Hi GM,
Most stuff easily available here is the modern pro stuff. JBL, Beyma, B&C, etc. Not much vintage stuff. I have been looking for a pair of jbl 2440's to play with.
Altec stuff hardly ever comes up. I am planning to import from JamminJersey when I'm ready to get the drivers. I bought my LE5 drivers from US ebay as they don't come up often here. Will probably get the 2440's at the same time.
Cheers,
Rob.
Most stuff easily available here is the modern pro stuff. JBL, Beyma, B&C, etc. Not much vintage stuff. I have been looking for a pair of jbl 2440's to play with.
Altec stuff hardly ever comes up. I am planning to import from JamminJersey when I'm ready to get the drivers. I bought my LE5 drivers from US ebay as they don't come up often here. Will probably get the 2440's at the same time.
Cheers,
Rob.
Greets!
Try some used B&C DE250 (or new if they're cheap enough) and use the Altec 20472-2 or other's 1" i.d. x 0.71" thick high density cardboard gasket if available. Otherwise you'll have to make your own. Most folks either don't realize how critical a smooth driver/horn transition joint is required for best performance or don't care, figuring they can EQ it.
FWIW, the ones that I was forced to sell had close tolerance DIY metal shims, then the assemblies were align honed. Final assembly included waxed paper gaskets. There's a reason the original compression horn designers used no initial expansion in the driver and a flange collar joint to the horn.
GM
Try some used B&C DE250 (or new if they're cheap enough) and use the Altec 20472-2 or other's 1" i.d. x 0.71" thick high density cardboard gasket if available. Otherwise you'll have to make your own. Most folks either don't realize how critical a smooth driver/horn transition joint is required for best performance or don't care, figuring they can EQ it.
FWIW, the ones that I was forced to sell had close tolerance DIY metal shims, then the assemblies were align honed. Final assembly included waxed paper gaskets. There's a reason the original compression horn designers used no initial expansion in the driver and a flange collar joint to the horn.
GM
Hi GM,
I should have mentioned I have a pair of Beyma 380 1" cd's. They are recomended to go down to 800Hz. I thought that modern drivers wouldn't get down to the 500Hz xo point that the old Altecs do?
Luckily my job is making press tools for cutting gaskets etc so that won't be a problem.
Cheers,
Rob.
I should have mentioned I have a pair of Beyma 380 1" cd's. They are recomended to go down to 800Hz. I thought that modern drivers wouldn't get down to the 500Hz xo point that the old Altecs do?
Luckily my job is making press tools for cutting gaskets etc so that won't be a problem.
Cheers,
Rob.
Greets!
Well, like most things, it depends.
The 1" WE 755 that the original 1" Altec and JBL drivers are derived from went to 50 Hz, but it took a ~8 ft^2 mouth/15 ft pathlength and the same basic Altecs of yesteryear were only rated to 500 Hz, then increased to 800 Hz, then to 1 kHz in more recent times due to one thing, the same thing that keeps todays 1" from going lower, and that's the rear loading cap's Vb kept shrinking to allow the driver to handle increasingly more power as it became readily available with the trade-off being a higher Fc.
Either replace it with a larger Vb rear cover or gap the exisitng one as required and the typical 'humped' response flattens out/LF lifts up for a flatter response over a wider BW at the expense of LF power handling. No 'free lunch' and obviously not acceptable for PA since it drops to typically 30-35 W peak/500 Hz, but fine for all but the most extreme HIFI apps.
No personal experience with the Beyma, but these are all basically the same design concept, so I don't see why it wouldn't work unless you're either half deaf and/or one serious Punk Rock 'headbanger'. Anyway, since you have the parts and some DIY skills it'll give you another project to keep you busy during the Winter.
GM
Well, like most things, it depends.
