Bedroom update 2

This morning I had to take care of something for work, and Kaitlyn headed over to the house before me and got the baseboards coated in Citristrip. By the time I got there they were ready to go, and we spent a while scraping the paint.

This part is gross, but… I got really pruney inside my rubber gloves. Not fun!

It also became clear that we need to think more seriously about popping these off and really finishing them well outside. It just isn’t that easy to get the edge that’s close to the floor. I read an internet tutorial, and it worked out pretty well. Fist you insert a couple of flat blades in between the wall and the molding:

You have to use really thin blades to get in there, and I already found out how easy it is to bend a corner. I might have to grind that off…

Anyway, the next step is to stick a pry bar in there and carefully work your way around all of the finishing nails to pull the trim off.

To our surprise, this baseboard is actually two pieces. There’s a small decorative piece at the top that came off with just a little patience, but the bottom board is plain and attached much more firmly. I think I’m going to get them off, but I had to call it quits for today. 

Another surprise from the house is the number plate.

What’s up with that? 

Apparently this used to be illuminated! I’m not sure if it’s on a switch, or what. It wouldn’t work very well with the numbers that are on the glass right now. I’ll need to do some work to get some back-lightable numbers, in case I ever get the illumination back.

12-16 volts… that means there’s a transformer in the wall somewhere! Next time we go back I will bring a multimeter to see if it still works. 

Bedroom Update 1

One of the first places we got to work was the bedroom, the one we want to be our room. It’s the one without water damage, and it is the farthest from neighbor’s houses.  Over the last few weeks we have stripped off all of the wallpaper and have prepped the walls for plaster repair.

Rookie mistake, we forgot to put down plastic first. We plan to redo the floors before we move in, but…. it just wasn’t good.

Better… for it all cleaned up, plastic down, as now we start on the molding. We spent about 10 minutes trying to sand it, and it was a stupid gummy mess that wasn’t going anywhere. Now we’re using Citristrip.

It goes on like spreading jelly, and it doesn’t smell too bad. I don’t bother with anything but safety glasses while applying it, but I use rubber gloves and a respirator while scraping it off.

This is what it looks like after two rounds of citristrip, and some rubbing with a scrub pad soaked in mineral spirits. We think it might be worth doing it all, and staining it. 

That’s going to take a while though! My P100 respirator wasn’t doing anything for the fumes, so we took Penny out to Orchard Supply and picked up some cartridges rated for organic vapor. After getting some box fans for enhanced ventilation I might get to keep some brain cells. 

Bonus picture of Penny in her OSH gear!

Bathroom update 2

This is just a mini update, but I was too excited at seeing the tiles that Kaitlyn picked to not post something! 

The contractor is still hard at work, and we are making sure that we have received all of the bits and pieces they need. The bathroom fan is installed, the replacement sink is delivered (and not shattered like the first one!), and all of the shower fittings are accounted for. I verified that the toilet’s waste hole has been relocated to move the toilet flush against the wall, so we won’t have any heartbreak moving it again. The next milestone is plumbing inspection. 

We are still waiting for our high efficiency toilet to arrive Monday, and I think that Katitlyn is picking up light fixtures from UPS this afternoon. 

Bathroom Update 1

We’re going to have a few fast updates this month! One of the very first projects that we’re tackling before we move in is the bathroom. We are spending a major  chunk of our house prep budget on a contractor to get it done quickly (and right), but there’s only one bathroom in the house so we wanted to get it taken care of before we’re living there and before we have the floors refinished. Here’s what the bathroom looked like yesterday:


50s/60s style vanity, and whoever lived her last really liked towel racks


This will be part of the dramatic before/after shot

The house was built in 1927, and our best guess is that the bathroom was renovated some time in the 1950s or 1960s. The floor was tile, but all of the green ’tile’ that you see is some kind of plastic. It wasn’t in terrible shape, but there was a bit of water damage and rot in the tub area. It seems like the toilet was replaced some time more recently, based on the strange spacer behind the tank.


The tub with water/hammer damage

One contractor told me that the wall was totally rotten and bad, and would definitely have to be removed. I didn’t know much about old houses at the time, and he stopped communicating well, so took a hammer to the wall and had a look to see what was behind the tiles. It turns out that it really wasn’t that bad, so although it was going to have to get busted up to do anything with plumbing and electricity, it probably wasn’t in imminent danger of destroying the house due to water damage. Regardless, we were committed. Redoing a bathroom is messy and tends to put it out of commission for a couple of weeks, so here we go.


