Pass J-Low, log


I recently built a pair of Pass J-Low's. I kept a log on another forum and I figured I might aswell post the information and pictures here too, as it might be of use for somebody also wanting to build them.

December 30th, 2007

After building the Cyburg Stick and Buschhorn I've really gotten the DIY-flu. I'll be working on a speaker project in the new year, and figured I'd keep a log up to date with my progress here. Going will be rather slow, not so much spare moolah laying around after december. :(

I've recently gotten a pair of Jordan VTL speakers sporting Jordan JX92s drivers. Much impressed as I am with these speakers, I can't help but wonder what they'll do in a no-compromise design. The VTL's are great speakers to hear and see, but they are rather small, and sexy as they may be, there might be more performance in the JX92s than the VTL can deliver.
Insides pointed me to the J-Low. They won't fit in my room though, so essentially, I'll be building a slightly modified version of the J-Low. Dubbed the Smaller Huge J-Low. I'll be keeping a fairly detailed log here, in case somebody else may want to build it (and because I'd like to be able to read back later where I've gone wrong...).

The J-Low

This is a design made by Nelson Pass. It's a no-compromise, back-loaded exponential horn using the JX92S that stands 1.82 meters tall, 4 cm less tall than I am. The original design is 60 cm wide -- too wide to fit my relatively small room. If I built them from the original design, I wouldn't be able to open the door to my room anymore. To get an idea of how large this thing really is, here's a small picture I nabbed off of


Another picture from a private builder:

Here are two PDF's with more information, including schematics and instructions on building the J-Low:

The Jordan JX92s

Information on this driver can be found here: Jordan JX92S specifications
A quote from that page:

Embracing a range of almost nine octaves, the JX92S offers the widest bandwidth of any single drive unit available. This not only provides an exceptionally smooth, high-definition, crossover-free sound quality but allows for a very diverse range of applications.

The JX92S can be successfully used with all types of enclosures including closed or vented boxes, transmission lines and horn loaded designs. It is eminently suitable for professional near-field monitors, high quality domestic hi-fi, home cinema and custom installations. The unit is magnetically screened, enabling it to be used in close proximity to computer monitors and television screens.

But why?

I said earlier that I wanted to see what the JX92s could be in an optimal design. That's part of the reason I want to build the J-Low. Perhaps even more important: I want to build them because they are insane! No, seriously, that is actually a large part in my reason behind building these. Hardly anyone has built these speakers because they are so wife/girlfriend-unfriendly and can't be used in a living room since guests would die of shock. Sadly (luckily in this case), I'm not being held back by a girlfriend (or wife!), and have no living room. Meaning: I can do whatever the hell I want for now, and I'll be damned if I'm not going to take advantage of that while I still can. :evil:

But they're huge!

Indeed. Too huge. I'm missing roughly 25 cm of space, so I need to make them slightly thinner than the original design. After some discussion with Tony from Humble Homemade Hifi he came to the conclusion that it's possible to make them about 15cm's smaller without effecting the sound. The only effect it is likely to have is a slightly less large contact area with the room, which could result in less bass presence and slam. This is hardly an issue in my small room, as they are more than large enough to provide all the slam I'll ever need. The room will be dominated by these speakers anyhow. So, they'll become 45 cm's wide instead of 60 cm, and will be just as tall and deep as the original design.

The schematics

I've modeled the SH-J-Low in Sketchup.
You can grab the Sketchup file here, if you want:

The schematics are based on 18 mm material. I'll be working pre-veneered 18 mm MDF. MDF is brilliant for making speakers. A very strong material and easy to work with.

The top and bottom part mismatch with 1mm since the original design is based around 19 mm (3/4") material. On a speaker this large, I'll be ignoring such a small difference. I can redo the schematic to make up for this single mm, but frankly, I can't be bothered.

Click to enlarge.

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That's it for now. Expect updates in this thread in the beginning of January.

