Small Syns

I usually copy Danley.

"if it ain't broke don't fix it"

Here's what I measured on the SH-50:

Midrange taps are 3/4" in diam, 3.5" from throat

Woofer taps are 2.5" in diam, 10.5" from throat

Woofer ports are 2.5" in diam, 14.5" from throat

Note that these dimensions require you to use the same xover points as the SH-50. YMMV
 
Cask05, I think the answers to some of those questions is to be found in a Hornresponse sim of each particular circumstance. For instance, port length and size and compression ratio aren't free variables -- there are relatively tight combinations of those (for a particular driver, horn, and crossover point) that you have to stay near to get the thing to even perform acceptably. That's why I always advise people to not just start drilling holes into their expensive waveguide until after they run a sim to see whether what they want even has a prayer of working!

My take on the ports in general is that they are not to the benefit of (and are likely bad for) drivers covering frequency ranges above the one being ported. Their effect may be acceptable (and all can work very well in fact) but I still see them as something to be minimized if I can. In other (overstated) words: having a zillion drivers ported through a perforated horn would not be better than one driver through one or two ports if the one driver can cover the range and SPL levels needed. Four midrange drivers is not necessarily better than two or one, and for home use is probably worse (particularly when already using a pro midrange driver that is normally used, in pro applications, without a horn at all!). And bigger drivers aren't necessarily better than smaller ones, again for home use, either.

Shape? I did a bunch of test at one time (didn't save any data though) on some port shapes on woofers ported into the CoSyne design. Several small ports of the same total area seemed to do better than one large one in not disrupting midrange performance. Oval ports with long dimension going radially out from the horn axis seemed to cause less midrange trouble than when the same area ports are shorter in the radial directions (though the perturbations seemed more narrow in frequency range, that might possibly be more preferable?). The ports further out from the throat didn't cause too much trouble for the tweeter, but did for the midranges -- as Danley says, the tweeter pattern is already set before the wave gets very far out into the horn.

I also did some tests with lossy ports -- IOW, putting cloth over the ports to try to make them "opaque" for higher frequencies but transparent for lower frequencies. That didn't work until I used a cloth of such tight weave that it hurt the LF output and started to make obnoxious noises from air squeezing through! I also tried some honeycomb material in the ports (at be lots of tightly packed small ports instead of one big open port) -- no measurable effect at all with that one.

BTW, I like the expression "Multi Entrant Horn", but "MEH" is an acronym that (in the current slang) expresses a VERY distinct lack of interest! "Synergy" and "Unity" are trademarks, so maybe "Coincident Horn" or just "Broadband Horn" would do.
 
Hi,
I've been thinking between your sealed and ported designs and I'm leaning towards the ported full range one. As space is somewhat limited I began to wonder that what if I were to build a floorstanding version of the ported one. I'll position the speaker very close to wall, and if I manage to keep the depth in 9" range the quarter-vawe cancellation happens somewhere around 350Hz where the loudspeaker has still some directivity left to minimize the effect. So instead of going to deeper ported box, I'd make a taller one. If my calculations were correct, when positioning the tweeter to ear height (about 33") it would give me 55 liters of empty box space below the sealed-design box (keeping the width and depth same), which should be more than enough for ports and such.
 
Judging from a lack of responses (other than the proximity of ports that Bill made, just above), I believe that it would be useful to have links to the threads/posts where port size, position, and their effects on performance stated. Questions still arise on the following:

7) Should the ports be round, elliptical, or slotted? What are the effects? What are the effects of multiple small through holes (i.e., a "grating") on top of a larger through port?

I edited the quote for brevity.

Like bwaslo I've done some testing of different port shapes. I really liked the idea of a bunch of small holes. It tested well with a 4" closed back mid on a flat baffle. I never tried it on the horn once I realized that the total area covered by all the holes (to equal one larger slot or hole) would pretty much make the entire throat of the horn look like Swiss cheese when adding in all the drivers [emoji6]. That and I thought that the varying port length from hole to hole on my elliptical horn might be an issue.... Of course a horn with flat walls would fix that.

I was also afraid that a bunch of closely spaced small holes might look like a single large hole at HF due to the shorter wl.
 
I edited the quote for brevity.

Like bwaslo I've done some testing of different port shapes. I really liked the idea of a bunch of small holes. It tested well with a 4" closed back mid on a flat baffle. I never tried it on the horn once I realized that the total area covered by all the holes (to equal one larger slot or hole) would pretty much make the entire throat of the horn look like Swiss cheese when adding in all the drivers [emoji6]. That and I thought that the varying port length from hole to hole on my elliptical horn might be an issue.... Of course a horn with flat walls would fix that.

I was also afraid that a bunch of closely spaced small holes might look like a single large hole at HF due to the shorter wl.


I think the thing that matters most is the port length. The thinner the horn wall, the thinner the port length and thus the smaller hole size that suffices. I've done HR simulations that if you cut port length in half you can also cut your hole size in half for the same particle velocity and frequency response. And I built a synergy horn with quite small mid port holes. (My synergy corner horn... thread)

That is the value of "frustrumizing". Thinning out the horn wall in proximity to the hole ts permits significantly smaller holes. The smaller the hole, the less you need to worry about its shape or proximity to horn wall.

Simulating will tell you there is {hole size, port length} that optimizes bandwidth. For any port length, there is a corresponding optimum hole size that is practical to find only with simulation. I went with a .25" port length through a 12 mm horn wall, routed the horn wall down to .25" in the 120 degree sector containing the hole, then filled some of that back in when I found I had too much air under the cone.
 
