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3rutu5 12th July 2019 12:50 PM

T line \ bass reflex enclosure suggestions
 
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people, still kicking tires trying to think of some ideas for a boombox build.

TLines, (or bass reflex) enclosures, how would i look into sizing something like the photo?

This particular one the gentleman used bass box pro and 3d printed an enclosure for a small 3 inch sub, but i was thinking of its application for a small boombox.

i did find some posts from 2010-2014 on here and one had a spreadsheet, but i dont know if it is for the same application.

There was a number of taper selections but 1/11 was what seem to produce the smaller box, but i honestly dont know what that actually represents, it would be great to see a picture of what the internals would be. The required length was about 80cm which seemed ok and the FS around 60hz, which is what i would be chasing from a small 3.5" FR driver.

I've made a small T-Line once before by copying a design on here, but dont know what was done to size it and it had about 2 folds, which not sure if that satisfied anything. It sounded good, but lacked those lower notes.

If there is any direction it would be greatly appreciated, if i can picture something in my head and get some idea into sizing (keeping in mind im a noob, not audiophile) i can start trying to CAD up some options.

3rutu5 12th July 2019 12:53 PM

Only thing i really want out of this, is the smallest enclosure which can provide about a FS of around 60hz and most amount of folds :)

I know i can build a 0.17cuft ported box that easily hits 58hz, so now the challenge is something a lot smaller and cooler.

Scottmoose 12th July 2019 01:26 PM

In which case, build anything you like because your requirements are unfortunately incompatible.

OK, some basics.

-QW / TL enclosures tend to be physically larger for a given LF tuning than, say, a regular vented box.

-A large number of folds is of no benefit in itself, and in many cases (not all) can have a negative impact on performance.

That out of the way, a few more points regarding design.

-A QW / TL, like any other enclosure, needs to be designed for a given drive unit; they form a system, so you can't design a box, stuff any old driver into it, and expect good performance. Unfortunately, it doesn't work that way.

-With the above in mind, a QW / TL variation is not a panacea that allows you to tune lower than the driver is capable of. There's a limit to what can be done, i.e. how far you can go with a quality alignment.

-Tuning frequency of a QW / TL variation is a function of acoustical length; this is a function of physical length and the taper of the line. An expanding line (horn) needs to be physically longer for a given tuning frequency, a contracting line is physically shorter for a given tuning frequency. How much so depends on the degree of taper.

-Folds typically exist simply to pack the desired line into a box with the desired driver & terminus locations, rather than purely for the sake of themselves.

planet10 12th July 2019 05:07 PM

Quote:

TLines, (or bass reflex) enclosures, how would i look into sizing something like the photo?
There are number of designs that look like that,mostly called horns, that are really a bit of a joke. People like the looks, but that may be their only asset.

dave

3rutu5 12th July 2019 08:32 PM

Ok, that was just an example as there has been generally some confusion as to what that actually is, ie rear loaded horn, maze, transmission line etc

I guess I used that as a poor example, but thinking the was a straight fold TL. I will take a screen shot of the spreadsheet, but don't really know what a 1/11 taper is, I've heard of 1/4 wave and wondering if there is something lost in translation as I think it may have been a Dutch original.

Scottmoose 12th July 2019 09:45 PM

There's no technical confusion as far as I know, just that there is a lot of misinformation out there.

1:11? Using conventional notation, that would imply an expanding line (horn) with a 1:11 throat - terminus expansion ratio i.e. the terminus has a CSA 11x larger than the throat. Assuming whoever wrote that got it backward, it means a contracting line with an 11:1 taper ratio, i.e. the throat has a CSA 11x greater than the terminus.

3rutu5 12th July 2019 10:04 PM

1 Attachment(s)
Oh ok, makes sense.

What would this be? I thought it was a TL.

On the assumption that it is,would I need to size the first enclosure? Ps this was called a transmission line for a subwoofer and I have just scribbled on it, so please pardon the mess

planet10 12th July 2019 11:00 PM

Quote:

Originally Posted by 3rutu5 (https://www.diyaudio.com/forums/full-range/340145-line-bass-reflex-enclosure-suggestions-post5850188.html#post5850188)
What would this be? I thought it was a TL.

A poor one likely, certainly not anywhere near being optimal. Likely too small and doesn’t take advantage of driver offset.

dave

planet10 12th July 2019 11:03 PM

Here, some background: If the TL was designed using classic techniques it will VERY likely be underperforming. So that you know what to look for to avoid here is a good description of classic design methodology.

Classic TL Design -- Jon Risch

dave

freddi 12th July 2019 11:50 PM

eough guess of a 6.5 woofer in an undamped line as the nice sktech vs reflex of about the same volume. For the given bulk, that line is tuned higher. Its pipe harmoncs could be tamed with damping material but will lose bass.

https://i.imgur.com/wrIApdi.png


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