Physics Rant

Physics Rant

Hi everyone! This is a little different for the blog, but I started to type it up for social media and realized that it was going to run long, and I wanted to include links and inline images.

First things first, spoiler alert. If you haven’t watched The Expanse seasons one and two, or Lost in Space (2018, Netflix), then either watch them now or make you peace with spoilers.

I watched The Expanse a couple of months ago, and I found it fairly enjoyable. What I really appreciated about it was that other than a few specifically chosen (and mostly acknowledged) violations of known science, the physics was pretty solid. What really made me sit up and take note was a scene where to people are running across a walkway when the giant spaceship’s engines cut out, and everybody goes into zero-G. The protagonists are left floating helplessly a couple of feet above the walkway while people are shooting at them, and without missing a beat one of the main characters clipped a tether, pushed off the other and used conservation of momentum to get his magnetic boots back in range of the deck. It was great! Here’s a clip:

This was an example of The Expanse getting the small stuff right, and that was just great. Now, how about Lost in Space?

Lost in Space tries to sound smart. They throw in enough sciencey sounding stuff and concepts that are close to right that somebody who didn’t know any better might miss it. I can totally forgive that, unless the plot uses incorrect physics as a major point of conflict. One example is in Episode 7 two of the main characters drive their land vehicle into an extraterrestrial tar pit.

Trapped in tar!

They realize that what looked like mud is actually a black liquid tar, and they’re sinking in. That big vehicle they’re in is mostly air, has room for several additional occupants, and the doors and windows seal tight. Somehow this vehicle is heavy enough to sink to the bottom of the tar pit, where they then use a helium balloon to create a vertical tunnel to safety. Hey, an alien tar pit that traps the pair when time is of the essence is a great plot device! Seriously, it makes sense that it would happen and it can be really dramatic. What doesn’t make sense is that they would keep sinking all the way to the bottom. Tar is denser than water, and if you take a regular car and tape it shut, it’ll float pretty well. This thing is so big, and because it came from a space vehicle it would be weight optimized, so unless the air was leaking out and liquid was coming in, it would float like a duck.

1960s Duck

That’s the small stuff. I’m getting worked up about this, so what if I just make it into a bullet point list.

Lost in Space

  1. Gets the scale of space wrong by:
    1. Listing Alpha Centauri as the destination
    2. Taking colonist families there with the intent of reaching the star system in their lifetime
    3. Explicitly stating the colony ship’s top speed as 276,000 miles per hour
    4. Not using any kind of stasis or suspended animation
    5. Neglecting to do the math that at this speed it would take almost 11,000 years to reach the destination
  2. Ignores practical considerations by:
    1. Making the well appointed, overbuilt, stuffed with food and furniture colonist ships capable of reaching orbit on their own by burning liquid fuel
    2. Making these ships able to convert poop to rocket fuel with solar energy, and able to do it much faster if they have better quality poop
    3. Never really worrying about radiation exposure
    4. Being fairly inconsistent with the robot’s capabilities

The Expanse

  1. Gets the scale of space right by:
    1. Including communications delays due to the speed of light
    2. Showing preparation of a colony ship intended to fly for over 100 years to Tau Ceti
    3. Having the development of a revolutionary new engine as the main driving technology for expanding beyond earth orbit
  2. Pays attention to practical considerations by:
    1. Making air/water/nutrient recycling systems a major concern for characters
    2. Making radiation a huge problem to be dealt with
    3. Giving everyone magnetic boots
    4. Has a scene were characters press their helmets together with radios off in order to have a private conversation
    5. Regularly have characters personal effects floating around in zero G until the ship fires its thrusters
    6. Shows blood and liquid in ways that are realistic for the gravity and acceleration in that scene

I’m a big fan of the attention to detail in The Expanse, but I’ve got a few gripes too. Is there a good reason why everyone’s into haircuts with the sides of their heads shaved? Why isn’t anybody fat? Why aren’t drones a much bigger deal? Why did they portray zero gravity sex as something fun and cool until the engines turn on (when you fall forcefully onto the bed, ouch!) instead of something way safer where you basically strap into a sleeping bag with your partner? Was Alex really getting hammered alone while waiting for his crew to go do their thing on Ganymede? None of the stuff with the ‘protomolecule’ bothered me, since it was a major part of the story that this stuff was weird and alien with unknown and incomprehensible powers. For what it’s worth, some of the Lost in Space robot’s ship capabilities felt the same to me. At least if something is weird then everybody should act like it.