The bathroom, today

Today demolition started, and it honestly looks like they demolished most of what they needed to demolish. The upper dividing wall above the shower curtain is gone, everything is down to the studs, the tile is out and hardiebacker is down. So far so good!


Tile debris, 2017

I was worried that the backing under the tile would be so thick that we would end up with a significant level mismatch between the tile and wood, but as thick as this is I’m hopeful that they’ll get close to a match.I don’t understand how the wire mesh worked structurally, but the floor seemed to be in decent shape after 90 years. I’m just hopeful that what we’re putting in now will last as long. My lovely wife Kaitlyn picked a really cool tile pattern to replace it, and I’m looking forward to a bold reveal post.


A note from under the flow

Is this a time capsule? I think it may have been a piece of packaging from bathroom accessories that fell beneath the cement when they started making the bathroom. I don’t think it was worth digging out and deciphering, but it was interesting enough to get a picture.


Here’s another piece of the house’s history. This is one of the light switches, and it appears to be not original, it appears to be grounded, and… maybe not connected to any knob and tube? One of the things on my to-do list is to get an electrician in here to check everything out and see if any of the knob and tube wiring is still live.


knob and tube in the bathroom wall

This one *is* a piece of knob and tube wiring, and it was attached to a two prong outlet that was hidden behind the vanity. It looks like it was cut off a long time ago, and the outlet had what was probably an original 1927 unpainted brass cover plate. It’s neat to see, and I hope that it’s also good to find this kind of thing and see that people working on things in the past didn’t leave too many scary kludges in the electrical system.

That’s all for tonight’s bathroom post tonight, so here’s a shot of Penny exploring our place!


Room equalization

This is a topic that I’m still fairly shaky on, so anybody out there reading this as a possible reference should probably take this all with a grain of salt. After building the LX521 speakers I could tell that they weren’t delivering precisely the sound that I know that they’re capable of when they’re set up correctly. As you’ve probably seen in photos, Siegfried Linkwitz’s home does not have any visible acoustic treatment, just some normal ‘stuff’ around the room. Furniture, a nice rug on the ground, nothing like walls full of acoustic foam or avant garde looking diffusers. It’s just a regular room, and most people who build his designs agree that you don’t to do anything special to get the good sound.

Before we go too much farther, I should say that there are two different things that I’ve noticed about the sound in my system that differ from what I heard when I auditioned the original. First, I hear a bit more of the room in the bass response than expected. Things boom/echo just a bit, and its’ the difference between a natural sounding reproduction of a sound that can truly fool you, and the sound of a speaker in a room. We’re not *quite* there yet, though it’s miles better than what I had before. The second part is that there’s a bit of imprecision in the imaging. In the demo I could very plainly localize sounds in space, like I could hear a xylophone player moving up and down the keys and tell the left/right position of each key. That might sound like a wild claim, but that’s what I heard and what convinced me that this thing was worth building. Having my TV between the speakers may be hurting the sound a bit, but I think there’s more that needs to change than just that.

I’m setting out to learn how to improve the sound of the speakers in my room, and I want to be able to do this well enough that when we eventually move I’ll be able to repeat the process with a reasonable certainty that I’ll be able to make the stereo sound good there too. I’m using a program called Room EQ Wizard (REW) to perform measurements. I use a Behringer ECM8000 room measurement microphone that I’ve had for years, a small powered mixer, and my computer sound card to capture the sound. Based on the reputation of the microphone and a loop-back measurement that I did with the rest of the signal chain, I think I have a fairly accurate measurement system…. if I can figure out how to use it right.


For my first measurement I put the microphone on a tripod positioned at the spot where my head would usually be, and ran a test sweep from 20hz to 400hz. I did a few more, but for the purposes of room equalization I thought that I was interested in things below 200hz.

raw measurement

The first thing that you’ll notice is that this response looks totally ragged and nasty. It’s hard to say exactly where the average is if it was ‘flat’, and there are clearly peaks and dips of 10db. That’s partly because this is a real in-room measurement, the room isn’t treated with much of anything, and it’s like a big echoing box. Concrete floor, flat ceiling, thin rug that doesn’t cover much, and not much stuff on the walls yet. Regardless, there are some good things about it. The response doesn’t drop like a rock below 30hz, and I can tell you that the woofers really made some impressive sounds in the mid 20hz range. The system can do bass, but the room still needs help. Lets see what we can do.

