PDA

View Full Version : 1/4 Wave TL Advantages/Disadvantages



iDesignBoxes
03-25-2008, 01:47 AM
I'm doing some research and wanted to know what the advantages and disadvantages of a 1/4 wave TL box are... and what they have over a ported box.

Lets use an example of 2 15" MAW-15 subwoofers on 600 watts in a 6 cube net TL or a 6 cube net ported box for this...

twisztdauthorit
03-25-2008, 01:50 AM
disadvantage : space

iDesignBoxes
03-25-2008, 01:53 AM
disadvantage : space

True enough, but lets leave space out of this :)

I am contemplating building a 1/4 wave and I have 52" depth x 37" width x 40" height to work with.

twisztdauthorit
03-25-2008, 02:30 AM
efficiency

xtremebassjunky
03-25-2008, 02:31 AM
hmmm....

hempy
03-25-2008, 02:45 AM
I know very little about the design, but I am pretty sure you're not going to fit a TL (even 1/4 wave) for 2 15" woofers in 6 cubes.

dragnix
03-25-2008, 02:47 AM
they're not designed to get loud

iDesignBoxes
03-25-2008, 02:49 AM
I know very little about the design, but I am pretty sure you're not going to fit a TL (even 1/4 wave) for 2 15" woofers in 6 cubes.

Net doesn't account for port area or subwoofer displacement.

BrianChia
03-25-2008, 04:27 AM
Net doesn't account for port area or subwoofer displacement.

Port area and subwoofer displacement are irrelevant here. There is no "box volume" and there is no "port". Two 15's just aren't going to work in the space given.

iDesignBoxes
03-25-2008, 04:35 AM
Given that I have 52" depth x 37" width x 40" height to work with, what are the advantages of a properly built 1/4 wave TL opposed to a ported box of 6 cubes with the same drivers and same power?

BrianChia
03-25-2008, 04:58 AM
The driver will behave similarly to a free air or IB setup, but the rear wave of the driver is reversed in order to bring it back in phase and help extend the low end. Because there is no actual "enclosure," instead just a wave/phase guide, it will sound "clean" like a good IB or free air setup because you don't have the complex system of enclosure reflections or port resonances conflicting with the driver output. The sound is characteristic of a true IB setup, but rolloff behaves closer to a 2nd order system whereas a free driver or IB is a 1st order system. The rolloff is thus similar to that of a sealed box but typically with much lower extension.

Given your dimensions, you might get away with using 1 15", but I still doubt it. You'd have to calculate a correctly designed line length/taper/folding pattern to know for sure.

iDesignBoxes
03-25-2008, 06:54 AM
http://img.photobucket.com/albums/v486/mykul_16/tlfinal.jpg

Bingo.

I think it's right... It's my first attempt.

I needed 10.8654 feet of port length... which is 130.3848 inches. I was able to come up with 130.4375 inches.

I needed 234.453469 square inches of port area. 11 7/16 x 20 1/2 = 234.46875.

Immacomputer
03-25-2008, 08:23 AM
Transmission line enclosures are not correctly designed by taking the Sd and Fs of the driver and making them your line length and cross sectional area. It will work but it won't really be optimal.

T-lines are not always more efficient than ported or bandpass systems and many times they transfer gain for bandwidth.

The sound is just like Brian described as the driver can sound very natural and the roll off is much more shallow than compared to ported enclosures. The electrical impedance also should stay pretty flat and the natural peak around resonance should either be lowered or about the same as the nominal frequency. The extra air mass in the line will act like a mass on the drivers and it will substantially lower the resonance point of the system.

For instance, my AV12 has an Fs of 24hz and 76in^2 of cone area. I designed a line with only a 35hz line length and only 42in^2 of port. The sound is phenomenal but efficiency is much worse than the ported enclosure I had that was 2.2 cubes tuned to 32hz. I had to greatly increase the gain to get respectable output but when I did, I got a very smooth response that got very low and blended with my front speakers effortlessly. It sounded much better than the sealed enclosure I had it in and could get much lower.

This is the measured response I got in car at low volumes (high volumes not possible due to using only a 100wrms amp):

http://i26.tinypic.com/28bcivc.png

Above 60hz, I'm out of the main boost from the transfer function. With the mids playing, the response is boosted and is pretty **** flat. I don't have those measurements on my PC though.

iDesignBoxes
03-25-2008, 06:22 PM
Transmission line enclosures are not correctly designed by taking the Sd and Fs of the driver and making them your line length and cross sectional area. It will work but it won't really be optimal.

T-lines are not always more efficient than ported or bandpass systems and many times they transfer gain for bandwidth.

The sound is just like Brian described as the driver can sound very natural and the roll off is much more shallow than compared to ported enclosures. The electrical impedance also should stay pretty flat and the natural peak around resonance should either be lowered or about the same as the nominal frequency. The extra air mass in the line will act like a mass on the drivers and it will substantially lower the resonance point of the system.

For instance, my AV12 has an Fs of 24hz and 76in^2 of cone area. I designed a line with only a 35hz line length and only 42in^2 of port. The sound is phenomenal but efficiency is much worse than the ported enclosure I had that was 2.2 cubes tuned to 32hz. I had to greatly increase the gain to get respectable output but when I did, I got a very smooth response that got very low and blended with my front speakers effortlessly. It sounded much better than the sealed enclosure I had it in and could get much lower.

This is the measured response I got in car at low volumes (high volumes not possible due to using only a 100wrms amp):

Above 60hz, I'm out of the main boost from the transfer function. With the mids playing, the response is boosted and is pretty **** flat. I don't have those measurements on my PC though.

Now, after reading this, I am a bit skeptical about going with the TL.

This guy makes them seem like the perfect box and this was one of the reasons I had originally decided on going with a TL.

http://www.stevemeadedesigns.com/board/index.php?showtopic=1828

Decisions, decisions...

dragnix
03-25-2008, 06:24 PM
Now, after reading this, I am a bit skeptical about going with the TL.

This guy makes them seem like the perfect box and this was one of the reasons I had originally decided on going with a TL.

http://www.stevemeadedesigns.com/board/index.php?showtopic=1828

Decisions, decisions...

I believe it has been proven that what that guy says holds little validity and in fact his design of his TL box is flawed.

What i heard :D

iDesignBoxes
03-25-2008, 07:39 PM
Well, ****!

:(

Immacomputer
03-25-2008, 08:28 PM
www.quarter-wave.com

Read the PDFs there and you will learn a ton. There is some complicated math there so be ready!