Need some help for designing a MLTL

[Mutuano]

Hello guys!

I've been thinking to build a straight MLTL in a 6' midbass + 1' tweeter configuration with a midbass which has the following T/S parameters:

Fs = 36Hz
Qts = 0.34
Qms = 2.81
Qes = 0.38
Vas = 31 L
Re = 6.9 Ohms
Le = 0.34 mH
Sd = 0.0131 m2
BL = 7.6 T-M
Sens = 87.98 dB

Reading sites as t-linespeakers.org, quarter-wave.com, from Planet10, Bob Brine and Troels Gravesen I've reached a frankstein cabinet sized around 970mmH x 189mmW x 205mmD and 76mmDia x 102mmLenght vent, 102mm up from the bottom (internal). Plus tweeter should be positioned roughly from 750mm to 800mm from the floor.
Actually I didn't simulate anything and I'm wondering to get your help in:
1. to correct the dimms if necessary;
2. positioning the mid and tweeter; and
3. to stuff the cabinet;

I appreciate your help in making these design come true.
Regards,

[GM]

Greets!

Assuming I did all the conversions correctly and the dims are i.d.:

38.189" H x 7.441" W x 8.071" D (1.327 ft^3)/2.992" dia. x 4.016" long vent 4.016" i.d. from bottom - tweeter between 31.496" - 29.528" from floor.

I calculate zdriver = 14.194" for smoothest response, which coincidentally works for your desired tweeter location. It sims a somewhat underdamped 'classic' vented alignment with a ~44 Hz tuning. My sim assumes minimal stuffing, i.e. lining the top, one side and back with 1" acoustic fiberglass.

For my records, what brand/model is this and its Pe, Xmax?

GM

[Mutuano]

Hi GM,
Greetings from Brasil!

The midbass is an Akron KB6 and the tweeter is an Akron KBT25 (please see http://www.akronaudiotec.com.br/akronconcertoeng.htm; http://www.diyaudio.com.br/2007/03/mid-akron-kb6.html for KB6;
http://www.diyaudio.com.br/2007/03/b...ron-kbt25.html for tweeter).
This guy is a very well reckon Brasilian audiophile and equipment/loudspeakers builder. It's worth take a time to surf through his website. You going to find very cool things.

Answering your other question the Xmax is 7mm and sorry for the dumb question: what is Pe means? But I guess you can figure out from the link above. Please note that some parameters has changed. I have updated info.

And when you said: "I calculate zdriver = 14.194" for smoothest response," this means from the top, right?

Once again, many thanks for your kindly help.
Best,

[GM]

Greets!

I've wanted to visit Brazil ever since reading about Brasilia during its construction, but alas, some things aren't meant to be.

Pe = electrical power rating = 60 WRMS for this driver.

Yes, MJK's worksheets are all calculated from the top down.

He does nice work, thanks for the links! If they perform as good as they look and you get the XO right, yours should be real winners.

You're welcome!

GM

[Mutuano]

Hey GM!

Brasilia is really beautiful. Oscar Niemeyer, the architect is celebrating his 100th birthday and according to the news his pencil is still sharp.

Attached you can see a sketch of the cabinet. I’m wondering to use 25mm thick MDF on front, rear, top and bottom panels and 18mm thick MDF on side and brace. What do you think? The braces is going to be based on Small Thor - swiss cheese style. (The sketch is just to see if we are at the same page).

Paulo from Akronaudio is a great person. He’s going to sell me the drives and the XO built (it’s a linkwitz-raley based design) and he will help me out with the stuffing and calibration. It’s really great for a newbie like me!

Feel free to suggest changes and corrections.

Many thanks,

[GM]

Greets!

You're welcome!

I much prefer to use no-void 11-13 ply 19 mm plywood such as Baltic Birch or Appleply as it requires much less bracing/damping, but if you use MDF, then the sides need to be thick too since it takes ~1.125" (28.6 mm) thick MDF to match the 19 mm plywood's stiffness. Note that due to the high pressure points being at the top/bottom regardless of material used, a massive top plate made from marble, slate or similar to mass load the cab is desirable. At least double up the material thickness.

WRT bracing, assuming you mean something like this, then it's fine for 19 mm MDF, but a bit overkill if >25 mm or the suggested 19 mm plywood, though there should be a driver support/mass loading brace: http://www.greenie512.net/greenie512...a_100_1427.jpg

I imagine you'll want to lower its tuning to around Fs with up to a ~204 mm long vent, which will require an elbow, so initially make the vent removable and use Play Doh or similar to temporarily seal it, ergo no need to flush mount it during tuning.

WRT the cab drawing, it's fine except my sim is based on the vent length being from the front of the baffle with the distance up from the bottom being an inside one.

Yeah, he sounds like a Dan Wiggins (Adire Audio) kind of guy, so you're indeed lucky. Anyway, looking to forward to a review with final vent/stuffing chosen, etc..

GM

[Mutuano]

Hi GM!

I knew you would suggest plywood! Good and certificate plywood is hard to find, so I would go with MDF. Hope you don’t mind

Actually I’m betting that I would get good stiffness using WRT bracing.

Anyway attached you can find 3 sketch with your suggestions, except for the wood.

When you’ve said Play Doh you meant that modeling stuff for kids? If you have my daughter will get a new set for Xmas

Waiting for your thoughts,

Thank you!

[Scottmoose]

I'm not GM, but MDF should be OK, providing you increase the thickness to the levels he suggests. MDF is dirt-cheap, so easiest way would be to laminate 1/2in to 3/4in panels, or simply double up the 3/4in thickness. You'll need it if you want to avoid unplesent resonances -bracing will help, but you'll need both the thicker panels & the bracing if you really want to push them out of the cab. passband. Still not as good as the ply though.

[Mutuano]

Hi Scottmoose,

Definitely! I'm thinking at the same way. I mean, double the thickness using 2 15mm panels, reaching 30mm at the end.

I'm a little concern about the internal dims. It might be a little off at the end.

I'll go back to the computer and render another sketch.

Best,

[GM]

Greets!

Why should I mind? I'm not the one that's going to listen to it. Anyway, what Scott said.

I give up, what program opens your file? I unzip it, but none of my programs will display it.

Yes, or similar that's not too oily.

GM