DIY 4520 bass horn build

[NickH]

Im building a pair of jbl 4520 bass horns. This will be my second speaker project and my first from the ground up build. Im not too versed in carpentry so Im taking my time. Im also only using mdf since nice plywood is expensive. Plus since im not to good at carpentry Im going to trash some wood. Ill feel better about trashing cheaper mdf this some high dollar plywood. I should be done with the first horn soon. All depend on how much energy I have left after work at night. I finished the frame for the first horn. Drew out the plans on the inside of one of the sides then transfered it to the other side by drilling hole through it at verious points. I had the other side clamped underneath that side. Then I just played connect the dots.

I used one side for painting a chassis so thats why theres the black spot on it. These will either be painted or maybe veneered. Havent thought that far ahead. I have a pair of gpa 416-8b driver that Im going to try in them first. But Im not setteld on that yet. I only decided to build the 4520 for the longer horn path. I really didnt need 2 woofers. I might just center the woofers in them and just us one.

Ya I know crappy cellphone camera.




Nick

[Lee in Montreal]

Hmmm... I smell a single JBL 2240H driver for pipe organ music. fs of 30Hz and a Qts of 0.23 and quite able to sustain considerable power. Plenty on eBay for $140.00 with original JBL cones. And make that cabe a few inches narrower for a single 18" That will help with WAF...

[NickH]

Well a subwoofer is the next project. I wasn't going to use any jbl drivers though. I was going to stick 2 Dayton 15" dvc sub woofers in a 7 or 8 cuft box and tune the port for 20 Hz. There 90 db sensitivity. I was going to feed 250 watts to each woofer. 125 per voice coil. Then sit back until the police arrive, or my house tears itself apart. I did the math. At max excursion they would be moving 21 liters of air. . That enough to rattle a few teeth out. Who needs fiber in your diet when you can hit the brown note with your home stereo.

Sorry couldn't help it.

Hmmm... I smell a single JBL 2240H driver for pipe organ music. fs of 30Hz and a Qts of 0.23 and quite able to sustain considerable power. Plenty on eBay for $140.00 with original JBL cones. And make that cabe a few inches narrower for a single 18" That will help with WAF...

[NickH]

Got a little work done last night. It was my own idea to put strips on the sides that hold the pieces of the horn flare in place. And something I can shoot a few brads through to hold it in place as the glue dries. Not much but its progress. Im hoping to have one cabinet done this weekend. Hopefully,

[NickH]

Cut the internal panels for horn number 1 today. Hope to put it together tomorrow and post some photos.

[Mike F]

Shouldn't the baffle be recessed or are you building a narrower version?

[NickH]

Shouldn't the baffle be recessed or are you building a narrower version?

Good call. Yep its not a exact copy. Its only 24" wide so I moved the baffle to the front. I was originally going to have it on the outside. But I figured this way is better. Its going to be used for home use so those few inches helps. It minimised the risk of me cramming a corner of it into a wall while I'm moving it. I don't want to gave to do any painting when I'm done.

As I'm sure you can tell, I'm no carpenter. I'm quite happy that I've gotten this far. We'll see how I feel after the first ones built.

[Lee in Montreal]

The recessed front panel has two purposes in my opinion. The first one is to protect the woofers by the surrounding frame. That also allow to esthetically blend in purposefull reinforcing ribs on the sides and bottom of the mouth to keep them from vibrating.

http://www.audioheritage.org/images/jbl/photos/pro-speakers/d55050.jpg

http://www.lajazz.us/audio/JBL-4520/JBL-4520_001.jpg

[NickH]

Just an fyi, never use a nap roller with hammer tone paint. Use a foam one. Just trust me on this one.

[more10]

I can never get two boards to be cut the exact same length.

I use a flush trim bit on a router to make one piece exactly the same as another.

I love this tool :-)

Mårten

[NickH]

I use a flush trim bit on a router to make one piece exactly the same as another.

I love this tool :-)

Mårten

Hey Marten,

I actually have that bit in my router. Well close to it. The guide bearing is on the shaft end though. I havent used a router free hand yet. My issue with board not being exact is just not measureing the kerf of the blade perfectly. But im improving. I havent really done much of this stuff before so Im learning as I go. And then there the whole tast of fractional measuring. I do tons of measurements at work but its not fractional. I use calipers and micrometers so all me work stuff is to the thousands decimal place. I work with metals. Machined components and stuff.

Painted last night when I got home from work. Just a little more to do tonight. I havent taken a new picture yet though. This one is when I was testing them out last tuesday.

[intercity125]

I use a flush trim bit on a router to make one piece exactly the same as another.

I love this tool :-)

Mårten

Hey Marten,

That's a very good idea! I have a flush mount bit for my laminate trimmer, but now I am going to have to get me a larger bit to go with my big router. Thanks!

Willy

[NickH]

Finally started cutting mdf on horn number 2 today. I also tested the rip cut. It actually works pretty well. You have to push from both ends of the guide. I should be able to cut all the internal pieces and maybe get some parts glued and screwed.

[NickH]

Well its that time of year again here in Texas. Spring, which brings the pine pollen. Its really put a damper on me getting the second horn built. By the time I get home from work I dont feel like working in the garage.

We have got a lot of rain over the last few days and the temp has dropped so hopefully the weekend will be good. Ive got a lot of work to do.


As for the built horn there are some issues. Not with the horn but the room. Im getting a wicked bass nullification. Ive moved them away from the wall and Ive moved toward them. Its helped but the output is no where near what it should be. Standing right in front of them is like a earthquake at high output. Makes the whole hose shake at high volume. So I know there working right. Im thinking its about time for some traps.



Nick

[NickH]

I'm probably going to use a piece of trim around the edge. Like the mister Carl Huff mentioned in #52 in your waldorf thread. By the way, that was the hard discussion to make. Build a waldorf/ imperial or the 4520. I decided on the 4520 for size reasons. But this is my first start from scratch build. So maybe the imperial will be next.