Mini-Synergy Horn Experiment - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 12-12-2015, 07:24 PM - Thread Starter
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Mini-Synergy Horn Experiment

Since I've been in the habit of dual posting my projects on DIYA and here I figure I might as well keep it up

I've been interested in building a Synergy horn for 3, maybe 4 years now. The SH is what got me interested in high eff speakers, horns/wgs, etc. The more that I build and learn about audio the less I think a Synergy is ideal for home use......the ports near the comp driver exit being my main beef. Thinking and knowing are two different things and so before I write it off completely I figured I might as well build the dang thing. It's not like I haven't had a case of Synergy mids (Celestion TF0410MR also used I believe in the 893?) laying around for 3 years or anything . I've seen some data comparison of ports/vs no mid ports but not quite at the level of detail I'd like to see to make any kind of determination. Some of the best data I've seen is of Paul Spencer's big elliptical job. Looks to be high q resonances in the normalized fr polar, so to my way of thinking what look like off axis resonances are actually mostly present in the 0° curve.

OK........on to the experiment. First I want to say that yes, I do understand that the Synergy horn "should" be a rectangular section and I understand why. My reasoning to go elliptical is 1) I don't see a square section horn as being the ideal shape for the wave, and 2) I have an eoswg just laying around, but no square horns. Elliptical it is. The wg is an EOS job that I built a little over a year ago. 18" wide with a roughly 90x60 pattern, and a 1.5" radius roundover: https://www.avsforum.com/forum/155-di...-progress.html. The drivers are the aforementioned 4" Celestions and a BMS 4524. I don’t have any pics of the mid chambers at the moment, but they consist of a 2” counterbore frustum that’s .5” deep and a .3" wide x .8" long slot port (note that in the pic is a round port that I tried first) with a port length of about .200". The counterbore is filled with plumbers putty and shaped into a conical section leading to the port. I didn’t intend to make the mid chambers that deep but my horn wall was thicker than I remember. The frustum is offset so the edge is at the edge of the driver, and the slot port is offset as well. Distance from the center of the port to the cd exit is about 1.8". I’ve done enough Horn Resp models over the years to know that this would get me close. I’m using 3 mids for this, with the ports spaced equally, wired in parallel.

Data coming next....
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post #2 of 17 Old 12-12-2015, 07:32 PM - Thread Starter
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Ok these measurements were taken last weekend in my backyard. I have a measurement rig that I hang off the back of my deck giving me about 8' to the ground and I placed the mic 8' away. This yields 8ms of clean data. Horizontal fr and contour plot followed by the vertical fr plot (I forgot to save the 20° curve for the vertical data set). The vertical was taken on the "top" port side of the wg to see if the effect from the port is greater, but I didn't do the other side. I just measured +/- vertical indoors today and each side is pretty much the same.

I sent the horizontal data set to Geddes and he has it posted in his PolarMap sw. You need to view that with a Microsoft browser if you want to check it out.

More to come...
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post #3 of 17 Old 12-12-2015, 07:38 PM - Thread Starter
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Here's the main reason I built this thing.........to investigate the effect of the ports on the hf response. I measured the wg without the ports, then I drilled the ports and re-measured. These measurements are of a .5" dia hole rather than the slot port I ended up with but the result is the same. I overlaid individual curves to better show the effect which is quite minimal. This was a pleasant surprise and as a result I'm going to spend the winter designing a Big Boy Synergy Horn to be built in the spring. You can see that the 40° curve is lower in level with the port added. I think this is due to decreased pressure in the first few inches of the wg causing a broadband decrease in output.
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post #4 of 17 Old 12-12-2015, 07:42 PM - Thread Starter
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Just to see if I could I also whipped up a linear-phase(ish) xo. No FIR correction just standard IIR filters and the "magic" of the Synergy configuration. I think this can be improved with a compression driver that has more low end capability or getting the mids to play a bit higher.

I'm currently using this crossed at 300hz to the dual 15 stack shown in the op as a basement gym/workshop speaker. It works quite well and sounds much better than it should for something just hacked together.
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post #5 of 17 Old 12-13-2015, 01:39 AM
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What do you mean by a port in this context? Does it mean the mid fires through that hole (this is the port?) into the horn and that you have moulded something to smooth the transition from the driver to the hole? Seems like the reverse of a small horn? Dumb question maybe, haven't read much on synergy horns.

