Want to try omni - Am I on the right path, or where do I go? - diyAudio
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Old 19th November 2012, 10:07 PM   #1
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Default Want to try omni - Am I on the right path, or where do I go?

Hi all.

I've been doing the CD thing with horns/waveguides and would like to try an omni. My current plan is:

A down firing woofer about 10" off the floor in a cyclinder the size of the woofer frame. Likely a 6.5" woofer. Have some PE buyouts that would work good.

Active XO around 300hz

An upfiring 4" just below ear height. I have a pair of CSS EL70s I think would work well because they have throw. Mounted in a cylinder the size of the frame.

Passive XO around 1500hz

Forward firing SB29RDCN non mounted, just free field. Roughly 4" above the Mid.

And I'll run my subs down below 80hz. Thinking along the lines of Pluto, only adding the woofer downfiring.

All just a thought at this point. Need to find some proper cylinders to even do this. This should allow all the cross over points to be below the baffle step diffraction peak. The tweeter pass band will play into diffraction up above 3khz or so. How bad will that be. I'll measure 180d outside to ensure everything is behaving in an omni fashion.

Any suggestions or words of caution would be appreciated.

EDIT to add: my main concern is the mid to tweet cross over. Want to keep it low to maintain omni. But 1500hz into 4pi might be asking a lot, even though I've experienced first hand how capable the SB29 is. I am will to keep the listening level low, in order to satisfy my experimental experience, and then look for a solution to higher power handling later if that's a good way to go.

Last edited by tuxedocivic; 19th November 2012 at 10:11 PM.
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Old 19th November 2012, 10:16 PM   #2
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by tuxedocivic View Post
Any suggestions or words of caution would be appreciated.
be careful with tubes
wide and short would be best
omnis dont need to be at accurate listening height
might have positive effect to angle upper driver 'forwards', just a bit
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Old 19th November 2012, 10:39 PM   #3
Nanook is offline Nanook  Canada
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Default Cheap and quick omnis to get a taste.

I made a 37" long 4" tube using pcv piping. The Vifa coaxials I have are dirt cheap. Get a crossover pair off of eBay (or build some as per instrux at Apex Jr). Ensure the open end of the tube is at least a few inches off the floor. Stuff pipe until the pipe resonances are tamed.

Now you can have some fun:
  • create some sort of reflectors from pooched cds or cd rom disks
  • get some hard plastic balls larger than the driver diameter and play around with positioning (I found some close-out Alfred Sung 5" diameter Christmas bulbs a couple of years ago perfect for this)
  • make a larger than life paper cup . Mount it pointy side up and cut a K-slot into it
  • make a larger than life paper cup and mount it above the upward firing co-ax, pointy side down. Experiment with positioning.
  • pull the tweeters from the coax, and extend the tinsel leads. Make a mount for it by replacing the dust cap/ tweeter mount of the woofer with a dowel, and mount the tweeter to the dowel facing in the horizontal direction.

    The "tubes" and "Retros" located on Apex Jr's Vifa coax project page are mine.
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Last edited by Nanook; 19th November 2012 at 10:42 PM.
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Old 19th November 2012, 11:30 PM   #4
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Quote:
Originally Posted by tinitus View Post
wide and short would be best
I understand and am comtemplating your other three suggestions, but can you elaborate on this?

Quote:
Originally Posted by Nanook View Post
Make a mount for it by replacing the dust cap/ tweeter mount of the woofer with a dowel, and mount the tweeter to the dowel facing in the horizontal direction.
That's an interesting idea... My EL70s have damaged dust caps. I wonder if they can be removed and do this dowel trick. I'll ask Planet10 about it next time I see him.
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Old 20th November 2012, 07:20 AM   #5
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by tuxedocivic View Post
I understand and am comtemplating your other three suggestions, but can you elaborate on this?
you might say they come in pairs
apart from tube dimension, which would be the first two, wide and short, the next two are both part of the same thing, low height

be careful with tubes
wide and short would be best
omnis dont need to be at accurate listening height
might have positive effect to angle upper driver 'forwards', just a bit


actually, low height could be the main advantage of omni design
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Old 20th November 2012, 11:45 AM   #6
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Here is a site :6.283 Audio Pages
And another:http://www.linkwitzlab.com/Pluto/Pluto-2.1.htm

Last edited by båndsei; 20th November 2012 at 11:48 AM.
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Old 20th November 2012, 03:31 PM   #7
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bandsei, is that 6.283 audio your site? The Demokrit-T catches my eye. That's somewhat along the lines of what I was thinking about. But 4 way (an extra 2 radiators handling below 300hz or so). Thanks for the link.
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Old 20th November 2012, 03:43 PM   #8
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No.
But i have the pluto´s in a cloned version.

Bernt
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Old 20th November 2012, 03:45 PM   #9
OllBoll is offline OllBoll  Sweden
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Keep in mind that if you use a forward firing tweeter it isn't really an omni all the way. Something that works well is to use multiple tweeters, I for example have a clone of the pop box which used 4 tweeters mounted inwards firing in a ring around the midrange.

Stig Carlsson did lots of such testing with omnis and did lots of interesting speakers.
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Old 20th November 2012, 04:09 PM   #10
OllBoll is offline OllBoll  Sweden
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Addition: If you haven't bought the tweeters yet an option is the Obi T22-oa, which is a cone tweeter with controlled directivity such that you can use multiple ones without having to handle that directivity is so different at low/high frequencies like with domes. It was specifically designed to be used in omni speakers (OA5-MMX).
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