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Accidental MLTL Technique
Accidental MLTL Technique
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Old 6th November 2018, 06:16 PM   #421
GM is offline GM  United States
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Originally Posted by xrk971 View Post
Usually adding stuffing in MLTL from closed end to driver and maybe lining two of the walls with felt gets rid of boomy bass.
FWIW, for my acoustically large, non tapered MLTLs I sim +3-6 dB at tuning when using a typical basic T/S BR program, recommending no damping beyond lining the top, back, one side down to below the vent with 1" acoustic fiberglass insulation [OC 703] since I know from experience that a MLTL will be much too over damped in most cases, with worst case scenario requiring a bit more damping and/or only needing to 'critically' damp the vent to remove any audible 'ringing'.

Indeed, when folks used MJK's MathCad software's simmed recommended amount of polyfil, the folks that did update me/us on their final 'as built' system more often than not said they had to pull some, to nearly all, of it back out, so finally just began suggesting folks 'stuff to taste'.

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Old 7th November 2018, 02:02 AM   #422
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Originally Posted by perceval View Post
This is what happens when you go bigger and taller.
With a basic reflex, not a proper MLTL. Please see my response to X re peaking, etc., so we'll have to 'agree to disagree' since even if it does happen with some drivers, the minor amount of damping deals with them and if for some reason a vented alignment actually has too much bass [a very rare occurrence, especially with smaller drivers], then the tried n'true tweak 'stuff a sock in it' normally solves the problem.

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Old 8th November 2018, 03:18 PM   #423
jwicaksana is offline jwicaksana  Indonesia
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Originally Posted by perceval View Post
Hi Jonathan,

I should always proof read my post, but I don't always, especially after a camping night when we didn't sleep much! Some family member having trouble with the police in China... long story short, young kid got scared, all fine now!

Yes, 18x18x95 will be great. Making it taller or bigger will unbalance the whole thing, and make it sound boomy. Very un-natural.

Your vent dimensions are perfect and thanks for picking up my mistake... it is 7cm long... not 0.7cm. Damn beer!

My sim had the driver at 42cm (centre point of the driver) from the top.

If you place the driver at 20cm from the top, you get this -2dB ripple between 200 and 350Hz. If you are ok with that, then go ahead and place the driver higher up.

Click the image to open in full size.

If your tweeter has a closed back, it will be fine. If you have to make a box for it, you'll have to adjust dimension a little to compensate.

As X mentioned, you may or may not need a BSC.

Placing the enclosure up on the wall will give it a bass boost, and you might not need it. If you prefer the extra imaging from the enclosures off the wall behind them, then you might consider a BSC to bring the top down a bit. All will be according to your taste.

Hopefully all this is correct as there were a few beers involved again tonight!
This is it, rendered as discussed. Driver center is placed 20cm from the top. And tweeter face is rendered here. Actual cutout should be smaller. Do I need to make the enclosure taller?
Also, I don't know if this tweeter is sealed or not.

acr 9kh - Google Search

I am thinking I can put the tweeter on top: open baffle or U-baffle, or inside the enclosure, with a dagger. What do you guys think?
If I understand correctly, crossover frequency plays a part in determining center to center (CTC distance). I am looking to cross somewhere between 3000-6000Hz depending on how high and how well the woofer reaches.

Oh BTW I've placed an order for the woofers, and have ordered a Dayton UMM-6 that a friend will bring from the States. Thanks guys for nudging me in the right direction.
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File Type: png MLTL.png (124.4 KB, 80 views)
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Last edited by jwicaksana; 8th November 2018 at 03:23 PM.
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Old 8th November 2018, 03:35 PM   #424
xrk971 is online now xrk971  United States
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Accidental MLTL Technique
What tweeter are you using? In general, most teeeters are sealed to make installation easy and to prevent any chance of woofer movement from blowing out the tweeter diaphragm.
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Old 8th November 2018, 04:12 PM   #425
perceval is offline perceval  Taiwan
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ACR really needs to update their website.

