Small Syns

CA glue is an interesting option. Obviously not the more common gel formations but the brittleness of the glue isn't really an issue here. Paraffin wax, while super simple wouldn't be stiff enough to do much except dampen.

Active with a couple simple sallen key filters in front of the amps? :)
 
Today's exercise: more 2nd harmonic distortion

Well, remember yesterday when I found out that the harmonic distortion from the midrange driver disappeared when I clamped down on the inductor with a pliers? Today I put the speaker together again and took measurements with and without cable clamps on the inductor cores and..... what do you know... 450Hz 2nd harmonic distortion again! The clamps did little to nothing. So I have to take back about half of what I said.
hd%20with%20clamps.png
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When I clamped down on the cores with big pliers, rather than killing distortion, the contact with the pliers actually just increased the inductance enough to push the distortion peak down into a response null in my setup (the mic and speaker were both flopped on the floor when I did that test). Today, using pieces of plastic (the cable ties) between the pliers and the core showed no real effect from just pressure; but without plastic between the pliers and core, the distortion peak moves down in frequency. That distortion source (when measured through the midrange, with woofer disconnected but the inductor still sucking current) is still indeed the ERSE laminated core inductor, but there doesn't appear to be an easy cleanup for it. (When I used a 2mH air core inductor, the HD2 peak from the midrange went away for real). So either live with it, or use a bigger metal core inductor, or an air core.

Another day of tracking things down, relearning what I used to know about distortion back when I was still an RF engineer. The first rule of distortion troubleshooting is to try to analyze one distortion source at a time and remember there are probably several.

This time a distortion peak at 450Hz is coming out of the woofer, when by itself, EVEN WITH THE AIR CORE INDUCTOR. I tried different capacitor types (no change) and different capacitance values (much change). The distortion peak still seemed to be where the current peaks through the inductor and capacitor, which threw me for a while. But the problem (when an air inductor is used) isn't the inductor or the capacitor. Of course, where the current peaks through those parts is also where it peaks through the woofers!
woofer%20currents.png
The purple trace is driving the woofer by itself, blue is with the usual 100uF cap (note the peak near 450Hz), orange is with 50uF, green is with no cap at all (but still with inductors). Seems like inductors (at least air core ones) are good, capacitors are bad? Duh, of course not, they are used to shape responses, not just selected because of how they affect distortion!

And (took me a while to understand this!) it is the response shape, or rather the drive to the woofers, that is affecting and shaping the distortion and making the (apparent) narrow HD2 peak from the woofer. It is difficult to see that just from graphs, particularly when there is always a noise floor at the bottom of a distortion plot below which you can't see what is going on, and because distortions don't just shift up and down with the same levels as the drive levels!
Here's a pdf I made while trying to understand the issues here - http://libinst.com/SynergyDIY/SmallSyns/hi%20order%20xover/Cap%20effects.pdf

For the math oriented: (Going back to radio days) there is a thing in distortion analysis called "intercept point". It is a calculated value used to characterize a device's distortionbehavior (assuming one simple source for the distortion), and is based on how distortion products (the second harmonic, third harmonic, etc) grow as the device gets driven harder. 2nd Order products (harmonic or intermodulation) grow 2dB for every 1dB increase in the drive level. 3rd order products grow 3dB for every 1dB, etc. For speakers (decent ones, anyway) we usually only have to worry about 2nd and 3rd order.

If your device follows that behavior (meaning again that there is only a single dominant source of distortion inside it), then for any drive level in that range take the output level, in dB at the fundamental, double it, and subtract the level of the 2nd harmonic distortion product (also in dB!). You'd find that the result is also (ideally) constant. That's the "intercept point" (IP2), the output level where it would appear that the 2nd harmonic distortion product would get as big as that level.

In that pdf linked above, I calculated the intercept point at 1m from the speaker with each change of crossover component, since those also changed the drive levels. That gave relatively consistent values between 134dBSPL and 139dBSPL. Those are reasonably close, seeing as the one at the high end was looking at products down near the noise. So I'll take that as good evidence that the distortion peaks I'm seeing, when crossover components are clean, are reasonable for these woofers. The appearance of the distortion curves in the plot without any crossover is what made me go through all this -- it seemed so much worse and didn't seem to make sense, but it all seems to add up. The IP2 at 1kHz (156dBSPL) also appears to be believable when you run the numbers, even though the no-crossover curves look so much worse at a glance.

ANYWAY -- the conclusion after all this (and I hope this is a conclusion, getting pretty tired of soldering and desoldering stuff in!) is that the distortion from the inductor is there, but seems to be at or below the same distortion levels coming naturally from the woofers. So probably not a lot of reason to get crazy with the inductors, or at most, maybe only use a bigger more expensive one for the first inductor (that sees more current, see simulation at 100W below) to keep distortion from also affecting the midrange driver via the speaker cables.
Currents%20in%20two%20inductors.png

(I hope this isn't boring everyone, I'm now sort of using this forum as a lab notebook! Skip it if it all seems too geeky :rolleyes:)
 
Active with a couple simple sallen key filters in front of the amps? :)

Undoubtedly the best option! But not viable for a lot of users, particularly if they are trying to equip a multichannel surround setup without cashing in the family savings account.:(

edit: actually, that's only second best. Best is to use a nice DSP crossover to replace your DAC. You can get FIR filtering to get XRK's s'got quarewaves' easy then!
 
Oh, absolutely, but if I remember right, you have an abundance of amps lying around.

