ALL constant directivity waveguides need EQ. If it is flat on axis then it can't be constant directivity - this is the physics of the problem. And usually this EQ is quite complex. The cost of CD and the sound quality that it brings is a complex EQ.
I sell some waveguide as stand alone. I have some 10s and 15s. E-mail me seperately and I can quote you on them.
I sell some waveguide as stand alone. I have some 10s and 15s. E-mail me seperately and I can quote you on them.
Earl, about the waveguides you have listed on the Summa page:
http://www.gedlee.com/Summa.htm
... are these fiberglass cutouts from AI cabinets, or something new?
http://www.gedlee.com/Summa.htm
... are these fiberglass cutouts from AI cabinets, or something new?
They are fiberglass. For now the 10" are cut from ESP molds, the 15"s are not. I am looking at casting the 10"s in poly without a baffle and eventually the 12"s too. I figured out how to do that without much trouble. The cast poly will have a 1/2" flange all the way around which can be screwed or glued into a baffle. There will never be a cast 15" because it is just too big and fiberglass is the better material choice in this size.
Update on Nathans and Abbeys
I have been meaning to update on the status of these projects and since I am here I will do that.
I finally got the wood from John for the Nathans and I can start shipping those out once again. These wood parts are very well cut as the photos show.
I have finished an Abbey prototype and attached the early measurements for it. The box itself is kind of rough - being a prototype - and I'm not inclined to show a photo. This speaker will ave an enormous output capability as the 12TBX100 is only slightly less output capability than the 15TBX100 in the Summa and the CD is the same. The Abbey is very close in performance to the Summa at a fraction of the cost.
I have been meaning to update on the status of these projects and since I am here I will do that.
I finally got the wood from John for the Nathans and I can start shipping those out once again. These wood parts are very well cut as the photos show.
I have finished an Abbey prototype and attached the early measurements for it. The box itself is kind of rough - being a prototype - and I'm not inclined to show a photo. This speaker will ave an enormous output capability as the 12TBX100 is only slightly less output capability than the 15TBX100 in the Summa and the CD is the same. The Abbey is very close in performance to the Summa at a fraction of the cost.
Ed LaFontaine said:
All axisymmetric waveguides will have a hole on axis - it has to be there or something is wrong. This is why I am looking into an elliptical waveguide as the hole will not be as deep - broader, but not as deep.
The angles are at 7.5 degrees.
Remember that in my setups "on-axis" is away from the listener by about 22.5 degrees. I design for flat OFF-Axis response and pretty much ignore the on axis response since no one should ever be on axis. This same hole exists in the Summa and is obviously not a problem.
tinitus said:
Sure I will, but as stand alone parts they will be quite expensive. The material is ridiculously expensive, very difficult to cut, lots of waste and it has a patent pending. All of which adds up to high costs. Fortunately they are cheap to ship
E-mail me if you are seriously interested.
And, they will actually only fit waveguides that are exactly like mine. Custom cut ones would be way too much trouble to deal with.
A few months ago I was arguing that the 12" might end up being superior to the "real" Summa. This is because it's very difficult to push a 15" woofer into the midrange, even with shorting rings and the best motor that money can buy.
These measurements seems to echo my suspicions; the transition from the woofer to the compression driver is a bit smoother on the new speaker.
Of course the response on the Summa is nothing to complain about, but this seems to be slightly better, by a db here and there.
Very interesting!
Here's the Summa's response:
http://www.gedlee.com/downloads/Cum laude.pdf
These measurements seems to echo my suspicions; the transition from the woofer to the compression driver is a bit smoother on the new speaker.
Of course the response on the Summa is nothing to complain about, but this seems to be slightly better, by a db here and there.
Very interesting!
Here's the Summa's response:
http://www.gedlee.com/downloads/Cum laude.pdf
Crossover for the Abbey's
Earl,
Do you now have a fixed design for the Abbey crossover? I am assuming that it will work with the fibreglass waveguides you sent.
A question about the waveguides in all the speakers - do the internal sound waves from the large/powerful bass units have any significant effect on the waveguide? I ask because the waveguide presents a large target inside the box and I was thinking about trying to damp them on the inside - with something a little heavier / denser than the foam plugs.
Regards
Alan
Earl,
Do you now have a fixed design for the Abbey crossover? I am assuming that it will work with the fibreglass waveguides you sent.
A question about the waveguides in all the speakers - do the internal sound waves from the large/powerful bass units have any significant effect on the waveguide? I ask because the waveguide presents a large target inside the box and I was thinking about trying to damp them on the inside - with something a little heavier / denser than the foam plugs.
Regards
Alan
Re: Crossover for the Abbey's
Good point!!! I should do a different crossover for the center speaker shouldn't I? The Summa does not have nearly the same level of hole as the 12 exhibits so its not such a problem in my setup. Maybe there is an advantage to the 15" waveguide? I would say that short of the use of the 12 for the center channel this is an excellent design, but yes, I will have to think about that center channel issue. This is all work in progress.
John
Those are old Summa responses, not quite the same as you have since yours is a more updated crossover. I now downplay the axial response to optimize the power response. In the figures that you attached you can see some clear resonances in the response as peaks in all the off axis curves at the same freuency. This is most obvious in a polar map. I have learned that it is better to ignore the axial response and minimize these peaks. A peak in the power response is quite audible even if there is nothing on-axis.