The 1" WE 755 that the original 1" Altec and JBL drivers are derived from went to 50 Hz, but it took a ~8 ft^2 mouth/15 ft pathlength and the same basic Altecs of yesteryear were only rated to 500 Hz, then increased to 800 Hz, then to 1 kHz in more recent times due to one thing, the same thing that keeps todays 1" from going lower, and that's the rear loading cap's Vb kept shrinking to allow the driver to handle increasingly more power as it became readily available with the trade-off being a higher Fc. Either replace it with a larger Vb rear cover or gap the exisitng one as required and the typical 'humped' response flattens out/LF lifts up for a flatter response over a wider BW at the expense of LF power handling. No 'free lunch' and obviously not acceptable for PA since it drops to typically 30-35 W peak/500 Hz, but fine for all but the most extreme HIFI apps.
No personal experience with the Beyma, but these are all basically the same design concept, so I don't see why it wouldn't work unless you're either half deaf and/or one serious Punk Rock 'headbanger'. Anyway, since you have the parts and some DIY skills it'll give you another project to keep you busy during the Winter.
GM
Recently I've discovered the value of back to back driver mounting which is used in the Lab horn to reduce box vibration. I discussed this in another thread:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=87520
I have a new design which uses both back to back mounting and push pull, like Wayne Parhams 12pi horn.
I think this new design is more interesting in terms of looks, not quite "form follows function," but more of a "form expresses function" design.
The bottom part is an audio rack, with cutouts for source componets. On the right is the sealed chamber for the drivers with a port hole to show the driver. This is for two reasons:
1. I want to see the driver excursion for safety (probably not really necessary but I like to know)
2. I have a hard time giving up seeing these drivers - they look great
On the left hand side is another concealed rack, probably with pull out drawers. Audio stuff is kept from prying fingers, and its all quite neat.
The screen pulls down and you can see most of the horn. I'd probably build it in a few parts which can be assembled - perhaps three. I think this new design could be made more solid.
Now for some more detail. This is a section showing the push pull part:
The driver section is based on an accurately measured model, although I had to guess the pole piece (and it's not likely I got it right).
Unlike most bass horns, I'd like to actually curve as shown for 2 reasons:
1. I like the look
2. Stiffness
I realise it could be faceted with no acoustic penality.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=87520
I have a new design which uses both back to back mounting and push pull, like Wayne Parhams 12pi horn.
I think this new design is more interesting in terms of looks, not quite "form follows function," but more of a "form expresses function" design.
An externally hosted image should be here but it was not working when we last tested it.
The bottom part is an audio rack, with cutouts for source componets. On the right is the sealed chamber for the drivers with a port hole to show the driver. This is for two reasons:
1. I want to see the driver excursion for safety (probably not really necessary but I like to know)
2. I have a hard time giving up seeing these drivers - they look great
On the left hand side is another concealed rack, probably with pull out drawers. Audio stuff is kept from prying fingers, and its all quite neat.
The screen pulls down and you can see most of the horn. I'd probably build it in a few parts which can be assembled - perhaps three. I think this new design could be made more solid.
Now for some more detail. This is a section showing the push pull part:
An externally hosted image should be here but it was not working when we last tested it.
The driver section is based on an accurately measured model, although I had to guess the pole piece (and it's not likely I got it right).
Unlike most bass horns, I'd like to actually curve as shown for 2 reasons:
1. I like the look
2. Stiffness
I realise it could be faceted with no acoustic penality.
Just out of curiosity, I decided to work out how many sealed subs using the same driver would be needed to match the output at 20 Hz. I was a little surprised. This horn with two 12" drivers (AV12) with an xmax of 23mm has a maximum SPL of 140 db @ 20 Hz. A rumble filter is required, otherwise the max SPL is only 135 db. 140 db only requires 800 watts.
To achieve the same output with the drivers in a sealed box, how many do I need and how much power? I need around 64 drivers! That is 147L of displacement!
The power required is a killer at 50 kw!
So the sealed sub requires around 60x the power and 64x the displacement. The size of the subs combined would be 2240L (approx 35L each which is quite small). In other words, the small sealed subs are around the same size but need more power and cost a lot more.
Let's look at it in terms of cost.
Drivers cost AU $320 each.
