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Accidental MLTL Technique
Accidental MLTL Technique
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Old 9th November 2018, 03:08 AM   #431
GM is offline GM  United States
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Quote:
Originally Posted by jwicaksana View Post
Thanks GM. I agree, I always pay attention to tweeter height. Depending on the chair, when I sit my ears are at 110-120cm height. As drawn, the tweeter center is at 90.5cm and driver-tweeter border 86cm.
Now my room is very very small and if I am 'critically' listening, I am only 150cm away from the speaker baffle. Therefore, I am interested to make the tweeter sit at ear level. Any suggestions?
You're welcome!

Well, for one thing, the driver, vent should be at a TL's odd harmonics and the most common driver offset is the 3rd harmonic [~0.349], so using an average 115 cm hear height [Lb] and 1.8 cm thick panels, all dims inside [i.d]:

[Lb] @ 3rd harmonic = 115-1.8 = 113.2 cm
height [L] = 113.2/[1-0.349] = 173.886 cm
driver offset [Zd] = 173.886-113.2 = 60.686 cm
vent offset [Zv] @ 4/5th harmonic = 173.886*0.848 = 147.455 cm

Some folks have their own way to calculate the net volume [Vb], hence width x depth [cross sectional area/CSA], but most just use Hornresp's Loudspeaker Wizard [LW] or other software that can design TL/horns to find it, which due to the driver's tiny Vas combined with it's higher than average [Lb] makes for a relatively huge cab [~102.6 L = ~584 cm^2 CSA for example], which in turn 'demands' a large vent area [Av] and since it's generally not a good plan to have an [Av] > driver [Sd], highest tuning winds up being limited to ~40 Hz with just a baffle thickness ~116.9 cm^2 cutout, right at the lowest practical of 56*0.707 = ~39.6 Hz.

Up against a wall, and especially in a corner, it will provide a surprising amount of [mid] bass from such a 'puny' driver.

But you want/need as small as practical, so putting the driver at the 2nd harmonic results in much more 'ripple' in the bandwidth [BW], so will need considerably more damping as the trade-off to smooth it out as much as the larger cab will naturally be:

[Lb] @ 2nd harmonic = 115-1.8 = 113.2 cm
height [L] = 113.2/[1-0.21] = 143.291 cm
driver offset [Zd] = 143.291-113.2 = 30.09 cm
vent offset [Zv] @ 4/5th harmonic = 143.291*0.848 = 121.511 cm
vent area [Av] = 116.9 cm^2 x 1.8 cm long
net volume [Vb] = 17.79 L [Vas] *4 = 71.16 L
WxD [CSA] = 71.16*1000 = 71160/143.291 = 496.612 cm^2

All dims inside [i.d.] and approximate, so some rounding up is fine and damp [stuff] to 'taste' to get the desired 'fast'/tight', etc., in room response.

You can shrink [CSA] if still too big, just understand that the bass is already rolled off somewhat, so any smaller reduces bass output. Shrink it down to your 342 cm^2 and for smoothest roll off ideally need to reduce Av = 70 cm^2.

GM
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Old 9th November 2018, 08:46 AM   #432
perceval is offline perceval  Taiwan
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And this is the sim following GM's guideline, in case you're interested.
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Old 9th November 2018, 09:27 AM   #433
GM is offline GM  United States
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Looks nothing like that in real life, much less once damped and why I don't use that program. Does look like one of my big vent reflex BLHs before damping though, but construction wise nothing like a MLTL.

Of the ones I've used, MJK's MathCad worksheets does them best overall, but don't have it loaded, so use HR as an acceptable substitute since DB made so many upgrades, refinements.

Blue line = 496.61 cm^2 CSA/116.9 cm^2 vent

Red line = 342 cm^2/70 cm^2 vent

GM
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Old 9th November 2018, 10:20 AM   #434
jwicaksana is offline jwicaksana  Indonesia
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Hi GM and perceval, thank you again for this wealth of information.
So to sum up, I have a couple of options here:

Option one: Driver at ear height at 3rd harmonic
L = 173.886cm | CSA = 584cm2 | Vent = 116.9cm2 cutout only at 4th or 5th harmonic

Option two: Driver at ear height at 2nd harmonic
L = 143.291cm | CSA = 496.612cm2 | Vent = 116.9cm2 x 1.8cm at 4th or(*) 5th harmonic

Option three: Driver at ear height at 2nd harmonic, smaller foot print
L = 143.291cm | CSA = 342cm2 | Vent = 70cm2 x (**) at (***)

The (*) above denotes my further questions:
(*) Placed at either 4th or 5th is okay? Is 5th harmonic = end of the line opposite from driver side?
(**) What is the length of the vent, or is this just with baffle thickness?
(***) Placed also at 4th or 5th harmonic?

Re: the need to make it as small as practical, allow me to ask, is this related to my listening space area? I wager the answer is yes and my room is tiny, at 2.4x2.9m. Thanks again!!
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Old 9th November 2018, 03:11 PM   #435
Scottmoose is offline Scottmoose  United Kingdom
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I like those two Greg. Prefer the larger, obviously. But the little one still has that extra gain that comes in handy & should have a decent kick to it for a speaker that size. I didn't get chance to tweak the damping for either in the software as I only had a minute; larger is a touch less, smaller a bit too much. Never mind, near enough for jazz & they still look good.
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Old 11th November 2018, 06:09 AM   #436
jwicaksana is offline jwicaksana  Indonesia
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Quote:
Originally Posted by perceval View Post
If you want to raise the speaker, make a base for it.
Even better if you can fill it with sand.
Hi Perceval, I must have missed this post, but it's really a practical idea. Thank you for this.
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