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2x15" front loaded horn F2B

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Contour Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2020 at 1:24pm
So if I would make design where 10 driver share one mouth I could get same response as 10 boxes of ten times the total size? That would be nice, however it does not work like that, no free lunch. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TribeGut Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2020 at 4:26pm
Originally posted by Contour Contour wrote:

So if I would make design where 10 driver share one mouth I could get same response as 10 boxes of ten times the total size? That would be nice, however it does not work like that, no free lunch. 

I doubt thatLOL but also think that just simulate it as a halve horn is not perfekt.
Would totally appreciate it if you are right because that would mean splitting them in halve and build singles would work so no reason to build doubles. Never the less from experience I am skeptical 
 
with S4=2750

with S4=5000:


Obviously it wouldn't make sense to build Single cabs with a mouth area this big. But making them a bit wider to fit existing cabs would also improve the output, the bigger S4 the better results i get in the simulation. 

Please correct me if I'm wrong, still learning Wacko 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2020 at 4:40pm
two half cabs is exactly the same as one full cab.
if you change the shape of the half cabs you have changed the system so it's going to have different response.
the F2B was designed to be use in multiples.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2020 at 6:39pm
Google the term "bifuricated horn". It will probably give one or two results from this forum (and posts from myself!) but will also give an explanation of the theory behind it.
Chas n Dave : it's like Drum and Bass but with beards.             E=mc² ±3dB
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jazomir Quote  Post ReplyReply Direct Link To This Post Posted: 05 January 2021 at 7:27pm
Originally posted by Contour Contour wrote:

So if I would make design where 10 driver share one mouth I could get same response as 10 boxes of ten times the total size? That would be nice, however it does not work like that, no free lunch. 
Isn't that what Danley does with the Jericho cabs and, for h.f., the paraline lens?
Regards

Jazomir
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2021 at 2:53am
Originally posted by citizensc citizensc wrote:

Originally posted by snowflake snowflake wrote:

when I design something of this scale I usually round all the parts to the nearest 5mm and work from the mouth backwards adjusting all the parts to meet up. just makes it easier when you are cutting as most rulers and tools have their scales clearly marked in 5mm increments - will save a lot of squinting. round angles to 5degrees if possible. and most router depth guages have 3mm increments so make all your rebates either 3mm or 6mm.


This does sound like a good idea, I think i'm just so paranoid about killing the 'magic' of the F2B that is described by people that have experienced it.

If I'm understanding things correctly (and I'm by no means any sort of expert!) I think you are probably right to be paranoid.


Slot loading, presents asymmetric cone loading, which causes the diaphragm to flex significantly. I know this for certain, because powerful strobe lighting was a thing, in the early 90s UK rave scene! Also, I used to periodically rotate the drivers in my 215s through 90 degrees, to stop the diaphragms getting bent too far out of shape. Interestingly, the drivers were mounted with L clamps, so perhaps this practice was foreseen/intended by MA?


My theory (and please do tell if I'm talking shite!) is thus - the flexing of the cone diaphragm is intentional and key to the performance of these cabinets. It has two effects, which fall completely outside the scope, of established, conventional, speaker design principals:

1) The flexing somehow divides the 'effective' circumference of the driver, such that it behaves like a smaller driver, enhancing HF extension. Of course the narrow throat, permits a lower tuning, in a smaller cabinet also. Hence the remarkable, seemingly impossible, bandwidth and efficiency of F2B and similar slot loaded cabinets.

2) The flexing, along a single axis, forces cone breakup into a state, where 2nd/even order harmonics dominate, such that the massive amounts of HD, thus produced, enhances both output and tone, in a way that sounds pleasant. Unlike most other designs, well tuned slot-loaded FLH actually sound better when spanked hard!

With this in mind, it can be seen, that the tuning of the flare is absolutely critical. Because to avoid growling or similar, the HD produced by diaphragm flexing must be kept within the pass-band. And the energy from out-of-band HD, acoustically filtered, has to go somewhere...

Faithful reproduction it isn't...but if it sounds great, who cares!


Incidentally, having read some of your previous posts, about what you are aiming to do with your rig, I think you will find F2B very interesting. 

Its worth me pointing out, that F2 was pretty much the default rig, in the early 90's UK breakbeat hardcore/jungle mega-rave scene. That was IMO, to to this day, the largest single-genre dance scene, that ever existed, with single-arena events of 10K-50K attendance not uncommon, as well as a huge number of smaller events, every weekend. From the mid 90s on, the scene split and fragmented musically, resulting in the multi-arena/festival type formats that are more common today, in the UK at least.

