Billet Aluminium Mark K ER18DXT build.

[Joe-Trojan]

Hello all.

I've browsed this forum over the years from time to time but now it's time to post.

I am embarking on a Mark K ER18DXT build with enclosures made from 19mm thick panels machined from solid 6061-T6 aluminium. Planned corner and panel bracing is 19mm square bar drilled, counterbored, and bolted to the panels with an overkill of M6 cap head screws (allen key bolts) from the inside. The only screws visible from the outside will be that for the drivers and the speakon connector at the rear. My initial drawing shows 9mm deep curved surfaces sunk into the inside of each panel in an attempt to eradicate parallel planes within the box. It will be interesting mounting the x-over hardware with comfortable clearance from the aluminium enclosure.

These will be used with a sub. Any advice regarding if I should go sealed or ported, and any words of wisdom on anything that will help for nearfield use would be great. In fact any thoughts/input/advice/critisism/questions are more than welcome.

Initial design:



Wireframe depicting curvature on inner walls:

[JonP]

Wow... looks like you've caught a dose of Magico Madness! 8O

They certainly will be amongst the stiffest enclosures built by humans.

I've heard MarkK's vented originals at the NorCaDIY, great sounding design! They had rather prodigious bass for a .5 cu ft box system.

If you go vented you might want to pick his brain in regards to stuffing and port placement, to optimize that. Sealed, you could go smaller, which would save tooling and aluminum.

Either way, some thought should be given to damping the inside of the cabs, both to catch any residual HF ringing of the box, and more importantly, absorbing material to soak up reflections inside the box.

Awesome! 500% overkill! If something's worth doing, its worth overdoing! ;x(

[JonMarsh]

+1! :t

[dsrviola]

This would be a fantastic ....

....opportunity to compare the impact cabinets made on the sound. Wishful thinking on my part. <sigh>

[Joe-Trojan]

Yeah, I'm in Australia, any other members in Sydney or close to it? Any other members near Sydney that have a set of ER18DXT's? I don't plan to do any testing other than listening. My speaker testing and design skillset is zero.

I'm thinking I will go ported. I am building these things to last and I'm sure between now and when the Sun runs out of Hydrogen and expandes into red giant there will be a time when these speakers will be used without a sub. I will machine up port extentions to try out different port lenghts if no one has the definitive port length. More drawing to be done.

Can anyone kindly tell me precise dimensions of that off the shelf plastic port with flares? I am guesing 2" ID with 1" radius flare. I actually bought a pair just to size up, but I seem to have lost them or possibly threw them out in a recent move.

[dar47]

Yeah, I'm in Australia, any other members in Sydney or close to it? Any other members near Sydney that have a set of ER18DXT's? I don't plan to do any testing other than listening. My speaker testing and design skillset is zero.

I'm thinking I will go ported. I am building these things to last and I'm sure between now and when the Sun runs out of Hydrogen and expandes into red giant there will be a time when these speakers will be used without a sub. I will machine up port extentions to try out different port lenghts if no one has the definitive port length. More drawing to be done.

Can anyone kindly tell me precise dimensions of that off the shelf plastic port with flares? I am guesing 2" ID with 1" radius flare. I actually bought a pair just to size up, but I seem to have lost them or possibly threw them out in a recent move.

According to PE the inside diameter is 2" with the outside flair of 5 1/4" and the inside flair of 4 3/16". The outside flair cut out is 4 1/4".

I'm not sure what the port length is, Mark doesn't mention it in his documentation. I'm interested in building these for surrounds but I would like to port out of the front and was wondering if I could make them work in a .7 cub box just to get the height to put the port below the woof.

[JonP]

A while back I visited the Perfect Port site, (or at least a rep) and there were measurement sheets available for their ports. Should be findable around. I think I have a 4" in my garage someplace, but not a 2" or 3"

You might try leaving Mark mail, see his site. Might raise him here, or on PE Tech Talk...

[Joe-Trojan]

According to PE the inside diameter is 2" with the outside flair of 5 1/4" and the inside flair of 4 3/16". The outside flair cut out is 4 1/4".

I'm not sure what the port length is, Mark doesn't mention it in his documentation. I'm interested in building these for surrounds but I would like to port out of the front and was wondering if I could make them work in a .7 cub box just to get the height to put the port below the woof.

Thanks. I did notice that info on the PE site but it doesn't really explain the actual flare radius exactly. Having said that, and looking at the pics closer, if the outside flair diamater is 4 3/16" then the flare radius itself might only be 1 3/16", that is, 1 3/32" flair radius + 2" port + 1 3/32" flair radius = 4 3/16". I am referring to the flair cross section radius when I mentioned flair radius before.

Port on the front in an option for me too, but first need to work out the port lenght to see if there is going to be a problem. I'll see if I can get some sort of confirmation and I will post a 2d drawing up.

A while back I visited the Perfect Port site, (or at least a rep) and there were measurement sheets available for their ports. Should be findable around. I think I have a 4" in my garage someplace, but not a 2" or 3"

You might try leaving Mark mail, see his site. Might raise him here, or on PE Tech Talk...

This site?

http://www.psp-inc.com/index.html

I'll send them an e-mail to request this info. I might bug Mark at his site too.

