It's going to be a straight horn. I'm just trying to find a reasonable mouth area for the horn to be able to play 20 hz. 11 sq. meters is a little to large for my liking. It sounds like a pipe dream but I'm confident in my building skills. I might give the Dayton Audio PA subwoofer a shot. Nobody talks about that driver and it seems well priced.
Hi,
if you are prepared to accept an enormous ripple in the low end response then you can truncate the horn even more.
I quoted other experiences of 60% but you could try more reduction in area. But do not change the flare rate.
If the truncation is too much you can very easily add on a mouth extender to increase the horn length and mouth area, sticking to the original flare rate.
For outdoor use and one boundary loading the physics predicts the mouth size, but your ears may accept less than optimum.
if you are prepared to accept an enormous ripple in the low end response then you can truncate the horn even more.
I quoted other experiences of 60% but you could try more reduction in area. But do not change the flare rate.
If the truncation is too much you can very easily add on a mouth extender to increase the horn length and mouth area, sticking to the original flare rate.
For outdoor use and one boundary loading the physics predicts the mouth size, but your ears may accept less than optimum.
Yeah, could you maybe summarize what you said about downsizing the horn in the previous post? It kind of confused me 
I understood some of it but I might need some more clarification. I think building mouth extender(s) would be easy to make also.
Didn't the 6090 horn only have 2.8 square meters of area or did I read a typo? I've calculated about 10+ square meters. That's huge!!!
I understood some of it but I might need some more clarification. I think building mouth extender(s) would be easy to make also.Didn't the 6090 horn only have 2.8 square meters of area or did I read a typo? I've calculated about 10+ square meters. That's huge!!!
Hi Wink,
you seem to need more reading. Download some design articles on horn DESIGN.
He did say 2.88 square m and no-one queried that at the time, but he also said and bass wings without an indication of size.
It's difficult to judge sizes when looking at the photos but 1mhigh and 2.88m wide could be about right.
Floor loading takes it to an effective 5.8sqm plus wings.
Note, how he emphasises length repeatedly. He is effectively telling us not to reduce the flare rate. To get a smooth 16Hz to 18Hz he needs a flare rate for half an octave below this. So it appears he has designed his flare to about 12Hz and this is why he has ended up at 8.8m long but starting with his small throat.
I think he is also confirming that a very large truncation works if the flare is maintained.
Email him and ask him to confirm some numbers/design.
you seem to need more reading. Download some design articles on horn DESIGN.
He did say 2.88 square m and no-one queried that at the time, but he also said and bass wings without an indication of size.
It's difficult to judge sizes when looking at the photos but 1mhigh and 2.88m wide could be about right.
Floor loading takes it to an effective 5.8sqm plus wings.
Note, how he emphasises length repeatedly. He is effectively telling us not to reduce the flare rate. To get a smooth 16Hz to 18Hz he needs a flare rate for half an octave below this. So it appears he has designed his flare to about 12Hz and this is why he has ended up at 8.8m long but starting with his small throat.
I think he is also confirming that a very large truncation works if the flare is maintained.
Email him and ask him to confirm some numbers/design.
From a practical point of view, you may consider using several smaller horns with loading down to 50Hz, say four, and rely on mutual coupling and maybe reflex loading of the back chamber for the bottom octave. The main advantage of that approach is reduced size, increased SPL in the 50Hz to 250Hz critical range, and clean output up to much higher frequencies.
I'm definately no horn expert here, but I researched bass horns a little some time ago, and wrote up some of what I found in wiki pages. I have a few suggestions.
First, I would use a rear compression chamber. This is basically a sealed box so that on one side of the driver you have this chamber, and on the other, the horn. I suggest it for 2 reasons:
1. smoother response (you can model the effect in hornresp and you probably won't like it - the default display assumes there is a chamber, but if you use the tool to show rear driver output as well, it gets ugly)
2. driver excursion below fc is controlled - otherwise you may bottom the driver - it might only move a few mm most of the time, then some deep bass comes in below horn loading and the driver moves like crazy
Regarding drivers I'd consider something like the Lab horn drivers. I've tried modelling many different drivers, and my AE speakers AV12 drivers (2nd run - older version than current) model better than anything I've found. In fact I'd try a pair of either 12" or 15" sub drivers with high excursion and high thermal power handling. For some reason two seem to model much better.
I'd also consider a mounting method very similar to the Lab horn. Make it so the two drivers operate in symmetrically opposite directions. This will cancel the forces and reduce box vibration. This reduces the need for thick walls and extensive bracing. I've found with other boxes it makes a HUGE difference. A box that would otherwise be too thin and vibrate too much suddenly becomes ok.
I'd also suggest thinking again about folding it to keep it to a more sane size.
Regarding the box, you might want to consider building it in segments which are bolted together. That way it can be moved with less than 100 people helping you.
If you did make a straight horn, then I'd suggest you could look at curving the walls to make them lighter yet still rigid. Make an internal brace and cut it with the jigsaw. This can form a template to then bend the walls that will curve. Done this way, you would end up with a series of straight segments each with curved walls. Instead of using 18mm ply you could use say 9mm if there is enough curve to it. Another interesting way to approach it would be some kind of composite panel - 3mm MDF + sheet metal, or even heavy cardboard (to get the shape) with fibreglass layed over it for strength.
