I haven't followed discussion of MDF vs plywood, but is ply really that much better to justify the extra cost? It's at least 3x the cost last time I checked. Keeping in mind there will be bracing which I have not shown.
Regarding group delay, most horns do seem to have a funny GD. At which point does it need attention?
GM, what do you suggest re: GD?
I'm not building the room, I'm moving into it. It has 10mm plasterboard on a timber frame. If I were building it, I'd make it double layer on channels on staggered studds at least. I don't know if you guys have plasterboard, or call it drywall, but it's not the most solid of materials.
I can include digital delay on the mains. How do you work it out with a horn. I'm not sure where the acoustic centre really is.
Regarding group delay, most horns do seem to have a funny GD. At which point does it need attention?
GM, what do you suggest re: GD?
I'm not building the room, I'm moving into it. It has 10mm plasterboard on a timber frame. If I were building it, I'd make it double layer on channels on staggered studds at least. I don't know if you guys have plasterboard, or call it drywall, but it's not the most solid of materials.
I can include digital delay on the mains. How do you work it out with a horn. I'm not sure where the acoustic centre really is.
To Ply or not to Ply
Hi Paul
Long time lurker in the shadows.
From personal experience I would say that MDF is the way to go when you factor in the cost, the almost guaranteed uniformity and the freedom of loose plys in the mix. The weight is the trade off.
It has been said that a good plywood enclosure is more lively. I have built many enclosures using Birch marine plywood and MDF. Both if properly constructed and braced will perform admirably.
One will cost considerably less!
Mark
Hi Paul
Long time lurker in the shadows.
From personal experience I would say that MDF is the way to go when you factor in the cost, the almost guaranteed uniformity and the freedom of loose plys in the mix. The weight is the trade off.
It has been said that a good plywood enclosure is more lively. I have built many enclosures using Birch marine plywood and MDF. Both if properly constructed and braced will perform admirably.
One will cost considerably less!
Mark
Hmm. I built 2 labhorns from mdf a year ago, and am just preparing to make another 4 in mdf. Can't hear any ringing / smearing / muddiness.But then don't have a ply version to compare. Will try and do some waterfall charts when they're done to see if anything dodgy is going on....
Do you reckon it would show up if I measure the 2 in my front room ? Or will the rooms ringing be so bad as to completely mask it ?
Rob.
Do you reckon it would show up if I measure the 2 in my front room ? Or will the rooms ringing be so bad as to completely mask it ?
Rob.
paulspencer said:
Greets!
Yeah, it really is, especially in the initial expansion where the pressure's highest. Consider that stiffness goes up at the cube of thickness and 3/4" no-void ply has a MOE of ~1.8 m psi, while typical MDF is ~527 k psi, so it takes ~1.125" thick MDF to match the ply's base stiffness and it follows that bracing increases stiffness much quicker with ply than MDF. Factor in that acoustic energy falls at 1/f, so the higher the cab's Fs is, the less damping required and if you can push it above the intended passband it doesn't get excited at all. MDF OTOH starts out with a relatively low Fs, so increasing thickness or adding mass quantities of bracing to gain stiffness lowers its Fs, requiring more mass/bracing to increase stiffness, etc., until with a sub you wind up needing it many inches thick since it's the quickest way to gain stiffness to drop Fs to below the passband............
Many folks claim they have 'dead' MDF speakers, but try to stand a quarter on end while it's playing.
A decent compression horn wil have a nominally flat impedance in its passband, ergo GD should be the same, so the horn has to be long/big enough for GD to fall to its sealed cab levels around 35-50 Hz depending on your phase hearing acuity. Of course if you're going to XO it below this point with a steep slope, then it's moot.
WRT wall construction, the last thing you want is an acoustic energy absorbing system! I mean would you put a thick layer of insulation over your mid-bass or mids? Just like with the horn's construction, you want rigidity to contain/reflect since it has to extend the horn's axial length/mouth area. Of course if it's backed up with poured concrete exterior walls or at least a brick facade, then it's somewhat more acceptable, but still far from ideal.
