Open Baffle Questions???

[mikejennens]

I'm thinking of trying an open baffle project, but I have no idea what makes a speaker a good candidate for an OB. I have a few speakers I could try:
W5-704
W4-1337SD
Fostex FE-127
I have a few others laying around, but will one of these three work? What should I look for as a start for the right speaker? I'm not opposed to adding a tweeter and I plan on using a sub if I go ahead with this.
All suggestions are welcomed!
Thanks,
Mike

[Ryan_M]

The 704's were used OB in a version of the Aethers, and the 1337's were used open back in the Statements. So there's those two at least.

[diy speaker guy]

Any of the drivers you listed will work just fine as OB mids but won't be able to reach low enough to meet with a sub due to the baffle step losses unless the baffle is massive. You will need a helper woofer. MJK has an excellent OB paper at his quarter-wave.com website that shows how this works.

I highly recommend that you read that and start modelling. You can use MJK's software for modelling if you like but it's not free. For free software you can try XLBaffle for really quick and easy models or try Bagby's software for much more accurate results but it's not as quick.

Or you can request someone else to model for you, I don't mind doing it sometimes but I highly suggest reading MJK's OB paper first so you can understand the design compromises first if you plan to use passive crossovers.

[mikejennens]

Thanks for the info so far. I downloaded MJK's paper, so now I'll try to wrap my mind around it. I also downloaded XLBaffle. We'll see where these take me.
Thanks again,
Mike

[arlis_1957@yahoo.com]

i was doing some reading on the linkwitz site and most of it went right over my head but, i thought i read that a woofer in an open back does not create pressure to induce room gain so it does not need baffle step. did i read it wrong? did i also read somewhere that a high qts is good for ob?
i too am thinking about this for the future.

[diy speaker guy]

Thanks for the info so far. I downloaded MJK's paper, so now I'll try to wrap my mind around it. I also downloaded XLBaffle. We'll see where these take me.
Thanks again,
Mike
_________

Great! Read the flat baffle paper with the Alpha15 first and then the H frame paper with the Goldwood. XLBaffle is not perfect but it's great for getting used to the concepts.

[diy speaker guy]

i was doing some reading on the linkwitz site and most of it went right over my head but, i thought i read that a woofer in an open back does not create pressure to induce room gain so it does not need baffle step. did i read it wrong? did i also read somewhere that a high qts is good for ob?
i too am thinking about this for the future.

No room gain is correct. But there will be massive baffle step losses with any OB. I also recommend MJK's paper to you. Much easier to absorb and understand than Linkwitz.

[diy speaker guy]

There's also a couple of pages from my website that may help a bit. These are really quick and easy reads, 5 minutes or less each with lots of pics, very non technical and easy to understand.

http://sites.google.com/site/amateur...eory/ob-design
That one is about easy OB design without using a computer or any math at all. Basically just subtract the baffle losses from the driver's IB response and expect some diffraction starting about an octave or so above the step frequency. You can guess pretty accurately what is going to happen with any given driver on any given baffle (within reason) using just your head.

http://sites.google.com/site/amateur...he-smallest-ob
This one is a project my buddy did with a 4 inch driver on an 8 inch wide baffle that plays down to 150 hz. It is possible and this shows what is required - basically a very large qts and an fs near your desired LF cutoff. It works but power handling is very low.

My whole website needs a massive rewrite but you might learn something from these pages anyway.

[arlis_1957@yahoo.com]

please investigate the new point source 8" driver for ob. its a very sexy looking driver.

[diy speaker guy]

I've never looked up the specs but unless it has extremely high qts it can't be used full range on OB. It will work great as a mid and up though.

[arlis_1957@yahoo.com]

yes, as a mid up to 2k.
i have seen designs with an ob mid a tweeter and a woofer in an inclosure. it this the accepted norm?

[greywarden]

You should download both BoxyCad and Response Modeler. Play with baffle sizes and driver positions to reduce the baffle step, then plug your numbers into BoxyCad so you can see whatabouts it will look like.

[diy speaker guy]

yes, as a mid up to 2k.
i have seen designs with an ob mid a tweeter and a woofer in an inclosure. it this the accepted norm?

I'm not sure there is an accepted norm. There are many systems like you describe but there are many more that do not used boxed bass. There's probably even examples of OB bass with closed mids if you look around. There is no "correct" combination, just different flavors.

Basically any driver will work as an OB mid, even a 2 inch "fullrange" driver with 1 mil xmax as long as you don't need it to go lower than about 6 - 800 hz and don't need it louder than around 104 db. Below the baffle step frequency is where things start to differ greatly from other alignments. (There are diffraction differences above the step too but the major issue here is overcoming the massive step losses.)

[diy speaker guy]

You should download both BoxyCad and Response Modeler. Play with baffle sizes and driver positions to reduce the baffle step, then plug your numbers into BoxyCad so you can see whatabouts it will look like.

I second the recommendation to use Response Modeller but not BoxyCad (not even sure what that is). If you do use Response Modeller, I'd use Jeff's other tools as well, the Diffraction Simulator and PCD to do the model. The PCD suite is the best OB modeller I am currently aware of since it accounts for more factors than any others.

Nothing is easier than XLBaffle for quick and dirty modelling though.

[arlis_1957@yahoo.com]

how does one model an ob in pcd? or by suite you mean rm?

[Ryan_M]

In RM3, when calculating the diffraction there is a box to select OB. That's what I did. Arlis, FWIW, here's the design I'm working on which is like the box you mention. Still tweaking the XO..... & trying different stuff.

[diy speaker guy]

By PCD suite I am referring to all Bagby's spreadsheets.

Ryan is right, you can do it all in Response Modeller, but I don't because Response Modeller alone can't simulate the boundary effects. I use the Diffraction Simulator spreadsheet to get the baffle and boundary response, then load that into Response Modeller and sum it with the driver .frd. From there, it's on to PCD as usual. Easy as pie and extremely accurate but it takes WAY longer than a quick XLBaffle model.

[Ryan_M]

... Response Modeller alone can't simulate the boundary effects. I use the Diffraction Simulator spreadsheet to get the baffle and boundary response, then load that into Response Modeller and sum it with the driver .frd

I didn't know about that... I'll have to look into that.

[Starkiller4299]

Tolvan's The EDGE program is pretty darn simple for modelling baffle step effects. Fun to play with, at least .

[dlr]

I'm thinking of trying an open baffle project, but I have no idea what makes a speaker a good candidate for an OB. I have a few speakers I could try:
W5-704
W4-1337SD
Fostex FE-127
I have a few others laying around, but will one of these three work? What should I look for as a start for the right speaker? I'm not opposed to adding a tweeter and I plan on using a sub if I go ahead with this.
All suggestions are welcomed!
Thanks,
Mike

See this post by John K., he's now making his excellent Excel spreadsheet available free of charge.

dlr