Cornwall port dimensions

[IB Slammin]

Terry,

First of all, could you tell me about your avatar? Creeps me out a bit, but then the acid I took could be comming on.[]

Hey! That's my poor wittle ol' piggy bank. He's just a bit malnourished!

Oh thats what it is. I am relieved.

I would like to make a few suggstions if you don't mind.

1) IMHO, a top hat on a 3/4" to 1" riser that is a bit wider than the bass bin could look pretty cool and simplify the bin build. (remember to subtract the volume of the K600/K55)

I thought of this from the get-go, and ran it by Maria (who has taken a surprising interest in this project for fear of it ruining her living room) and we both agree that if anything, the top hat might look good smaller than the bass bin, but not wider. Just my opinion.

She is prob right. I may be rationalizing to make thing easier for me. Truth is, every time I think about building them, I spend the $ on a more needed component.[]

2) Dump the K55's and replace them with Altec 902's on the 511b.

Funny you should mention this. I have both a pair of K-55M's and a pair of 902-8B's, and was planning on trying both to see which I preferred.

3) Cross them at 400hz (disregard the published spec's for the low cross) and run up the next cross point to 9000 or so.

I will definitely have some X-over questions, but that'll be for another post when the time comes. Expect me to pester you a bit since you've got a similar setup if I remember correctly [].

4) Keep it three way for the sparkle at the top.

5) Brace the bin. Extra 3/4" plywood on the back. Cross brace the motor board.

Hmmm... Do you mean make the back panel twice as thick? And cross brace the motor board where? I'm just having trouble picturing it.

Screw a slightly smaller 3/4" piece (to clear the screws) to the back. Run 1-1/2 X 1-1/2" angle iron across the inside of the MB in a few places. Cover with dampening material.

6) Allow enough room in the top hat to accommodate a JBL baby-cheek tweeter.

What are the dimensions of the JBL 2404 and what size cutout would it require? For now, that'll put me over budget, but I was thinking of going with the APT-200, which is the same driver as Bob's tweeter, but with a baby-cheeks horn lens. About the same cost, too.

Let me know how the APT-200's sound. The new 2404's seem to be a bit above my pay grade.[] Rather not buy used tweets.

For me, the ultimate Cornwall spec's are listed above.

I and others call it Alcorn. There ain't no Scala to it.

I still kinda like "Voice of the Corn." Always makes me think of Isaac and Malachai standing atop a giant Cornwall in a huge cornfield!

Yea, but "Alcorn" is New Testament![A]

Welcome to the madness, and good luck with the build.

Thanks!

Regards,

Terry

PS: You have a super nice guy in your corner. Pop will be a great asset to you.

After seeing pictures of his work, the "nice guy" is just a pleasant added bonus!

Joe

[Jim E]

I'm a bit of a stickler for details also. If there are any errors on the layout, I would be happy to correct them in the drawings. To the best of my knowledge the measurements supplied to me by the forum members were correct. I doubt a small change in the port opening will result in a noticable decrease in performance.

Jim

Cornwall.pdf

[Jim E]

This is the two port layout.

Cornwall2Port.pdf

[tagger]

Hi Jim,

Those are the prints I was referring to as the "Forum Drawings." I'm using the baffle cutout dimensions from those diagrams, but my overall port volume will be slightly larger. As the good Dr. pointed out, however, there should only be a negligible difference in port tuning. The way I see it, I can always add some more thickness to the shelf supports (decreasing volume) if I ever notice a problem.

Joe

[dtel]

Thanks Dtel. The rise of the woofer was for other reasons besides the porting.

Thanks for the port info. Say when you say 2 1/4 high...do you mean from the from the bottom of the shelf to the topside of the bottom of the cabinet or is 2 1/4 the height of the holes in the baffle?

No the cutout is 2 1/4" that is the size of the hole/slot, the port starts 3/4" from the bottom of the motherboard and is open to the bottom . So that would make the port 3'' tall on the inside.

Also....22" wide seems a little weird as the external width of the CW3 is 25.31". That would mean there is 3.31 inches of wood thickness to make up some where. Is there a chance the width of the internal port could be 22 3/8"?

I just checked there are 3 slots across the bottom each about 6 7/8" wide and 2 1/4 tall. The space on each side of the port is about 7/8". Kind of like this

Side wall 7/8---6 7/8---7/8---6 7/8---7/8---6 7/8---7/8 Side wall

The port does measure 22" wide I may be a little off on the space between each port and each side of the speaker.

The 7" from the back of the port shelf to the fron tof the baffle...is this right?

Yes

If you stick a tape in and hook it on the inside end of the port it measures 7" to the front of the mother board, so if the mother board is 3/4 the port shelf would be 6 1/4 on it's own.

Also if you stick your finger in the port, far left or far right it is almost flush with the port, about 1/8 wider. The sidewall is 3/4" they added another 3/4" board on the inside by the port to make the side 1 1/2" thick by the port. The port starts about 7/8" from the side on the motherboard that is why their is about 1/8" difference. Port measures 22" on the motherboard but on the inside it's 22 1/4'

This is hard to explain !

Thanks for the input. As you can see....I'm nutty over details.

jc

Sorry it took so long I just seen this thread again . If you have any questions send me a message and I will measure or try to explain better , no problem.

[jwc]

Dtel. man... thanks. I know that took work. So that is the CW3 port.......I would say a good bit different than my 84 Cornwall (CW1.5).

[brians7]

Great information here.

I am going to try and build a pair of CornScala's myself.

Personally I like the slimmer profile, and was going to build a pair with the basebin dimensions being 21.5 wide, 21.5 deep, and 28 high, this should give the interior volume 6.2 cu. ft.

Now for the port shelf, if I am understanding this correctly the port needs a cross-sectional area of between 70 and 75 cu in. and if the interior width of the cabinet is 20 in. and I make the support board for the shelf the enitre height of the port that makes the width of the port 18.5 inches wide, and if the port is 4 in high 4x18.5 is 74 cu. in.

The port shelf length remains 9.5 in.

I hope that if these calculations aren't wrong in any way, because I plan on starting this project really soon. And if the they ARE wrong that someone will chime in and revise them for me.

A bit more insight about the speakers, they will be split top design.

I will be using Crites Speakers CW1526C Cast Frame Woofers, Altecs 811 horns which I already have, Great Plains Audio 902, and JBL 2404H baby cheeks which I also already have, ALK Engineering crossovers.

Thanks. Brian.