Transmission line: flared?

[tyler_fitz 10+ year member]

i'm thinking about building a t-line and was wondering if putting a flare on the end of the port would mess anything. to my understanding, a t-line needs to have a specific area the whole length, and adding a flare on the end of it would change the area, but only at the end, would that make a huge difference?

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[terra 5,000+ posts]

ya

 

[Immacomputer 10+ year member]

No, it will not affect the performance greatly but will reduce possible chuffing at high volumes. And no, transmission lines do not have to have a constant line area all the way through, that is a conceptual error. Transmission lines can expand and they can also taper. An expansion at the end of the line is a good way to help better couple it to the transmission line that the cabin of your vehicle creates.

 

[ciaonzo 5,000+ posts]

No, it will not affect the performance greatly but will reduce possible chuffing at high volumes. And no, transmission lines do not have to have a constant line area all the way through, that is a conceptual error. Transmission lines can expand and they can also taper. An expansion at the end of the line is a good way to help better couple it to the transmission line that the cabin of your vehicle creates.

A true transmission line does not have an exit at all but a transmission line that is intended for bass duty of course does. A transmission line that is designed properly will have zero chuffing at any volume, even with an applied taper to 80% of Sd. And while a TL can theoretically perform with a flare as opposed to a taper, there is no point to this as it does nothing to help the frequency response and actually detracts from the intended performance. The single biggest misconception involving a TL is that it must be "tuned" to the Fs of the driver. There is no need to flare the end of a TL to aid in coupling with a vehicle's transfer function. What you're describing is is a more likely attribute of a horn. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[fshanda 10+ year member]

The single biggest misconception involving a TL is that it must be "tuned" to the Fs of the driver.

Im curious about this. I just built one for my 12" TC-9 tuned to the Fs at 27hz. With only 600 watts its a beast compared to the 10" type R in a tuned box that the T-Line replaced. This thing shakes the hell out of my truck, something my last setup never did. I have the feeling though that its tuned to low and have bottomed out the sub twice when it drops to the really deep notes and I had to back off the volume to stop it. Would raising the tuning be a good option to stop this from happening? Im guessing I would have to build another box but was also wondering if I could just close down the exit of the port a bit to change the tuning. The last bend to the opening is 21" long from the bottom to the top of the box.

Im pretty happy with the outcome but wondering if I could make it sound even better.

 

[Immacomputer 10+ year member]

There is no need to flare the end of a TL to aid in coupling with a vehicle's transfer function. What you're describing is is a more likely attribute of a horn. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

It's an attribute of any 1/4 resonator, which the cabin of your vehicle is.

 

[ciaonzo 5,000+ posts]

Im curious about this. I just built one for my 12" TC-9 tuned to the Fs at 27hz. With only 600 watts its a beast compared to the 10" type R in a tuned box that the T-Line replaced. This thing shakes the hell out of my truck, something my last setup never did. I have the feeling though that its tuned to low and have bottomed out the sub twice when it drops to the really deep notes and I had to back off the volume to stop it. Would raising the tuning be a good option to stop this from happening? Im guessing I would have to build another box but was also wondering if I could just close down the exit of the port a bit to change the tuning. The last bend to the opening is 21" long from the bottom to the top of the box.
Im pretty happy with the outcome but wondering if I could make it sound even better.

Assuming that you have a traditional line with the appropriate cross section area to suit the Sd and Vas of the driver and the actual physical line length to support a quarter of a 27hz wavelength, you're most likely unloading in the low 20's. What's happening is that the pipe is offering maximum damping to the cone at 27hz but after that, depending on how large the cross section area is in conjunction with the terminus area (the exit of the line), it will offer a varying degree support as it unloads. Going with a shorter line will only make this situation worse, you want to go the other way and make the line longer. A band-aid approach might be to reduce the terminus area by adding a temporary/adjustable board and adding more stuffing to drive Fp downward but that will be at the expense of sensitivity. What you want to do is offer the actual physical line length for the lowest frequency you wish to produce regardless of the driver's Fs. This goes against some ideals but I can tell you from experience this is extremely effective. The offset of the driver's Fs and Fp will actually produce a less volatile phase/impedance plot, and with the minimum amount of stuffing necessary to smooth out impedance, your amplifier will be in heaven. But more importantly, you will not have the problem you described.

 

[ciaonzo 5,000+ posts]

It's an attribute of any 1/4 resonator, which the cabin of your vehicle is.

Indeed. Although I must say, I think of a car with one window down as more of a Helmholtz resonator than a quarter wave resonator. Now a school bus... //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[Immacomputer 10+ year member]

Indeed. Although I must say, I think of a car with one window down as more of a Helmholtz resonator than a quarter wave resonator. Now a school bus... //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

They model much more like a mass loaded line than a Helmholtz resonator. I have crunched the numbers and with my sunroof open, I should have a tuning frequency around 40hz or something like that but I have the most air movement at 22hz. Treating it like a mass loaded line, the numbers came closer to 25hz.