Cressy's Banned Omniset

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Simon Hickie
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Re: Cressy's Banned Omniset

Unread post by Simon Hickie » Thu Nov 09, 2017 9:17 pm

I'm looking forward to joining in the fun. We completed on the sale of the old house a couple of weeks ago and will complete on the purchase of the new one in just under two weeks. Current plans are for a Cube 2 sized mid/tweeter unit on top of a BBBB (or Big Bar-steward Base Box) using the Richard Allan drivers acquired from Jayman and my own Seas tweeters.
“The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.” George Bernard Shaw.

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SteveTheShadow
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Re: Cressy's Banned Omniset

Unread post by SteveTheShadow » Thu Nov 09, 2017 11:29 pm

antonio66 wrote:
Thu Nov 09, 2017 7:29 pm
I don`t believe Steve will mind Stu. I`m certainly no expert but side firing mids I would be unsure about. Still, will be interested in your results. :grin:

Any more news on your doubled tweeted Omni Steve?
I don’t mind at all Stu. :mrgreen:

The double tweetered omni works great. It balances up the top end against the efficient bass/mid driver. Treble was a bit down with just the one tweeter. Now the treble is up and the array both directs and spreads out the high frequencies to the front, so they don't get bounced away and attenuated. Designing your own omnis is an absolute b'stard, but it is worth persevering with them, because if you can get it right, there are few speakers that will equal the sense of music happening in your room.

Looking forward to reading about your own omni adventures Simon.
BTE Designs modified Lenco L75 idler turntable, Rega R200 Tonearm, Goldring E3 MM cartridge, NVA Phono1 phono stage.
Mac-Mini music server with iTunes, AppleTV4 media streamer, Musical Fidelity M1 DAC,
NVA A20/P20, 25WPC stereo power amplifier/passive control unit,
own design, semi-omnidirectional, transmission line speakers- "The Flatback Banned".

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SteveTheShadow
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Re: Cressy's Banned Omniset

Unread post by SteveTheShadow » Sat Nov 11, 2017 10:21 pm

Image

Back at this original config now.
Finally decided to stop fooking about with tweeter arrays and attenuate the bass/mid unit by 3dB, with an Lpad using two fixed power resistors. Should have done this in the bloody first place, would have avoided a great deal of grief.

Config is now:
bass/mid with 2R7 series resistor and 18R across the drive unit.
Treble unit with 5.6uF series capacitor.
BTE Designs modified Lenco L75 idler turntable, Rega R200 Tonearm, Goldring E3 MM cartridge, NVA Phono1 phono stage.
Mac-Mini music server with iTunes, AppleTV4 media streamer, Musical Fidelity M1 DAC,
NVA A20/P20, 25WPC stereo power amplifier/passive control unit,
own design, semi-omnidirectional, transmission line speakers- "The Flatback Banned".

antonio66

Re: Cressy's Banned Omniset

Unread post by antonio66 » Sun Nov 12, 2017 6:32 am

Wow! That's a change of heart, the only thing I will say is they do look more attractive without the extra tweeter.
ps I'm a big fan of Acoustic Alchemy. :dance:

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SteveTheShadow
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Re: Cressy's Banned Omniset

Unread post by SteveTheShadow » Sun Nov 12, 2017 11:32 am

It's a long story but basically, the missus was not happy with the looks of the speaker. WAF is not important if you have a separate room to listen in, but if the system shares main living space with the rest of the household then it needs to be domestically acceptable.

The experimenting with scattergun tweeters was fun, and taught me a lot about omnis and their own peculiarities, so it was useful from a speaker development perspective. Experimentation was also relatively cheap, using cones, but because of the unnaceptablity in the living room, I had to find a way to get the treble right, with just the single SB Acoustics, ring radiator tweeter.

Replacing the Faital Pro 6PR110 bass/mid driver was not an option, as the whole cabinet and quarter wave line had been designed around it specifically. Can't get the tweeter loud enough? Then you have basically two options:

1. multiple tweeters - done that. OK but not domestically acceptable in the format I used.

2. reduce the bass/mid level to allow the tweeter to breathe unaided and assert itself properly above the din from the rest of the freq range.

I chose the second option.
L Padding a main driver is not ideal, but needs must and apart from anything else, the Faital bass/mid driver doped with a little bit of shout removing PVA had such a good overall tone, I would have been a complete eejit to want anything else.

The whole speaker system now has an overall efficiency of around 91dB/Watt, so is still pretty sensitive as speakers go and the tweeter, being 94dB efficient, is now properly able to make itself heard.

The results are quite exquisite, which is all I'm prepared to say. These could go to any home based bake-off and not be found wanting in any way. I'm now confident I've cracked the semi-omni conundrum. Not an easy process, I can tell you, and all credit to Richard, for the sound of the his Cubes.

Having done something similar, I can appreciate the amount of work that must have gone into getting them right and also the fact that omnis don't play by conventional design rules. They need a huge amount of effort, thinking and empirical experimentation to voice up properly. No amount of measuring gear or computer plots is going to cut it. OK you could say the same about point and squirt speakers, but omnis are another level entirely in terms of the effort needed to get them right.

