How did you calculate the spread column? Did you factor in the estimated compression modulus of the material (different materials have a different compression modulus which is the ratio between 65% ILD divided by 25% ILD) which can also affect how much a material compresses under load.
Different materials will also affect how the load spreads relative to depth (a cylinder in the case of a spring and more conical in the case of different foams).
How did you calculate the surface area and weight distribution for each part of the body (shoulder, torso, hips) to calculate the stress on the material under each part of the body?
Is there any simple way to calculate the continuously changing surface contact area that comes in contact with the mattress as you sink in deeper or to account for different body shapes, weight distributions, or with different sleeping positions (moving the arm for example from under the body to an arm forward position will change the surface area in contact with the mattress and affect the load)?
I’m assuming the numbers are designed to reflect side sleeping?
This is interesting (and complex) stuff … and thanks for sharing the results of your work
Pheonix, How did you calculate the spread column?
The load is assumed to spread x% per inch of compressed material (x=12%, guessed). If the layer is compressed 50% from 3" to 1.5", then the load would decease by 1.5x when applied to the next layer. This is not quite conical but close enough for me. This helps model the fact that bottom layers affect the feel less. As you can see though, the bottom layers are still important.
How did you calculate the surface area and weight distribution for each part of the body ?
I guessed at these values. I do not think these add much to the comparsion. I did not model the shape of the body either. It is interesting that the guessed load values closely produce the deflections that I personnelly experience.
I’m assuming the numbers are designed to reflect side sleeping?
Yes, I was trying to calculate the deflection at the shoulders, torso and hips of a person in the side position. I think this part of the spread sheet is over-simplified and not useful. I would like to add body shape and weight distribution, but I am running out of motivation.
I can certainly understand this and there are many cases where my own more technical research can lead to more avenues to be explored than it leads to answers and the process can seem to be never ending
As you know … for some people (such as the authors of the books I linked before) this whole area of investigation is the subject of a lifetime of research that involves some very complex math and some specialized testing equipment and it can be daunting for a layman (such as myself) to try and understand all the variables and even more difficult to “translate” it into meaningful results that can be easily used to predict the experience of individual people on different mattress designs and materials.
Having said that … I think that the fact that your numbers are such a good reflection of your actual experience and the fact that you had already considered much of what I mentioned and factored it in says a lot about your methodology and knowledge.
If there was one additional set of numbers that I think would be particularly relevant and interesting it would be adding a 4th section for how the lower back that includes the inward curve of the lumbar compares to the shoulders, torso, and hips since this is a fairly critical area that can be important … particularly for some body types that either carry more weight there, have a more athletic build, or that have a wider differential between their hips and waist or their shoulders and waist.
I removed the crappy box springs (cardboard/ wide slates) and replace them with a home made frame. The mattress came to life and feels flatter. A noticeable improvement. The mattress is a Queen Spindle Abscond with two firm layers on top of a medium.
After sleeping on the Spindle Abscond for three months, I have decided that it was not firm enough for me. Initially, this bed started off with a medium layer on top and two firm layers as support. The medium layer was quickly moved to the bottom. A few days ago, I called the KTT Enterprises and had them cut the medium layer in half and purchased a 2" layer of 40-44 ild blended talalay to place on the bottom. I noticed that the firm layers (dunlop) were firmer on the bottom with larger holes. I placed these on the talalay with the bottom side up. The medium layer seamed more consistent (top to bottom) so I used the top half of this layer as the final comfort layer. The result was a bed with more support and softer comfort layer. If more support is needed, I will move the talalay up.
Thanks again to KTT for there great customer service and this board for all its ideas.
