My kitchen has had halogen lighting for 20 years, from back when it was a slightly more efficient choice than incandescent lighting and had a pleasing, cooler (bluer, meaning the filament runs hotter) color temperature.
Progress has moved on and while fluorescent lights still have a lead in maximum luminous efficacy (lm/w), for example the GE Ecolux Watt-Miser puts out 111 lm/W, they’re less versatile than LEDs and installation is a hassle while low voltage LEDs are easy to install and look cool.
The goal of this project was to add dimmable, pleasing light to the kitchen that I found aesthetically interesting. I wanted a decent color rendering index (CRI), ease of installation, and at reasonable cost. I’ve always liked the look of cable lighting and the flexibility of the individual, adjustable luminaires.
I couldn’t find much information on how variable output LEDs work and what can be used to drive them. I have a pretty good collection of high quality power supplies, which I wanted to take advantage of, but wasn’t sure if I’d be able to effectively dim the bulbs from the documentation I found. So I did some tests.
I bought a few different 12V, Dimmable LEDs and set up a test configuration to verify operation and output with variable voltage and variable current. The one bit of data I had was that using standard commercial controllers, the lowest output is typically stated to be around 70% of maximum output: that is the dimming range is pretty limited with standard (PWM/Transformer) controllers. The results I found were much more encouraging, but revealed some quirks.
I used a laboratory-grade HP power supply with voltage and current control to drive the LEDs, decent multimeters to measure voltage and current, and an inexpensive luminance meter to measure LED output.
I measured 3 different LEDs I selected based on price and expected compatibility with the aesthetics of the project and because they looked like they’d have different internal drivers and covered a range of rated wattage.
These bulbs have internal LED controllers that do some sort of current regulation for the diodes that results in a weird voltage/current/output response. Each bulb has a different turn-on voltage, then responds fairly predictably to increasing input voltage with increasing output, reaches the controller stabilizing voltage and runs very inefficiently until voltage gets over the rated voltage and then becomes increasingly efficient until, presumably, at some point the controller burns out. I find that the bulbs all run more efficiently at 14V than at the rated 12V.
As a side note, to perform the data analysis, I used the excellent
xongrid plugin for excel to perform Kriging interpolation (AKA Gaussian process regression) to fit the data sets to the graphing function’s capabilities. The graphs are generated with WP-Charts and the table with TablePress.
Watts v. Volts
This chart shows the wattage consumed by each of the three LEDs as a function of input voltage, clearly demonstrating both that the power consumption function is non-linear and that power consumption in watts improves when driven over the rated 12V. Watts are calculated as the product of the measured Volts * Amps. Because of the current inversion that happens as the controllers come fully on-line, these LEDs can’t be properly controlled near full brightness with a current-controlled power supply, though it works well to provide continuous and fairly linear dimming at low outputs, once the voltage/current function changes slope, the current limiting controller in the power supply freaks out.
4W LED 5W LED 7.5W LED
Lux v. Volts
This chart shows the lux output by each of the three LEDs as a function of input voltage, revealing the effect of the internal LED driver coming on line and regulating output, which complicates controlling brightness but protects the LEDs. The 5W LEDs have a fairly gentle response slope and start a very low voltage (2V) so are a good choice for a linear power supply. The 4W LEDs don’t begin to light up until just over 6V, and so are a good match for low-cost switch mode supplies that don’t go to zero.
4W LED 5W LED 7.5W LED
Lux/W v. Volts
This chart shows the luminous efficiency (Lux/Watt, Lumen measurement is quite complicated) by each of the three LEDs as a function of input voltage, showing that overdriving the LEDs past the rated 12V can significantly improve efficiency. There’s some risk it will overheat the controller at some point and result in failure. I’ll update this post if my system starts to fry LEDs, but my guess is that 14V, which cuts the power load by 20% over 12V operation with the 7.5W lamps I selected, will not significantly impact operational lifetime.
4W LED 5W LED 7.5W LED
Total System Efficiency
The emitter efficiency is relatively objective, but the total system efficiency includes the power supply. I used a Daiwa SS-330W switching power supply I happened to have in stock to drive the system, which cost less than a dimmable transformer and matching controller, and should be significantly higher quality. The Daiwa doesn’t seem to be easily available any more, but something like this would work well for up to 5A total load and something like this would handle as many as 40 7.5W LEDs on a single control, though the minimum 9V output has to be matched to LEDs to get satisfactory dimming. It is important not to oversize the power supply too much as switch mode supplies are only really efficient as you get close to their rated output. An oversized switchmode power supply can be extremely inefficient.