Behringer EP2500 ~$600
Material cost about the same so won't be included.
The horn version costs $1240 + cost of the box >>> $1,600
Sealed version
64 Drivers: $20,480
20 Amps: $12,000
>>> $33,000
In other words, the sealed version costs 20x as much!
Of course, the sealed version has one nice feature - a wall of subwoofers could look great!
Now I wonder why more don't think seriously about doing a bass horn.
To achieve the same output with the drivers in a sealed box, how many do I need and how much power? I need around 64 drivers! That is 147L of displacement!
The power required is a killer at 50 kw!
So the sealed sub requires around 60x the power and 64x the displacement. The size of the subs combined would be 2240L (approx 35L each which is quite small). In other words, the small sealed subs are around the same size but need more power and cost a lot more.
Let's look at it in terms of cost.
Drivers cost AU $320 each.
Behringer EP2500 ~$600
Material cost about the same so won't be included.
The horn version costs $1240 + cost of the box >>> $1,600
Sealed version
64 Drivers: $20,480
20 Amps: $12,000
>>> $33,000
In other words, the sealed version costs 20x as much!
Of course, the sealed version has one nice feature - a wall of subwoofers could look great!
Now I wonder why more don't think seriously about doing a bass horn.
You're fun, but silly
I have four 18" woofers in two 15 cu.ft. enclosures in my great-room. The room measures 25 feet by 25 feet with 13 foot ceilings. I can literally shake the table cloth on a nearby table. During deep bass passages, the air around me feels as if I turned on a small fan! The first train scene in Polar Express brought about a great deal of excitement in my household!
I run a Behringer Europower 2500 with the Ultra-Curve EQ. There's about 600 watts available per channel with a four ohm load.
The woofers cost me $90.00 each from Mach 5 Audio. The amp cost me $300.00. The UltraCurve was around $140.00 on EBay. The plywood was free scraps from a job-site. Now that's a lot of entertainment for $800.00!!!
Your horn is a wonderful experiment, but unless you're loading a stadium, you're simply delighting your mind with an exciting, but self indulgent hobby. I'm all for exciting and self-indulgent hobbies!
John:
I have four 18" woofers in two 15 cu.ft. enclosures in my great-room. The room measures 25 feet by 25 feet with 13 foot ceilings. I can literally shake the table cloth on a nearby table. During deep bass passages, the air around me feels as if I turned on a small fan! The first train scene in Polar Express brought about a great deal of excitement in my household!
I run a Behringer Europower 2500 with the Ultra-Curve EQ. There's about 600 watts available per channel with a four ohm load.
The woofers cost me $90.00 each from Mach 5 Audio. The amp cost me $300.00. The UltraCurve was around $140.00 on EBay. The plywood was free scraps from a job-site. Now that's a lot of entertainment for $800.00!!!
Your horn is a wonderful experiment, but unless you're loading a stadium, you're simply delighting your mind with an exciting, but self indulgent hobby. I'm all for exciting and self-indulgent hobbies!
John:
paulspencer said:
Make sure you double check what pressure that glass is going to see. A horn decreases the swept volume required by increasing the pressure the cone must exert, right? It seems to me that if you see 140 dB at the horn mouth, you would probably get significantly higher (160+) inside that sealed chamber.
I'm sure you can figure out on your own how to keep the glass from breaking, but I just thought I'd chime in and say that I think it's an issue.
John there is something I like about extreme sub designs! I have seen those drivers you are talking about - are they musical?
I have ultracurve and EP2500 (great minds think alike). For this bass horn with a rumble filter running I can get 140 db @ 1m with just 400w from each channel, so in reality the fanless A500 amp would be more than enough. But I like the EP2500 so much I don't like the idea of getting rid of it and may even find another use, or put it in another room to get around fan noise.
In my current similar room (to the one I have in mind for this design), listening position SPL is about 9db down from the 1m SPL, so it follows the -6db/double distance rule perfectly, confirmed by measurements. I listen at 3m.
