And that expensive speaker, it's a real laboratory of measurements vs. experience. The off-axis sounds very good to me, but the overall tonal balance never did. I attributed the latter due to compression, but also really trying to stretch a small woofer beyond its capabilities.
I won't go into it here, as it causes a lot of passion, but I encourage anyone who can to look at the specs and listen. It's interesting what does and does not correlate with experience.
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@audiokinesis
Like a lot of tests, there is no way to exclude all other dimensions or confounds.
You are absolutely right in that these tests cannot be completely devoid of thermal issues.
And yes, price is no guarantor. Wharferdale Diamond's for instance have outstanding tweeters in regards to linearity, and many have expressed surprise at how good they sound after inexpensive cap upgrades. :)
Best,
E
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Thank you for that information and for digging up those examples, Erik! Interesting that the less expensive speaker beats the more expensive one not only in deviation from linearity, but also in radiation pattern smoothness - look at the 45-60-75 degree off-axis curves. I tip my virtual hat to Paradigm. Considering how SoundStage makes their Deviation from Linearity measurement, I think it includes not only mechanical effects but thermal ones also, because at 90 dB the speaker is seeing 10 times as much excursion but 100 times as much wattage as at 70 dB. At any rate, given that peaks 20 dB above the average are quite common in recordings that aren’t overly compressed, the deviation from linearity going from 70 to 90 dB may just be the "tip of the iceberg" for real-world effects, if the speaker is driven to average levels higher than 70 dB/1 meter. My impression is that excursion-related non-linearities decrease gradually with level until they reach a certain point and then they shoot up rapidly. The same thing is more or less true for thermal effects: It’s not uncommon for a driver to exhibit less than 1 dB of thermal compression at 10% of its AES rated power, often rising to about 2 dB at 50% of its rated power and then maybe 3.5 dB at 100% of its rated power. In other words, in that last doubling of input power, we only get about half as much increase in SPL as we "should have" (1.5 dB instead of 3 dB), Now these ballpark figures come from eyeballing the spec sheets of those few prosound manufacturers who publish compression specs. These numbers are for long-term thermal compression rather than short-term thermal modulation (which has a very rapid onset and then a slower release, unless another peak comes along before the voice coil has had a chance to cool down). My assumption is that there is a correlation between the short-term thermal modulation behavior and the long-term thermal compression behavior. (Note that the AES rated power is a fairly conservative yardstick; typically the "music program" power rating is double that, and then the "peak" power rating may be double the music program rating, and we probably don't know which of these the manufacturer is using... and real-world, the excursion-limited power handling may be significantly lower than any of these at low frequencies.) Duke
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Hi Duke, I may be using the term incorrectly. Generally when I read about compression, it’s not thermal. This may be due to the fact that I don't read or do much with professional level gear, in which this is a major concern. Thermal compression can be seen with tone bursts, and you can see that after the first couple of cycles the output drops remarkably. "Static" or common compression is measured by comparing the FR at 2 different input levels. Find your level for 70 dB at 1kHz. Measure the FR. Add 20 dB of input voltage. Measure FR. The output should be +20dB everywhere. Wherever the output is NOT +20 dB is evidence of compression. Thermal compression is caused by heat, and therefore it’s effects are changing with previous input. What I’m calling "static" compression is related more to the limits of the driver’s linear travel. Look at the "Deviation from linearity" charts. Here is a speaker with excellent "linearity" or lack of compression: http://www.soundstagenetwork.com/measurements/speakers/paradigm_studio10_v5/And here is one with relatively poor linearity: http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1564:nrc-measu...Best, E |