With the Daiwa, driving 13 7.5W LEDs, I measured 8.46A at 11.94V output or 101 Watts to brightly illuminate the entire kitchen, and providing far more light than 400W of total halogen lights. I measured the input into the power supply at 0.940A at 121.3V or 114 Watts. That means the power supply is 88.6% efficient at 12V, which is more or less as expected for a variable output supply.
Increasing the output voltage to 14.63 Volts lowered the output current to 5.35A or 78 Watts without lowering the brightness at the installation; I measured at 168 lux at both 12.0V at 14.6V. The input current at 14.63V dropped to 0.755A or 91.6 Watts, meaning the power supply is slightly less efficient at lower output currents (as is usually the case).
- Overdriving the 12V rated LEDs to 14.63V improves plug efficiency by 20%.
At the low end, the SS-330W’s minimum output is 4.88V, which yields 12 lux at the counter or a 14x dimming ratio to 7% of maximum illumination, a far better range than is reported for standard dimmer/transformer combinations.
- 7.5W LED modules from JackyLED
- Daiwa power supply (alternate version)
- 16 gauge speaker cable
- MR-16 cable lamp mounts
- Digital light meter
(MS Excel file, you will need the
xongrid plugin to update the data as rendered in the graphs)
In December of 2002 (really, 2002, 12 years ago), I decided that the crappy former Sony self-amplified speakers with blown amplifiers that I had wired into my stereo as surround speakers really didn’t sound very good as they were, by then, 7 years old and the holes in the plastic housing where the adjustment knobs once protruded were covered by aging gaffers tape.
At least it was stylish black tape.
I saw on ebay a set of “Boston Acoustics” woofers and tweeters back in the time when ebay prices could be surprisingly good. Boston Acoustics was a well-respected company at the time making fairly decent speakers. 36 woofers and 24 tweeters for $131 including shipping. About 100 lbs of drivers. And thus began the execution of a fun little project.
Design Phase: 2003-2011
I didn’t have enough data to design speaker enclosures around them, but about a year later (in 2003), I found this site, which had a process for calculating standard speaker properties with instruments I have (frequency generator, oscilloscope, etc.) I used the weighted diaphragm method.
WOOFER: PN 304-1150001-00 22 JUL 2000 80MM CONE DIA = 8CM FS = 58HZ RE = 3.04 OHMS QMS = 1.629 QES = 0.26 QTS = 0.224 CMS = 0.001222 VAS = 4.322 (LITERS) 264 CUBIC INCHES EBP = 177.8 NOMINAL COIL RESISTANCE @ 385HZ (MID LINEAR BAND) 3.19 OHMS NOMINAL COIL INDUCTANCE (@ 1KHZ) 0.448 MHENRY
TWEETER: PN 304-050001-00 16 OCT 2000 35MM CONE DIA FS = 269HZ RE = 3.29 OHMS QMS = 5.66 QES = 1.838 QTS = 1.387 CMS = 0.0006 VAS = 0.0778 (LITERS) EBP = 86.7 NOMINAL COIL RESISTANCE @ 930HZ (MID LINEAR BAND) 3.471 OHMS NOMINAL COIL INDUCTANCE (@ 1KHZ) 0.153 MHENRY
Awesome. I could specify a cross over and begin designing a cabinet. A few years went by…
In January of 2009 I found a good crossover at AllElectronics. It was a half decent match and since it was designed for 8 ohm woofers, I could put two of my 4 ohm drivers in series and get to about the right impedance for better power handling (less risk of clipping at higher volumes and lower distortion as the driver travel is cut in half, split between the two).