Now I want a show that has the attitude of Firefly with the physics of The Expanse and the longevity of Stargate.

Acoustic treatment

Acoustic treatment

A lot of time has passed since my room equalization post in August 2016, and the stereo is now in a different room. Looking back, I think that one of the biggest problems that I had in my attempt at equalization was that I was aiming for the wrong target response, and wasn’t doing enough to actually treat the acoustic problems before equalizing. With the two of us basically living in one room and a bedroom I wouldn’t have been able to really add a lot of acoustic treatment without it being too ugly for Kaitlyn to put up with, but now we have an office in the house where I can make things as ugly as I want. So, here’s the ugly office…


There are a few major acoustic problems here.

First, it’s a square room. Any reflection or reverberation that goes from the front to the back wall also happens from side to side, so the shape is fundamentally bad for even bass reproductions. This is a 12x12x8 foot room, so since the speed of sound is 1125 feet per second you’d expect the first resonance to happen at about 47 hz. The math behind that is 1125 feet per second/12 feet = 93.75 cycles per second, and the first resonance happens with the pressure fluctuation (zero velocity) on the wall, and velocity fluctuation in the center of the room, so a half wave, so the resonance happens at half of 93.75.

Here’s a raw measurement of one of the speakers playing before I’ve done anything to help:


So, what’s wrong? Obviously there’s a huge peak in response a little lower than that predicted 47hz, but there’s something else going on too. As I said, my first attempt at correction in the old place was aiming at the wrong target response. When I applied the correction filters it sounded weak in the bass and I didn’t understand why. It turns out that there’s something called the Harman Target Curve that describes the frequency response that sounds most natural. You’d think that it would be perfectly flat, but when a sound system is set up that way it sounds weak in the bass and too bright in the highs. The preferred shape is a bass boost starting below ~150hz, flat response up to 1-2khz, then gradually falling response above that.

It turns out that the high frequencies were pretty good, and when you line up the bass according to the desired curve, that big peak at 47 isn’t even the worst problem.

Target response

In the new office, this is something I can hear. The bass between ~60 and ~200 is what gives bass that tactile feeling, where you can feel the drums, and that’s what not coming through like it used to, or like I know it could. The problem is that you can’t just boost frequencies that are too low. They’re too low because things are physically cancelling out or are driving modes that have dead spots at the listening position, and increasing the drive level doesn’t help much and adds distortion, cone excursion, and power usage without much benefit.

In order to address some of this, I looked at SBIR, speaker boundary interference response, and found that I should have a pretty big cancellation around 90hz because my chair is 30″ from the rear wall. It’s really hard to absorb frequencies below 500hz, and most of the acoustic foam panels that you can buy do very little at these frequencies. You need something that goes deeper, a lot deeper. I looked at a page of a bunch of absorption coefficients, and played with a porous absorber calculator to see what it would really take to be able to address these frequencies and kill the reflected signal and get my bass back. I settled on [Roxul Safe’n’Sound]( which was cheap, relatively non-hazardous, essentially fireproof, and capable of absorbing very low frequencies. In order to hold it in place at a distance from the wall, I used some Ikea Ivar shelves that I already had available. This produced a 6″ thick absorber with 6″ of air space between it and the wall.

Here’s a graph showing the effect of the absorber.


