Official Semi-Omni Metronome Build Thread.

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

Post by Cressy Snr »

So I was talking a few posts ago about the third octave spectrum analysis of the OmniMet after I had been messing about with the crossover and had made it second order to the tweeter, with the mid/bass unit wide open.
Empirically and subjectively speaking, the speakers sound better and the spectrum analyser reported a flatter frequency response, but I didn't post the spectrogram: anyway I have now...because..
I have had a play around at the bottom end :wink: and this is the result, in-room, at 2m with third octave pink noise and as usual, the speaker backed right up to the rear wall:

Image

That'll do very nicely thank you.
I think that the idea that these speakers use the room to help them produce a good sound all round is well supported by this analysis, and also the subjective impressions tend to agree with the visual impression given by the measurements.
May give a lack of sparkle for our younger listeners, looking at that fall off right at the top of the top end, but you can't have everything....that's speakers for you.
I'm not about to p*ss about with different tweeters for the sake of an "impressive" hyper detailed sound.
I've built what I wanted and I think I've got close enough to my idea of what sounds right.

Funny as I said to Simon, these things were not designed to be "hi-fi" but their fi seems quite hi nonetheless. :lol: :lol:
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#92 Re: Official Semi-Omni Metronome Build Thread.

Post by simon »

What did you do wrt to the bass Steve?
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#93 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Just took a bit of the stuffing out of the narrow end of the line.
I had A/Bd them with the ones you had at your place and the loan pair you had been using went deeper.

Sorting the stuffing, in my pair, evened up the score at the bass end. Now I know I'm probably in the right zone for the amount of damping they need in the line. That spectrogram doesn't look half bad at the bass end now. :D

Just shows what you can do with a midrange driver, a bit of lateral thinking and creative use of a transmission line.
I'm well happy.
Just need now to get on with bringing the loan pair up to scratch by modding its crossover.
Need to order some better quality caps and the inductors.
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#94 Re: Official Semi-Omni Metronome Build Thread.

Post by Dr Bunsen Honeydew »

Don't throw the baby out with the bathwater.
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#95 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

No chance of that Doc. That spectrogram is as far as I go with measurements. It's useful, but my ears are the final arbiter and to me the speaker sounds great now; musical as hell and tonally bang on....in my room and another one, twice the size and far more "live"
Where I am now is as far as I'm prepared to go with it.
From bitter experience I've found that it's all too easy to break the sound of something by going just that little bit too far with the p*ssballing about. Then you realise you have fooked up and can't get back to where you were.

That ain't gonna happen with this thing. :)
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#96 Re: Official Semi-Omni Metronome Build Thread.

Post by Dr Bunsen Honeydew »

This may give you an insight into why the upward driver is working well near the back wall.

https://www.google.com/patents/US3983333
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#97 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

Cheers for that Doc.
I've had a good read this morning and not only has it given an insight into up firing drivers and how they interact with wall boundaries, but Mr Allison has also (in his notes) put me onto a way to improve further, both the performance of the OmniMets, and to make both the external enclosure and the internal expansion a damned sight easier to build, whilst still keeping the basic aesthetic more or less intact. :)
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#98 Re: Official Semi-Omni Metronome Build Thread.

Post by Cressy Snr »

I'm off out now, but I'll PM a few bits of ideas to run past you later.
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#99 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*.
As y'all may recall, around six weeks ago, I made a bit of a song and dance about changing my simple low order, 6dB/octave, single capacitor tweeter crossover to 12dB/octave.

Well, six weeks down the line and I'm afraid the novelty has worn off. We are back to a very high quality, single cap tweeter feed.

No glare...either we have a driver running in issue that has now resolved or the slight treble glare was caused by something other than the speakers themselves.

All's well with the music.
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#100 Re: Official Semi-Omni Metronome Build Thread.

Post by cressy »

Ive been gifted the empty cabs for this pair due to the broken terminal plates.
Dad has the flat ones and the sapele pair, plan is to nail the drivers out of my mets into them. Drivers are the same sb acoustics twatters but mine have a larger mounting flange so i should be able to fettle the cabs to get the twatters to sit at the same height, and the 6"er is a faital 6fe100.

The 6pr200 worked fine in the mets so should be the fe should be fine in these.

We shall see.

To be continued
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#101 Re: Official Semi-Omni Metronome Build Thread.

Post by cressy »

Having swapped all the bits over into these cabs and redrilled the holes for the twatters so that they are now level, I can say the 6fe100 works fine in these cabs.

I plated over the terminal tray hole with some 6mm ply then set the 4 pole speakon socket in it so the external crossover plugs in. No need to faff with it.

Had to pull the port out of the mets too, they didnt like the original port in these
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#102 Re: Official Semi-Omni Metronome Build Thread.

Post by cressy »

Its odd not having the tall mets

Image

With the larger tweeter mounting flange, my lad theo says they look like kevin the minion......
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