My understanding is that there are two general areas of thermal compression effects. The one that has been studied and documented the best is what we might call long-term compression, which arises from both voice coil heating and magnet heating, the latter inducing a (usually temporary) loss of magnetic strength. Less well studied is what we might call thermal modulation, which as you describe happens very quickly - quick enough to reduce a sudden peak, thereby reducing the dynamic contrast, which in turn reduces the emotional effect of the music because musicians often use dynamics to convey emotion. I would expect thermal modulation to be primarily a voice coil heating phenomenon (with an accompanying increase in resistance)... when the voice coil of a speaker is hit with a 100 watt peak, it’s like touching it with a 100 watt soldering iron. Apparently JBL has patented a voice coil alloy whose resistance doesn’t change much as it heats up, presumably to combat thermal modulation. Others have worked on this too, but far as I know JBL is the first to include it in commercial products (some of their big high-end studio monitors). A couple of years ago I had an exchange with Floyd Toole about thermal modulation, and he said they had definitely found it with some of their measurements at Harmon, and that in some cases it was pretty bad. He mentioned testing a 3-way speaker whose midrange driver was effectively compressing on peaks by about 7 dB! He’s the one who told me that thermal modulation is an area that needs to be studied more. My own approach to thermal compression and thermal modulation ended up being the brute force method - high efficiency drivers with big motors and big voice coils that won’t start going non-linear until they reach much higher SPLs than are typical for home audio. This just happened to be a fortuitous side effect of giving radiation pattern control a high priority. I’d like to learn more about "static compression", but apparently my Googling skills are weak... I couldn’t find a website for speakermeasurements.com, but apparently it is associated with SoundStage. I’m aware of their "Deviation from Linearity" test, is that what you’re referring to? Seems to me it includes thermal effects as well. Anyway kudos to them for running it - Richard C. Heyser used to do something similar back in the day for Audio magazine. Duke |
@audiokinesis
While this thread is focused on tweeters, we should realize they provide the least contributions to the music, measured by energy content. Lots of listeners could loose both of their tweeters and not realize it by hearing. :)
Also, compression comes in at two types, as far as I know.
Thermal compression means the driver heats up, and efficiency is lost. This can happen extremely quickly, within a couple of Hz. What makes this so nasty is that essentially your speaker plays differently after warming up than it did at the start.
Then there's static compression, which all drivers have, but some more audibly than others. This is a limit of the suspension and linearity due to the coil and magnetic field. The static compression is relatively easy to measure, and AFAIK Speakermeasurements.com is the only commercial speaker reviewer that does so. IMHO this is something Stereophile should have incorporated decades ago.
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Erik wrote: Let's focus on learning
about choices speaker designers make and what that may mean to the
end user.
Duke replies: I can't speak for any
other designers, but for me speaker design starts with figuring out
what the priorities are, and then hopefully finding a way to
accomplish them (or come as close as is practical) within whatever
constraints are imposed. So the system concept comes first, and then
the design specifics follow. Thus I see tweeters (and every other
part of a speaker) as just part of a system, and no more than a means
to an end, which in high-end home audio is usually something like “a
sufficiently convincing perception of listening to live music”.
Erik: First, for any given type of dispersion, speakers need to
roll off more or less evenly. You don’t want to be 15 degrees off
axis and only hear the mid-range. Ideally the speaker’s dispersion
is even across as much of the response as possible, but usually this
can only be done starting in the upper bass.
Duke: Yes! The radiation pattern plays a far greater role in
what we perceive than most people appreciate. Most of the sound we
hear in most home audio systems starts out being dispersed off-axis.
Erik: Next, the wider the dispersion, the more early reflections
you may encounter, which can severely affect the frequency response
and imaging.
Duke: Agreed. In general early reflections are detrimental, but
later reflections can be quite beneficial.
Erik: The very large diaphragms of ESL speakers (Martin
Logan/InnerSound, etc.) have fabulous clarity thanks to this effect.
They can sound like you have headphones on even with very little room
treatment. Duke: Dipolar electrostats typically have a narrow radiation
pattern that minimizes early reflections, and then have a
spectrally-correct backwave that reflects off the wall behind the
speakers. If the panels are far enough out into the room, that
backwave energy is sufficiently late-arriving to be quite beneficial.
Erik: Drivers with different dispersion patterns _may_ also have
different rate of decay. Consider a hybrid ESL + cone woofer. The
woofer radiates omni-directionally and the wavefront looses energy
the fastest, while the ESL panel is a plane wave, with narrow
dispersion and looses energy more slowly.