HTTP://WWW.ALLELECTRONICS.COM/MAKE-A-STORE/ITEM/XVR-21/2-WAY-CROSSOVER-INFINITY/1.HTML CROSS OVER FREQUENCY 3800HZ CROSSOVER LOW-PASS: 18DB, 8 OHM HIGH-PASS: 18DB, 4 OHM
Eventually I got around to calculating the enclosure parameters. I’m not sure when I did that, but sometime between 2009 and 2011. I found a site with a nice script for calculating a vented enclosure with dual woofers, just like I wanted and got the following parameters:
TARGET VOLUME 1.78 LITERS = 108 CUBIC INCHES DRIVER VOLUME (80MM) = 26.25 CUBIC INCHES = 0.43 LITERS CROSS OVER VOLUME = 2.93 CUBIC INCHES = 0.05 LITERS SUM = 0.91 LITERS 1" PVC PORT TUBE: OD = 2.68CM, ID = 2.1CM = 3.46 CM^2 PORT LENGTH = 10.48CM = 4.126" WIDTH = 12.613 = 4.829" HEIGHT = 20.408 = 7.82" DEPTH = 7.795 = 3"
In 2011 I got around to designing the enclosure in CAD:
There was no way to fit the crossover inside the enclosure as the drivers have massive, magnetically shielded drivers, so they got mounted on the outside. The speakers were designed for inside mounting (as opposed to flange mounting) so I opted to radius the opening to provide some horn-loading.
I also, over the course of the project, bought some necessary tools to be prepared for eventually doing the work: a nice Hitachi plunge router and a set of cheap router bits to form the radii and hole saws of the right size for the drivers and PVC port tubes.
Build Phase (2014)
This fall, Oct 9 2014, everything was ready and the time was right. The drivers had aged just the appropriate 14 years since manufacture and were in the peak of their flavor.
I started by cutting down some PVC tubes to make the speaker ports and converting some PVC caps into the tweeter enclosure. My first experiment with recycled shelf wood for the tweeter mounting plate failed: the walls got a bit thin and it was clear that decent plywood would make life easier. I used the shelf wood for the rest of the speaker: it was salvaged from my building, which was built in the 1930s and is probably almost 100 years old. The plywood came with the building as well, but was from the woodworker who owned it before me.
I got to use my router after so many years of contemplation to shape the faceplates, fabricated from some fairly nice A-grade plywood I had lying around.
Once I got the boxes glued up, I installed the wiring and soldered the drivers in. The wood parts were glued together with waterproof glue while the tweeters and plastic parts were installed with two component clear epoxy. The low frequency drivers had screw mounting holes, so I used those in case I have to replace them, you know, from cranking the tunage.
I lightly sanded the wood to preserve the salvage wood character (actually no power sander and after 12 years, I wasn’t going to sand my way to clean wood by hand) then treated them with some polyurethane I found left behind by the woodworker that owned the building before I did. So that was at least 18 years old. At least.
I supported the speakers over the edge of the table to align the drivers in the holes from below.
The finished assembly looked more or less like I predicted:
The speakers sound objectively quite nice, but I was curious about the frequency response. To test them I used the pink noise generator in Audacity to generate 5.1 6 channel pink noise files which I copied over to the HTPC to play back through my amp. This introduces the amp’s frequency response, which is unlikely to be particularly good, and room characteristics, which are certainly not anechoic.
Then I recorded the results per speaker on a 24/96 Tascam DR-2d recorder, which also introduces some frequency response issues, and imported the audio files back into Audacity (and the original pink noise file), plotted the spectrum with 65536 poles, and exported the text files into excel for analysis.
Audacity’s pink noise looks like this:
It’s pretty good – a bit off plan below 10 Hz and the random noise gets a bit wider as the frequency increases, but it is pretty much what it should be.
First, I tested one of my vintage ADS L980 studio monitors. I bought my L980s in high school in about 1984 and have used them ever since. In college I blew a few drivers (you know, cranking tunage) but they were all replaced with OEM drivers at the Tweeter store (New England memories). They haven’t been used very hard since, but the testing process uncovered damage to one of my tweeters, which I fixed before proceeding.
The ADS L980 has very solid response in the low frequency end with a nicely manufactured 12″ woofer and good high end with their fancy woven tweeter. A 3 way speaker, there are inevitably some complexities to the frequency response.
I also tested my Klipsch KSC-C1 Center Channel speaker (purchased in 2002 on ebay for $44.10) to see what that looked like:
It isn’t too bad, but clearly weaker in the low frequency, despite moderate sized dual woofers and with a bit of a spike in the high frequency that maybe is designed in for TV and is perhaps just an artifact of the horn loaded tweeter. It is a two way design and so has a fairly smooth frequency response in the mid-range, which is good for the voice program that a center speaker mostly carries.
