Baffle step/roundover question

[sploo]

Hoping there's a baffles expert around!

I understand that having a large radius on the edges of a baffle reduces diffraction effects. I also understand that the "half space/full space" radiation transition frequencies are related to the distance of a driver from baffle edges (simplification: call it the width of the baffle).

Imagine I have a speaker with a 10" (25cm) wide front baffle, with the vertical edges of the baffle rounded over with a 1/2" (1.27cm) radius. Is the baffle considered to be 25cm wide (with 1.27cm roundovers) or is it considered to be 25 - 2 X 1.27 = ~22.5cm wide?

I ask because I'm wondering about (for various reasons) taking the above speaker, and giving it a much wider roundover - effectively 3.8cm, such that the total baffle width would now be around 30cm wide, but the flat width across the baffle would be the same as before: 30 - 2 x 3.8 = ~22.5cm.

Would this have a significant effect on the response of the system, such that any baffle step correction in the crossover would need to be changed to account for the new baffle width. And if so, for what width?

On the same subject, at what angle should we consider something to be baffle, and when to consider it the sides? A perfect 10cm cube obviously has a 10cm wide baffle, as the sides are at 90 degrees to the front. But what if the sides were at 45 degrees to the baffle? Or 30 degrees with a large roundover? How do you account for this?

 

[lsiberian]

The positive diffraction effects are not considered very significant until you get into a larger radius. I don't think you will gain much with this modification.

 

[Swerd]

Hoping there's a baffles expert around!

I understand that having a large radius on the edges of a baffle reduces diffraction effects. I also understand that the "half space/full space" radiation transition frequencies are related to the distance of a driver from baffle edges (simplification: call it the width of the baffle).

Imagine I have a speaker with a 10" (25cm) wide front baffle, with the vertical edges of the baffle rounded over with a 1/2" (1.27cm) radius. Is the baffle considered to be 25cm wide (with 1.27cm roundovers) or is it considered to be 25 - 2 X 1.27 = ~22.5cm wide?

I ask because I'm wondering about (for various reasons) taking the above speaker, and giving it a much wider roundover - effectively 3.8cm, such that the total baffle width would now be around 30cm wide, but the flat width across the baffle would be the same as before: 30 - 2 x 3.8 = ~22.5cm.

Would this have a significant effect on the response of the system, such that any baffle step correction in the crossover would need to be changed to account for the new baffle width. And if so, for what width?

I'd like to say that you're over thinking this, but I could only say that if I actually knew the answers.

I would treat it as two separate variables, overall baffle width, and edge round over. Your baffle is still 10" wide whether or not the edges are rounded over. The wavelengths affected by the baffle step caused by a 10" wide baffle are too long to be affected by any rounded over edges. The frequencies that actually are affected are likely to be much higher.

I know of one example where a speaker, in two 8" wide cabinets, was measured. One cabinet had squared edges and the other had ¾" radius rounded edges. The frequencies affected were around 4-7 kHz. See this link. He didn't say it, but I would assume that the baffle step compensation in the crossover was the same for both squared and rounded edge cabinets.

¾" is about 2 cm. For 3.8 cm radius rounded edges, I would expect somewhat longer wavelengths to be affected, but still much shorter than those affected by the baffle step response for a 10" wide (25 cm) cabinet.

On the same subject, at what angle should we consider something to be baffle, and when to consider it the sides? A perfect 10cm cube obviously has a 10cm wide baffle, as the sides are at 90 degrees to the front. But what if the sides were at 45 degrees to the baffle? Or 30 degrees with a large roundover? How do you account for this?

 

[GranteedEV]

On the same subject, at what angle should we consider something to be baffle, and when to consider it the sides? A perfect 10cm cube obviously has a 10cm wide baffle, as the sides are at 90 degrees to the front. But what if the sides were at 45 degrees to the baffle? Or 30 degrees with a large roundover? How do you account for this?

Simply put - you don't worry about theoretical baffle step compensation.

You measure the response in the baffle, probably with some respect to intended placement in room to see if there is any boundary gain, and then equalize the baffle step flat based on what the measurements tell you.

Measure the drivers in the baffle and don't forget acoustic offsets and you will be fine!!

 

[sploo]

Thanks all for the responses. I kinda suspected that the baffle width was the baffle width (basically ignoring the round over).

My motives behind the mod are mostly to experiment with a cabinet with curved walls, but didn't want to mess with the existing crossover, so I was wondering what I could get away with. The mid-bass driver is fairly close to the width of the baffle, so I couldn't flare out the sides (to create curved side panels) without widening the width slightly.

I've spoken with the original designer, and gist is that extending the baffle width due to having slightly larger round overs wouldn't have a negative affect on the sound, given the existing baffle step compensation.

