[Telstar]

I've read that lowish inductance is favorable for an OB woofer.  Is 1.495mH considered low?

Thanks again folks!

Average. But Fs is high. With that money I think that you can get a better woofer for OB. The B200 go pretty low, dont they?

Check GR research OB woofer, and AE speakers.

[JLM]

I'd start by trying the B200 nude and see if you're satisfied.  If the B200s behaves anything like the Hawthorne Silver Iris drivers, you can use any size baffle you want.  The only question is how high off the floor you want the drivers to be.  With the various Silver Iris drivers I've heard, the baffles aren't much bigger than the driver.

If you own your place, I'd consider infinite baffles for the woofers (subwoofers).  A friend used two 15 inch woofers face to face in his attic (in Michigan) with a slot cut into the ceiling.  Frankly the amount of deep bass boost (compared to even the 10 inch Silver Iris driver) was rather minimal, except when playing "bass effects" music/home theater material.  The Cult of the Infinitely Baffled can help with a complete website. 

Another simplier option is trying a small, inexpensive, sealed sub (or two).  For music in "normal" sized rooms, this would probably be all you need.  You might be able to borrow such a little beast to play with.

[brianpowers27]

If you would like to estimate the response of the woofer in question download the excel spreadsheet from http://www.t-linespeakers.org/downloads.html called xbaffle.  THis will allow you to quickly simulate the effect of on open baffle woofers. 

[EProvenzano]

Thanks for all the suggestions thus far gents!
I have tried the B200 "nude", and I'm finding it very light in the bass.  I'll want to augment them without a doubt.

Any comments on the appropriateness of this driver:
http://swanspeaker.com/product/htm/view.asp?id=326

These are available from a Canadian based company so I should be able to get my hands on them relatively cheap.

Thanks.

[Rudolf]

I simulated a configuration that would allow the B200 to work above 200 Hz. Your baffle should be 40 cm wide and 120 cm tall with the B200 mounted at 90 cm. If 80 cm for the B200 would be ok, you could shorten the baffle to 110 cm.
 


In the left diagram the upper black line is the on-axis response, the lower black line is the power response. The hump in the power response is due to the wide baffle, but you can't make the baffle smaller without sacrificing either the 200 Hz limit or the efficiency of the B200.

The dotted lines are without the 40 µF and 3 Ohm in the filter (diagram top right). You can adjust the high frequency response by changing the 3 Ohm resistor only, but with values below 3 Ohm the impedance will get below 4 Ohm.

The bottom right diagram shows the off-axis response. Not optimal, but that's the price for insisting on a wide range driver, affording a wide baffle.

In this configuration the B 200 will give you 110 dB at 1 m and Xmax from 200 Hz up. But you will need to add a 200 Hz high pass filter of at least 12 dB/oct to keep lower frequencies away from the B200.

[Rudolf]

Any comments on the appropriateness of this driver:
http://swanspeaker.com/product/htm/view.asp?id=326

H frame 40 cm wide and 40 cm deep (front to back). With a 2. order LR lowpass at 80 Hz you will have a natural H baffle roll off at about 250 Hz.

[JohnR]

Excellent information, thanks, helps me a lot to see how the B200 could get used.

[EProvenzano]

I simulated a configuration that would allow the B200 to work above 200 Hz. Your baffle should be 40 cm wide and 120 cm tall with the B200 mounted at 90 cm. If 80 cm for the B200 would be ok, you could shorten the baffle to 110 cm.

Rudolf, thanks for all this great information.  I'm learning more than I expected here.  I appreciate you taking the time to show me these options.

My baffles have already been cut, including the driver holes for the B200.
They are 115cm tall x 41cm wide, with the driver center at 90cm.  Being that the total height is 5cm shorter than you suggested, will this be a problem?

How would one achieve a 200hz high pass on your suggested circuit?  Although I will likely use a pair of plate amps to drive my woofer system I would rather not utilize the on board high-pass filters for the B200's.

Thanks again!

[Rudolf]

My baffles have already been cut, including the driver holes for the B200.
They are 115cm tall x 41cm wide, with the driver center at 90cm.  Being that the total height is 5cm shorter than you suggested, will this be a problem?

Almost no difference. The following simulation accounts for your present baffle dimensions.

How would one achieve a 200hz high pass on your suggested circuit?  Although I will likely use a pair of plate amps to drive my woofer system I would rather not utilize the on board high-pass filters for the B200's.

I have added a 200 Hz second order high-pass to the filter. Dotted lines are for 150 µF instead of 220 µF. This in case you need -6 dB at 200 Hz instead of -3 dB.



Note the 3 Ohm in line with the 4.7 mH coil. This is including the resistance of the coil. So you don't need to buy an expensive low resistance coil. 3 Ohm are critical to keep the impedance above 4 Ohm.

The above simulation should be pretty exact up to around 1.5 kHz. Above that region the cone of the B200 is in break-up-mode, no longer radiating like a stiff piston. This can not be simulated. You need to adjust the response in that range to taste by the second 3 Ohm resistor - as explained before.

Rudolf

[jeenie67]

...density, inertness, machinability, and directivity! Whew! As the summer proceeds, so does my research into OB design criteria and the numerous related replies on this forum. Although I will be constructing my OB's from a specially formulated concrete mix (the multiple ingredients and their measures calculated during correspondence with an engineer at a commercial concrete firm), to be poured into forms in my work room, and finished with Clear Cast epoxy resin, I would look into the possibilities of utilizing aluminum stock for the baffle. A little online inquiry and search of local fabrication shops may produce a cost effective result. I worked at a precision fabrication shop years ago (it's still in existance) and the scrap drop-offs I observed there could easily of made some interesting cabinetry. Machining the speaker cutouts would be the only expenditure. Also I would look into using Baltic Birch, 17 ply, plywood laminate as it can be had for a few dollars over the cost of MDF (a 4'x5'x1.250" piece in Buffalo, New York costs $45). A search of demolition lots (almost new buildings being torn down to erect another one in it's place) might produce some possible material canidates.      As stated in the first sentence: research the design factors that will produce the most productive baffle for your design application. Have a great weekend!  Jeenie.

[zipidachimp]

pardon for butting in: canuck dealer for eminence woofers etc:  http://www.loudspeakers.ca/    waterloo, ontario.

[jeenie67]

...as I start the next semester at a private college with a $16K academic achievment scholorship award, I've started thinking about the posibilities of fabricating a mounting for the drivers consisting of a composite carbon fiber/polyesterine material. I'm required to take upper level physics and chemistry courses for my BA, so why not do my research papers on the possibilities of melding these two materials. For both subjects they do have an open research program where you prepare an outline of your intended research or project and submit it to the professor for approval. I'm looking for the qualities concrete has with the extra rigidity and lightness of carbon fiber. The key here is to make it cost effective. I do have some resources to contact in the carbon fiber bicycle parts business. It's worth some thought....what do you members think? College should be fun...learning should be fun. I think building di-poles for credit would be fun also.  Have a great week everyone...and thanks!  Jeenie.
PS: just adding some thinking material for everyone!