relatively inexperienced eyes, this driver+horn combination looks really good from the polars..

Can this horn+driver combo be crossoved over at 1kHz?
It looks better to highpass above 1.5kHz but still I am curious..

I have to do full polars (vertical and horizontal) but next time I do any measurement, I really need to get a better rotating turntable setup.. hmm..

 

[vineethkumar01]

Since it looked good to the eyes, here is the normalized frequency responses measurements. All measurements upto 60 degrees above normalized to the on axis frequency response measurement.

 

[jcga]

Very nice, well done
Maybe a 25dB range instead of 50 dB would give more details.
Of course a 0-180° or at least a 0-90° both horizontal and vertical would help too.
Sorry to read that you damaged your horn, hope it can be fixed without too much pain

 

[vineethkumar01]

Very nice, well done
Maybe a 25dB range instead of 50 dB would give more details.
Of course a 0-180° or at least a 0-90° both horizontal and vertical would help too.
Sorry to read that you damaged your horn, hope it can be fixed without too much pain

Thank you..
I will try to repair the horn and see if it is usable. Else, I have to print two more of these horns. I will take full polars once I get the overall set up ready again.
But if anything, my measurements only just show that the excellent polar responses that mabat and others before me have shown using BEM simulations and actual measurements for these kind of horns can be repeatedly obtained

 

[vineethkumar01]

Sica 5.5C1.5CP coaxials have arrived

So the Sica 5inch coaxial drivers have arrived.

I took the drivers out of the box and took an impedance measurements

Woofer

Tweeter

Combined impedance magnitude plot

I see some wiggliness in the woofer impedance plots between the 100-200 Hz region. Interestingly, both drivers I have have got similar thing going on..
I have the following questions:
1) What could be causing it. Will it go away after some "break in" ?

2) Will it be matter if i cross the midwoofer over to my Satori WO24P somewhere above 300-400 Hz?

3) I am yet to take frequency response and (hopefully) distortion measurements. What do i need to look for in the frequency response in this area to see if whatever causes the impedance response to be wiggly.. Sharp dips/peaks?

 

[hifijim]

I see some wiggliness in the woofer impedance plots between the 100-200 Hz region. Interestingly, both drivers I have have got similar thing going on..

I often see that, and it usually goes away once the drivers are firmly mounted in an enclosure. My theory is that the chassis frame is moving back and forth slightly at those frequencies.

Try placing the driver on a thick layer of foam. Make two scans, one with the driver at rest on the foam, the other with you firmly pressing the magnet into the foam. If the wiggles change between the two scans, you know that it is driver movement causing them.

Another thing that can cause wiggles is an acoustic reflection from a nearby surface.

 

[vineethkumar01]

ITry placing the driver on a thick layer of foam. Make two scans, one with the driver at rest on the foam, the other with you firmly pressing the magnet into the foam. If the wiggles change between the two scans, you know that it is driver movement causing them.

Another thing that can cause wiggles is an acoustic reflection from a nearby surface.

Thank you. I will definitely try this out and get back..

 

[krivium]

Hi,
Second part ( scroll down):
www.Linkwitzlab.com/frontiers_2.htm#N