Diagonally cut vs rectangular baffle?

Moskvich

Member
2019-12-01 7:46 pm
Hi guys, slowly getting into this stuff and now wanting to start my first build using a 5,25" driver and a 1" dome tweeter into a tower.

Now I´ve been reading a bit on diffraction and baffle step and in my mind a diagonally cut baffle should help compared to a rectangular one. But it seems no companies are doing it.

So would it or would it not make sense to do the extra work of making the top of the tower more pointy?
 

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Moskvich

Member
2019-12-01 7:46 pm
But isn´t that true for really big (infinite) baffles? In my mind, if you cant have an infinitely large baffle, a small baffle as possible is the next best, as the diffraction issues that will occur will only do so in the highest ranges where the least musical information is?
 
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AllenB

Moderator
Paid Member
2008-10-18 11:31 am
But isn´t that true for really big (infinite) baffles?
This is not the point. The point is that the sound in this case starts, and wants to continue to travel along a baffle.

Once it gets to a certain width, other things change as well.
as the diffraction issues that will occur will only do so in the highest ranges where the least musical information is?
Ok, now you are getting to the issues. You've decided to change the baffle near the driver. Doing so will cause diffraction, but making it gentle helps.
 
Moskwich, this is a fundamental thing with loudspeaker construction and well documented, expalained and tested, also innumerable simulation programs are available!
At least 50 different threads about this can be found at diyaudio.com

Please do some homework with these key words
loudspeaker, diffraction, baffle dimensions, baffle shape

Baffle Diffraction
https://site.diy-loudspeakers.com/baffle-diffraction-step
Speaker baffle design, diffraction and baffle step | Audio Judgement
Diffraction from baffle edges
etc.
 

Moskvich

Member
2019-12-01 7:46 pm
Thanks, I know there is a lot to read about the topic, and I have read some, but I just thought this thread would in a short sense make it clear to me why manufacturers mostly do the rectangular style baffle, even in pretty pricey categories, even so the litterature seem to point to making as small a baffle as possible.

Basically it´s hard for a beginner to just read the litterature without having someone to clarify when you get lost.
 
Well, designing a loudspeaker for mass production is business - you must make profit.

The big names of hifi loudspeakers like KEF, B&W, JBL etc., they know what they are doing, but still production costs are very important. Making angles other than 90deg or roundovers easily multiplies production cost of the box. Other important aspect for business is the look of teh speaker, brands must be identified easily. Some brands make series of different looking speakers.

Considering these business aspects, the measurable or audible effect of trapezoid or rounded baffle is still minimal. There are several other more important issues which can be done well or wrong.

With diy hobby, some designers who publish plans have mantras regarding baffle shape etc., some other try different shapes and concepts every time. You can for example check the variety of projects by these

Zaph|Audio
DIY-Loudspeakers
Speaker Design Works
DIY Loudspeakers Kimmo Saunisto
DIY Lautsprecher | Bausatze, Lautsprecher Entwicklungen
http://www.humblehomemadehifi.com/speakers.html
http://www.htguide.com/forum/forumdisplay.php?39-Missions-Accomplished
 
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I'd recommend having a play with "The Edge" Home of the Edge

With a rectangular baffle, placing the driver in an optimal location from the three closest edges can give very flat response as the diffraction from each edge cancels out the diffraction of the other edges. Roughly, the correct placement follows the golden ratio (1.618:1) so the driver will be a certain distance from one edge, x1.618 that distance to a second edge and x1.618^2 to the third. The tweeter placement in Zaph's ZDT3.5 roughly follows this (close to the top, further from right side, even further from left side)
http://www.zaphaudio.com/ZDT3.5-system2.jpg

Placing the driver equidistant from all edges produces the worst diffraction, so the 'pointy' baffle may well be worse than the rectangular one, at least with your current tweeter placement, as the diffraction from the top edge and two slanted edges will be similar and therefore add up instead of partially cancelling each other out.
 
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TMM stated the case rather well. I made a graphic to illustrate this concept (see attached pdf file). Imagine a small driver mounted in various baffles. The sound wave radiates from the driver along the baffle. I illustrate 4 different frequencies (wavelengths) and super-impose these on various baffle shapes.

Starting with a driver centrally mounted in a square baffle (near worst case), the transition from 2-pi to 4-pi radiation happens over a very short frequency range. Even worse is a driver centrally mounted in a circular baffle... here the transition happens at abruptly at a single frequency.

Moving to a rectangular baffle, things improve quite a bit, and now the transition from 2-pi to 4-pi takes place more gradually. Even better is a rectangular baffle with the driver offset horizontally. The final graphic is a trapezoid baffle, and clearly this results in a very smooth transition, but is it really better than the rectangle with a horizontal offset? Maybe not. It is possible to select an optimal rectangular baffle with an optimal driver placement which will result in a very smooth transition, one that is hard to improve upon even with a trapezoid shape.

Considering the extra complexity and cost of making a trapezoid cabinet, it may not be worth the effort.

Of course, if you are in the business of selling $20,000 - $100,000+ speaker systems (like Avalon), any possible improvement is worth the effort. Your customer base expects you to "spare no expense" in the pursuit of the finest possible sound reproduction. Even if the a design feature is very expensive, if it has even the slightest possibility of improving the sound, your customer expects you to incorporate that design feature.
 

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Moskvich

Member
2019-12-01 7:46 pm
Thanks all for contributions!

... The final graphic is a trapezoid baffle, and clearly this results in a very smooth transition, but is it really better than the rectangle with a horizontal offset?...

Since baffle reflections is another effect, wouldn´t the offset driver in a rectangular baffle "trap" lower frequencies on the baffle compared to the trapezoidal?

That is, if the transitions are smooth in both cases, shouldn´t the next objective be to lessen the baffle reflections as much as possible?
 

Moskvich

Member
2019-12-01 7:46 pm
What is wrong with sound being 'trapped' on the baffle? Can you describe it so I'm sure what you're talking about.

Well correct me if I´m wrong, sound that is trapped on the baffle will increase the output in those frequencies in a forward direction, and lessen them in the off-axis response. Like when a driver starts to beam. It might be possible to suffocate that increase with the crossover, but the off-axis response will still suffer?

A horisontally offset driver should also give different off-axis response depending on which side of the cabinet you´re at? Possibly that woud introduce other problems?
 

Moskvich

Member
2019-12-01 7:46 pm
A small source on a large baffle produces hemispherical radiation which will be evenly balanced at frontal off-axis angles.

Do you want 360 degree radiation, 180, 90? Thoughts on why?

Reading a lot of comments and articles, I get the impression that a wide radiation provides better imaging for the listener, don´t know if that is the case or why that would be.

Surely it should provide a better experience while moving around in a room, even if that is not the primary objective?