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Old 2nd May 2008, 05:03 PM   #3461
mige0 is offline mige0  Austria
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Quote:
Originally posted by Lynn Olson

. Even so, I was able to clearly see not one, not two, but three narrow resonances in the KEF B110 in the vicinity of 3.2~3.5 kHz - as I recall, they were around 3.2, 3.3, and 3.4 kHz, and were about 30~50 Hz wide each. These were dustcap resonances, of course, but simply removing the dustcap didn't get rid of them - new ones appeared elsewhere. (You always gotta measure, not just assume!)

Quote:
Originally posted by Charles Hansen

So when you are looking at a 4" large format compression driver, the diaphragm is breaking up in the 5 - 6 kHz range.




For those too young to know about the B110 from KEF I provide some pics and a quick CSD measurement.


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As can be seen by the CSD this ancient polyprop-driver easily can compete with current metal cones like from Seas/ Excel (or large format 4" compression drivers ?) when it comes to membrane breakup resonance.


Actually this particular B110 is a tuned version from the Linn Kan.
That small foot print speaker was really impressive at its days very good imaging, timing and tonal balance though it had kind of issue with piano music.




There were several modifications made by Linn at this speaker. Some can be seen at the pictures
- coating at both sides of the membrane (seems to bee very effective for the dust cap resonancies Lynn mentioned)
- strips of lead at the basket and at the magnet
- coating of the basket
- holes through the membrane for voice coil ventilation - a technique copied by Peerless later on as can be seen here:

http://www.diyaudio.com/forums/showt...67#post1279267




-----------------------------------




Some rather amazing CSD behaviours I've put together earlier:

Though these CSD reflect speakers in cabinets similar effects may be seen at speakers without cabinets once we would measure with higher resolution according to the faster decay of a speaker alone.


http://www.diyaudio.com/forums/showt...58#post1202358


When the stimulus is turned off - the stored energy is released in rather complex patterns of "hidden resonances".
Some effects are more clearly visibly with a sonogram. This is basically a CSD measurement seen from the top and displaying the "height of the mountains" in a color code.

What I observed, I haven't seen elsewhere or read about in such clarity before:

- different slopes for different frequencies
- build up of resonances at certain frequencies
- non linear slopes that are "walking down in steps"
- energy swapping between adjacent frequencies
- resonancies smoothly changing frequency with time of decay


Linn, could you tell about the enclosure your Eaton CSD has being taken with ?

Greetings
Michael
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Old 2nd May 2008, 07:59 PM   #3462
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Default Planar CSD

Other than the raggedness above ~11khz or so, does this look to be pretty good behavior? Down 30dB at ~ 1.25 msec...


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Old 2nd May 2008, 10:03 PM   #3463
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That B110 is just as bad as I remember. I hated those things - they required equalization up the yin-yang, burnt up the paper voice-coil former if you looked at them cross-eyed, and were the most inefficient and peaky driver I've ever used. That the BBC got good sound of them in the LS3/5A is nothing less than a miracle - but that still doesn't mean they were a good driver.

The driver I really liked in Audionics TL-M 200 was the one just below the B110 - a Richard Allan 7" cast-frame midbass driver with a Bextrene cone. Now that was a quality driver - much better in fact than the wretched B110 just above. Unfortunately, I "inherited" the TL-M 200 project from a designer that high-tailed it out of town and left no forwarding address (he was smart!), and I was stuck with the speaker as-is, and had the make the existing driver complement (B139, RA. B110, and T27) somehow work all together.

Talk about being thrown into the deep end of the pool. These days, I would ***t-can the drivers and tell the management they'd just have to write off the cost of the useless prototype boxes - not *my* fault the previous designer didn't have a clue what he was doing. That's why I still have a bit of a chip on my shoulder about so-called "genius designers" and their half-witted driver selections. In my first speaker project, I had to clean up after one of these clowns, and it wasn't any fun.

I guess this experience is also the reason I don't cut driver builders any slack. They get away with the stunts they do because most speaker designers don't hold them accountable for the dumb mistakes they make. I know from hard experience there are very real limits to how much you can work-around driver faults - and when you look at the sum total of hours-to-design and the net results, it's better to harass the driver builders and look as hard as possible for alternatives (your negotiating power is also a bit better if you're aware of the alternatives, and the exact ways in which the competitor has a superior product).

