Official Semi-Omni Metronome Build Thread.

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Cressy Snr
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#46 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Now you've done it Doc!
Those names are going to stick now. :lol: :lol:
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#47 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Latest iterations of this design are running in nicely. I have to conclude that the Mundorf Silver/gold foil, tweeter caps are the dog's danglies, in this particular application, although bloody expensive. Despite the high cost, I can't argue with the treble quality these caps give: in a word, gorgeous. :)

My mate and his wife have just left. She said, "you're not listening to the speakers at all are you? The music is just happening, and they look lovely as well".

Can't argue with that really. <cue insufferable smug expression> 8)
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#48 Re: Official Semi-Omni Metronome Build Thread.

Post by simon »

I finally finished undercoating at 10 to midnight last night so had about 13 hours with Huey and Dewey yesterday. Most of that time they weren't against a wall but still sounded coherent. They might be just the job, see what the boss thinks when she gets home tonight.
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#49 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Look fwd to getting her views, positive or negative: it all helps with the bigger design picture. :)
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#50 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Am half way through making the grile frames.
6mm MDF with the cutouts for the drivers, routed out and the edges of the apertures, bevelled. The top deiver will be protected with perforated steel mesh, with a chocolate brown covering of speaker grille cloth over that.
The front grille will be shaped to fit the cabinet profile and just the grille cloth will be used, no mesh underneath, then a badge will be fitted to the bottom right hand corner of each fromt grille.

Pics will follow of the finished articles.
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#51 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Brought the test mules back from Simon's place today.
Had a good listening session in the morning comparing Simon's Scott designed Alpair 12 (I think) MLTLS with Monacor ribbon supertweeters to the Beta versions of the OmniMets.

It was very interesting indeed, hearing the differences between the direct radiating and the semi-omni concepts; very enjoyable and I came away after a bit of discussion with Simon, with a slight modification to the OmniMet crossovers, which I have tested on my walnut ones.

Subtle but useful :wink: :)

Will carry out the crossover mod properly tomorrow, as well as finishing off the grilles
Test mules will get the mod too over Easter, then they'll be ready to go out again.
We're there now I think.
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#52 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

OK
So the crossover mod has been done to the OmniMets. It was quite simple, and involved a bit of maths, then taking my 1mH Monacor inductors out of their plastic bags, and unwinding them to a much lower value, then putting one across each tweeter. Working in conjunction with the series tweeter cap, we now had a 12dB/octave, second order filter on the HF unit, as is recommended by the manufacturer, SB Acoustics.

Whilst it is true that the tweeter roll in at 6dB/octave is in theory matched to the off-axis roll down of the bass/mid unit, in terms of the semi-omni configuration, we were working with, there had been a sense, with the test mules, as Simon had pointed out, of a slight glare in the lower treble and there was a spread from lower to mid treble that was a tad conjested, dulling some elements that were clearer on his Alpair MLTLS. It wasn't night and day, but once Simon had pointed it out, it was definitely there.

This is exactly what I like about this Beta testing programme or any little non-Owston audio meet, for that matter. You get wrapped up in a design and often fail to notice that there is something slightly askew with the sound of your project. A different pair of ears is the thing that brings these slight faults to the fore, so that they can be dealt with appropriately.

Back to the filter,
I tried the spectrum analyser and it reported very little change in the third octave bar chart readout. The in-room response looked same as it ever was apart from a flattening out through the 4KHz region by about 2dB. The in-room response is now virtually flat through the mids and treble from 400Hz, right through to 16KHz with a couple of dB loss towards 20K, which at my age I couldn't give a stuff about :lol: True, that droop right at the very top, could lead to this speaker sounding less "impressive" than another one in a demo situation. Equally however, the OmniMet is so far out of the mainstream it wouldn't matter. It's one of those speakers, you either "get" or you don't.

So all we've really done with this crossover mod, is to steepen the slope to second order, so that upper mids are being kept out of the tweeter to a greater extent than the first order cap filter was doing, thus giving the tweeter an easier time of it.

The presentation is "easier" going and the missus has just pointed out, without any prompting, that she can hear more music going on. The whole thing is cleaner. I don't think the OmniMet needs anything higher order than that doing to the crossover. The bass/mid driver is such a superb performer that it is quite happy to be left wide open.