So to get 120 db I need 130 db @ 1m. That gives me 10db headroom, which is a nice number to have, and I doubt I'm crazy enough to go past that. My mains would need serious upgrading to keep up. I have found that I'm quite happy to have the subs 10db louder, so the mains would need to be 110 db @ 3m and 119 db @ 1m. They can squeeze out about 95 db @ 3m but at that they have lost their finesse so I'll need to get at least 15 db more output and lower distortion to pull it off.
One thing that is interesting about the newer version of hornresp is that it shows GD,and the plots are unlike any I've seen for a sealed or vented box. It goes all over the place - on average lower than a vented box but will NEGATIVE GD in places with big peaks and dips.
I have ultracurve and EP2500 (great minds think alike). For this bass horn with a rumble filter running I can get 140 db @ 1m with just 400w from each channel, so in reality the fanless A500 amp would be more than enough. But I like the EP2500 so much I don't like the idea of getting rid of it and may even find another use, or put it in another room to get around fan noise.
In my current similar room (to the one I have in mind for this design), listening position SPL is about 9db down from the 1m SPL, so it follows the -6db/double distance rule perfectly, confirmed by measurements. I listen at 3m.
So to get 120 db I need 130 db @ 1m. That gives me 10db headroom, which is a nice number to have, and I doubt I'm crazy enough to go past that. My mains would need serious upgrading to keep up. I have found that I'm quite happy to have the subs 10db louder, so the mains would need to be 110 db @ 3m and 119 db @ 1m. They can squeeze out about 95 db @ 3m but at that they have lost their finesse so I'll need to get at least 15 db more output and lower distortion to pull it off.
One thing that is interesting about the newer version of hornresp is that it shows GD,and the plots are unlike any I've seen for a sealed or vented box. It goes all over the place - on average lower than a vented box but will NEGATIVE GD in places with big peaks and dips.
Hi Paul,
Just a quick note and I'll chat more later. The Mach 5 Audio 8 ohm, 18 inch drivers are very sweet sounding, much prettier than my bass horn. I use the ultracurve to kill anything over 80hz, along with the x-over in the sub-out port on my receiver.
They move so much air that I can feel a breeze during heavy bass effects, and they're 18 feet away! Just amazing!
Yes, sharp mind do think alike.
Your horn is a great passion, I'd never want to discourage you. It's just that I've done that shtick and find four 18s more than sufficient to make my jaw drop!
John
Just a quick note and I'll chat more later. The Mach 5 Audio 8 ohm, 18 inch drivers are very sweet sounding, much prettier than my bass horn. I use the ultracurve to kill anything over 80hz, along with the x-over in the sub-out port on my receiver.
They move so much air that I can feel a breeze during heavy bass effects, and they're 18 feet away! Just amazing!
Yes, sharp mind do think alike.
Your horn is a great passion, I'd never want to discourage you. It's just that I've done that shtick and find four 18s more than sufficient to make my jaw drop!
John
Update on plans
Well, I've dusted off my plans for this beast. In 2 months I'll have room I designed this for.
The driver may not be my AV12s powerd by Behringer EP2500. I will also try two Rythmik DS12 kits. The manifold will be bolted in so that I can easily swap the drivers/amps.
Building this horn is a big challenge. I'm breaking it down into segments bolted together. I need to be able to carry them, paint them, get them through doors, etc.
View of the new design:
3 segments are shown
3 is part of the rack (concealed
2 is bolted on to the shelf of the rack
then 1 is jacked up and attached to the rack, and bolted at the collar
The corner extends the effective mouth size and horn length, as shown below:
Plan view, horn in green
The red dotted line shows the biggest mouth hornresp will model. The dashed red line shows the extension I think is most realistic, since beyond this point, the void in the centre of the horn means it will expand more rapidly.
