[AUDFILE74]

hi guys, i have been looking around the internet and found some photos of the dunlavy sc-6 speakers. i saw the way the drivers were recessed to line up the voicecoils for, what i think is,  a mechanical alignment of driver output. now i 've looked at a lot of the phots of how the baffles for OB have been done. i noticed that most of the baffles were flat all drivers , except horns , on the same level surface. my question is, would the dunlavy approach help or hurt a true  OB setup?


btw Turbofc3s, ygm

[JoshK]

Time alignment of the acoustic centers is always a good thing regardless of OB or box speakers.   It can be done physically with driver offset or electrically with phase and/or delay networks.  It is just simpler to build flat baffles, so the alignment is then left to the electrical side, but one could do it physically coming up with some slick baffle.

[AUDFILE74]

thank you josh, but i still want to know if it helps or hurts an OB setup. for the front wave output it makes total sense. but with OB you have the back wave to factor in. how does this affect the sound of the backwave sonically?

[Davey]

Assuming you have some sort of dipole tweeter and you electronically delay its input to "line up" with the rest of the drivers for an on-axis measurement, you would create a situation where you made the "time alignment" of the rear radiation worse.  However, the rear radiation is subject to myriad reflections (and heard exclusively from) over many angles so the subject becomes moot.  I don't believe it's as simple as "helping or hurting" an OB setup.  By the very nature of an open-baffle design you've already made a decision that "time alignment" is not that high on the priority list.  Whether it should be is another subject. 

The Dunlavy's were designed with first-order acoustic crossovers and, of course, were not dipoles so this forced the physical alignment of the acoustic centers of the drivers.  This to achieve their "linear phase" operation claim.  IMHO they weren't anyway, but that's another subject.

Hope that helps.

Dave.

[AUDFILE74]

Thank youfor sucha thorough answer davey. now for my next query:

i understand the a wide baffle helps the sound for OB. i noticed that most of the OBsetups i've seen pics of do nothing to accoustically treat th front of the baffle out side of sufficient thickness. is there any benefit to acoustically treating the front face with say felt, neoprene, absorbant foam, etc. the reason i ask is the frontwave  is interacting with the baffle (especially in the case of the smaller drivers . for examplea 6.5 inch mid on a 17 inch wide baffle) so ,assuming that,i'd think it could be detrimental to the sound. am i right or wrong?

[Rudolf]

Generally speaking, any "obstruction" in acoustics must be larger than at least a quarter wavelength to have any audible effect at that wavelength (and higher). So for all hearable frequencies any common baffle material is perfectly smooth. Of course drivers (tweeters mostly) should be mounted recessed when applicable.

What you really should be concerned about is the baffle edge, where sound propagation drops from 2 pi (the frontal hemisphere) to 4 pi (full space). Making this transition as smooth as possible does infinitely more for reproduction fidelity than any treatment of the baffle surface. The bad news: You need edge radii > 2 cm to really improve things.

So think of baffles like knifes: Any smooth surface will do. It´s the edge that really counts. 

[AUDFILE74]

so a 2-3inch thick, 17 inch wide bafflewith roundovered edges will be good?  thanks for the insight rudolf. fellas, i have heard it said that OBis  DIFFERENT ANIMAL AND DIDNOT COMPREHEND TE TRUTH UNTIL NOW this is going to take me some time but it's creping past my logic