Two-way speaker system, WAY horn-loaded
- Thread starter tubino
- Start date
tubino
A guy with too many tubes
That would be a fairly typical response. Notice the up and down response, peaks and dips, where the woofer is in phase and out of phase with the sound radiation from the mouth of the horn. That is typical response of a "transmission line" speaker cabinet.
Look at the typical impedance/frequency of any horn that is too short/small, which is of course almost any that try to do LF... This is Olson, probably over 50 years ago, looking at the effect of altering mouth and throat sizes...
Then just today I found a very similar graph of "Acoustic resistance at the throat of the horn as a function of LENGTH" in "Computer Design of Horn Loudspeaker Systems" from Acustica journal, Vol 74 (1991).
tubino
A guy with too many tubes
Slow steady progress: I received my pair of JBL 2441 drivers (thanks, Ron C!), and Bruce Edgar assures me the 500hz salad bowls will be sent soon. The 2441's, pro 2" exit drivers, are MONSTERS. Just the driver is the better part of 30 lbs! Home use is like retirement for these guys! My loudest uses for them would be loafing compared to pro use!
I'm recalc'ing the values to use for a crossover... and will use a ~16ohm resistor ACROSS the 2441's to make them look like an 8 ohm load to the crossover -- with the side benefit of making the apparent load look more linear to the amplifier over the frequency range. Crossover will be at ~750 or 800 to match with the Altec 515E for the first round.
But when I first get the horns, I'm going to try the combination on top of the Tannoy GRF-R cabinets with Altec 414, crossing over at 1400-1600. Another nice thing about the 16-ohm driver paralleled with 16 ohm resistor is that I can use that same driver with the crossover I made for the 8 ohm Altec driver and horn now sitting on the Tannoy cabinets. That will give me an easy basis for comparison.
The room with the Tannoys has gotten cluttered with projects, so yesterday I took all the boxes of vacuum tubes, claimed a space in our converted porch room, and spent hours sorting them into labeled brown paper lunchbags. Didn't quite finish, but I can see the end now. Rather a lot of work to sift out some 6SN7, 6V6, 5U4, 5Y3 etc. from the 17v damper diodes, 33v compactrons and other crap, but might have found some sellable old-timey radio tubes I'm not very familiar with and won't miss if I sell them.
It's all good -- except the waiting!
I'm recalc'ing the values to use for a crossover... and will use a ~16ohm resistor ACROSS the 2441's to make them look like an 8 ohm load to the crossover -- with the side benefit of making the apparent load look more linear to the amplifier over the frequency range. Crossover will be at ~750 or 800 to match with the Altec 515E for the first round.
But when I first get the horns, I'm going to try the combination on top of the Tannoy GRF-R cabinets with Altec 414, crossing over at 1400-1600. Another nice thing about the 16-ohm driver paralleled with 16 ohm resistor is that I can use that same driver with the crossover I made for the 8 ohm Altec driver and horn now sitting on the Tannoy cabinets. That will give me an easy basis for comparison.
The room with the Tannoys has gotten cluttered with projects, so yesterday I took all the boxes of vacuum tubes, claimed a space in our converted porch room, and spent hours sorting them into labeled brown paper lunchbags. Didn't quite finish, but I can see the end now. Rather a lot of work to sift out some 6SN7, 6V6, 5U4, 5Y3 etc. from the 17v damper diodes, 33v compactrons and other crap, but might have found some sellable old-timey radio tubes I'm not very familiar with and won't miss if I sell them.
It's all good -- except the waiting!
jaymanaa
RIP 1961-2018
Interesting thread Tubino,and what a coincidence. I spent last night listening to horns and sorting tubes too. My living room is tube trashed and the wife isn't very happy.