Hi,
I've been thinking between your sealed and ported ...... I'll position the speaker very close to wall, and if I manage to keep the depth in 9" range the quarter-vawe cancellation happens somewhere around 350Hz where the loudspeaker has still some directivity left to minimize the effect. So instead of going to deeper ported box, I'd make a taller one. If my calculations were correct, when positioning the tweeter to ear height (about 33") it would give me 55 liters of empty box space below the sealed-design box (keeping the width and depth same), which should be more than enough for ports and such.

Hi Cardiole,

Seems like a good idea. In fact, I've drawn up plans and ordered parts for a "Shallow Shelf Ported" version that is pretty much like that except not a floor stander (just a tall on-stand type, though no reason floor stander wouldnt be as good... cosmetic choice). I wasnt going to post those plans till I build it (once table saw weather returns in a few months) but I can copy them to pdf if that would be any help.
 
Hi Cardiole,

Seems like a good idea. In fact, I've drawn up plans and ordered parts for a "Shallow Shelf Ported" version that is pretty much like that except not a floor stander (just a tall on-stand type, though no reason floor stander wouldnt be as good... cosmetic choice). I wasnt going to post those plans till I build it (once table saw weather returns in a few months) but I can copy them to pdf if that would be any help.

I'd love to see those plans as well. Sounds like great potential for a bedroom system.
 
OK, here they are as they are atm -- I don't have the 'step-by-step' assembly diagrams and markup lines written up yet, but it shouldn't be too hard to figure out if you're in a hurry. --http://libinst.com/SynergyDIY/SmallSyns/ShallowShelfPorted/SmallSynsShallowPorted%20temp.pdf

SPSmallSyns%20appearance.png
 
It was mostly so the horn would be at ear level without the box being below the level of the credenza in our living room. I also wanted to try the horn at center to keep the top/bottom cabinet edges a little further from it, might smooth some of the cabinet diffraction ripples (I don't expect that to make a lot of difference, though, because of the horn directivity).
 
Yeah, I didn't talk about that since it is pretty much common knowledge around here. For the SEALED version, I basically stuffed it with cotton (blue-jeans) based insulation material. Hard to get too much, though you don't want to be packing it in with a plunger of course.

For the PORTED versions, you don't want too much stuffing in there because it can kill the box's low frequency resonance needed for the ported operation. For that, I took some sheets (about 8"x8", an inch thick) of the cotton-based insulation pads and hung them with a stapler behind the woofers, making sure there is still a good indirect air path from the cones to the port area. Of course the midrange and tweeter don't need any of the insulation as their surfaces are isolated from the inside volume of the box. It helps that the design is a true 3-way, and the box basically plays only bass and doesn't play much into the midrange at all. The volume damping is to tame midrange effects basically, not for the bass range.

I do have the back wall of the cabinet damped against the back of the woofers and the tweeter compression driver, using felt padded furniture adjusters (the tweeter CD is damped to the back wall by putting several layers of the cotton pad between it and the wall, squashing it in when the horn screws are tighted). That seems to do a very good job of deadening the back and front panels.
 
More questions...
It seems the seos-horn I can easily order here in Europe is the glassfiber one made by Auto-tech and that horn is nearly 1/4" thick. As I've undestood from other synergy threads the depth of the midrange hole affects how big the hole has to be, so do you know or can you measure the thickness of the plastic seos you are using, if there is a diffence to affect the building plans?
Also how millimeter-exact the midrange port position has to be? I'm wondering that if the hole is smaller in diameter, it also has to have its center positioned closer to tweeter so the closest point of the hole is at same distance form the tweeter as in the plans.

--
Build status: tweeters arrived, though I had to order them from Parts-Express because I couldn't find them in Europe.
 
The plastic SEOS horn is about 0.375" thick (!). I think you could make up this distance (for the port length) by building up some of the filler putty beneath the midrange cone.

I don't understand the question about the hole being smaller in diameter -- why would it be, again? If for some reason the hole size was to be different, I think you'd want its center to be in the same place so the aperture averages in the same spot. I don't expect it would have to be millimeter-exact, though. The most important thing is to not let it get much farther from the tweeter (to keep the 1/4 wave reflection notch out of the midrange's band).

One concern I have about using the glass fiber SEOS15, though, is that it looks like its circular tweeter driver mounting plate might be thicker than on the plastic SEOS15 (not sure of that, it's been a while since I had a glass fiber one). That might make it difficult to get the midrange driver to fit in there with its port centered in the same place. I guess I never considered anyone might use the glass fiber SEOS15. What country are you in?
 
I remember reading in other synergy threads that if the midrange hole was shorter, it could also have smaller diameter, but could be that I remember wrong, my memory is not what it should be due to sleep deprivation from night time baby diaper changes etc.

Seems that there are too many possibilities (thickness, mounting plate thickness and diameter) to go wrong with the glassfiber horns, so I'll register to a shipping forwarder and order the plastic horns from Diy sound group.
 
OK, I just measured a plastic SEOS15 horn. First, the thickness of the walls, when measured perpendicular to the wall surface, is actually about 0.35" (8.9mm).

The thickness of the tweeter mounting plate is also about 0.34" (8.6mm).

Bill

Hello Bill.
I tried to sim 8FE200 woofers, I need them to work from 90hz and they seem to provide a little more bass than 6FE100. What you think?
Thank you.
 

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