Message started by tom.gnade on 03/27/13 at 03:57:11

Title: ZOB build
Post by tom.gnade on 03/27/13 at 03:57:11

My FRX2 arrived today, looking very nice. I'll start building my speakers shortly and will post the results here as I go.

Title: Re: ZOB build
Post by beowulf on 03/30/13 at 03:04:11

Would love to hear about your build ... please check in and let us know how it's going!

Title: Re: ZOB build
Post by tom.gnade on 04/03/13 at 04:06:14

4x8 sheet of baltic birch on order for cabinets, 6/4 sapele for front baffles. Will pick them up this weekend. Still need to pick up a router jig for the circles and a rabbet/dado bit. Started burning in the speakers tonight in their shipping boxes. Listened to them a bit and of course they sound like a pair of tin cans right now. Here's to hoping they shape up in final form!

Title: Re: ZOB build
Post by tom.gnade on 04/10/13 at 15:55:33

I am thinking of using a "squishy" mount for the driver. Since this is an open baffle speaker, I thought I could take advantage of the fact that there is no need to air-seal the driver to the baffle, and instead create a highly damped connection to eliminate vibration.

The current plan is to use a pair of 3/16" thick vibration mounts at the top and bottom of each mounting bolt, which will pass completely through the baffle and be lightly compressed by a nut on its back surface. The driver flange will be recessed into the baffle and mounted flush. I will oversize the recess by about 1/16" at its outer diameter, so the lateral surface of the driver flange will make no physical contact with the baffle. This will leave a 3/16" gap underneath the flange between each mounting bolt, and a roughly 1/16" gap around the entire outer perimeter of the driver.

My question is this: does anyone think there will be a disadvantage to allowing a free-air gap around this driver?

Title: Re: ZOB build
Post by 4krow on 04/12/13 at 07:29:27

Good question Tom. I am inclined to believe that there would not be a difference that could be heard. This would be because of the lack of reflection coming from the back of the speaker itself.
I did an experiment with a short horn mounted over the rear part of the driver, and yes in this case, it changed the sound considerably. In the end, the short horns came off, as I still liked the more open sound of the OB design in the first place.

Title: Re: ZOB build
Post by Chris K on 04/12/13 at 13:50:33

Yes the bass would suffer loss with a gap IMHO. The whole idea of a baffle of any kind open or otherwise is to separate the front and back wave of the driver. What level of separation or isolation is required is debatable. Bass waves are large enough to cancel even on a baffle the size of a large door. If you leave an unsealed gap around the driver flange what is the baffle doing to help the bass frequencies? Something? Yes. Lots less than if it were sealed. If you use a 1.5" thick or more baffle any vibration that might make it to the driver is inconsequential compared to the loss of bass energy that would not give the speaker a pleasing frequency response. If you left the gap in and filled it in with some strips of craft foam stuffed into the gap that might do the sealing you need for bass response and still keep the driver isolated from baffle vibrations. Steve and others might like to clarify this point but most of the time I have not seen serious builders of open baffle speakers fuss over not having the driver mounted to the baffle directly but have chosen to rely on baffle stiffness and mass to overcome vibration. Also a baffle that has sandwich layers of softer less dense material alternating with harder heavier dense material is a possibility. Hope this helps. :)

Title: Re: ZOB build
Post by deanincalgary on 04/12/13 at 16:58:24

just finished mine

they have about 40 hours on them so far

All I can say is WOW, incredible

I will have to listen to all my CD's and albums all over again now....

Title: Re: ZOB build
Post by 4krow on 04/12/13 at 20:20:05

Congrats brother, you will never hear music the same again. Photos please

Title: Re: ZOB build
Post by tom.gnade on 04/14/13 at 17:39:05 a midrange driver from the cabinet

Looks like some big names are using a decoupled mount. I'm still trying to reason out how to loosely mount it without allowing an air channel. I'm also still deciding whether to do a constrained layer baffle or not. A friend of mine owns a machine shop and has offered to cut out a 3/8" thick aluminum sheet that I could attach to the wood baffle with green glue and a few dabs of epoxy. The total thickness would be around 1.5".

Title: Re: ZOB build
Post by tom.gnade on 04/14/13 at 17:51:14

Here's one more that talks about motor mounting the driver. Sounds like a very soft foam will do the trick for the air gap.

Title: Re: ZOB build
Post by 4krow on 04/14/13 at 18:06:24

Tom, I was reading on the Sorbothane site that there were various products that would help in this situation. They make sheets of course, but also there are 'T' shaped grommets that could extend through the mounting screw holes as well as give the head of the screw a soft surface.

Title: Re: ZOB build
Post by tom.gnade on 04/17/13 at 19:53:18

I took a look at them but I think they're too large for this and the load is too small. I order the 1/4" sheet product and I'm going to use some metal punches to cut my own out of it. I'll experiment a bit and put up pictures if I get something that works.