My brother's coming by to pick up the chaff and sell it on epray. The only complaint I've ever had with my horn setup is in the very high frequencies. It seems as though the 511Bs that I'm using with 902 drivers, just don't want to go way up there. I'm waiting on a set of Emilar horns to show up for a trial run, and also a pair of Heil ribbon tweeters that I may end up adding. The Edgars should be very interesting and I'm looking forward to reading your impression of them. I noticed what you wrote earlier about good bass with minimal cone excursion, and that's what I really like about the big folded horns. I normally run 300Bs that make around 5 or 6 watts, so there is absolutely no chance of heating up a VC enough to change the Z. Nice job of documenting your experiments too, I surely appreciate you sharing your results. For me at least, the horn set up is in a constant state of change. They're just sooooo tweekable.:thmbsp:
My brother's coming by to pick up the chaff and sell it on epray. The only complaint I've ever had with my horn setup is in the very high frequencies. It seems as though the 511Bs that I'm using with 902 drivers, just don't want to go way up there. I'm waiting on a set of Emilar horns to show up for a trial run, and also a pair of Heil ribbon tweeters that I may end up adding. The Edgars should be very interesting and I'm looking forward to reading your impression of them. I noticed what you wrote earlier about good bass with minimal cone excursion, and that's what I really like about the big folded horns. I normally run 300Bs that make around 5 or 6 watts, so there is absolutely no chance of heating up a VC enough to change the Z. Nice job of documenting your experiments too, I surely appreciate you sharing your results. For me at least, the horn set up is in a constant state of change. They're just sooooo tweekable.:thmbsp:
Paul C
Super Member
Tubino: Here is a paper on Transmission Lines, and the effect of damping on the line.
You will notice the graph of the undamped line is VERY similar to the JBL 4530 graph.
http://audiokarma.org/forums/attachment.php?attachmentid=21400&d=1153768442
See page 4 (marked as 4 on bottom of page) and page 13 (marked as 18 on bottom of page) of the pdf document.
The graph of the undamped line is exaggerated. And look at the effect of damping the line.
You will notice the graph of the undamped line is VERY similar to the JBL 4530 graph.
http://audiokarma.org/forums/attachment.php?attachmentid=21400&d=1153768442
See page 4 (marked as 4 on bottom of page) and page 13 (marked as 18 on bottom of page) of the pdf document.
The graph of the undamped line is exaggerated. And look at the effect of damping the line.
tubino
A guy with too many tubes
Thanks, Paul! I will eagerly read this tonight.
What I'm trying to get my head around now is the nature of the non-linearities of a reasonably well-designed straight horn (not BLH or transmission line) that is driven below the lowest frequency gracefully managed by the horn by size.
It seems pretty clear that if it's emptying into no boundaries or one boundary (typically the floor), and not into 1/8th space (corner), the mouth and length dimensions are never* large enough to avoid some impedance mismatch/reflection at 30-40 hertz. The graphs I posted earlier are just one of many I've found on the subject of measuring or modeling horn impedance at the (too) low end, with dimension too low for that frequency, where it goes all goofy, the waves and troughs getting LARGE.
And that's with a straight horn, no cancellation issues. Add the folds and out-of-phase cancellation, and it's a wonder any of them sound as good as they do.
Yet... they do.
Night before last someone called wanting to try his electrostatic panels with the Jensen Imperial boxes. By sheer coincidence, I stumbled on a patent for a hornloaded electrostatic speaker the next day. I'm going to hand him some blank precut baffle boards, and we'll try it out. Will a non-piston design sufficiently compress the air to make the horn work???
In my eagerness to hook the 2441s up to something, I pulled out some big homebrew horns and ribbon tweeters built according to a Speaker Builder article back in the early 90s. I thought I might be able to try the 2441s with those horns -- which is do-able, but would take some cutting and drilling and monkeying... so I think I may try these horn-loaded ribbons instead. I never really gave them a chance since getting them years ago. Maybe it's TIME!
Paul C
Super Member
"Well kids, we hope you are enjoying your tour of Angola.
(Angola is the Louisiana State Prison)
"Next a real treat. Now this is one of those reasons, no, the MAIN reason you kids need to make sure you don't end up here.
"Besides the best prison rodeo in the world, we are also famous for this.
"Heah before you is the famous 'Ole Sparky'. Yep, the 'lectric chair. Many a vile murderer has gone to meet his maker ridin' Ole Sparky.