I'm very, very pleased with the way this strange project has turned out. As I was saying to Simon yesterday, these speakers are not designed to be hi-fi. What they are designed to do is play music in the home to a good standard, be able to be listened to for hours on end without fatigue and allow several people to listen at the same time, without one getting the better sound, by being in a sweet spot. In these respects, I think the OmniMet is a resounding success.
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#53 Re: Official Semi-Omni Metronome Build Thread.

Post by andrew Ivimey »

What's happening below 400Hz?
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#54 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Just the usual.
it is pretty flat going downwards until we get to around 100Hz, where there is gentle 2dB plateau until we get to 50Hz, followed by steepish roll down to 20Hz, which is as low as the chart goes.
Bass response is unchanged from what it was. They don't thunder at the bottom end, but for what they were designed to do, they work well down there.
Last edited by Cressy Snr on Sun Apr 09, 2017 5:40 pm, edited 1 time in total.
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#55 Re: Official Semi-Omni Metronome Build Thread.

Post by Dr Bunsen Honeydew »

Well I would have done it differently and by going 2nd order you now lose some music or lose some musical *communication*. I had what you heard on a Doc Mod I did with a JPW one of the bigger ones I don't remember which as it was a couple of years ago. I single light pass with a spray of Plastimix on the dome did the job.

The difference is I didn't stop it going lower I stopped it reacting to going lower.
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#56 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Dr Bunsen Honeydew wrote: Sun Apr 09, 2017 5:39 pm Well I would have done it differently and by going 2nd order you now lose some music or lose some musical *communication*. I had what you heard on a Doc Mod I did with a JPW one of the bigger ones I don't remember which as it was a couple of years ago. I single light pass with a spray of Plastimix on the dome did the job.

The difference is I didn't stop it going lower I stopped it reacting to going lower.
Aye that'd definitely do it. Drop the resonant freq of the HF unit, by adding a tiny bit of mass, with some damping thrown in, but the tweeter I'm using is a bit expensive to be spraying it. I would be sh**ting myeslf if I tried that. :)
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#57 Re: Official Semi-Omni Metronome Build Thread.

Post by Dr Bunsen Honeydew »

I am so used to doing it now as I have done it to loads of tweeters. I know how much to do for different audible anomalies. On a couple of cheap tweeters that had plastic front plates doping the plates even tamed things.

The major benefit in doping tweeters is that you can get some cheaper ones to perform like the very expensive ones.
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#58 Re: Official Semi-Omni Metronome Build Thread.

Post by andrew Ivimey »

So 50 Hz to 20kHz these speakers are within 2dB of a flat frequency response - measured with pink noise presumably, with nothing obvious in the room producing measurable artefacts.

What are the drivers please. From the text I can see what Scott' speakers have but only your crossover gets specc'd'?

I'm very impressed by such data even if that would get Dr.Brian growling.

You sound very happy with the sound of music so PHROARRRRHHHHHHHHH!! as someone might exclaim. Well done!
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#59 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Hi Andrew.
Yes, the speakers were measured with third octave pink noise.
Drivers are Faital Pro 6PR110 for the bass/mid and the tweeter is an SB acoustics SB29RDNC-C000-4. It is 94dB efficient and has a neodymium magnet.

The speakers are flattish in a room but at the bottom end they are boosted significantly by the next to wall placement, so how even they will be at the bottom is down to experimenting by moving the things about in small increments until they sound right, but having said that they are pretty easy to set up.
Gawd knows what their conventional anechoic response would be: probably not a pretty sight; mid to treble without the wall/ceiling reflection, who knows? Bass would probably go off a cliff edge :shock:

In terms of the bass loading, they follow on from the work me and Scott did years ago with the original unfolded Metronomes, first I did some little fostex drivers, then Scott, did a load of bigger units. The only difference now is that the line is folded and I worked them out by hand calculations rather than MJK's worksheets. The principle is the same, but MJK is a lot slicker about things than me :lol:

The main contributor to the excellent, uncoloured, in-room bass response is the down-firing, mass loading port that terminates the quarter wave resonator. This enables close to wall placement to help out the bottom end, without causing room modes to start up. Scott knows more about that aspect than me, but 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:
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#60 Re: Official Semi-Omni Metronome Build Thread.

Post by Dave the bass »

Cressy Snr wrote: Sun Apr 09, 2017 7:12 pm Bass would probably go off a cliff edge :shock:
I'm OK at the moment, though thanks for the concern :)
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