The acoustic center of a compression horn is either at the phase plug, or if it doesn't have one, then ~the center of the driver's VC. With the horn folded up though, this doesn't mean you can align them with the mids/HF just by having them all on the same plane, you'll have to delay the mains by however long the bass horn's effective axial length is.
GM
RobWells said:
Greets!
Deja vu! Seems we've had this conversation before.
There's usually exceptions to any rule and the LABhorn's bipolar layout and ultra compact radial construction probably won't benefit nearly as much from using ply as other layouts, though some additional mouth bracing may help. Still, it would be interesting to do a comparison. One way to hear how much the material contributes is to tightly cap off the mouth and play some pink noise to see if any narrow BW stands out.Without a waterfall plot of a 13 ply BB LABhorn to compare to, just what are you going to look for? Regardless, unless you have a huge room, I imagine you'll need to do outdoor measurements on a bass horn, but not having ever done it, it's pure conjecture on my part. All I know for sure is that the pros measure outdoors far enough away to get a far field measurement.
GM
Firstly, thanks to everyone for their comments and input. I'd hate to embark on a project like this only to find there was something wrong with it!
So I modelled it as Rob suggested.
1. the horn itself into 0.5 pi (dark line)
2. the horn with the extension modelled as part of the horn, loaded into half space
Here it is:
As you can see, the response is different, but similar. The big difference is the efficiency. The lower line can't be right. If I put these drivers in a vented box I can get 118 db.
Now I tried modelling the lab according to the same rules, but assumed its sides extended to the ceiling. Similar result, but max SPL is 125 db. Modelled into corner space without the extension, response is very similar, but with about 10 db more output.
In my model the excursion is only 10mm one way below 20 Hz, so I could sacrifice a little bottom end, turn on the rumble filter and give it more juice. Gets to about 140 db in the midbass (more than enough).
What I'd like to achieve is 120 dB @ 20 Hz at 10 metres, hence 130 dB @ 1m. It seems I'm just under (taking the corner loaded version), which is fine, since it is a crazy goal.
Why 120 dB? I'd my mains (when upgraded) to reach 105 db @ 10m and the subs to be able to handle 15 db more at the listening position. I understand commercial cinemas design for a peak level of 105 db for the mains with 12 - 15 db more output in the subs, although with less extension. Perhaps I'm mistaken but it seems I can reach that goal with this bass horn 10w into a CD and 100w into a 98db sensitive mid (12" pro driver).
I've never been called a lurker before!!! I used to post here every day (for my first 1000 posts or so). Now I'm a bit more of an occasional poster.
Rob had mentioned that his lab horns out of MDF were just fine with vibration, so I was going to just do it braced MDF. I thought that the manifold would be the most critical, so it would be 2 layers thick 18mm.
I use curves where possible to increase stiffness. Bracing also (not shown).
What I'm considering now is a hybrid - using some ply where it is more critical and where bracing and thicker walls can't be used. Perhaps for the largest segment, since it is the biggest and if made too thick will be too heavy to assemble.
Well, I couldn't resist a challenge like that. We don't have quarters, but I put a 20c coin on my mains which are MDF (18-36mm thick) when playing loud - it was quite easy (not bad considering the tops are curved). So I tried it on my crappy prototype H frame dipoles (15mm chipboard) and it even stood up on them despite a lot of vibration.
I see your point though. I hadn't seen actual data on MDF vs ply. Is there a significant difference between plys? I just got a price for construction grade. It's about 2.5x the cost of MDF.
One question. Hornresp says the cir value is greater than 1 when I model the room walls as part of the horn, and that this will give incorrect horn throat impedance value. Is this significant? The value is around 1.7
So I modelled it as Rob suggested.
