The fins are just for show yes, but the centre part also functions as a rear chamber if i'm not wrong
The link I posted shows stunningly low harmonic distortion for the sb26, Troels had to recheck the measurements.
Some tweeters seem to manage low distortion even through the Fs, which I'm not sure how they're accomplishing it.
By brickwall I mean about 500 db/octave, so almost a cliff.
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By brickwall I assume 0dB above 1kHz, -999dB below 1kHz. None of the tweeters discussed here will cope with 100dB near 1kHz. Around 90dB @ 1k they can barely cope with.
I'm not suggesting or advocating the use of a brickwall, quite the opposite in fact. LR4 is much better. A LR4 1.2kHz filter will bring the level down -9dB @ 1kHz, -6dB @ 1.2kHz, -3dB @ 1.5kHz which will at least keep distortion under control until 100dB or so.
It only shows 2nd and 3rd order though and is plotted on linear scales so it is exceedingly difficult to determine what is happening when the trace goes below -50dB (0.3%). It just looks like a flat line at that point.
When plotted on logarithmic scales with 4th and 5th order harmonics shown the difference between an good tweeter and an excellent tweeter becomes apparent. Note the difference here between the SB29 and SB26STAC (fabric dome):
http://www.zaphaudio.com/tweetermishmash/SBAcoustics_SB29RDC-HD.gif
http://www.zaphaudio.com/temp/SB-Acoustics-SB26STAC-C000-4-HD-sample2.gif
In Troels results the SB29 has higher 2nd order but lower 3rd order compared to the SB26. It looks a lot worse because it's plotted on a linear scale. It only equates to a few dB.
From Zaphs results you can see that the higher order distortion (4th, 5th order) is lower too on the SB29.
Once a crossover is put in place the 2nd order will come way down.
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SB26ADC has one of the lowest 4th and 5th order harmonic distortion i've seen
SB Acoustics SB26ADC-C000-4 | HiFiCompass
Compare it to the rest:
Measurements and compare | HiFiCompass
SB Acoustics SB26ADC-C000-4 | HiFiCompass
Compare it to the rest:
Measurements and compare | HiFiCompass
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Wow, who uses midrange drivers in ported enclosures ?
I agree it's not the best, however there are a few around like the Wilson WATT. I think some of the other Wilson models use ported mids too.
Well that is much better than the 26STAC above 2kHz, nice. Maybe still not quite as good below 2kHz compared to the SB29 though. Both are very good. Note that the measurements at HifiCompass are versus voltage instead of SPL and the SB26 is about 4dB lower sensitivity than an SB29. To compare them fairly the SB26 would be at 5.6V and the SB29 somewhere in between 2.83V and 4V.
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Unless the sb26dac (metal dome) has a very unusual distortion profile then it distortion is very low, probably inaudible. However, dynamics comes into play since a transient peak might cause high excursion and distortion at much lower listening volumes.
It seems like a great tweeter but there is a lot damping used on these tweeters in general, and I would want to listen to them at lower volume. I doubt they maintain detail at lower levels like horns can.
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Even considering voltage and SPL relations, SB26ADC is better all the way down to 1700Hz which is at practical limit for use of any dome tweeter without a waveguide - in my opinion. With crossover point at that place, distortion HD 2,3,4 and 5 are going down -6dB. But above 1700Hz it is quite superior to SB29 regarding distortion - about 10dB lower for all.
That being said, i've lived with SB29RDC-C0004 for quite some time and i think it is one of the most natural sounding tweeters when done right.
You're right on the money. That's why i removed the ferrofluid from my Morels DMS30s and put them in a waveguide. Removing the back chamber or making it bigger is one more option - just not for ring radiators i'm afraid.
I'll just do copy/paste of my post from another forum.
About the distortion - Recently i've been told about German DIY-er named Rainer Feile that constructed a small two way loudspeaker he named Tafal. While being nothing revolutionary in itself, it gained much popularity among the European DIY-ers because it's made with high value drivers and with a good number of smart design choices. The thing i liked about it (among other things) was that, while he did use Seas alu-dome tweeter that has break up at 26KHz, he treated it with a notch filter.
As expected, there was 3rd HD peak at roughly 8.7KHz that reaches 0.3% line. What surprised me is that when notch is applied at dome resonance, the 3rd harmonic distortion peak decreases dramatically - from 0.3% to 0.04%. What's also interesting is that it lowered 3rd order HD through the entire tweeter range. Measurements before and after:
https://s10.postimg.cc/86ou22weh/image.gif
Now, i know that this should be tested. I'm certainly testing it as soon as i deal with my notebook gremlins, but with nothing but the notch at the cone resonance.