"No, you don't want to sit yourself down and try it out.
"Zzzzzzzt! Hah! Just kiddin'!"
(Angola is the Louisiana State Prison)
"Next a real treat. Now this is one of those reasons, no, the MAIN reason you kids need to make sure you don't end up here.
"Besides the best prison rodeo in the world, we are also famous for this.
"Heah before you is the famous 'Ole Sparky'. Yep, the 'lectric chair. Many a vile murderer has gone to meet his maker ridin' Ole Sparky.
"No, you don't want to sit yourself down and try it out.
"Zzzzzzzt! Hah! Just kiddin'!"
Steve Mac
New Member
Here's a couple of very nice pdf documents from Jensen
on this much copied speaker design:
Jensen Imperial Tech Bulletin
Jensen Imperial Do-It-Yourself Spec
on this much copied speaker design:
Jensen Imperial Tech Bulletin
Jensen Imperial Do-It-Yourself Spec
tubino
A guy with too many tubes
Impedance mismatching and reflections in horns
Okay, I've been trying to read through Augsburger et al with the goal of understanding the huge-to-small peaks and valleys in impedance due to reflections as you move up in frequency. (See the HornResp graph I posted.) I was going to try to type it up as much for my own learning as anything.
Then I picked up the March 2008 AudioXpress, with the big article "How Horns Work" by Bjorn Kolbrek. The graphs there show it really well, and remember that we're talking about something true of almost ALL BASS HORNS to varying degrees (and frequencies. To minimize reflection in a certain frequency range, make the mouth circumference of an exponential horn at least one wavelength at the cutoff frequency of the horn, so that K(Rm)>=1, where Rm is the radius of the mouth.
Let's try that with a 100hz horn. The wavelength can be calculated with the speed of sound etc., but here’s an on-line calculator:
http://www.mcsquared.com/wavelength.htm
Tells us 100hz = 11.3 feet, or about 136 inches.
Circumference = pi(2R), we’re solving for R, assuming a circumference = 100 hz wavelength = 136 inches, divide by Pi = 43.3 inches for diameter or 2 x radius. Think about that. Three and a half feet of DIAMETER for the mouth of a 100 hz horn to minimize reflections! Double that for 50 hz, and again for 25 hz! For comparison, my 30 cu. ft. Jensen boxes have a mouth size of ~36 inches x 32 = 1152 sq inches= equiv circle size of diameter 38.3 inches, circumference = 120.3 inches = a mere 113 hertz. (Another useful calculator, this time for circle calculations: http://www.csgnetwork.com/circlecalc.html)
That is why I say that it is unfortunately not practical to completely eradicate the reflection problem for BASS horns. Firing into a corner Klipsch-style, though can really help out with the load/impedance matching…
Okay, I've been trying to read through Augsburger et al with the goal of understanding the huge-to-small peaks and valleys in impedance due to reflections as you move up in frequency. (See the HornResp graph I posted.) I was going to try to type it up as much for my own learning as anything.
Then I picked up the March 2008 AudioXpress, with the big article "How Horns Work" by Bjorn Kolbrek. The graphs there show it really well, and remember that we're talking about something true of almost ALL BASS HORNS to varying degrees (and frequencies. To minimize reflection in a certain frequency range, make the mouth circumference of an exponential horn at least one wavelength at the cutoff frequency of the horn, so that K(Rm)>=1, where Rm is the radius of the mouth.
Let's try that with a 100hz horn. The wavelength can be calculated with the speed of sound etc., but here’s an on-line calculator:
http://www.mcsquared.com/wavelength.htm
Tells us 100hz = 11.3 feet, or about 136 inches.
