There is a speaker manufacturer in my city and their expensive speakers have a very nice look and finish. They are too expensive for me so at first I did not listen to them. I bought crossover coils from that speaker manufacturer that I used in the speakers I made, the coils were labelled with the inductance. But my latest speakers sounded bad so I measured their response and the crossover was all messed up. The inductances were wrong!
I spoke to the manager of the manufacturing plant and asked to hear his expensive speakers. They sounded as bad as mine so I pulled out my real time audio spectrum analyser and showed him the awful frequency response caused by his inductors with wrong values. They made the inductors there and quickly fixed the problem. How many people bought those speakers with the wrong inductors? And did not notice the bad sound? Another type of audiophools.
Amazing - the moral here: never trust anybody and check everything.
Many of our group built trasmision-line speakers, and ripped-off the xover design from the commercial version. We wound the inductors on styrene solder bobbins with 18 SWG wire. All calibrated to 0.5% on the companie's inductance bridge.
Same priciple as you, but about cars (autos). I bought a Ford Granada 2.8lt V6 auto. It was the best car I ever had- long , leggy luxury. But boy, did it drink juice (gas), specially at a ton (100MPH). Juice was cheap then, so no sweat. You could drive all day and still feel fresh as a daisy. But in the winter the Granada huffed and puffed on idle. I checked everything, points, thermostat and so on; couln't find a thing wrong, so I gave up and decided to live with the poor idle in cold weather.
Some time later, while changing the air filter, I noticed that the end of a small rubber tube that connected to the inlet manifold had cracked with the heat. So I thought: cause of the poor idle. I was going to use the old dodge of cutting off the perished end and re-fitting, but, when I took the tube of the boss, there was no hole into the manifold- just ally.
I unbolted manifold from the engine and, sure enough, there was no hole. So I drilled it out, fitted the manifold and shortened tube, and never a problem with rough idle again (the pipe connected to a thermostativally controlled valve and then to a vacuume servo which moved a flap: either cold air or hot air from a shield on the exhaust manifold). Similar to you, I wondered how many people were driving around in the winter with rough running Granadas!