I don't think it's a standing wave, due to the fact pushing on the rear cover or putting damping sheet on the back makes it go away for the most part.
I'll post some impedance measurements of before and after when I get a chance. The CSD or FR isn't that conclusive when I measured it with the driver in the enclosure. I only get a small trail at 2k similar to the published info posted before. A direct measurement without xover of the tweeter installed shows minimal extended decay on its own. Thats the tricky part as its not a cut and dry obviously visible thing. Only a louder 2k sine would aggravate it and if it wasn't for trying that, it wouldn't have been so conclusive there actually was a definite problem. This is a gireat example why I struggle to quanitify everything I hear with typical measurements alone. Gedlee would be ripping into me right now for saying this, but I've found many examples where basic measurements haven't explained the audible presentation. It could be due to the fast gating of the test signal or how the mic only picks up the direct sound. There may be a reason for it which I can't measure with basic equipment. I may try some off axis measurements and see if that shows anything.
I'll post some impedance measurements of before and after when I get a chance. The CSD or FR isn't that conclusive when I measured it with the driver in the enclosure. I only get a small trail at 2k similar to the published info posted before. A direct measurement without xover of the tweeter installed shows minimal extended decay on its own. Thats the tricky part as its not a cut and dry obviously visible thing. Only a louder 2k sine would aggravate it and if it wasn't for trying that, it wouldn't have been so conclusive there actually was a definite problem. This is a gireat example why I struggle to quanitify everything I hear with typical measurements alone. Gedlee would be ripping into me right now for saying this, but I've found many examples where basic measurements haven't explained the audible presentation. It could be due to the fast gating of the test signal or how the mic only picks up the direct sound. There may be a reason for it which I can't measure with basic equipment. I may try some off axis measurements and see if that shows anything.
Pulling tweeters apart to change the dampening characteristics is not anything new. There are dozens of threads here on DIYaudio where a user found some issue with the manufacturers scheme/construction.
I still have a set of Dynaudio D28 tweeters sitting on my shelf that were fiddled with......about 35 years ago. 🙂
Good luck.
Dave.
I still have a set of Dynaudio D28 tweeters sitting on my shelf that were fiddled with......about 35 years ago. 🙂
Good luck.
Dave.
Yeah, I have as well. You can remove ferrofluid, remove the chamber and add a bigger one, modify the wadding, etc, etc.
My point being......you need to make sure when you fix one issue you don't create another one/two/three. 🙂
It's fairly easy to chase your tail with these efforts.
Dave.
My point being......you need to make sure when you fix one issue you don't create another one/two/three. 🙂
It's fairly easy to chase your tail with these efforts.
Dave.
Overall what is being observed or heard
Is a classic trait anyone can find with classic tweeter designs.
A agree with most statements.
You can add mass or improve the rear chamber design.
Obviously you cant change the rear chamber.
For the most part the low 2 K crossover point is to low.
Classic remedy has always been higher order filter
such as 3rd or 4th order instead of 2nd.
Especially if your really shooting for 2k crossover.
Assuming Fs is 1100 to 1400
using normal rules of thumb, Crossover needs to be higher
at 3000 for a 2nd order filter.
You can add mass to hide what the speaker does.
eventually it is what it is.
Some have even proved that ferro fluid can also cause weird
resonances. But adding fluid to tweeters is rather typical for thermal
reasons.
Not to knock the specific brand, it is seen with many brands.
Price mark up is high and performance is assumed " higher"
when it is just a typical tweeter other brands offer for less.
but get disregarded because they are " cheap" but your buying the
same general design.
AKA use smaller mid and crossover at 3 or 4 K
The diaphragm is either large enough to cover 2k
or the rear chamber has to support resonance well
below 800 Hz to support 2k crossover with 2nd order.
Is a classic trait anyone can find with classic tweeter designs.
A agree with most statements.
You can add mass or improve the rear chamber design.
Obviously you cant change the rear chamber.
For the most part the low 2 K crossover point is to low.
Classic remedy has always been higher order filter
such as 3rd or 4th order instead of 2nd.
Especially if your really shooting for 2k crossover.