The 15TBX100 is a bit better driver than the 12TBX100 because the 12 has a slight spider resonance that the 15 has better controlled. Other than that the two drivers are quite comparable (same VC and motor) and the 12s polar response does work a little better as a match for the waveguide.
I have learned a lot along the way, but the original Summa design is still holding up as the best. Its just that the manufacturing techniques used are very expensive.
I generally used a fixed crossover topology for all my designs, but this changes somewhat over time and with application. In pro applications I have found that a different topology helps to save the tweeter from burn-out but this is expensive to do and not required for home use. Some use three LRC circuits for the HP and some only two. I am always conscience of the cost of added components in the crossover that don't add value, but the crossover is always the heart of any design so its best not to skimp there.
But, of course, the exact component values in the crossover have to be matched to the exact acoustic components. You can't use Abbey component values with a 15" waveguide even though the topology is the same. The resonances just end up being in different places.
I would generally not use a naked fiberglass waveguide in a system. My cast waveguides are solid as a rock and well damped and they wouldn't need any assitance, but the fiberglass ones would benefit by some back fill. I glue the fiberglass waveguide into the baffle with a thick rim of epoxy, about 1" thick. This helps a lot, but the device will still ring. After the baffe has setup I coat the back of the fiberglass with a dense coat of polyurethane foam (16 lb density - like a rock). This ends up being about 1-2" thick all the way to the throat. The waveguide now has no apparent ringing at all.
This added thickness is the reason that I always use a mounting plate. Without a mounting plate the thoat has to be very thin to get the screws into the driver. I don't care for two hole mounts and I don't like threaded but the mounting plate onto a very solid waveguide works very well indeed.
Dustin B said:
Good point!!! I should do a different crossover for the center speaker shouldn't I? The Summa does not have nearly the same level of hole as the 12 exhibits so its not such a problem in my setup. Maybe there is an advantage to the 15" waveguide? I would say that short of the use of the 12 for the center channel this is an excellent design, but yes, I will have to think about that center channel issue. This is all work in progress.
Patrick Bateman said:
John
Those are old Summa responses, not quite the same as you have since yours is a more updated crossover. I now downplay the axial response to optimize the power response. In the figures that you attached you can see some clear resonances in the response as peaks in all the off axis curves at the same freuency. This is most obvious in a polar map. I have learned that it is better to ignore the axial response and minimize these peaks. A peak in the power response is quite audible even if there is nothing on-axis.
The 15TBX100 is a bit better driver than the 12TBX100 because the 12 has a slight spider resonance that the 15 has better controlled. Other than that the two drivers are quite comparable (same VC and motor) and the 12s polar response does work a little better as a match for the waveguide.
I have learned a lot along the way, but the original Summa design is still holding up as the best. Its just that the manufacturing techniques used are very expensive.
AlanElsdon said:
I generally used a fixed crossover topology for all my designs, but this changes somewhat over time and with application. In pro applications I have found that a different topology helps to save the tweeter from burn-out but this is expensive to do and not required for home use. Some use three LRC circuits for the HP and some only two. I am always conscience of the cost of added components in the crossover that don't add value, but the crossover is always the heart of any design so its best not to skimp there.
But, of course, the exact component values in the crossover have to be matched to the exact acoustic components. You can't use Abbey component values with a 15" waveguide even though the topology is the same. The resonances just end up being in different places.
I would generally not use a naked fiberglass waveguide in a system. My cast waveguides are solid as a rock and well damped and they wouldn't need any assitance, but the fiberglass ones would benefit by some back fill. I glue the fiberglass waveguide into the baffle with a thick rim of epoxy, about 1" thick. This helps a lot, but the device will still ring. After the baffe has setup I coat the back of the fiberglass with a dense coat of polyurethane foam (16 lb density - like a rock). This ends up being about 1-2" thick all the way to the throat. The waveguide now has no apparent ringing at all.
This added thickness is the reason that I always use a mounting plate. Without a mounting plate the thoat has to be very thin to get the screws into the driver. I don't care for two hole mounts and I don't like threaded but the mounting plate onto a very solid waveguide works very well indeed.
Re: Re: Crossover for the Abbey's
Earl - I have been able to find the foam you talk about - but only for sale in the USA - not the UK! Over here we got rid of pounds (lb), feet, inches etc so trying to relate UK products to US products is never easy. But as with the epoxy paste I will eventually get what I need.
Alan
gedlee said:
Earl - I have been able to find the foam you talk about - but only for sale in the USA - not the UK! Over here we got rid of pounds (lb), feet, inches etc so trying to relate UK products to US products is never easy. But as with the epoxy paste I will eventually get what I need.
Alan
How about just tipping the center forward or backward?
This is actually a silver lining for those of us with center speakers below our screens; for my setup, all of the seats will be at least 9 deg off axis.
I know, I should have an acoustically transparent screen, but I need the gain to light up my 133" screen (Dalite Hipower).
This is actually a silver lining for those of us with center speakers below our screens; for my setup, all of the seats will be at least 9 deg off axis.
I know, I should have an acoustically transparent screen, but I need the gain to light up my 133" screen (Dalite Hipower).
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