Signing off to get insanely drunk and wake up sometime 2008 quite possibly in a ditch, under a bridge, or worse. Have a great new years eve folks! :)

January 3rd

What do you know, didn't even wake up in a ditch or under a bridge.

Local DIY store here sells decently (fake)veneered MDF in 2.5m x 60cm 18mm panels, so I made a panel schedule. That's 3mm less deep than the original drawings, but on 60cm that can be neglected. I'll need 7 panels in total for two speakers, giving me a bit more than half a panel spare. A panel of some light colored wood (completely forgot the name) is €25 per panel, and a sexy dark one is €35. Comes down to €175 - €245 in wood, depending on which one I go with. Haven't made up my mind.

January 4th

Quote by swt61
Cool Rik!

I'll be following this build. Not sure those are the right size for my own build, but it's great that you decided to document the process this time. :cool:
End quote

Thanks, I'm not all that sure about the size yet either, but we'll see where this goes. Either I end up with huge speakers in my room, or I have a lot of wood for the fireplace. :)

Quote by JadeEast
I've been curious about this design as well as the other double horns and the BIB designs being built. I'd love to play with one of these and maybe mount the driver on the side to load the corners more and get away with a bit more of a flush design and take advantage of the wide baffle. Being an apartment guy I'll just screw around with headphones right now and watch.

Go big.
End quote

The BIB design is also something that appeals to me, especially since a lot of people have built it and most of them are very satisfied.

What you said about expirimenting with the driver location.... it should be easy to make a switchable Fb so I could play with the driver location. Will give this some thought, great idea.

Made a huge mess of things in the earlier panel schedule so I removed it from my post. Here's the new one, including a Visio drawing of what goes where on the panels.

Click image for HTML file
Click here for Excel file

January 7th

Toe-in could become an issue with the J-Low's. From my experience, the JX92s sound best when crossing in front of the listening position (which corresponds to them being designed for a 30+30 degrees toe-in). This isn't possible for me with the J-Low, as it's a very tight fit in my room and they will have to be with their backs flat against the rear wall. I hope the large size of the speaker and horn mouths make up for the lack of toe-in. Two things can happen: speakers sounding too bright (though I doubt that'll happen since they are fairly bass heavy speakers), and loss of imaging. Will this be a problem? I dunno, hope not. Haha, not exactly rocket science this... just build them and hope they don't sound too awful. I'm liking that approach.

I have decided to make a J-Low from plain 18mm MDF first, before going with pre-veneered wood. It'll give me the possibilty to mess around with stuffing in the area behind the driver (keeping one side of the J-Low screwed-only, so I can easily take it apart and adjust if needed), and it gives me a bit of practise to avoid messing up a bunch of nice wood.
Februari 1st

Bought the wood today. A bit later than I had hoped, but school got in the way of starting last month. Decided to make them from plain MDF first before going with preveneered wood. MDF came out cheaper than I expected -- the MDF for both speakers cost me €90. I'm using four panels of 244cm x 122 cm of 18mm MDF. How I'm going to get the finished speakers out of the workshop, into the house, and then up a flight of stairs, I have no idea. I'm using a calculated 170 kg (~380 pounds) of MDF. A single speaker will not only be pretty much as tall as me, it'll weigh even more. :eek:

Pictures later! Also a new panel layout for the MDF. :)

Quote by Bjornboy81
wow...those things are huge for such a small driver! Very cool :)

I wish I had the equipment to build large speaker boxes. I'd love to get into to the single driver thing.
End quote

Not all single driver speakers are so big! There are plenty standmount designs too (though I doubt their level of bass...).

Here's some images of the work so far:

That *just* fit.

Where the magic happens. Notice the clean floor.

Have to saw some angles.

Angle sawing done!

No more clean floor :(.


February 2nd

Another day in...

Glueing corners isn't easy. Rubberbands are a great help though.


