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Old 6th May 2008, 10:40 PM   #3491
singer is offline singer  Belgium
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Default diffraction.....

just a small follow up to an earlier comment about the audibility of diffraction: i have full range statics, a dutch brand, an mdf frame. the frame is perpendicular to the stator for about 10mm then is rounded away over about 10mm (less than half an inch). out of curiosity i bought some pvc (i think) grey drain pipe. diameter about 100mm. i installed them the length of the stator (1350 mm) as close to the stator as possible to avoid rough edges.

the differences that i heard are subtle but with well know recordings clearly audible. some new details popped out of recordings. the spatial presentation somehow fills out and becomes more physical, and somehow a feeling of more liveliness and precision. ok it doesn't look very pretty but the cost was about 20 euro. i presume manufacturers could pretty easily provide fancy looking add-ons with a designy look. i presume that at least similar improvements might be available for other loudspeakers if similar approaches add-ons were tried.
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Old 7th May 2008, 12:20 AM   #3492
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Quote:
Originally posted by Charles Hansen


Well if you want to know what your speakers will sound like, just give a listen to the JBL K2 S9800's. That's pretty much what you've described. The 15" woofer has a paper cone coated with Aquaplas, and an alnico magnet with really cool multi-layer pole piece to keep flux modulation to a minimum.

We used a pair at the CES a couple of years ago and still have them here at our factory in Boulder. (We liked them enough to purchase them.) They have the "Special Edition" crossover that has much upgraded parts over the original version and we also replaced the Monster internal wiring with Cardas.

They're pretty darned good speakers, but certainly not perfect. The main differences between them and what you are planning to do are probably the open baffle (versus a vented box) for the woofer and the horn profiles. But in my estimation their greatest weaknesses (no speaker is perfect!) will not be addressed by your proposals.

To me the single biggest problem of these speakers is that there is *no way* to get a 15" (or even a 12") woofer to sound natural much past 300 Hz, let alone all the way to 800 Hz. But to each his own.

Let me know if you ever want to hear them. We're less than an hour from Fort Collins. From 800 Hz on up, the beryllium drivers create quite an extraordinary result.
Hi Charles, yes, I'd like to hear the JBL K2's. I live in Erie, no more than twenty minutes away from Boulder. You can see my e-mail address midway down the Nutshell High Fidelity website - let's make contact, I'd like to hear the big JBL's. I'm hoping they're in a somewhat higher class than the big TAD system I've heard so far. I appreciate the invite and would like to take you up on it.

I am partial agreement about the big woofers, which is why I'm keeping open the option of a pair of 12" drivers - again, used with a 700~850 Hz crossover. In this frequency range, I am more concerned about box modes than driver resonances.

The box modes in a big studio-monitor (or JBL K2) box are much harder to control, and to my ear, lend an annoying "droning" quality to the sound, a traditional part of the sound of big vintage loudspeakers. These modes are quite apparent when the drivers are pulled and you put your head in the box - you hear a droning, drumming quality to ambient sounds, and the box stuffing and damping, although reducing its magnitude, adds its own dull, murky quality to the droning sound. Many damping materials have their own sonic signature that overlays the basic box sound, resulting in a slow, sodden quality to the lower midrange and upper bass.

I used to be puzzled why these modes in the 300~800 Hz regions were so obstinately difficult to control, until I got MLSSA in 1991 and found it took 2 feet of a wide variety of damping materials to merely reduce the floor bounce by 20~25 dB. I started with what I thought was plenty of damping, several inches of the fancy commercial foam stuff, combined with several layers of audiophile-grade wool felt, and it only reduced the floor bounce by 5 dB or so! It was nearly worthless!

Now, above 2 kHz, then the commercial stuff started to make a difference that was more worthwhile, particularly if you wanted to reduce the slap off the back of the cabinet. But frankly, anything I could buy on the market, had only the slightest effect in reducing the box modes - and the bigger the cabinet, of course, the lower in frequencies these modes are, and the less effective any type of damping, at any price. So all of the fancy damping we see in big box cabinets is mostly effective above 1 kHz, and does surprisingly little below that frequency. What it does do, though, is add odd colorations of its own, which is why lightly damped old-school speakers can sound better than modern, heavily-damped speakers. It's one of those pick-your-coloration things.