After collecting this data I opened the REW equalizer window, and I selected “miniDSP” as my equalizer so that the program would know what it’s allowed to do in terms of suggesting correction. I assume that some of the other selections have more or less EQ bands available. Next I had to come up with the ‘target settings’. This is what tells the program what you want the ideal system to do. I have some trouble with this one, knowing what to set. I think maybe this is where a sweep to more like 20khz would have given me more information about where the average is supposed to be. Regardless, lets give this a shot.


I picked 72db as a target level, set the target as flat with a 24 db/octave rolloff at 20hz. For a full range equalization I hear that you are supposed to set a gradual rolloff above 1 to 3 khz, but I’m mostly interested in taming room modes here, and those are all well below 1khz.

In Room EQ wizard I clicked on the “filter tasks” tab and then “match response to target”. It twiddles things around for a second, and then gives five parametric EQ settings that shifts the response to something closer to the target.

target response

Here you can see a brighter red line that is closer to the blue target, and a brownish line that’s the original response. The bright red line is the predicted response if I load the EQ settings. I’m able to save those to a text file and then use my MiniDSP software to read those, or I could enter them manually. Clicking “eq filters” let me see what those are; they looked like this:

filter suggested

Overall it’s a few sharp cuts at specific frequencies, and a broad boost at 40hz, giving the flatter response. I loaded these into the second configuration slot on my MiniDSP, and now I can flip back and forth between the unmodified and equalized versions. That has been very interesting.

Subjectively it sounds as though most of the room ‘boom’ is gone. However, I still somewhat prefer the unaltered version. The equalized version seems to take too much of the bass away. That may have to do with my target curve, or it may have to do with the settings when I clicked “match response to target”. The MiniDSP 4x10HD allows four configurations to be stored, so I could even try a few different versions and audition them each without leaving the couch.

I’m going to hopefully meet with some local audiophiles to discuss this more, and when I get a chance I’ll repeat the measurements with a few changes. Other than dialing in the available EQ, I think that my next step might be to hang up something cloth on one or more walls to absorb some of the sound that’s bouncing around. It’s a lot to research, but I’ll keep reporting back as I figure it out.


LX521 Speaker build- the Hypex multi-channel amplifier

It’s about time I had an update! This is basically skipping to the end from the last post, building cables, but I’ve been pressed for time in getting them built so I didn’t keep blogging as I went. I have a few pictures of putting the cabinets together, but it’s boring. I didn’t design that part, and I’m not a master craftsman with fancy insight into how you’re supposed to do woodwork. Hopefully the amplifier is a little more interesting.

The LX521 is a four-way speaker with an active crossover, which means that a pair of them need a total of eight amplifier channels. In order to provide uniform sound, all eight channels need to be identical. The amplifier that the designer uses is the ATI 6012, a 73 pound monster that costs about $2800. It’s an excellent piece of gear, but I was trying to keep the budget a bit more reasonable. A pair of Outlaw Audio Model 5000 could have also worked for about $1200 total, but then I’d need to put two 50 pound amps someplace. For just a little more than that I was able to put together a 25 pound amp that keeps everything in one box, and theoretically measures a little bit better. Also, I think that the more you build for yourself the more fun it is!

The amplifier I put together is based on a Hypex UCD180HG class-D module. I couldn’t really figure out precisely what their fancy voltage regulator upgrade would do for the sound, so I skipped it. If you have a dedicated listening room with soundproofing and are *really* into this stuff, then maybe you can give them a try (or go hog wild building with the Ncore modules). Now that I’ve built it I realize that this is dumb, but I used two of the 1200 watt switching power supplies, the SMPS1200A180. There is no way in hell I need that much power. Maybe I could throw a rave some day, but for now it just means that I have a bottomless pit of reserve power that I’ll never touch. By my best estimate, as loud as I’ve turned it up I don’t think I’ve used more than a few dozen watts yet. Hey dad, that means you could run these off of a solar panel pretty easily!

Anyway, on to the case and construction! I used the Modushop Mini Dissipante as the basis for the enclosure. I did some calculations of waste heat and fin area and all of that, and I must have messed up a decimal place or something, because I definitely didn’t need all of that cooling area. Oh well, I guess the parts will just last longer since they run cool.

The finished amp looks like this in my living room:


It’s just a plain aluminum panel with an on/off switch. Minimalist, right? The next step will be to make the guts look so nice.

