10” MTM design help

[GM]

I’ll ask again…….is there anyone who can please help me come up with a box that might allow me to get into the f3 of 30/low 30’s range (giving some semblance of quality) with two of these 10” drivers per box?

GM mentioned expanding taper line would be best but size prohibitive……..is this the style mentioned ? (screenshot is from troels website, i dont guess it’s copyrighted?)

or if this is not going to work with these drivers and not a good idea, please say so……no hurt feelings here i’ll just use them sealed w/sub

Depends on the driver's specs.

Yes, that's a parabolic (expanding) horn.

I posted based on the delta 10b specs and just assumed the custom's specs wouldn't 'swing' it back enough to be a different flare type.

Any driver can work in a TL, though may not meet all your performance goals, so being a custom driver, please post specs.

 

[planet10]

That is a common way of doing that. Also:

ML=Voigt in the back, aperiodic midTL up front:

Metronome

I am sure wilder configurations could be conceived.

dave

 

[mountainman bob]

Depends on the driver's specs.

Yes, that's a parabolic (expanding) horn.

I posted based on the delta 10b specs and just assumed the custom's specs wouldn't 'swing' it back enough to be a different flare type.

Any driver can work in a TL, though may not meet all your performance goals, so being a custom driver, please post specs.

Thanks GM, specs were in the first post, and yes I believe they are different enough to change things……see pic below.

Thanks Dave, going for the simplest shape possible……exterior dimensions 14”w x 16”d x 55” h +/- (mtm horn centered on 38” height) these dimensions can vary except for exterior width (for 12” wide horn) and the 38” horn center height.

 

[planet10]

exterior dimensions 14”w x 16”d x 55” h +/-

A guess. And smaller than i would guess for 2 x 10”. The size will be determined by the drivers spec and the box design. A voigt is not the smallest.

dave

 

[mountainman bob]

Yah, like i said subject to change, and it can go wider also just no less than 14”w ……..probably no more than 60” tall and 20” deep would be my preferred max.

 

[GM]

Thanks GM, specs were in the first post, and yes I believe they are different enough to change things……see pic below.

Thanks Dave, going for the simplest shape possible……exterior dimensions 14”w x 16”d x 55” h +/- (mtm horn centered on 38” height) these dimensions can vary except for exterior width (for 12” wide horn) and the 38” horn center height.

You're welcome!

Brain 'fade' Those are the ones I used to ~ calculate size.

OK, a ~32 Hz Fb max flat MLTL (no fold) power limited to ~15 W below ~90 Hz with 38"/floor = 58.25" o.d./56" i.d. tall based on 0.75" panel thickness, width x depth = ~408.5"^2 i.d. = 18" i.d. square, so way too big at ~376.4 L net.

Shrunk to your max 14" x 20" o.d., Fb = Fs, power limited to 35 W, ~213 L net, vent = 8" dia. x 1" long and instead of a flat response, it sims a 'toe tapping' party speaker with a ~50 - 150 Hz +3 - 4 dB boost shelf.

 

[mountainman bob]

Thanks GM, if anyone can cause confusion it’d be me 😉

So no beuno on the TL, heres what i come up with in ‘speaker box lite’ for these 2x10” @ 100w in a 2.8 cf sealed (yellow) and 6.5 cf slot ported x2 (red)……these are the best alignments I could come up with, am I in the ballpark?

Dave, would a onken alignment be of any help here?

appreciate the guidance 😎

edit; Just curious, is the GM ML-Voight plan that Dave posted above yours GM?

 

[planet10]

would a onken alignment be of any help here?

I do miniOnken alignments, they tend to smallish with really well-defined articuate bass, but not LF extention.

A quick look suggests they could be fit into 150 litres with F10 in the low-mid 20s, F6 low 30s.

The shape you suggest is going to be a quarterwive pipe. I would really have to fight that.

33x53x86 cm internal (1st guess) for a CGR. 13x21x33"

dave

 

[GM]

Thanks GM

So no beuno on the TL, heres what i come up with in ‘speaker box lite’ for these 2x10” @ 100w in a 2.8 cf sealed (yellow) and 6.5 cf slot ported x2 (red)……these are the best alignments I could come up with, am I in the ballpark?

edit; Just curious, is the GM ML-Voight plan that Dave posted above yours GM?

You're welcome!

??? No driver height?

No way these are at 100 W! The sealed is ~7 W and the vented is the same as the MLTL, ~35 W; can't fool Mother Nature, so not many 'free lunches' in speaker design.

'in the ballpark' in what way? I mean there's nothing intrinsically wrong with them if they meet the needs of the app, otherwise both are too under damped for HIFI for most folks.

Yes, that's my ML-Voigt/MLhorn prototype I cobbled together for one of the long gone Atlanta DIY Meets that local (still active) member Woody took home and IIRC the driver was 'stitched' by Dave. It caused a bit of a stir overall as I don't think anybody that didn't know me believed it was an 'el cheapo' RS driver nor full of internal EQ frequency shaping filters due to its smooth, yet uncharacteristically 'fullness' down in the mid bass as at the time nearly all the attendees were Peeee Eeeee forum members with little/no exposure to MJK's TL docs yet.

 

[mountainman bob]

Thanks Dave, was just curious…….no need to fight! 😉

GM there‘s no input for driver height on that calculator l know its not exactly pro status but i was under the impression speaker box lite was fairly accurate? 100w was entered (see circled area in pic)

Cool story on the rat shack speakers. 😎

Well what box would you build for a mtm version of this speaker?

edit; I already have them so theres no turning back now!

