Very good points. But what's stopping us from a modern design that pushes the response from the vents up to a range where it can fill in below the horn gain? I was able to sim the vent fill relatively flat in 2pi space, but only to around 100hz. It's like running a ported box vs. a sealed box. My intention is to use with subs or bass bins, and a horn/waveguide tweeter. Having a port in the mid seems like it would expand the bandwidth and efficiency enough to match up better.
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Good lead....sounds like the 12" version is more common from searching around. But I can't figure if they are ported or just a normal horn midrange.
My current take on it is to design a square cone style for ease of construction, where the sides, top and bottom are are all angled, but flat wood. Then the port(s) is either on the sides of the mouth, below, or actually out the sides of the cabinet (at an angle near the front). Should be relatively easy build.
What I was trying to point out was that by the time you increase the output enough to reinforce the frequencies below cutoff of the direct radiator mounted behind the square horn opening the cone will slam into the back of the horn. Unless you make a spacer ring that matches the gasket on the driver and move it away from the back of the horn it will hit. Been there had that happen. It will take a lot of excursion with the port to come up to the output of the horn. You are going to really make that driver work at the excursion limit to do what you are trying to do. If you are planning to use a bass enclosure below the horn anyway you can make the horn enclosure much smaller without trying to use it as a bass reflex enclosure also. That is what happened in pro-audio years ago. Eastern Acoustics was one of the first to make their cabinets this way. If you make the volume of air behind the direct radiator small you can actually load the driver better and extend the range below the normal cutoff frequency. This was developed and published by Paul Klipsch years ago and I used that formula to match the front and rear air loading on the driver. With this method the excursion is very low and the output is at its greatest for the device.
Steven
Steven
Excellent and thank you for stepping in with your experience, I see what you're getting at. I'm personally looking looking for maximum efficiency, bandwidth, and minimum size, at the expense of power handling. I will accordingly model with space in front of the woofer as you state. I can see that a normal front loaded horn with sealed back would have better power handing in general, as they are much more common in modern pro audio. I'm looking for serious output from 25 to 50 watts, so I guess this is a specialized application.
With the model I have going right now with a beta 12A-II it hits maximum xmax at around 100w at 100hz. So what you're saying is clearly shown by the models. But it's doing 118 +/- 2 db in 2pi space from 100 to 1000 hz off that 100w....which I like. And it could probably be built into a below 30 lb total cab with a $80 driver.
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turbodawg,
This is off the top of my head but I am fairly sure that I remember this formula correctly. It has been awhile since I had to use this formula and I don't have my notes with me. Here goes: This is based on the exponential formula of expansion S1=So emx M and x are exponents. E is the napier's figure. Sorry I can't do the correct mathematical figures.
Volume of rear enclosure = 2.9x AxR
A= area of throat in sq. in.
R = the rate of expansion of flare rate
2.9 = the constant
You have to roughly calculate the displacement of the driver and add this to the volume for the rear enclosure. It will appear very small and that is correct. It works, I just don't remember how much the extension of the lower frequency cutoff is extended. I think it could be about 1/3 the cutoff frequency but don't hold me to that.
Steven
This is off the top of my head but I am fairly sure that I remember this formula correctly. It has been awhile since I had to use this formula and I don't have my notes with me. Here goes: This is based on the exponential formula of expansion S1=So emx M and x are exponents. E is the napier's figure. Sorry I can't do the correct mathematical figures.
Volume of rear enclosure = 2.9x AxR
A= area of throat in sq. in.
R = the rate of expansion of flare rate
2.9 = the constant
You have to roughly calculate the displacement of the driver and add this to the volume for the rear enclosure. It will appear very small and that is correct. It works, I just don't remember how much the extension of the lower frequency cutoff is extended. I think it could be about 1/3 the cutoff frequency but don't hold me to that.
Steven
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This is for a sealed chamber? Good stuff, thank you!
Appreciate your feedback as someone who as done this before. But I don't mind not knowing enough to be willing to try something!
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Kindhornman you're right about over excursion I heard this early in the 80's I was invited to a college dance this DJ from Astoria, Queens had a pair of A-7 copies with an Altec multi cell 1" horn it was so loud when it hit the lower notes you'd hear the cone slapping the baffle but he didn't care and I didn't know better back then because I did not understand PA setups back then.
Also turbo with straight panels it would be easier to build and 12" sweeter sounding and 100Hz is appropriate for this type of horn loaded midrange, Frakenstin back way Mel Brooks, LOL! I do not know much about the technical computations on designing but with a 12" Beta you think you can make it as high as 2.5kHz where a 1" can take over? Thanks! sounds promising . . .
Also turbo with straight panels it would be easier to build and 12" sweeter sounding and 100Hz is appropriate for this type of horn loaded midrange, Frakenstin back way Mel Brooks, LOL! I do not know much about the technical computations on designing but with a 12" Beta you think you can make it as high as 2.5kHz where a 1" can take over? Thanks! sounds promising . . .