This is a sketch of how I plan to do the manifold:
As you can see, driver are push pull. Large throat chambers seem to stuff it up in hornresp, so I've made it as small as it can be (shaded area). The tapered section similar to the Lab sub is there to correct the aspect ratio, and is part of the horn length. Not shown, but the sealed chamber is one, not two. There will be some kind of port hole, also for attaching driver. Either glass or many layers of perspex. Manifold is 36mm thick and baffle 52mm. The rest of the horn 18mm.
Hornresp sims to come ...
Well, I've dusted off my plans for this beast. In 2 months I'll have room I designed this for.
The driver may not be my AV12s powerd by Behringer EP2500. I will also try two Rythmik DS12 kits. The manifold will be bolted in so that I can easily swap the drivers/amps.
Building this horn is a big challenge. I'm breaking it down into segments bolted together. I need to be able to carry them, paint them, get them through doors, etc.
View of the new design:
An externally hosted image should be here but it was not working when we last tested it.
3 segments are shown
3 is part of the rack (concealed
2 is bolted on to the shelf of the rack
then 1 is jacked up and attached to the rack, and bolted at the collar
The corner extends the effective mouth size and horn length, as shown below:
Plan view, horn in green
An externally hosted image should be here but it was not working when we last tested it.
The red dotted line shows the biggest mouth hornresp will model. The dashed red line shows the extension I think is most realistic, since beyond this point, the void in the centre of the horn means it will expand more rapidly.
This is a sketch of how I plan to do the manifold:
An externally hosted image should be here but it was not working when we last tested it.
As you can see, driver are push pull. Large throat chambers seem to stuff it up in hornresp, so I've made it as small as it can be (shaded area). The tapered section similar to the Lab sub is there to correct the aspect ratio, and is part of the horn length. Not shown, but the sealed chamber is one, not two. There will be some kind of port hole, also for attaching driver. Either glass or many layers of perspex. Manifold is 36mm thick and baffle 52mm. The rest of the horn 18mm.
Hornresp sims to come ...
I did some calcs on the weight.
18mm MDF weighs ~ 40kg per 1.2 x 2.4m sheet
or about 15 kg/m2
I estimate I'll need about 4 sheets (rough guess)
so probably about 200 kg including the shelving
So now I've done the sims on hornresp as four straight segments, the last segment is the corner extension from the mouth to the (guessed) effective mouth (red dashed line in prev diagram). Not quite as smooth as the ideal looking curves I get when I just put in the throat and mouth areas, but not bad.
As you can see, the response is dominated by the horn rather than the drivers.
Excursion:
As you can see, given the correct amount of power, they are almost identical. The Rythmik driver exceeds xmax but the bass extension filters should correct this. Its xmech is actually 33mm so its amplifier can't bottom the driver no matter what the signal. There is an 11mm safety margin (one way). AV12 is just at its xmax without filtering.
Group delay is interesting:
For comparison, I modelled AV12 in a vented box to get -3db points at 20 and 65 Hz. Group delay rises from 10ms @ 65 Hz to 20ms @ 40 Hz then peaking at 90ms @ 18 Hz - the rumble filter stuffs that up. Without it, GD drops down about 20 ms.
A sealed box version has about 17 ms @ 20 Hz if no rumbe filter is used, but now we are down to only about 100 dB!
What I find curious is negative GD! I didn't know it existed.
Here are the hornresp data entered:
18mm MDF weighs ~ 40kg per 1.2 x 2.4m sheet
or about 15 kg/m2
I estimate I'll need about 4 sheets (rough guess)
so probably about 200 kg including the shelving
So now I've done the sims on hornresp as four straight segments, the last segment is the corner extension from the mouth to the (guessed) effective mouth (red dashed line in prev diagram). Not quite as smooth as the ideal looking curves I get when I just put in the throat and mouth areas, but not bad.
An externally hosted image should be here but it was not working when we last tested it.
As you can see, the response is dominated by the horn rather than the drivers.
Excursion:
An externally hosted image should be here but it was not working when we last tested it.
As you can see, given the correct amount of power, they are almost identical. The Rythmik driver exceeds xmax but the bass extension filters should correct this. Its xmech is actually 33mm so its amplifier can't bottom the driver no matter what the signal. There is an 11mm safety margin (one way). AV12 is just at its xmax without filtering.
