Altec 816 copies with different woofer and wood?

[turbodawg]

Originally Posted by Kindhornman

djlivex,
I think what everyone forgets is that the original Altec and JBL horn reflex cabinet enclosures were designed to go behind a movie screen and the bass response is not that good. The response of the ports below the cutoff frequency of the horn is down by more than 6db and the integration with the horn is really not very good. Why not just use the horn without the ports, sealed back and add a true bass tuned cabinet. That is what happened to all of the PA enclosures during the 70's, the ports were deleted from most of these types of cabinets. The Eq required to bring the level of the bass up to the horn gain is severe and the amplifier power required is heavy to do this. Also you get into the uncontrolled excursion of the driver at these frequencies and it was common for the cone to slam into the back of the throat of the horn. Just an observation from someone who has been there with these enclosures since the late 60's. Believe me I moved my share of A7 and A2 enclosures.

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.

[turbodawg]

Originally Posted by djlivex

Looks nice with the vents on the side, you think the standing waves on front can be eliminated as per GM with an angled piece top and bottom of the horn mouth from the baffle instead of the straight piece. How about the plans for EAW MR101 which is the 10" version used in clubs in NYC previously by Paladium in the '90s from Richard Long Associates nice sounding back then and loud if I can remember. They have the phase plug infront mounted on the screen mesh. Typical EAW if you look also on the EAW KF850 concert cabs!

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.

[Kindhornman]

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

[turbodawg]

Originally Posted by Kindhornman

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

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.

[Kindhornman]

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

[turbodawg]

Originally Posted by Kindhornman

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:

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 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!

[Kindhornman]

Yes this is the Klipsch rear chamber formula. I have used this many times and it works. Don't think that it is to small, it is supposed to be.

Steven

[djlivex]

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 . . .

[djlivex]

Also GM you mean cutting the lower half of the A7(825/828) as per Kindhornman you are actually sealing the vents and making it smaller for higher cutoff? Thanks!

[Kindhornman]

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