Duke: This would be an example of an extreme radiation pattern
discrepancy (narrow-pattern line-source panel combined with
quasi-omni point-source woofer). Unfortunately it is not possible to
equalize such a system so that the first-arrival sound and the
reverberant sound have the same spectral balance (something that
would be psychoacoustically desirable – I can explain why if anyone
is interested). The best we can hope for is a juggling of tradeoffs
that works at our chosen listening distance. In general, the lower
the crossover frequency between woofer and panel, the better, as long
as we don't overly compromise something else.
Erik: Two of the most important measurements for me are
Cumulative Spectral Decay and compression. The first measures energy
storage, or "blur" that a tweeter adds to the sound because
it won’t stop fast enough. The second measures how a tweeter’s
response changes at different volumes.
Duke: We want to minimize anything that's a source of audible
coloration, and in the tweeter region, what's happening in the time
domain matters a great deal.
You mentioned compression – great job of paying attention to
something that matters, but doesn't show up on a spec sheet! Thermal
compression effects not only suck the dynamic life out of the sound,
they are often responsible for a speaker system's tonal balance
changing with volume level, which can happen if the various drivers
have differing thermal compression characteristics (which they
usually do).
Erik: Usually when I hear about issues integrating woofers with
very light tweeters it's a frequency response issue, and integration
with the room issue.
Duke: Note that the “frequency response” we hear is NOT the
one in the published curve – that is only the on-axis response,
which may not even be our first-arrival sound if we're sitting
off-axis. And then the reverberant energy – remember that's
usually most of the sound that reaches our ears - may well (and
usually does) have a significantly different spectral balance. At
the risk of over-simplifying, the “frequency response” that we
perceive is a weighted average of the two. So what comes across as a
room integration issue may well have its roots in a radiation pattern
discontinuity in the crossover region. Thus the room gets blamed for
colorations that can be traced back to problems in the radiation
pattern, which in turn are (arguably) loudspeaker design
deficiencies.
A few additional thoughts:
Imo one incorrect approach to speaker design would be this: Take
“the best woofer”and “the best midrange” and “the best
tweeter” and combine them using “the best crossover” and put
them into “the best enclosure”. This can easily result in an
overly expensive speaker whose different parts do not play well
together, resulting in a lack of coherence that becomes distracting
over time. This would be an example of putting the design specifics
first.
Imo one correct approach to speaker design would be this: Choose
all of the components based on how well they will work together with
each other, with the room, and even with the amplifier towards
achieving an intelligently-selected perceptual goal. This would be
an example of putting the system concept first.
So my opinion on tweeters is, they are just one part of a system,
and imo it's not cost-effective to trade off good system synergy for
the sake of using “the best tweeter”. To give an example, I
don't think anyone has accused Andrew Jones of using the best
tweeters, but those of us who compete with him must admit that he is
a master of system synergy.
Given my particular, perhaps somewhat unorthodox set of
priorities, tweeters whose radiation patterns change significantly
with frequency are not the ideal tools for what I'm trying to do,
though they can be made to work reasonably well with careful juggling
of tradeoffs. My preference is generally for tweeters that use a
particular type of waveguide or horn: Constant-directivity with low
diffraction, with the intention of crossing over where the woofer's
radiation pattern approximately matches the horn's. System concept
first, design specifics second. |
...arriving late, as usual...
Hey, bgpowell...I've heard of and been to the Newform site. Been curious about their drivers, how do they sound to you vs. any other line source ribbon/planar of that design that you may have run into? Most of that type (
Bohlender-Graebner
's, and the like) tend to be dipoles instead of monopoles. Being a dipole/omni fan in general, I'm curious and would like to hear a critique'...*S* |
Thanks Tim!! I'm done with speaker building for a while. I made the speakers they'll bury me with, though I still keep tweaking the crossovers. :)
Best,
E
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sorry I didn't say... to your question, yes, it is because their inherent capacitance, without a crossover, they come in on their own at 1800 hz.