The amp modules have a blue aluminum T-shaped piece with two M3 holes tapped in it. I decided to put all of the holes into an interface plate, and then bolt the plate to the heat sinks. First I drilled and tapped some holes in the aluminum heat sinks, as shown here: note that I used an old T-shirt to protect the kitchen table, and the glass of beer with a lime in it was in fact a mexican style beer by the local brewery, 21st Amendment.


Next I laid out the interface plate using some calipers and an automatic center punch to give even spacing. You can see that tool in the upper left corner of this picture. This is really useful for achieving a medium level of accuracy in an apartment with hand tools. It’s not like when I had a techshop membership and would do this stuff on a mill, but it at least keeps the hole positions accurate enough that I can generally get them to line up.


There are two 1/4-20 pan heads at each end of the interface plate, and if this were going to have a really significant heat load then I would have used more of them (and a different head) to ensure solid contact along the full length of the heat sink base. It was reasonably convenient though, and I’m not producing that much waste heat, so i thought it was a corner worth cutting.

The power supply module comes with six M3 screws already installed, holding a compression piece against an L-shaped plate. You have to take these out in order to have access to tapped holes to get this face against the heat sink interface plate. You could mount another way, and the manufacturer even says you can just let this thing hang out in free air, but I know that if I keep things cool they’ll last longer (like to pass down to my kids some day).


The amp module is surprisingly small for something that can do 180 watts and drive a one ohm load. I slathered on the heat sink grease before attaching them to the interface plate.


Once they’re all mounted it’s ready to mate up with the heat sinks assembly. You might be able to see that I did some really rough and rowdy countersinks to get those M3  screws to sit flush below the surface of the interface plate. I have some slight concern that some day one of them could be pressed against a capacitor and wear through from vibration and short something out, but probably not. I’m just documenting that concern in case anybody cares, and as something to think about for next time.


I know you wanted to see this all greased up. Look at those nasty countersinks! Eww!


IMG_6465 IMG_6466

There it is! Four 180 watt modules with a 1200 watt supply, all ready for assembly.

And…. Oops. I built them the same, and that’s not going to work for wiring. I had to redo one of these.


This is a really useful tool that I wanted to take a minute to talk about. This is a ratchet offset screwdriver, and it lets you reach into tight spaces that a regular screwdriver can’t reach. A well designed product won’t require this, but sometimes the designer just can’t be bothered to think about tool access… so that’s when you break this out. The best one I know of is what they used to work on medical linear accelerators at Siemens, and it’s the Chapman. You’ll notice that compared to mine, the ratchet area is much smaller, and the divisions between ratchets are signficantly smaller. That lets you reach into smaller spaces and tighten screws when you don’t have space for much rotation.

This is how I connected the mains power to the front panel toggle switch. It’s a DPDT switch rated for 20 amps, and I made sure that it was large because I wasn’t sure what kind of inrush current the power supplies would draw. As it turns out, they seem to have a nice polite soft-start, or else their inrush is much smaller than the spec sheet indicated because they’re just getting US voltage instead of the 230V that europeans are working with.


This ended up being a little easier than I expected. The power supply sends a few leads over to the terminal blocks, and each amp takes a positive, negative, and ground input for power. The worst part was all of the crimping. I think I ended up doing about a hundred crimps. There’s a reason they make machines to do that.

In the lower right of this image you can see the twisted pairs of wires going to the speaker output jack, and the black cables soldered directly to the XLR jacks. I need to go back and get everything twisted and trimmed more appropriately before I’ll say I’m done, but for now it works.


The last thing I did was put channel numbers on each of the amps so that I can keep things straight, and I checked a test signal on each to make sure it wasn’t putting out a measurable DC voltage and a full range music signal sounded right with one of my old speakers. During this step it was really promising to hear music coming out of my old speaker that (I think!) sounded better than the eight year old cheapie receiver that had been driving them.

One thing you’ll notice here is that I used blue paper painter’s tape as a temporary measure to keep anything from shorting out. The maximum voltage in here is 48 volts relative to ground, and 96 volts from the positive to negative terminals. Everything is firmly connected to screw terminals inside of insulated blocks, but a little bit of metal peeks out at the edges, and so I didn’t want to take any chances on something shorting out. The end goal is to have the terminal blocks bolted to the bottom panel of the enclosure in a neat row so that the wires can be routed in a clean and proper way.