Result so far. I plan to do some expirimentation with different drivers, so I made the front baffle holding the driver switchable. I can just unscrew the front, and screw a different one containing a different driver in place. The baffles which fall in place are already made, but don't contain driver holes yet.

The center pieces are all done and glued together (aside from the driver baffle) -- just not glued to the side (yet).


February 11th

Milling out the driver compartment.

More of the same.

Glueing the last part of the front piece. The rest of the parts can be seen on the right.

Glueing the top in place. I can only do one piece at a time since I only have three large enough clamps. :(
It's not glued to the rear plate yet -- it's only clamped to it to make sure it stays at 90 degrees while the glue dries.

All that's left over from the huge amount of MDF I started with... :)
February 13th


Oh look, it's an almost finished J-Low! :D

February 14th

Edit, ok, now it's almost finished.


Glueing front piece of second speaker.

The first will be playing tomorow! :D
Hope to have the second one done on Sunday.

February 15th


Holy crap the bass! There's tons of it. I'm thinking 'very cool', but am afraid what'll happen once I get the right channel playing too. I'm afraid there'll be way too much bass. Nothing that can't be fixed with a simple filter though. :)

February 16th


Taadaa! :D

I'm getting used to the amount of bass. While it's definitely bass heavy at this point, it's not very bass heavy. I think that the problem yesterday was that there was only one speaker in the corner, so bass just sounded odd. They have a very 'live' sound to them, which I'm loving. They improve on the Jordan VTL's in exactly the way I had hoped they would. Very satisfied. So much, that I'm thinking about turning them into an 'all out' speaker.
I've shot Nelson Pass an email with a couple thoughts about some modifications/additions to the speakers that I'm thinking about doing. I really like these and I wonder how far I could take them.

February 17th

Quote by Kees
Nice work!
Must have been a hell of a job to get them upstairs!
End quote

It was a tight fit, and pretty damn heavy. We managed though. :)

Quote by Kees
What kind of modifications do you have in mind?
End quote

I'm thinking this:


Followed by a horn tweeter on top crossing over at somewhere between 5-7Khz:


After that, maybe a large woofer for the area under 50Hz.

Crossover would be done either passive or active, I'm not too sure yet. I like the idea of active and biamping. I want to see if I can turn the J-Low in something that'll last me years. The J-Low using the JX92s would be the perfect basis for such a speaker, absolutely brilliant sound from mid-low to pretty high. Augmenting the highs and the lows at the very top and very bottom would turn it into something very special, I think.

Thanks for looking, and comments, critique, or anything else is much appreciated. They aren't done yet, as you can see from my plans... but it might be a while before I start the modifications.

Soundstage is a problem in my room. I can't get a very big and wide soundstage with any speakers I've tried. There's decent placement but never a very wide 'real' stage extending behind the speakers. My room is 3m x 3.5m, almost square. Added to that, it's two floors with the ceiling only extending through half the room. That sounds a bit odd, I know. Basically, I end up with a 2.5 meter high ceiling on the front side (where the speakers are placed), and halfway it changes to a 5 meter high ceiling. You can see the trouble.... :(

However, the J-Lows, being so large and having a horn exit both below and above the driver, are able to throw a very large sound compared to the speakers I've used before. Exact placement is decent but there's no real soundstage as could be heard in bigger rooms. Alas, I can't say much about it.

Any tips on how to overcome this room issue are most welcome!
Beautiful looking! Then again I'm not a living room or a wife! I t

I believe that Nelson Pass designed them to produce a bit too much bass, then he equalized them to roll off some of the bass so that there wasn't excessive cone excursion-which is the first limitation you will run into with those drivers. Did you do this? If not then you would have too much bass and very little power handling..

