[dewar]

I'm looking to make some new baffles, smaller for aesthetic reasons and also to get rid of a 50hz hump from the B200's in my room. I've got stereo dipole subs and will shortly be getting a DEQ so bass from the B200's not an issue really. But I dont want to loose any midrange clarity or focus.

There are a few questions I have that I'm hoping for some opinions on before I cut, even if there is not consensus on the matter. They've probably all been touched on before but looking now at every thread in this OB circle I cant find any treads where these issues are collated, and the discussions on dimension almost always seem to factor in frequency response. So, to wit:

Wings or not, if they're not needed for bass?
Is narrower centre panel always better for imaging?
Countersink driver or not?
Driver heights effect on imaging?
Effect of front/back absorbing material on imaging?
Rounded edges effects on imaging?

Anyone care to take a stab at an ideal baffle for those of us with bass augmenters and DEQ.

Many thanks

Bevan

[mcgsxr]

Dewar, I too am interested in the outcome of this thread, as I am in the middle of structuring my next baffles also.

It is my belief, based on the experience of others, that wings are critical for use with midrange etc, so no to those for me - at least, not the significant wings I use today - perhaps 2-3 inch, just for added effective width of baffle.

Width seems to be the enemy of imaging, in broad strokes - but with the need to have some width to achieve a reasonable Xover for bass, it will be a compromise like everything else.  What frequency are you thinking of Xover for the b200 to helper woofer?

I will countersink, but I don't think it is critical for mids, or at all - strictly visual.

Height and where you aim it will effect imaging.  I prefer higher off the ground - roughly 24-30 inches for the center of the b200. 

I highly recommend the Planet10 phase plugs - really helps the treble, and allows for less toe in, which for me translated into better soundstaging.

Those who have played with cork, felt etc on the baffles are outspoken about the benefits.

I recommend rounding the edges, but am not sold on all the work done for truly minimizing the edge diffraction - I think that 3/4 roundover likely takes you at least 50-60% of the way towards the 3 inch roundovers etc I am seeing on some experimental work out there - never heard it though, so I could be way off.

I like the look of this project for my next attempt at b200 and at least 1 12.  I hope to use Baltic Birch for the baffle, flush mount the b200, magnet mount the 12's, and have the bass wings separate from the main baffle - thus, minimizing the vibrations I experience with the 12 directly mounted to the b200 main baffle.

http://home.comcast.net/~audio-worx/page70ArvoPartProject.html

Does that help, or am I thread poaching for my own good!?!

[scorpion]

Frankly, I do not think that you can do much better than to copy my (See: http://www.audiocircle.com/index.php?topic=40594.0 ) and Oldtimer/Mr Content/Nigel's design in some way. My B200s have not sounded any better. I'll go for the Phase Plugs later when I feel for a change, the sweet spot is narrow.

/Erling

[mcgsxr]

A great design, and incorporates things I absolutely will - the angled top (which has been a mainstay in my own design for 2+ years), the separation of bass and b200 etc.

Is the 18 inch width required for the 150Hz Xover?  Could a 15 inch with slight wings work for that frequency?

[scorpion]

Mark,

Sincerely I do not know. My sources were my own simulations, Oldtimers and others appreciation of his speakers and also a discussion in German Hobby HiFi over the B200 and baffle size, MJK's OB project and the desire to keep the same dimensions all out. Here is a very good study of different baffles, shape and size: http://www.troelsgravesen.dk/OBS.htm .

/Erling

[dewar]

Great help, thanks. Seems we in the same boat. Though you not going the DEQ route are you?

Was thinking to cross over at maybe 80 and use DEQ to flatten from 80-200 or wherever roll off starts. Also thinking of boosting my subs(they have their own parametric eq, the DSP1124) buy maybe 15db and then running auto eq on the DEQ thereby actively relieving my B200's of a lot of heavy work.

Was thinking of keeping my 10" centre panel and then scaling down the wings significantly to 2-3 inches like you were thinking of doing. But with the flexibility of EQ I'm wondering if I shouldnt use an 8" centre panel? Thats my main unanswered question at this point, and whether wings will benefit anything other than bass output.