And how about those new ones?
Well… not great, a little more variability than one would hope, and (of course) weak below about 100Hz. I’m a little surprised the tweeters aren’t a little stronger over about 15kHz, though while that might have stood out to me in 1984, it doesn’t now. Overall the response is quite good for relatively inexpensive drivers, the low frequency response, in particular, is far better than I expected given the small drivers. The high frequency is a bit spiky, but quite acceptable sounding.
And they sound far, far better than the poor hacked apart Sony speakers they replaced.
The drawings I fabricated from and the raw data from my tests are in the files linked below:
Alas, nobody to chauffeur around. But nothing like driving around in a giant land barge to make you think about global warming: ‘scuse my effluents!
Kind of a comfy car in a rolling barcalounger way. Room for 6. The power open and close trunk firmly inserts “lazy” between “quintessential” and “american”
It is quiet and the stereo is pretty good. The dash is a giant slab of plastic, but this isn’t really a driver’s car.
The engine is surprisingly effective given the mass of the vehicle and the queasy squishy suspension.
We had some amusing rental cars in Italy. First and last a Ford Focus that was quite competent, had enough room, and handled quite well. Then we went to Portugal and rented a car to drive to Spain. Perhaps because Spain and Portugal still have some hard feelings, it is absurdly expensive to rent a car in one country and return it in the neighboring company. It would cost less to pay someone to push the car back.
So we were given a “Spanish car” in Lisbon, a Toyota Yaris with a really pronounced fuel delivery problem at anything above 1/2 throttle which had the car juddering and barely making it up hills. Hertz sent out the mechanic who asked if we had the AC on (yes, it was 40 out) and then said it was normal. I told him it felt like it was running on 3 cylinders and he said that was right, it had 3 cylinders. Now we’ve rented a couple of Yarii before, and they make it up the mountain in Italy fine with the AC on, and would easily have climbed the hills of Lisbon, but they wouldn’t take it back and besides even if they wanted to there simply wasn’t another car available in Iberia. So we got a reservation from EuropeCar and called Hertz and were told we could drop the sick Yaris off at LIS.
But when we got there, that wasn’t the case – apparently Hertz Spain would charge Hertz Portugal €25,000 if they accepted it. As we made it clear we wouldn’t be driving it away, there was suddenly another Spanish car at the Hertz downtown office.
We drove downtown where they were super nice and promptly produced another of the same competent Ford’s we had in Italy with one minor variation – the driver’s side mirror had been destroyed by the car wash just before we got there. So they gave us a nice Portuguese Renault Laguna III with the key card ignition system. It worked great and was a fine car to drive with a useful 6 speed manual transmission.
It got us to SVQ without any problems and we could even keep up with our friends in their Mercedes C230 with the strange transmission that switched into “limp home mode” immediately. Yes, the car rental adventure was not ours alone, their car, a high end rental Mercedes was flawed as well. They asked “why does the car redline at 150? Is that bad?” It took a little work to be sure there wasn’t a button or feature being missed (like some manual shift override), but no… it was a “feature” not a bug, and was to remind the driver to get to a service station before the transmission fell out of the car. It made it to Spain and back in 2nd.
When we got back to BLQ our Focus was touring around Florence, so we picked up the cheerful Yellow Fiat Panda. Pandas are great little (little) cars. They handle surprisingly well, have surprising pickup and, like the tardis, are bigger inside than outside. Even so, a panda can’t really hold more than two people and their normal travel luggage, and three is a tight squeeze even if one is only 80% full size. But we all packed in and zipped back home suddenly noticing that the yellow panda must be the year’s most popular car.
Finally we returned the Panda, got our Focus, and drove to Rome with three adults, one awfully tall 12 year old, and a lot of luggage in relative comfort and in good time.
- Quiet – generally quiet, but got a bit noisy on the 401. The AC system is a bit too zealous – it’s hard to just get a vent function on a nice day and the windows open are noisy.
- Comfortable – fairly comfortable.
- Engine – a moderate engine, responsive but not astonishingly so.
- Suspension – it works well enough but isn’t super agile.
- Basic amenities – everything that could be reasonably powered is.
- Stereo – it was good enough but the high frequency speakers point straight to the center and so it sound unbalanced (the driver’s side tweeter pointing at the passenger and being inaudible to the driver).
- Security – the trunk is large and secure.