New MJK Baffle Article

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#321
marec said:
Ah, you mistake me!
I would imagine that the 108 was nowhere near it's limits. This is a small room and I don't listen loud....

I did wonder whether a cheap inductor might be saturating, but I even doubt that.

I could stick an ac voltmeter across the loudspeaker if this might help. Personally I wouldn't know what was ok!!

Mark
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I have used Fostex full range FE167E in OB config. before, it sounds ok but a little thin, when it driven a little harder it sounds like breaking up.

I then switched to two parallel SEAS woofers, with tweeter, the sound improves, it has more body and handle power better.
 
#322
Colin said:

Although off-topic, I'd be interested in GM's and MJK's thoughts on this construction technique for MLTLs, as well as OB.
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It's very much on-topic as OBs oscillate at whatever its Fs is, ergo no different than a regular rectangular box in this respect, so either lower/raise it to below/above its passband as required. As you noted, the > the aspect ratio the > the loading at the ends due to pipe action, ergo less along its length. That said, large areas require damping and/or bracing regardless of aspect ratio. This 1955 article on testing a particular speaker kit winds up 'preaching' the need for rigid construction, so not exactly a recent concept: http://gainclone.com/Karlson/index.php?topic=71.msg408#msg408

GM
 
#323
Colin said:
Art Ludwig's article is interesting and comes to much the same conclusion as Dudley Harwood in the 1970s BBC research which led to the LS3/5A and related designs. He used bitumen felt pads for constrained layer damping, testing how many were required and the effects on different thickness wood. This last test revealed that 18mm vs 9mm ply was no better at limiting vibration but required twice as much damping....
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A recent opportunity to borrow a set of LS3/5As has me exploring this further (which we compared to the Fonkens*). I have borrowed a set of BC-1s from the same person to see if we get similar results (i sold them to him new so i know where they have been and how well they have been treated -- the LS3/5As were of unknown heritage).

*(Fonkens are thin wall, braced to push panel resonances up, and no panel damping)

dave
 
#324
marec said:
Additional information: When driven a little harder, the image collapses, the sound becomes confused.

At the listening levels used early morning I was delighted that i could detect no vibration on the speaker. At the later levels, there was significant vibration on the baffle.

If the flapping baffle is responsible for this degradation, I have two solutions:
(1) Mass load the driver and isolate from the baffle
(2) Improve the characteristics of the baffle.
Any suggestions?

If it isn't the baffle vibration, what else might it be?

Mark
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Couple of questions/suggestions.

1) To eliminate baffle vibration as a cause, you could clamp a 2 x 4 in the vertical direction to try and reduce motions and listen again.

2) How are you holding the panel at the base, could your joint be weak enough to allow the baffle to rock back and forth?

3) Have you used the FE-108EZ drivers in another design, could one of the drivers have an issue? Is it only one speaker or both that sound harsh. You also mentioned that the system was a little bright, I would recommend padding down the Fostex a few dB and listen again, if a system is too bright it can sound very harsh and even distorted at higher volume levels.

4) What kind of amp are you using, could the amp be running out of power or be struggling with the speakers impedance swings? If you are using a low wattage tube amp it may not have enough juice, have you tried a higher powered SS amp? You might want to swap the amp just to see if the problem is repeatable.

5) Did you check all of your connections to make sure one is not loose? If the baffle is shaking it might be stressing a poor contacting connection.

Please let me know how you make out.

Hope that helps,
 
#325
Hi Martin,
Thanks for all that. I was going to clamp some reinforcement in before I went through the lamination exercise (I like my baffles laminates of expanded polystyrene a la Briggs). However I didn't and thought instead. The onset of the distortion was quite sudden and at relatively low volumes. The amplification I'm well used to (it's a car radio). I wondered if it was the way the loudspeaker interacts with the room, which is quite hard. I teased out some long fibre wool and put a layer behind the 108, and there was that problem solved!

I re-read one of my earlier posts and realised that some of the language used may not travel well.
In the UK, people of a certain age and background say that something is "Quate Nace", when bestowing high praise.
I think this is a wonderful loudspeaker.

I'm not sure that the vibration I feel in the baffle IS actually causing a problem, it's just received wisdom for me, but I may rebuild the panel. On the other hand, I might just listen to it!

As for the supporting base, for the moment, it's just a couple of battens screwed to the side. Something more elegant is required.
Any recommendations?

Mark
 
#333
Most US Southerners would rather ask for forgiveness than ask for permission 😀
 

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#336
Took out the 108 drivers and mounted in a set of FE87. a world of difference, now everything sounds balanced and the imaging improved. These are going to become my home speakers now. I believe if the mid/HF driver is just a bit too efficent it unbalances the sound. Plus the 87 has a high Qts which appears to blend in with the 15" high Qts driver.
Now yall are going to ask how i mounted them in a larger hole. Well at Hobby Lobby you can buy 10" dia wooden rounds (diffraction be damned). Just cut a hole and glue to the baffle.

I would not reccomend this with a 2 watt SET. I tried all my amps and the best sound came from my old tweaked Marantz 2238.

I totally endorse this design, its about as simple/cheap as it can get (hell, i built them) and the clean balanced un loaded OB sound is very very good. I believe its more matching the drivers than anything else. Just allow enough room between walls and the baffle. Positining is a move and listen for the best results.
Drawbacks: still dosent have that LF slam that a properly designed BLH does.

ron


(no advanced puter programs/physics/math were abused/violated during this test, just build and listen)

(Quote from my prof/mentor/friend "the hardest thing you can do is to make something simple)
 
#337
I totally endorse this design, its about as simple/cheap as it can get (hell, i built them) and the clean balanced un loaded OB sound is very very good. I believe its more matching the drivers than anything else.
Click to expand...

Thanks Ron, that is very high praise!

I agree they are simple, cheap, and easy to build. Matching of the driver's relative SPLs, the high Qts of the woofer, and the size of the baffle all combine to provide a reasonably flat SPL response. Everything works together.
 
#338
I agree they are simple, cheap, and easy

But Martin.......so am i.(Dont tell my new wife)

Really i believe by going to a higher Qts mid/HF driver the end result is a very balanced system. The OB sound is different, its very spacious and fast (no loading beyond atmospheric) so the mechanical actions of the cone movement are not (or to a much less degree) affected.
The difference between the 108 and 87 is a great magnitude.
I would encourage builders to try a higher Qts drivers with up to 10 db difference in effiency and the smallest focal spot(dia) they can get away with.

ron

Good job Martin!
 
#340
So the end result is after two degrees in college and 30 years of building /designing speakers and endless computer program design and development projects, endless study into acoustics and the physics behind the actions is:

I have a flat panel of plywood holding two drivers with some electronics sitting in my living room with near 50 year old amplification.

Makes me think.

ron
 
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