Amen. Best goal to have given that it brings more enjoyment to more people.
No, don't try extending the line length. The 3:1 taper already gives a lower tuning than an untapered line of the same length, and adjustments means altering everything else. Also, trying to tune these drivers lower in a line is looking for trouble -amongst other things, you'll increase the speed of the roll-off, which is already about as fast as I personally would be willing to accept from a sub.
No, don't try extending the line length. The 3:1 taper already gives a lower tuning than an untapered line of the same length, and adjustments means altering everything else. Also, trying to tune these drivers lower in a line is looking for trouble -amongst other things, you'll increase the speed of the roll-off, which is already about as fast as I personally would be willing to accept from a sub.
Thanks. Ok, no problem; so sticking with your original design Scottmoose, i'm trying to figure out some box dimensions.
With a tapered line is the tapering linear? I assume it is, meaning halfway down the line we have 2sd area. That also means the average area is 2sd. That is 0.476m squared. If I multiply that by the line length of 2.54m I get an internal line area of 1.209m cubed (I think). I'm not sure where I'm going after that. I thought i'd need to divide by the cabinet width (say 0.22m) then by the cabinet depth (say 0.6m) to leave my cabinet height. That doesn't seem to work though. I know there will be some deviation for the area occupied by the internal dividers too.
Yes, I definately plan to veneer this once it's finished. It will also be active, with each driver powered by 70W amps (similar power to the PMC model). Got most the parts for that already. The amp will be fixed to the back as usual but externally rather than integral to the cabinet
With a tapered line is the tapering linear? I assume it is, meaning halfway down the line we have 2sd area. That also means the average area is 2sd. That is 0.476m squared. If I multiply that by the line length of 2.54m I get an internal line area of 1.209m cubed (I think). I'm not sure where I'm going after that. I thought i'd need to divide by the cabinet width (say 0.22m) then by the cabinet depth (say 0.6m) to leave my cabinet height. That doesn't seem to work though. I know there will be some deviation for the area occupied by the internal dividers too.
Yes, I definately plan to veneer this once it's finished. It will also be active, with each driver powered by 70W amps (similar power to the PMC model). Got most the parts for that already. The amp will be fixed to the back as usual but externally rather than integral to the cabinet
1.2 cubic meters is a mammoth sized box!!! That's 1700 litres!!! Live in that, you could.
You are going to have to scale the dimensions of the line to fit a convenient size box. Maintain the taper though.
You might want to think about Eq for it, such as a Linkwitz-transform (if you're handy with the circuits )
Goodluck
You are going to have to scale the dimensions of the line to fit a convenient size box. Maintain the taper though.
You might want to think about Eq for it, such as a Linkwitz-transform (if you're handy with the circuits
)Goodluck
I think I must have done it wrong, the design doesn't actually come out to that size does it . I realised after multiplying the PMC dimensions gave about 0.05 it must be wrong. How would you actually do it, rather to fit that line into a box as-is? Planet 10's design is more or less the sort of size I was thinking of, a bit smaller would be nice though realising I have fairly limited space
I thought about the EQ'ed subs and it probably would be easier for me to make, but I prefer the idea of extending the bass response acoustically rather than with electrical power. If I mess up and this fails badly then I'll probably end up with a sealed box and EQ though
. I realised after multiplying the PMC dimensions gave about 0.05 it must be wrong. How would you actually do it, rather to fit that line into a box as-is? Planet 10's design is more or less the sort of size I was thinking of, a bit smaller would be nice though realising I have fairly limited space I thought about the EQ'ed subs and it probably would be easier for me to make, but I prefer the idea of extending the bass response acoustically rather than with electrical power. If I mess up and this fails badly then I'll probably end up with a sealed box and EQ though
The one proper way to design a TL is to use Martin King's mathcad models to plot the line and predict the outcome. If you do not have access to his models you can guesstimate by using the drivers Fs and Sd. Calculate the quarter wavelenght of Fs - this will be your line lenght. It can be shortened by tapering it smaller. Start the line with a cross sectional area of at least Sd.
A Google search will locate a wavelenght calc.
As for Eq, you can use it for a TL too, just need to make sure your drivers have enough excursion to handle it.
A Google search will locate a wavelenght calc.
As for Eq, you can use it for a TL too, just need to make sure your drivers have enough excursion to handle it.
Where do you get the models from? I couldn't find them on the page you posted up initially. Is Scottmooses design designed with them?
Also, on stuffing again, how much of this am I likely to need:
https://secure.wilmslow-audio.co.uk...d=265&osCsid=d377af0e24712b37813b4cbc73bea6cf
And is this relevant (I only ask because it looks most similar to the PMC foam material):
http://www.studiospares.com/pd_401076_ACOUSTITILE PRO 75 BLUE.htm#
Also, on stuffing again, how much of this am I likely to need:
https://secure.wilmslow-audio.co.uk...d=265&osCsid=d377af0e24712b37813b4cbc73bea6cf
And is this relevant (I only ask because it looks most similar to the PMC foam material):
http://www.studiospares.com/pd_401076_ACOUSTITILE PRO 75 BLUE.htm#
MJL21193 said:
Scott already did that (and Scott knows how to use the software as well as anyone). I drew the box Scott simmed, folded down into a shape approximating the PMC. The width is determined by how wide you need to fit the drivers, and 3 folds is practical given the target shape.
