Treble, how to be good?


I think I need some help, because I feel frustrated. Where to begin? As the title says, I am not satisfied with my system's high frequency reproduction. When listening, the high frequencies always calls attention to itself over the rest of the range. I can attenuate any part of the high frequencies of the speakers (thanks to the DSP) but then the sound becomes dull, airless etc and still hearing "anomalies" that is not natural to my ears. Like ssss, ccc maybe a little lower frequency thsss. So overall, like a high pitched sibilance

The problem appears in the higher range, clearly not in the crossover region which is acoustical LR4 at 2100Hz now. The worst range is maybe 6-7 kHz and up.

The midrange driver cone-break-up around 4-5 kHz is well attenuated and EQ-ed out (ok, I know the time domain problems of the break-up either), so I don't think that is a problem.

As I sit closer to the speakers for less room effect, the main signature remains unchanged.

The system is a Hypex Fusionamp based 3-way (analogue or digital input, it doesn't matter). The problematic range comes from a pair of Scan-Speak D3004/6600. Previously a SEAS 27TFFC was used which was (audibly) clearly worse than the SS Illuminator but the problematic range was lower in frequency if I remember correctly.

In other (commercial) designs I heard the 6620 version of the Illuminator dome and the sound signature was similar. Even the Classic D2905/9700 was very similar with the overly shiny, fake, piercing top-end (as I heard).

A very good tweeter sound I heard was some B&W metal dome, but the influence of the metal membrane resonance was audible with certain sounds.

Maybe it's possible that I'm overreacting or draw false conclusions but for example the usual Multiplex cinema I go to, I really like the overall sound where nothing sticks out of the soundtrack.

So what can I do to get better treble? Do you think the SS tweeter simply is not for me? I can not think of anything else. But if anyone has any other idea, I'd be happy to.

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First reflection points on the sidewalls is around 1.5 m, but maybe the front and back wall are the problematic because it's closer (the back) to the listening position and the front (to the speakers) than the side walls. Yeah, I sit next to a longer wall, otherwise it's not possible, even if it's not optimal.

The room RT60 is below 0.4 s at the low frequencies and below 0.3 s at 400 Hz and above.

The first reflection points are treated with diffusers but the treating doesn't did much to the treble especially to the higher range.
I think a lot of us have had a hard time with soft dome tweeters.

To the extent of trying cone tweeters like the Monacor HT22:


Ring radiators have theoretical advantages too:


The waveguide metal SEAS DXT is one I'd like to try too:


IMO, any tweeter sounds best 4th order filter above 3kHz. Low order and low crossover point seems to make things worse.
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With DSP you should be able to get some very high order filters, so try at least fourth, and raise your crossover another third octave for comparison(try both points).

Also try isolating problem notes using the DSP equalisation, just keep narrowing the band.

If you still have a problem with all of these very capable tweeters, you should check your hearing for points of high sensitivity.

I myself have two, different notes in each ear, and a loss in one.
It is terribly difficult to test, some online tests can be done at different levels, the doctors are concerned mostly with the lowest levels at which we can hear a note(and voice intelligibility), not what music feels like at normal levels.
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As I said, the problem is not around the crossover region. I started from 2.8 kHz and decided to go lower in 100 Hz steps and ended at 2.1 kHz which sounded the best to me.
Even at far horizontal off-axis I get a good reverse null and not so bad frequency response.

The D3004/6600 produces a significant 2nd harmonic distortion peak around 7 kHz, maybe that is the point where the dome begins to sound not so good, just guessing.
A soft dome tweeter goes into breakup at around 6kHz. That's it really. You can see it in the phase response:




Atkinson: But can't you add damping to control the dome breakup, or use a material which has high intrinsic damping?

Marshall: Yes, but the damping makes things worse. You look at a soft-dome's frequency response—and that's how most people judge a tweeter—and if it's nice and flat, it's wonderful, isn't it? What it's not telling you is that the first worrying resonance, the second resonance, may be at 6kHz. It's heavily damped, it's very low-Q, but that means it's actually worse than if it's an aluminum dome. If you looked at it in the old-fashioned way of judging hi-fi in the 1970s and early 1980s, a low-Q resonance is great because you can't see it. But a low-Q resonance is far more worrying than a high-Q resonance.

Robin Marshall: A Modicum of Genius Page 4 |
To be honest my two D3004/6600 have a not so nice bump around 6-7 khz (like the 2nd harmonic peak) in the frequency response which I lowered with the DSP to get flat response. However a slight ridge remained in the CSD graph at that point.

These drivers clearly not have the same frequency response as in the data sheets, and not because of baffle diffraction, that's sure.
From recording and mixing perspective: mics and instruments can have resonances, and they can be tamed with very narrow notch EQ. I find them narrow resonances very bad to brain and it is a must to try to tame them. Ear gets used to the resonances somewhat but brain gives listening fatigue. Narrow resonances aren't obvious untill you put a notch filter and then AB it. It could take 2db, or even 10db cut. But, it is pretty hard to narrow down the resonance exaclty by ear, unless you do it often and train the ear. I don't know if it is the ear or brain that makes narrow peaks and dips kind of hide and disappear but still make very annoying feeling for long listening sessions.

So, eyes to rescue: use a measurement mic and try to find if there is resonance in the 7kHz region as you suspect. If you find one use very narrow parametric filter and cut it as much as needed and see if it helped any.