Title: Re: ZOB build
Post by 4krow on 04/17/13 at 20:06:24

I don't think that is a bad choice Tom. On the rear of the baffle board, You will still need to have some kind of material to isolate the bolt heads. I'm sure that you have already considered that. It will be most interesting to me to see what you find in the end.

Title: Re: ZOB build
Post by tom.gnade on 04/28/13 at 17:54:00

4x8 baltic birch before cutting

Title: Re: ZOB build
Post by tom.gnade on 04/28/13 at 18:02:07

Almost all cuts completed. The initial cuts were done with a circular saw and a bora clamp edge guide using a 140 tooth plywood blade. Even with that it's tricky to get a straight cut. Inside corners for the baffles were cut wide with a jigsaw, then sanded and filed to dimension. Once the main cuts were complete and the board was more manageable, I switched to my table saw with a fine blade to get all the dimensions more exact. Even with a sharp blade there is some deflection, so best to use the factory edges against the fence and run the cuts a hair wide. I needed to pass them through the saw a few times to get it nice and straight.

Title: Re: ZOB build
Post by tom.gnade on 04/28/13 at 18:04:07

Waste from the 4x8 sheet. There is just enough to replace one of the larger panels if I blow it somehow.

Title: Re: ZOB build
Post by 4krow on 04/28/13 at 19:23:55

Tom, It's easy to see that you got this right! I'm glad to see it done that way. Good material and good tools will pay in the end. I know what you mean about that one long cut with a 6 degree angle, or something like that. It was a bit of a challenge for me too. The clamp I wanted to use was just short of what I needed, so I was stuck with a sabre saw, and then carefully finish up to the line with a sander. Now, you get to use your imagination again when it comes to glue up with panels that are not cut at 90 degree angles. I used inside brackets to help hold the panels in place. Worked out ok, but again line up was still a challenge. As you already know, placing slats for your gaps will be of great help in maintaining  correct gaps. You can use good tape to hold the slats in place. Keep up with the photos, and don't rush it, think it through.

Title: Re: ZOB build
Post by Lonely Raven on 09/26/13 at 15:18:08

Were there any finished pictures of this project?

Title: Re: ZOB build
Post by tom.gnade on 09/17/15 at 16:45:30

I know this is stupid but I left the speakers sitting until 2 weeks ago, just had too many other things going on. I have them nearly completed now, and will post a few build pics when they are done.

Title: Re: ZOB build
Post by tom.gnade on 10/05/15 at 05:19:26

I have the speakers assembled but not glued or finished. I spent a few hours listening to them last night for the first time, and I can say that the effort of building the ZOBs was well worth the trouble. They have outrageous imaging and soundstage, and very good dynamics. A touch soft in the mid-bass region, but my Vandersteen subs fill in the low end nicely and seem like a nice match. The acousta-stuff may even out the low-end response a bit once I seal and stuff the cabinets.

Since I listen to a lot of rock, I was worried they wouldn't have the dynamics I love, but they do. They aren't the heaviest hitters, but I knew that going in - my highest priority is the openness of the baffle setup, and that is delivered quite well.

They are extremely sensitive to, or maybe I should say revealing of, the recording material. There is a very open and airy sound to them, probably typical of all open baffle speakers, and I agree that it is similar to an electrostatic speaker - I've had Martin Logans and Magnepans. They both had integration and soundstage issues I didn't like, nor could they deliver anything like the dynamics you easily get from the ZOBs - though the Martin Logans came close. Needless to say, with my better recordings, I had a few smiles on my face. Of course they probably have a bit of a shine on them because after all this work I simply couldn't bear for them to sound mediocre - so I want to avoid hyperbole. Obviously, there are better speakers to be had, but probably not for anything near the money I DIY'd these ZOBs for.

I used a single sheet of baltic birch plywood for the cabinets (per earlier posts), and quarter-sawn sapele for the baffles. The joinery is simple dowling - not perfect, but good enough. A plunge router and circle jig were extremely useful for cutting the port and driver holes, and for cutting the groove for the sliding panel. I've included a few pictures in the following posts. I will final sand and finish them in the next few weeks.

Title: Re: ZOB build
Post by tom.gnade on 10/05/15 at 16:55:47

Look Ma! Standing up and jammin without a drop of glue. :D

Title: Re: ZOB build
Post by tom.gnade on 10/05/15 at 16:57:26

Construction pic - mounting the baffles.

Title: Re: ZOB build
Post by tom.gnade on 10/05/15 at 16:58:28

Frames complete.

Title: Re: ZOB build
Post by tom.gnade on 10/05/15 at 16:59:58

The very first step in assembly...

Title: Re: ZOB build
Post by 4krow on 10/12/15 at 12:01:22

Good for you Tom, your almost there....ummmm that's not you in the stroller is it? I AM impressed.

Title: Re: ZOB build
Post by tom.gnade on 10/14/15 at 17:36:00

Ha! No, that's Cookie, the build supervisor and main reason my speakers sat unbuilt for 2 years. Lol.

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