# A tweeter distortion analysis



## npdang (Jul 29, 2005)

Testing was done with Praxis using a chirp stimulus and frequency response and distortion acquisition method. The "compensate for response" option was checked, such that distortion levels aren't so exaggerated toward the driver's low end rolloff. The tweeters were tested at 1/4m, adjusted spl to ~96db at 1m. I felt that this output level best represented a typically "loud" listening point.

I used a "soft" baffle, in other words a large sheet of foam with a tweeter hole cutout. I suspect it may have some effect on the frequency response, but if this really bothers you feel free to skip this review  I believe the measurements correlate well with subjective listening tests.

The red line that you see across the screen is the 1% distortion limit. There will be 3 plots presented. The one marked THD represents total harmonic distortion up to the 5th harmonic. The one labelled HD2 represents second harmonic distortion, and HD3 represents 3rd order distortion. The yellow line you see is the frequency response, and the green line is the distortion plot.

This thread will be continually updated as more drivers arrive. The first set I tested:

1. Seas 27TAFNC/D 
2. Seas Lotus RT27F
3. Rainbow cal28 prototype w/o rear venting holes
4. Alpine variant xt19
5. TangBand 25-1414sc titanium dome w/ plastic rear chamber

*Seas Lotus rt27F*




























Very clean, outstanding performance through the lower region. A 1.5khz crossover point seems very achievable, albeit with a steep rolloff. 3rd order distortion rises dramatically beyond 2khz. Interestingly, the rear chamber loading seems to have a strange effect on the low end sensitivity between 1 and 2khz. Still, this is the best option for someone looking for the absolute lowest crossover point possible in a compact dome.

*Seas 27TFANC/D *





























Another good performer. A suitable crossover point seems to be 2khz, with a steep rolloff. Distortion above 2khz is a bit better than the Lotus RT27F (perhaps due to the higher xmax), but the Lotus's longer coil proves to be better at lower frequencies. A more affordable, and a little better performing driver above 2khz than the Lotus.

*Rainbow cal28 proto*




























Nothing new here, another great performer. Remarkably low 3rd order distortion below 5khz. Looks like 2khz is the hard cutoff for this driver, with distortion on par with the Lotus above that. It's also worth noting the other 3 drivers have good sensitivity down to at least 1 octave lower than this one.

*Alpine variant Vifa xt19 neo *




























The tiniest driver of the bunch, surprisingly it also has the best low end sensitivity. Looking at the THD plot, I probably wouldn't use this one below 3khz. Fairly good 3rd order distortion performance, matching that of the Seas drivers but very poor 2nd order performance. Nothing out of the ordinary for a nearly even hung driver with a diaphram about 40% smaller than the others.

* Tangband 25-1414sc *




























Great performance above 5khz. Notice the strong breakup node at ~18khz typical of titanium domes. Remarkably low 3rd order distortion across it's entire bandwidth. Crossover point could really be anywhere from 1.5khz and up, although it's worth mentioning that performance below 5khz doesn't approach the level of the Seas or Rainbow tweets.


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## kappa546 (Apr 11, 2005)

since you're doing compact domes, why not test the uber cheap aura 204


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## cvjoint (Mar 10, 2006)

How about the diy whore LPG 25NFA? I can drop these off one day if you want.


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## FoxPro5 (Feb 14, 2006)

What does the dip in FR at about 12k on the Seas Neo mean?


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## npdang (Jul 29, 2005)

I'm betting it's something to do with the diffusor on top of the dome.


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## npdang (Jul 29, 2005)

I forgot to mention that I made a small mistake and didn't adjust the voltage sensitivity for each driver. It was set for a 6 ohm tweeter, the Seas lotus. The 4 ohm drivers were actually playing about 2db louder than shown, and the 8 ohm driver was about 2db less.


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## dingaling (Apr 14, 2005)

i think u should do a watch distortion test sometime in the future  how many milliseconds off are they hahaha 

good job on the testings!


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## kappa546 (Apr 11, 2005)

npdang why is the response so ragged in the lower trebble on most of the tweeters? have anything to do with mounting? i mean jeez look at the huge null on the alpine xt19's from 3-7khz


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## npdang (Jul 29, 2005)

1db scale and foam baffle.


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## ddsBMW (May 31, 2007)

You should test one of my morel mdt43's. I will be in town in a couple weeks.


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## iyamwutiam (Nov 20, 2006)

npdang said:


> I forgot to mention that I made a small mistake and didn't adjust the voltage sensitivity for each driver. It was set for a 6 ohm tweeter, the Seas lotus. The 4 ohm drivers were actually playing about 2db louder than shown, and the 8 ohm driver was about 2db less.


So would it be fair to say tht the test is most accurately calibrated toward the Seas Lotus tweeter? Would this also affect the distortion specs - as Leon said- in milliseconds 

Also - I asked a question earlier in another post - - don't know how it would affect this post per se- but here goes-
How would you be able to know if one tweeter has better dispersion than another (objectively) IF they are measured at 1/4 meter - which I think is like 9.5 inches or so???


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## npdang (Jul 29, 2005)

Definitely biased toward the neos. I didn't measure off-axis response here, but if I did you would have to move the mic 30 degrees off at the same distance.


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