About the distortion - Recently i've been told about German DIY-er named Rainer Feile that constructed a small two way loudspeaker he named Tafal. While being nothing revolutionary in itself, it gained much popularity among the European DIY-ers because it's made with high value drivers and with a good number of smart design choices. The thing i liked about it (among other things) was that, while he did use Seas alu-dome tweeter that has break up at 26KHz, he treated it with a notch filter.
As expected, there was 3rd HD peak at roughly 8.7KHz that reaches 0.3% line. What surprised me is that when notch is applied at dome resonance, the 3rd harmonic distortion peak decreases dramatically - from 0.3% to 0.04%. What's also interesting is that it lowered 3rd order HD through the entire tweeter range. Measurements before and after:
https://s10.postimg.cc/86ou22weh/image.gif
Now, i know that this should be tested. I'm certainly testing it as soon as i deal with my notebook gremlins, but with nothing but the notch at the cone resonance.
I'll just do copy/paste of my post from another forum.
About the distortion - Recently i've been told about German DIY-er named Rainer Feile that constructed a small two way loudspeaker he named Tafal. While being nothing revolutionary in itself, it gained much popularity among the European DIY-ers because it's made with high value drivers and with a good number of smart design choices. The thing i liked about it (among other things) was that, while he did use Seas alu-dome tweeter that has break up at 26KHz, he treated it with a notch filter.
As expected, there was 3rd HD peak at roughly 8.7KHz that reaches 0.3% line. What surprised me is that when notch is applied at dome resonance, the 3rd harmonic distortion peak decreases dramatically - from 0.3% to 0.04%. What's also interesting is that it lowered 3rd order HD through the entire tweeter range. Measurements before and after:
https://s10.postimg.cc/86ou22weh/image.gif
Now, i know that this should be tested. I'm certainly testing it as soon as i deal with my notebook gremlins, but with nothing but the notch at the cone resonance.
It's not often that I see something new and interesting on diy forums these days but this is. Good find
What kind of notch filter is it ? Active ? A passive shunt notch filter ? A passive series notch filter ?The thing i liked about it (among other things) was that, while he did use Seas alu-dome tweeter that has break up at 26KHz, he treated it with a notch filter.
As expected, there was 3rd HD peak at roughly 8.7KHz that reaches 0.3% line. What surprised me is that when notch is applied at dome resonance, the 3rd harmonic distortion peak decreases dramatically - from 0.3% to 0.04%. What's also interesting is that it lowered 3rd order HD through the entire tweeter range.
In theory a notch filter at 26Khz (at least an active one) would have no effect on the 3rd harmonic distortion generation at 8.7Khz - because the tweeter is not being driven with a 26Khz signal when it is mechanically generating a 26Khz 3rd harmonic from an 8.7Khz source signal - so there is no 26Khz for the notch filter to notch out, thus no effect on the 3rd harmonic.
The only mechanism I can see that might cause the claimed reduction in distortion products at 26Khz would be if a passive shunt notch filter was used, and that somehow allowed the low impedance of the notch filter at 26Khz to provide some electrical damping of the mechanical resonance, something akin to the source impedance of a woofer near it's Fs providing additional damping in the form of Qes.
This would only work with a shunt notch where a low impedance is presented across the driver at resonance - a series notch which presents a high series impedance at resonance would if anything make it worse, (since the damping from the amplifier would disappear) and an active notch which only changes the frequency response would have no effect.
As for the claimed reduction in distortion over a wide frequency range - I fail to see how a notch filter at 26Khz would cause that. It's probably an artefact of the measurement technique, and I would suggest that in a swept or stepped sine measurement no such improvement would be shown.
Answer to all of your questions is in link i posted in my previous post.
As for reduction at wide frequency range, i think that it could be that resonance (when excited) amplifies distortion a little bit everywhere. By damping the resonance, the dome doesn't enter that kind of nonlinear behaviour - that's my assumption - until i check for myself i couldn't tell more. I even don't feel comfortable stating previous sentence because i really don't know the answer yet.
As for reduction at wide frequency range, i think that it could be that resonance (when excited) amplifies distortion a little bit everywhere. By damping the resonance, the dome doesn't enter that kind of nonlinear behaviour - that's my assumption - until i check for myself i couldn't tell more. I even don't feel comfortable stating previous sentence because i really don't know the answer yet.
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For those who speak German ?
Anyway I trawled through the sight and I see that as I suspected it is a passive shunt notch.
My point still stands though - it is largely a measurement artefact and will depend on how the distortion is measured.
If many frequencies are excited simultaneously including the resonance, there may be an effect on distortion at lower frequencies. However if the resonance is not excited the distortion of the lower frequencies will not be affected.
Likewise you will get different results depending on measurement technique. If you use a distortion measurement system that is using stepped tones (such as ARTA STEPS) it would not show an improvement of distortion at lower frequencies that are not exciting the resonance via their 2nd or 3rd harmonics, while something that is exciting many frequencies at once including the resonance may.
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