The smoothing is a different scale to make things easier to see as averages, but the main takeaway is that the green line is about 6db higher at 100hz than the purple line. That means that by adding these sound absorbing panels behind my chair the bass notes at 100hz got twice as loud. There were other benefits too. The overall response got a little more even (see 500hz), and the clarity of the sound was improved because I no longer hear the reflected sound behind me delayed by ~4ms. Any early reflections happening before 6 milliseconds will blur the apparent location of the sound source; our brain/ear averages those out. Reverberations happening between 6 and ~50ms are integrated into the perceived sound as loudness, but the first occurrence of the sound is what is used by our brain to determine location in space. This is called the precedence effect, I hope I’ve explained it right. This is why speakers and chairs really need to be at *least* three feet from any walls or major reflecting surfaces for optimal stereo sound, and why most households just don’t get to have that type of sound reproduction.

This is what it looks like on a graph; this is the “Energy time curve“or ETC graph. The graphs shown above show magnitude of sound with respect to frequency, but these show magnitude of sound with respect to time. A perfect source would look like one big sharp spike with nothing after it. A real room shows a series of peaks afterward, the reflections.


Ideally you’d want nothing sticking up within 6ms of that first peak, and nothing sticking up above the -20 mark at all, and everything steadily decaying. I’ve circled that first peak at a little after four milliseconds, that’s my reflection from the back wall. Here’s another ETC graph showing what the absorber was able to do.


That first peak is totally gone, and many of the later peaks are lower in level. I suspect that the two large peaks that are till hanging out at around 8 and 10ms are reflections from the floor and ceiling. I think that the other peaks that went away were from sounds that made a round trip from the back wall to the front and back. I can hear a difference, and the stereo image now sounds clearer, with a more realistic presentation of the performers and instruments occupying specific points in space. Bass is fuller and more even, and things like plucked double bass sound more realistic. That 47hz resonance is still there, but it’s very easy to use an equalizer to knock just that one down a little bit without robbing the rest of the bass.

So, what’s next? There’s still a big dip in response from 100-300hz, and 100 could be louder still. My next step will be to add more absorbing material into the corners of the rooms to make bass traps to absorb some of that resonant energy. This isn’t a high priority since we are making preparations for Baby Carrow to join us soon, but I may do it by the end of the summer since it won’t cost very much or take very long. In the longer term, I may purchase some software to further process the sound. I had a free trial of one package that made a very noticeable and favorable improvement, but it’s really not a priority right now and if I wait then the price might come down or a competitor could come up with something better.

Sewer lateral complete!

Sewer lateral complete!

Finally, something really worked out! The last expensive move-in project with a strict timeline that we had hanging over us was the sewer lateral. Our county requires that whenever a property is sold the sewer pipe from the house to the street has to be inspected and pass a pressure test. This is to make sure that we aren’t all leaking poo water into the neighborhood soil, and I guess I understand why that’s a law. They make you put up a deposit of $4500 that’s forfeited if you don’t finish that within six months of closing, so it’s kind of a big deal. The thing is that for almost every single ~90 year old house around here you would expect the pipes to fail to hold pressure. As far as our report said, we didn’t even have a clean-out where they would connect such a test.

When we bought the place the disclosures had a quote for having it done for $7k, and we were told that it was likely we could find someone to do it for less. After all of the other surprises we’ve had, I really assumed that the company had lowballed and was going to flake when they didn’t call me right back when I wanted to get the work done. I did some research and called a couple of the most highly rated companies in town for this kind of stuff, and one came out and gave me a quote for $19k. The reviews for the cheap guys had a couple instances of people saying that they’d been hit with delays and extra charges of thousands of dollars, and so I was afraid I was looking at a >$12k headache from the cheap guys or a $19k super-premium treatment from the other guys. Either way, I as already worried we’d be on a payment plan.

Today we got the happy ending!