Group delay is interesting:
An externally hosted image should be here but it was not working when we last tested it.
For comparison, I modelled AV12 in a vented box to get -3db points at 20 and 65 Hz. Group delay rises from 10ms @ 65 Hz to 20ms @ 40 Hz then peaking at 90ms @ 18 Hz - the rumble filter stuffs that up. Without it, GD drops down about 20 ms.
A sealed box version has about 17 ms @ 20 Hz if no rumbe filter is used, but now we are down to only about 100 dB!
What I find curious is negative GD! I didn't know it existed.
Here are the hornresp data entered:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi Paul,
I see you have entered corner loading using 0.5*Pi.
Is it correct to then expand the horn mouth out from the corner?
That is defeating the loading that Hornresponse is using.
I think you are right to take account of the expansion from physical mouth upto the corner, but not on the way back out.
70kgs on a trolley should be quite manageable, but how wide (front to back) have you made it?
Re=1r49? Is that 2r98//2r98?
I see you have entered corner loading using 0.5*Pi.
Is it correct to then expand the horn mouth out from the corner?
That is defeating the loading that Hornresponse is using.
I think you are right to take account of the expansion from physical mouth upto the corner, but not on the way back out.
70kgs on a trolley should be quite manageable, but how wide (front to back) have you made it?
Re=1r49? Is that 2r98//2r98?
Andrew, thanks for bringing that up. I have wondered that previously about the corner. Correct me if I'm wrong.
I believe it works like this:
When specified as corner loaded, it considers that outside the mouth, radiation angle is confined to eigth space, but this will not increase the effective length in my understanading. Since I'm considering that the walls will effectively extend the horn length and increase mouth size to a certain point, I think those numbers fit. Beyond that it will radiate into eigth space until it hits the diagonal of the room, then it will be more constrained.
Now lets say it was not running floor to ceiling. In that case I couldn't include any of the room in the simulation since the vertical expansion stuffs it up.
I could be wrong. Feel free to argue that I've done it wrong. William Cowan brought this up earlier, apparently one of his horns extended lower than the hornresp model and he puts it down to this. Room gain. His comments lead me in that direction.
If I am wrong, I hope I find out before I build it! Still, the design doesn't fall apart in this case, since it still models fine without the extra extension. The main difference is in the smoothness.
I think I'll have parts heavier than 70 kg. I hope to keep them under 80 kg. Depth is ~500mm (I might have to make it slightly more so the manifold isn't so tight.)
I believe it works like this:
When specified as corner loaded, it considers that outside the mouth, radiation angle is confined to eigth space, but this will not increase the effective length in my understanading. Since I'm considering that the walls will effectively extend the horn length and increase mouth size to a certain point, I think those numbers fit. Beyond that it will radiate into eigth space until it hits the diagonal of the room, then it will be more constrained.
Now lets say it was not running floor to ceiling. In that case I couldn't include any of the room in the simulation since the vertical expansion stuffs it up.
I could be wrong. Feel free to argue that I've done it wrong. William Cowan brought this up earlier, apparently one of his horns extended lower than the hornresp model and he puts it down to this. Room gain. His comments lead me in that direction.
If I am wrong, I hope I find out before I build it! Still, the design doesn't fall apart in this case, since it still models fine without the extra extension. The main difference is in the smoothness.
I think I'll have parts heavier than 70 kg. I hope to keep them under 80 kg. Depth is ~500mm (I might have to make it slightly more so the manifold isn't so tight.)
Hi,
WC's results confirm some kind of room gain.
I don't have a formula for that, but it does depend on sealing/stiffness of room walls as well as total cone area and room volume.
With a horn, is the total cone area equivalent to the mouth area? It's certainly the area that moves the room air!
Now, do a leaky room gain calculation with that equivalent area and there will be room gain. Even the Japanese paper walls probably have room gain if that applies. I wonder if that is part of the reason the Japanese import so many of Tannoy's Westminsters?