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Hi @erik_squires over the years, at Marcof we heavily modified the old Motorola Piezo's... In the end, a tweeter with the reputation of being harsh and brittle ended up being pretty good. They are amazingly fast, they remind me of a dryer version of a ribbon after mods... The best current single current model available now is the CTS KSN-1141.....If you ever end up wanting to try them, private message me and I'll send you mods for them. Tim
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Hey Wolf,
A tweet that did not require a crossover would be quite an unusual find for me. Point me at a spec sheet?
Is this because of their inherent capacitance?
E
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I have to mention the extremely inexpensive piezo tweeters that don't require a crossover. HERESY! Although an audio snob myself (a fan of aluminum, magnesium, titanium, ribbons, all that), I've experienced these things over the years in cheap "pro" gear and actually stuck one to a little "Hot Spot" monitor I used mounted to my mic stand when gigging…a little vocal monitor a foot or so from my face that worked really well. Go figure. I have a pair of rarely used little Peavey speakers with 10s and a piezo that sound amazing and cost bupkis. This note should serve as a thank you to piezos everywhere. |
Hey Doug!
I think it depends on the ring radiator, but also the designer.
A lot of DIY designers cut their teeth on soft dome’s which naturally have a roll-off in the last octave. Switching to a ring with perfect extension past 20 kHz really can bite them in the butt, or the ear canal. :)
I’m using the Vifa/Peerless XT25BG (the dual magnet versions) and I have nothing but good things to say about their sound and measurement. However I have read some complain about it’s harshness, something I absolutely cannot find in the 3 I use.
Of course, like everything, Ring Radiators vary a lot! :) The XT25 comes in at least 3 different off-the-shelf versions (who knows about custom?) and I have not heard them all. Versions been used in designs from Magico, Sonus Faber, YG, Krell, Polk. Harshness was not attributed to them.
I have listened to speakers with the top line ScanSpeak's with the needle-like phase plugs and never been overwhelmed.
Best,
E
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"please keep ads for your 4th dimensional sound or whatever off this thread. Thanks. " Ha, love it! :)
Boy, I love 'em all! I recall Giani Borinato (apologies if misspelled) of Pathos used to say of tubes, "They're like women, they're all beautiful!" What a nice man, a pleasure to chat with when I reviewed the Pathos Classic One (three different versions I wrote up for Dagogo.com). Man, Pathos gear is gorgeous, and so smooth, utterly unfatiguing sounding.
I feel the same about drivers of various sorts, including tweeters. They all are lovely when set up well. The only one to date which was a bit too strident to my ears was the ring radiator. Laser-like precision but tough to calm. However, that was a while back since I used it.
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Alkaloid,
Nothing wrong with that! I’ll take a silk-dome with a strong, modern motor over a lot of poorly implemented Be or AMT’s any day. :)
Their natural rolloff also helps with crossover design and prevents harshness.
Best,
E
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I still like the old silk domes. The lighter the better, and good mathematics to match the power of the magnet to the moving mass. I often read Science Daily and one topic area is new materials. They are continuously coming up with thinner and lighter and stiffer materials, so I hope the speaker manufacturers are paying attention and ready to take advantage of the latest and the greatest. Don't forget laser vibrometers. Accuton has a driver that has no breakup at 5oooo hz. The biggest problem I get frustrated with is the lack of standards with recording. Signal quality all over the place. |
Hi Sean!
For those who don’t know, the P7 preamp is unusual in an audiophile preamp for both having a pair of 5.1 channel inputs as well as pretty versatile bass management.
I think it’s a matter of the particular circuit choices in the P7, and not an issue of crossovers in general. It sounds dynamically compressed. To my ears, I don’t think Parasound took the same care in the bass management circuit as they did the rest of the pre. I felt that the sound coming out of my main speakers was just not nearly as transparent whenever the high pass filter was engaged.
This is NOT an issue i have with movies, but then all the bass management is being done digitally in the Oppo 103.
I probably could have tried running L and R full range, with the sub but meh... Instead I decided to optimize the Subwoofer, especially the EQ section, for movies, and it's fab.