Seems a shame to cut the mouth of the horn in two... Better to put a little vase and some ceramic figures on them as in the photo!! Maybe put decorative shape wood trim around the perimeter....
Variac said:
Beautiful looking! Then again I'm not a living room or a wife! I t

I believe that Nelson Pass designed them to produce a bit too much bass, then he equalized them to roll off some of the bass so that there wasn't excessive cone excursion-which is the first limitation you will run into with those drivers. Did you do this? If not then you would have too much bass and very little power handling..

Seems a shame to cut the mouth of the horn in two... Better to put a little vase and some ceramic figures on them as in the photo!! Maybe put decorative shape wood trim around the perimeter....

You're right - the J-Low has a pretty fat bump under 100Hz. Nelson has played a bit with first order high pass filters, and one calculated at 100Hz seemed best. I'm waiting to do some measurements myself before I build a filter -- since I'm in a small room for the speakers I may need a slightly different (stronger) filter. I hope to have a decent mic to do this this weekend or next. Till then, the J-low sounds best at low to mid volume levels, but playing them loud does cause the bass to get out of hand a bit.

No vase, ceramic figure or anything else will ever be placed *in* one of my speakers. That's sacrilege! I will most likely paint them though -- black. So they look even smaller. ;)

I'm not sure at all yet about chopping them in half, though making a chopped speaker from the start isn't all that hard or time consuming. It does mean I'll have to find a place to store the J-Lows when I'm playing with the chopped speakers, and that could become a serious problem.

Nelson Pass said:
Great job. :cool:

The master speaks! Much appreciated. :D

Scottmoose said:
I like it, I like it... :)

Aye, thanks.

I've wondered.... what's there to refrain me from placing the filter before my poweramp rather than after? I think that would reduce costs quite a bit.
Scottmoose said:

Nothing, though you'll need substantially different values of course, and to make sure your preamp can pump enough juice for it to work. ;)

Thanks, that was pretty much as I was reasoning. I think my preamp has the juice needed as it's (as is usual with most equipment it seems) volume hardly ever goes above 9 o' clock. Plenty headroom. And if it can't pull it off well, not much lost. :)
peterbrorsson said:

Why? Put an ad in a newspaper, put in sofa + a bed and rent them out:D
Or, I can store them for you, got 55 square meters waiting:angel:

Nice work!!


If you're willing to come pick them up and carry them downstairs, sure. I think they may be a bit large for the postal system. ;)

I'd love to hear the J-Lows in such a large room.

I forgot to say this in my initial posts, and it's too late to edit them now.

To people who aren't very experienced with woodworking, I should mention this:
Do not make a full length support like I did on your sawing table. You see the yellow metal part of the support? That's its original size. Extending it can be dangerous as it tends to turn sawing tables into cannons firing wood instead of bullets. Do not stand 'behind' the wood you are sawing at any time, but especially not with a support that extends beyond 1/3rd of your saw blade, as it enables to blade to grab the wood from time to time and send it flying into the wall (which could potentially harm and even kill (!) you if you're in the way... be safe). It might be handy, but it's definitely not safe.
Zen Mod said:
try somewhere in some Babowana's thread ( btw - these pics with vase and thingies in Jlow are his) - he opened few holes from back - in both upper and lower horn chambers , and stuffed them with something dense ; he claim that , that way, he get rid of some resonance in these chambers

Thanks for that tip! I didn't find his post -- but I did find his website where the modifications are also described (along more pictures of his J-Low's (they look stunning!). There isn't much resonance in mine, but I'll see about filling the chambers up.

He has also applied dampening material to some parts of the horn. I might play with this as well, interesting stuff.
(Excuse the flash -- friend borrowed my tripod.)

Placed them on small wheels, so I can roll them into the right position for some serious listening. And wow, did they improve!

The large sound that they threw placed against the wall and closer together just became huge. The sound is more balanced too -- the bass moved from slightly to the left to the center. While I still don't have a filter for the lows, I'm becoming more and more impressed by these speakers by the minute.

Yes, wheels are a bit odd, but just think of them as fancy spikes. :D