1. the horn itself into 0.5 pi (dark line)
2. the horn with the extension modelled as part of the horn, loaded into half space
Here it is:
An externally hosted image should be here but it was not working when we last tested it.
As you can see, the response is different, but similar. The big difference is the efficiency. The lower line can't be right. If I put these drivers in a vented box I can get 118 db.
Now I tried modelling the lab according to the same rules, but assumed its sides extended to the ceiling. Similar result, but max SPL is 125 db. Modelled into corner space without the extension, response is very similar, but with about 10 db more output.
In my model the excursion is only 10mm one way below 20 Hz, so I could sacrifice a little bottom end, turn on the rumble filter and give it more juice. Gets to about 140 db in the midbass (more than enough).
What I'd like to achieve is 120 dB @ 20 Hz at 10 metres, hence 130 dB @ 1m. It seems I'm just under (taking the corner loaded version), which is fine, since it is a crazy goal.
Why 120 dB? I'd my mains (when upgraded) to reach 105 db @ 10m and the subs to be able to handle 15 db more at the listening position. I understand commercial cinemas design for a peak level of 105 db for the mains with 12 - 15 db more output in the subs, although with less extension. Perhaps I'm mistaken but it seems I can reach that goal with this bass horn 10w into a CD and 100w into a 98db sensitive mid (12" pro driver).
I've never been called a lurker before!!! I used to post here every day (for my first 1000 posts or so). Now I'm a bit more of an occasional poster.
Rob had mentioned that his lab horns out of MDF were just fine with vibration, so I was going to just do it braced MDF. I thought that the manifold would be the most critical, so it would be 2 layers thick 18mm.
I use curves where possible to increase stiffness. Bracing also (not shown).
What I'm considering now is a hybrid - using some ply where it is more critical and where bracing and thicker walls can't be used. Perhaps for the largest segment, since it is the biggest and if made too thick will be too heavy to assemble.
Well, I couldn't resist a challenge like that. We don't have quarters, but I put a 20c coin on my mains which are MDF (18-36mm thick) when playing loud - it was quite easy (not bad considering the tops are curved). So I tried it on my crappy prototype H frame dipoles (15mm chipboard) and it even stood up on them despite a lot of vibration.
I see your point though. I hadn't seen actual data on MDF vs ply. Is there a significant difference between plys? I just got a price for construction grade. It's about 2.5x the cost of MDF.
One question. Hornresp says the cir value is greater than 1 when I model the room walls as part of the horn, and that this will give incorrect horn throat impedance value. Is this significant? The value is around 1.7
Greets!
You're welcome!
What can I say, my quarters can barely be stood on end, much less handle any vibration.
Yes, only advertised no-void ply is suitable for a HIFI app and even then it ideally needs to be 13 ply, though 11 has worked fine for me even with the DIY Contrabass cabs. Lower grades such as furniture grade, or worse, construction grade, can have spurious creaks due to voids, puttied patches, loose knots, or splits coming loose and can be very hard to find. For sure no construction grade I'm familiar with is suitable for HIFI apps, only Appleply, Russian Baltic Birch and no-void marine grade (what I used) if you can find it since it's no longer guaranteed no-void like it once was, at least in my area of the USA.
In your case, maybe a laminate of 3/8 MDF with 3/8" no-void glued to it and some bracing will suffice without costing/weighing so much.
I don't use Hornresp, what is 'cir' value? Flare factor? If so, your drawing indicates the horn is loading into a linear expansion (assuming a flat ceiling) which has no flare factor, so won't be accurate no matter what you input.
GM
You're welcome!
What can I say, my quarters can barely be stood on end, much less handle any vibration.
Yes, only advertised no-void ply is suitable for a HIFI app and even then it ideally needs to be 13 ply, though 11 has worked fine for me even with the DIY Contrabass cabs. Lower grades such as furniture grade, or worse, construction grade, can have spurious creaks due to voids, puttied patches, loose knots, or splits coming loose and can be very hard to find. For sure no construction grade I'm familiar with is suitable for HIFI apps, only Appleply, Russian Baltic Birch and no-void marine grade (what I used) if you can find it since it's no longer guaranteed no-void like it once was, at least in my area of the USA.
