My turn to build JC's DBB

[Rudy81]

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=260-516

This is what I used and put it on the rear, one side and the top of the box. Pictures look great, anxious to hear what you think with the tops running. I know you're going to take measurements on it, but I'm more interested in how it sounds to you, heads up against your K Horn. Have a great weekend.

Pete, I only took one of those tanks upstairs and that was a challenge. I just wanted to make sure it would at least work before I continued with the top section and the finish. My first impressions are that the bass output is higher for a set volume, the DBB can reach higher in frequency and if you get close to the cabinet with any sort of volume it will thump your chest cavity. HOWEVER, once cabinet vs. one Khorn bin is no comparison. I will have to wait to do a listening comparison until I can set up both DBB's vs. both Khorns and play them as a pair. Then, I will be able to tell.

I just need to figure out how to best 'tune' the DBB with fill etc to give it the best chance as good performance.

[Rudy81]

I decided today to see if I could determine what kind of structural reinforcement the cabinets needed. I used a very technical method, by banging on the panels with my fist. Every panel sounded nice and solid except for one. The divider shelf had a very noticeable vibration at a much higher frequency than the other panels. I realize once I add the baffle, things will tighten up. BUT, I still felt the mid shelf was not sturdy enough for my taste. So, I added two braces per woofer enclosure. The result was a noticeable change in the mid shelf's resonance. now it sounds like the rest of the panels. I can only assume that it will only get better once I add the baffle.

I now just need to add some sort of fill to some of the panels. Then sand and either paint or veneer.

Meanwhile, I will build the top hats this week. I have decided to make then rectangular and only as deep as the first side panels. The angled pieces are not necessary since you can't see the angled sides unless you walk around the speaker. No use in making the build of the top hat any more complicated than it needs to be.

[jwc]

I just got back in town from a camping trip.

Rudy, those look amazing. Have you had those put in the corner for testing? That isn't required but curious.

I used sonic barrier on opposite parrallel side walls.....one wall bare...opposite wall with soninc barrier.

jc

[jwc]

Old photo

Look at the inside of the top half. That "bar" that runs underneath the top panel is a 1 1/2 hardwood strip used for bracing. There is one underneath the mid-panel that seperates the two cabinets. The bottom panel was braced by having a "riser" panel like the las scala has.

That black stuff is sonic barrier. Can really give opinion on that materail....but wanted something in there.

jc

[jwc]

Here is a funny one. "So how do you hook it up to the network"?

Man...I haven't looked through this stuff in awhile. Good memories.

[Rudy81]

JC. You cannot go off on some camping trip at a critical time like this. Work is one thing, but camping? Please!

I hope you had a nice time. I have bee doing quite a bit of reseach on ported cabinets and had surmized I needed to beef up the cabs. I'm glad I did since I had not asked you about that. Here is what I did. I hope it does not affect the sound in a negative way. I used the bang the sides method to see what I needed to do.

[Rudy81]

I did have some old 1" acoustic foam lying around from a previous project. I intalled it on one shelf to see if it would work. As you can see, I went crazy with the glue, screws, the caulk and even the fiberglass resin. I found a site that mentioned that using just the fiberglass resin works well. I figured that out by being lazy. When I tried to put fiberglass in the corners, that became an incredible mess. I had noticed that the resin itself dries hard. So, I just used the resin to coat all corners. So, these cabinets are NOT coming apart.

[jwc]

Looks good to me.

The only thought would be to add more bracing to those horizontal panels. They are really large and prone to resonance. Other than that.....jam on.

Can you tell us more how you did that measurement. Where was the cabinet sitting? Any chance to move the cabinet outside? I know that is a lot to ask

[Rudy81]

Looks good to me.

The only thought would be to add more bracing to those horizontal panels. They are really large and prone to resonance. Other than that.....jam on.

Can you tell us more how you did that measurement. Where was the cabinet sitting? Any chance to move the cabinet outside? I know that is a lot to ask

JC, I will look into adding more bracing tomorrow.

The measurement was taken in my media room. Microphone was 2' from the baffle, midway between the woofers. The cabinet was just in front of my khorn cabinets, so it was not in the corner. That's why I made some comment about it only getting better if I placed it closer to the corners.

