Ring Radiator Comparisons

[gibber]

The difference in what is heard is not so much what is above 15K, but what is actually happening in the 8-9K region. The 2402 have a much deeper dip in this area than the 2405, and the ear readily hears this difference as a loss of detail.

Time domain effects might have an influence on listener preference, too. But i would actually suspect that the 2402 horn is better in that respct than the later designs due to no folding / slotting / etc. after the initial compression*). The 2403 could be as good but is second in my book since it sports the same phase plug as the 2405-fram versions of the 2404, so some extra complexity for the sound path.

Back to the frequency domain effects -- i fully concur that the 15 kHz behavior is likely of secondary importance compared to the 9 kHz aberrations. So big Q is, are these dips due to the 2402 horn or are they a consequence of the much-larger 2402 fram? 1Audohack's post #195 showed Bode plots of the 2402H-5 vs the normal 2402H version, but doesn't resolve the issue coz both of his tweeters do not seem to suffer much output loss at 8..10 kHz (the larger fram just a little bit at 8 kHz, but far away not only in severity from the 9.5 kHz dips in MrWidget's post that started this thread).
You mentioned the dip of 2403 to be almost as bad as 2402 in this respect and Grumpy's post #150 points to a possible source, as off-axis responses show a relative level increase for that frequency range, meaning in turn that the on-axis response might be weak at same frequency if we assume relatively flat power response into the room. That said, Grumpy's findings are more in the area around 8, not 9.5 kHz ...

The weekend's coming, will be interested how the audition turns out -- Ralph




*) anyone remembers Fostex 725 that did away with the initial compression?

[toddalin]

So big Q is, are these dips due to the 2402 horn or are they a consequence of the much-larger 2402 fram?

The weekend's coming, will be interested how the audition turns out -- Ralph




*) anyone remembers Fostex 725 that did away with the initial compression also?

Primarily because of the bigger fram.

IIRC, when I put the 2405 fram in the 2402, the dip largely went away and the result was pretty much like the 2405 tweeter with the 2402 dispersion. (JBL did make some 2402s with 2405 frams.) You can use a elastomeric filter (rubber band) too further smooth out the >10K response and even push it beyond that of the 2405 while adding to the dispersion of the 2402 at the cost of dB. This really turns the 2402 into a "super tweeter."

But, you can also put the band on a 2402 with the 2402 fram, kill most of what's below 9K and extend and smooth the response above that. You won't get it as high or as much volume as with the 2405 diaphragm, but if you have an RTA and a rubber band (the ones used on asparagus work well), it's fun to try.

Push the rubber band over the "nose cone" evenly around using a wooden stick, paint brush handle, etc., while running white noise though it and watching it on the RTA. Just before the ring closes up, the slot gets very narrow and you will see the frequency range change as the lower frequencies drop way. Physics says, the narrower the slot, the greater the dispersion, and we confirmed this. If you go too far, a pin can pull it back out.

[Dr.db]

The difference in what is heard is not so much what is above 15K, but what is actually happening in the 8-9K region. The 2402 have a much deeper dip in this area than the 2405, and the ear readily hears this difference as a loss of detail.

Thanks a lot, I missed out on your previous post. Thanks for posting again!

[gibber]

Short report on what turned out only as the beginning of that listening comparison. We had quite a bit of preparations to do, so there will be a second date. The tweeters were passively added @ ca 7kHz (3rd order 1u/.3mH/1.5u) to a 8" vintage die-cast frame Grundig paper cone full range w/o whizzer cone or even dust cap. Contenders are a bronze horn flare waiting for a motor and
1) pr gray ferrite 2402H-5 w/ 2405 fram; 2) pr blue fram 077; 3) pr yellow fram 2402H; 4) pr 2402 w/ 2405 yellow frams; 5) pr 2404H w/ yellow 2405 frams; 6) pr Coral H100; 7) pr 076; 8) pr 2405; 9) pr silver fram 2402H.

Also a pr of Beyma Cp21F, a single Beyma Cp21 alnico w/ vintage fram & single 2402 / orig. fram

Auditioned were only 3/5/7/8. No level adjustment was used so far, will do once the measurement gear is used. Classical, Jazz and Pop were tried; #3 and 5 produced something that can only be likened to a kind of "grey" hiss alongside the music. Sound was veiled in comparison to 7/8. The latter two markedly differed from each other only very high up with the cat eyes having quite a bit less in highest overtones or cues to the "mechanics" of music-making such as the soft string squeak you can often hear, etc. No clear winner here: 076 a little more recessed/relaxed, 2405 a little more revealing. As toddalin predicted: surprisingly similar sound given the two very different horns ...

to be continued

[gibber]

Well, sorry for long quiet period. In the end it was four weekend dates and the best part of a day at an amateur audio meeting, so it took some time to get a clear picture ...

Here's a few measurements that my friend and i wanted to make in order to shed some light on the time-domain related arguments made in this thread, ring radiators first :

[gibber]

Here's an interesting effect (sorry for the X- and Y- axis jumping a bit) in that the 077/2405 shows a double peak at the beginning of the response train :

[gibber]

We used a 22cm "fullrange" unit made by Grundig in the 50's. These speakers came with various frames (made from sheet metal or diecast) and magnets (mostly alnico types). The one we used had a thin diecast frame and a chunky alnico ring magnet (so not inside the coil as that is ca 25mm only). That alnico ring was somewhere between round and square outside and had recesses for the bolts that hold the magnet on the basket.

