DIY Synergy/Unity spreadsheet

Effect of large woofer port holes on waveguide

I did some tests today on some (relatively mild) response irregularities seen in my horns. I currently have them crossed over using a MiniDSP 2x4 (one one each) and the "4way advanced" plug-in for a reasonably linear phase design. BTW, if anyone is going this route and wants the filter coefficients to use with the coSyne design, drop me a PM.

Anyway, I have noticed that there is a dip at around 4500Hz at on-axis vs about 22deg off horizontal axis. The phase response also bumps up in that area. From some previous work, I knew this was from the largish woofer port openings up stream, so I thought I'd see what putting some sort of cover on the holes would do. The goal was to find something that would let highs reflect off (and continue to propagate down the horn unmolested) while still letting lows through.

I started of (and finished for now) with plastic shipping tape. This blocked the woofers too much. I thought it would just vibrate with the air, but it made bad noises as the vibrations pulled at the adhesive while also dropping the response by several dB in places.... not a good approach. But, here is a plot of the effect on the tweeter's on-axis response:
The "with tape" curves are reduced 10dB to separate them from the "normal" ones. As seen, it does reduced (but not eliminate) the funniness around 4500Hz. I'd like to have this do better, but the tape is already bad news for the woofer.

So, I think a better approach would be to try a different shape and placement of the woofer holes. Right now, mine are long and oval along near the horn corners. I wonder if round and pushed right onto the corners would give smoother results? I don't know whether this is audible, but it is something that could be improved. Tom, are you reading?? What type port holes work best?
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Here are the response curves with some further EQ (horn section only at about 20", not including port output, and no subwoofers in measurement) for the coSynes using the MiniDSP crossover and crossover based on a design Tom Danley kindly put together for me. I plan to work with some allpass filters to fix up the phase response some when I have time to do some simulation on it.

Freq Response:



Impulse Response:


Wavelet Spectrogram (mid-room):

 

ExA, I hope you haven't ordered your parts yet -- you have the wrong tweeter driver, the CDX1-1440 is a titanium driver, the CDX1-1445 that I used is a mylar diaphragm tweeter. Not that the titanium wouldn't work, but it would probably want a slightly different crossover!

 

Here are the cutting plans for the horn enclosure Tony Seaford made. This fits the Synergy horn as designed above, but with a sealed box instead of the huge ported box I used (the sealed will need to be crossed over a bit higher to a sub). Nice, easy size to maneuver and looks really nice, too.

http://libinst.com/SynergyDIY/Tonys/TonysCab.pdf



Tony's notes:

 

Hi Coco,

Thanks. I've thought about doing the next as a 2-way, but I'm not sure whether I can do it with linear phase (which, again, I don't know whether that is even audible, but at least it's measurable unlike lots of audiophile kinds of goodnesses!). The Aura NS6 will go up high enough, but a larger tweeter driver would be needed (I was thinking the Celestion CDX1-1745 or the Denovo 360).

Here is the modeled curve (red) on top of the measured woofer curve (black). Levels not actual, I just aligned them via eyeball.

Not a great match, might be because I used an oval port hole into the horn.

 

Because you need wide overlaps for passive linear phase. With DSP (particularly FIR filters ), no prob, of course.

There are drawings earlier in this thread showing the oblong port dimensions and placement. That causes other issues though (I think ).

Bill

 

Garric33, mtg90,

Yup, despite my constant asking for licensing of the Synergy patent, I've never been able to get Tom and his business partner to give me an ok (never got a definite turn-down, either, if that's of any help). So for the immediate future (and probably always) it will be for from-scratch builders, only. Sorry.

 

I was revisiting my HornResp model for the woofers and found a rather large mistake -- I was miles off on the value for Vtc. I hadn't put a lot of time into the HornResp model for the woofers, as I wasn't expecting the horn to do anything at the woofers' frequencies -- I just wanted to assure that the horn wouldn't mess them up. The woofers are in the horn just to get them close in to the other drivers for point-source behaviour, not for horn gain (would need a bigger horn for that).

So, here is the modified HornResp curve superimposed on the measured (at the horn mouth) response.:


Better match, but off at the HF rolloff (the measured curve, black, is nicer!). Probably because the port opening is oblong rather than just a round hole.

Here is the HornResp model:


note: the back chamber is modeled as sealed above, 1cuft. I actually used it in a ported box, but that won't model in HornResp with the front stuff I needed.

I'll probably stay with a 3-way for the next build, as I like being able to do the passive linear phase response. Probably the only change will be to move the ports into the corners of the horn rather than have them on the walls.

 

...a taste of things to come...

 

just like the cabs the original ones are in. Ply with red oak veneer actually. Revised cutting scheme, no "vertical sleds " involved. And entry ports right in the corners this time. New spreadsheet will be posted. ..

 

Hi John/Patrick
I think his partner(s?) aren't too keen on the idea, Tom seemed to be in favor but probably couldn't make a good business case for it. Owning Synergy is probably one of the company's strongest assets, likely income from licensing to us probably doesn't seem worth the risk.
It's unfortunate because I think the Synergy speaker is like the home hifi holy grail, pretty much does all you could ask of a speaker.

----
John, are you in the Portland area?