Plan for open baffle Jamo r909 clone

grsimmon · « **Reply #20 on:** 20 Feb 2012, 05:32 pm »

Quote from: jonirvine on 20 Feb 2012, 08:47 am

I've seen this done before but I'm not sure I understand the concept, sonically speaking. Can you explain briefly and/or point me in the direction of an online resource?

A great online resource is the Linkwitz Labs website, just google those 2 words and off you go. He has tons of info. available, not just for his speakers but lots of links, references, articles, etc including measurements that back up his claims that omnipolar and dipolar using an open baffle framework are the best signal launch methods.

jonirvine · « **Reply #21 on:** 22 Feb 2012, 12:37 am »

*UPDATE*

Here's the pieces for the 1" MDF I will be CNCing this week:

Next Step: Lots of sanding and painting to get the piano black finish I'm looking for!

jonirvine · « **Reply #22 on:** 22 Feb 2012, 10:36 pm »

And here's the 3D render:

grsimmon · « **Reply #23 on:** 23 Feb 2012, 12:38 am »

Perhaps this will rival user "Prelude"'s recent Linkwitz Orion DIY build! Just kidding guys, just saying this is looking pretty interesting.....best of luck on this project

Bob in St. Louis · « **Reply #24 on:** 23 Feb 2012, 02:35 am »

Great design to emulate Jon. Best of luck.

The 909 has always looked to be quite the sexy beast for an open baffle speaker, as far as I'm concerned.
I'd love to hear a pair someday.

Thanks for the CNC images. Please post photographs of the build progress, if at all possible.

Bob

jacozz · « **Reply #25 on:** 23 Feb 2012, 08:10 pm »

Hello!

I have to agree with Scorpion here.

My humble advice is to stay away from High QTS drivers.
Although, I have to admit, I never used Eminence Alpha drivers, but I tried a cheap high qts driver in my open baffle with really bad results.

I would suggest to use a driver with QTS between 0,4 - 0,7, with a healthy Xmax instead. Use EQ to compensate for the roll off.

jacozz · « **Reply #26 on:** 23 Feb 2012, 10:58 pm »

To clarify my statement.
I think folks in general focus to much on the frequency response, and forget that the quality of sound production is a lot more than frequency response. Even though cheap high qts woofers will sound perfectly ok in open baffle, (compared how they do in a regular box), there's still more parameters to consider to get great bass than just low frequency response.
In open baffle, my experience, I prefer high quality bass, to let say, 40 hz with roll off compared to 25 with muddy, rumbling soft bass.

But that's me and my personal opinion. Other folks may like the "round" full bass sound, but I'm more for the "kick in the chest" type of guy. So it depends a lot what you kind of sound you are looking for.

jonirvine · « **Reply #27 on:** 24 Feb 2012, 03:06 am »

Fresh off the press:

jonirvine · « **Reply #28 on:** 25 Feb 2012, 03:16 am »

All pieces cut and ready to sand:

Poultrygeist · « **Reply #29 on:** 26 Feb 2012, 12:58 am »

Very handsome and you should be very proud of your efforts.

I don't have the patience or smarts to get a good finish coat on MDF so I've started convering it with textured wall paper which makes it easily paintable.

jonirvine · « **Reply #30 on:** 26 Feb 2012, 04:15 am »

Thanks Paul! I'm planning on doing wood filler, oil based primer, then Sherwin's line of SureChem raven black. With lots of sanding in between coats, I hope I can get that piano black finish. On the back of the baffle and the base I'm going to cover with Quiet Kote sound dampening spray. I'm not sure of that will make much difference, but it can't hurt you know?

studiotech · « **Reply #31 on:** 27 Feb 2012, 12:36 am »

Quote from: jonirvine on 26 Feb 2012, 04:15 am

Thanks Paul! I'm planning on doing wood filler, oil based primer, then Sherwin's line of SureChem raven black. With lots of sanding in between coats, I hope I can get that piano black finish. On the back of the baffle and the base I'm going to cover with Quiet Kote sound dampening spray. I'm not sure of that will make much difference, but it can't hurt you know?

No harm in using the Quiet Cote. It can only help. Baffles look excellent. Don't you just love CAD machines? When I made my prototype baffles out of a 3 layer sandwich of Plywood/MDF/plywood, they were still a little resonant feeling. Almost a little spongy if that make sense. Yes, it is layered, but the dimensions are large considering no sides or bracing as in a typical box build. Once I jumped into the bamboo, the added stiffness of that material really made a significant different in the rigidity of the baffle.

Keep the picts coming....

Greg

studiotech · « **Reply #32 on:** 27 Feb 2012, 12:48 am »

Are you still set on the Alpha 15s? Did you check the link AJ sent you? Seems like a good choice without breaking the bank for some AEs. Never used the ones he linked, but Alphas are not the greatest and you are obviously investing a lot of effort and time, so.....

