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.
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.
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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
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:
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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I understand and am comtemplating your other three suggestions, but can you elaborate on this?
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.
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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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.
Stig Carlsson did lots of such testing with omnis and did lots of interesting speakers.
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).
Hi OllBoll. Interesting points that I was wondering about. The tweeter will transition from omni to direction at some point, I'm guessing around 4khz. How much will this matter?
Multiple tweeter? Hmm. Wont I get nulls where they interfere?
I already own the SB29RDCN and a few other domes, small 2 and 3" full rangers, compression drivers, etc. Just need to know how to make it happen. The wavelengths above 2khz get so small I'm having a hard time knowing what to do, theoritically.
Multiple tweeter? Hmm. Wont I get nulls where they interfere?
I already own the SB29RDCN and a few other domes, small 2 and 3" full rangers, compression drivers, etc. Just need to know how to make it happen. The wavelengths above 2khz get so small I'm having a hard time knowing what to do, theoritically.
While I haven't tried to build a half-omni half-forward firing like the pluto but rather only vanilla speker and full omni even Linkwitz himself thought that multiple tweeters were an improvement in the Orion since he permanently added the backwards firing one.
But like I said, I'm not sure exactly of how much difference it does. Obviously the Pluto is already different from a normal speaker if one trusts the impressions people have of it so it might be marginal.
Personally I just like the idea though that I can be anywhere in the room and the only difference I get is volume difference from left/right, but still get perfect response.
And about nulls and such, well yeah but so do you in real life. Your amazing brain doesn't care though so while a measurement microphone can pick them up your ears can't. Think about a choir for example, that's a lot of peaks and nulls from the interferace of all the voices but still it sounds kinda nice if you have a twice as big choir =)
but isn't this Pluto thing just boring?
why not trying sth really new? not thinking along any lines
I would follow tinitus' suggestions
for my part I say make it as short as possible, use coincident driver, bass or subbass in a separate enclosure, if crossed not too low You would not even need an enclosure for the main driver, simple baffle would suffice or even a bare driver - ask tinitus if do not believe me
do not angle anything forward but be prepared do equalize passively or actively for the treble loss (the most of treble energy would come through ceiling reflection)
You still can angle it forward with the use of spikes or else, if necessary
good luck!
best!
graaf
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That would be me.
Cross around the Schroeder Frequency of your room (180Hz...250Hz ?) and let the sub handle only the modal region. Then above use an acoustically small speaker with as little diffraction as possible. The SB29RDCN is probably to big for this application.
The xover to the tweeter is best placed at the border of the ITD (1800 Hz) listening range or above.
Full omni is kinda of cool but a small and controlled directivity above the ITD range makes a better stereo image.
Or longer than about half the wavelength radiated by the driver with some stuffing.
This is not acousdtically small, which I and many others have found to be very important.
but isn't this Pluto thing just boring?
why not trying sth really new? not thinking along any lines
Except I'm not really looking to be innovative here, rather use some fundamental rules of thumb and proven ideas, combine that with my resources (drivers and materials), to see what omni is all about.
How about a 2" upfiring (instead of the 4" I mentioned) with a forward facing dome in a waveguide crossed around 1800hz or even lower? I also have a pair of Dayton ND28 which are extremely compact when you remove the faceplate. Probably 32mm diameter. Could either of these arrangements work better?
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