All it takes is a little playing around with MLSSA, or any MLS program, and looking at what it really takes to absorb the floor bounce. Since MLS systems can examine the frequency response of the bounce itself (by gating away the direct sound from the loudspeaker), you can examine at leisure what various damping material do in terms of absorption vs frequency. Carpeting, for example, does nothing below 8 kHz - it might as well be glass.

It was this discovery that made me realize just how hopeless the situation with conventional box speakers really is. The only way to get around it is confine the box speaker to very low frequencies (below the first mode) and use a sharp-cutoff crossover to avoid contaminating the more critical region of the spectrum. Otherwise, the box is going to result in murky, opaque, and congested bass - I suspect much of the merit of transmission-line speakers amounts to little more than clever control of box modes in the 300 to 800 Hz region. That's what I had in mind with the Ariel - it was the box-mode region I was most interested in, not the deep bass. Even so, transmission lines have their own set of awkward compromises in this frequency region.

Although I grant that big drivers in the 12 to 15-inch range are starting to get into trouble, with the spider and surround being the first resonance to appear, I feel the box modes are the most prominent and objectionable - and due to the lack of good LF absorbers, the hardest to control. My instinct is that more than 20~30 dB of smooth, broadband absorption is needed, and existing damping and absorbing materials just don't provide that in the box-mode region. Thus, the proverbial "box" coloration which is so noticeably absent in bass horns and dipoles - since we are all so used to this particular coloration, it is most noticeable when it disappears.

For me, the charm of OB isn't so much the dipole radiation pattern, with the claim to less room coloration (which I am not all that sure of), but the more genuine advantage of side-stepping a prominent coloration in a very important frequency range - upper bass and lower midrange. True, driver colorations remain, but I feel these are much milder in the 300~800 Hz region than the much more noticeable 1~4 kHz region, where small-format midbass drivers are commonly used.
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Old 7th May 2008, 01:09 AM   #3493
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By the way, I'd like to thank John Janowitz for the information and graphs on the AE Speaker Lambda TD-15M. That certainly look like a contender - let me know if you're considering Alnico, that would make it even more attractive, and would justify a higher price. (I can't believe I just said that!)

In my experience, Alnico isn't so much about adding a guitar-friendly coloration, but more about noticeably better rendition of instrumental subtleties and a more palpable, in-the-room quality to the instruments - a palm sliding across the surface of a drum, the sound of wood in the cello, more vivid tone colors that sound less artificial and more real. The difference is most apparent in the 200 to 1 kHz region, from what I heard.

In the amplifier world, this isn't a clever type of coloration you can add, but more a matter of reduction of distortion, or an improvement in a power supply. Alnico does something better, and I don't know what it is, although my guess is something to do with back-EMF's induced in the magnet structure. It does sound very much like better core materials in audio transformers, for those of you who have auditioned different transformers.
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Old 7th May 2008, 01:37 AM   #3494
SamL is offline SamL  New Zealand
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Default Re: Measurements, and PHL 1120 as a midrange

Quote:
Originally posted by FlorianO
Speaking of measurements, and how they can be sometimes tricky to interpret:

Regarding the PHL 1120 that was named as a midrange

[Side note: Lynn, Aleksandar from RAAL seems to recommend the PHL -- in particular the PHL 1120 above -- and not the PHY (or PHY-HP, whatever you want to call them) -- as a midrange. Quite a bit of difference]



That will make three of us.

Is it just me or in the measurments above the ripples above 2.5k are the talesign of cone breakup ? Did anyone noticed that with the PHL 1120 ?

OTOH other detailed measurements of that very same driver -- namely these -- look very different.

... And suggest (from the impedance plot) that the driver is good down to about 400 Hz (or 300Hz, but maybe that's pushing it ?)

Anyone care to comment on that ?
PHL 1220 driver question
Old post with brief comment on PHL1120, more on Audax PR170M0.
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Old 7th May 2008, 04:40 AM   #3495
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Quote:
Originally posted by Lynn Olson
By the way, I'd like to thank John Janowitz for the information and graphs on the AE Speaker Lambda TD-15M. That certainly look like a contender - let me know if you're considering Alnico, that would make it even more attractive...
My wish list to John_J for a wide bandwidth 10" dipole midbass would include:
* NdFeB magnet.. BL ~17
* Smaller NdFeB motor size would be less restrictive rear waves for best dipole
* NdFeB with high flux would allow BL > 17 in an underhung motor
* 8mm linear Xmax
* curvelinear profile kevlar-in-paper treated cone. Long kelvar strands also seem to reduce breakup
* MMs ~40 grams
* two 8 ohm voice coils...series 16 ohm for high Qts dipole and 8 ohms for MTM
* Qts ~0.6 with 16 ohms
* Le < 0.2 mH
* long phase plug / heatsink
* ~94 db/watt @1m


I stiill have about 20 Lambda 15" Dipoles and several 99db SPL DIY dipole ribbon tweeters, so I just need a full-voice 10". I also have Lambda TD15Ms, but vocals do not sound right on them with the 1.4K xover frequency I tried to capture those lovely sopranos.