In your case, maybe a laminate of 3/8 MDF with 3/8" no-void glued to it and some bracing will suffice without costing/weighing so much.
I don't use Hornresp, what is 'cir' value? Flare factor? If so, your drawing indicates the horn is loading into a linear expansion (assuming a flat ceiling) which has no flare factor, so won't be accurate no matter what you input.
GM
CIR in hornresp is ...
exp or hyp-exp horn free space normalised mouth circumference in flare cutoff frequency wavelengths
Can anyone explain what this actually is?!
I'm considering some alternatives:
* higher fc (I'll have to find out but I don't think room gain will help much if at all)
* 2 horns - one fires to the left corner, the other to the right - this gives potentially twice the mouth area so I'm not counting on the room walls
I'm trying to find the balance (not easy).
If I sacrifice some depth, I can get better GD and a smoother response.
Fitting in 2 horns is not easy. I can use 2 or 4 drivers here. I'd give up the design with the void in the middle which I like, replacing it with boxes with a lot of work put in to squeezing as much horn as I can into the space, probably also increasing the depth.
I don't want to give up the lab horn style driver arrangement as this makes a big difference with vibration.
exp or hyp-exp horn free space normalised mouth circumference in flare cutoff frequency wavelengths
Can anyone explain what this actually is?!
I'm considering some alternatives:
* higher fc (I'll have to find out but I don't think room gain will help much if at all)
* 2 horns - one fires to the left corner, the other to the right - this gives potentially twice the mouth area so I'm not counting on the room walls
I'm trying to find the balance (not easy).
If I sacrifice some depth, I can get better GD and a smoother response.
Fitting in 2 horns is not easy. I can use 2 or 4 drivers here. I'd give up the design with the void in the middle which I like, replacing it with boxes with a lot of work put in to squeezing as much horn as I can into the space, probably also increasing the depth.
I don't want to give up the lab horn style driver arrangement as this makes a big difference with vibration.
Hi,
I never knew what CIR was, is the definition in there?
I think this
Put that into an example. If you describe the flare rate using areas along the horn length, the program calculates the frequency to match the flare.
The program also calculates the mouth area times the boundary loading factor. Using equivalent circumference for a circular mouth the program can estimate the frequency that matches the actual mouth area. If both frequencies are equal then CIR=1. If the horn is truncated then the flare rate (and frequency) are unchanged but the mouth area is reduced and this shows as CIR>1.
Who invented English? hang them!
I never knew what CIR was, is the definition in there?
I think this
is saying that if CIR=1 then the mouth area matches the flare rate.
Put that into an example. If you describe the flare rate using areas along the horn length, the program calculates the frequency to match the flare.
The program also calculates the mouth area times the boundary loading factor. Using equivalent circumference for a circular mouth the program can estimate the frequency that matches the actual mouth area. If both frequencies are equal then CIR=1. If the horn is truncated then the flare rate (and frequency) are unchanged but the mouth area is reduced and this shows as CIR>1.
Who invented English? hang them!
Thanks Andrew, that makes sense.
One issue is that this is my first bass horn. There is an aspect of "what if I build it expensively and it takes a very long time, only to find I don't like it." MDF is affordable, but even the lowest grade not-good-enough ply is a bit pricey for first attempt.
What if I just build it out of MDF, brace it as much as I can (including curves where possible rather than faceted segments) and see how it goes? I can consider adding ply to the outside if I'm otherwise happy with it. In that case I'd probably have to add on the rest insitu, put down drop sheets and then paint it in the room.
GM: one question: what if the cheaper ply were used on the outside OVER 18mm MDF - does the construction grade then become acceptable?
