Otto's IB ~~ Coming Together (w/ pics)

[Otto]

Hi everyone!

Inspired by Ayreonaut, I went out and bought four MJ-18s from Mach 5 Audio in Canada. Actually, I'd never come across those subs before that post. So... I'd been thinking about doing an IB for a while, and for that price, it was enough to get me to pull the trigger. I think it was about $350 after shipping to Colorado. FWIW, UPS sent me a bill for customs after the fact for about $40. Anyone else get this? I was not expecting it, haven't fully analyzed it and have also not yet paid it. I would have expected that to be included in the shipping cost.

Anyway, here are the drivers, as they sit in my living room this morning:

Four18s.jpg

Here's Veena, my helper for the day. Well, the first day, at least... She's kinda small, gets tired easily, and also tends to drool.

Helper.jpg

I made all the cuts with this quick-attach guide and a circular saw. It's been a while since I've built a sub box -- high school and shortly thereafter, for cars. This box could be more perfect, but it's not bad for my "new first", especially without using a table saw...

Starting Out.jpg

I'm a little light on clamps, so I just stacked heavy things on top while it was gluing:

StackedAndGluing.jpg

Got all the double thickness pieces together, and it looks like the whole thing kinda fits together!

Pieces Cut And Glued.jpg

Driver fits!

OnePieceWithDriverIn.jpg

BoxWithDriverIn.jpg

BoxWithDriverFromBack.jpg

I made a couple mistakes.

First, I wanted the drivers to mount from the inside, rather than the backside. I cut the insets for the drivers too deep -- almost through one layer of MDF. A stupid oversight on my part. I'm going to reinforce the baffles with screws (I don't really think they are going to come apart, but I'll take a little extra insurance).

Second, if you look at the last picture, you can see that there's a notch in the "arms" by which the box will hang, at the top. That should have been filled in to the edge by the inside tall piece of MDF. I don't think it'll matter.

So, I got the box together and I already had a couple BFDs and an EP2500 on deck for this project. The box is spraypainted black on the inside (I may line it with vinyl if I think it needs it). It's made its way into the basement, and need to get into the crawl space.

I hope it turns out half as good as some of the others around here -- they look great!!!

Have a nice day!

[Sonnie]

Precious helper you got there...

Nice work too.

I cut the insets for the drivers too deep -- almost through one layer of MDF.

How deep would you normally have cut the inset?

What are you using to secure the drivers... looks like some sort of flange nut with a bolt. This seems like it might be a good idea for securing the drivers.

[Otto]

Sonnie wrote:

Precious helper you got there...

Nice work too.

How deep would you normally have cut the inset?

What are you using to secure the drivers... looks like some sort of flange nut with a bolt. This seems like it might be a good idea for securing the drivers.

Thanks, Sonnie! Well, I was wanting the added stiffness from the double layer baffle. I cut it pretty much at 3/4" for the inset. Next time I might do 1/4", enough so it has a place to sit. In the end, if you have clearance such that the drivers don't bump into each other at max excursion, I guess you don't really need an inset at all. Check Ayreonaut's box where he's mounting the subs from the backside. His insets look about right. When it's all said and done, I think mine will be all right. But if I had it to do over again, I'd cut them more shallow.

As for securing the drivers down, I'm screwing them from the front of the driver using 2" 10-24 machine screws (I think that's what they're called, I never pay much attention to those numbers as long as they all fit together). Those fit into matching T-nuts that are mounted up against the backside of the box. Fit seems good and strong when they're screwed tight.

FWIW, I think I saw another post somewhere around here about hammering the T-nuts into MDF. I did just that, and had no problem with cracking the MDF. The T-nuts may pop out of the socket if applying too much pressure against the screw that is being unscrewed, but that's easily remedied.

I keep working on it little by little, as time allows. Father-in-law is coming this weekend, so I'm not sure how much progress will be made until next, next weekend!

Have a great day!

[brucek]

First, I wanted the drivers to mount from the inside, rather than the backside

That's something I always wanted to ask about.

I have always seen drivers in speakers mount from the business end (as you call from the inside). This then allows the front of the driver to be somewhat flush with the mounting material.

The first time I saw them mounted from the magnet end using those clips I thought it looked rather insecure, not to mention the large step of MFD material around the front of the driver. I have seen this clip method used quite a bit with IB's though....

Is the clip method preferred now?

brucek

[Otto]

brucek wrote:

The first time I saw them mounted from the magnet end using those clips I thought it looked rather insecure, not to mention the large step of MFD material around the front of the driver. I have seen this clip method used quite a bit with IB's though....

Is the clip method preferred now?

brucek

I had also seen the clip method prior to starting this project. I decided to go the "inside" way because I might run into a corner in the crawl space where it would slightly difficult to address the screws properly. The way I have it now, I can get to them directly from my living room floor when the IB is all installed.