I wonder what type of DIY speaker Charles Hansen would build? My ears agree that 800 Hz xovers are not the best solution. LR8 at 80Hz and LR4 at 3Khz sounds pretty good on long ribbons.
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Old 7th May 2008, 04:48 AM   #3496
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Default Linesource,

I live near you....can I hear one (or two) of your Dipole15's?

I'm in Santa Clara. You can PM me at chris_mercurio@hotmail.com.

Thanks,

C
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Old 7th May 2008, 05:00 AM   #3497
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Quote:
Originally posted by mige0
As you can see the breakup is clearly at around 1.5kHz (exceptional clean below ! ).
All I can tell you is that CSD (waterfall plots) are not a very good way to examine the behavior of the diaphragm. They will show very gross problems, but are completely unable to show more subtle problems.
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Old 7th May 2008, 05:06 AM   #3498
Salas is offline Salas  Greece
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Quote:
Originally posted by Charles Hansen


All I can tell you is that CSD (waterfall plots) are not a very good way to examine the behavior of the diaphragm. They will show very gross problems, but are completely unable to show more subtle problems.

Laser interferometry is your best suggestion?
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Old 7th May 2008, 05:16 AM   #3499
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Quote:
Originally posted by Lynn Olson
Hi Charles, yes, I'd like to hear the JBL K2's. I live in Erie, no more than twenty minutes away from Boulder. You can see my e-mail address midway down the Nutshell High Fidelity website - let's make contact, I'd like to hear the big JBL's. I'm hoping they're in a somewhat higher class than the big TAD system I've heard so far. I appreciate the invite and would like to take you up on it.

I am partial agreement about the big woofers, which is why I'm keeping open the option of a pair of 12" drivers - again, used with a 700~850 Hz crossover. In this frequency range, I am more concerned about box modes than driver resonances.
Wow -- great post! I agree 100% with everything I snipped out, and have independently reached the same exact conclusions.

I left in the things that I don't fully agree with. First of all, in my estimation the TADs are overall better than the K2's. We have them both at the factory, so you can compare them for yourself if you like. But if you didn't like the TADs, I'm not sure you will like the K2's any better.

This will take a bit of planning, as you have a bum leg and I'm now paralyzed and in a wheelchair. So we will have to do it at a time when there are some able-bodied people around to help move things. Also, the TADs have been playing non-stop since the CES and are fully run-in. In contrast, the JBL's have been sitting unplayed for over six months now. It would probably take several days of continuous play to get the JBL's back up to snuff.

Finally, while the box resonances are a huge problem (and one big reason why mini-monitors have their charms!), I find that the diaphragm resonances of *any* driver running in break-up mode to be audibly problematic. So in my opinion, both problems need to be solved.

Please note that we (Ayre) used the Linkwitz-designed Audio Artistry Beethovens at a CES many years ago. At that time he was using the ScanSpeak paper cone midranges. I urged him to try some different drivers for that application (such as the then-new SEAS metal cone models), and he eventually took that advice with the advent of the Orion. In that design he has minimized the problems of both cone resonances and box resonances to achieve a very fine result, although I agree with your reservations regarding dynamic restrictions and complex multi-way crossovers (especially implemented with the ubiquitous op-amp approach that SL seems to find no problems with).

I'll contact you privately.
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Old 7th May 2008, 05:38 AM   #3500
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Quote:
Originally posted by salas
Laser interferometry is your best suggestion?
It's a great way to go if you have an extra $50,000 or $100,000 lying around.

I developed a much less expensive method when I was designing speakers over 20 years ago.

One method that works (although it is somewhat cumbersome to build and use) was described by Keith Johnson in Speaker Builder magazine back in (I think) 1988. The cover showed a contraption that looked like a pair of scissors with electret microphones attached. You could probably duplicate that setup for around $100. It won't give you the lovely pictures that the lasers will, but it will tell you a lot about the cone behavior if you can figure out how to interpret your results properly.
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