For the rest of us, AV receivers with bypassed inputs (i.e. no post processing) are dirt cheap, and at low levels, good enough. Well, at least the sonic benefits of active vs. passive can move the price point of the amp well down. That said, it'd be amusing to see someone with 1 AV receiver spitting out it's pre-outs to a massive X-over box (N channels x M-way) to a respective half-dozen inexpensive AV receivers to power it all.

I jest...sort of.

And to add--thanks, of course, for documenting your adventures!
 
In case there's anyone following this thread, I'm still on it. Had to take about a week out to work on some software, which this project actually help uncover some clunky behavior I also needed to clear up.

BTW, I did add traces for intercept point into Omnimic. Kind of cool, though I doubt any but a few here will really follow what it's trying to be about.

(If you haven't been following this thread, well..... I guess you aren't reading this either :) )
 
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Would it make sense to get the big SEOS24 or 30 waveguides and turn them into Syns?
I would guess that the 2" throat version would be best as it cuts down distance to the mid drivers.

But starting with a larger HF throat also will result in some beaming and (usually) breakup in the highest octave. Even a 1" compression driver and throat shows narrowing up near 15kHz and other than some beryllium diaphram types, are getting into breakup up there.

But several people here have made synergyish horns with larger throats and liking the results. Weltersys and XRK971 have both made synergys using larger cone fullranges and a large throat for HF. Cask05 made a pair of big synergies starting with a Klipsch K402 30-something inch horn, using a 1.4" throat, and swears by it. Those probably work because, while we all think we hear to 20kHz, and many claim to have been 'tested' to beyond that (though audiologist's gear doesn't function that high!) not many really hear with much significant sensitivity to even 15kHz.
 
Oh, absolutely, but if I remember right, you have an abundance of amps lying around.

For the rest of us, AV receivers with bypassed inputs (i.e. no post processing) are dirt cheap, and at low levels, good enough. Well, at least the sonic benefits of active vs. passive can move the price point of the amp well down. That said, it'd be amusing to see someone with 1 AV receiver spitting out it's pre-outs to a massive X-over box (N channels x M-way) to a respective half-dozen inexpensive AV receivers to power it all.

I jest...sort of.

And to add--thanks, of course, for documenting your adventures!

https://www.minidsp.com/ht-series/nanoavr-hd
 
But starting with a larger HF throat also will result in some beaming and (usually) breakup in the highest octave. Even a 1" compression driver and throat shows narrowing up near 15kHz and other than some beryllium diaphram types, are getting into breakup up there.

But several people here have made synergyish horns with larger throats and liking the results. Weltersys and XRK971 have both made synergys using larger cone fullranges and a large throat for HF. Cask05 made a pair of big synergies starting with a Klipsch K402 30-something inch horn, using a 1.4" throat, and swears by it. Those probably work because, while we all think we hear to 20kHz, and many claim to have been 'tested' to beyond that (though audiologist's gear doesn't function that high!) not many really hear with much significant sensitivity to even 15kHz.

Very interresting thread again,

My understanding about the challenge with these drivers is their off axis in a horn when the frequencies raises.... But not having a XO higher than 2K in a speaker is certainly a good idea if we believe all the designers through the world...

Now with the foam horns xrq971 experienced more than many, it should be also possible to have a close center to center tweeter above the 8K Hz by piercing the foam horn with a little K-tube for tweeter. The delay being setuped in FIR domain. The idea is a 3/4 tube is not so intrusive for the horn response !
Of course this for people whom like to use 2" or a little greater at the apex and whom need a tweeter yet for polar needs more than highs (for instance like Troels Gravsen WHo XO a SS 10F full range at 3K Hz ! my idea with the K-tube tweeter would be more upon 8K)

The idea also of xrq971 and likes was the cone drivers are more linear and less distorsed while may have the profit of horn efficienty for domestic spl level.

Now I'm very curious of all these compression drivers with their new materials : which can be good between 1 to 1.5K HJz to ....15/18 even 20 K Hz.... (so without the need of a tweeter cause their strong motor allow dispersion lense at their outputt for the off axis highs).

My feeling (but having no clue about horns) is to use them with apex at the same size in relation to their outputt to have the best behavior about distorsion. The game being to find the more linear compression !

I'm looking forward to hear what about this Peerless and likes.... cause there is not only a soundstage in a speaker. Btw I'm asking also if the reason is Something like the 400 000 law when it comes to have a shorted high end (in relation to the low end...) and a good sound.
 
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Hi Eldam,

But not having a XO higher than 2K in a speaker is certainly a good idea if we believe all the designers through the world...

Maybe I'm too much a measurements guy, but -- if the crossed-over drivers are concentric, and the response (and maybe the phase?) is done so that the crossover point isn't identifiable with either polar or on-axis measurements, I don't see how it would matter where the crossover is. I certainly don't hear the crossover point in my 'Cosyne' synergys, and people who have heard it (and who didn't know the build details) have not been able to tell how many drivers there are. Since all the sound comes from the same horn, the usual assumption is that it is some kind of full-range.
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Are there any measured curves of K-tubes around? Build threads I've seen never seem to show any. I know the (few) response curves I've seen of Karlson bass cabinets looked almost random and far from good!
 
I believe this is because you know very well how to make a passive crossover as you already prove it with your speaker (the avatar and the nice pdf :) ) !

I saw some posts about it, measurements I don't know ! The goal behind this odd idea (certainly bad) is to make closer the c to c in vertical position without // the tube and the fat driver at the apex (it can be a little curved or simply angled to approach the apex driver while having space enough at the opposite side to load it with a driver).

Now it's certainly simplier to putt at the apex a tweeter and close 2" or 4" firering through the synergy ports around it :)...

I like the larger width than the deep, is there a goal behind that instead making a narower tower (else than putting the cabinets on shelves near a wall) ?
 
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