I got a call yesterday that they discovered that at some point in the not so distant past somebody had already replaced the 90 year old pipes with modern stuff, they just did it unpermitted, and left the clean-out in a really inconvenient spot under the stairs. All they had to do was install a real clean-out, then get it inspected and permitted properly. And it was going to cost less than the quote! Today that actually happened, and we can put this behind us. After we get the check back from the city this won’t have eaten into our budget for other stuff, which is very cool.

Curtains up!

Curtains up!

It’s been a little while, and we’ve been busy on some things other than the house (plus I had issues with the blog). We hosted Christmas dinner, helped Kaitlyn’s dad move his shop, and had some much needed down time. Kaitlyn seems to be getting some energy back now in her second trimester, so this weekend we located the curtain rods and got these up in our room.

I wish that I could say that this took less than four hours! Anyway, I’m glad we got it done, the bedroom feels much more cozy now.

Less happy news, it’s been three months since the bathroom was finished and the grout is already cracking.

We haven’t decided exactly what we’re going to do about it, but it seems that the contractor that did the work is out of business. Their contractor’s license is canceled, and their website is gone. We may still have some recourse, and the floor may not be beyond repair… but this isn’t good.

Today we are having our sewer lateral updated, so hopefully I’ll have good news on that soon.

Here’s Penny!

Also, this is the salamander who lives under our compost bin:

Starting yard work

Starting yard work

It doesn’t feel like there are any huge milestone new lately, but we have been shuffling boxes around and built a couple of book cases to unpack more books and things. Anyway, we did get around to some yard work this weekend.

I’m not sure what plants Kaitlyn bought (maybe she’ll come do a post and tell us about them!), but to get them planted the bushes had to go. At first I was concerned that it was a really old bush that would have deep roots, and I’d be destroying something healthy and old by taking it out. On the contrary, it was super rotten and full of beetle holes. This was probably one of the havens for the beetles that were starting to eat the house. It still tuckered me out to dig and chop it out, but it’s gone now.

Next we have to dig out the rest of the weeds, roots and debris before mixing in some bags of soil and planting the new things. It’s getting dark around 5:00 now though, so it’ll have to wait until the weekend.

In other news, I’m getting the office set up, and can finally listen to my stereo again! I hope to do some acoustic measurements soon, and I expect that I’ll need to add some absorbing panels to one or more walls to make it sound right. Those will be non-house posts.

Lighting update

Lighting update

This weekend we had a couple of lucky breaks on lighting, and got some good stuff done! The “nook” light replacement was going to be an antique with a funny hole pattern, and it took some finagling to get the holes to line up with the ceiling box. I figured it out though, and now it’s looking pretty good.

I wasn’t able to get a picture of it turned on that also shows the details, so that’s it.

Kaitlyn spent a while hanging a bunch of little crystal blobs, so we have a bedroom light now:

And then we got the dining room chandelier up! Restoration Hardware screwed up shipping so I had to go back to our old apartment to pick up the part, but it worked out. It turns out it was missing a coupler (maybe some people would call it a nipple) that was threaded on the inside, and a smaller threaded tube that connects to the chandelier body. Of course the packaging was enormous for a part that should have been the size of a piccolo, but at least it’s here.

Progress! Victory! No more floor lamp in the dining room, it’s going to look a lot more normal for our first thanksgiving dinner in the new place!

Finally, you know I need to wrap this post up with a Penny shot. Kaitlyn really wanted to get a Christmas tree, and although the Carrows have a tradition of doing that the day after thanksgiving, I gave in.

She was really unsure of it, but I think she’s used to it now. Also, the lights have voice commands. It’s the future.

Refrigerator update- game day

Refrigerator update- game day

Game day? Everyone jokes about it being like Tetris, but this weekend we also had some Jenga and 2048. 2048 because I caught myself shuffling back and forth hoping that something would suddenly condense and give me space to work… Overall I’d say we were victorious, and nothing got too dinged up.

When we moved in there was nowhere to put the refrigerator, the kitchen is tiny, and we think that the previous owner blocked a doorway to fit a fridge. Maybe she had it somewhere else… anyway, this is where we had the delivery folks leave ours.