First, I would use a rear compression chamber. This is basically a sealed box so that on one side of the driver you have this chamber, and on the other, the horn. I suggest it for 2 reasons:
1. smoother response (you can model the effect in hornresp and you probably won't like it - the default display assumes there is a chamber, but if you use the tool to show rear driver output as well, it gets ugly)
2. driver excursion below fc is controlled - otherwise you may bottom the driver - it might only move a few mm most of the time, then some deep bass comes in below horn loading and the driver moves like crazy
Regarding drivers I'd consider something like the Lab horn drivers. I've tried modelling many different drivers, and my AE speakers AV12 drivers (2nd run - older version than current) model better than anything I've found. In fact I'd try a pair of either 12" or 15" sub drivers with high excursion and high thermal power handling. For some reason two seem to model much better.
I'd also consider a mounting method very similar to the Lab horn. Make it so the two drivers operate in symmetrically opposite directions. This will cancel the forces and reduce box vibration. This reduces the need for thick walls and extensive bracing. I've found with other boxes it makes a HUGE difference. A box that would otherwise be too thin and vibrate too much suddenly becomes ok.
I'd also suggest thinking again about folding it to keep it to a more sane size.
Regarding the box, you might want to consider building it in segments which are bolted together. That way it can be moved with less than 100 people helping you.
If you did make a straight horn, then I'd suggest you could look at curving the walls to make them lighter yet still rigid. Make an internal brace and cut it with the jigsaw. This can form a template to then bend the walls that will curve. Done this way, you would end up with a series of straight segments each with curved walls. Instead of using 18mm ply you could use say 9mm if there is enough curve to it. Another interesting way to approach it would be some kind of composite panel - 3mm MDF + sheet metal, or even heavy cardboard (to get the shape) with fibreglass layed over it for strength.
Andy Westcott said:
the PD1850 is a seriously good driver but you'll be limited on the lower frequency to around 25Hz (0.8 of Fs)
the PD2150 having an Fs of 22Hz will net you ~18Hz as well as having a larger displacement
i definately second pauls recommendation of a rear chamber as air cushion loading acts as a much better suspension than the drivers spider
somethings to consider regarding bass horn design:
horn length controls the lowest frequency it will produce whilst the mouth area controls the spl at that frequency
a rear chamber in tandem with the horn length and mouth area will provide 'reactance annulling' effectively smoothing the lowend response and giving a 'hard' knee around Fc thereby controlling the drivers excursion
the size of the rear chamber also effects the lowend response by messing around with the effective Fs of the driver
carefully choosing your volume here can usably lower it to 0.8 without detriment to the driver
a front chamber acts as a lowpass filter and will greatly smooth your upper response
when all areas are working in tandem you should be able to design yourself a horn with a 'bandpass' looking response curve
I have tried hornresp using back chamber and without.synergy said:
I have never been able to achieve a low frequency response with a back chamber.
Is there a method for selecting a range of back chamber volumes that is close to the correct value to get this reactance nulling that so many talk about.
I fear my stabbing in the dark at various volumes misses the correct setting and so I never see the low response nor the smooth low phase attributable to this design method.
My cluster of four Lab subs do quite well outdoors.
Had a "bass" complaint from four miles away once on an overcast night.
http://www.prosoundweb.com/lsp/
Had a "bass" complaint from four miles away once on an overcast night.
http://www.prosoundweb.com/lsp/
Hi,
what did Madonna have in Leeds about 16years ago?
But it wasn't just the low bass that travelled the twelve miles or so to Harewood that night. I could make out the songs at that distance that night, maybe the wind was in my favour, (yes I am a closet Madonna fan - but don't tell anyone).
what did Madonna have in Leeds about 16years ago?
But it wasn't just the low bass that travelled the twelve miles or so to Harewood that night. I could make out the songs at that distance that night, maybe the wind was in my favour, (yes I am a closet Madonna fan - but don't tell anyone).
danielm said:
Probably the result of a very low altitude inversion layer.
The sound bounced between the ground and the bottom of the inversion layer instead of expanding equally in all directions (including upwards) and dissipating naturally.
Easy to check if an inversion layer exists as the smoke from chimneys drifts horizontally despite a lack of wind.
Bass carries well because there is little natural damping at low frequencies.
Elephants, Whales and some other large mammals have deep voices to carry over great distances.
Very low frequencies can hug the ground and can travel several times round the globe. (Google for infrasonic listening posts for nuclear tests)
But you knew all this anyway.
Thats pretty close to the labhorns cutoff. If you have ~$1800 for drivers then 6 labs would do pretty well outside for garden parties 
Admittedly the amplification would cost some.....
Looking forwards to seeing some progress reports - not enough building going on in the subs section lately
Cheers,
Rob.
Admittedly the amplification would cost some.....Looking forwards to seeing some progress reports - not enough building going on in the subs section lately
Cheers,
Rob.
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