The 120V mains line goes to the switch on the front panel using a tightly twisted pair of 14 gauge wires in some ring terminals. I used fork terminals for the rest, but for 120VAC I used insulated ring terminals so the screw would have to fall completely out before the crimped part could fall and contact something else. The rear panel has a three-prong jack, and there’s an earth ground that’s similarly connected to the chassis (you can make that out in the photo above).


The back of the amp looks fairly neat thanks to Front Panel Express making the panel for me. The large cutouts in thin aluminum and added threads saved me a *ton* of work, and I know they made it look nicer than I could have. I’ll add more labels when I’m done, but for now I know how they’re laid out well enough that a prompt of “1” and “2” is enough that I won’t plug something in wrong. If I did do that, it would blow up my tweeters.


Ok, so that’s all I’ve got for now. I’ll leave you with a cell phone picture of the speakers and amp in the living room. They sound pretty good. I hope you’ve enjoyed reading!


LX521 build- speaker wires

This is is the very first post in my LX521 build, not counting a couple of background posts saying what I’m building and why I’m building it. Tonight I got started on making my speaker wires. The LX521 is a four-way speaker with an active crossover, meaning that for a stereo pair I need eight amplifier channels and I need to plug in a total of sixteen wires in the correct fashion or I risk blowing up some drivers. If I swap the tweeter channel with any other channel it will probably destroy the tweeters right away. If I switch any of the others it might not break them right away, but it will sound very wrong. If I flip the polarity of anything, it will sound wrong but I’ll probably have a hard time putting my finger on it at first.

One way to tackle this would be to get a bunch of the typical binding posts that you see on any speaker, and just label everything carefully. That’s a little tedious, it takes up some space, and it won’t look very good. Another way to do it is to get a speaker cable with eight conductors in it and use a single plug with eight terminals. I got a set of 8-pole Neutrik Speakon connectors, and once I get those set up correctly I won’t have to worry about it again.


The connector has eight bars around the inside and outside of the barrel that are locked into place when the connector is inserted into its receptacle and rotated about a quarter turn. They’re rated for 30 amps per contact and 250 volts, so one of these plugs could pass over 25kW of musical power if it had to. These are commonly used for the kinds of speakers used at concerts. They’re overkill, but they were basically the same price as using four times as many of the regular connectors.

It was a little tricky to figure out how to assemble them at first, but it’s not so bad. They have eight screw terminals to accept the wires, which is nice because I don’t have to crimp or solder anything.


I wasn’t able to find any eight-conductor cables sold in small quantity, so I’m just going to double up on some four conductor wire from monoprice. I don’t think that it’s terribly important for the wire pairs to be individually twisted, but I do plan on running the tweeter and sub channels through two different lengths of cable just to be safe. I’m putting the two lengths of cable through some Techflex to keep them tidy.


I consider all of this to be a safe level of overkill, even though it’s by no means the pinnacle of what could have been done. It’s a twelve foot run of 14AWG stranded wire, so that should add about 0.06 ohms of resistance in series with each driver. The woofers will be in parallel and will present a two ohm load, so this is about 2.5% of the speaker impedance. Because this system uses an active crossover the increased resistance won’t have an effect on the crossover frequency or slope, but it will attenuate the woofers by about 0.2 dB. The mids and tweeters are 4 and 8 ohms so the impedance will affect them less. When I’m done I may measure the inductance of the cables to verify that they’re not causing any rolloff in the tweeters, but that’s it. A lot of speaker cable vendors go on about all kinds of magnetic/metallurgical voodoo, but I work with a lot of electrical engineers with PhDs who spend all day designing and building sensitive high performance analog circuits, and I have never once heard them talk about the kinds of things that audiophile speaker cable companies base their products on. As far as the EEs are concerned, a wire has resistance, capacitance, and inductance. If anybody out there wants a really honest measurement and has some expensive cables, get in touch and maybe I can bring them to someone who knows how to use the fancy equipment so that we can compare.

I think that’s probably enough posting about speaker cables, you’ll see more of them when it’s all installed. If you want to read a real EE’s opinion, go back to Linkwitz.

Just a few details on the build… It is a little hard to see the markings on the black plastic  that say circuit and polarity, so I marked up an image.


For my build I’ll do:

1 – Tweeter (green circuit, cable 1, red positive, black negative)
2 – Upper mid (yellow circuit, cable 1, green positive, white negative)
3 – Lower mid (blue circuit, cable 2, red positive, black negative)
4 – Woofers (red circuit, cable 2, green positive, white negative)

Lets hope I don’t cross any wires!

