Plan for open baffle Jamo r909 clone

ecir38 · « **Reply #100 on:** 17 Apr 2012, 02:22 pm »

I always used wood putty with great success, easy to sand too.

puppet · « **Reply #101 on:** 18 Apr 2012, 03:13 pm »

A couple suggestions ... think about putting a "quirk" @ the seams of the MDF panels. (where they sandwich). This can be done now with a router and a shaft that will accept slot cutters. This joint will show no matter what later on ... work with it. A nice 1/8" x 1/8" groove is easy to produce .. and a guy could accent that with a contrasting color, silicone caulk, wood/laminate inlay .... you get the idea.

As you guys fabricate your parts don't get into a rush to assemble. Take the time to sand all of your work beforehand. Doing it later is a real PITA.

It would be an extremely good idea to at least primer your parts as well at this stage. Raw MDF is like a sponge. Get it sealed up right away. Doesn't matter too much with what ... just get something on it.

Looking good so far!

Phil

Bob in St. Louis · « **Reply #102 on:** 18 Apr 2012, 03:21 pm »

Quote from: puppet on 18 Apr 2012, 03:13 pm

think about putting a "quirk" @ the seams of the MDF panels. (where they sandwich). This can be done now with a router and a shaft that will accept slot cutters.

Exactly!
If you can't hide it, accentuate it!

Sometimes it's easier, and adds a nice visual touch too.

Bob

jonirvine · « **Reply #103 on:** 18 Apr 2012, 11:11 pm »

I was thinking about wood puddy and even bought a big can to do so a month ago... maybe I'll try that after a layer of the glue/water mix. Then go crazy on Primer. That should do it, and geeze if it doesn't this is the last time I'm working with MDF. Speaking of which, I'm already starting a new project using bamboo plywood... very excited to use this material and not deal with all the sanding and finishing of MDF (ugh).

Bob in St. Louis · « **Reply #104 on:** 18 Apr 2012, 11:38 pm »

Quote from: jonirvine on 18 Apr 2012, 11:11 pm

............. this is the last time I'm working with MDF..(ugh).........

That's a good choice.

jonirvine · « **Reply #105 on:** 22 Apr 2012, 03:02 am »

So today's weekend project was adding a rear firing super tweeter. The "baffle" for it is temporary but i found a good use of some spare IKEA metal braces laying around. Overall, I "think" I like the addition to the rest of the system but am still questioning whether I "like" the crisper highs I'm hearing. When I A/B them (on/off) I can def tell my TB's alone aren't producing the same amount of brightness however, I might say there's a more balanced and even warm tone without the tweeters. hmmmm.. SO the jury is still out.

Does anybody have any advice on where to face the tweeters? I currently have them parallel with the rear wall and have designed the framing so I can play with different directions. Any advice?

Here's some pics:

Bob in St. Louis · « **Reply #106 on:** 22 Apr 2012, 03:24 am »

Most creative Jon ....Go boy go !!!!!!!.

studiotech · « **Reply #107 on:** 22 Apr 2012, 06:38 am »

If I had to guess, that tweeter is quite a bit more sensitive than the other drivers. You might try padding it down some to find a happy balance of more highs without sounding too bright...

You could pick up some L-pads from Rat Shack and then have a variable set-up. Much better than attaching various resistors a million times till you find the sweet spot.

Also, how are you crossing it over? Are you picking off a parallel feed from the TB and using a cap?

Greg

jonirvine · « **Reply #108 on:** 22 Apr 2012, 04:46 pm »

Yeah you're right... it is more sensitive with an SPL: 104 dB 1W/1m. I have it running on it's own amp right now so it's not networked with the FR or anything. I've never used those L-Pads but will def look into it. I like the idea of being able to play with different options. Of course, I'm thinking of going with a MiniDSP real soon here so I might hold out and just adjust it from there. For now, I think simply toning down the volume/level on the amp has helped it not be so bright.

The capacitor included is 3.3uF, which will put the crossover frequency at approximately 6kHz.

I still don't know what direction sounds best as I don't have an "assistant" available to turn it as I listen... i have to keep getting up and down trying to remember what each version sounds like.

Badwater · « **Reply #109 on:** 22 Apr 2012, 05:18 pm »

Try some smaller caps without an L-PAD. I am running a Fostex 90A super tweeter with a 0.33 uf cap. Buy some cheap caps of say 1.0, .68, and .33 and see where it gets you. I run mine facing the front. I tried rear facing and didn't like it.

studiotech · « **Reply #110 on:** 22 Apr 2012, 11:31 pm »

Quote from: Badwater on 22 Apr 2012, 05:18 pm

Try some smaller caps without an L-PAD. I am running a Fostex 90A super tweeter with a 0.33 uf cap. Buy some cheap caps of say 1.0, .68, and .33 and see where it gets you. I run mine facing the front. I tried rear facing and didn't like it.