Curious how loud you listen? If you have a DIY speaker you could try to add a waveguide to get some more SPL out before distortion, but it affects the directivity as well. At cinema they have compression drivers in waveguides for high frequencies, to have the required headroom and coverage. Could be constant directivity, frequency response drooping after 10kHz and listening distance that they sound more calm up top :) Certainly not as bright systems as dome tweeter on baffle and close range listening spot.
Of course DIY speakers. Yes, there are visible resonances around 6-7 kHz which I tried to tame with narrow band filtering, but maybe that was not enough in quantity.

And what about CD + constant coverage waveguide at short distances?
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YSDR, as often happens, you are not forthcoming with woofer details. What is it? It matters. For time alignment and frequency response.

The Scan D3004/66000 tweeter is easy enough to find:

This is the phase response of one of my 8" plus 3/4" soft dome experiments:


You can see the 8" woofer's problems at 3 and 6kHz. Also the tweeters issues at 6kHz.




Not a bad sounding speaker. Sony retro 8" bass, and Morel CAT 298 aka MDT29. I still listen to it, albeit I have got cleverer with crossovers.

I think it's called the Hilbert Transform that relates FR slopes to phase and group delay. Whatever, Michael Chua at Ampslab use CSD waterfall plots to see stored energy in a 4" 830870 plus 1" MDT29 speaker:

Solitaire – Peerless 830870 with Morel MDT29 – AmpsLab

But higher crossover and steeper crossover also helps ALL tweeters:

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.

Mr. Lynn Olson knows what he is talking about.
Of course DIY speakers. Yes, there are visible resonances around 6-7 kHz which I tried to tame with narrow band filtering, but maybe that was not enough in quantity.

And what about CD + constant coverage waveguide at short distances?

Tried to note the fact that a cinema sound system and environment is very different.

A CD would be overkill for close distance listening :) Constant coverage at close listening, why not, a bit bigger sweet spot so maybe easier to adjust the EQ.

I don't know your background if you've had CD speakers at home? so they might be one thing to try if all dome tweeters seem to sound bad. I haven't had any ribbons or other types of tweeters, but there seem to be plenty others too than the dome. If you liked the cinema sound you could try to hunt some standards they use to align speakers / room response? I don't know much about cinema sound, but there must be some standards how the systems are aligned to sound the best for such a large amount of seats, both front to back and side to side.
I don't used CD + waveguide yet, but some says it's good for small places because of less environment interaction than a bare dome on a baffle.
What you mean about overkill? Of course in a normal living room (usually) there is no need that sound pressure level which can achievable with a CD. So less power needed to the driver = less stress to that driver. Or not?
The advantage of narrow directivity in a speaker is you hear more of the speaker and less of the room:


There is another way to do this. It's called MTTM:


Thanks to Craig at Selah Audio for this great ribbon design.

In fact SEAS suggest this sort of approach in lousy, overly lively rooms:


Where you have a symmetry, you get a conservation law: Noether's theorem - Wikipedia

My whole approach to loudspeakers is mathematical. In our own 3 dimensions plus time, we get 5 platonic solid symmetries: Platonic solid - Wikipedia

I am as happily comfortable in 4 dimensions, where we gain a 6th. symmetry known as the 120-Cell. After that it's 3 symmetries all the way down. :cool:

At the very bleeding edge of mathematics, we have String Theory in multi dimensions. We also have the Standard Model which needs less dimensions.

Who knows what works? :D
These drivers clearly not have the same frequency response as in the data sheets, and not because of baffle diffraction, that's sure.

Are you sure?

It "sounds" exactly like diffraction, though not the typical cabinet edge diffraction, rather driver "inset" (or "outset") on the baffle.

-try filling-in around the tweeter frame with some putty you can remove, then measure again and listen to the difference.
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My intuition of shrill treble that then becomes unfocused and muddy when lowering the level, is that it's a diffraction/dispersion/reflection issue (i.e not originating in the raw driver response itself). Which is how I tend to treat it.

My understanding is that narrow band notches in the tweeter passband tend to not work very well because it was noted that dome breakup is an issue with all soft domes, and it is. It's better to treat breakup by crossing before/after it is an issue but with tweeters it's not really possible.

Some good domes will push this out to the 10k+ range, where they can then be treated with a notch, or tilting the baffle, or putting woofer on top (which also time aligns the speaker in most cases).

Remember with a 24dB/octave crossover around 2k you still have some output (~1dB) from the woofer, so do make sure it's not actually woofer breakup. When combined with a natural bump in 5-7k range (common with stiff domes to tame breakup), this can sound harsh. It is better to get the woofer out of earshot if this were the case.

Do you have a picture/crossover/measurements to share?
I don't used CD + waveguide yet, but some says it's good for small places because of less environment interaction than a bare dome on a baffle.
What you mean about overkill? Of course in a normal living room (usually) there is no need that sound pressure level which can achievable with a CD. So less power needed to the driver = less stress to that driver. Or not?

Sorry we have slight confusion with what was referred as close listening, which I think as really close like 1 meter. Compression drivers at living room, works fine. By overkill I ment they are capable to very high SPL levels, ~110dB/W/m sensitivies, easy to get hearing damage loud. But it is already much less at the sofa 2 meters away.

Yes, the narrower directivity changes how the speakers sound in a room. Some people like it, some don't. A waveguide could be added to your current dome tweeter as well to increase SPL towards the listening area. Check out some Patrick Bateman threads. In general, less stress to the driver = less distortion as you said. Compression drivers and horns have their own set of compromises so it is matter of application and preference, what the brain likes :) So yeah, worth trying out at some point if you liked the sound in the cinema.