If room gain were the reason for the truncated horns performing better than the models, then discount the extra length and just ensure your minimum length (cone to corner) is longer than the half wavelength or quarter wavelength if you are short. I don't know what happens between these two lengths, is it extra ripple or fall off in sensitivity?
I see the logic that due to the horn filling room height, the Pi/2 loading is incorrect, that must be similar to a line array that falls off @ half the rate with distance, so maybe you are more right.
But if Pi/2 does not apply, what do you substitute instead?
WC's results confirm some kind of room gain.
I don't have a formula for that, but it does depend on sealing/stiffness of room walls as well as total cone area and room volume.
With a horn, is the total cone area equivalent to the mouth area? It's certainly the area that moves the room air!
Now, do a leaky room gain calculation with that equivalent area and there will be room gain. Even the Japanese paper walls probably have room gain if that applies. I wonder if that is part of the reason the Japanese import so many of Tannoy's Westminsters?
If room gain were the reason for the truncated horns performing better than the models, then discount the extra length and just ensure your minimum length (cone to corner) is longer than the half wavelength or quarter wavelength if you are short. I don't know what happens between these two lengths, is it extra ripple or fall off in sensitivity?
I see the logic that due to the horn filling room height, the Pi/2 loading is incorrect, that must be similar to a line array that falls off @ half the rate with distance, so maybe you are more right.
But if Pi/2 does not apply, what do you substitute instead?
If pi/2 doesn't work at least from the mouth of the physical horn, then I'm stuffed! Actually, it's still useable, but a bit more peaky, and 20 - 30 Hz drops down a bit lower.
A factor to consider is that the floor is ~ 19mm pine strip flooring, and walls are timber framed 10mm plasterboard. The outside cladding is light. The construction of my current room is similar, and I note that I do get a significant room mode peak along the length of 35 Hz, but not much evidence of room gain. This current room has similar dimensions but not as long so I expect probably that peak will occur more around 40 Hz.
I'll have to sort out my measuring setup and measure this thing properly. At the moment I rely on ultracurve, which gives a good idea, but has less resolution than a proper measurement.
A factor to consider is that the floor is ~ 19mm pine strip flooring, and walls are timber framed 10mm plasterboard. The outside cladding is light. The construction of my current room is similar, and I note that I do get a significant room mode peak along the length of 35 Hz, but not much evidence of room gain. This current room has similar dimensions but not as long so I expect probably that peak will occur more around 40 Hz.
I'll have to sort out my measuring setup and measure this thing properly. At the moment I rely on ultracurve, which gives a good idea, but has less resolution than a proper measurement.
paulspencer said:
Greets!
After all that's been posted WRT MDF Vs no-void ply, I find it interesting that you still plan to use MDF, especially in an app where rigidity is paramount.
Hmm, GD is just another way to look at phase rotation WRT frequency, implying this horn's going to 'ring like a ten penny nail struck with a ball-peen hammer', though I imagine the room will mask it if it's not too lively.
GM
What type of material are you using beneath the plaster-board? Is the plaster-board stiff enough to support the bass wave without flexing?
I don't know if you have the room constructed; if not, perhaps you should put plywood backing in concert with the plaster-board.
Do you have a delay device to compensate for the lagging bass wave? The bass tends to sound slow/sluggish if it lags too far behind the upper frequencies.
edit: you could position the driver cabinet in such a way that you can experiment with rear loading techniques. This would bring a portion of the bass wave in phase with the high frequencies
Sounds like one hell of a project. Best of luck!
John
I don't know if you have the room constructed; if not, perhaps you should put plywood backing in concert with the plaster-board.
Do you have a delay device to compensate for the lagging bass wave? The bass tends to sound slow/sluggish if it lags too far behind the upper frequencies.
edit: you could position the driver cabinet in such a way that you can experiment with rear loading techniques. This would bring a portion of the bass wave in phase with the high frequencies
Sounds like one hell of a project. Best of luck!
John
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