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Recommended Ratio Of Piston Volume To Room Volume

Dennis Foley September 26, 2014 No Comments
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I had a question sent in this past week with relation to the speaker size versus room size video I made (see below). It read “Please elaborate on the recommended ratio of piston (ribbon panel) volume to room volume.”
Okay so we have the word piston and we have the word ribbon in one sentence. So piston volume is a dynamic driver. Speakers and drivers are interchangeable so that’s a common driver that we see. Dynamic is another word for it. Ribbon is a whole different concept. It’s a moving screen, a moving diaphragm so to speak. It’s made of lightweight material, not paper, plastic like a dynamic driver.

So I think I understand what the questions means. It really doesn’t matter what type it is, it’s all about surface area and output. But let’s just stay with subwoofers because that’s I think the easiest thing for people to understand.

Let’s take a 10-inch subwoofer, let’s take a 12-inch subwoofer, 2 inches larger on the surface area for the 12-inch versus the 10-inch. What does that 2 inches of additional diameter and surface area mean in our room? It means plus 2 to 3 dB more energy because it’s bigger and larger. So what does that 2 or 3 dB of increased energy give us in our room? The question to that depends on how well your room is treated, how well your room is able to handle the low frequency energy because now you have 2 dB more energy.

Is your room smaller than before?

Smaller rooms really can’t handle more energy and here’s where the problem arises, we try to put too much pressure generating surface area, diameter of the speaker into our room that’s a certain volume with certain dimension and the speaker and the room are not going to fit together. They’re not going to work together because the speaker is going to produce more energy than the room can handle unless it’s treated correctly which we never see and I look at hundreds of rooms a month and I never see one that has the low-frequency issues addressed.

But I always see people wanting to add more speakers. Well you have to be very careful about this. I know it’s cool getting gear. I like gear just like everybody else but you have to stop. When you’re taking that gear and you’re putting it in your room, especially if it’s a speaker because now you are in the room with the speaker and those two, that marriage has to be a good marriage. If one is larger than the other or one is smaller than the other, then you’re going to have all kinds of issues.

Certain diameter low-frequency drivers sound the best with rooms of certain volumes

So in our experience of building and testing rooms, what we found was that certain diameter low-frequency drivers sound the best with rooms of certain volumes and we’re going to have a graphic of that pretty soon for an upcoming seminar we’re doing for Danny Wyatt and Dubspot. But we found that certain diameter low-frequency drivers need a certain amount of volume and it makes sense if you think about it. They need a certain amount of volume in order for their energy to just kind of expand itself and fit into the room. So the 6, 8, 10 and 12-inch drivers we’re going to have a graphic pretty soon that shows the room volumes that you need to have to get them to sound good.

So you have to match the size of the speaker to the volume of the room, you really have to match the size of the speaker to the dimensions of the room. So if you satisfy the dimensional requirements for room modal pressure issues then the volume will just fall into place because if you choose the length, width and the height that our database tells you will minimize low pressure issues, then volume is the logical next step. That’s defined by simply multiplying those three numbers together.

So you could put a subwoofer in a closet but getting that subwoofer in the closet is a whole other issue. When you confine and restrict the breathing space if you will, of a speaker it’s going to produce energy that’s not going to be happy in that room size. So I have people all the time say things like “Well can I put a 12-inch subwoofer here? Can I put a 10-inch subwoofer here?” you can put them anywhere. Getting them to sound good is a whole other issue and that requires a lot of thinking and a lot of analysis on your room size and volume and stuff like that.

Subs in Home Theaters

Here’s a good way to look at it. One of the ideas in home theaters, is that you use multiple subwoofers because you distribute the pressure in the room more equally and it’s all about pressure and that’s correct. And subwoofer manufacturers that recommend multiple subwoofers for home theaters, they have my attention because they’re really not trying to sell more product, well maybe they are but they’re mainly concerned with the physics inside the room. They want to make sure their product matches the physics of the room. They know that the room is going to be probably too small for their product. They just know that because ninety percent of the rooms we look at are too small.

So I’ve got to believe that their experience is very similar to ours. So that said putting multiple subwoofers in your room and pressurizing the room equally in the areas that the subwoofers are at is really important. But there again you have to match the number, the diameter and where you put them in the room. They don’t all go to the floor some of them may have to be installed in the ceiling.

I built a home theater one time for myself. I had the subwoofers coming out of the ceiling on chains attached to winches, those winches you put on your jeeps and your vehicles when you go 4-wheeling to get you out of a stuck area that’s what we used. We lowered them, different heights in our test facility and we found that pressure equalization in our room is good but how high the device is within the chosen ceiling to floor dimension is also critical. So more devices equalize pressure but the placement within the room is critical. So you have to match that to the room size. You will get the most out of it. It’s not quantity when it comes to low-end, it’s quality and quality is best defined and measured and heard by less energy.

In Summary

If you would like your room acoustic issues analysed for free by me then please fill in the form here and I will be happy to take a look for you.

Thanks
Dennis

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Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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