Circumference = pi(2R), we’re solving for R, assuming a circumference = 100 hz wavelength = 136 inches, divide by Pi = 43.3 inches for diameter or 2 x radius. Think about that. Three and a half feet of DIAMETER for the mouth of a 100 hz horn to minimize reflections! Double that for 50 hz, and again for 25 hz! For comparison, my 30 cu. ft. Jensen boxes have a mouth size of ~36 inches x 32 = 1152 sq inches= equiv circle size of diameter 38.3 inches, circumference = 120.3 inches = a mere 113 hertz. (Another useful calculator, this time for circle calculations: http://www.csgnetwork.com/circlecalc.html)
That is why I say that it is unfortunately not practical to completely eradicate the reflection problem for BASS horns. Firing into a corner Klipsch-style, though can really help out with the load/impedance matching…
tubino
A guy with too many tubes
This is what I'm talking about in the post just above:
Plenty of evidence that Paul C is right, that the right damping of a transmission line will reduce the problem of impedance-mismatch reflections causing cancellations/throat impedance variations/lousy FR response, but that's just one special case that can be managed in a certain frequency range. I don't think that is an adequate solution for these problems below say 80 hertz in exponential horns...
Plenty of evidence that Paul C is right, that the right damping of a transmission line will reduce the problem of impedance-mismatch reflections causing cancellations/throat impedance variations/lousy FR response, but that's just one special case that can be managed in a certain frequency range. I don't think that is an adequate solution for these problems below say 80 hertz in exponential horns...
tubino
A guy with too many tubes
Go get the March 2008 AudioXpress for "How Horns W
I finally had a chance today to finish reading that article. It's a great starter piece about horns, and I'm really looking forward to part two.
Once again, it's the March 2008 AudioXpress, and the article is "How Horns Work" by Bjorn Kolbrek.
One very interesting thing is the use of the ratio of the cutoff frequency's wavelength to the horn mouth circumference. I knew what happened when the mouth is considerably smaller than the wavelength, but had never come across data on what happens with the mouth is considerably larger (e.g. circumference is >1.4 x wavelength) for a given length. Turns out it's about as bad as too small.
I had also not come across such a clear explanation of which equations were developed assuming a plane wavefront, which ones with a spherical wavefront, and what difference it makes. I'm still scratching my head about the effect on flare rate between plane and sphere... I thought I understood that using a spherical wave calc, with its greater surface area per horn cross-section area, would increase flare more rapidly. But then Kolbrek says, "But the distance between successive curved wave-fronts increases faster than their areas, so the outer parts of the horn will have a lower cutoff"... and I'm lost.
I finally had a chance today to finish reading that article. It's a great starter piece about horns, and I'm really looking forward to part two.
Once again, it's the March 2008 AudioXpress, and the article is "How Horns Work" by Bjorn Kolbrek.
One very interesting thing is the use of the ratio of the cutoff frequency's wavelength to the horn mouth circumference. I knew what happened when the mouth is considerably smaller than the wavelength, but had never come across data on what happens with the mouth is considerably larger (e.g. circumference is >1.4 x wavelength) for a given length. Turns out it's about as bad as too small.
I had also not come across such a clear explanation of which equations were developed assuming a plane wavefront, which ones with a spherical wavefront, and what difference it makes. I'm still scratching my head about the effect on flare rate between plane and sphere... I thought I understood that using a spherical wave calc, with its greater surface area per horn cross-section area, would increase flare more rapidly. But then Kolbrek says, "But the distance between successive curved wave-fronts increases faster than their areas, so the outer parts of the horn will have a lower cutoff"... and I'm lost.
tubino
A guy with too many tubes
Thanks! By my calculations, if I read this stuff every day for about 3 or 4 years, I *might* be able to see the forest around a particular tree. What I would really like to be able to do is look at a horn design and have a pretty good idea of the trade-offs/compromises and strengths involved -- and how those would change by altering some variables.
I also would like to visit another planet, and go back in time.
Paul C
Super Member
"That is why I say that it is unfortunately not practical to completely eradicate the reflection problem for BASS horns. Firing into a corner Klipsch-style, though can really help out with the load/impedance matching…"
With a corner horn, the room boundaries, that is, floor, walls, and ceiling, are actually part of the horn, and the horn extends out into the room.
With a corner horn, the room boundaries, that is, floor, walls, and ceiling, are actually part of the horn, and the horn extends out into the room.