Jamo R909 Clone?

JohninCR · « **Reply #20 on:** 10 Dec 2006, 03:04 am »

Quote from: scorpion on 9 Dec 2006, 03:34 pm

As I wrote earlier these speakers are OK for OBs, not as outstanding as some reviews might make you think. I have heard them only
under Show conditions.

To copy them you would have to have really efficient bass-speakers (suitable for OB), which hold god efficiency down into the 50 Hz range and show a rising
response in the upper bass, I think. None of the standard B&C chassis seem to fit the bill.

Then you pair this bass foundation with less efficient (but superb) midranges-/tweeters. At least this is the way Jamo did it.

/Erling

Erling,
Why would you want a rising response in the midbass? Ideally, I would want a decreasing response from 40hz on up. Decreasing at 6db per octave would make it a dream driver.

oldtimer · « **Reply #21 on:** 10 Dec 2006, 04:50 am »

Frankly why would you want to copy them...... you can achieve much better results other ways. aa

Happy listening

scorpion · « **Reply #22 on:** 10 Dec 2006, 09:44 am »

John,

If I read the Jamo leflet right, it seems that they in fact cross quite low and utilize a rising bassrespones to counter initial crossover loss and achieve
a level performance. Then when woofer response level out the crossover starts to have its effect. A link to the Jamo Whitepaper for R909:
http://www.jamo.dk/Default.aspx?ID=1469 .

/Erling

JohninCR · « **Reply #23 on:** 10 Dec 2006, 04:21 pm »

Erling,

The rising bass response is after the dipole roll-off, which Jamo says starts
at 200hz with their relatively small baffle. Then they apparently use a 1st order
filter on the woofers to net a flat response up to Fequal. I've used the same
approach with all my bass augmenters and it works very well. I do the same with
my current active XO system, and add a steeper slope XO above Fequal.

scorpion · « **Reply #24 on:** 10 Dec 2006, 06:11 pm »

John,

I think we mean the same thing. I start from the left while you seem to start from the right if we are looking at the response curve.

/Erling

schrottie · « **Reply #25 on:** 30 Jan 2008, 10:22 pm »

Hello,
I´m planing a clone of these speakers (baffle-wise). Although my chassis-setup will be pretty different. I´m going to use vintage Alnicos all the way. Tweeter will be Saba, Mid-Range will be Saba, woofers will be Jensen/Magnavox. The Low-End won´t be as low that way. The XO should be as simple as possible. I was pretty much inspired by this site:
http://www.lampizator.eu/
I wonder whether this is XO is suitable for woofers like those:
http://www.lampizator.eu/SPEAKERS/PROJECTS/P12/endorphin%20XO.jpg
http://www.jensenvintage.com/p15n.htm

What do you think of this project? Is there a chance of the result being a high quality speaker?

JoshK · « **Reply #26 on:** 30 Jan 2008, 11:06 pm »

Quote from: schrottie on 30 Jan 2008, 10:22 pm

Hello,
I´m planing a clone of these speakers (baffle-wise). Although my chassis-setup will be pretty different. I´m going to use vintage Alnicos all the way. Tweeter will be Saba, Mid-Range will be Saba, woofers will be Jensen/Magnavox. The Low-End won´t be as low that way. The XO should be as simple as possible. I was pretty much inspired by this site:
http://www.lampizator.eu/
I wonder whether this is XO is suitable for woofers like those:
http://www.lampizator.eu/SPEAKERS/PROJECTS/P12/endorphin%20XO.jpg
http://www.jensenvintage.com/p15n.htm

What do you think of this project? Is there a chance of the result being a high quality speaker?

Excuse my confusion, but I am not sure why you would want to use such a woofer for OB dipole. Those look to be guitar speakers, even suggesting "bright when overdriven". Look at the 1.0mm xmax. These are intended to be have a very small linear range and purposefully become nonlinear quickly to yield a pleasant crunchy sound for guitar use. This doesn't speak hi-fi to me at all. Different purposes entirely. Am I wrong?