I do however have some basic measuring equipment, so could rig up a couple of curved edges to temporarily attach to the baffle and get some readings with/without before venturing into some cabinet building.

 

[j_garcia]

My uneducated guess is that since we don't see a lot of speakers with large radii, that there's no benefit, or it is small enough as to not be a factor.

 

[sploo]

My uneducated guess is that since we don't see a lot of speakers with large radii, that there's no benefit, or it is small enough as to not be a factor.

That's a fair point. As I understand it, the smoother the rounding (larger radii), the smoother the step in amplitude across the baffle step.

Because creating passive filters (in crossovers) is easier when the filter slope is shallow, it's easier to compensate for such baffle steps. How bad the problem is for normal box speakers I don't know - I'm not aware of any papers comparing the effect.

There should also be fewer diffraction effects from the baffle edges, but again I don't know of any research looking into audible effects.

There is of course the fact that building speakers with large baffle radii is more complex and expensive, so perhaps not attractive commercially.

My plan is to build new cabinets that are a teardrop shape (seen from the top). So, in theory they'd have less diffraction effects, and due to the rear of the box curving towards a single vertical line, potentially less re-radiation of the mid-bass rear wave (from bouncing off the back of the box). Oh, and the fact I want to try to build some curved speakers because they'd look nice!

 

[j_garcia]

Well, curved sides make sense to me, and the tear drop shape perhaps even moreso, but heavily radiused edges would seem to be maybe a bit less aesthetically pleasing. This could be another factor, where despite the fact that there may be a benefit, the looks don't make the grade. Large radii shouldn't be more complex than a curved cabinet, but with large manufacturers, we certainly aren't seeing it styling wise. I'd say baffle width likely is a bigger factor than the corners, and I'd expect curved cabinets would be as well. I thought curved cabinets were also intended to minimize internal standing waves, plus it generally looks cool

My speakers have a fairly typical radius IMO

I had been thinking about this as well, since I've considered building the A/V-3 floor standing version of these guys and had pondered how much the radius affected the sound in the event I wanted to increase it when building new cabinets. A more generous radius might make the veneer easier to apply too (I did not build the cabinets shown).

That tear drop shape has sort of been done, more extensively than I think you are talking about though, by Norh. I call them "ham hocks" lol.

 

[sploo]

Well, curved sides make sense to me, and the tear drop shape perhaps even moreso, but heavily radiused edges would seem to be maybe a bit less aesthetically pleasing. ... I'd say baffle width likely is a bigger factor than the corners, and I'd expect curved cabinets would be as well. I thought curved cabinets were also intended to minimize internal standing waves, plus it generally looks cool

My speakers have a fairly typical radius IMO

...

That tear drop shape has sort of been done...

Love your speakers above. Very nice. Yes, a reasonable radius on those. The second image, well, I'd describe that more of a 'torpedo'. I've knocked up similar prototypes (balls etc.) but the size required for the speakers I'm wanting to mod would be too big for my room. Off topic: having just search for some examples, I've found something almost exactly like what I'd done (even the same driver): http://i754.photobucket.com/albums/xx183/robandjulz/Audio Stuff/08112009956.jpg, http://i754.photobucket.com/albums/xx183/robandjulz/Audio Stuff/08112009947.jpg.

By teardrop (in this instance) I'm meaning something looking like your speakers, but where the radius on the baffle edges extends out to a longer, wider, curve, then the side panels curve back in to a single vertical line at the rear centre of the speaker.

A bit like this (http://www.hometheater.com/images/archivesart/910polk.2.jpg) but from the top looking more like this (http://www.icollector.com/images/238/17468/17468_0452_1_lg.jpg).

Yes, there's obviously the internal standing waves benefit (again I don't know how audible), as well as hopefully reduced reflections from the internal face of the rear panel (because going down to a point will cause more bouncing around before the reflected rear wave radiates through the mid-bass diaphragm.

I suspect that major benefits from a very large radius external shape would only come with an associated crossover design (i.e. taking advantage of the smoother full space to half space baffle step).

In any event, this project is more due to a necessity to change the shape of a pair of speakers (re-laying out a room), and wanting to experiment with something a bit different to a square box, while not adversely affecting the existing sound quality.

 

[j_garcia]

I know what you are talking about for tear drop profile, and I do think it is a good idea. There are a few on the market with a profile similar to that as well, though more like the Polks that do not extend out to a point at the back. Those round ones you did are pretty interesting too. There are also the cabinets from PE:

I like the idea of unusual shaped cabinets in an effort to improve the sound since I appreciate both the aesthetic aspect as well as the sound