Official Semi-Omni Metronome Build Thread.

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andrew Ivimey
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#61 Re: Official Semi-Omni Metronome Build Thread.

Post by andrew Ivimey »

Guffaw...
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#62 Re: Official Semi-Omni Metronome Build Thread.

Post by Thermionic Idler »

Cressy Snr wrote: Sun Apr 09, 2017 7:12 pm ...my goodness it works, as Dave and Meredith would be only too happy to tell you, as they now own my Scott/later Cressy Snr designed five footers :wink:
You would have to pry them out of my cold, dead hands.
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#63 Re: Official Semi-Omni Metronome Build Thread.

Post by simon »

It's been a pleasure having the OmniMets for the week. There's something very 'right' about them, and that main driver is a bit special. Vocals are particularly good with a naturalness that's uncanny. The bass weight when sited up against a wall is impressive, let alone for such a compact cabinet.

What I really like about them is that I didn't need to turn the volume up to make them LOUD so they sounded dynamic, as I can find myself doing sometimes. Even at modest levels they were excellent.

As Steve has discussed, I just felt the tweeter was competing with the main driver at times. Of course I could have been kidding myself, imagining it after the improvement I had changing the T90A supertwatter from a simple cap filter to second order. So it's interesting that Steve says the inductor has tidied the treble up.

The presentation is a touch different I guess. I don't tend to hear a large stereo image so I'm not the best person to judge this, but the sound fills the room in a more homogenous way than traditional forward firing speakers. They're very easy to spend a lot of time with - they were on for over 20 hours last weekend when I was decorating with the Squeezebox on random.

I think they are hi fi though. They're high fidelity no doubt, and carefully designed with a high quality sound. Hi fi. They're a little bit different to mainstream 'hi fi' though. In a good way I reckon.

My reservation about the treble notwithstanding I could very happily live with them, and if I'm honest I'm kinda missing some of the things they do. And those main drivers are very nice.
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#64 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Thanks for that Simon. These rather odd speakers are my most successful design up to now and its nice to see them being appreciated for what they do.

Speaking of the main driver, there's a story behind that: in the other thread I started when the first ideas for the folded semi-omni Metronome concept were being bandied about, I mentioned that when I design a speaker I tend to start with the all important midrange and then worry about the bass and treble afterwards. When I got sidetracked into single driver designs, all that seemed to go out the window, because there were seemingly insurmountable problems with "shout" unless one was prepared to spend a lot of dosh on upmarket full-rangers or try to eq the peaks out; it was dosh I didn't and still don't have.

Before I even thought of using the semi-omni configuration, I had been thinking for a while. I know that's a dangerous thing for someone like me to do....but humour me. :wink:

The arguments still persist among speaker folk about three-way versus two-way systems and which are the more musical. Now, whilst I was reading one of those interminable arguments (forgotten where now) it occurred to me that the three-way advocate's point, that the midrange is the most important and therefore it needs a separate driver dedicated to it, could be used to make an arse-about-face two-way speaker design. First a bit of a preamble.

The usual argument in terms of three-ways being superior, is that your average 8 inch bass/mid unit can't get high enough to cover the upper mids, so tweeters have to be crossed in, right in the middle of the area where the ear is most sensitive.

A smaller driver can however be used in multiples of four to make up the bass, in a 2 and a half way method, by using say one of the drivers to cover the mids and handle the transition to the tweeter, whilst another three are cut off below and handle the bottom end, making up the bass deficiency by sheer force of numbers.
But...then you get comb filters, lobing effects and phase anomalies that all have to be put right with complex crossovers, that have frequency dividing duties, impedance flattening, baffle-step compensation and phase correction to contend with.

Now, for those who haven't yet lost the will to live, I'll plough on.
I got to thinking...why not design the top half of a three way. ie three way philosophy but without the bass driver? Get hold of a midrange driver with Fs of around 100Hz with a high Q factor and lowish Vas, then, I might be able put it in a bigger cabinet and load it with a transmission line to make up for the lack of bottom end.

By my (often flawed) logic, you would get the advantage of a specialist midrange driver's flat midband, it would go up higher than a comparable bass/mid unit and be able to be crossed to a tweeter, well away from the telephone band. Without a bass driver underneath it, there would be no need for a bandpass filter. With this config, we now would have a speaker that did voices and midrange details properly. Cross to a high quality tweeter and we have the silky highs we want, the fly in the ointment would be the bass, so, in the absence of a dedicated bass driver, how do we solve that problem?

Well I did find the ideal driver for my arse about face design; one that would do the mids properly and have a big enough total Q factor to allow the TL loading to output a wider spread of bass reinforcement.