Best,
E
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I would use it all the time but engaging the crossover in the preamp I use (Parasound P7) really diminishes the sound. Sorry for being random Erik, but why does engaging the crossover in the preamp diminish the sound? |
bgpowell,
Cool, what do you think? :)
E
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Let me throw in an unmentioned ribbon tweeter. Newform Research produces a 30 in and 45 in ribbon tweeter. This is a true monopole line source. I have owned a couple of module 30's including an no holds barred model. Different radiation pattern altogether. |
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I was thinking of something, for those who think I’m a super AMT fan, I’m not, but I have the most experience using them in designs. :)
The following is true for me:
Some of the worst sounding, and best sounding speakers I’ve ever heard used AMT tweeters. I ascribe this to the vastly different quality of the tweeters, and the effort needed in the crossover by the inferior tweeter to get it to integrate with the rest of the design.
So to me having an AMT tweeter is no mark of quality, and I think the same for other types of drivers. It's the final execution of the driver itself, and then the speaker and it's environment.
Best,
E
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I don't mind talking driver brands... we're unlikely to get a ScanSpeak or Faital troll to show up and start harping on the quantum effects of their drivers. :) Plus it helps to talk about specifics in case we want to point to specifications. :)
So maybe we should say "No proprietary drivers" discussed? :) Then we can talk about a specific midrange, and talk about who might be using it. But yeah, really don't want a paragraph or 20 talking about how speaker brand X is so amazing it isn't even a speaker anymore.
Best,
E
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Agreed...although I've got my preferences and invoked the name of a specific driver to clarify that, I don't want us to drift into a 'cable/interconnect' style pull-pull this vs. that arm wrestling match. And I'm infamous for off-topic drift....
There's stellar examples of all types of tweet designs, granted. And the design and engineering of all and the compromises that come with the pursuit of excellence of any driver at this point are, as timlub points out, pretty well canon. And the matching of tweeter A to woofer Z reminds me of human marriages; some you understand, others...*shrug*....you shake your head and walk away....*G*
Eric invokes design principles, which is what I interpreted Eric had opened this forum over and about. Like most things, it's difficult to stay on 'theory' without the mention of particular manufacturers' offerings as an example, because that's what we know in the specific...and cite...
IMHO...it's become hard to stay on topic within any discussion about Anything of late, whether it's tweeter design, cars, underwear, or *deep breath & 10' pole* politics...;)
If I wanted to throw gasoline onto 'this fire', I Could point out my personal pursuits of DIY Walsh speakers. I would hope that might take us into a discussion of Real Esoteria, say plasma or even dustier corners of the audio reproduction realm. But would that take us off topic even further?
Perhaps.....
But, in review of the original query by Eric, our OP, I interpret it to mean 'what do you like and why?' without descent into a 'turf war' over it.
OK...I like my ribbons. I like my Walsh's better, even with their 'warts' as DIY stuff tends to have (I'm working on that...). *G*
Next.
Lets' have fun, and keep it light 'n sociable. ;) |
Hey SoundsrealAudio, can we stay off ads for specific speaker brands in this thread please?
I really would like to focus on general design theory. As soon as brands get thrown in threads get really dirty.
Thanks,
E
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I agree @timlub
I also only meant to criticize myself for going off topic, since I had originally only meant to talk about tweeters, but so long as we stay away from bashing specific manufacturers and stick to design principles I guess it's all good.
Sorry if that sounded like I was criticizing you at all.
Best,
E
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@erik_squires
"Well, We're far off topic now"
I was hearing a discussion of trying to blend ribbons with heavier mass drivers and how speed affected the blend with @asvjerry. You said that you could blend 15 inch woofers. I was giving a basic explanation of mass vs motor and driver speed isn't necessarily based on the size of a driver, but the balance of the total design. That theory hold true on all traditional drivers tweeters to subwoofers.
