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?

[mdocod]

I am a rank amateur so consider the following with added sodium:

Skimming through this: Baffle Step Compensation and focusing on the part about a sphere shaped enclosure is very revealing and should help answer the question.

Based on that information, the baffle step loss transitions such that when the wavelength is smaller than the diameter of the sphere, the baffle gain (transition to 2pi space) is fully realized.

Since that works on a sphere, I have to assume that you can treat the full cabinet width as your baffle width regardless of edge treatments.

I could be very wrong

Eric

[5th element]

What mdocod said

[nickf]

In my simplistic understanding "Half space/full space" radiation transition is a different effect from diffraction, it creates a steady rise from -6 to 0db (or 0 to +6 db depending on the measurement reference). The frequency of the rise is related to the baffle width - so yes, adding wider round-overs will change the frequency at which this rise occurs as some of the round over will count towards the width - perhaps a good estimate is to use half way around the round-over?

Diffraction supplies the wiggles on the frequency response graph. Again I can't tell you how large a radius you need to get rid of it - perhaps someone else can comment. What I can say is the larger the better - the 300mm sphere in the linked page above seemed to be free from these wiggles so this is obviously large enough

Nick

[Starre]

I have read that you need at least 3/4 of an inch (about 2cm radius) to have a good effect.

[planet10]

Originally Posted by nickf

In my simplistic understanding "Half space/full space" radiation transition is a different effect from diffraction, it creates a steady rise from -6 to 0db (or 0 to +6 db depending on the measurement reference). The frequency of the rise is related to the baffle width - so yes, adding wider round-overs will change the frequency at which this rise occurs as some of the round over will count towards the width - perhaps a good estimate is to use half way around the round-over?

Unless the enclosure is a sphere (or a teardrop), the BS rolloff is not smooth, it will have ripple.

The BS happens at "low frequency". With a baffle of the size the OP is suggesting the waveforms will not even see a 1/2" roundover, so the baffle width remains 25cm.

Even if the round over was 12.5 cm radius, the baffle would still be 25cm -- the transition would be much smoother thou.

dave

[Inductor]

Originally Posted by planet10

Unless the enclosure is a sphere (or a teardrop), the BS rolloff is not smooth, it will have ripple.

The BS happens at "low frequency". With a baffle of the size the OP is suggesting the waveforms will not even see a 1/2" roundover, so the baffle width remains 25cm.

Even if the round over was 12.5 cm radius, the baffle would still be 25cm -- the transition would be much smoother thou.

dave

Yes, at higher frequencies.
He (sploo) will probably end up with "invisible" speakers...

[Shaun]

And now... a tool (or two) to simulate all of the above:

Home of the Edge
Baffle Diffraction Simulator

[sploo]

Thanks all for the responses. 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.

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.

> He (sploo) will probably end up with "invisible" speakers...

Cool idea . Stealth. Would make them very "wife friendly"

Shaun - I've seen those baffle tools before, but not tried them. Can they simulate the effects of adding (extreme) rounding to the edges of baffles?

[Inductor]

Originally Posted by sploo

"He (sploo) will probably end up with "invisible" speakers... "

Cool idea . Stealth. Would make them very "wife friendly"

Meaning invisible to your ears not to your wife. The baffle straight edges and "big size" make them more prone to location in space. Nothing is said if the sound is better or not, and this can be very questionable (by other members, that I will not).