Something stirs in the Undergrowth

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Scottmoose
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#2776 Re: Something stirs in the Undergrowth

Post by Scottmoose »

IslandPink wrote: Sun Mar 07, 2021 6:54 pm Funny, I was talking to Colin about the same subject recently, Scott. I said I have never really liked standard dome tweeters since I heard a good ribbon ; however the beryllium ones he's used recently are a different matter - the first time he demoed them at Owston I knew they were a significant improvement. I suspect they are pistonic up to past 10Hz ?
Yes indeed, the main advantage of beryllium, diamond etc. is that you can push the bell resonance way up. The 1in Satori unit Colin and I used for the Edingdale GT is up about 40KHz as are Scan's two equivalent size beryllium dome models. By contrast, most 1in aluminium, magnesium, titanium domes tend to have a let-go point in roughly the 24KHz - 27KHz region. The reduced mass of a beryllium or diamond dome for a given size / thickness relative to the others also mean they have the potential for staying flat out past 20KHz. Most 1in aluminium domes for e.g. start to have an SPL drop-off above ~15KHz due to the mass. Neither are necessarily problems in themselves -in the former case the audibility of distortion amplification lower down will depend on how good the motor design is & the baseline HD levels. In the latter, it comes down to how much 'air' you need on the top end & what the off-axis response looks like (if it holds up well / is consistent it's unlikely to sound lacking). Beryllium domes can significantly reduce issues in both these regards, or at least make life easier for the driver designers, so I'm a fan of good ones.
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#2777 Re: Something stirs in the Undergrowth

Post by simon »

Would it be fair to say then, in very broad terms, that beryllium, ribbon and AMT-type tweeters are technically the best? Are there others? Or is it horses for courses?
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#2778 Re: Something stirs in the Undergrowth

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From my own experience (FWIW) both the AMT and ribbon type tweeters require steeper crossover slopes and are not really happy being crossed over below 3KHZ, some recommended XO higher than that. The Beryllium tweeters I am using in the Edingdale GT speakers are crossed over at just above 1kHz and require a lower order filter. So you are using the most of the clean pistonic sound of the tweeter to it's best and not relying on a mid-woofer to reproduce HF where it is not most happy. Most the mid-woofers and some the fullrangers start to have breakup modes in their frequency plots above 3k and so making the transition XO to say a ribbon or AMT type at these frequencies problematic. Not true with all drivers but certainly the case with the mid-woofers I have used in the past. I'm sure Scott will put me right if I am mistaken in any way and may have his own take on preference of tweeter type?

So my vote would go with the Beryllium dome type tweeter.
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#2779 Re: Something stirs in the Undergrowth

Post by andrew Ivimey »

I got my AMTs (HEIL) down to a bass mid unit which began to roll off 6dB slope at about 800hz. A chum down on the south coast still loves this combination. There is still great enthusiasm for real AMTs in Germany, I am told.

These new AMTs from China, I believe, are not bi-directional even if they have bought into or ignore western patents. I don't think they are the same as Oscar Heil's tweeters at all.
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#2780 Re: Something stirs in the Undergrowth

Post by chris661 »

simon wrote: Mon Mar 08, 2021 1:43 pm Would it be fair to say then, in very broad terms, that beryllium, ribbon and AMT-type tweeters are technically the best? Are there others? Or is it horses for courses?
Well, I'm currently in the compression driver camp. More clean output than a dome, especially towards the bottom end, and options to control directivity. In my opinion, those benefits put them at the top of the pile for a lot of applications.

That said, I've also been tinkering with the SB65 wide-range unit, and that thing does treble rather well IMO. Well worth the (rather cheap) asking price.

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#2781 Re: Something stirs in the Undergrowth

Post by simon »

Right, so no simple answer then :lol:

The beryllium tweeter going a fair bit lower could be quite handy.
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#2782 Re: Something stirs in the Undergrowth

Post by IslandPink »

I still think a ribbon tweeter is the best of all if you can use it only above 3kHz. There's no mechanical damping and the moving element is less than 0.05g, which I hear as more delicacy and micro-dynamics in the upper frequencies. The beryllium domes are are certainly interesting, and more versatile, though.
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#2783 Re: Something stirs in the Undergrowth

Post by jack »

Are these pure beryllium or alloyed with aluminium?