(thinking now, centre panel will have to be wider than 8" as I want to cut the edge away at 45 degrees to round them off a bit.

Scorpion, I cant figure it out, is your Behringer only doing Xover, and your Eq passive? Your B200 is above ear height it looks like? I take it you dont think there's any need for wings on the top baffle? thanks.

I'm running full felted baffles at the moment but am not sold on the aethetic so will experiment. Luckily its an easy experiment, just hang towels over and see. I'm surprised cork has any effect on higher frequencies but I dont doubt peoples ears. Looks good but I need to find some thats less than the $30/m I've found so far.

I just got the phase plugs and am very happy. Am now toeing out more.

Came upon a post somewhere today from JohninCR and another chap agreeing that small wings better on the inside and larger ones on the outside. Keen to test that out.

Will post my finding but it wont be just yet as I'm waiting for some ribon tweeters to arrive and want to listen to them in a familiar setup, before I make and baffle changes.

cheers,

Bevan

[scorpion]

dewar,
I use my dcx2496 for crossover and eq, see my answer to Polarbear (Björn) how this is done in the 'venetian blind' thread:
http://www.audiocircle.com/index.php?topic=40594.0 . It is just marginally above ear height for me. I am currently
in the process of deciding if felt in the back of the speaker or no felt is the proper thing to have listening to them. I have a feeling I will keep
the felt, not anything very easy to pinpoint.

/Erling

[JohninCR]

On the topic of imaging, my best imaging baffles remain the little OBs I have for my FE108's.  I have no doubt that baffle shape affects the sound, especially in the interaction of the front and rear waves in the frequencies above the baffle cutoff.  A shape like Nigel and Scorpion use which smooths the HF dipole ripples is definitely a good thing, and there a plenty of ways to skin that cat by creating different pathlengths for the rear wave all around the baffle.  With different size and tapered wings you can even create a speaker with a uniform look while still addressing pathlength around the baffle.

I believe more important to imaging is that you don't want your baffle to be a source of sound.  This can come in different forms.  OB baffles don't have the same support structure as a box, so if you rigidly attach your main driver to the baffle, energy will be transferred from the driver frame into the baffle.   The contruction material you use will determine how much of this energy travels to the edges to escape as sound.  I use a lot of real wood, so the vibrations at the edges are quite prominent compared to other materials, and Nigel, Scorpion, myself, and others can all agree how important it is to decouple the driver from the baffle, especially a flat baffle.

Another way the baffle can be a sound source is from diffraction of sound at the edges.  It's commonly accepted that you don't have to worry about edge diffraction with flat baffle OBs because the front and rear wave components are directly out of phase and cancel.  JohnK tells us that the ideal baffle would be infinitely thin to ensure they are directly out of phase when they meet.  I'm not convinced.  I took a flat baffle and tapered the edges to a point.  With a decouple driver there was still significant vibration in the baffle, especially at the edges.  With that setup the only source of energy that could create these vibrations is the pressure change at the edge.  I'm still up in the air as to how to best address this issue, but I think the end result won't be a flat baffle.  Instead, the front side will include large radius roundovers, and direct the sonic results of edge diffraction rearward.

Large baffles help minimize diffraction effects because the pressures are much lower, however, the problems with big baffles are just aesthetic or space related.  JohnK has some specific reasons to limit the baffle size for the main driver.  Plus I find that when you block the rear wave reflections by putting a large panel in the way, it is detrimental to imaging.

[FlorianO]

Mark,

Sincerely I do not know. My sources were my own simulations, Oldtimers and others appreciation of his speakers and also a discussion in German Hobby HiFi over the B200 and baffle size, MJK's OB project and the desire to keep the same dimensions all out. Here is a very good study of different baffles, shape and size: http://www.troelsgravesen.dk/OBS.htm .

/Erling

Erling,

Not sure if you have the possibility (your U baffle looks fixed) but -- since he's asking for imaging and midrange clarity -- I guess on-axis and 90 degrees measurements flat vs. winged will be quite telling..

With appologies (and thanks) to John K  aa

Florian