[chakija]

Hi all !
After T-Bass tryout, i decided to build new baffle for my alnico oval...
Problem is i don't have any parameter's, only that they are 4Ohm 5W rated.
Can u plz suggest what baffle shape and dimension could i use for starting point ??

[scorpion]

I think for the oval shape baffles should be at least 4 x 4 meters, otherwise I would recommend IBs ?

/Erling

[scorpion]

However, I suppose you will not go back the the Fantastic SP130 X/8s. So if not doing bass from these units 40-45 cm baffle width will be very accurate to produce output down to 200 Hz. Beware of the new subtle design for OB coming next about here.

/Erling

[Rudolf]

chakija,

best baffle width will VERY much depend on the Qts of the driver. For old SABA ovals with their typical 1,7-2,5 values and Fs of 70-100 Hz 40 cm would be well enough and should not be exceeded. No baffle size will be able to push those significantly below their Fs.

For drivers with Qts<=1 you can go as wide as you want. Don´t you really have any information about make and age of your alnicos?

Rudolf

[scorpion]

I say,

new MJAO is coming. Do nothing til you hear of this.

/Erling

[chakija]

Hi guys again !
Thanks for your replies !
I will postpone this project for now...I actually find that although Graham's circuit gives very good bass it still negatively effect rest of the FR specter. It may sound nice after all ,but i have no clue what to do to adjust that. Instead, i returned T-bass on alpha 15" but i putted additional 80uF in parallel on it's terminals. I don't have idea what is it's real effect on alpha's response ,but with my T-bass and that little inductor in line, it attenuate mid's very good. Now, overall sounds is great even though i removed one side of U frame  . I found that actually without it bass is better ?!?
I apologize for my ignorance and spamming with new subject without previous reconsidering of alternative solutions. It is just that bloody alnico FR that sounds so great... (or i have maybe became a little deaf  )

[scorpion]

New Bassie

[Viridian]

I say,

new MJAO is coming. Do nothing til you hear of this.

/Erling

Since OB is such a paradigm shift to begin with and lately old assumptions of mine have been destroyed.......

I'll wait and see what you are up to Erling. It better be good or you're gonna get some stick for raising our expectations!

Erik

[Graham Maynard]

It is my experience that any side wings should be the same to both front and back in order that driver transduction does does not become differential pressure modified.

Better than wings are side rolls of carpet.

Cheers ......... Graham.

[chakija]

Will try definitely...but i think that I baffle is maybe best sounding 
Thanks again mr Maynard !

[Viridian]

It is my experience that any side wings should be the same to both front and back in order that driver transduction does does not become differential pressure modified.

Better than wings are side rolls of carpet.

Cheers ......... Graham.

So, this JE Labs type baffle which I and many others have tried isn't necessarily ideal. Last night I removed the side wings on my 24" baffles and lo and behold, better midrange and treble. And it may just be my impression but I think I gain a little in efficiency as well. I'll have to scrounge up some carpet to try your suggestion with carpet wings Graham. The "magic carpet" tweak.

Thanks,
Erik

[panomaniac]

Better than wings are side rolls of carpet.

Works well on horns, too. 

[Graham Maynard]

PS.  I mean with the rolls end on to the baffle, like the circles of a figure eight with minimal baffle separation between them = O--O

Carpet does not cause resonance; the front-to-back pressure loss path at LF is extended; the symmetry of cone transduction is maintained.

As the roll diameter approaches the baffle width I found it possible to bring the rolls closer together behind the driver more like =  O_O, though I ensured that rear exit area was not less than forward cone area.

Cheers ........ Graham.

[panomaniac]

Got it.   Thought that's what you meant.

BTW, do you leave an empty space in there like the O - or do you make it a solid roll?
Reason I ask is that I've done the same thing with beach towels, but a solid roll.  Carpet may be somewhat transparent at lower frequencies if  not thick enough.

[Graham Maynard]

Hi Pano,

I used ordinary deep and close pile carpet with tufts outwards in a roll never less than two layers thick.
The carpet backing was strong enough the mantain cylindrical shape.  Maybe foam rubber rolled within the carpet could do the same thing.
The baffle board was pressed into to the pile at its longitudinal point of contact.

I know that LF waves could pass through such a lightweight structure, but where the rolls are used the propagating waves have not yet been formed and there is such resistance to airflow through the carpet roll, that the baffle effectively becomes extended. 
Also pressure induced defamation at say the rear does not automatically become equally radiated by the front half roll; and vice-versa.

Cheers ........ Graham.

[JeffB]

Who/What is MJAO?