I see some closed back 2x12 speaker cabs with a horizontal "sound bar" running internally from the speaker baffle to the back of the cab. I assume the purpose is to transfer vibration to the back of the cab. While some major vendors do not have the "sound bar or bass bar". When I put my arm against the back of a cab without the bar, I hear a slight increase in volume and low end frequencies. Much like when you touch your guitar headstock against a table or wall, when it's vibrating. So, I imagine the sound bar is a good thing. However, maybe it's only purpose is to support or strengthen the cab. Also, wondering if it's anything like the sound post in a violin, which travels from the top to the back of the body. The positioning of this post is a large factor in the violin's tone. Can someone with experience shed some light on this horizontal bar's purpose and mystery? Is it structural or tone related?