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Chris A

Nearly Full-Range Multiple Entry Horns (MEHs)

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On 5/6/2021 at 12:00 PM, NBPK402 said:

 

 

14b33141a64881dcab7ed8e231721831.jpg

 

e43014426593cf58c7ccbf679b3a2fe9.jpg

fantastic ,  great job ------keep on showing us the pictures

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fantastic ,  great job ------keep on showing us the pictures
That is from the one I made in 2017. Hopefully I will get the bendable plywood in a week or two. The picture shows how I made the mounting plate for the compression driver, and I think I will do it the same as it is much easier to install the driver. In addition I plan on marking the square opening of the throat and blending it to the 2" driver size.

Sent from my SM-G985F using Tapatalk

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2 minutes ago, NBPK402 said:

That is from the one I made in 2017. Hopefully I will get the bendable plywood in a week or two. The picture shows how I made the mounting plate for the compression driver, and I think I will do it the same as it is much easier to install the driver. In addition I plan on marking the square opening of the throat and blending it to the 2" driver size.

Sent from my SM-G985F using Tapatalk
 

the mounting plate  for the compression driver in your cabinet seems to complete  the horn perfectly  and ihe stronger construction will make for 0 resonance or vibrations  once it's tightly screwed in and sealed

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Posted (edited)

Here's a current project that is exploring different port shapes in the center of top and bottom horn walls. On-axis ports!

Meant ror traditional conical syn/meh's; and ones that use a single sized driver to bridge between CD and subwoofer.

In this case, there is a pair of 10"s crossing at 500Hz to a dcx464.  

 

What you're looking at is a couple of air bake pizza pans, cut to lay on top of 7" diameter holes in the horn, which are centered over the 10" cones.

I duct tape over the plates holes, to try different port shapes.

673278194_platefrowna.thumb.jpg.724756527e08e3431a175f2eaaf510f2.jpg

The small holes, for what ever area is exposed, match the freq response of the same area completely opened, surprisingly quite well.

I began the project by putting the plates over existing round hole synergies to see if the correlation was good.  Had to pass the smell test, to get started  ya know .

The small holes caused about a dB and a half loss on the cones lower end response on the syn7 (for which i posted polars on on the K-402 MEH thread)

 

So far, pure circular ports were marginally bested by vertical slots. Horizontal slots weren't as bad as expected.

The frowny faced ports are the best yet.  By best, I mean polars hold up the best after tuning.

All non-taped, uncovered port areas, have been the same, 1/10th Sd. 

 

I have a couple of 22 gauge steel sheets coming, that I will cut the frowny face slots into. 

Seems worth a try already, because the polars look pretty good to me, especially for a test horn without secondary flares. 

Here's 0-45 horizonal in 15 deg increments. Red, green, blue, brown in order.  Psy smoothing used, as that seems to be the norm here..

821620775_frownwithholes0-45H.jpg.d0b206e1dc29cd872e767995494c95f8.jpg

 

 

 

 

 

Edited by gnarly

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Posted (edited)

Hi Mark

 

I have been wondering about "time-smearing" (maybe the wrong word for that effect?) due to different distances to the apex of the "open area" of the ports (off- or on-axis). What defines the wave-front of the woofers response, i.e. acoustic center!? It apparently is no big issue with round holes! Chris wrote something about it some time ago. That the cancelation-notch is "spread" out due to differences in distance of the outer/middle/inner part of the port relative to the apex. I hope you do understand what I am trying to explain!?

 

1 hour ago, gnarly said:

The frowny faced ports are the best yet

 

I would have expected a "happy face/🙂" to be best!?

 

If I imagine the sound-wave-front to progress out through the conical horn as a segment of a sphere (like a soap-bubble), then the surface of the sound-bubble would "cut" the horn-wall as a "happy face" ( equal distance to the apex at all positions). You can se a bit of that in the big Jericho synergy´s with 6 times 18" drivers firing through holes that are arranged in an arc, following the intended sound-bubble!

 

Could you try a happy face to? Following the sound-bubble. I think it would be an arc with the center in the apex. But I think you can figure it out. 🙂

 

Steffen

 

PS: Thank you for experimenting and sharing!

 

 

Edited by Supersteff

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1 hour ago, Supersteff said:

Hi Mark

 

I have been wondering about "time-smearing" (maybe the wrong word for that effect?) due to different distances to the apex of the "open area" of the ports (off- or on-axis). What defines the wave-front of the woofers response, i.e. acoustic center!? It apparently is no big issue with round holes! Chris wrote something about it some time ago. That the cancelation-notch is "spread" out due to differences in distance of the outer/middle/inner part of the port relative to the apex. I hope you do understand what I am trying to explain!?

 

I think i get what you are saying...not sure, but the idea to me has been that the "acoustic notch" from the CD to mid ports, gets spread out in time more with larger ports, due to a greater distance span.

1 hour ago, Supersteff said:

 

I would have expected a "happy face/🙂" to be best!?

 

The  preceding exchange is why i used a frowny face.  I think it maximizes the port-to-CD distance-spread variation.

1 hour ago, Supersteff said:

 

If I imagine the sound-wave-front to progress out through the conical horn as a segment of a sphere (like a soap-bubble), then the surface of the sound-bubble would "cut" the horn-wall as a "happy face" ( equal distance to the apex at all positions). You can se a bit of that in the big Jericho synergy´s with 6 times 18" drivers firing through holes that are arranged in an arc, following the intended sound-bubble!

