Small Syns

[bwaslo]

Originally Posted by Eldam

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 ?

Too early to say.. I've only heard it much with test tone sweeps . I actually found the plastic Celestion CDX1-1445 to sound smoother to the ear than the B&C plastics, but it doesn't handle going low in frequency very well (measurably, though sound doesn't seem bad to me).

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

The polar map shown earlier is for the VERTICALS, and it's a 40° horn vertically (+/-20°).

Horizontally, it's a 90° horn, I didn't show the polars for horizontal, but here they are --

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

See the post just above about bass. As-is, these sound kind of anemic without either subs or LT. Probably these particular boxes will go back downstairs (where subs are ok with the management) and shelf-ported full-response versions will take up residence in the living room.

[xrk971]

Nice work Bwaslo!
Very promising compact design. Home synergies needn't be big or expensive as we are seeing.

I love that you "passivated" it. Is this XO good to go or still being tweaked? Very simple design - but does it "got squarewaves?"

[bwaslo]

Did a crossover tweak today, just component values (will post it when I post the rest of the build details, in case anything changes still).

Here are the horizontals du-jour:

It don't got squarewaves, to get that you'd need a miniDSP 2x4HD (I'll have a file available for that when I get to making it). Not enough delay on the tweeter and too high order filters on tweeter and woofer.

Going to try the 'near the wall' crossover tonight if I can, but I just heard company arrive, so probably not....

[AllenB]

Would it be possible to see polars for the mid alone please?

[bwaslo]

Allen,

It would be a lot of work to do with only mids playing, but here are 0. 20. 30. 45 and 60 degrees curves (without the crossover) that were taken to do the crossover design with



Here is a plot showing the same angles (I think) for all three drivers (tweeter was the Celestion when this was done), to show the array effect in the woofers.

[bwaslo]

I've been trying to put a cut into the midrange drive in the crossover down around 300Hz, where it doesn't add much to the response but seems to be distorting more than the very clean (now) tweeter. I haven't found a way to do that, though, that still keeps the mid and woofer in phase with each other over the range where they trade off. When those don't track, the vertical pattern goes all to hell....

I guess the other option is to use two midranges. Cost on doing that isn't a problem, the drivers are rather inexpensive. But mounting them onto the horn is one of the more time consuming parts of this, I hate to double that without good reason. Also, the box would have to get a little higher to accommodate the midrange driver bump sticking off the top of the horn. For a ported box, though, it has to get taller anyway.

With the single mid, the midrange distortion still looks lower than the woofer's (as it usually goes....). I still like the idea of minimizing port holes into the waveguide.

If anyone wants to try doubling midranges, I think it should be just a matter of adding the other driver the same position and sizes as the first, and wiring them in series. Impedance doubles so power absorbed halves, but efficiency doubles too, so things should break even? Except the crossover components, have to cut capacitor values in half and double resistor values. Second harmonic distortion should drop by about 6dB (to 1/4 the percentage).

First test on the 'against the wall' indicate that I really screwed something up in my sims or, more likely, measurements. In the basement, with the Small Syns against a wall, the response shape is much better controlled than I measured upstairs. I suspect the wall behind the mic might have been getting into the act too much (don't want to design taking that into consideration). So, I'm doing a new crossover for "against the wall", it looks like it will be more similar to the "out from the wall" crossover. It would be nice if it could be made switchable without using too many extra expensive parts..

[AllenB]

Thanks. These (horizontal along vertical 0 degree plane?) polars appear to show a reasonably clean resonance at the notch. Can I assume the ports are at just under 2" axially from the throat where the horn height is a little under 3"?

[bwaslo]

Hi AllenB.
Those are at the 0 degree vertical (and are horizontals). The rest I'd have to check....

The ports are as close to the horn throat as I could reasonably get them. The notch is at 2.15kHz. I don't run the midrange very close to the notch as I didn't want to use difficult-to-document and duplicate frustrums on the port holes I'd need to get the high frequencies up to it). The ports are simple holes cut with a wood drill bit through the 0.35" thick horn walls, though I do fill the volume in the mounting plate with putty, with finger-shaped paths from center to the holes (those don't seem to be be critical at all).

[bwaslo]

Well, I figured out a crossover that cut out the drive to the midrange near 300Hz where distortion was indicated, while still keeping the woofer and midrange in phase with each other where they trade off, while still behaving off-axis, and without getting impedance too low anywhere. It even makes the response flatter.

So, I measured distortion, and the distortion near 300Hz is nice and low, but there's now a narrow 2nd harmonic distortion peak at ~450Hz! I spent several hours fighting this as well as other distortions that crept in during the process. The more I looked around, the worse it seemed to get. Like a switch on my power amplifier that decided to go cruddy then (I of course took apart the horn assembly, removed woofers, etc, thinking it was something in the speaker). And a too-long screw when I put the horn back in, that started buzzing against the cone of one of the woofers. But in figuring out and fixing all that, I found out that the 450Hz distortion peak isn't even coming from the midrange (and now I wonder whether the 300Hz stuff was?).

It's from the woofers, both of them I think! (but not sure... hard to tell and I was worn out from all the fun by that time). It's there even with the midrange disconnected (disconnection was caused by the crossover hodgepodge falling off the table onto the floor). I guess I need to take a woofer out and see if I can measure it by itself outside of the box.

Does anyone have any ideas what might be causing it? It shows as a 2nd harmonic distortion when driven at 450Hz and the woofer's impedance curve shows a wiggle right about 900Hz (the published curve on the data sheet also shows that). A resonance of the surround? Could it be getting excited when the woofer is doing 450Hz, and reading as distortion? The peak is very high-Q, so I think it has to be something mechanical.

The distortion curve with new crossover -

The impedance curve of the woofers (in the box)-

The HD2 is on the order of a percent on the peak, it mostly just bugs me wondering where it is coming from.

[AllenB]

Their impedance curve does show some irregularity at about 900Hz (resonance in the rubber surround?), would that be expected to result in a measured narrow disortion peak when driven at 450Hz?

Spider maybe? If I understand you are not measuring distortion per se, but the level of the harmonic? I was also thinking something to do with the cabinet?