Greg

Sorry, just realized those woofers are 12" and you have you holes for 15" at this point.

jonirvine · « **Reply #33 on:** 27 Feb 2012, 04:22 am »

Quote

Once I jumped into the bamboo, the added stiffness of that material really made a significant different in the rigidity of the baffle

I looked into the pricing of bamboo actually.... very expensive! I would love to do a project with that one day. Maybe even make a nice component shelf even.

Quote

Are you still set on the Alpha 15s?

Well yeah... I went back and forth between some cheaper and more expensive drivers (including AJ's link). And yeah they're already ordered and waiting for me at my local speaker shop (Jamac in Portland, which I highly recommend btw). The Alpha's are well tested for OB context and 15's make it congruent for a r909 clone. Perhaps down the road a lil swap out if I'm not happy with the results but for now they seem like a trusted sub... and for someone like me who's a newb to this diy audio world... I'll take as much proven experience as possible. I've got a lot to learn!!

scorpion · « **Reply #34 on:** 27 Feb 2012, 12:26 pm »

I hope you will be satisfied with your 'Jamos'. Regarding Alpha15s and Beta15s there are evidence that the Betas sound more articulate and clearer than the high Qts Alphas as I posted above.

Alpha15 has Fs = 41 Hz and Qts = 1.26 and Beta15 has Fs = 35 and Qts = 0.58. Mostly (in OB) you have to cross from bass to midrange about 200-300 Hz were in fact you will cover a lot of instrumental and voice fundamental tones in the bassrange. I have used Alpha15, AE IB15 and A&D R1524. I cross at 277 Hz sharp between bass and midrange and to me the difference between AE IB15 and Alpha15 is like Night and Day, like you pull a veil from the speakers. I have no experience with the Beta15 but others say they are that better than the Alpha15.

But Alpha15 bass superiority is a bit of a myth. Simulation of the units on a 40 x 20 " baffle, two of them placed about the same as on your Jamo baffles looks like this:

Alphas first, crossed at 200 Hz 2nd order L-R:

Betas, crossed at 160 Hz, to give the same SPL level as the Alphas, 2nd order L-R:

So what is the main difference. The Betas may be about 3 dB down compared to the Alpha at 40-50 Hz in all other frequencis they will be more or less equal.
This is the trade-off then, some dBs in the very low bass instead of overall clarity and articulation.

/Erling

jonirvine · « **Reply #35 on:** 27 Feb 2012, 03:35 pm »

Thanks for these comparisons! I'll def consider the beta's more in the future. Luckily it seems like both are good candidates.

I wonder what the Tang Bands would look like on one of these simulations? I don't have a PC (Mac only home) so I can't download Edge or that other one that begins with a B. Can anyone recommend a similar program for the Mac? Or do me a solid and plug in the TB's values and post them? I'm running them wide open at first so I'm trying to determine my c/o point for the Alpha's. MJK does 200hz but his is a networked c/o with Fostex. Poultrygeist does 80hz and his setup is nearly the same as mine as he runs his TB's wide open too. Therefore I imagine there's a good reason to go lower than 200 hz... I just don't know how low. 80? 100?

zmyrna · « **Reply #36 on:** 27 Feb 2012, 03:44 pm »

Why haven't you considered making your main baffle sand filled?
That mid layer in your sandwich could easily be replaced by a sand filled cavity.
That tall and narrow baffle is gonna vibrate quite bad.

jonirvine · « **Reply #37 on:** 27 Feb 2012, 04:01 pm »

Quote

Why haven't you considered making your main baffle sand filled?
That mid layer in your sandwich could easily be replaced by a sand filled cavity.
That tall and narrow baffle is gonna vibrate quite bad.

I have no idea what sand filling is. Just using the best methods I know.

Bob in St. Louis · « **Reply #38 on:** 27 Feb 2012, 04:38 pm »

Quote from: jonirvine on 27 Feb 2012, 04:01 pm

I have no idea what sand filling is. Just using the best methods I know.

Hey Jon,
I've made a few sand filled baffles. It does help to cut down on resonance, vibrations, etc...
Check > Here < and > Here <
Something to think about for your next build. Hope that helps.

Bob

jonirvine · « **Reply #39 on:** 27 Feb 2012, 05:28 pm »

Wow Bob, those are nice builds! I've never heard about this method until now. Zmyrna, you're right, this would have been a fairly easy modification considering my design.

I know that the Jamo's are made of 7 layers of MDF so that's why I decided to go that route. I guess we'll see how these sound without sand and def consider them next time. (Wait, "next time"? This is the build that was supposed to bring me eternal audio contentment)