The Studio Design Trick You Can't Ignore: Focus on Width, Not Height
Aug 26, 2024When designing a home studio, many people focus on the height of the room, thinking that higher ceilings will automatically lead to better acoustics. However, recent research highlights that the length-to-width ratio (l/w) is actually more critical for achieving balanced sound, especially in small rectangular rooms.
1) The Science Behind Room Dimensions
The key to good acoustics lies in how sound waves interact within a space. In small rooms, low-frequency sound waves (20-200 Hz) tend to build up, causing "room modes" or resonances. These resonances can create uneven sound distribution, leading to bass-heavy or bass-light areas. The challenge is to design the room so that these resonances are spread out as evenly as possible, avoiding "hot spots" where certain frequencies dominate.
The best way to understand room modes is to imagine your are building a fort as a kid. Each low frequency room mode is a cushion holding up your blanket as a roof. Now a great fort would have plenty of cushions to support your blanket without it drooping. A great fort would have a taught blanket with evenly spaced cushions. Now a bad fort would have big spaces between cushions causing the blanket to droop and sag.
This analogy is how acousticians look at a room's sound quality when analyzing modes. The more evenly spaced the room modes are in the lower frequencies the smoother the low end will sound. And by smooth I mean accurate: without big boomy areas and empty "no-bass" areas in your room.
Now what's cool about this new research is that it says you can get a good solid fort by focusing more so on the l/w ratio versus all three working together perfectly. The research indicates that the l/w ratio should ideally fall between 1.15 and 1.45. This range helps to evenly distribute room modes, leading to more balanced acoustics. In contrast, the height of the room is less critical, although it should not be ignored entirely. The height plays a role, but its impact is secondary to the l/w ratio.
Below is a diagram representing a bad "fort" and a good "fort"
2) A Brief History of Room Mode Research
To fully understand how the article came up with this new l/w ratio let's briefly look at the history of the acousticians who have developed this research:
- Sabine (1900): Criticized simplistic ratios like (1:1:2) as ineffective.
- Volkman (1942): Proposed ratios like (1:1.26:1.59) for small rooms.
- Bolt (1946): Found (3:4:5) to be optimal based on frequency mode distribution.
- Louden (1971): Suggested (1:1.4:1.9) as the best ratio for minimizing frequency spacing issues.
- Walker (1993): Proposed specific ratios for studio rooms, like (1:1.19:1.40).
- Cox & D’Antonio (2001), Meissner (2018): Used numerical methods to optimize room dimensions for flat frequency responses, highlighting ratios like (1:1.20:1.45).
What's important for our look into this article is the work of Meissner who came up with three new ratios labeled A,B and C.
A (1:1.20:1.45)
B (1:1.40:1.89)
C (1:1.48:2.12)
3) Understanding the Frequency Spacing Index (FSI) in Home Studio Design
In the article we are studying they mention the Frequency Spacing Index. Now you might be wondering, what the heck is the FSI and what does it have to do with home studio design? The FSI measures the variance in spacing between low-frequency room modes, aiming for evenly distributed modes to ensure smooth sound. Remember, from our fort example above the more evenly spaced our modes the better the blanket is held up. Ideally, the FSI should be as low as possible, with an FSI of 1.3 considered nearly perfect for aspect ratios around (1:1.20:1.45). The researchers found that by looking at the FSI for different room ratios they noticed that the l/w ratio (length-to-width) is far more influential on room acoustics than the w/h ratio (width-to-height), emphasizing the importance of focusing on the longer dimensions in your studio design.
In practical terms, this means that while room height does affect acoustics, achieving an optimal l/w ratio will have a more significant impact on your studio's sound quality. Let's look at an example of this in action. Below are two rooms. One room has a height of 8' and a width of 15', while the other room has a height of 10' and a width of 15'. By using the rule the researchers came up with, if we make our length 1.5 times the width we should still get a good sounding room regardless of our ceiling height.
Based on the above example we can see that the two room modes are distributed similarly even with a two foot height increase. The only big difference I see is that around 55hz you get an axial mode that will help "prop up" our fort analogy thus smoothing out that big gap in the 8 foot ceiling height. However, when ceiling heights cannot be easily changed this research is welcomed for us home studio designers.
4) Practical Implications for Home Studios
For home studio designers, this means that when you're planning your space, you should prioritize getting the length-to-width ratio right. For example, if you're working with a room that's 10 feet wide, aiming for a length between 11.5 and 14.5 feet would be ideal. This ensures that the room modes are evenly distributed, reducing the need for extensive acoustic treatment.
If you already have a space where the l/w ratio isn't ideal, don't worry. There are still ways to manage room modes, such as using bass traps, diffusers, and other acoustic treatments. However, starting with the right dimensions will save you time and effort in the long run.
Conclusion
In summary, while ceiling height is important, the length-to-width ratio of your room should be your primary focus when designing a home studio. By getting this ratio right, you can create a space that naturally sounds better, making it easier to achieve professional-quality recordings. I will say there is a limit to how low your ceiling can go before you run into issues with the reflections off the ceiling coloring the sound of instruments. This can be especially true for drum overhead mics. Nonetheless, we do the best we can in home recording studios and this tool is another one to use when designing your studio.
For those interested in diving deeper into the science, you can read more about the research here.
Works Cited:
Preferred dimension ratios of small rectangular rooms. (2024). JASA Express Letters, 1(2), 021601.
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