Taking the cabinets outside is no problem. They are now back in my shop which is 'outside' relative to the house. The problem is getting my measuring geat outside. I use a desktop pc which is my HTCP to run the tests. I''m not sure if my laptop audio card can do the test. I will look into it chen I can.

[Rudy81]

Old photo

Look at the inside of the top half. That "bar" that runs underneath the top panel is a 1 1/2 hardwood strip used for bracing. There is one underneath the mid-panel that seperates the two cabinets. The bottom panel was braced by having a "riser" panel like the las scala has.

That black stuff is sonic barrier. Can really give opinion on that materail....but wanted something in there.

jc

JC, can you explain the 'riser'? I have a La Scala,but am not sure what you mean.

[jwc]

The original la scala has a 3/4 inch panel on the bottom which is the covering for the woofer chamber. Well....if you put a "riser" panel underneath your bottom dbb panel...then it won't need bracing. Just the mid horizontal panel and the top panel need it.

Just curious on an outside measurement to understand the dip on the dbb after 200Hz.

If you are interested.......I can send you two Bob Crites cast frames just for curve purposes and for you to compare. For one to know if the Crites handles higher frequencies better. Just thinking out loud here.

jc

[jwc]

Rudy. is there a reason why you measurements don't show a low end response. The Khorn is used as a reference here and it doesn't show it going as low as it is supposed to.

jc

[Rudy81]

JC: I will try to see if I can set my laptop up to run the tests. I happen to have an amp available as well as two crites cast frame woofers I am trying to sell. It would be interesting to compare the performance between the drivers.

I now know what you meant by a riser. Good idea. I had removed my riser from the La Scala when I made the ported enclosure for it.

Thanks.

Rudy

[Rudy81]

Rudy. is there a reason why you measurements don't show a low end response. The Khorn is used as a reference here and it doesn't show it going as low as it is supposed to.

jc

JC, to be honest, I have always gotten that type of response. It is entirely possible that I am screwing something up. Are you saying the area below 50Hz or so should show a higher SPL? I did comapre your DBB plot with what I have and they are not that far off. Of course, my room is causing anomilies you did not show.

I know I have a Khorn FR plot from Klispch around here somewhere. I'll see if I can dig it up.

[Rudy81]

JC, I found this on another post. It is a Khorn response from an article. There could be a couple of reasons for the lack of very low response. One is, the Khorns are not up agains a true corner because I have windows about a foot from the corner...so, I have false corners. Of course, my room could be causing that problem as well. The fact that the DBB seems to do better leads me to beleive it is a corner placement issue and the Khorns are not properly coupled to the room.

[seti]

When I found my measurements didn't show low end it was usually because I didn't change the microphone for input from internal computer mic to external mic. If I hadn't measured for a while this isusually my first oops. You might not have done this but I thought I'd mention it because I have.

[Rudy81]

When I found my measurements didn't show low end it was usually because I didn't change the microphone for input from internal computer mic to external mic. If I hadn't measured for a while this isusually my first oops. You might not have done this but I thought I'd mention it because I have.

It has been a long time since I set my HTPC up, but will double check when I get a chance. The setup is rather convoluted with the audio card. Then there is mic calibration etc.

Thanks for the idea.

[John Warren]

Dual unit bass enclosures are a nice solution. I've built a number of these units over the years. Dual JBL 15".

Ports are rear located.

The unit pictured is two separate enclosures, each about 4 cubic ft, double wall MDF.

[Rudy81]

John, that looks like a product you pick up at the audio store. Nice job.

[John Warren]

Here's the AFT end of the thing. Two plastic ducts, 6" diameter tuned to 42-44Hz. As you are also measuring, this concept has better bandwidth than a Klipschorn bass unit and therefore better transient behavior. Efficiency with the JBL units is around 100dB/W. The McCauley carbon cone 15"s sound better IMO in the mid-bass but the JBL has more low-end. In this setup I have the L and R channels feeding L and R drivers, respectively. Too much upper end output, thus the chokes.