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Well I am not a fan of any of the afore mentioned tweeters. My favorite is Wilson Benesch's tweeter made in house. For years they never varied from there beloved soft dome tweeter. Then they began experimenting by adding a super tweeter to some of there speakers all the while working to improve their own. The result is a soft dome tweeter that has been re-enforced with carbon fiber. The results are stunning, Wilson Benesch ( http://www.wilson-benesch.com) today announces that it has been named a CES 2017 Innovation Awards Honoree in the High Performance Home Audio / Video category for its newly launched A.C.T. One Evolution P1 floorstanding loudspeaker. "just a small ad" |
My current "ideal" system is a 6.5" mid-woofer with subwoofer. This let’s me use significant DSP on the lower 2-3 octaves, but I truly only use it for movies. I would use it all the time but engaging the crossover in the preamp I use (Parasound P7) really diminishes the sound. Not a problem during movies though.
I can’t imagine trying to get those lower octaves in an apartment without a sub and that EQ feature set.
Of course, I also use bass traps and panels from GIK Acoustics.
Best,
E
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Well, we're far off topic now, but I believe the Snell A models used woofers with added mass to lower the resonant f and gain bass extension. A poured potting compound or something like that.
Also shortened the lifespan of the driver since the suspension wasn't built for it... but hey! That's what upgrades are for.
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Hi Guys, Looking at the last few comments about mixing light mass drivers with heavy mass drivers, speed and matching. I recently was on another thread where there was an argument going on about mass and speed. A lot of folks out there just don't understand what it takes in drivers.... I guess I'm going to tackle it by comparing it to 2 cars...Lets take a 1970 Cadillac Deville with a 472 cubic inch engine and a 1970 Volkswagen bug with a 97 cubic inch engine... Put the Volkswagen engine in caddy, will it move? it sure wouldn't move well, how would it accelerate? what about if you down shifted and had to slow down? The engine could not properly power this automobile without some serious souping up. Lets put the Cadillac engine in the bug.... Well, It'll be fast for sure, but the bugs suspension would not handle the big engine, if you stomped on the accelerator the car would be all over the road. You would have to seriously beef this automobiles suspension to have any chance of handling this engine.... Speaker Drivers aren't a whole lot different. A certain amount of mass requires enough motor to move it. We can tune the suspension to help, or turbo charge the engine (maybe neodymium) to improve performance but in every case matching mass & motor is what its all about.... On any driver, add mass and sensitivity will drop, MMS/QMS/QTS will rise, as you add motor the driver moves easier, get too much motor and the QMS/QTS get so low that the driver will no longer go down to its lower frequencies, a real problem on a woofer, but accurate for all traditional drivers.
Ribbons are a different beast, very light I have a pair of Founteks here at my house now as well as a pair of the old ESS Folded horns that were mentioned above... They are fast, but with careful selection they can be matched....I also love how wonderful impedance and phase are on ribbons. I'd love the Ess with a well matched 15. I really like ribbons, but you know, I still love a good dome too.
Tim
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I'm with Jerry on this one.
I can still remember the sound of my Heil ESS AMT "rock monitors".
Cleanest, sharpest & fastest highs I've ever heard.
I bought them over 40 years ago & I kept them until the late '90's.
Nothing I've had since can ever make me forget them.
Only wish I knew now what I knew then!
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Hi, Eric, and back atcha'...*S*
No real argument from this mortal about that....room integration is everyone's devil, and freq. response I beat over the head with active eq. And yes, it's unfair to try to get high mass to respond as quickly. So I'll just be unfair about it and be the devil's advocate. *L* Not likely to be my first foray into That territory. ;)
Smaller woofers with less mass seem to do better in that regard, 8" being the 'break point' to my ears. I deal with the issue by 'high bass' going to a 6" with a passive, then to 12" for the lower end. For the deep stuff, a small ported sub...
I'll bet getting a 15" to behave is a major pain. Kudos for the ability to attain that niche. I've got an old 18" driver in great shape that I'm looking to torture into being a sub, but I'll match it with things of it's era just in an attempt to 'be fair about it'. Damn things' nearly as old as I am, and I wouldn't ask self to try to move quickly, either. *L*
I'm a sucker for 'antique audio'....maybe due for therapy over that...;) |
Hey @asvjerry
Usually when I hear about issues integrating woofers with very light tweeters it's a frequency response issue, and integration with the room issue.