Speaker Projects – Part 2, aiming higher

What am I building? It’s the LX521. Here’s a picture of me feeling starstruck.


Part 2a- The LX521, compared to what else?

Ok, so they cost about $3k to build on a tight budget… what are they competing against? The LX521 speaker was created by Siegfried Linkwitz, and he’s the original designer of the Audio Artistry Beethoven. These went for about $25k brand new in the late 90s, and the LX521 was designed to surpass them. The Beethovens might play the tiniest bit louder than the LX521, but in every other way the designer considers the new design to be superior.

Another speaker that you could call a direct competitor would be the Jamo R909. These sold for about about $19k new, circa 2009, and as far as I have been able to sleuth out they use a pair of Peerless SLS 15″ subwoofers, and so the math indicates that with their 8mm of excursion and narrow baffle they should have nearly identical low-bass capability as the LX521, reaching nearly 100db at 30hz for a pair playing together.

What these speakers have in common is that they’re open baffle dipoles- they don’t have a box, just a board that separates the front of the woofer from the back. This means that when the speakers move toward you and create a sound wave, they are also producing a sound wave of opposite polarity moving away from you. The positive and negative waves cancel out when they meet each other at right angles to the direction of motion, so the radiation pattern is like a figure 8. This reduces how much of the sound bounces around the room, and it prevents the woofers from setting up resonances in the room. It’s hard to describe what this sounds like, but what I  heard was very neutral and clean. Played side by side with regular monopole speakers, it’s pretty obvious how much you hear the room’s contribution.

An entirely different kind of speaker that operates as a dipole is a range of Martin Logan ESL speakers. Most of their speakers include standard box woofers for the lower frequencies because it’s hard to make a big membrane behave properly when it’s moving very far from its centered position. The CLX ART series does this with a special double membrane, and runs you about $25k before you buy the very-beefy amplifiers that are required to run the them.

Part 2b- sound byproducts

All of these speakers deal with the sound radiating from the rear of the speaker by allowing it out into the room where it can bounce around, and it reaches you after some delay and with some attenuation. I’m not going to give a full explanation of why that’s OK, but Linkwitz gives some useful explanations on his pages describing speaker/room interaction, and has many more pages on room acoustics and dipole bass. What’s important for my blog readers to understand is that this is just one way of dealing with the half of the sound that must (by definition) be produced by a membrane or cone oscillating in the air.

Another reasonably good way of dealing with the rear wave is to completely absorb it. This doesn’t help reverberation or resonances caused by the room (you can get rid of many of those with extensive room treatments like foam wedges) but it does clean up the midrange. A typical bookshelf speaker might have internal dimensions ranging from 8″ to 18″, and has three sets of parallel walls. The parallel walls allow standing waves to resonate inside the box at frequencies corresponding to even fractions of a wavelength. Full wavelength, half wavelength, and quarter wavelength for a typical box would span from about 180 hz up to 1600 hz, and that’s the range of frequencies where the air inside the box will show a resonance. There are a couple of problems with that.

First, that frequency range is notoriously hard to absorb. Take a look at the ratings for some sound studio acoustic foam; it has a coefficient of absorption of 0.96 at 1000 hz for a 2″ thick piece, and it has to be twice as thick to have that performance at 500 hz. That four inch thick piece only has a noise reduction coefficient of 0.5 by 250 hz. As the frequency goes down you need a thicker layer of foam or fiber to affect the sound because the wavelength is longer and it interacts with the fibers less.

Second, it happens to be right in the middle of the frequency range of the human voice. Our ears are very well tuned to this range and we do a good job of noticing sounds here. We also tend to listen to a lot of music with voices (and I watch Netflix with dialog), so this frequency range gets a lot of exercise.You can see that if we line the whole inside of a speaker cabinet with 4″ thick foam it won’t even absorb all of the sound in a key frequency range where the box has resonances, which is also a frequency range where the human voice lives.

Part 2c- Transmission lines

Another class of speaker deals with the rear-wave in a different way altogether. A transmission line speaker (mh-audio, guides the rear-wave through a long tube that is near the quarter wavelength of the lowest note that the speaker can produce. This, combined with damping material, allows the majority of the sound to be either attenuated or redirected with a delay. If the sound is allowed to escape from the end of the tube, typically only the lowest frequencies would make it through the bending turning tube to get there. It’s not a way to magically get more bass, and it’s not clear to me that the bass you get is automatically better. What it does do is create a cabinet that is mechanically rigid due to the short unsupported wall length, and a column of air that doesn’t reflect resonating frequencies back out through the cone. I encourage you to read the sites that I’ve linked, and, since I’m sure that I’ve butchered the explanation of how they work.