If you'd like me to move the drivers to the front, and add dimensions so you can build it, that is not a problem.
Gross volume is about 96 lites.
dave
Martin King has stopped free access to his models because too many people were using it for commercial purposes with no return of benefit to him. I got it before he did this and I would assume scottmoose did likewise.
Like I said, scottmoose has the models, the design should be accurate using the drivers specs.
Stuffing: On the site you linked to they say:"120g pack is sufficient for cabinets with an internal volume of up to 20 Litres"
In my opinion you shouldn't need more than one pack. Remember, the whole line doesn't get stuffed, just the first 1/3 or so.
This foam would be good for either sealed sub or bass reflex box. The stuffing in a TL is to smooth midrange ripple and slow down the passage of air through the line. This foam will not do that.
Start with very little stuffing and work your way up, will be tedious.
Goodluck
Like I said, scottmoose has the models, the design should be accurate using the drivers specs.
Stuffing: On the site you linked to they say:"120g pack is sufficient for cabinets with an internal volume of up to 20 Litres"
In my opinion you shouldn't need more than one pack. Remember, the whole line doesn't get stuffed, just the first 1/3 or so.
This foam would be good for either sealed sub or bass reflex box. The stuffing in a TL is to smooth midrange ripple and slow down the passage of air through the line. This foam will not do that.
Start with very little stuffing and work your way up, will be tedious.
Goodluck
If you could re-draw it with the speakers on the front that would be fantastic! Starting to think I should have found somewhere to put it in my room before doing it, because it's going to turn out fairly large (though still slim, about 22cm wide I think would be nice). Anyhow, it'll be as big as it needs to be and i'll figure out positioning afterwards
Fair point on the models, annoying a few people people abuse the free access like that
I guess to determine the stuffing is pretty trial and error, by clamping/screwing the side on and listening with various amounts
Fair point on the models, annoying a few people people abuse the free access like that
I guess to determine the stuffing is pretty trial and error, by clamping/screwing the side on and listening with various amounts
MJL21193 said:
Scottmoose has a commercial licence
The stuffing acts as a low pass filter for the terminus. It does not slow the passage of air. IMF, Fried, & PMC all use foam to good effect in their TLs. I usually line the walls with cotton felt, and use polyfluff in the critical parts. How much depends on your end goal. If you want maximum useful output from the terminus you use as little as possible to still achieve the target low pass characteristic. At the other end is the "official" TL (rarely built) which is primarily an artifact of Bailey calling it a non-resonant enclosure -- ie stuff it enuff and the line becomes aperiodic (close to total absorbtion of the back wave)
dave
planet10 said:
No problem. Sound needs a medium to travel through, in this case air. As the air is impeded by the stuffing, sound disperses. Simple sound deadening principle.
Dave, I an enjoying both this discussion and the other on materials properties, but I get the impression that you are getting annoyed. If you prefer that I keep my opinions to myself, let me know and I will move on and bug someone else
I have said a lot of things on this forum, and have been corrected on most of them. Still, I have not said anything that is incorrect.
Big thanks for that design planet10! I will be building this project according to it . Big thanks to every one who has posted in this thread too, given me a lot to take in . I have the drivers, veneer and stuffing on order now too, leaving me with the wood, some heatsinks and some tools to get (already got most the amplifier section components; nice 300VA toroid, 20,000uf per rail and 35A bridge for £22 or so ).
I will naturally be taking numerous photos along the way and will let you all know how it goes
Again, many thanks.
. Big thanks to every one who has posted in this thread too, given me a lot to take in . I have the drivers, veneer and stuffing on order now too, leaving me with the wood, some heatsinks and some tools to get (already got most the amplifier section components; nice 300VA toroid, 20,000uf per rail and 35A bridge for £22 or so ).I will naturally be taking numerous photos along the way and will let you all know how it goes
Again, many thanks.
Dr.EM said:Just out of interest, how come the design is based on the Sd of a single driver? I guess they don't add together like I originally thought, it would be an enormous box if they did
Sd actually has nothing to do with the size of a TL, Vas does (just like every other speaker).
But because when Martin started working on his sheets Sd was considered important, he chose it as a variable unit of area. That is unfortunate because it keeps people thinking in terms of Sd.
(Those rare times that i have used the sheets I usually just set the Sd to a convienient SI unit like 10 cm^2 for instance.)
dave
Not a bad plan. Luckily, most of the latest sheets have moved away from the idea of using multiples of Sd as a data entry value.
BTW -just line the front of each internal wall with a light layer of damping. XO below 100Hz, you should with the usual ~6db of room gain below 100Hz have 91db sensitivity at 30Hz. Not too bad for these drivers.
BTW -just line the front of each internal wall with a light layer of damping. XO below 100Hz, you should with the usual ~6db of room gain below 100Hz have 91db sensitivity at 30Hz. Not too bad for these drivers.
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