"The Flatback Banned" OmniMet

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Toppsy
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#151 Re: "The Flatback Banned" OmniMet

Post by Toppsy »

Cressy Snr wrote: Thu Oct 26, 2017 3:52 pm
As you say, the other Monacor tweeters are 10W and only 90dB efficient, so might not be loud enough with the bass/mid drivers. However I wouldn't say no to your offer. I'll find something to use with them that's for sure. :D.

Shame about the chrome effect dustcap though; soooooooo late 70s :mrgreen: :mrgreen:
Ah! I had the same thoughts as you so I have stained the chrome dust caps black and this improves the look no end.

Email me your address Steve and I post them on.
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#152 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

Got the tweeters Colin,
Thanks. :)
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#153 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

Inspired by Stu's adventures over on HFS, with his Heath Robinson semi-omnis, I've now set up a paired tweeter array with my own and Colin's cones. All done with blu-tack and clipleads. Pics tomorrow :D
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#154 Re: "The Flatback Banned" OmniMet

Post by karatestu »

Nothing wrong with a bit of blutack :D

Being from a farming family i should have used some baler band in my design :lol: Useful for so many things - boot laces, belts, gate fasteners.............

Whats the verdict then Steve ?
:bigsmurf:
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#155 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

karatestu wrote: Thu Nov 02, 2017 7:18 am Nothing wrong with a bit of blutack :D

Being from a farming family i should have used some baler band in my design :lol: Useful for so many things - boot laces, belts, gate fasteners.............

Whats the verdict then Steve ?
Much the same as you get with your setup.
The image is more widescreen in nature, both in width and height.
Central focus is improved and as far as I can detect, there are no phasey issues when walking around the room when the music is playing and top end level stays even. Also there is a bit of a shelf lift, which is useful with a SET driving the speakers.
All in all a good result.

Just need to devise a way of mounting the tweeters so it doesn't look like a dog's dinner. :D
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#156 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

Right!

I've been doing quite a bit of work on the speakers over the past few days. The tweeter arrangement, has been a constant pain in the arse with this design.
All of the top end problems I have had with this design are a direct result of my own stubborn refusal to implement any form of high order crossover and also of another stubborn refusal to use >100dB horns or ribbon HF units with with the high efficiency bass/mid driver.
Both these attitudes go against every definition of common sense speaker design imaginable and it could be argued that I've suffered needlessly as a result.
Today however, vindication has come in the form of the twin tweeter operation below:
Image
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#157 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

There are two first-order crossovers in the tweeter leg of the internal wiring.
The first is a 3.3uF series cap to the 8 Ohm, 92dB, Monacor cone tweeter, which brings it in above 6Khz, with a shallow overlap from the bass/mid; which is just what you want.
In parallel with this tweeter, the 4 Ohm, 94dB, SB Acoustics ring radiator has a 3.3uF series cap too, which brings it in above 12KHz, again with a shallow overlap from the cone; again, just what you want. The higher by 2dB efficiency of this tweeter compared to the cone helps to maintain the high treble right up to 20KHz.
Knock 3dB off the 96dB bass/mid efficiency due to the up firing and way off axis listening position from it and we have a very nice match between all of the drive units.
The slight sensitivity drop to the cone tweeter is counteracted by the slight rise from the wide open running bass/mid, over the bottom of the cone's operating band. The ring radiator then adds its bit to the top end of the cone, giving a better sense of sparkle.
The cone swivels on a gimbal mounting and can be angled to focus the stereo image.

The thing with the semi-omni principle, is that done right, it can create both space and a good stereo image.
These are sorted.
Last edited by Cressy Snr on Tue Nov 07, 2017 4:03 pm, edited 1 time in total.
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#158 Re: "The Flatback Banned" OmniMet

Post by Nick »

In parallel with this tweeter, the 4 Ohm, 94dB, SB Acoustics ring radiator has a 3.3uF series cap too
Just to be awkward, I would suggest this is a higher order filter, C, L, C, Tweeter,
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#159 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

Aye, if you take into account the little bit of inductance from the other tweeter. But I'm well known for being rather vague and never getting anything quite right. Not a desirable property to exhibit when in the presence of engineers and scientists, but I'm embracing it rather than fighting it, because:

A) It's part of who I am.

B) Makes me a bloody sight happier. :)
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ed
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#160 Re: "The Flatback Banned" OmniMet

Post by ed »

I feel your pain brother...I'm about to invest in a Behringer dcx to try and prevent this tearing out of hair for my next OB venture....this is where I seriously regret selling my winding engine a couple of years back...

onward, ne pedibus carborundum illegitimi
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#161 Re: "The Flatback Banned" OmniMet

Post by Dave the bass »

ed wrote: Tue Nov 07, 2017 4:29 pm ne pedibus carborundum illegitimi
You're not sure if the walking resistive bus has parents?

There's a song title.
"The fat bourgeois and his doppelganger"
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#162 Re: "The Flatback Banned" OmniMet

Post by Cressy Snr »

One thing with that SB Acoustics ring radiator is that maybe it does have a remarkable Fs of 680Hz and is capable of going quite low, but it sounds ten times better as a supertweeter, with lower frequencies kept firmly out of it. Upper harmonics are exquisite with not a trace of hardness or fizz if it is used that way. Just because the thing can go low, does not mean that you should make it so.

If in the context of an omni speaker, this excellent ring radiator is used in conjunction with a swivelling cone, that takes lower treble and upper mids in its stride, the resulting tweeter array sings in the highs, offering beautiful string tone, fab cymbals, detailed tinkly bits, and excellent upper registers of female voices, and won't descend into nasality or sqwawk. The efficiency of the tweeter array is also enough to blend in seamlessly with a high sensitivity up firing bass/mid driver, running wide open.

What I'm talking about here is peculiar to omnis and semi omnis and has absolutely no application for front firing speakers, which if made up of high sensitivity bass/mid drivers, to go with low powered single ended valve amps, would just drown out the treble units; compression drivers, horns or high efficiency ribbons are required for those.

Most DIY audiophiles have no interest whatever in omnis or semis, never will, and who can blame them. The things are an absolute bastard to design and voice up. Only a few crazed eejits would be daft enough to take on the design of one. But once you crack it.... :wink:
Anyway I think I've said all I want to say about this rather controversial way of reproducing recorded music in the home, it's become a tedious hobby horse that has been done to death, so I'll spare you lot any more of my blithering about it. :lol:

Good luck with the baffle reboot Ed.
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