No offense but it seems like you are just being sold on Alnico uber alles. There is more to picking an appropriate dipole woofer than its magnet material IMO.

scorpion · « **Reply #27 on:** 31 Jan 2008, 12:38 am »

I agree with JoshK !

Go with Lampizator project 19 and use Eminance Alpha15 or A&D R1524 for the woofer.
I think you will have to calculate some more on the crossover values. And also read MJK's OB study: http://www.quarter-wave.com/General/OB_Design.pdf

/Erling

schrottie · « **Reply #28 on:** 31 Jan 2008, 08:52 am »

Well, you´re right. Of course the linked Jensens are Bass/Guitar Speakers. And you´re right with your suggestion about me having a kind of Alnico Magnet fetish. That is because I heard the Saba Greencones in open baffle and I was stunned. I had never heard such great voices an detail. So my thought was: "Wow, they built great speakers back then. Let´s buy 1960s woofers!"

I didn´t mean to buy exactly those Jensens. I linked them to give you an Idea of the direction. If you search for vintage 15" speakers on ebay, you´ll find Jensens, Magnavox, Altec, Philco, Fisher... Those where often used in quite open systems, not entirely closed boxes not only in guitar Amps, but also studio monitors, Hammond organs, tube Consoles etc.

Thats why I thoght, they might be suitable. What would you say: Are they just not perfect or total waste? From what I see at least they have a high Qts.

dewar · « **Reply #29 on:** 31 Jan 2008, 10:44 am »

I had the Jamos to myself for half an hour last month, was quite impressed. But I can honestly say that I dont remember them being better than the Hawthorne Sterling Silver Iris speakers I built recently. Not to say they couldnt be better, but from memory my SSIs (with Peerless XLS bass driver and a bit of digital EQ) have me not wishing I owned the Jamos. Long live DIY.

The Jamo template has also inspired some baffles I'm working on. They look good to me and build quality seemed impressive. If only I had a cnc machine...

-Richard- · « **Reply #30 on:** 31 Jan 2008, 05:41 pm »

Hi JohninCR ~

I just found this thread last night and I am really impressed with your latest OB designs... quite beautiful!!!!!
They are easily one of the best OB designs I have ever seen... dripping with class, chic, functional... a work of art!!!!!! If you had the means to produce them efficiently and could work out the shipping issues you should be able to be quite successful selling them. They would also blend into ones living spaces very nicely indeed. Congratulations, John!!!!!!!

Also generally speaking: many first time listeners to the OB experience may feel that there is something utterly exceptional about this or that design that they have heard... like the post-modern-chic Jamo "reference" speakers which are listed with a selling price of $7,500 or even $18,600 depending on who is selling them.

From my own experience, I think that it is the OB experience itself that is catching their fancy in many cases... in other words, any decent OB sounds so incredibly good... is such an amazingly revelatory audio experience... that the person might think that what they are hearing is unique to that OB speaker... when in fact, it is the OB experience itself that is beguiling them.

It is really amazing how close to the expensive commercial designs one can get with a cheap simple thoughtfully implemented DIY OB. That is why Dan Mason suggested it was a "revolution" in speaker design. Because it simply sounds better than any other speaker design no matter what the cost. And you can do away with the clumsy overdesigned box forever.

Warmest Regards ~ Richard

navin · « **Reply #31 on:** 1 Feb 2008, 04:42 am »

Quote from: JohninCR on 27 Nov 2006, 04:10 pm

Not a clone, but you can see that the Jamo influenced my design.

Which drivers are those? 15" Hawthorne Augie and B200?

JPotgieter · « **Reply #32 on:** 9 Jul 2008, 10:35 am »

I've been busy the last year of so with a Jamo clone. Used the same tweeter and midrange but for the 2 woofers used 15" Alpha's.
So far I'm very happy with the sound, have build at least 20+ crossover models and physically build about 5 of them. Currently busy tweaking what I would hope would become the final crossover. I never thought I would say this but with 2 x alpha's it is easy to have too much bass.