Regarding the earlier mention of compression drivers and direct-radiator domes, one point I didn't make is that phase-plugs and horn/waveguides do not change the inherent sound of the diaphragm material. If you don't like plastic-dome tweeters, you shouldn't expect a plastic-dome compression driver to sound all that different. Similarly, aluminum, titanium, and beryllium dome tweeters will have noticeable kinship to their compression-driver equivalents. This is just one of those things you have to deal with.

Although the phase-plug and horn/waveguide don't do that much to damp diaphragm breakup and resonances, one huge difference is efficiency and headroom - about a 50X to 100X difference. A typical dome tweeter is about 90 dB/metre efficient, and the highest I've ever seen is 95 dB/metre. By contrast, 109 to 111 dB/metre is the norm for compression drivers with the appropriate horn/waveguide.

The rated pink-noise power capacity of an Altec 288-G is 15 watts (modern SR drivers are several times higher) with an efficiency of 110 dB at four feet. Let's convert that to 111 dB at one metre for ease of calculation. A direct-radiator dome tweeter is doing pretty well if it is 91 dB/metre efficient. For the dome tweeter to put out the same level of acoustic watts as the 288-G, it would have to accept 1500 watts! Well, maybe it could, but only for a few milliseconds, only once, and it would be pretty distorted during that brief interval.

By contrast, the Altec rating is a commercial rating intended for continuous use in an application where driver failure results in considerable expense and inconvenience for the theater-owner. That's rather different than the rather optimistic power rating for consumer products, where the number seems to be picked out of the air.

So the tradeoff becomes 100X the headroom vs diaphragm breakup happening one to two octaves lower than the direct-radiator. We can now buy very good supertweeters from several vendors, and can measure and design crossovers with far more precision (not true back in the Fifties). Hmm, which way should we go?
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Old 2nd May 2008, 10:33 PM   #3464
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Quote:
Originally posted by auplater
Other than the raggedness above ~11khz or so, does this look to be pretty good behavior? Down 30dB at ~ 1.25 msec...

John L.
The gated time window is much too short at 2.17 mSec. If possible, try to re-measure with at least 7~8 mSec interval. This will require the annoyance of the two-foot-high pillow pile, but it is unavoidable if you want a usable CSD. I can assure you the CSD looks *very* different with a longer time window. If you cannot get a clean time window of at least 5~6 mSec, I regret to inform you that you cannot perform CSD's or reasonably detailed FR measurements.

What gets my attention is the rough FR at the back of the CSD. Although not very high in resolution, it is not too smooth in overall peak-to-dip magnitudes, which should appear in the CSD - and doesn't, thanks to premature truncation of the time window. Rest assured that uneven frequency response always has a visible impact on the time domain - provided the measurement is allowed to show it.

On the other hand, the ups-and-downs could be completely benign, and nothing more than simple comb filtering from the large vertical radiating area. If this is the case, measuring at different distances and microphone heights (close-up, 1 meter, 2 meters) will reveal that the bumps-and-dips move around with measuring distance. If the bumps-and-dips stay the same, that's not so good - that means the large diaphragm itself is going into breakup modes, and there's nothing you can do about it. Suppressing modes from large plastic diaphragms is not trivial - the electrostatic folks have spent decades on that one.

Regarding the B110 measurements shown above, that is nearly as bad as it gets. If the time interval were longer, and the 1/12 octave smoothing removed (the protocol I use), then it would appear considerably worse, and the fine structure of the multiple resonances in the 4~5 kHz region would start to appear. When those multiple, highly directional resonances are excited by female choir, the B110 can really shriek at you - the notorious "shhh" coloration of so many Bextrene speakers.

I guess the reason I'm so touchy about these obnoxious 1~5 kHz colorations is that I've spent so much time trying to get rid of them - from what I can tell, magazine reviewers can't seem to hear them at all, and some demented audiophiles actually think that is what "resolution" and "detail" sounds like.

P.S. The Eton measurements were taken with a larger-than-IEC flat baffle, with the Eton mounted about 20% off-center, the driver centerline about 2 meters off the floor, and the flange of the driver flush with the baffle. Unless the test driver is mounted in a near-spherical enclosure, the test box will contaminate the time response and make it very difficult to see driver artifacts.
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Old 3rd May 2008, 12:02 AM   #3465
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Default CSDplot

Thanx Lynn. Always good to get an eval. from someone with extensive experience in the field. This is ~10 yr. old data I pulled from somewhere on the net years ago (probably John Whitacre's study), so I doubt anyone's done much more exploring this driver.