OK but the thing is still a midrange unit, and even with the TL loading, bass is still rolling off below resonance at an alarming rate. We need the LF spread to hold it up, so can't tune the line too low or there'll be a noticeable hole in the LF response, so fire the TL at the floor to get maximum bang and stick the whole thing up against the wall for that last degree of oomph, so that we are using the floor/wall boundary to get the absolute maximum bass output that we can wring out of a midrange driver.

So up on top, we have the semi-omni radiation pattern from a driver designed to get the best out of the midrange, a driver that is well behaved further up towards the treble region, when listened to way off axis, so we can run it wide open, without any surface treatment of the cone. On the front, we have a high quality HF unit to give a nice smooth treble (now we have the filter slope sorted) and to help with localisation cues.

Down at floor level because of our high Q driver, we have a wide, smooth port output at the bass end, being reinforced by both the floor and the wall boundary, and when it is all put together, we have a music output that sounds good in your average living room, without intruding on the floor space.
There chaps, you have been given a possibly disturbing glimpse of the strange world inside my head.

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#65 Re: Official Semi-Omni Metronome Build Thread.

Post by Scottmoose »

Sounds good to me Steve. The only thing I'd note is your comment about multiple LF drivers requiring complex filters. That's not necessarily the case; the Edingdale for e.g. had (has) a single inductor on its LF driver array. You have to factor listening distance and the precedence effect into the design, both of which mitigate the issues you mention. People tend to read far too much into simplistic measurements (e.g. 1m on-axis) which are rarely very representative of actual performance. Similar aspects apply to your new semi-omni speakers -I'm looking forward to hearing them. :)
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#66 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Scottmoose wrote: Mon Apr 10, 2017 5:47 pm You have to factor listening distance and the precedence effect into the design, both of which mitigate the issues you mention. People tend to read far too much into simplistic measurements (e.g. 1m on-axis) which are rarely very representative of actual performance.
Cheers Scott,
Bugger! I completely forgot about listening distance with short line sources, my bad.
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#67 Re: Official Semi-Omni Metronome Build Thread.

Post by Scottmoose »

So did I, when Nick & Andrew first suggested it to Colin. So alone you ain't. :lol:
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#68 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Grilles are made and on:
Image

I'm happy with them, but I can see that the speakers themselves can be made even more attractive with a slight redesign of the cabs so that the top driver and part of the front baffle are inset into the body, so that the grilles can be made flush. This will make the lines cleaner and the speaker will give a clear message that it is intended to be used with the grilles firmly attached :) These minute detail aspects may seem like unnecessary messing about, but to me they are important.
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#69 Re: Official Semi-Omni Metronome Build Thread.

Post by Nick »

You could also make the grills wrap around the entire speaker and look more like a hat than a panel stuck on. You could also recess the grill part to make the surfaces flat.
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#70 Re: Official Semi-Omni Metronome Build Thread.

Post by Dr Bunsen Honeydew »

I prefer the round ones. Perhaps put cloth around those or some cheaper more open ones. http://www.ebay.co.uk/itm/Round-Metal-s ... SwDNdVrYSg
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#71 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Nick wrote: Tue Apr 11, 2017 3:40 pm You could also recess the grill part to make the surfaces flat.
Yes, that's what I was talking about, when I mentioned insetting the tops and part of the front baffle, by the thickness of the grille frames. That will clean the lines up very effectively. Round grilles the Doc mentioned could also be accommodated with the same method.
Surprisingly given the general disdain for grilles within the hardcore hi-fi community, these speakers sound better with the grilles on than with them off. Omnis seem to do the exact opposite to what you'd expect.
Last edited by Cressy Snr on Tue Apr 11, 2017 5:04 pm, edited 2 times in total.
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#72 Re: Official Semi-Omni Metronome Build Thread.

Post by Dr Bunsen Honeydew »

It looks too plodding and angular with those grills. The contrast with round grills was good.
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#73 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Dr Bunsen Honeydew wrote: Tue Apr 11, 2017 3:52 pm It looks too plodding and angular with those grills. The contrast with round grills was good.
Aye..you're probably right. Recessed round grills look to be the way to go, with round surface mounted top grilles the things look like daleks, but inset the round grilles to clean up the lines and I think we'll have a winner.
Roy Allison did that with the sixes IIRC, didn't he?
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#74 Re: Official Semi-Omni Metronome Build Thread.

Post by cressy »

I think I still have the round grilles I made for tue chr70 mets if you want them
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#75 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Yes fetch them up.

I sense a rebuild of the test mules, incorporating all the mods, ie the modded crossover and inset round grilles coming on, Veneered in oak, they'll look the biz I think and won't be too expensive to make, as I have the drivers already.

Shan't bother with a thread, as everything that can be said about the speakers; construction, operation method, design process, my own philosopies, has already been said. I'll definitely have the new mules ready for Owston.

Nick, the Doc, thanks for your constructive comments on the aesthetics. :)
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