I'm exploring my options at the moment. I'm also considering combining one bass horn driven by my Rythmik subs with one or two tapped horns for LFE duty where I have about 4.66 litres of displacement and 2.4kw of power. I could possibly get away with putting two large ones under the room and cutting small openings in the floor, inserting grates but leaving the carpet intact.
If I went this way, the horn would be on all the time, the tapped horn would be for LFE use. I'd have some more flexibility with placement to optimise room mode issues, and could potentially gain up to 10 db if it turns out to work well with a closer placement.
One issue is that this is my first bass horn. There is an aspect of "what if I build it expensively and it takes a very long time, only to find I don't like it." MDF is affordable, but even the lowest grade not-good-enough ply is a bit pricey for first attempt.
What if I just build it out of MDF, brace it as much as I can (including curves where possible rather than faceted segments) and see how it goes? I can consider adding ply to the outside if I'm otherwise happy with it. In that case I'd probably have to add on the rest insitu, put down drop sheets and then paint it in the room.
GM: one question: what if the cheaper ply were used on the outside OVER 18mm MDF - does the construction grade then become acceptable?
I'm exploring my options at the moment. I'm also considering combining one bass horn driven by my Rythmik subs with one or two tapped horns for LFE duty where I have about 4.66 litres of displacement and 2.4kw of power. I could possibly get away with putting two large ones under the room and cutting small openings in the floor, inserting grates but leaving the carpet intact.
If I went this way, the horn would be on all the time, the tapped horn would be for LFE use. I'd have some more flexibility with placement to optimise room mode issues, and could potentially gain up to 10 db if it turns out to work well with a closer placement.
Greets!
I didn't have any luck with it, the ply didn't stiffen it up enough to keep the PB (never tried MDF) from exciting it, but others claim to have had some success with MDF, so as always YMMV.
WRT 'CIR', the bottom line is that it's not dumping into free space, but a finite room, so the flare frequency should match the horn's + room's 1/4 WL reflection back to the throat with the appropriate flare factor to match it to the corner.
Well, when I did my first 'anything' DIY construction I just cobbled it together from free scraps and surplus lumber at the nearest construction scrap pile and experimented away until either I felt I had something worth building in earnest, or not. Most folks today live their lives in a 'fast food' paced, computer simulated world, coming to the forums wanting/expecting others to give them enough help/info to skip most/all the intermediary steps to a good performing system and you seemed no different to me, but based on these latest revelations I recommend you file away any useful info for a finished product you may have gleaned from us/others and go cobble together a prototype or three and get the answers you need rather than a bunch of semi-educated opinions/thoughts from us.
GM
I didn't have any luck with it, the ply didn't stiffen it up enough to keep the PB (never tried MDF) from exciting it, but others claim to have had some success with MDF, so as always YMMV.
WRT 'CIR', the bottom line is that it's not dumping into free space, but a finite room, so the flare frequency should match the horn's + room's 1/4 WL reflection back to the throat with the appropriate flare factor to match it to the corner.
Well, when I did my first 'anything' DIY construction I just cobbled it together from free scraps and surplus lumber at the nearest construction scrap pile and experimented away until either I felt I had something worth building in earnest, or not. Most folks today live their lives in a 'fast food' paced, computer simulated world, coming to the forums wanting/expecting others to give them enough help/info to skip most/all the intermediary steps to a good performing system and you seemed no different to me, but based on these latest revelations I recommend you file away any useful info for a finished product you may have gleaned from us/others and go cobble together a prototype or three and get the answers you need rather than a bunch of semi-educated opinions/thoughts from us.
GM
GM said:
It's worth knowing that an AUS 20 cent coin is much heavier and thicker than a US "Quarter". An AUS 10 cent coin is almost exactly the same size and thickness and would be more comparable to the "quarter" test.
And GM, thanks for your reply on the Altec forum regarding the MLTL. I'm still digesting it.