I wondered about the gating vs. resolution issue...I notice many CSD's offered don't include the res. info... looks like the Eton is gated @ 1.511 msecs?? and the KEF @ 2.97 msecs...? so does that make these waterfalls less than useful?


The BG's sure sound pretty mello and sweet in my setup, tho... so I wonder about the usefulness of the CSD's vs. what I hear...

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Old 3rd May 2008, 12:04 AM   #3466
soongsc is offline soongsc  Taiwan
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4inch metal cone
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3 inch metal cone
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Old 3rd May 2008, 12:12 AM   #3467
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by Lynn Olson


The gated time window is much too short at 2.17 mSec. If possible, try to re-measure with at least 7~8 mSec interval. This will require the annoyance of the two-foot-high pillow pile, but it is unavoidable if you want a usable CSD. I can assure you the CSD looks *very* different with a longer time window. If you cannot get a clean time window of at least 5~6 mSec, I regret to inform you that you cannot perform CSD's or reasonably detailed FR measurements.

...
Could you elaborate on how the CSD would vary with a longer window? Are there any comparisons that can be shown to help us better understand the influence? Normally I would expect the differences to occur at the lower frequencies and at extented time normally at much lower levels. The higer frequencies and the shorter time duration would remain unchanged.
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Old 3rd May 2008, 12:54 AM   #3468
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Default plots vs. hearing

here are some freq. response plots presented in various formats... any of them mean anything at all wrt. what one actually hears??
Rd75
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RAAL tweeter
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ATC Neoplanar
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Peerless 6 1/2" mid woofer
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and a polar plot to boot..
ATC Neoplanar
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or is all this data just for naught as far as designing and subsequent listening goes??

thanx

John L.
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Old 3rd May 2008, 11:25 AM   #3469
mige0 is offline mige0  Austria
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Hi Lynn

not sure whether your negative recption of my B110 posting is due to my interference with a long time vendetta of yours as a reviewer and some specific companies or anything else.

Anyway, it delivers hard data valid in the range presented. No academic study about the B110 was intended nor promised elsewhere though.
My subjective and very positive comments about the Linn Kan are widely shared and explicit do not apply to the bigger speakers of that time like the Sara and the Isobaric, where you can HEAR the effects of energy transfer between one and the other bass speakers as kind of crude beats ("Schwebung" in German).
Rogers on the other hand were designed to be studio monitors afaik not as consumer product and they for sure were not the only company that succeeded in balancing out downsides of the material they had available.

If you crank up resolution in terms of less smoothing yes - you will see more artefacts. But you also will have to make a LOT more measurements to make sure what they are telling you and even than the interpretation of its sonic relevance will be highly subjective.

To my knowledge no one ever has put together a set of patterns that clearly can identify from analysing a CSD measurement for example - different materials of cones surroundings baskets VC formers etc.

If you crank up resolution in terms of larger time window no there wouldn't be that much more to see, except at the low frequency end where invalid data is cropped in ARTA.
And no, no need to stude the subjet for centuries to grasp the main issues displayerd clearly on CSD measurement.

What my B110 CSD's are really telling can be read between the lines: no progress concerning cone break up during the last centuries - regardless of cone material.

One has to accept that crossing at 2,5kHz requires a speaker of less than 4" - 6" maximum maybe even less, when liking low order networks.

This may be hard to digest even more so if combined with the desire of achieving low IM which restricts the usable bandwidth covered by a single speaker at high output even more.

With your approach of high output at low IM and low order XO you are defiantly dancing along the borders of physics .

Among others, this makes your thread "juicy" and interesting for me and makes me contributing from time to time.



Yes the KEF B110 was an inferiour speaker - in what you outlined (guess why I have ONE spare).

And no, the KEF B110 was an excellent speaker - you will be hard pressed to find one that is substantially better in fast decay BELOW it's cone breake up resonnace.


Greetings
Michael
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Old 3rd May 2008, 11:55 AM   #3470
soongsc is offline soongsc  Taiwan
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Default Re: Re: measuring 'colorations"

Quote:
Originally posted by Lynn Olson


Well, let's put it this way. I didn't come up with this protocol; the BBC did some forty-plus years ago. I've been to Britain, visited the BBC Research Labs, and heard their most advanced recording and playback systems. To this day that was some of the best sound I've ever heard. So I'm partial to the BBC/Spendor/Quad philosophy, both esthetically and sonically. Other people prefer other schools of design.

...
Do you have links to any of the studies they have made about this? I also noticed the importance of CSD.
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