I would contact them and ask if it is sealed or not. If it is, just mount as is. If not, you will have to build a small chamber behind it, nothing too big.

As for the XO and CTC, with a bezel that large, I wouldn't worry too much... you won't be able to get so close to the woofer anyway!

Cool to see that you got the ball rolling!
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Old 8th November 2018, 06:36 PM   #426
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Originally Posted by jwicaksana View Post
Do I need to make the enclosure taller?

I am thinking I can put the tweeter on top: open baffle or U-baffle, or inside the enclosure, with a dagger. What do you guys think?
If I understand correctly, crossover frequency plays a part in determining center to center (CTC distance). I am looking to cross somewhere between 3000-6000Hz depending on how high and how well the woofer reaches.

Thanks guys for nudging me in the right direction.
You're welcome!

Normally, barring any speaker max height limitations, the tweeter is placed at the [average, if > 1] listening ear height [Lp], so what is it?

Correct, ideally it needs to be < a 1/4 WL of the XO point away [~34400 cm/4/Hz], but history has shown that this goal only needs to be its perceived height at the [average] [Lp], so often can be pretty far apart on the baffle or 'focused' to this [average] point when the components are quite large, such as huge PA/cinema systems.

As you can see then, at 3-6 kHz the ideal c-t-c spacing even at 3 kHz is impractically small, but back up far enough from the physical minimum dictated by the driver sizes and it's doable in a reasonable size room when typical cone/dome drivers are used; big horns like I prefer, not so much.

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Old 8th November 2018, 10:56 PM   #427
jwicaksana is offline jwicaksana  Indonesia
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Originally Posted by xrk971 View Post
What tweeter are you using? In general, most teeeters are sealed to make installation easy and to prevent any chance of woofer movement from blowing out the tweeter diaphragm.
It's called ACR 9kh. ACR is an Indonesian brand, I've always read that they were associated with Fostex back in the day, and they are the OEM manufacturer for big brands. Most recently, they are known internationally for their SB Acoustics line. I want to know how their lower end line hold up against mid-low level international brands
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Originally Posted by perceval View Post
ACR really needs to update their website.

I would contact them and ask if it is sealed or not. If it is, just mount as is. If not, you will have to build a small chamber behind it, nothing too big.

As for the XO and CTC, with a bezel that large, I wouldn't worry too much... you won't be able to get so close to the woofer anyway!

Cool to see that you got the ball rolling!
Well I've contacted them for a number of times asking for information and heard nothing from them. It seems to me the main core of their business is PA speakers, so that section of the website is quite well-maintained.
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Old 8th November 2018, 11:14 PM   #428
jwicaksana is offline jwicaksana  Indonesia
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Originally Posted by GM View Post
You're welcome!

Normally, barring any speaker max height limitations, the tweeter is placed at the [average, if > 1] listening ear height [Lp], so what is it?

Correct, ideally it needs to be < a 1/4 WL of the XO point away [~34400 cm/4/Hz], but history has shown that this goal only needs to be its perceived height at the [average] [Lp], so often can be pretty far apart on the baffle or 'focused' to this [average] point when the components are quite large, such as huge PA/cinema systems.

As you can see then, at 3-6 kHz the ideal c-t-c spacing even at 3 kHz is impractically small, but back up far enough from the physical minimum dictated by the driver sizes and it's doable in a reasonable size room when typical cone/dome drivers are used; big horns like I prefer, not so much.

GM
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?
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Old 8th November 2018, 11:17 PM   #429
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Hmm, 1" VC, 2-20 kHz, seriously doubtful it's open back. Open back historically were rated much lower at Fs.

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Old 9th November 2018, 01:45 AM   #430
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Originally Posted by jwicaksana View Post
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?
If you want to raise the speaker, make a base for it.
Even better if you can fill it with sand.
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