Also what is the magic that facilitates a linear (ish) phase xo there? Can you show the overall iir shape?
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post #6 of 17 Old 12-13-2015, 05:10 AM - Thread Starter
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Quote:
Originally Posted by 3ll3d00d View Post
What do you mean by a port in this context? Does it mean the mid fires through that hole (this is the port?) into the horn and that you have moulded something to smooth the transition from the driver to the hole? Seems like the reverse of a small horn? Dumb question maybe, haven't read much on synergy horns.

Also what is the magic that facilitates a linear (ish) phase xo there? Can you show the overall iir shape?
My technical writing skills must not be as bad as I thought because you got the gist of the port. What happens is the mid chamber/port combination forms an acoustical lpf. The corner f is determined by the driver parameters and the geometry of the chamber/port combo. This also has the benefit of filtering distortion products as well. The port is placed near the cd exit so that it is within 1/4wl at the xo freq, and we have a 1/2wl notch from the mid due to the wave reflecting off the phase plug/cd diaphragm. When placed correctly this notch falls just beyond the lpf corner in the stop band to provide more acoustic filtering.

Despite the fact that the mids are physically closer to the mic the acoustic lpf causes delay and the comp driver output arrives first. The xo in this case is quite simple. I applied cd eq to the compression driver and flattened the mid response which shows a peak before the lp corner due to the mid chamber. There is a 1st order lpf at 2khz on the mid to further filter hf and shape the phase, and there's a 1st order hpf on the comp driver at 1.5khz iirc with a .5ms delay. Then a peq centered on the acoustic xo freq is needed to flatten the response thru the xo.

In what I've got here I can actually move the ports farther down the horn to move that 1/2 wave notch down. This will also have the effect of centering the port on the mid cone better which I've found increases hf due to more equal path lengths across the cone in the mid chamber. The port can also be enlarged a bit to get more hf response. A more robust comp driver really is needed as well to get more low end there......the 1" vc 4524 runs out of gas at 1.1khz and distortion is rising. Basically lots of overlap is key to getting a linear phase through the xo region.

What's cool too is that the mids have about 6dB more spl than the comp driver when wired in series.
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post #7 of 17 Old 12-13-2015, 05:41 AM
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Do these measurements really need to be that accurate? I see that you listed them to the thousandths of an inch. How much wiggle room is there?

It looks like the ports are already very close to the CD, how much closer can they get before the mids basket runs into the CD? That must be a tight cluster of drivers behind that WG.

Edit, sorry just noticed the second pic showing the drivers behind the WG.

It's hard to imagine moving them much closer to the CD back there.
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post #8 of 17 Old 12-13-2015, 05:47 AM - Thread Starter
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Quote:
Originally Posted by Samps View Post
Do these measurements really need to be that accurate? I see that you listed them to the thousandths of an inch. How much wiggle room is there?

It looks like the ports are already very close to the CD, how much closer can they get before the mids basket runs into the CD? That must be a tight cluster of drivers behind that WG.

Edit, sorry just noticed the second pic showing the drivers behind the WG.

It's hard to imagine moving them much closer to the CD back there.
Ha! No that kind of accuracy probably isn't needed.........I'm a machinist/cnc programmer so it's habit.

The mids are physically as close as they can get. What I was talking about is moving the port farther away (towards the mouth) from the cd exit. The actual drivers will stay put.
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post #9 of 17 Old 12-13-2015, 06:15 AM
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Oh I thought the port was centered in front of the cone.

I guess closed back mids are almost required for this? Not much room for little cabs.
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post #10 of 17 Old 12-13-2015, 06:25 AM - Thread Starter
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Closed back mids are the easiest way for sure as we're basically turning the mid into a compression driver so the rear chamber needs to be quite small to work properly. There have been some who have had luck sealing the back of small drivers with cardboard tubes, pvc end caps, etc. I think bwaslo's CoSyne 3-way Synergy speakers use a mid that he seals up.