Regardless, one of the more famous transmission line speakers that I know of, and perhaps one of the best regarded, is the Bowers and Wilkins Nautilus. A pair of these will run you about $50k. They’re art, I think they’re gorgeous, the materials are top notch, and the design principles are quite sound. They have some good explanations on their site, and some cutaway views. I also found a brochure with a lot of cool information on the Nautilus. Although this top-tier speaker is a transmission line, I don’t think that transmission lines are not that common as commercial products. They’re necessarily larger than bass reflex or sealed  boxes, and they use more materials so they cost more and weigh more for shipping. They’re popular for DIY, but the main place you’ve probably heard them is in the (not so good) Bose wave radio.

Part 2d – The sound in the room

The last part of all this that I want to talk about is what happens once the sound is in the room. If you’ve been following the links I’ve been including in this post, and especially if you are following them one or two clicks deep, you’ll have noticed that what happens after the sound gets out of the speaker has a big influence on your perception of it. You obviously want to have a flat frequency response at the listening position, but the speaker doesn’t just send all of the sound straight to you. It also important that the sound bouncing around the room before it gets to you should have a similar frequency response. If it doesn’t, it sounds less natural because your ears expect a sound around you to radiate the same way into the room in all directions. The way the frequency response changes with direction is called the polar response. It seems that we want both the frequency response and polar response to be well behaved.

Comparing the speakers that I’ve linked above, some to better than other at this. The Beethoven speakers probably had some problems because they ran an 8″ woofer up to 2khz, and the Jamo R909 might have some slight issue with running the 15″ woofer up to 250 hz. The Martin Logans have a different radiation pattern because they have such a large radiating surface. I’ve heard a lower end set of ESLs before, and it was a little bit like wearing headphones. There was a small sweet spot, and not much interaction with the room.

The LX521 and Nautilus both split the sound up into four driver groups that are acoustically small and fairly close together. I haven’t seen a polar response of either of them, but I’m guessing that it’s pretty good. Another way of controlling this is with more speakers and DSP to send different sounds in different directions. The Beolab 90 (about $80k) is one such speaker. As processing and amplification becomes cheaper, I think that we’ll see more like this.

What DSP can’t do a very good job of, and what maintaining a good polar response won’t help with, is resonances within the room. Similar to how a speaker box will have standing wave resonances in the midrange, a listening room will have standing waves in the bass. There are calculators available to show what frequencies will be a problem for a given room size and shape, and there are more sophisticated simulation tools to take that to the next level. What’s cool about dipole bass is that it excites the room modes a lot less. You hear more of the bass and less of the room, it’s less boomy, more clear and even, and you don’t need to bend over backwards to get good bass at your listening position. That’s a large part of what made me zero in on the LX521 as the system to build. I believe it’s going to hang with systems that cost 10x as much that I’ll probably never be able to afford, and couldn’t justify buying if I could.


Speaker Projects – Part 1

I’ve been interested in speakers and sound for a very long time, and if I had to pick some point in time that started this it might have been in the summer of 2000 when I was working for Radio Shack. I only worked there for that summer before college started, but I had been there long enough to think it was weird when a guy came in and walked straight to the register to ask if we had a certain part in stock. He knew the number without having to check notes, it was the 40-1197. I can remember that number still, he wanted to know if we had any in stock since they were discontinued. I checked for him and had a good look to see if one was lying around, and when I didn’t find any he let me in on why he was looking for it. Apparently this driver could be used in a DIY design that rivaled commercial designs costing many time the cost of materials.

We didn’t really have Google yet in 2000. It had been founded, but I don’t think I knew about it. I was probably still using Infoseek or Ask Jeeves. Regardless, I found some websites and forums dedicated to DIY sound projects, and learned about the Pioneer B20FU20-51FW  and I saw that people were discussing all sorts of designs that used this driver. People were painting thin coats of glue onto parts of the cone to change the frequency response and tune resonances, people were putting modeling clay onto magnet and basket structures, and they were putting this driver into all sorts of boxes and tubes and… *not* boxes, just putting them onto flat panels called ‘open baffles’. More on that soon.