That’s right in the dining room, and it didn’t let us have enough space for a dining room table with chairs on all sides, and we were just sort of crammed in there. The thing is, the doors are 29″ wide, and the fridge is about 32″x32″ with the doors on. I thought I was going to take off the swinging door to the kitchen and go through that way (avoiding most of the hard wood floor and new paint), but fortunately Kaitlyn was able to talk some sense into me, and pointed out that the living room door is just as wide, and we wouldn’t need to disassemble nearly as much stuff to go that way.

I had to take *everything* off the front of the fridge, and used these cool felt and foam sliders to move it around. It only took two trips to Orchard Supply Hardware to get the mini-socket and torx drivers, but everything came off pretty smoothly. We also taped some cardboard over the floor furnace grate for better sliding. That totally worked.

Anyway, here it is.

Yay! Let’s see it with the wide angle!

If you turn around, here’s what the living room looks like now:

And here’s how the dining room is coming together:

There’s going to be a really cool brass chandelier in there soon, with shades that basically match the living room sconces, but there’s a small obstacle to getting that up. Can you tell what it is?

A replacement part is on the way, but I’m not optimistic that they didn’t just run the wrong size tap into the body of the chandelier. That’s too bad because it’s been discontinued and we wouldn’t be able to exchange it, but it’s a really expensive model that we got for really cheap, so if it comes down to it I’ll make an adapter. I’m confident that I’ll be able to match the threads and make it work if I have to, and should be able to make it invisible, but it might be a little slower and more expensive than I was hoping. Fortunately I know a lot of machine shops and places that can 3D print in stainless steel and brass, so this thing is totally going to happen.

That’s all for now! Here’s a picture of Penny looking really concerned about us moving things around.

Also, one of her skittering around. Also concerned. She will probably be happier than us when the last cardboard box is gone.

Laundry works!

Laundry works!

A few new updates- it took a few trips for more parts, but out washer and dryer work now! I’m happy to report that they are surprisingly quiet. 

Picture of the laundry room view… the door is in storage now:

Another update, Kaitlyn made some awesome progress organizing, unpacking, and cleaning the kitchen.  We hope to be able to cook something tonight.

The plumber yesterday was able to unclog both drains and only charged us for one, and he was really fast and friendly. We’ll definitely call him the next time something happens. 

Moved in!

Moved in!

I guess I owe an update- it’s been just over a week since we started sleeping here, and we just finished with cleanup at our old place. We’ll be down to one address any time now!

The situation feels dire. We just spent way more than I was happy with on movers, and we haven’t had a chance to get rid of all our debris yet. Kaitlyn inherited furtniture from three houses last year, and we’re trying to fit it all in so that we can organize a big garage sale. 

It feels like we’re living in one of those hoarder reality shows or something. Or maybe I’m just being dramatic.

Today I crawled under the house and reattached the dryer vent that was knocked loose (side note- a four foot section of it seems to be made out of copper, the rest is galvanized steel, and what I replaced is now aluminum), and successfully hooked up the dryer’s gas line. Fortunately I was able to get angles with a mirror and a lot of soapy water to be positive that I got that right.

Found a weird bowl with a bone in it under the house, seems like I find more of that stuff whenever I go under.

I’m only pausing to make this blog post right now because we have a plumber unplugging the utility and bathroom sinks. I don’t know if the contractor we had redo the bathroom cut corners, or what. The toilet and shower are fine, but the sink fills up by the time you’re done brushing your teeth.

Speaking of contractors…. is it normal to leave the junction box in a crawl space uncovered like this? Is it a safety problem? I’m gonna look that up when I have some time. 

One good thing- our painter has done a careful and meticulous job, and the place is starting to look better and better. More pictures soon. 

Oh yeah, and Penny is very happy that we finally brought her slumber ball. Having that, a rug, and the couch all together seems to make her feel at home.

Here’s a shot of her waiting in the car while the movers worked: