[NiToNi]

Hi all,

I am new to open baffle speaker designs but thought I'd try it out with a pair of Supravox 215 Signature Bicone drivers that I have come across.

Initially, I would like to try running them full-range on a simple baffle, probably made out of MDF.

I may augment the frequency extremes with a seperate subwoofer and/or super tweeter at some point down the road but not for now.

I will most likely try to drive the drivers with a PrimaLuna Prologue II, mostly because I have a spare one which I am not using at the moment.

What I am looking for, from some of the more professional and experienced members of this board, is some helpful advice on the design of the baffle. Hopefully, there is an optimal baffle plan for this particular driver so I could get it right in the first place 

I have looked at some of the software solutions but although I may look more into these later, the learning curve seems too high (edge diffraction compensation, baffle step etc) just for trying out this modest driver on a piece of board.

My listening height is slightly higher than on the typical couch/chair since I will be sitting on an office chair (studio). I would say ear height 110-120 cm.

Any advice would be most welcome!

[nullspace]

I'd recommend Thorsten's baffles.

Regards,
John

[NiToNi]

nullspace,

Thanks for the suggestion. However, I cannot find the exact measurements for this particular baffle. And to quote from the thread you linked to:

Sjef: Can you tell me something more aboute the measurements of the baffle and the measurements of the speaker placement.

Loesch: No, as these are prototypes for a commercial design I am not at liberty to disclose the CRITICAL items.

And Thorsten is off the DIY public arena now after he's gone commercial so no help to be had from the horse's mouth.

And is his design also what would be considered the "optimum" from a theoretical viewpoint?

[Jacq.]

Perhaps you could get inspired by plans published by supravox. 

http://www.supravox.fr/kits/panneauplan.pdf

Jacq.

[nullspace]

I took Thorsten's comments and innuendo to mean that the baffle is 24" wide by 42" high. The driver is offset, ~15" from one side edge and and ~25" from the bottom edge.

Thorsten's pretty knowledgable about audio in general, and those drivers on that baffle in particular, so I take it as a given that it's a well-done project. Whether or not it's the optimum design for that driver, who can say...

Regards,
John

[NiToNi]

Jacq,

Thanks, I've been looking at Supravox's own plans but since they are designed with a bass driver, I'm not confident that the plan translates very well for a single driver only.

[NiToNi]

nullspace,

Excellent - thank you very much!

Since the driver offset is approximate, how sensitive is this? Do I need to chase down the actual accurate numbers?

And would you know at what height the drivers is on the baffle?

[Rudolf]

And would you know at what height the drivers is on the baffle?

Thorstens own input into his Xlbaffle.xls would suggest a height of 65 cm above floor - same as the baffle width.

[NiToNi]

Rudolf,

Thank you. I tracked down the spreadsheet and found the measurements of his baffle in there, except for the exact offset of the driver from the left and right edges (and the angle of the backwards tilt of the baffle)

Also, 65 cm driver height is a bit on the low side for me. Ideally, I would have the driver at 100-120 cm, the same as my ear height (provided the design/driver is meant to be listened to on-axis...).  And I'm assuming that just raising the speaker (e.g. by placing it on a stand etc) won't do the trick.

So I played around a little with the spreadsheet, increasing driver and baffle height, but since I am a total novice I don't really understand how to interpret/assess or discriminate what's important between the various graphs. If anything, I just seem to make it worse. I figured so much that the height was 1.618 times the width (golden mean) but even keeping that ratio constant doesn't make it any better.

So any help on modifying this design to accommodate a higher driver placement would be very useful. 

[nullspace]

The thing is, all else being equal, the farther you move the driver from the floor the more the bass will droop. You stated in your opening post that for now no subwoofer, so you'll want the driver to be as low as possible on the baffle.

If it were me, I'd build it as Thorsten laid it out: baffle 65cm wide by 105cm high, with the driver 65cm high and ~40cm from one side. Then, you have a typical listening height of 110-120cm and a typical listening distance of XXcm, and it becomes a trig problem to calculate what the angle should be. It's really not a problem to have the driver below ear height and tilt the baffle up. I've used baffles well lower than that (JELabs) without issues; that's another baffle to try, btw.

Regards,
John

[nullspace]

Okay, I messed around with MJK's worksheet and came up with this: 178cm high x 110cm wide, driver offset 110cm from bottom and 68cm from one edge. Looks pretty good to me. Ignore >1000hz; theile/small #s aren't much good for simulating freq. response by that point. Here's the result:
.

Regards,
John

[NiToNi]

Brilliant John! Thank you very much for this.

I hear you on the bass drop as I move further up on the baffle. What I meant in my opening post however was no bass driver on the same baffle. I will probably try to carefully integrate two free-standing subwoofers (location, traps, digital EQ). Does that make you more comfortable in recommending your own suggestion over Thorsten's plan?

At what frequency would you recommend I low-pass the sub and how steep? Should I leave the Supravox running full-range or high-pass it? 

Baffle width of 110 cm will be quite imposing in the room unless I build it in Lexan. If I were to fold the baffle wings backwards (say 1/3rd plus 45 degrees, 1/3rd zero degrees and 1/3rd minus 45 degrees), can I do that as long as the total length is still 110 cm?

What is the physics/rationale for making the baffle as high as 178 cm when the driver is so much lower (curious)?

BR Nick

[nullspace]

Hi Nick,

Sorry for the delay, but I wanted to think about this over the weekend...

If you're going to be using subs, I wouldn't think that you would need/ want the monstrosity I proposed in the previous post -- more an exercise than a serious suggestion, in any case.

I also took a look at Supravox's posted freq response graphs (here), for what that's worth, and came up with something a bit more feasible:

The baffle is 24" wide by 44" high. The driver is 10" from the side and 38" from the bottom. The bump in freq. response form the baffle around 350-700hz should help mitigate some the driver's response dip in that region to some degree. However, I do wonder if 100-200hz will sound a bit lean, depending on the ability of your subs to integrate.

I can't really say where you'll want to low-pass the subs; you'll need to figure that out firsthand. As a first-guess, I'd start around 75hz or so and start to work your way up.

Whether or not you should high-pass the Supravox, or any widerange driver for that matter, is the subject of great religious debate. You should try it both ways and decide for yourself.

If you haven't read it already, I would recommend perusing Martin King's website; there's a wealth of information there on open baffles -- MJK's Quarter-Wave. With open baffles, everything is a trade-off...

Regards,
John

[NiToNi]

Hi John,

I really appreciate that you have taken the time to come up with this suggestion for a suitable baffle. I guess I need to cough up for the MJK spreadsheet and learn MathCad in the long run but for now that is a bit above my head and this will get me going.

I am happy also that the dimensions have shrunk a bit . The only thing is that I am worried that the driver height is again a bit on the short side. I had hoped to listen as close to on-axis as possible without having to tilt the baffle (easier foot construction). And that bump - it won't sound honky, will it....?

[nullspace]

Hi Nick,

Martin's work has been very helpful to me as I've worked on open baffles. Worth every penny of the $50 I've sent him over the years.

How close will you be sitting to the baffles? You said ear height is 110cm and the drivers are at 96.5cm. If you're sitting 10' feet away, that works out to be about 3deg off-axis, which isn't much.

And, the bump helps compensate for a small dip as seen in Supravox's freq response graph for that driver. The baffle is the size it is and the driver is located where it is specifically so that that bump in response is where it is.

Regards,
John