The version we had at hand is one with a surprisingly high resolution capability. The thin paper cone has no dustcap or dispersion dome (just an open pole piece) and is subjectively very "fast". As bit of a "forwardness" was observed, we tamed it by a simple strip of sticky tape. The unit was used without a filter and rolls off by itself. Crossover for the tweeters, as mentioned in an earlier post here, was 3rd order at ca 7kHz. Resistors were used in parallel/series to ensure roughly comparable levels.




Attached is the frequency response of the mid-bass, the sound is much less rugged than the response might make you think. Response shown is of the 22cm with a 10cm "Sachsenwerk" cone tweeter added at nom. 7kHz:




We used a baffle for most of the tweeters. The baffle had a strong effect on axis for wide-dispersion designs only. Not used on baffle were 2404H, Coral H100, HH/Multicell HF200, and TOA HT371, although the latter is a wide-dispersion design and was shown to benefit from a baffle when doing measurements after the listening test. Here's two Bode plots showing the effect of the baffle on a 2405 slot, first one with the baffle, the second plot w/o :




Missing in the previous post, here's the pulse resp for 076 #2 :

[gibber]

My friend and i took the two enclosures/X-overs/baffles plus the equivalent of two L100s in tweeters to an audio gathering and demo'ed the setup there. Since we offered it, a number of people turned up and listened to the bass-mid with various tweeters of their choice.

Some interesting comments were made, of which i will list some here:

1) the JBL's were regarded the most "dynamic-sounding" of the field (the non-JBL types are mentioned elsewhere in this thread).
2) especially the two JBL slots 077 and 076 (the cateye is a slot, just a little less extreme than than the 077/2405) were commented on as being best in speech intelligibility. Fostex T825 and 2404Hs (and a makeshift 2404 alnico version) did not find so much applause.
3) among the nominally same-type JBL diaphragms, large differences (sound & later also measurement) were observed.
4) among the various types of JBL diaphragms (best ones of each chosen), the 077/2405 was preferred over 076/2403 and 075/2402 frams. We even put together a cat eye with 2405 frams and it was rated as better than the original by the audience.
5) using a good pair of 077/2405 frams makes the choice between 076 and 077 really difficult. Even listeners on the very side did not prefer 077/2405 over the cateye with 2405 frams (but did over the standard cateye). The ring radiator (alnico or ferrite) was deemed slightly inferior to these slots even if it had 2405 frams installed.
6) the longer/large diameter bronze horn was installed instead of the normal 2402 front pieces but was not found superior with this 7kHz/3rd order configuration -- perhaps it's real advantage is extending the 2402 towads lower frequencies.


Admittedly, this listening test might be flawed in that each tweeter pair was only combined with that very pair of Grundig full-range at hand, so take the above with the usual grain or two of salt.

We tried to also find out if a preference ferrite vs alnico exists, but as outlined elsewhere, the parts are not easily exchanged between the two. A 2404 (no "H") was put together and tried vs 2404H but results seemed to indicate there is no difference. The 2402H we had with us came with inferior frams compared to the 2402 alnicos (as measured later) and hence were deemed inferior in this comparison. And while we look at diaphragm quality variance in a ring radiator, this certainly was previously stated for the slots...

The on axis response of the 2405 is indeed more linear and a bit more extended (but really, how cares about extension above 17kHz ??), but if you look at unit to unit matching all these consideration become moot anyway...

Fostex T825s at this event were considered very smooth, a little too polite for most, but very neutral and well resolved despite a apparent lack of top-end sparkle. Listeners to the extreme side of the room did again not necessarily favour this slot radiator over the non-slots such as the Goto tweeter. I wonder how Fostex T845 might have fared, as they seem to be very close in construction to 077/2405s...

The Goto, despite the hype, fared well but not better than the 2405 or the 076 with 2405 fram. Reason as before was the better portrayal of dynamics and superior intelligibility of speech and song with the JBL 2403/2405, while the Goto like the T825 did offer slightly better resolution and "refinement".

All in all, this event's results were in contradiction to my predictions as outlined previously in this thread. Although the 077/2405 did show funny time domain behaviour as expected, the listening panel did not prefer bullets w/ 2405 frams but judged otherwise.

Ralph

[pos]

Hello Ralph

Thanks for these interesting measurements and listening comparisons.
This double spike in the 2405 IR is also something I measured on all of mine.

What diaphragms did you try in the 2403 core?

[gibber]

What diaphragms did you try in the 2403 core?

One blue & one silver 2405 fram, if i recall correctly. And actually, not in the "2403 core"; we took quite a bit of trouble to make it happen. The cateyes were never opened before (sealed by 076 typesticker on back). So in order not to break that seal, we removed the elliptical horn from the front and used the same pieces of metal taken from a buttcheek in order to build up a cateye with proven quality 2405 frams.

[script56]

While on the subject, I'm wondering how 075 diaphragms are used for 076 replacements. The original 076 has pointed diaphragm and 075 has hole for metal bullet

[JeffW]

While on the subject, I'm wondering how 075 diaphragms are used for 076 replacements. The original 076 has pointed diaphragm and 075 has hole for metal bullet

The pointy part is the phase plug. Remove it and there's a hole just like the 075.

[script56]

Oh. Ok. I bought some 076 horns (without driver). I was going to try to attach them to a 075 magnet assembly, but I guess it won't work.

[JeffW]

Oh. Ok. I bought some 076 horns (without driver). I was going to try to attach them to a 075 magnet assembly, but I guess it won't work.

It should work, I think all of the motors are the same. You'd just need the 2403 phase plugs.

To my knowledge, all of the motor assemblies are interchangeable from a mechanical standpoint. The ferrites probably have a little more flux level than the alnico’s but that is all. The main difference in them is the horn or bullet or whatever is mounted on the front side. Any diaphragm can go in any body. Results will vary.

[script56]

Yes that's the problem. Any idea where to find them?