Angaria · « **Reply #33 on:** 9 Jul 2008, 12:53 pm »

Please publish the crossover when you're happy with it - sure there would be interest here.

scorpion · « **Reply #34 on:** 9 Jul 2008, 04:53 pm »

If you are Josepho of a diy-Audio thread I think I said already there that one Alpha15 would do it. And I also think I recommended MJK's worksheet to you: http://www.quarter-wave.com/Models/MathCad_Models.html . However I think that this is of some general interest, so here is a simulation with one Alpha15 and Seas Hexagonal W15CH001 driver. Alpha is crossed 2nd order Linkwtz-Riley at 250 Hz lowpass and the Seas at 350 Hz highpass likewise on a 48 x 20 " baffle with Jamo likening (I have in fact had this simulations since the discussion in this thread earlier) :

If you go up to 24" width, it will simulate like this:

This is a brilliant example of what you can achieve spending some time with this excellent software.

/Erling

JPotgieter · « **Reply #35 on:** 10 Jul 2008, 05:13 am »

Erling,

Our paths cross again.

I am a great fan of MJK and has build his MLTL using Fostex FE206E as my first project about 3 years ago and was very impressed. Generally speaking I really can understand why single driver speakers has such a big following. Unfortunately for me personally the open baffle design is just so good that the MLTL speaker (cherry veneer finish) is headed for the fireplace. I do plan to build the MJK open baffle design using Alpha + Fostex. I'm really keen to compare theoretical model with actual measurements and more importantly do some listening tests for comparison with the commercial Jamo design.

I have looked at Martin's mathcad models and has used a combination of his model output to adjust for floor bounce and EDGE for baffle simulation and have based my own modeling on his work. Yes, I could have done this a lot quicker but I'm really keen to understand the underlying models and hence do not mind getting my mind dirty with a bit of mathematics. It has also been an interesting journey for me trying different crossover designs to discover the pro/cons of each.

My plans going forward is to complete my Jamo design using both small (IMO influenced by form over function) and also using a larger baffle. Then I'll build the MJK open baffle. Maybe then I might try a Linkwitz active crossover. I'll publish all my measurements and listening tests as and when each step is completed, I do have to warn you I'm really enjoying this hobby and aint in no hurry.

scorpion · « **Reply #36 on:** 10 Jul 2008, 09:57 am »

Speaker building is trial and error, so Good Luck with your design. I was not assuming active driving with the simulations, passive will work well.

/Erling

hum4god · « **Reply #37 on:** 14 Jul 2008, 02:58 am »

hi

here is an interesting link , scroll down about half way to the Jamo look alike OB:

http://timemachines4.blogspot.com/

JPotgieter · « **Reply #38 on:** 14 Jul 2008, 05:37 am »

The latest crossover I'm busy tweeking has a large 20 mH inductor in series with the 2 x Alphas (wired in parrallel). The Alpha's starts rolling off at 100Hz. They measure -3db at 45Hz, +3db at 100Hz and from there has a 1 order slope. The goal is to choose this inductor to get a smooth transition to the mid even if giving up some of the low end. The inductor resistance is very important as it also impacts the roll-off starting point. The crossover to the mid is at 208 Hz. This pushes the mid as low as possible still allowing pretty loud volumes (max excursion limits). Probably a better crossover point would be around 280, will push it up and do some listening... Crossover from mid to tweeter is at 2600Hz, I've seen guys pushing the revelator down to 1500, but I'm following the Jamo design. Unfortunately a 6 ohm resistor is necessary to tame the high end a bit. The tweeter has a bit of a rising response and is about 6 db too loud for the midrange.

Allin all have to say I was very impressed how close models came to actual measurements. Obviously there is a lot more noise in the actual measurements.

JPotgieter · « **Reply #39 on:** 17 Jul 2008, 04:53 am »

Posted measurements http://www.diyaudio.com/forums/attachment.php?s=&postid=1563705&stamp=1216269784
and crossover http://www.diyaudio.com/forums/attachment.php?s=&postid=1563710&stamp=1216269979
in this forum http://www.diyaudio.com/forums/showthread.php?s=&postid=1563711#newpost