[impala454]

I'm curious Joe, what method are you using to machine the aluminum?

[Joe-Trojan]

I got a reply back from the port people, while they didn't give me exact measurents (fair enough) they confirmed the flair radius is basically 1". That is enough for me to draw up the ports. Now I just need some time.

I'm curious Joe, what method are you using to machine the aluminum?

Billet, aka machined from the solid, using a CNC mill/vertical machining center.

Slightly exploded view, showing the individual panels:



I did toy with the idea of making the cabinet two pieces split down the middle between the front and rear, but that is just far too much $$$$.

[impala454]

Very cool. Can't wait to see how it turns out.

[Joe-Trojan]

I'm not sure what the port length is, Mark doesn't mention it in his documentation. I'm interested in building these for surrounds but I would like to port out of the front and was wondering if I could make them work in a .7 cub box just to get the height to put the port below the woof.

I've decided to stick with the rear port config. Looks like you just make the port as long as you are comfortable with. There really isn't excessive depth for the port considering the advice to mount the port directly behind the tweeter. I managed to get 210mm in there including flares which doesn't seem to be much. I might look at extending the depth of the cabinet depending on what volume I'm at after I complete everything.

Anyway, I drew up the ports. I have access to a mill, but not a lathe so ports designed to suit manufacture on a mill just using 3 axis. Not sure what I will do for feet yet.

[john trials]

If you are going to machine ports, you should make them external, to show off their beauty. It would be a shame to have such cool port tubes, only to hide them inside. That will give you more cabinet volume without having to increase the size, too.

[Joe-Trojan]

Hmmm I'll think about that. If I can mount the flair portion elegantly (no fasteners from the outsuide) it could be a winner.

Now, is there any reason why I should machine the external panels with a perfectly smooth finish, or can I machine them like this which is to scale?



The inside curved surfaces will look like that.

[technodanvan]

I would not think having a rough surface would greatly affect the sound - it would look really cool if you gave it some texture!

[dar47]

I've decided to stick with the rear port config. Looks like you just make the port as long as you are comfortable with. There really isn't excessive depth for the port considering the advice to mount the port directly behind the tweeter. I managed to get 210mm in there including flares which doesn't seem to be much. I might look at extending the depth of the cabinet depending on what volume I'm at after I complete everything.

Anyway, I drew up the ports. I have access to a mill, but not a lathe so ports designed to suit manufacture on a mill just using 3 axis. Not sure what I will do for feet yet.

Thanks for the info. I guess the only other concern would be to allow at least 1 port diameter distance from any obstruction in front of the internal end of the port. Is your port lined up with the back of the tweeter or does that front brace come into play? Could just be the iso view.

[Joe-Trojan]

I would not think having a rough surface would greatly affect the sound - it would look really cool if you gave it some texture!

That texture is exactly what I have in mind. Will add some machining time, but oh well.

If you are going to machine ports, you should make them external, to show off their beauty. It would be a shame to have such cool port tubes, only to hide them inside. That will give you more cabinet volume without having to increase the size, too.

Your idea is looking good, but not quite finished the 3D drawing just yet. Looks like I'll go with 2" out the back and while I'm at it I'll machine up a plate to seal off the rear panel with the port removed, if I ever want to change the config to sealed.

Thanks for the info. I guess the only other concern would be to allow at least 1 port diameter distance from any obstruction in front of the internal end of the port. Is your port lined up with the back of the tweeter or does that front brace come into play? Could just be the iso view.

The views I am rendering off show no perspective which doesn't help. 210mm port length including flairs with the tweeter depth of 65mm, has 30mm between port flair and the back of the tweeter, cabinet depth of 305mm. The diamater of the rear of the tweeter is 65mm.


My port position is slighty lower than the tweeter, because my 19mm corner brace on the back would otherwise interfere with my overly bulky port at the rear where it mounts on the inside. Now that I am moving the whole port back 2 inches, clearance at the front is a non-issue for me.

The easy part is done, that is, buying the parts. If you look closely you might be able to see some "Parts Express" stickers.

[Tomato]

I am very excited about this speaker and can not wait to hear more

[Joe-Trojan]

Me too! Things have been very slow, busy with some big billet projects at work. Getting another CNC mill delivered in a month or so. Should have more time for this project after all that happens and I catch up on the backlog of work.

I have redesigned the port, simplifying its construction and mounting, but I'm yet to finalize the outer port section. I have also taken out some weight of the enclosure while increasing the internal volume slightly.

[SpeakerGuy]

Have you been able to get the enclosures made?

[JonP]

This site?

http://www.psp-inc.com/index.html

I'll send them an e-mail to request this info. I might bug Mark at his site too.

Ahh, yes.. How did I manage to screw up their name? Hmmm, they totally changed their site. Used to have drawings for the ports.

Looks like you're CNC'ing the ports, I'd make sure what the dimensions are supposed to be... a port with a flare has a correction factor to it's length, depending on flare size, one flare or two, etc. You'd want to be sure you're going to hit Mark's design tuning... since it won't be as easy as recutting a plastic tube and sliding the end pieces back on!

Can't wait to see some pics...