Open baffle bass behaviour

[Klimon]

Hello!

Are there any general (and corroborated!) rules that show the way to acceptable bass-behaviour from an open baffle? I just played a little with a 30-20cm oval console driver (light paper cone - alnico magnets - high Qts - accordion surround - very low Xmax) in a 1,2 * 1 meter cabinet.

First with the driver mounted very close to the ground: there was a large peak in the bass that messed things up (like the effect of the bass-boost on my girlfriend's Sony)

... then I turned the baffle 90° so that the driver was half-way up in height and to the extreme left (or right for that matter): bass peak was gone but now the bass got very slow.

The aim would be reasonably flat bass-output untill around 100-150hz, where a pair of subwoofers could fill-in. Not simply 'bigger is better is more low-end' when that low-end isn't worth much.

Thanks (and more questions to come about this subject)

Simon

[buble_corp]

-> Klimon

Maybe you can find something interesting on audiocircle forum
http://www.audiocircle.com/circles/index.php?board=90.0

[Geoff H]

Hi Simon, this has been covered in other posts. Basically, keep the driver away from the floor to preserve mids. Wings can be added to increase the width of the baffle, and also provide support, and a shelf above the driver to extend the minimum front to back distance.

Regards,
Geoff.

[Klimon]

Buble_corp: thanks for that link!! Took a quick look and it's a whole vault of OB info I wasn't aware of - more reading to do in the coming days...

Geoff: Thanks for the quick reply - I've been reading alot about OB and the placement (floor/ ear-level) seems to be disputed; e.g. the JE-labs or almost any design with helper woofer puts the low (or only) driver close to the floor. When simulating using 'the edge' the benefit of close-floor mounting is evident (apart from the lower f3 there is less floor-bounce). I'll have to experiment some more to find the best solution using only one driver. Going from near-floor to ear level with these really didn't make a difference regarding midrange, only bass changed (from peaky to slow )

A few other questions that are even more relevant as I'm planning to build the final versions of two OB line arrays and wouldn't want the same dubious results after all that work; basically my question is if the bass will get slow or 'peaky' (in the audible range) when adding more baffle, the fact that these are line arrays (much more Sd) might change things:

-- First line array uses eight 4" woofers pro side; seventies paper cone, high Qts, low xmax (accordian surrounds)... I've been playing these with smallest possible baffle (just one narrow line to hold the drivers) and the bass-quality is good. In the final version I was planning to add baffle to get more extension, in the form of wings (110-140 degrees vs. front baffle) + bottom + lid (like a box with sloped sides and without a back), basically to extend the bass. Will there be great danger to mess up the bass by doing this, e.g. making it slow / getting annoying peaks?

-- Second line array uses six 8" midwoofers, high Qts, foam surrounds and higher xmax; Same 'cabinet' plan as for the previous array; different variables here are the even higher overall Sd and Xmax; same question: in how far is such a line array prone to reduced bass quality when adding baffle?

Thanks --- Sorry for the long post // no easy questions I'm sure but any advice is welcome!!

Simon

[Geoff H]

Simon, are you adventurous? Given the drivers you have, I would place the 4 of the 8" in to a bass dipole (H shaped, with top and base) and the 8 4" on a line array baffle, optimised for about 130 Hz.

Aim for a crossover of 150 Hz. If that combo works, a line array of ribbons above 1/2 the frq limit of the 4" array.

I haven't heard a base dipole yet, but they seem interesting. I can't find the links, I thought I saved them.

BTW, I have dropped my xo down to 100 Hz. It's not going back. Better on sax, tuba, acoustic guitar, (esp 12 string) violin, voice, applause, and percussion. And it's not bi-amped yet.

Regards,
Geoff.

Afterthought: 3 or 4 bass dipoles with 2 8" in each, in a line array across the floor.

[Klimon]

Geoff, all ways end up in Rome (or how does one translate that??) -

My first plan was to do something similar (following a tip from johnincr: manifold with the woofers mounted push-pull) but there are several minussen:

-- efficiency of the 8" woofer ensemble would be lower than the 4" line array (unless I biamp which isn't for the very near future)

-- the woofers are very useable in the midrange, with a relatively smooth roll-off

Now I gather with some extra baffle I'll be able to reach 100hz with both arrays and a pair of subs will suffice.

I like the ribbon line array idea but that's a long shot from my budget - the mentioned woofers cost me 2$ apiece Too much plans at the same time have left me with no money (and a lot of parts )

When thinking things over I don't expect much deterioration in bass-quality with the winged line arrays, whole different story than single-driver - atleast in my head.

Cheers,

Simon

[roddyama]

Hi Simon,

Take a look at this thread , in particular the open baffle speakers by Peter Daniels. I have since heard these speakers and there is no shortage of clean solid bass.

[Klimon]

thanks Rodd - the reason why that one goes so deep is probably the high Sd(2 15inchers/ speaker) --- My line arrays will be also benefitting from that; curious what they'll do with the little wings.

Simon

[Geoff H]

Hi Simon,

Did you see this thread? U-Baffle

It has links to the sites I was referring to.

Geoff

[Dumbass]

Get yourself well-acquainted with this web page:
http://linkwitzlab.com/models.htm

And regarding the frequency-dependence of boundary reinforcement, check out this draft of a whitepaper I started last year. It's not perfect, but it shows why boundary reinforcement is different for different frequencies:
http://www.stat.ucla.edu/~erickson/tmp/boundary.pdf