I do see that the clip method allows the user to get their screw holes away from the perimeter of the driver. You can see that mine are within an inch of the main hole itself, where the pic you posted (of Ayreonaut's box) are well outside the perimeter of the hole. Back when I was a kid doing sub boxes in cars, we were using wood screws to mount the drivers directly to the wood. We certainly had problems with the particle board splitting up at the holes, especially after taking the driver in and out more than once or twice. Here, using the T-nuts will help with that problem greatly. That said, I still think I run a higher risk of crumbling my wood around the mounting holes than does Ayreonaut. That said, I have had no problem with crumbling MDF at all, and I've mounted in and out a couple times, applying enough torque to the screws to strip a couple heads out (to make a long story short, there's a reason I stripped the heads out).

Is there any sonic benefit? None that I know of. If there is, I would imagine it to be extremely subtle.

[Exocer]

Great work. Nice job on the T-nuts too. Had I not cut my driver hole too large (actually I followed the recommendation) I would've gone that route myself.

May I ask how large the listening room is?

[Otto]

Exocer wrote:

Great work. Nice job on the T-nuts too. Had I not cut my driver hole too large (actually I followed the recommendation) I would've gone that route myself.

Thanks! It's been fun so far. I was concerned about cutting too big as well. I actually had to come around and "touch up" the hole to get it big enough. You can see some of that in the pics.

May I ask how large the listening room is?

Sure. I wrote all this stuff out previously, so I just happen to have it (had to dig through the recycle bin, though).

Main room, measured in feet, is 19 x 15 x 8.5. It has faux vaulted ceilings that range from 8.5 to 11.0.

Assuming that I did the math right when I wrote it on this page, that's ~2775 ft^3. This room opens to a dining room that's ~935 ft^3, as well as to a foyer/staircase to the basement/hallway area. There's a picture below.

The IB will be where the red circle is, and you can see the edge of my M&K MX-90 ("for sale") where the arrow is.

LivingRoom.JPG

[Exocer]

Yeah, I definitely learned my lesson...I followed the same method as you with my second DIY project. Its always better to have the holes a little too small than too large obviously

Wow, your room is a very nice size for what you've got planned Looking forward to your impressions once everything is said and done

[Ayreonaut]

Nice work Otto. I'm eager to compare our impressions of 4xMJ-18 IBs.

I'd never built a speaker of any kind before, so I went strictly by the book, the book of Thomas that is. I wondered about the strength of the 1/2" conduit clamps that I bought, but I figured with eight of them per driver it ought to be secure. I neednt have worried. The leverage from just one clamp at the top was enough to securely support the weight of the woofer while I made up the other seven! Its not going anywhere.

I was not sent a bill for customs. I did pay more - $438 including shipping to Virginia.

[Chrisbee]

So called furniture screws have a large flat head with a hex socket and come in various lengths up to 3" long. (possibly longer) Price is much the same as ordinary hex-head machine screws bought in small packs at most DIY superstores around here.

I used these on my (very) visible, front-mounted drivers in my IB array with t-nuts behind the baffle.

These screws have a pleasant (pale gold) rustproofing finish and the hex socket means no nasty screwdrivers pointing at your precious drivers. Nor do they show they've been tightened like the usual crosshead screws which quickly loose their finish.

The nice broad head with flat underside means no ugly washers are required to hold the driver's rubber sealing gaskets firmly without squashing them completely flat.

[Otto]

Made some progress today...

Cut the hole:

LRHole1.jpg

LRHole2.jpg

LRHole3.jpg

Sent a driver down:

FromTheCrawlSpace.jpg

Puttin' it together:

Install1.jpg

One mostly in:

OneWoofer.jpg

[F1 fan]

Lookin Good.

That pic with the drill scares me I tend to be accident prone so I would probably have the bit stuck into the woofers cone or surround in about 3 seconds.

[Chrisbee]

F1 fan wrote:

Lookin Good.

That pic with the drill scares me I tend to be accident prone so I would probably have the bit stuck into the woofers cone or surround in about 3 seconds.

Absolutely terrifying ! That's why I use a hex key and hex-socket screws.

[Otto]

Chrisbee wrote:

Absolutely terrifying ! That's why I use a hex key and hex-socket screws.

Yeah, I've stuck a drill through a driver before -- long time ago. I really thought about getting those furniture screws you posted above, but only for the positive connection of the bit. I'd still stick a hex key in the drill to turn 'em!

While we're on the topic of the screws, I can say that screwing in from the front rather than the back, as we discussed above, is a pain; at least it was for me, working alone. The first problem is that you want get that driver in position and hit that top screw first. But the mass of the magnet keeps the bottom of the driver from sitting nicely in the hole. Just imagine picking up a driver from its edge (by pincing it with fingers and thumb) -- it'll swing out. If I were to come from the back side, getting the top screw in would allow the driver to rest naturally against the baffle while installing the rest of the srews.

