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Multi-Way Conventional loudspeakers with crossovers

Treble, how to be good?
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Old 14th January 2020, 06:18 PM   #11
tmuikku is offline tmuikku  Finland
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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.
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Old 14th January 2020, 06:32 PM   #12
YSDR is offline YSDR  Hungary
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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?

Last edited by YSDR; 14th January 2020 at 06:38 PM.
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Old 14th January 2020, 07:34 PM   #13
system7 is online now system7  United Kingdom
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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:
https://www.scan-speak.dk/datasheet/...004-660000.pdf

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

Click the image to open in full size.

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

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

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:

Quote:
Originally Posted by Lynn Olson View Post
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.
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Old 14th January 2020, 07:37 PM   #14
tmuikku is offline tmuikku  Finland
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Quote:
Originally Posted by YSDR View Post
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.
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Old 14th January 2020, 08:03 PM   #15
YSDR is offline YSDR  Hungary
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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?
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Old 14th January 2020, 09:36 PM   #16
system7 is online now system7  United Kingdom
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The advantage of narrow directivity in a speaker is you hear more of the speaker and less of the room:

Click the image to open in full size.

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

Click the image to open in full size.

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

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

ACOUSTIC SPECIAL SOLUTIONS

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.

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?
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Old 15th January 2020, 04:44 AM   #17
ScottG is offline ScottG  United States
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Quote:
Originally Posted by YSDR View Post

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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Old 15th January 2020, 05:00 AM   #18
Sangram is online now Sangram  India
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Treble, how to be good?
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?
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Old 15th January 2020, 05:52 AM   #19
YSDR is offline YSDR  Hungary
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I will post some measurements.
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Old 15th January 2020, 07:05 AM   #20
tmuikku is offline tmuikku  Finland
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Quote:
Originally Posted by YSDR View Post
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.
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