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turbodawg,
I think that trying to push this horn up to 2.5khz is much to high into a 1" compression driver. On a large radial horn with a 1" driver this is typically 800hz and up. Tell me what your timeline is for this project. I have many horn lenses in storage but I haven't been there for quite some time. I have a small lens for 1" drivers that works from 1.6khz on up. I also have some mid horns that work from 600hz on up with a 6 1/2" cone driver. This would fill in the mids and get you into the 1" at a better crossover point. Depending on your schedule I could just send you a pair of each. What are your intentions for the system. Is it going to be fixed or are you going to be moving it around? Let's see if I can help you out, nothing like making friends in a new group and I need to go get some things from the storage anyway. Look at my avatar and you will see two of the horns. They are the two lower horns in the picture. They are not radial horns, they are equal dispersion lenses in the vertical and horizontal. It really depends on your final usage and the needed dispersion angles. Let me know.
Steven
I think that trying to push this horn up to 2.5khz is much to high into a 1" compression driver. On a large radial horn with a 1" driver this is typically 800hz and up. Tell me what your timeline is for this project. I have many horn lenses in storage but I haven't been there for quite some time. I have a small lens for 1" drivers that works from 1.6khz on up. I also have some mid horns that work from 600hz on up with a 6 1/2" cone driver. This would fill in the mids and get you into the 1" at a better crossover point. Depending on your schedule I could just send you a pair of each. What are your intentions for the system. Is it going to be fixed or are you going to be moving it around? Let's see if I can help you out, nothing like making friends in a new group and I need to go get some things from the storage anyway. Look at my avatar and you will see two of the horns. They are the two lower horns in the picture. They are not radial horns, they are equal dispersion lenses in the vertical and horizontal. It really depends on your final usage and the needed dispersion angles. Let me know.
Steven
Not everyone.
Well, for one, if the port is high tuned it yields more overlapping gain BW, allowing a ~1/2-1 octave lower XO point depending on the slope order, which may/may not be desirable depending on the app.
That said, by the late '60s, which was before the 816/817 came along, I was chopping down A7s for both 'small' sealed and vented alignments depending on the needs of the app. Ditto 210/211 cabs.
It appears I got started before you, though I only did it as a fairly serious hobby.
GM
Hmm, I first saw this in the Cohen and later Badmaieff/Davis books, though neither gave Klipsch credit. Since they were all part of the Altec conglomerate, guess that's not too surprising.
Regardless, you had better luck than me with it as I always had to reduce its net Vb to get the acoustical balance [AKA reactance annulling] of the HF compression horn drivers.
Anyway, in today's T/S driven software design routines, it's an old rule-of-thumb that IMNSHO needs to stay relegated to its footnote in history.
GM
Again, depending on the app I would either shorted the cab enough to use a ducted port vent to raise Fb up to around 90 Hz or cut it off right below the horn and seal it up, which leaves 'close enough' to the desired Net Vb required for most of the Altec 416, 421, 515 series drivers if the horn cavities are sealed up.
I quit messing with these cabs circa '75 except for occasionally tweaking the 210 cabs that were the foundation of my rig until 2000, so don't know about later drivers without simming them.
GM
Thank you much for the generous offer! But I really don't have a timeline for this project yet and wouldn't be the best use for them. Also, I'd prefer to go with one of the standard econowave waveguides since they are almost the standard for DIY. But thank you!
On the crossover, it seems the common point for the econowaves is around 1500 to 2000 hz. I'm thinking with the right woofer this mid could get up into that range.
Zilch's AK Design Collaborative - Econowave Speaker - AudioKarma.org Home Audio Stereo Discussion Forums
Gm,
I still remember moving the large A2's around along with RCA W-horns. The RCA's were very large folded horns and made good bass but were way to heavy to be moving around for live sound reinforcement. RCA had the nicest of the horn enclosures back in the day as they were a radial horn design with two 15" drivers with a reflex design. They still have them as in one of the most well known studios in Los Angeles called Ocean Way studios as a set of mains. Flush in the wall. I have the throat sections for 8 double 18" horn enclosures. The throat section is molded fiberglass and they go from round to elliptical and then to the square transition that was attached to a wooden exponential flare. Four per side equaled a true 50hz mouth cutoff size. Knock you over bass in a live sound system. The throat area created a 25% loading of the driver and this was a smooth transition from the driver to the throat minimum. The mathematics for the flare transition and connection were part of my original waveguide patent.
Steven
I still remember moving the large A2's around along with RCA W-horns. The RCA's were very large folded horns and made good bass but were way to heavy to be moving around for live sound reinforcement. RCA had the nicest of the horn enclosures back in the day as they were a radial horn design with two 15" drivers with a reflex design. They still have them as in one of the most well known studios in Los Angeles called Ocean Way studios as a set of mains. Flush in the wall. I have the throat sections for 8 double 18" horn enclosures. The throat section is molded fiberglass and they go from round to elliptical and then to the square transition that was attached to a wooden exponential flare. Four per side equaled a true 50hz mouth cutoff size. Knock you over bass in a live sound system. The throat area created a 25% loading of the driver and this was a smooth transition from the driver to the throat minimum. The mathematics for the flare transition and connection were part of my original waveguide patent.
Steven
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