Accidental MLTL Technique

[ShoreDude]

@perceval . , weird that they would block...

They are only 3/8 inch thick, but I think @xrk971 has used 1/2 inch foam boards with paper skins before to good effect.

I wouldn't use it for a long term build, but a quick prototype?

And now you got me thinking... what if you laminate 2 together to get 3/4 inch board that a "constraining layer" of cork? That might be a stiff and non-resonant board...

Interested in any thoughts...

 

[perceval]

He used the gator boards for very small and curvy designs, like the Nautilus shaped one, and the Karlsonators, with smaller 3" drivers.

For bigger projects involving woofers, at least 1" of XPS foam. Plus, it will be a lot cheaper than that board, limited at 20"x30"
XPS I got here was 36"x 72"x 1" for about $6.

 

[xrk971]

Looks like cork board used for making bulletin boards to pin stuff. Not sure if stiff enough (if there is paper under the cork then it should be). But combine this with paper faced foam core and it would look quite nice and have damping abilities.

Screenshots for those unable to see link.

 

[ShoreDude]

@xrk971 ,

yeah - that was my initial guess. I'm gonna try to do a quick build with it. I am also interested in gluing two together to see if it acts as constraining layer dampening with significant improvement.

I'd kinda like to to have the cork on the outside for appearance and handling.

wrt cost: yeah, I agree with @perceval , big sheets of XPS are cheaper. But if it's a nicer build of a small speaker, might be worth the extra cost.

 

[jjasniew]

Get a quick fair estimate of what the final build will sound?

Sometimes I've read where the jokes on you and those protos sound better than the final box material. God's humor; just because one wouldnt think so.

Oh, I did a cork laminate once on a pair of OB panels. They still ring some, but not as bad as plywood.

 

[ShoreDude]

one more thing wrt cost:

• the image had a the single board price. I bought a 10 pack for $44 = ~ $1 per sq ft
• compare to 2" Owing FOAMULAR 4 x 8 ft sheet at Home Depot is $54 = ~ $1.69 per sq ft

So not that bad from a cost perspective.

 

[tnvijay]

I installed the latest Winisd and entered my driver parameters and started my first project.. For a accidental MLTL. The driver is a 6 inch Fullrange, made in India. In the vented option we have many like EBS6, EBS3 etc.. Which one to choose?
I chose EBS6 and did simulate a graph... Now I get Box volume of 79.09 litrs, Tuning freq - 39.67 HZ and vent area 81.7 sq. cm. Now in the advanced option ( below vents, filters, and signal) , if we click, we get an option to check "use transmission line model for port simulation.. This changes the response graph... To check it Or not? I simulated with transmission line model ticked on and I get the green graph as in the image... Can someone point me am I in the right direction? here are some screen shots showing response with and without transmission line model

 

[xrk971]

I didn’t know WinISD has a TL mode. I am not sure if what it shows matters because you just need to follow the recipe here and assume bass reflex. It will work out if driver has moderate Qts.

 

[David McBean]

I simulated with transmission line model ticked on and I get the green graph as in the image

With the transmission line model selected, no end correction is added to the port tube length. This makes the effective length shorter (it becomes the same as the physical length) which raises the Helmholtz resonance frequency as shown in the chart comparisons.

If you want to design a true bass reflex loudspeaker then the dimensions of the port tube need to be such that the air inside acts as an acoustic mass. This means that the transmission line model should not be used for the simulations.

EDIT 1 - I just realised that you wanted to design a MLTL rather than a BR 🙂.

EDIT 2 - Note that there is an error in the WinISD transmission line model. The post linked below refers:

Post in thread 'Discrepancy between WinISD & HornResponse'

2017-08-27 11:14 pm

I stumbled on a white paper(attached) on the box modeling approach used for WinISD here:
http://jahonen.kapsi.fi/Audio/Papers/enclosuremodelling.pdf

Scanning the equations used for modeling the port of a vented enclosure, it suddenly came to me what was wrong with the WinISD “transmission line” port model. In simplest terms, WinISD is basing the acoustic output of the port on the volume velocity “ENTERING” the port from the enclosure side. Hornresp bases the port output on the volume velocity “EXITING” the port to the listening room. The assumption is that the air in the port is...

• bolserst

• 

 

[tnvijay]

So, I should uncheck the Transmission line model and take the values of volume and Port dimension.. Another question- Do I need to deduct port dimension and create a Box volume for wood panel dimension?

Thanks

 

[tnvijay]

I didn’t know WinISD has a TL mode. I am not sure if what it shows matters because you just need to follow the recipe here and assume bass reflex. It will work out if driver has moderate Qts.

Hi, Thanks. The driver had qts 0.69,Fs 77hz and Vas 18.2 litres.. So I should take the Box volume of 80 litres, convert into a transmission line of say 36 inch length and size the CSA. The port area should be excluded from the volume?

 

[xrk971]

Yes. But the port volume won’t make that big of a difference.