Below 400 Hz especially, woofers are going to have issues the tweets will never have, so it's kind of an unfair comparison in my mind.
I can make a lot of reasonably good 15" sub's sound as "fast" as any ESL/planar/magnetic. But it's a giant PITA. :)
Best,
E
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I use and enjoy a pair of ESS AMT's (the 'big black blocks) as a reference for high end hilarity. Fast and clean, and hard to find woofers to keep up with them. Other ribbons can be in that range but the only way to improve is to 'line source' them, which can pretty pricey pretty quickly...
All of that, of course, IMHO....
I use them as a benchmark for the Walsh tweeters I'm fabricating. Dipoles are nice, but if I can make an omni that follows That act...sweet. *S*
If I 'get there', y'all will hear of it second. I'll obviously be the first. *L* |
Pistonic motion critical
starts and stops both measured
impulse prrformance
breakup where does it occur and relative to crossover or in case of tweeters... how far above 20 k
i own and listen to two legendary tweeters every day - carbon fiber dome and a 24" true ribbon.....
ah....
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Driver Quality Lots of high tech labels may be ascribed to drivers. Such as: - Beryllium
- Diamond
- Ceramic
- AMT
- Ribbon
- Ring Radiator
And that’s fine, but truth is that in all of these types of tweeters manufacturing quality varies a great deal. For instance, Accuton makes at least two different ceramic cone 6.5" midwoofers, with vastly different price points, both have a ceramic diaphragm. The prices for the same size AMT may be between $30 and $500 (from very diff. manufacturers), and yes, they are completely different. About the only thing they may share is dispersion, but frequency response, distortion and dynamic range are simply not the same. One of my pet peeves is diamond or Be tweeters with micro drivers. Tiny motors barely larger than the diaphragm. They are never that smooth or have that much dynamic range. Two of the most important measurements for me are Comulative Spectral Decay and compression. The first measures energy storage, or "blur" that a tweeter adds to the sound because it won’t stop fast enough. The second measures how a tweeter’s response changes at different volumes. Really outstanding drivers have very fast decay, and very little compression. Among the top-class Be/Ceramic/AMT/Ribbont tweets they all achieve this. Then there is everybody else! :) |
Dispersion -
This measures how wide or how tall a driver’s output is vs. frequency response. Like many other factors, there is no 1 best type of dispersion.
The wider a driver’s output, the wider the "sweet spot" or where a listener may be and still hear a credible stereo image. However!
First, for any given type of dispersion, speakers need to roll off more or less evenly. You don’t want to be 15 degrees off axis and only hear the mid-range. Ideally the speaker’s dispersion is even across as much of the response as possible, but usually this can only be done starting in the upper bass.
Next, the wider the dispersion, the more early reflections you may encounter, which can severely affect the frequency response and imaging. Acousticians designing a theater or monitoring room trade off dispersion vs. room treatment. A very tightly controlled speaker needs less room treatment and care.
A number of things affect dispersion, including the obvious things like wave guides (YG Acoustics, Revel’s F series, Krell, first gen. Magico) or horns, diaphragm size (larger = narrow) and crossover points.
The very large diaphragms of ESL speakers (Martin Logan/InnerSound, etc.) have fabulous clarity thanks to this effect. They can sound like you have headphones on even with very little room treatment.
Drivers with different dispersion patterns _may_ also have different rate of decay. Consider a hybrid ESL + cone woofer. The woofer radiates omni-directionally and the wavefront looses energy the fastest, while the ESL panel is a plane wave, with narrow dispersion and looses energy more slowly.
This means that changes in distance from the speaker causes the woofer to loose dB faster than the ESL panel. This has a very simple solution however: Put a volume control on the woofer.
With smaller drivers, like say 5" tall ribbons or AMT’s this difference may be too small to worry about and can be handled strictly in the crossover, though a volume control switch may also be used if absolutely required.
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