I don't get the point behind your recommendation. Caps of those values will put the knee of the crossover at approx. 20,000 , 30,000 and 60,000hz respectively. Sure, sound will still be getting through with only a 6dB/oct slope, BUT why do this rather than a proper crossover where you might want it and then some padding to lower the level. I'm not suggesting to leave the variable L-pad in place, just use it to tune to taste and then swap it out for the value resistors that work best for the situation.

Jon, you might to swap out that nasty little cap that came with the tweeter and replace it with a nice Dayton poly or something....nothing too boutique. It's at least a cheap tweek. Might make a difference, might not, but you're only out a couple of bucks to try it.

Greg

studiotech · « **Reply #111 on:** 22 Apr 2012, 11:36 pm »

Quote from: jonirvine on 22 Apr 2012, 04:46 pm

Yeah you're right... it is more sensitive with an SPL: 104 dB 1W/1m. I have it running on it's own amp right now so it's not networked with the FR or anything. I've never used those L-Pads but will def look into it. I like the idea of being able to play with different options. Of course, I'm thinking of going with a MiniDSP real soon here so I might hold out and just adjust it from there. For now, I think simply toning down the volume/level on the amp has helped it not be so bright.

The capacitor included is 3.3uF, which will put the crossover frequency at approximately 6kHz.

I still don't know what direction sounds best as I don't have an "assistant" available to turn it as I listen... i have to keep getting up and down trying to remember what each version sounds like.

Yikes, 104?!?!? Holy highs Batman! You gotta tame that sucker. IF you use the L-pad, you could attach long wires to it and play with it from your seat in real time. You might even find a stereo one and set both speakers simultaneously.

I would keep them pointed about straight back. This should give the you the most even, consistent spread once you have the overall level lowered. Pointing off to the side too much might give you some reflected hot spots side to side along your listening axis. You might even play with a little diffusion on the wall behind them for a more natural reflective spread.

Greg

Badwater · « **Reply #112 on:** 23 Apr 2012, 01:18 am »

Why? It works and it is what Fostex recommends, not that means anything and it is cheap and easy to do.

studiotech · « **Reply #113 on:** 23 Apr 2012, 01:34 am »

Quote from: Badwater on 23 Apr 2012, 01:18 am

Why? It works and it is what Fostex recommends, not that means anything and it is cheap and easy to do.

Actually, the data sheet shows 1.0-1.5Mfd cap AND an L-pad. Just sayin...

jonirvine · « **Reply #114 on:** 23 Apr 2012, 04:54 am »

hmmm... great advice here! Thanks for the input! I def think this "nasty" crossover is the issue. Now I just need to decide if I should mess with the passive solutions mentioned or just wait till I get a miniDSP in a month or so. It's about time for me to disassemble and start painting so I might just wait for the miniDSP.

jonirvine · « **Reply #115 on:** 23 Apr 2012, 05:17 am »

Oh this is funny... Jamo mentioned me on Twitter:

jacozz · « **Reply #116 on:** 23 Apr 2012, 01:20 pm »

That is funny

Jon, have you heard the original Jamos?

From my understanding, they did a clever thing with the XO:s for the woofers.Instead of using high QTS drivers, they choosed to lowpass the first woofer around 60-70 hz (or somewhere around there), but with the second driver lowpassed around 250 hz (or somewhere around there), so it's actually a 3 1/2 way speaker.

jonirvine · « **Reply #117 on:** 23 Apr 2012, 06:04 pm »

I have but was not completely blown away by the sound as much as I was the design. I knew going into this I didn't have the skills to put together a crossover system anywhere close to theirs so I went with the tried and true design of MJK.

Quote

they choosed to lowpass the first woofer around 60-70 hz (or somewhere around there), but with the second driver lowpassed around 250 hz

That's interesting, I did not know that. I'm planning on getting a miniDSP soon and maybe I'll play around with something like that instead of running the Alpha's parallel.

SteveRB · « **Reply #118 on:** 25 Apr 2012, 08:55 pm »

Quote from: jonirvine on 22 Apr 2012, 03:02 am

Does anybody have any advice on where to face the tweeters? I currently have them parallel with the rear wall and have designed the framing so I can play with different directions. Any advice?

convention seems to be that the rear tweeters should be square with the speaker to keep the dipole radiation pattern. However, there are a few examples of upward firing tweeters.

Seems like it might be a trial and error style integration based on your system and your listening room set up. I am actually going down this road soon with a rear firing tweeter to match my sealed front tweeter.

Maybe you should ask your new friends at Jamo and see what they say...

Bob in St. Louis · « **Reply #119 on:** 25 Apr 2012, 09:37 pm »

Quote from: astronaut_glen on 25 Apr 2012, 08:55 pm

Maybe you should ask your new friends at Jamo and see what they say...

That's funny.