Assuming Fs is 1100 to 1400
using normal rules of thumb, Crossover needs to be higher
at 3000 for a 2nd order filter.
You can add mass to hide what the speaker does.
eventually it is what it is.
Some have even proved that ferro fluid can also cause weird
resonances. But adding fluid to tweeters is rather typical for thermal
reasons.
Not to knock the specific brand, it is seen with many brands.
Price mark up is high and performance is assumed " higher"
when it is just a typical tweeter other brands offer for less.
but get disregarded because they are " cheap" but your buying the
same general design.
AKA use smaller mid and crossover at 3 or 4 K
The diaphragm is either large enough to cover 2k
or the rear chamber has to support resonance well
below 800 Hz to support 2k crossover with 2nd order.
I tend to see most newer, better designed soft domes use advanced rear chamber geometry to control the rear wave instead of just dampening material alone. The biggest problem I see in most of the domes is a double impedance hump caused by the air volume behind the VC gap. This causes most of the bad artifacts in the decay spectrum down low. The TW034 has this issue very pronounced at 2.2k as a separate impedance peak. This is an ancient design tweeter though.
Some of the higher end Seas and Scanspeak tweeters use a fancy rear chamber. TheT35C002 has a rather crude looking folded up piece of felt in addition to the donut shaped chamber to aid dampening. Scanspeak alsp has that Revalator rear chamber with the individual neo discs in the motor which is really slick. Morel uses a nice back chamber in the TSCT1104, which i regard as one of the best soft domes ever made.
I tend to favor larger domes as you can cross them lower without sacrificing much of the top octave.
Some of the higher end Seas and Scanspeak tweeters use a fancy rear chamber. TheT35C002 has a rather crude looking folded up piece of felt in addition to the donut shaped chamber to aid dampening. Scanspeak alsp has that Revalator rear chamber with the individual neo discs in the motor which is really slick. Morel uses a nice back chamber in the TSCT1104, which i regard as one of the best soft domes ever made.
I tend to favor larger domes as you can cross them lower without sacrificing much of the top octave.
I agree that 2k is too low in a typical situation using a 27 - 30mm soft dome with a 2nd order filter.
If you use an impedance notch to flatten the Fs resonance, as I did in my case, you can push the tweeter that low with a shallow slope as long as you don't ask excessive SPL from it (limited by xmax).
The 27TFFC copes with this very well aside from the rear chamber wall resonance. Once that has been identified and dealt with, its a very nice sounding tweeter crossed that low and doesn't sound like its strained at all, even at high 90s SPL. Normally I'd use a Morel CAT308 crossing that low, but the Seas 27TFFC sounds more open and extended.
Another trick with the 27TFFC is to change the rear pole damping from the little piece of foam to a felt disc and a pinch of sheeps wool stuffed in the pole vent. That gets rid of the wiggle above 10k and opens up the treble even more. Troels recommended this mod on his site.
As with many 2 way designs.
Your hoping to be at 2k
all fine and dandy at lower listening
until you crank up the volume.
As with any system, some sort of distortion is found.
An odd note since " Jazz" was mentioned
Being a big fan of older recordings.
I have often questioned my speakers.
Then realized a little squawk and distortion
is in the recordings.
And often a very good tweeter can make it
more obvious.
Specially with some of my favorite horn players.
A very good speaker can often reveal.
Microphone distortion in the actual recording.
Your hoping to be at 2k
all fine and dandy at lower listening
until you crank up the volume.
As with any system, some sort of distortion is found.
An odd note since " Jazz" was mentioned
Being a big fan of older recordings.
I have often questioned my speakers.
Then realized a little squawk and distortion
is in the recordings.
And often a very good tweeter can make it
more obvious.
Specially with some of my favorite horn players.
A very good speaker can often reveal.
Microphone distortion in the actual recording.
Many of the older Cannonball Adderly recordings have alot distortion in them. He plays very precise and cleanly, with nice tone and great dynamics. I have some of the earlier mono albums from him. The one he did with Nancy Wilson is a good example of how the limitations in recording technology put a damper on his playing. This is a case where you really have to just listen past the recording and pay attention to the music itself.