Very nasty stuff, beryllium. Don't inhale any tweeters...
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#2784 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

IslandPink wrote: Mon Mar 08, 2021 10:32 pm I still think a ribbon tweeter is the best of all if you can use it only above 3kHz. There's no mechanical damping and the moving element is less than 0.05g, which I hear as more delicacy and micro-dynamics in the upper frequencies. The beryllium domes are are certainly interesting, and more versatile, though.
Having tried ribbons and AMT’s -I preferred the presentation of the AMT’s to the Decca Kelly ribbons I had for a while. I have never successfully got a compression driver to work, always to much sibilance for my liking. The closest was ring radiators the JBL 2405’s I ran with the Lowthers were alright at the time although not directly compared them with the AMT’s - the later with its bigger surface area seems to portray more airiness, not just the tizz you get with some HF units.
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#2785 Re: Something stirs in the Undergrowth

Post by Scottmoose »

simon wrote: Mon Mar 08, 2021 1:43 pm Would it be fair to say then, in very broad terms, that beryllium, ribbon and AMT-type tweeters are technically the best? Are there others? Or is it horses for courses?
It's more about what your goals are to be honest. Everything has its swings & roundabouts. Personally I regard beryllium or diamond as the optimal currently available materials for conventional tweeter domes, since in a 1in format they are pure pistons to at least an octave above the audio band, i.e. the domes are non-resonant so have no sound at all of their own. Any audible colouration / character the tweeter has comes from the suspension or motor design. Ceramic, magnesium & some high quality alloys come next. Which isn't to say soft domes are bad -some are storming. To give one example, the evergreen Scan 9900 (the original Revelator) is almost 30 years old now & is still probably the best performing soft dome on the market; I'd take it over a poor metal dome without even thinking about it.

AMTs and ribbons I tend to be a bit wary about. I like good ones, but with a handful of exceptions smaller examples tend to have poor distortion performance at the bottom end, requiring a highish XO frequency and higher order slopes. Coupled with the limited vertical dispersion ribbon types tend to have, that can sometimes make for questionable system polars, which in turn can affect tonal presentation. Good ones though as noted -great. I do rate the big Beymas for instance.

Compression units are my personal favourite alternative to domes; as-is they usually don't get too low but they're fairly flexible, have high sensitivity & good ones usually have very low distortion.
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#2786 Re: Something stirs in the Undergrowth

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jack wrote: Mon Mar 08, 2021 11:50 pm Are these pure beryllium or alloyed with aluminium?

Very nasty stuff, beryllium. Don't inhale any tweeters...
Pure beryllium foil. No health issues in solid form -just don't make a practice of licking it, chuck it down the hatch, or plonk onto the fire while breathing deeply. ;)

A few years back there was some controversy about 'beryllium' tweeters that were actually a beryllium-copper alloy. Usher had one of those (it was otherwise identical to the RS28a-4 they made for Dayton at the time -the current RSt28a-4 is unrelated). As I recall, Tang Band and a few more obscure brands in the China / SEA region had a few Be-copper domes too. Zero advantage to them over aluminium, it was just a marketing stunt, a bit like titanium is -again, little or no benefit over aluminium or an aluminium-magnesium alloy (which is what Seas often use, not for marketing purposes, as they're often just described as aluminium).
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#2787 Re: Something stirs in the Undergrowth

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Scottmoose wrote: Tue Mar 09, 2021 12:26 pm
simon wrote: Mon Mar 08, 2021 1:43 pm Would it be fair to say then, in very broad terms, that beryllium, ribbon and AMT-type tweeters are technically the best? Are there others? Or is it horses for courses?
Coupled with the limited vertical dispersion ribbon types tend to have, that can sometimes make for questionable system polars, which in turn can affect tonal presentation.
and some have none whatsoever...hateful things!

re soft domes, the scan 9500s have a good press as well. Check out Lynn's original discourse on them. Notwithstanding my limited experience, they're the best I've ever heard.
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#2788 Re: Something stirs in the Undergrowth

Post by simon »

A fascination discussion chaps, thanks. Lots of food for thought, though it seems, perhaps unsurprisingly, that there's no substitute for hearing all the alternatives for one's self. Which is a rather expensive mission.
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#2789 Re: Something stirs in the Undergrowth

Post by vinylnvalves »

I way of getting around the weaknesses of the AMT...https://audioxpress.com/news/the-airblade-transducer. It’s a shame this new driver is too expensive to just try on a whim..
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#2790 Re: Something stirs in the Undergrowth

Post by shane »

Interesting to see that PJC is now putting AMTs into his designs for Wharfedale:

https://www.wharfedale.co.uk/evo4-4/
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