So, in the picture above with the drill, you can see that I ended up in the basement, installing from the "front". I did not reach down through the throat of the IB and install while on my belly on the living room floor, although that was my original intention. I thought it would be "easier" because I didn't want to carry each of the subs through the crawlspace. That turned out not to be a problem because my wife was able to hand them to me through the throat of the IB. If you had a "outside" mount, you wouldn't be able to do this because the drivers would not fit through the holes to be able to get them to the mounting position. However, you could put them through the IB cutout before actually mounting your manifold, and put the drivers aside for when you are ready to mount them.

So, I said I didn't reach through the IB throat while on my belly. Well, that's true for the first three drivers. The final one I had to reach through the throat, as there was no other way for me to mount the driver. So now just take the problems I listed above and add "upside down", "can't see" and "awkward angle" to my complaints.

In the end it wasn't all that bad, just a little clumsy -- either way, I got them all in!

[Chrisbee]

Logic suggests the bottom screw should really go in first then? The magnet weight will hold the driver tight against the manifold while you fix the rest of the screws. The bottom t-nut would have to be securely in place first though.

I made the mistake of fitting all the drivers with my 1.5" thick array baffle board lying flat across some boxes. Trying to lift and walk the finished array in from the IB enclosure space (where I'd been working) was very hard work! I then had to lift the whole thing bodily onto my 10" high stage. The array was so heavy and the centre of gravity was so far behind the baffle it held itself against the hole in wall effortlessly. The baffle only needed fixing screws to stop it rattling. I cannot imagine how heavy a double-layer MDF manifold and 4 x 18" drivers weighs altogether.

Isn't it strange how these big drivers change size depending on what is in the picture with them? Sometimes they look enormous and other times they look quite small.

[Otto]

Chrisbee wrote:

Logic suggests the bottom screw should really go in first then?

Yeah, I played around with that, too. It all just seemed really slippery no matter what I did. If I had a helper that was older than six months, it would have been a snap either way. My wife was kind enough to hand drivers through the hole, but she's just not the DIY type, I guess.

[Otto]

Hi everybody,

So I was able to hook everything up yesterday -- BFD to EP2500 to 4xMJ18s. I made a couple quick sweeps with REW, and things look OK. I put in a couple filters without too much thought. I'm really just looking for preliminary results for now.

So I ran a couple demo scenes -- Darla Tapping from "Finding Nemo" and the Asteroid Chase from "Attack of the Clones". Also briefly played a few audio tracks -- Tool's "The Pot" and "Prison Sex", Gorillaz "Dare" and a couple tracks from Diana Krall's "The Girl in the Other Room".

I was listening to the movies pretty loudly. Both clips were tactile and extremely present. The Darla tapping scene was ridiculous. Everything was shaking. Really, my drink on the coffee table, candles in the dining room, the walls, etc. It was waaayyyyy louder than I think I would ever need.

I knew that I was running the sub way hotter than the mains, but wanted to see what it could do. I cannot imagine that I will ever listen to movies or music loud enough to require the levels of bass that the IB can produce. Essentially, I have tons of headroom in the sub department.

I quickly turned down the sub output on my pre and listed to the music tracks. I don't want to gush over the sound, as I just don't have enough time with it, but first results seem very promising.

I also played some pure tones through it at volume. At 10Hz, I couldn't hear much, but the large plants were moving as if a gentle wind were blowing on them. The drivers were excurting beautifully, and I never came near clipping on my amp, and the drivers never bottomed out. I could have pushed it harder, but at this point, why?

So now I need to dig in with REW, get some good filters into the BFD and match levels across all channels. It could take a week or two to get it right...

[norpus]

Chrisbee wrote:

Logic suggests the bottom screw should really go in first then? The magnet weight will hold the driver tight against the manifold while you fix the rest of the screws. The bottom t-nut would have to be securely in place first though.

I made the mistake of fitting all the drivers with my 1.5" thick array baffle board lying flat across some boxes. Trying to lift and walk the finished array in from the IB enclosure space (where I'd been working) was very hard work! I then had to lift the whole thing bodily onto my 10" high stage. The array was so heavy and the centre of gravity was so far behind the baffle it held itself against the hole in wall effortlessly. The baffle only needed fixing screws to stop it rattling. I cannot imagine how heavy a double-layer MDF manifold and 4 x 18" drivers weighs altogether.

Isn't it strange how these big drivers change size depending on what is in the picture with them? Sometimes they look enormous and other times they look quite small.

Hehe yes found the bottom screw was the one on the weekend when installing mine, or the driver wants to slip as you found.

Yes, bloody heavy drivers in manifold, about 80kg my first IB manifold weighed (200lbs). I used a car tow rope as a strop over my back to lower and raise the system when adjustments to the voicecoils were required and I needed to et back into the hole in the floor

[Exocer]

Otto wrote:

I also played some pure tones through it at volume. At 10Hz, I couldn't hear much, but the large plants were moving as if a gentle wind were blowing on them.

Thats a sure sign of moving lots of air..always a good thing