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Old 13th June 2011, 12:15 AM   #11
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Interesting debate with a lot of good points.

My tactic is to use the HF drivers perpendicular to the listening axis. EQuing them is a compromise between direct axis measure and 30°, but with the stuff I have, it's the best way of managing some spaciousness without the "shhh" and without falling on the dull side.

I use bipolar drivers, open back 1" CD with small horns
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Old 13th June 2011, 03:00 AM   #12
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I said "you can" - not that most are.

There are numerous examples of tweeters today that are much lower in distortion than in years past, and many that extend past 20kHz very nicely.

There are woofers that are quite superior to the AR woofer today. Many.
And, at what level was that "5%"??
Besides the AR woofer didn't produce any sibilance, did it?

I am not in agreement as to the "cause" of sibilance being the one you're suggesting.

Imo, sibilance is a type of distortion, plain and simple.
The question is what is the cause.
Imo it seems like it is not due to a single cause, and does not occur in a single component. My experience with it seems to indicate that it can be generated anywhere and everywhere in a given system, not just in the tweeter. Perhaps it is a summation of harmonics due to non-linearities. I don't see it being the result of the polar response of a given driver, per se. That's not to say that a given driver might not be able to generate sibilance because of the way it is designed - be it due to the way it was designed for narrow dispersion or not.

It is important to differentiate in the discussion between the "best" available and the "norm" (be that of yesteryear or today). Also to differentiate between outcomes and causality.

As far as there being drivers today - especially HF drivers that are an order of magnitude lower in distortion than decades past, I am quite sure this is true, although there were still exceptional HF drivers of note from decades past, some of which are still worthy of use and consideration...

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Old 13th June 2011, 03:20 AM   #13
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Quote:
Originally Posted by poldus View Post
I bring mid-highs down quite a bit and use a ribbon tweeter coming in quite a bit louder (itīs an active system) at 9khz. I need to hear that sparkle or it will sound dull and unexciting to my ears. I also find a subwoofer necessary to make it fall into balance or it will sound plain bright. Itīs amazing how the lower and higher ends of the spectrum need each other to shine.
i agree 100 %
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Old 13th June 2011, 11:10 AM   #14
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Excessive sibilance is caused by excessive high frequency energy reaching the listener's ears from a single direction in phase at the same time. It's the same cause that makes modern speakers sound unbearably shrill and bright although this FR distortion is less easily identified in much music by those who are not familiar with the sound of real acoustic musical instruments. The way in which they propagate sound into space and the way it arrives at the listener whether in a small room or a vast auditorium is entirely different from the way loudspeakers work. Walk around a street busker or a piano at a piano bar and the timbre (tonal balance) of what you hear hardly changes at all. Walk around a speaker placed in the middle of a room or better yet outdoors and it changes drastically. Bose was so annoyed by this shrillness nearly 45 years ago he marketed a speaker that seems to me not to produce any high frequences in the top ocatave at all.

Efforts to mitigate this effect usually include devices or equipment that reduces system HF output to the speakers. Wires with high shunt capacitance and/or high series inductance, vacuum tube amplifiers with output transformers having high HF losses due to eddy current and hysteresis losses, heavy tracking moving coil phono cartridges which shave the HF components of phonograph records off with excessive pressure are just a few. From the industry's point of view, the more expensive they are the better. That is why bass and treble controls and equalizers which do the same thing are shunned, there's no money in them. Ultimately the listener throws his hands up and buys another speaker which invariably suffers the same defect.
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Old 13th June 2011, 11:56 AM   #15
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Soundminded, please explain where the "excessive HF energy" comes from??

If one has a nominally "flat" FR on axis (for example), or pick any other curve you wish, where is this "excessive HF energy" from??

So, will and Ohm F or MBL speaker produce "sibilance" due to the phenomenon you claim?
How about a Magnat plasma tweeter (the round one)??

How come I can swap out amp A) with amp B) - both of which are "flat" way beyond 20kHz, probably into >200kHz+ - and have the characteristic of said "sibilance" change? By your theory there should be no audible change whatsoever, if the cause is in the design of a HF driver in a speaker. Clearly, if the characteristic of sibilance changes when one changes amps, the issue can not be solely in the driver or the driver's polar response shape.

The example you gave of a live music being played and how you hear it as one moves about does nothing to explain "sibilance" in a reproduced sound. While it is generally true that live sound is propagated differently than sound from most speakers, that has little to do with why there is "sibilance" or what causes it when sound is reproduced by speakers.

What "efforts" are made that may or may not work or may be misguided are not really relevant to understanding what is actually going on.