I've also seen larger format comp drivers used with more typical 8" (open basket) drivers with a lower xo and a BR enclosure for the mid with the ports exiting near the horn mouth. There's several ways to approach this but the underlying "rules" are the same.
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post #11 of 17 Old 12-14-2015, 08:27 AM
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Nate - FYI, the PolarMap software no longer requires MS Explorer to work. I found that error. It should run under any browser. It still requires US language setting in the OS (to read numbers with decimals instead of commas).

Earl R. Geddes
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post #12 of 17 Old 12-14-2015, 01:06 PM - Thread Starter
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Quote:
Originally Posted by gedlee View Post
Nate - FYI, the PolarMap software no longer requires MS Explorer to work. I found that error. It should run under any browser. It still requires US language setting in the OS (to read numbers with decimals instead of commas).
Ahh cool. I'll give it a shot later
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post #13 of 17 Old 12-15-2015, 07:48 PM
 
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Nice Nate.
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post #14 of 17 Old 12-16-2015, 04:39 AM - Thread Starter
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Thanks. I'll be using this as my first attempt at a passive xo....
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post #15 of 17 Old 10-15-2017, 10:25 AM - Thread Starter
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I've been away from audio for a while but I picked this project back up. Moving on from the experiment stage to the "let's cut of some perfectly good hand made waveguides" stage. There's more work to be done as far as the response goes but it's headed in the right direction. I need to get some outdoor measurements to get a better idea of what's going on with the mids. Eventually I'd like to build some enclosures for the wg and I'll build new cabs for the woofers. If I play my cards right I'll have full access to the CNC equipment at work so I might just build new waveguides.

Each speaker is using a BMS 4552nd cd, two Celestion TF0401MR mids and two TD15M's in sealed cabs. XO at 300hz and 1.3khz.

Dang cats are always photobombing me
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post #16 of 17 Old 10-15-2017, 12:26 PM
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Quote:
Originally Posted by Nate Hansen View Post
I've been away from audio for a while but I picked this project back up. Moving on from the experiment stage to the "let's cut of some perfectly good hand made waveguides" stage. There's more work to be done as far as the response goes but it's headed in the right direction. I need to get some outdoor measurements to get a better idea of what's going on with the mids. Eventually I'd like to build some enclosures for the wg and I'll build new cabs for the woofers. If I play my cards right I'll have full access to the CNC equipment at work so I might just build new waveguides.

Each speaker is using a BMS 4552nd cd, two Celestion TF0401MR mids and two TD15M's in sealed cabs. XO at 300hz and 1.3khz.

Dang cats are always photobombing me
So how do they sound to you? What other speakers do you have or had that you could compare them against as for sound as in differences or strengths or weakness?

HTPC, Sony 40es, 120" Silver Ticket, 7702mkii, Sunfire Amp 225w, JBL 590, JBL 520

PSA XS30, Seaton Submersive, 2 Um-18 8cf sealed, Outlaw Ultra x 12, Kappa Pro 18LF, BFM Tuba 60 horn, B&C 18TBW100 6cf 41hz, 34hz, 28hz tune

iNuke 3000 & 6000 DSP's, Crowson Motion Actuator
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post #17 of 17 Old 10-15-2017, 06:04 PM - Thread Starter
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So how do they sound to you? What other speakers do you have or had that you could compare them against as for sound as in differences or strengths or weakness?
Of the many things I'm not good at describing what I hear is one of them. That said since I started on this project a couple years ago I noticed something "different" about these synergy horns. More coherent maybe? The only thing I've really listened to the last couple years were my big 3 ways (with the same wg sans mid ranges) from the last post in this thread: https://www.avsforum.com/forum/155-di...-cardioid.html. I haven't had any commercial speakers in 6 years or so. These still need work but I guess I'd say these are more natural and the midbass response is better with the dual woofers running up to 300hz. I know that's not giving you much but I prefer to let the data do the talking.

Here's some in room data from the lp I took today. RTA avg swept around the mlp and then hit it with psychoacoustic smoothing. No subs here obviously just the mains. These will be good speakers to play with linear phase.
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