 

[GM]

I'm not familiar with the program, just know what you posted is misleading at best.

Well, 'BIB' (bigger is better) 'ruled' my active DIY 'career' and still advocate it, but the folks around the world quickly/politely set me strait that as a whole their listening rooms were closer to my bedroom closets in net Vb, so personally would build the full size max flat MLTL and EQ as required in room, but even the little one outperforms the basic BR overall and if wanting the same LF extension you can use a longer vent to roll it off a bit, which in room is often a good plan if near a wall and especially in a corner.

Note that a bit of damping smooths out all those vent harmonics comb filtering with the drivers.

 

[AllenB]

what box would you build for a mtm version of this speaker?

Are you considering something for mode management, such as multi-subs? How do you envision the low end happening overall?

 

[mountainman bob]

OK, so I found this calculator which is from the same site you linked to a few posts back, I’m assuming its a reputable site? http://www.mh-audio.nl/Calculators/TQWT.asp?c=y#ready

Heres a screen shot from it, i entered double Sd for the two drivers but not sure how to deal with driver placement as its only set up for one? Is this closer to what i need to be looking at? Had to cut off a little because i couldnt fit it on the screen, but the pertinent info is there…….it doesnt seem that large at all.

Allen, not quite sure what you mean…..isn‘t that a issue for after its built, or are you suggesting there’s something that can be designed in? In this case i‘m just looking for a 30hz main if it needs subs later then address it, no?

 

[mountainman bob]

Upon further digging, it seems (according to scottmoose in another thread…..if i understand correctly) to incorporate two drivers into this scenario one needs to use the center between the two in the same place the single driver was centered and all should fall back into equilibrium? It will fit that way (barely) and to get my proper tweeter/ear height i’ll have to build up a base a few inch’s (unless internal dimensions are commensurate, as in taller but less deep?

GM, upon mocking up the size of the above speaker i see it is rather large after all, but do-able.
the vent size it requires is exactly the i.d. of schedule 80 pvc pipe so thats no problem. I did see you make mention in another thread of less port length the better on down to baffle thickness?

 

[GM]

Within the limitations of the design, yes.

FWIW I simmed it in HR as a default single driver and the vent was tuned almost an octave below Fs and even opening it up to an Av = Sd, 1.8 cm baffle thickness vent it was still tuned a bit too low with the excessive 'ripple' of such a large reflex vent, so don't see it working for you either without going somewhat bigger than 2x mine since excessive damping will in theory be required, rolling off the woofer's below ~100 Hz and why my original SWAG was so big.

Don't recall making such a general statement since it depends on the app, though in theory Av = Sd is a general limit for a baffle thickness BR vent, which I've used many times on MLTLs with drivers that had a large Vas.

 

[mountainman bob]

Thanks GM, the generalization was more my take away of your preference, not a strict rule.……apologies, I didnt bookmark it.…….. ive been skimming through any/all info related and its kindly making my head spin……..so many opposing views, terminology contradictions, even just defining what the letters mean seems contentious!

Anyways, all this still leaves me scratching my behind raw…….gonna need the XL tub of Desitin cream before it over with! 😆

So out of curiosity is my doubling of the Sd in the above mh-audio calculator (post #33) not appropriate for modeling the two drivers of a mtm? Is that model just plain wrong or is it me?

 

[GM]

You're welcome!

Yeah, been 'fighting that battle' all the time I've been on the various audio forums, plus I 'muddied the waters' with my trying to get MJK to expand basic TL, TQWT to better describe all their variances (MLhorn, etc.), which he strongly refused.

No, you're right.

 

[mountainman bob]

OK, well thanks again for putting up with my ignorance, so i should forget about that mh-audio calculator all together or can anything useful be gleaned from it? I really like that configuration (even if its wrong!)

I wouldn’t be putting so much effort into this but the reports of effortless bass and less stressed mids (if done correctly) has me wanting to at least try it……..i know these may not be the ideal drivers but they have some of the attributes (for TL) i’ve seen mentioned in a positive light.

So for lacking any more direction than i started with…..what next?
I did download LTspice and the version spicyTL (it all works on mac) but for the life of me cant figure out how to use it! 😵
https://www.diyaudio.com/community/threads/spicytl-transmission-line-simulation-model.365782/

 

[GM]

Well, the calculator is riddled with enough 'cautions' to help guide folks that except for the grossly wrong port design it works better than the traditional DIY way (pre MJK) unless using horn theory as I do and if you were to adjust dims to put the 'tweeter' at the 38" o.d. height (H), which lengthens the acoustic path-length (T4) to a larger depth (D), base area (Se/Sd) you would come closer to what I calc'd volume (Vb), area wise (WxD).

No clue, have only ever used MJK's and DmB's HR for the various TLs/horns.

 

[mountainman bob]

kindly sure I’m following you, keep everything the same lengthen t4 (from the lower/wider point) so that tweeter height is 36 (i remeasured and i can do 36”) then increase depth to keep t1 the same.
So do i raise the upper driver to center it on the same spot where the single (as drawn) was centered or put the horn and second driver beneath the single? Then just have to figure out a better port, i’d guess a slot port at the bottom would be easier and more attractive……would a aperiodic type of port be an option?

thanks again,

I’ll sketch something up in the morning