I am building a couple of TL subs using 8 inch drivers that I already own (this is until I can afford to build my dipole subs).
I am planning on each TL sub sitting behind my open baffle speakers and have come up with the design below which avoids too many 180 degree bends.
As you can see, the line end is in the middle of the box and has to exit through the side. My question is this. What would happen if I cut an exit aperture in both sides instead of one?
I am planning on each TL sub sitting behind my open baffle speakers and have come up with the design below which avoids too many 180 degree bends.
An externally hosted image should be here but it was not working when we last tested it.
As you can see, the line end is in the middle of the box and has to exit through the side. My question is this. What would happen if I cut an exit aperture in both sides instead of one?
I'd be more worried about the last bend being 180 degrees right in the maximum velocity zone. IME, simpler is better when it comes to TL bends. Can't you get your target line length in a single or double fold? Maybe a spiral pattern would work; like some of the japanese backhorns.
I don't know what drive you're using or what BW you're aiming to reproduce, but a TL that long is likely to act more like an IB than anything, so it may require some EQ depending on the room and placement, etc. (less than a dipole)
GB
I don't know what drive you're using or what BW you're aiming to reproduce, but a TL that long is likely to act more like an IB than anything, so it may require some EQ depending on the room and placement, etc. (less than a dipole)
GB
My'problem' is trying to fit everything in behind the open baffles!
The drivers are 8 inch Seas P21HEX and I am aiming for a line length of 8’6” (1/4 wavelength @ 33Hz). The subs will fill in up to around the 70 Hz point and I have been advised this makes the usual 'rules' on TL design not so critical.
I could probably just get away without that last 180 degree bend if it makes an improvement.
Thanks for your advice.
The drivers are 8 inch Seas P21HEX and I am aiming for a line length of 8’6” (1/4 wavelength @ 33Hz). The subs will fill in up to around the 70 Hz point and I have been advised this makes the usual 'rules' on TL design not so critical.
I could probably just get away without that last 180 degree bend if it makes an improvement.
Thanks for your advice.
Nuuk said:As you can see, the line end is in the middle of the box and has to exit through the side. My question is this. What would happen if I cut an exit aperture in both sides instead of one?
I'm no TL expert, but as I understand it the line would appear a bit shorter, and the velocity at the exit(s) would drop.
As long as the total exit area is correct it doesn't matter much. However, it looks from your picture that you don't need to do so- but I can't tell how wide the box is.
The 180 bends will have no effect on the long wavelengths that pass the line and in fact they are beneficial as LP filters against the higher frequencies that you want to damp out anyway.
The 180 bends will have no effect on the long wavelengths that pass the line and in fact they are beneficial as LP filters against the higher frequencies that you want to damp out anyway.
i think that you forgot that the wave won't be matched if the distance of the opening and the front of the speaker is not also tunned nah ?
that is why striaght line TL works better than folded type
for the openning i'd say let it open on both side and see how u like it!
sure would look coool
that is why striaght line TL works better than folded type
for the openning i'd say let it open on both side and see how u like it!
sure would look coool
In theory, sure, it's not supposed to make a difference. In practice, I find that it does. I built a TL once which I later decided needed to be ~12" longer. This was a single fold type. I tried both 90 and 180 degree extensions - either way was going to be dorky looking. The 90 degree one had considerably more output. This was years ago, I don't have numbers on it anymore.
As I implied before, my theory was that this was because its location in a high velocity zone of the line, where aerodynamic drag becomes a factor. That's my theory anyway, I reserve the right to be wrong.
Anyway, I'm going to have to disagree with you gents until someone convinces me otherwise.
Regardless, I strongly recommend sim'ing the TL in MJK's mathcad model, if this hasn't been done already.
GB
As I implied before, my theory was that this was because its location in a high velocity zone of the line, where aerodynamic drag becomes a factor. That's my theory anyway, I reserve the right to be wrong.
Anyway, I'm going to have to disagree with you gents until someone convinces me otherwise.
Regardless, I strongly recommend sim'ing the TL in MJK's mathcad model, if this hasn't been done already.
GB
You might get more output from an unstuffed or understuffed line passing midbass frequencies with 90 bends but below 100 Hz a 180 bend is no obstacle, for the same reason that subs radiate omnidirectionally below 100 Hz.
I see nothing fundamentally wrong with the design; it's actually quite ingenious and very much resembles the inverse case, a coiled folded horn, if you swapped the driver and vent positions.
I don't have P21 HEX specs, but the P21 REX with Qts .37 and Fs 33 Hz would give an F3 of about 66Hz, so it's far from a perfect match unfortunately. If the P21 HEX has a higher Qts things would be better.
I see nothing fundamentally wrong with the design; it's actually quite ingenious and very much resembles the inverse case, a coiled folded horn, if you swapped the driver and vent positions.
I don't have P21 HEX specs, but the P21 REX with Qts .37 and Fs 33 Hz would give an F3 of about 66Hz, so it's far from a perfect match unfortunately. If the P21 HEX has a higher Qts things would be better.
Thanks again for the interest guys!
There does seem to be some difference between designing a TL for sub use and for full-range use. If 180 degree bends help filter out higher frequencies then I may go back to an earlier design that has about six of them! But I appreciate that speed in the line may also affect the amount of output.
The internal width of the cabinet is 10 inches so the start of the line is 65 sqare inches and the end of the line is 31 square inches. Length of line is 8 feet six inches. The drive units are Seas P21REX (not HEX as I stated earlier).
