Ghetto synergy-ish experiment with scrap parts

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Disclaimer: this is a scruffy ex tempore build from scraps and random bits, i AM putting lipstick on a pig, i am not exchanging any parts, so please bear with me and if you are inclined, share your thoughts on optimization.

I have had this plastic hf horn laying around. It's from an EAW cinema system, loaded with a b&c de75. I noticed recently that this horn has a flat section that would lend itself for mounting a mid driver. I have wanted to experiment with synergy loading for some time, and since the horn is laying around unused, and is too big and too cumbersome to build a conventional two way box, i decided to do a quick and dirty synergy project.

I have removed the plastic bracing ribs from the back of the horn, and added 3mm spacers to mount my mid drivers on and have some excursion clearance.

Now the big question is about the taps. Size and placement. Afaik from reading a few synergy threads, they should be placed as close to the horn throat as possible. I am thinking about two taps per driver, maybe 10mm to start with? Is there any ballpark figure for the size? How big can i expect to go? I remember some people starting small and slowly increasing size to find optimum size by trial and error.

The distance to the horn throat is in the order of 12-13 cm, so i can expect to cross over around 600 hz at highest?

Looking forward to the synergy gurus' feedback!


  • 20200125_201916.jpg
    1,021.5 KB · Views: 336
  • 20200126_202253.jpg
    909.7 KB · Views: 340
Founder of XSA-Labs
Joined 2012
Paid Member
Yes, as close as possible to allow the highest XO point as possible. The farther away it is, there will be a cancellation reflection dip in the mids that is function of speed of sound and distance the mid is from CD membrane. If done well, you can get maybe 1500Hz. If not, it might be 700Hz or 600Hz. CD’s don’t like to go that low for a XO point. You might try a full range driver in the throat with adapter to allow the tweeter to go to 600Hz.

You might find some info here useful:
A Bookshelf Multi-Way Point-Source Horn
As mentioned, i have been scanning a few threads for information on midrange tap placement and scaling, but it is hard to find amongst the general development conversation.

I want to start by drilling a small pilot hole for each tap, and then gradually enlarge with a consecutively larger drill size, and maybe a reamer if necessary.

With this method, i need to have a rough idea how large the taps will be, so that i can optimize pilot hole placement, to make sure it is neither too far nor too close to the edge.

I drew two taps on one of the horns just to get a feeling for it. They are not aligned, i just wanted to get an idea of the scale. Does it look too small? Is it completely off? The cone driver gasket is 13 cm in diameter.


  • 20200127_173329.jpg
    807.5 KB · Views: 264
Founder of XSA-Labs
Joined 2012
Paid Member
It depends on how powerful the motor is on the driver and what kind of a bandpass effect you want on the output. It really should be simulated. But as you don’t seem to be concerned about exact amounts and values, pick something - looks at cross sectional areas of vents on a bass reflex vs cone area. Typically 15% or so. A larger hole will let more air through and disrupt your horn profile. The trick is to make it just large enough to let the sound out nicely and not ruin the horn profile for the tweeter. You can also use a Dremel tool and then not confine yourself to round holes guided by pilots. They can be arcs, mesh like holes, slits, etc. they can be asymmetric. Have fun. Start small and enlarge is good as you can’t go back very easily.

I did once by 3D printing a curved piece and glued it back in place when my aperture was too big.

Probably no bigger than 30% of cone CSA. Start at 15% and enlarge up.
xrk, thank you for your input. I did a bit more reading, and am scratching my head again. :confused: OCD alarm has been triggered! :rolleyes: I thought I was going to fudge around and have some fun, but now my gut feeling says I probably have to put this project on the back burner and do a lot more reading, and calculations. :shutup:

The EAW horn is detachable in halves, and hence very easy to work with. It is a constant directivity horn with two sections. The first section is a gentle transition from the circular throat to a vertical rectangular diffraction slot. After the slot it opens up to 90° horizontal.

My original idea was to just put a 5" fullrange driver on the second, larger section to play around with. The B&C driver is rated for full output down to 800 Hz, and according to the datasheet takes the dive below 500 Hz. So in theory, at bedroom levels, it should be just about doable.

But then I realized that the first, transitional section is big enough to accomodate a TC9FD on each side.....

So this has me scratching my head, wondering if I should go the extra mile and get some TC9FD and do the job properly. I could get VERY close to the horn throat, and probably push the xover at least an octave higher. Also, the second horn section is large enough to accomodate a 6" woofer, which got me thinking even further..... I could potentially go three way, almost fullrange.... :eek:
But then I realized that the first, transitional section is big enough to accomodate a TC9FD on each side.....

That was my first thought as well, just put the mids in the diffraction slot so you get close the compression driver. Not sure if a TC9FD is any good as a synergy mid though... If you don't wan't to spend a lot of money you might try Visaton FRS8, is about 10 euros, and in the past people have used it as a synergy mid. Just buy a single one and test it out before spending much more...

I'd be very interested in the results of using a diffraction horn as a synergy.
Founder of XSA-Labs
Joined 2012
Paid Member
TC9 is an ok driver to do this with - although not the best as it has a rather weak motor with Qts in the 0.8 range. Wonderfully smooth though, compact, and inexpensive.

Perhaps look into a sealed back midrange - that will save you from having to make a separate rear chamber of you go with a 3 way.

This unit might be a bit too large, but you get the idea:

Pyle PDMR5 5" Sealed Back Midrange Speaker Driver
hmm.... thank you for the driver recommendation 4real. budget price is a plus.

in the trynergy the TC9FD is used as the horn driver, not as a midrange.

just looking at the datasheets, the Visaton FRS8 and the TC9FD look quite similar, except for some Q value variance, and the TC9FD being 3-4 dB more sensitive across the board. Similar xmax, BL. Just based on the sensitivity, I would probably want to spend the ~6€ extra per driver to have more headroom/go louder.

Have to do more research.

whats up with synergy calc by the way? I was able to download the instruction pdf, but the main page is unavailable (403).
After finding a local supplier with Visaton FRS8 in stock, i jumped the gun and went ahead with the project. The drivers didnt fit at first, due to the length of the screws that connect the mounting plate of the horn and driver to the yoke. Flipping the screws around gave me just enough clearance to assemble everything.

The midrange taps are 12mm in diameter at the moment.

Crossover is a Harsch alignment at 1kHz. The Visatons go down to about 200 Hz, but i cut them off at 300 Hz.

Sounds quite nice. Unfortunately i have only one horn.

I did some free field measurements with room eq wizard. Unfortunately i didnt have a lot of time to play around, due to weather, lack of time, and other inconveniences.

But in conclusion, with a budget of 30 euros, it was definitely worth a try, and i will keep working on it as time permits.


  • 20200519_001950.jpg
    813.6 KB · Views: 109
  • 20200519_002239.jpg
    744.2 KB · Views: 107
  • 20200519_172353.jpg
    826.8 KB · Views: 72
  • 20200519_172335.jpg
    842 KB · Views: 77
  • 20200520_201028.jpg
    1.1 MB · Views: 70
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.