Probably why there aren't many about.

Sunday morning bliss: :clap: 8-)
Image
BTE Designs modified Lenco L75 idler turntable, Rega R200 Tonearm, Goldring E3 MM cartridge, NVA Phono1 phono stage.
Mac-Mini music server with iTunes, AppleTV4 media streamer, Musical Fidelity M1 DAC,
NVA A20/P20, 25WPC stereo power amplifier/passive control unit,
own design, semi-omnidirectional, transmission line speakers- "The Flatback Banned".

Simon Hickie
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Location: East Staffordshire
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Re: Cressy's Banned Omniset

Unread post by Simon Hickie » Sun Nov 12, 2017 12:07 pm

Really useful write-up Steve. I'm intrigued to see that the bass/mid needs padding even though the tweeter seems to be very efficient. Is this as a consequence of the MLTL (?) plus semi-omni configuration? My SEAS tweeter is about 91db as are the RA bass and mid drivers I'll be using.

So it's on to the cube plus large bass unit next for you then!
“The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.” George Bernard Shaw.

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SteveTheShadow
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Re: Cressy's Banned Omniset

Unread post by SteveTheShadow » Sun Nov 12, 2017 1:28 pm

TBH I'm not sure. But you might find that the SEAS tweeters are not loud enough.

Even though the effective efficiency of whichever up firing RA driver is used will be less, due to the off axis listening position the tweeters on the evidence of my own work will still need to be 3dB more sensitive in terms of raw efficiency, so you might need a 94dB tweeter to keep the HF up.
The answer, as always, is to try it and see.

The outcome of the Huddersfield bake-off, when I had a chance to really sit down and think about it, was that there were two problems.

1. I had turned the cabs through 90 degrees and the tweeters were firing at people's knees

2. the tweeters were not loud enough in comparison to the main drivers.

The not loud enough tweeters, were throwing up a red herring in the notion that it was the crossover point that was the problem. I spent hours messing with that, but all I got was a forward, aggressive sound that got mistaken for more presence.
The original crossover point was right, the overall tweeter level was too low. Once the levels between the two drivers were balanced up, the sound clicked into place.

Also reverting to the slight upward tilt of the tweeter direction so that they fired at ears rather than knees, put things on an even keel.

I won't be doing cubes and bass boxes. More than my life's worth. :lol:
Last edited by SteveTheShadow on Sun Nov 12, 2017 1:44 pm, edited 2 times in total.
BTE Designs modified Lenco L75 idler turntable, Rega R200 Tonearm, Goldring E3 MM cartridge, NVA Phono1 phono stage.
Mac-Mini music server with iTunes, AppleTV4 media streamer, Musical Fidelity M1 DAC,
NVA A20/P20, 25WPC stereo power amplifier/passive control unit,
own design, semi-omnidirectional, transmission line speakers- "The Flatback Banned".

Simon Hickie
Posts: 487
Joined: Mon Feb 27, 2017 1:47 pm
Location: East Staffordshire
Great Britain

Re: Cressy's Banned Omniset

Unread post by Simon Hickie » Sun Nov 12, 2017 1:43 pm

Cheers Steve. I have the benefit of a dedicated listening room, so WAF is less of an issue for me. I did find that the SEAS tweeters were too inefficient when put in a traditional P&S box with SEAS 92db efficiency bass drivers. I'd much rather have a too efficient tweeter and just pad that down if needed. I have amassed a large collection of resistors and capacitors from previous developments! Time to look for a 95db tweeter perhaps.
“The reasonable man adapts himself to the world: the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.” George Bernard Shaw.

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SteveTheShadow
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Re: Cressy's Banned Omniset

Unread post by SteveTheShadow » Sun Nov 12, 2017 1:48 pm

Yes, the over-efficient tweeter, padded down to meet the main driver, is the proper way to go. Better than padding the main driver. Mine was not your typical case and I wouldn't advocate doing it. I got away with it nevertheless and have a great sound, but all the same.....

I've seen mids and tweeters with level controls on old fashioned three way speakers, so it's not entirely unprecedented.

Padding a bass unit though, would be just plain silly.
BTE Designs modified Lenco L75 idler turntable, Rega R200 Tonearm, Goldring E3 MM cartridge, NVA Phono1 phono stage.
Mac-Mini music server with iTunes, AppleTV4 media streamer, Musical Fidelity M1 DAC,
NVA A20/P20, 25WPC stereo power amplifier/passive control unit,
own design, semi-omnidirectional, transmission line speakers- "The Flatback Banned".

pgarrish
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Re: Cressy's Banned Omniset

Unread post by pgarrish » Mon Nov 13, 2017 9:31 pm

Apologies if I missed it Steve but where is 'The Aether'? I'm having a bakeoff next month and my room would be a cracking test for a pair of Omnis....
Rega Planar / Teac T1 / Chromecast Audio - Teac TD1 DAC - Rotel RC850 - HHS500D or DACT passive - Mullard 5-20 Monos - Tannoy Cheviots + Wharfedale sub

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