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Old 13th June 2011, 05:27 PM   #16
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I thought my explanation was plain enough however here's an example of what I mean by the focusing of high frequencies. Have someone whisper in your ear. You will hear considerable sibilance, all of the HF energy from each sylable is focused in one direction and arrives at the same time. Now move the source 15 feet away and make it 40 to 50 db louder. That's the effect you get from modern loudspeakers. If there is a HF peak anywhere along the chain including back to the microphones that recorded it, that only makes it worse.
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Old 13th June 2011, 05:38 PM   #17
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A common but unsuspected cause of sibilance is crossing the tweeter too low, or using a shallow-slope crossover. Many designers - unfortunately, a lot of them in the high-end biz - forget that direct-radiator drivers increase excursion at a rate of 12 dB/octave. Thus, it takes a 12 dB/octave highpass filter to merely keep excursion constant in the frequency range between nominal crossover and the Fs of the tweeter.

For example, if the tweeter has a typical Fs of 700 Hz, and the intended crossover is 2.8 kHz (again, typical), it takes a 12 dB/oct electroacoustical filter to merely keep excursion constant in the very critical 700 Hz ~ 2.8 kHz range. Part of the reason that this range is so critical is that audibility of distortion is at a maximum in the 1~5 kHz region. (Perception of distortion similar to, but not quite the same as, the Fletcher-Munson curve.)

Staying with the same example, if the electroacoustical filter is 1st-order (6 dB/octave), then excursion actually increases from 2.8 kHz on down, until 700 Hz is reached. Below 700 Hz, the excursion finally starts to decrease, but not very fast, only 6 dB/octave. This is troublesome because the maximum spectral energy of many recordings is around 300~500 Hz, so energy from this range can crossmodulate with the tweeter output.

This is why auditioning with little-girl-with-a-guitar program material and a full choral piece sound different. The LGWAG is spectrally sparse, and there isn't as much chance the tweeter will be struggling with IM distortion. Throw a dense, high-powered spectrum at the loudspeaker, though, and the tweeter will start to scream - and it is very audible on massed chorus as complete breakup.

At any rate, regardless of distortion of a particular tweeter (none of them are free of IM distortion), crossovers matter. Many designers want to take the tweeter as low as possible because the polar pattern is prettier and certainly measures nicer, but the inevitable price to be paid is more IM distortion resulting from increased excursion (the linear region is most tweeters is less than 1mm). Choosing a crossover is a difficult tradeoff between narrowing of the vertical polar pattern, IM distortion from out-of-band excursion, and how close the designer wants to approach the region of midbass driver breakup. The tradeoff is made more difficult when a rigid-cone (Kevlar, metal, ceramic, etc.) midbass driver is chosen, because the onset of breakup commonly falls in the 3~5 kHz region, right where the ear is most sensitive to distortion.

As you can see, the worst possible solution is a 1st-order crossover combined with a midbass driver that has a severe breakup region (Kevlar drivers, I'm looking at you). The 1st-order crossover fails to control out-of-band excursion, so program material in the 700 Hz-2.8 kHz region results in IM distortion in the tweeter's working range, while plenty of midbass breakup in the 3~5 kHz range gets through as well. And midbass breakup sounds the same as a bad tweeter, since the distortion and resonances fall in the same frequency range.

As a side note, most transistor amplifiers (including very expensive high-end products) go from Class A operation to Class AB around 1 watt. Feedback helps, but cannot fully overcome the two-to-one shift in transconductace as the AB region is traversed. In addition, thermal tracking is typically several seconds to a minute late (depending on the thermal mass of the heatsink and location of bias sensor), so the correct AB bias point is actually several seconds behind the program material. There are various sliding bias-tricks available (which avoid complete turnoff and associated switching transition), but they are all several seconds late. The more output transistors, the more AB transitions there are, since it is impossible to have transistors exactly match the switching transition - in production, they are matched for beta (current gain), but not usually for other parameters. Change the die temperature a bit, and the careful hand-matching goes away.

To recap, if you want lots of sibilance, use a midbass driver with severe breakup in the 3~5 kHz region (this is usually obvious from unsmoothed FR curves), pick a tweeter with limited excursion capability (not always spec'ed), select a 1st-order crossover at a low crossover frequency, and use an amplifier with a very large heatsink, many transistors, and somewhat unstable Class AB biasing (thermal overshoot). That should do the trick. Plenty of distortion from many different sources, even though the overall FR curves may look harmless.

Last edited by Lynn Olson; 13th June 2011 at 06:05 PM.
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Old 13th June 2011, 05:49 PM   #18
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Two easy ways to get sibilance:

1. Drivers with large upper midrange peaks. I'm thinking of Nelson's fetish objects as an archetype.

2. Large diaphragm condensor mikes.
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Old 13th June 2011, 06:09 PM   #19
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Quote:
Originally Posted by SY View Post
Two easy ways to get sibilance:

1. Drivers with large upper midrange peaks. I'm thinking of Nelson's fetish objects as an archetype.

2. Large diaphragm condensor mikes.
Agree completely. 5~10 dB peaks that fall in the region of maximum audibility are not cool, no matter how famous the designer.

Point 2: The use of "de-essers" for vocalists in recording studios speaks volumes about the microphones being used.
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Old 13th June 2011, 06:22 PM   #20
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As well as the miking technique. The main issue I have with the musicians I record is getting them to back away from the damn mike.
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