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bwaslo 5th June 2016 03:02 AM

Small Syns
I posted a few plots of this speaker build on another thread of xrk971's, so thought I'd stop hijacking his thread ( and start a new one.

Edit Dec 18, 2016:
Since this thread is long and meanders a bit (or a lot -- including extended debugging times), here are links to full plan sets, final crossover design, polar and distortion measurements:
When the weather lets me out to work with the saw again, I'll be building a shallow version of the Shelf Ported Small Syns. A 29" tall, 20" wide and only 9" deep box for mounting near the wall with minimal room intrusion.

This one is about a project to use a SEOS15 in a partial Unity/Synergy arrangement, with a midrange driver bandpassed into it and woofers ported just outside and below the waveguide through a pair of slots. The idea is to extend the horizontal directivity a little lower with the array effect of the woofers, while keeping their output locations close enough to the center of the waveguide to keep vertical polar behavior (relatively) well behaved - an essentially point-source behaviour with directivity. I posted some plots of an earlier attempt of it using a small Celestion CD for the tweeter, but it had some distortion issues trying to go too low in frequency. So starting here will be the version using the new Peerless DFM-2535R00-08 driver (which, contrary to angst and gnashing of teeth comments within this thread, is NOT discontinued, and is in fact available from Parts Express at a very reasonable price!).

Here's some pics of the cabinets to show what it looks like.

What I'm going for is:
  • smaller size than most Unity/Synergy variant speakers
  • better WAF (a non-flashy understated cabinet, works well in any room)
  • designed to work close to wall behind it
  • Easy to build without exotic tools (buzz saw and jigsaw, and drill mostly)
  • Good polar behavior, particularly in the horizontal
  • Good sensitivity >93dBSPL 2.83V/1m
  • Tolerable impedance (4 ohm nominal, try to stay above 3 ohms min) (ended up with a dip to about 2.9 ohms)
  • Relatively simple crossover (got less simple, but still not bad)
  • A sealed version (will need subs for any real bass) and a ported full-response version for full-range
I'm NOT going for linear phase for these designs, as I think it is much more practical to linearise phase after-the-fact with a FIR equalizer if that quality is judged to be important (I'm not entirely sold on it after some tests -- polar pattern, single point source, and response shape seem to be a lot more important, from what I've been able to hear in different speaker designs).

The trick to this design is to blend between the midrange and the woofer pair to get reasonably flat, but dropping in level, off-axis mid-high response. It's not very easy to get! I've been simming this in XSim using separate driver objects for each driver type at each angle, connecting the matching types to balance the off-axis response by trial and error.. It takes a fair amount of time to work into something reasonable, but build results do tend to match the simulations quite well.

Harmonic distortion in the tweeter range is pretty good now with the Peerless tweeter and a little more agressive crossover slope

Another midrange could be added on the other side of the waveguide, but I think this is ok without it and minimizes diffraction within the waveguide for the tweeter.

When I get things more complete, I'll put up some build details, including how to modify the SEOS15 waveguide for synergy operation, in case anyone wants to duplicate the design or use it as a starting point for further developments. Please stay tuned!

edit Feb 22 2017:
Next (shelf ported) version --

I hope to get started on this in a month or two

bwaslo 5th June 2016 03:22 AM

Here is a view of the drivers' contributions to the total response (on-axis). Notice how the midrange hands off kind of slowly to the woofers. As you get off axis, the woofers' responses start to interfere with each other causing a dip, right about where the directivity of the SEOS horn goes away and the mids go toward omnidirectional. The output from the mids falls away there and the woofers take over and keep some pattern control going down below 500Hz .

DcibeL 5th June 2016 03:28 AM

Looking good Bill, keep it up, I look forward to seeing where this goes.

Maybe I missed it but what is the midrange driver you are using here?

bwaslo 5th June 2016 03:40 AM

It's a Celestion TF0410MR, one unit per horn. It's not an easy one to get in small quantities, but I'm going to try to get Erich at DIYSoundgroup to supply some (he has some and can order more, I have about a dozen of them here as well). Woofers are FaitalPro 6FE100.

bwaslo 5th June 2016 03:50 AM

Here is how the midrange mounts to the waveguide. The flat mounting plate board is glued on, and sealed with, epoxy putty. I'll have cutting diagrams and dimensions, as well as hole drilling info in some later posts.

Here is shot showing how the woofers hide from behind the waveguide, the baffle is milled/routed out down to two different levels. That can also be done with less tooling and no jig fabrication by jigsawing thinner wood panels and them laminating them together with wood glue.

bwaslo 5th June 2016 04:00 AM

There also need to be spacers between the woofers and the baffle that they mount behind to keep them from slapping into it. I just cut thosr out of 1/4" MDF with a jigsaw. They also get laminated onto the baffle. You can also see some plywood bracing strips glued to the back panel and to the box walls to keep the panel quiet.

edit: by the way, do you see that patched area just to the bottom right of the waveguide mounting area? Kind of gray, like a hole was filled with wood putty and a dowel? Well, I don't want to talk about it...

bwaslo 5th June 2016 04:13 AM

Here's where I'd like to be doing measurements - sadly, the crossover being measured in the picture was a miserable failure from about a month ago, horrible vertical pattern. I live right between two elementary schools, so I can't do outdoor measurements during weekdays till summer break. I'm pretty sure the scary alien noises made during speaker testing would have them sending a SWAT team out on me.... I got a couple of troubled visits from the neighbors the Saturday I took this pic. It's near 100F here this weekend, so I'm not up to dragging out all this stuff until the weather cools again.

The jist of saying all this is that the measurements shown earlier were made in a somewhat cramped basement, so they don't go very low in frequency and have some unavoidable reflection interference....

wesayso 5th June 2016 09:37 AM

Very cool project and an interesting approach with the woofers outside of the actual horn, but still behind a band pass hole. It would be hard to resist putting in one more mid though. At least for me it would be.

What is going to be the bottom end for this? You mentioned a ported enclosure that would require a bigger box. Is the drop off to steep to try a Linkwitz Transform?
Would depend on the woofers too I guess.

Eldam 5th June 2016 04:58 PM

Very Interresting : cheap + off the self horn = :)

How is performing the Tymphany compression driver VS the very good plastic diaphragm from B&C or Beyma please ? As non fatiguing but more detailed ?

Can we consider it's 20 horn seing the polar map ?

the woofs are ok to around 100 Hz (so sub-woofers plated amp are needed ?) or a Linkwitz transform without subs ???

bwaslo 5th June 2016 08:22 PM


Originally Posted by wesayso (
What is going to be the bottom end for this? You mentioned a ported enclosure that would require a bigger box. Is the drop off to steep to try a Linkwitz Transform?
Would depend on the woofers too I guess.

The ported enclosure is planned to be just a similar box of about double the volume (deeper box and a little taller to keep it looking small in a room). Same drivers, predicts to be about 42Hz f-3.

I've been running these in the living room (Celestion tweeter version) and an (aggressive) Linkwitz transform works pretty well for that application here, but it doesn't get played very loud. Pretty sure it would get rough if we tried loud hard rock on it. I also had quite a bit of other EQ applied (for the midrange bump and wall effects, as well as FIR phase eq), and with all that it works out pretty nice (big sound except for low bass) but not too elegant a way of getting there.

Downstairs, away from walls and with well-placed subs they sounded very good without EQ, though. The worry about the distortion with the Celestion tweeter is mostly intellectual, they didn't really sound bad at all. I also wanted to play with the new Peerless driver:p

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