FE127 project

[jim_vt]

Looks good!

I'll be building mine shortly...

 

[edjosh23]

Are you going to use GMs design or another design?

Josh

 

[jim_vt]

Just going to be using that design...with a round port.

 

[edjosh23]

GM,

Thanks for the design and help.

I was wondering if you could explain to me your 9:1 ratio.

total volume is 761.58"^3
1/9th that is 9.4"^3
volume of your calculated port is 10.48"^3
volume of my port 8.2473"^3

So I'm guessing you calculate port volume as being greater than a 9:1 ration of box volume to port volume? Why is that? and why not exactly 1/9th total volume? I've read MJKs papers but I don't remember this information. Also I've been wondering why TLs should be 4xSD cross sectional. I don't remember either being in MJKs website.

Thanks,

Josh

 

[GM]

Greets!

You're welcome!

The aspect ratio of the vent's length to height. Yours is 7.43/0.5 = 14.86:1, so is theoretically somewhat aperiodic due to all the added acoustic resistance.

TL's don't have to be 4 x Sd. TLs are just another vented alignment in that net Vb is the main factor, then it's just a matter of dividing the length into it to get the CSA.

GM

 

[edjosh23]

I'm still a little confused about the vent ratio, can you go into more detail about how you calculated 2.28" . My understanding of what you have said is that my port should have been more like 3/4" instead of .5"?

Also, I don't have time right now but I will try and find it, I think on Bob Brines's website under the TL how to tutorial it says that MLTLs should be 4xSD.

Thanks,

Josh

 

[edjosh23]

Well I was able to do a little searching and on this page Bob has a chart comparing straight, TQWT, and "conventional" TLs. He also says that port length is .5xSD. But I don't know if that is for that speaker only.

Also, if I remember correctly in MJKs mathcad sheets when you download it has his models from his Focal speakers, and the box was 4xSD. I'm not sure, but I think that is how they came.

I'm trying to understand TL design a little more.

Thanks,

Josh

 

[planet10]

it says that MLTLs should be 4xSd

Keep in mind that using Sd is just a convention that was established with classic TL design. In actual fact Sd has no correlation* with the size of a TL. It is Vas that largely detrmines this.

*(except for the general trend that the larger a driver tends to have a larger Vas)

dave

 

[edjosh23]

Thanks Dave,
but is there a good way to calculate port volume?

Thanks,

Josh

 

[GM]

I'm still a little confused about the vent ratio, can you go into more detail about how you calculated 2.28" . My understanding of what you have said is that my port should have been more like 3/4" instead of .5"?

Also, I don't have time right now but I will try and find it, I think on Bob Brines's website under the TL how to tutorial it says that MLTLs should be 4xSD.

Thanks,

Josh

Greets!

Please read his caveat underneath the chart.

7.43/9 = ~0.82" height (11/16" is close enough), causing an increase in the vent's length.

What's confusing? The mass of air in the vent acts as a piston of 'x' mass and as a duct morphs from round to square to rectangular with increasing aspect ratio, wall friction and terminus edge diffraction increasingly damps (distorts) its output.

I didn't calc 2.28", I said the length needed to be ~2.82", which is just scaled up from the original vent size of 1.5" dia. x 1.125" long (attained using MJK's WS) to your slot vent's 2.175" equivalent diameter. Since a slot vent terminates on the inside with three parallel boundaries it needs a different end correction than a round one, so the toplate of the vent needs to be somewhat shorter than the scaled 2.82" (if round) to achieve the same Fb.

Since we're mirror imaging the termination's area on three sides this puts it in 1/8 space, so the toplate's cut length is ~2.82" - (8/(3*pi)*SQRT((0.5*7.43)/pi)) = ~1.9", or a bit shorter than my comment that your 2.22" was close enough (I apparently had a 'senior moment'), ergo it's theoretically tuned a bit lower than when a round vent is used.

GM

 

[edjosh23]

I think I got it now, sorry for the typo, I meant to say your calculation was 2.82".

I'm still new to this whole TL idea and I'm trying to get things straight. I'm gonna have to go back to MJKs website and read again. Its difficult for me because I have tried to read MJKs articles 2 times first time, complete failure (way over my head at the time) second time I understood quite a bit of it, the more I read the more I understood the sections before, because I was still learning. I'm 17 and have not been designing speakers for long, so hopefully with one more read through I can understand it better.

Thanks,

Josh

 

[jim_vt]

One question before I start construction...

I've never worked with a TL design before, so I'm unsure of if I should do this or not. The enclosure seems like it could benefit from the use of a brace a few inches below the driver, stiffening the cabinet in the middle. I realize the cabinet would have to be made slightly larger to compensate for the lost volume due to the extra material, but would this hurt the performance of the TL at all, having cross pieces set up like that?

Just curious before I fire up the table saw...

 

[GM]

Greets!

You're welcome!

I'm 17........

Ah! This explains alot. I remembered you mentioning somewhere that you had an SC300, so made the leap to you being much older........ you are quite fortunate.

