Few questions about MJK build

retiredmxer · « **on:** 15 Dec 2012, 05:36 am »

Hi everyone,

I'm going to be building MJK's open baffle design this week. I have a few questions and was hoping someone could help out

1. I'm going to be using 3/4" plywoood. Should I double up on this for the baffle?

2. I've seen builds from different people and it looks like some people angle the baffle back, while others keep it vertical. What is the logic for this?

3. Last one. I had to get the fe103en rather than just the 103e. It isn't circular. Gonna be pretty tough to flush mount that driver. Any opinions on surface mounting it? Good/Bad? I'm still going to flush mount the woofer.

thanks very much for any help

Blake

JCS · « **Reply #1 on:** 15 Dec 2012, 03:42 pm »

<<<1. I'm going to be using 3/4" plywoood. Should I double up on this for the baffle?>>>
IMO, a single sheet of 3/4" ply is not rigid enough to support a 15" woofer. Below is a pic of what I did, using 3/4" ply and 2x4"s. The top to bottom taper is for WAF; it has no effect on the acoustics. The added side panels meant that I added a few Hz on the low end and necessitated moving the woofer's XO point from 200 Hz to about 160 Hz; I used 12 mH and 80 micro farads.

<<<2. I've seen builds from different people and it looks like some people angle the baffle back, while others keep it vertical. What is the logic for this?>>>
Think about the height of the tweeter and where your ears will be.

<<<3. Last one. I had to get the fe103en rather than just the 103e. It isn't circular. Gonna be pretty tough to flush mount that driver. Any opinions on surface mounting it? Good/Bad? I'm still going to flush mount the woofer.>>>
I wouldn't waste any time trying to flush mount the drivers.

Cheers, Jim

guest60106 · « **Reply #2 on:** 16 Dec 2012, 03:11 pm »

Hi Blake,

My build is located here:http://www.audiocircle.com/index.php?topic=112067.0

Although it is not quite the same as MJK’s, I did read his work in great detail and drew quite a bit of knowledge and inspiration from it.
As far as my build goes I am working on the next iteration of the design (Mrk ll) based on what I have found based strictly on listening tests. One of the revisions I will be making is the baffle board thickness. The current design is ¾” plywood. With 4 10” drivers and 5 motors the baffle board vibrates audibly. I could brace it, but since I want to add another driver as part of the design change I may as well build a new baffle. For the next iteration of the Mark ll I will be using 2 pieces of 1” thick commercial grade MDF. I will then oversize and chamfer the back side of the holes to open them up. I believe this will effectively dampen the baffle but if it doesn’t I have other design ideas.

I leaned the baffle back 5 degress on my design because the tweeter/midrange center is at 28 inches from the floor which I feel is a bit low. I still haven’t decided whether this is a good idea because I may be causing more problems (sound stage/image) than I am solving. I will be doing some listening tests for this hopefully today buy shimming the stand legs to both a more vertical position as well as a deeper angle. This will give me a better idea of whether to continue this option or just raise the mid/tweet on the baffle (taller baffle which I was trying to avoid) to a better height. I will keep you posted on that.

The countersink on the driver I have no opinion on because I have never done any testing on that but there are many people on this sight that have. I always sink my drivers but it is purely for aesthetic reasons. This often requires me to make jigs and can be very time consuming but it is a necessary evil I have chosen to deal with. I don’t recommend it unless you have a concrete audio reason or more time than money.

Hope this helps
Matthew

retiredmxer · « **Reply #3 on:** 27 Dec 2012, 05:22 pm »

Thanks to both of you for your reply. I went ahead and built them, doubling up on the baffle thickness. I'm pleased with the result

Here's a couple pics.

guest60106 · « **Reply #4 on:** 27 Dec 2012, 07:28 pm »

Nice Build

MJK · « **Reply #5 on:** 27 Dec 2012, 07:33 pm »

Very nice.

What is the black pipe on the back? I like that method of bracing.

planet10 · « **Reply #6 on:** 27 Dec 2012, 09:03 pm »

Quote from: retiredmxer on 27 Dec 2012, 05:22 pm

Looks like the back of the driver cutout is not champhered?

With the thin bezels of the Fostex, no rebate is not much of a hardship.

dave

retiredmxer · « **Reply #7 on:** 27 Dec 2012, 10:37 pm »

The bracing is just 1" steel plumbing pipe that has been sanded, primed and painted. I used biscuits to connect the base to the baffle, but didn't feel like that would be very durable.

The back driver cutouts are chamfered, but it is hard to see in the pic. I used danish oil to finish everything, but it didn't change the color very much on the chamfered edge.

I still have to clean up the cables. I plan on using some techflex and heatshrink to make it look a little nicer. Am also considering building a box for the crossover. Couldn't wait on all of that before listening though