This was originally written and posted on a open baffle forum on Facebook. But once you post something on Facebook it is gone by the end of the week and impossible to find. I have had a couple of people ask me again about this information so I figured it best to re-post it here in the GR Research circle so that it can be easily found and referenced.
I was seeing big wide baffles pictures posted all the time. So I put together some information and measured data to show the effect of the baffle and side wing designs. I know this is long, but it might be very helpful for many people.
I want to start by saying that what you hear from your speakers isn't just what comes from the drivers themselves. What you hear is drivers plus the surface reflections from the baffle, front wall behind the speakers, side wall reflections, ceiling reflections, etc.
The baffle is the first reflection point and is the transition from two dimensional to three dimensional sound. As the baffle size increases so does the perception of the sound coming directly from the speaker. A huge baffle has the effect of the speaker playing through a megaphone then opening the megaphone out flat. The presentation is from the surface forward. Once the baffle gets as big as some that I have seen, then the drivers might as well be mounted in a wall. Transparency, sound stage layering, and the three dimensional sound field that separates open baffle designs from a boxed speaker design really goes away when the baffle size is large.
And don't get me started on a big flat wall behind the speakers with zero diffusion or absorption. The room is part of the system!
I understand that a larger baffle size is used to further separate the front wave from the back wave, and it can be used to tune and shape the response and the low end roll off. But there is a better way to do it than a big flat baffle. And it is even worse if the driver or drivers are mounted right in the middle of it. Offset the driver or drivers to one side and then fold the baffle back to create side wings.
Careful testing and measuring will show the advantages of having the right shape. You must also be careful not to box in a driver playing up high enough in frequency that the wavelengths that it is playing are short enough to propagate within the boxed in space or it will set up cavity resonance. For instance, an H frame or U frame design is great for a low bass driver and can really help load the driver and tune it to play much lower. But you can't do the same thing with a mid-range driver. As the driver plays up higher the wings really need to get asymmetrical and the short wing has to be pretty short or it will cause a cavity resonance and really mess up the response.
When I design an open baffle speaker I don't just model a baffle design. Baffle size and shapes are too critical for modeling. I build and measure the response of each baffle and side wing combination. Some times I use card board side wings to get it close. I then replicate it in a foam sheet that is 1/2" to 3/4" thick. After that I build it with MDF.
I am going to post links to two examples of how the baffle and side wings effect the response. Look closely at the measurements and the comments regarding the side wing sizes. Note how the side wings can be used to flatten out the response.
Always start with a baffle no bigger than the size of the driver. The size of the frontal area is critical. Bigger is not better. Bigger can get real bad, real quick.
This first example is for a design that we did for Hawthorne Acoustics using an 8" driver.
http://www.audiocircle.com/index.php?topic=154485.msg1651847#msg1651847This one was the latest baffle design for our Wedgie kit. It was named for the wedge shape. Note the measured responses.
http://www.audiocircle.com/index.php?topic=155092.0It all started here with the original development:
http://www.audiocircle.com/index.php?topic=126112.msg1330260#msg1330260 Take note of the small frontal area and asymmetrical shape.
The front baffle is only 4.5" wide. It is one of the most transparent speakers that I have heard. They can really reproduce a three dimensional sound field that is mind blowing. And a lot of it has to do with having little to no baffle.
I will conclude with an interesting story that illustrates this point. Years ago I was assisting one of my clients as they exhibited at the Axpona show in Atlanta, GA. The speakers were a tall thin tower as seen in the attached picture.
One of the reasons that I was there was to properly set up the room. It is an area that I specialize in. I basically take all the tools necessary to make the room as transparent as possible. And it is one of the reasons our rooms have stood out in ever show and usually win numerous show awards and favorite room mentions. We wall off the entire front wall with a heavy fleece curtain material and also bring it down the side walls. The rear wall or rear corners get curtained off as well. Behind the curtains are usually 12" thick foam wedges to soak up any bass boominess out of the room. A large diffuser is placed between the speakers as well as areas near the corners of the room. Shorter diffusers are used to the outside of each speaker and about even with the back baffle of the speaker to a few feet back. Diffusers are also added at the first reflection points and in the back of the room.
And we usually use our servo controlled subs to handle the lower octave or so. That gives us complete control over the bottom end. In some exhibits we use open baffle servo subs up front and sealed servo subs in the rear corners of the room to balance out room loading. I guess you can say that it is part art and part science.
Okay, now that you know the set up on with the story.
We had a reviewer in the room for quite some time. He was really liking what he was hearing, but had one issue. He was listening to a grand piano piece and said that while it sounded fantastic he thought that the system made the grand piano a bit small. The imaging of the piano was deep into the sound stage but too pin point. He felt that the piano should sound bigger, or fill a wider area in the sound stage. So I asked him if he'd like for me to make it bigger. He looked at me a bit puzzled and wondered how I would make it sound bigger. So I played it again and while it was playing I went to the diffusers that were on either side of the speakers and a bit behind them and I toed each diffuser outward about 10 degrees. As I moved the second one out a bit he kind of freaked out. The sound of the piano increased in size to just the way he wanted it. He then felt like it was perfect, and just like the sound of a real grand piano in the room. He could not believe a slight adjustment to the room treatment could do that.
Of coarse course when you have set a room up as many times as I have and made incremental adjustments to all the room treatments then you know exactly what the adjustments of each diffuser panel will do and what effect it will have.
If I take that same panel and move it up so that it is even with the front baffle then some of the depth goes away. And if I turn the diffuser around backwards then there is a flat surface facing forward instead of the broken up surface. And If I set that side facing forward and right next to each speaker then the sound stage becomes two dimensional and draws attention right to the speaker itself. It effectively makes a big baffle.
So I tend to cringe a bit when I see big flat baffles. Come on guys. It can be much, much better.