I understand where you're coming from, I would have found it a tough read too if I didn't already have a pretty good understanding of what's what, and I know some fairly savvy audio types that still don't have a clue and apparently determined to stay that way, so keep 'chipping' away at it and sooner or later you'll have an epiphany and wonder why the obvious plum evaded you.

GM

 

[GM]

Greets!

High aspect ratio cabs don't suffer as much from compression/rarefaction pulses as a standard ratio one, instead having more pressure along its length, so a rigid top and bottom is key to good pipe action. Doubling up material thickness at each end is a good tweak. An overdamped driver still needs a rigid 'platform' to 'work' from though, so bracing near it is normally a prerequisite for good performance. Hardwood dowels tied together in an 'X' frame works very well and don't reduce Vb enough to matter, but cabs this small don't really benefit from it if made from at least 11 ply 19mm (3/4") void free plywood. Until the braces present an obvious obstruction in the pipe, they are 'invisible' to the wave propogation of the super long WLs.

Preloading the driver can really 'tighten it up' if it doesn't have a well damped construction (few do): http://melhuish.org/audio/images/press-screw.gif

GM

 

[edjosh23]

I remembered you mentioning somewhere that you had an SC300, so made the leap to you being much older........ you are quite fortunate.

I understand where you're coming from, I would have found it a tough read too if I didn't already have a pretty good understanding of what's what, and I know some fairly savvy audio types that still don't have a clue and apparently determined to stay that way, so keep 'chipping' away at it and sooner or later you'll have an epiphany and wonder why the obvious plum evaded you.

GM

When I'm not at home doing hours and hours of school work I'm a mechanic at a shop near home, mostly during the summer working 40-50hrs a week. My sc300 has 180k+ miles on it. Its a 93 but in great shape. (bought it used and very cheap)

It is nice being seen as an adult on the forum, but sometimes things get over my head and I have to ask for explanations. I think I've learned a lot and my woodworking skills have improved a lot, but I'm not very good at TLs and I'd really like to try a horn. My first wr125s were TLs on accident. Tim told me that if the port was .5" taller it would be a tl, so I did it and then I started researching.

I'm also trying to do a little research paper on TLs for school, but I'm afraid I may not be able to go into too much detail. It is for the International bachelorette program at my school, we have what is called an "extended essay". This essay is supposed to be about 4kwords and is sent to any english speaking teacher in the world (that works for an International Bachelorette school) and they have to be able to understand my paper. For this I'm afraid I won't get very deep into the theory, but I want to mention the essentials and I'd like to be able to show equations for port size.

by the way GM, I saw you live in chamblee, I live just outside Decatur.

jim_vt,

I added a really small brace to this enclosure and I'm going to make up for lost volume by adding stuffing brace is only .5" x 1" x 4.58" a couple inches below the driver.

Thanks,

Josh

 

[youyoung21147]

I'm 17........

I'm 17 too lol, welcome to the DIY club

I'm right now also designing an enclosure for FX120 or FE127E, but it looks like a larger TQWT ( almost 1m tall). It should go down to 50Hz -0dB with the FX120, maybe a little more with Fe 127e. I'm now waiting for the enclosures, which a friend of mine will build for me (he's a carpenter )


Here are some sims I did for this enclosure. The hump is not an issue, it is there to :

1) help keeping baffle losses minimal
2) in a small room, the energy from the hump is "redistributed" at lower frequencies (look at my TangBand designs if you are not convinced)


Good luck with your speakers !

 

[planet10]

an enclosure for FX120 or FE127E, but it looks like a larger TQWT

Dimensions?

dave

 

[youyoung21147]

I keep the internal dimensions "confidential" until I know how it works

I designed it around 3 main goals :

- maximal bass extension (hence the large cabinet)
- clean impulse response (hence the TQWT choice)
- very low midrange pollution trough the port

and finally I gave up the horn solution, way too big in my bedroom

The external design is 960mm (tall) 350mm(deep) 200mm(large) so it is much larger than GM's design ! I hope it will get me all the bass possible from my FX120, these are promising drivers (2mm Xmax, not bad compared to Fe127's 0.6mm).

I'm very impatient to hear them !

 

[edjosh23]

I'm 17 too lol, welcome to the DIY club

youyoung21147,
I've been a member for over a year actually.

I've seen your website many times and I like the TQWTs you have done. I really like the fx120s. I've been trying to design a reference project for months now, but I can't come up with the right drivers. I was originally planning on using the fx200 until I found out it was discontinued.

Thanks,

Josh

 

[youyoung21147]

Hey, edjosh, you achieved more projects than me in fact ! I've visited your webpage, there are nice pictures !

I like the TB surrounds in the aperiodic box, with no parallel sides.
How do they compare with the B3-S you built for your philosophy class ? Are the boxes ported ? I assume the B3-S have more bass don't they ?

Concerning your FE127 project, I can understand you are jealous, the Fostex are better than the TB I think. I could directly compare my friend's FE127 with my FX120, there is again a world of differences. Both drivers justify their price .
I'd be curious to compare the CSS with the FE127, I assume the FE127 is more detailed, but has less bass.

So what is your next project ?