I'm hoping to build these boxes from scrap chipboard so I guess the thing is to build them and see how they sound. If I don't like the output, I could try another design assuming I can find enough chipboard!
Actually Bill, I came up with the following design last night!
There does seem to be some difference between designing a TL for sub use and for full-range use. If 180 degree bends help filter out higher frequencies then I may go back to an earlier design that has about six of them! But I appreciate that speed in the line may also affect the amount of output.
The internal width of the cabinet is 10 inches so the start of the line is 65 sqare inches and the end of the line is 31 square inches. Length of line is 8 feet six inches. The drive units are Seas P21REX (not HEX as I stated earlier).
I'm hoping to build these boxes from scrap chipboard so I guess the thing is to build them and see how they sound. If I don't like the output, I could try another design assuming I can find enough chipboard!
Actually Bill, I came up with the following design last night!
An externally hosted image should be here but it was not working when we last tested it.
There is no difference fundamentally between a TL sub and TL main as the vent is only supposed to pass low frequencies in both cases. What differs is that with a sub you just aren't feeding it any high frequencies.
Your redesign is OK, but you might want to consider if it's any better than a simple VB. The low Qts of your drivers won't let them energize the line down to it's 1/4 wavelength frequency, it really needs to be .5 or better to do so. A 55L VB will give an F3 of 38 Hz.
Even better is a dual chamber, 20L tuned to 55Hz and 40L tuned to 20 Hz will give an F3 of 32 Hz.
Considering the compexity and size of the TL I think I'd look to other alternatives with this particular driver as far as a pure sub is concerned.
Your redesign is OK, but you might want to consider if it's any better than a simple VB. The low Qts of your drivers won't let them energize the line down to it's 1/4 wavelength frequency, it really needs to be .5 or better to do so. A 55L VB will give an F3 of 38 Hz.
Even better is a dual chamber, 20L tuned to 55Hz and 40L tuned to 20 Hz will give an F3 of 32 Hz.
Considering the compexity and size of the TL I think I'd look to other alternatives with this particular driver as far as a pure sub is concerned.
Point taken Bill. One of the reasons for going TL on this one is that the drivers were originally in a TL enclosure and worked well down to 33 Hz. I am following the specs for those speakers as regards the line lenfgth and dimensions.
I appreciate that the driver spec may not seem up to this but in this case, it seems that practice doesn't follow theory.
I am building these subs from reclaimed chipboard so cost isn't really an issue and will allow me to experiment without regretting the money spent. In any case, this is an interim project until I can afford to build my dipole subs so it is no huge deal if it isn't 'perfect'. And at present I am really just looking to augment the full-range drivers on the baffles - not rattle the whole terrace to pieces!
I appreciate that the driver spec may not seem up to this but in this case, it seems that practice doesn't follow theory.
I am building these subs from reclaimed chipboard so cost isn't really an issue and will allow me to experiment without regretting the money spent. In any case, this is an interim project until I can afford to build my dipole subs so it is no huge deal if it isn't 'perfect'. And at present I am really just looking to augment the full-range drivers on the baffles - not rattle the whole terrace to pieces!
Leaving aside the TL exit question, what BW are you looking to cover? The TL design you have should work OK, but the midbass will be missing in action. By this I mean there will be a phase cancellation dip from ~90-180hz. I briefly looked at it, seems to rattle on to 30hz or so, with a nice low Q rolloff knee. It might actually do ~25hz in room if you have one of those little brick english houses.
Here's another solution, depending on your room gain. It's simpler and has better impulse response. This can be tweaked to customize the low end rolloff to fit the room curve.
GB
Here's another solution, depending on your room gain. It's simpler and has better impulse response. This can be tweaked to customize the low end rolloff to fit the room curve.
GB
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Hi Greg,
My open baffles drop away at around 70 hz so these TL subs are just to beef up the bottom end. I do indeed live in a brick-built house so there may be a little help there.
The dip at 90-180 hz may even be beneficial from a crossover point of view.
Thanks for the other option but with the largish OB's in a not-so-big room, a couple of five feet pipes may just be too much even for this batchelor!
My open baffles drop away at around 70 hz so these TL subs are just to beef up the bottom end. I do indeed live in a brick-built house so there may be a little help there.
The dip at 90-180 hz may even be beneficial from a crossover point of view.
Thanks for the other option but with the largish OB's in a not-so-big room, a couple of five feet pipes may just be too much even for this batchelor!
Just an update to say that I built the 'subs' according to the dsesign at the start of this thread and they work well.
They still have to be 'finished' and now that I have heard them in action, I am more inclined to make a good job of that.
They measure 6 db down at around 28 Hz and integrate beautifully with my open baffles. I modified the main baffles so that the 'subs' fire through them at ground level.
I use a first order crossover at 25 Hz and a second order at 120 Hz. At present each driver is powered from a single 3875 Gainclone. I will write up full details of the boxes and the control circuit as soon as I have time.
An externally hosted image should be here but it was not working when we last tested it.
They still have to be 'finished' and now that I have heard them in action, I am more inclined to make a good job of that.
They measure 6 db down at around 28 Hz and integrate beautifully with my open baffles. I modified the main baffles so that the 'subs' fire through them at ground level.
An externally hosted image should be here but it was not working when we last tested it.
I use a first order crossover at 25 Hz and a second order at 120 Hz. At present each driver is powered from a single 3875 Gainclone. I will write up full details of the boxes and the control circuit as soon as I have time.
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