Anyways, eventually Jungle morphed into what we now call Drum and Bass, so I think you can probably see, how that's all relevant, to what you are trying to do Smile


Edited by Sonic the hedge - 14 October 2021 at 3:20am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2021 at 8:32am
Originally posted by Sonic the hedge Sonic the hedge wrote:

Originally posted by citizensc citizensc wrote:

Originally posted by snowflake snowflake wrote:

when I design something of this scale I usually round all the parts to the nearest 5mm and work from the mouth backwards adjusting all the parts to meet up. just makes it easier when you are cutting as most rulers and tools have their scales clearly marked in 5mm increments - will save a lot of squinting. round angles to 5degrees if possible. and most router depth guages have 3mm increments so make all your rebates either 3mm or 6mm.


This does sound like a good idea, I think i'm just so paranoid about killing the 'magic' of the F2B that is described by people that have experienced it.

If I'm understanding things correctly (and I'm by no means any sort of expert!) I think you are probably right to be paranoid.


Slot loading, presents asymmetric cone loading, which causes the diaphragm to flex significantly. I know this for certain, because powerful strobe lighting was a thing, in the early 90s UK rave scene! Also, I used to periodically rotate the drivers in my 215s through 90 degrees, to stop the diaphragms getting bent too far out of shape. Interestingly, the drivers were mounted with L clamps, so perhaps this practice was foreseen/intended by MA?


My theory (and please do tell if I'm talking shite!) is thus - the flexing of the cone diaphragm is intentional and key to the performance of these cabinets. It has two effects, which fall completely outside the scope, of established, conventional, speaker design principals:

1) The flexing somehow divides the 'effective' circumference of the driver, such that it behaves like a smaller driver, enhancing HF extension. Of course the narrow throat, permits a lower tuning, in a smaller cabinet also. Hence the remarkable, seemingly impossible, bandwidth and efficiency of F2B and similar slot loaded cabinets.

2) The flexing, along a single axis, forces cone breakup into a state, where 2nd/even order harmonics dominate, such that the massive amounts of HD, thus produced, enhances both output and tone, in a way that sounds pleasant. Unlike most other designs, well tuned slot-loaded FLH actually sound better when spanked hard!

With this in mind, it can be seen, that the tuning of the flare is absolutely critical. Because to avoid growling or similar, the HD produced by diaphragm flexing must be kept within the pass-band. And the energy from out-of-band HD, acoustically filtered, has to go somewhere...

Faithful reproduction it isn't...but if it sounds great, who cares!


Incidentally, having read some of your previous posts, about what you are aiming to do with your rig, I think you will find F2B very interesting. 

Its worth me pointing out, that F2 was pretty much the default rig, in the early 90's UK breakbeat hardcore/jungle mega-rave scene. That was IMO, to to this day, the largest single-genre dance scene, that ever existed, with single-arena events of 10K-50K attendance not uncommon, as well as a huge number of smaller events, every weekend. From the mid 90s on, the scene split and fragmented musically, resulting in the multi-arena/festival type formats that are more common today, in the UK at least.

Anyways, eventually Jungle morphed into what we now call Drum and Bass, so I think you can probably see, how that's all relevant, to what you are trying to do Smile

not sure about this idea.

I don't think that drivers with particularly flexible cones have been used in designs like these. so there has been no intention to encourage greater cone breakup

I'm not sure breakup modes do give a musically nice amount of second harmonic distortion.

If anything slot loading puts a more even load on a driver. This can allow higher maximum powers through drivers as it stops the cone from ripping at points of exceptional pressure and stops the voice coil rocking and touching the sides of the gap.

Slot loading reduces path length differences in the throat which lead to a cancellation if one side of the driver is further from the horn mouth. This produces a cancellation at a wavelength twice the diameter of the driver which is 450Hz for a 15" driver.

If you did want to produce loads of second harmonic then just add some distortion with an effect unit.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2021 at 8:53am
All horns produce many orders of magnitude more second-order harmonic distortion than they do any other type.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 14 October 2021 at 11:42am
Originally posted by toastyghost toastyghost wrote:

All horns produce many orders of magnitude more second-order harmonic distortion than they do any other type.

a notable thing about the F2B is that its expansion approximates to hyperbolic with T=0 which maximises such throat distortion. there's a useful diagram in Olson showing distortion levels for power/area of an exponential horn but I have never seen the equivalent for a hyperbolic horn. Hornresp can calculate distortion for single segment horns - this suggests changing T from 1 to 0 (and changing the cutoff frequency to keep throat, mouth and length the same) increases distortion by 50%.

also all horns with increasing directivity at higher frequencies are going to concentrate the harmonics more on axis than the fundamental.

a third factor depends on how we think perception of loudness falls off with reducing frequency (big discrepancy between low volume tests with headphones (20db/octave) and high volume tests). second harmonic will be perceived as louder than the fundamental when it is somewhere between approx 1% and 3%. for the F2B this equates very roughly to 50-500 acoustic watts @200Hz.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic the hedge Quote  Post ReplyReply Direct Link To This Post Posted: 15 October 2021 at 2:08pm
Originally posted by snowflake snowflake wrote:

not sure about this idea.