GM, I can see where you are coming from. DIY wise I have tried many things. If something lends itself to a quick and simple prototype, I'll do it. I enjoy building as much as discussing. But why not do both?
Discussing it is enjoyable - it's an interesting topic. I also might learn a few lessons that otherwise would be very costly.
This is a huge project. The most challenging so far. I want to arm myself with as much as I can before building. Building three or four 200 kg bass horns is expensive! And time consuming. The bigger it is, the more work I have to put into making it practical, and working out how I'm going to assemble it without a crane. This project is a bit crazy, which is part of the appeal.
Discussing it is enjoyable - it's an interesting topic. I also might learn a few lessons that otherwise would be very costly.
This is a huge project. The most challenging so far. I want to arm myself with as much as I can before building. Building three or four 200 kg bass horns is expensive! And time consuming. The bigger it is, the more work I have to put into making it practical, and working out how I'm going to assemble it without a crane. This project is a bit crazy, which is part of the appeal.
Prototyping...fun...further enjoyment...gained experience. I can't seem to fault that logic despite my previous posts.
WRT it being crazy... I might take the side of no. After all, the masses don't often do it because it isn't practical for them (or perhaps the commercial entities) but that doesn't mean it's wrong.
I've already given my opinions, now I wish you success
WRT it being crazy... I might take the side of no. After all, the masses don't often do it because it isn't practical for them (or perhaps the commercial entities) but that doesn't mean it's wrong.
I've already given my opinions, now I wish you success
Thanks.
Unfortunately I can't get in the room for another 2 months - the tenant is still there. I won't finalise the design and start building until I can get in there and measure the room. Fortunately the place is in the family, so I can get away with a few things not usually possible. I'll be double glazing the windows and sealing the room up.
If I built it now, I'm not certain of the exact ceiling height.
What I'd like to do is experiment with all my options - horn, tapped horn, sealed, vented, H frame. By then I'll have four subs and 3 amplifiers to play with - my existing AV12 subs (2 x 12") & Behringer EP2500 amp, and two Rythmik 12" kits.
At the end I'll have either 1, 2 or 3 subs and may even sell what I have now. What I do know is it's going to be fun.
Hi Gm,
If I add my horn length (8.5m for one driver) to the corner to corner length of my room (10.5m) then the 1/4 wavelength comes out at about 5Hz. But I was planning a flare rate frequency of 15 or 16Hz and the mouth frequency about 19 or 20Hz (Pi/2 mouth area=3.6sqm).
Any thoughts?
that almost sounds like a design criteria to help decide what flare rate to choose.GM said:
If I add my horn length (8.5m for one driver) to the corner to corner length of my room (10.5m) then the 1/4 wavelength comes out at about 5Hz. But I was planning a flare rate frequency of 15 or 16Hz and the mouth frequency about 19 or 20Hz (Pi/2 mouth area=3.6sqm).
Any thoughts?
I will reiterate what Carpenter said. However, besides a vented box, consider an infinite baffle arrangement (if the house design allows it). While it would be less efficient at the upper frequencies than a horn, it will be more efficient at the lowest frequencies. For a home theatre system, you would appreciate the response below 20 hz which will be nonexistent with a 20 hz horn. If you have the chance, go listen to an infinite baffle system. You certainly don't need 140 db at 80 hz anyways. That is like bragging about a 600 hp motor in your car for running errands to the store.
Also consider that you will have to delay your mains to achieve phase alignment. I would suggest trying some phase delay devices with your main speakers before going that route. You might not like the effect (I would not!!). You will be disappointed if you build that horn and don't want to use it. Bert Doppenberg's concrete subbass horn sits idle because of phase delay.
Retsel
Also consider that you will have to delay your mains to achieve phase alignment. I would suggest trying some phase delay devices with your main speakers before going that route. You might not like the effect (I would not!!). You will be disappointed if you build that horn and don't want to use it. Bert Doppenberg's concrete subbass horn sits idle because of phase delay.
Retsel
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