At the time it seemed that most people agreed that the most Audiophile thing to do was to minimize the number of steps between the original sound being recorded and it hitting your ears. Traditional speakers have a tweeter and multiple woofers with electronic components called a crossover to split up the sound, and people on websites like Audio Asylum and the DIYAudio full range driver forum kept saying that the best crossover is no crossover. It made sense at the time, so I ran with it. In 2001 I built some Tapered Quarter Wave Tube enclosures out of 1×10 pine boards and some smaller drivers similar to the Pioneers. They had some interesting sound. They had no bass at all, but there was a kind of clarity in the sound they did make and I was hooked on the idea of it. This is the only existing picture that I have of them.


There they are, CD for scale. It wasn’t quite a success, but I was hooked. In 2003/2004 I tried again, and built some “mass loaded transmission line” speakers using Eminence Beta 8 pro woofers and some Morel dome tweeters. This is what they ended up looking like.


They had some really serious problems. The bass was too weak without major equalization, and the eight inch woofers were relied on to run up to about 5khz- they were doing almost the entire job of reproducing the sound. At the time I designed them I thought that was a good thing- the crossover frequency was well outside of the vocal range, and so it was supposed to be really natural sounding. It turns out that they were beaming like crazy. As you move around the room the character of the sound changes drastically, and even as you sit in place and move your head. The other problem with this is that there is a sharp discontinuity in the polar response of the speakers. This means that the frequency response of the sound reaching your ears traveling directly from the speakers had a drastically different frequency response than the sound that bounced around the room and reached your ears indirectly. This doesn’t sound very natural.

In 2015 I managed to fix these speakers (Most of the way) during a visit to my parents house, and now these speakers keep their barn cheerfully noisy. I used a MiniDSP 2×4 to replace the crossover, and a four channel amplifier to allow an active crossover. This let me move all of the bass equalization into the DSP, and fiddle around with the crossover frequency. By bringing the crossover down to about 2khz where the woofer is better behaved, and by using a sharper crossover slope, the sound was improved a lot. They still have some other problems, but I think those can be addressed with some extra panel bracing and acoustic stuffing.

When I moved from spacious upstate New York to the crowded SF Bay Area, I had to leave those beasts behind and start over. The first speakers that I tried building were some cardboard box speakers, just an experiment with junk parts.


Would you expect those to sound good? I didn’t. The next design I tried out was a little bit more unusual. I tried using heavy duty foamcore as the enclosure walls. I used a little internal bracing and my theory was that if the walls were stiff enough it wouldn’t matter much that they weren’t so strong and weren’t very heavy. Here’s what those looked like.


That’s right, I even used a little PVC pipe as a port. The drivers were the 3″ full range Aura NS3, and the boxes shook all over the place when bass played. I recycled these into surround speakers for the home theater, and although they were ugly as sin they actually kind of worked in that capacity.


They didn’t have any tweeters or anything to disperse the high frequency sound out at right angles so that it didn’t  have to bounce off the ceiling to get to you, but it was a bit of a step up from the foam boxes. They were at least partially inspired by the Linkwitz Pluto, though I may have had some other influences at the time because I was coming out of a long period of thinking that transmission line speakers are the best.

I can’t remember if it was before or after, probably slightly before the pipes, I built a pair of Modula MT speakers using aluminum cone woofers and a sophisticated passive crossover. The original forum post requires a login to view, but I recommend signing up to see it. The speaker was designed by an extremely experienced electrical engineer, and it allows an unusually steep slope in the crossover to allow a lower crossover point to keep the aluminum woofers happy. Here’s my miserable picture of what that looked like.


I purchased the cabinets and almost all of the parts from Parts Express, and I just had to cut out and counterbore the two large holes for the drivers. I also had to cut out the holes for the ports in the back, but you can’t see how ugly those are. These are the speakers that I still listen to today, almost nine years later, and now that I  have them set up on stands with some good distance from the wall I can say that they sound pretty OK. All in all I spend about $300 building them, and I compared them to some commercial products at twice the price that I didn’t think were clearly better. They scratched an itch, but I knew that I could do better. There are plenty of times I’m watching Netflix and I have to strain to hear what the male actors are saying, although some of that has to do with room interaction.

In the summer of 2015 I finally had a chance to hear the Linkwitz LX521 speakers at the home of Siegfried Linkwitz, and I decided that those would probably be the last set of speakers that I’d ever want to build. They’re expensive, expensive enough that I feel reservations about building them when that money could go toward something so much more practical and humanitarian, but if I divide that cost over the next ten or twenty years then it’s not so bad. That’s what I’m telling myself.