 

I kinda quit trying to think about wave front shapes, hasn't helped me make better sound.

1 hour ago, Supersteff said:

 

Could you try a happy face to? Following the sound-bubble. I think it would be an arc with the center in the apex. But I think you can figure it out. 🙂

 

Happy to , my #1 rule is OBSERVE MORE, think less......

That said, i kinda tried this before, albeit in wood.  It sucked.  

So I'll just spin the frowny plates 180 degrees.  Will be too far away from throat, but if it looks at all promising, I'll remake duct tape smiley closer.

1 hour ago, Supersteff said:

Steffen

 

PS: Thank you for experimenting and sharing!

 

 

 

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Hi Steffen, hi all, 

 

I've has some real run with these plate-overport experiments the last few drizzly days.

Long story short, I've tried many new things: smiley face, tear drop, vertical and horizontal open slots (without pizza pan), and a combination of s smiley face and a round hole.

Also remeasured my existing syn7 with 2.75" round centered ports, under the exact same testing conditions, . Syn7 has the same sized 90x60 horn, that the test horn does.

 

Probably the first graph to show is the benchmark....the CD on the horn with no ports at all. dcx 464 with 500Hz hpf, and xover at 3.8kHz.

All graphs reflect full tuning; flat mag and phase response with linear phase crossovers.

I settled in on just taking 0-45 deg horizontals, due to the amount of data being collected.

1191911243_hornonlydcx464hpf500Hz.jpg.3f3f3fae0d0c8b1dd6ac8267ebaa0a5a.jpg

 

So I think that's as good as polars can stay, after adding ports.

 

 

Next, to show what damage 2.75" centered round ports over the woofers do to the CD's response, are comparisons against the curves above at 0, 15, 30, and 45 degrees.

Easy to tell which is which, as the woofer ports push response down to 120Hz.

 

0 deg first.

2068209415_noportsvsround0d.jpg.da7638af2845225d323589e7716f93ab.jpg

 

15 deg

1057362342_noportsvsround15d.jpg.15601f32e63c849cc3422d65f5307d7a.jpg

30 deg

1324734375_noportsvsround30d.jpg.560014131a05af4e771321dba6c63610.jpg

 

45 deg

369311131_noportsvsround45d.jpg.6a84ccc8300f60b638f02ab1d33fb0a4.jpg

 

 

As you can see,  the round centered ports do very little harm to polars, until around 30 degrees.

 

 

To keep this post from getting too long, i will stop here and continue with a Pt2

 

 

 

 

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Pt2.

 

The reason for all the plate experiments has been to try to improve polars as they get wider.  I've been happy enough with round port response within +/-20 degrees.

I imagine some folks are wondering why not just put the ports in the corners (off-axis) like usual, but I need to use centered ports to be able to build synergies with top and bottom mounted woofers.  This makes construction so much easier, as the top and bottom panels can be used to seal the woofers in. It also is a big weight saving box design.

It's probably worth reminding though, that this  strategy does require a CD that can reach straight to the woofers, without any small mid-ranges.

 

Anyway, the best wide angle 'horn alone' polar matching has come from  smiley face ports.  Good call Steffen 😀

Here is horn alone vs smiley, at 30 and 45 degrees. The traces match much nicer against the CD than the round ports do..

1587069931_hornonlyvssmiley30and45deg.jpg.b40e1cf7145ed38907ad7aacecd8cee0.jpg

 

 

But within the +/-20 range of excellence for round ports, smiley is not nearly as good. 

So, I'm like, what if I put the two together, smiley and roundy, sized to keep area the same...

Like this lower plate...   top plate fell off...damn tape haha...but at least shows the 7" open hole under the plates

1147314667_combiplate.thumb.jpg.bf937bb8d4b16aed62e55e3c7d0d1738.jpg

 

Here is the polar graph for this combi-shaped plate.

So far it's the best overall compromise i think.

I need to compare verticals against the simple round hole, to decide if it's worth the extra build effort.

Hoping so, really 😄

 

1061388057_combiholeplussmile0-45deg.jpg.3098a1976b82a1f35ba2f29f993638be.jpg

 

 

If nothing else, I hope these two posts help encourage folks to try MEH ports, anywhere they want to try them !.

 

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Hi Mark

 

Nice work! Thanks for trying my idea.

 

I have been looking at the picture of your compromise, smiley with round hole. In a way it seems to me that it approaches my suggestion for at smiley (in average pulls the middle section of the port nearer to the apex/CD), constructed as an arc with the center in the apex. So it gets more 🙂 than 😊. That would for me be the geometrically most beautiful solution! Although I don´t know if that is a valid design-criteria!? I think it was good old Buckminster Fuller who said something like: "A good solution of a problem is often also a beautiful solution for the eye!"

 

If you have the time, energy and motivation then here is a new proposal: What if you make a 🙂/smiley with an open mouth. An elliptically shaped port, eventually a "smiling" ellipse. Still following the idea of an arc relative to the apex, but just wider in the middle section of the port. This could somehow be "the beautiful version" of the smiley/hole-version. Maybe you will have to place the "smiling-ellipse-port" off-center relative to your woofer, to get it near enough to the CD? Just an other compromise/trade off!!!!

 

Happy experimenting!

 

Steffen

 

 

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