I don't think that drivers with particularly flexible cones have been used in designs like these. so there has been no intention to encourage greater cone breakup

I'm not sure breakup modes do give a musically nice amount of second harmonic distortion.

If anything slot loading puts a more even load on a driver. This can allow higher maximum powers through drivers as it stops the cone from ripping at points of exceptional pressure and stops the voice coil rocking and touching the sides of the gap.

Slot loading reduces path length differences in the throat which lead to a cancellation if one side of the driver is further from the horn mouth. This produces a cancellation at a wavelength twice the diameter of the driver which is 450Hz for a 15" driver.

If you did want to produce loads of second harmonic then just add some distortion with an effect unit.

Originally posted by toastyghost toastyghost wrote:

All horns produce many orders of magnitude more second-order harmonic distortion than they do any other type.

a notable thing about the F2B is that its expansion approximates to hyperbolic with T=0 which maximises such throat distortion. there's a useful diagram in Olson showing distortion levels for power/area of an exponential horn but I have never seen the equivalent for a hyperbolic horn. Hornresp can calculate distortion for single segment horns - this suggests changing T from 1 to 0 (and changing the cutoff frequency to keep throat, mouth and length the same) increases distortion by 50%.

also all horns with increasing directivity at higher frequencies are going to concentrate the harmonics more on axis than the fundamental.

a third factor depends on how we think perception of loudness falls off with reducing frequency (big discrepancy between low volume tests with headphones (20db/octave) and high volume tests). second harmonic will be perceived as louder than the fundamental when it is somewhere between approx 1% and 3%. for the F2B this equates very roughly to 50-500 acoustic watts @200Hz.

All good points - thanks both. It looks like I have totally misunderstood the mechanisms here, but I'm happy to admit, I'm way out of my depth...!

I was struggling to see how cone flexing could not cause HD, because essentially flexing is breakup, just in a different axis. However I can see that if the total volume of air in front of the diaphragm remains the same as the cone flexes, the effect will be neutral. As you pointed out, in fact the flexing will probably help reduce 'conventional' breakup by preventing circular ripples from propagating. Also fully agree, that it will probably help the VC remain linear, both by limiting sideways movement of the suspensions, and by limiting excursion, keeping the VC 'in flux'.

I still think, maybe, there is something funny going on, with distortion/harmonics and/or psycho-acoustics, as you intimated. That's consistent with your analysis above, the other clues being the exceptional performance, from such a small enclosure, and also that MA were always very circumspect with their published specs i.e. 'substantially flat' and no curves published. I guess the only way to find out for sure, would be to measure an actual box.

It seems most people, who have actually heard F2B, agree they sound great. 

So I think it would be very useful, if the mechanisms behind the seemingly ingenious loading technique, were better understood, as that would allow others to create new designs using the same concept. That's obviously something well outside my knowledge and resources, but I think it would be great if someone could work it out. Perhaps it would be instructive, to model some of the earlier 215 designs, to see if any trends could be spotted?

Anyways, thanks for your replies, always learning from this forum.


Edited by Sonic the hedge - 15 October 2021 at 2:29pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 16 October 2021 at 1:47am
Have a look at the Loudspeaker Rocking Modes papers here:
https://www.klippel.de/know-how/literature/papers.html

That’s a term for one form of what you’re describing on the cone motion.

Throat compression is pretty well understood in the theory; Kolbrek & Dunker’s book is the best one-stop resource for this (and most other horn things). What hasn’t been analysed in detail as yet is the non-adiabatic effects of non-linear distortion of the air itself when horn throats are driven to high levels. I’ve seen one study that built an example setup to test this properly, but further work hasn’t been done.

Contrary to what many seem to think, inverse distance law applies inside the horn too!

As an example, I (shoddily) built some poplar scale model horns recently. I measured 137 dB linear peak at the throat, driven with a 2 Volts peak log sine sweep. That’s bloody loud, but more importantly, a 30 dB increase in level is well into the point where the air itself is distorting even if the driver or amp isn’t.

However, we seem to tolerate - or even prefer - some types of distortion much more than others.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 19 October 2021 at 2:37am
^Interesting, 
Cheers
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