My Little Soapbox
The industry, commercial and DIY, has gone to trying to use purely theoretical environments to judge their driver and speaker performance with the idea that building an environmentally neutral speaker will make it suitable anywhere. Part of this is not just what's best, but also what's most convenient, and more marketable. And honestly you can be very successful this way.Still, like Alison, I do not believe this to always be the best way to approach speaker design. My evidence is how many "bookshelf" speakers have become stand-mounts. The LM-1 was tailor made for music lovers with modest listening rooms and small budgets, so these measurements and methods are completely suitable and accurate for their intended purpose.
Frequency Response
Allow me to present the simulated vs. actual response. The blue line represents the simulated response, the green line is the raw far-field, 1/6th octave response of the entire speaker placed so the front baffle just overhangs a 16" wide bookshelf.
The level is offset for clarity. When overlaid, the two graphs are in almost complete agreement.The simulation used close-microphone techniques to eliminate the reflections which plague us during crossover design. The green line however was taken at 3'.
What was not expected in this design is the dip between the port and driver around 74 Hz. None of the box simulations show this. The port's actual tuning frequency is "too low." Others may call this a happy accident though, as this brings the bookshelf/desktop response to.... (wait for it!) 40 Hz in exchange for the dip at 70 Hz.
You may also notice that the curve slopes downward, which is a good thing and shows the LM-1 closely matches the famous Bruell and Kjaer target curves.
Efficiency
As a result of carefully matching the speakers to their environment, we've come up with some pretty sensitive (for small) speakers, around 88 dB /2.83V at 1 meter. That's quite nice. Not in the range of horns, but small speakers like this usually really can't get such a good result. Note that part of this is that my drivers measured more sensitive than spec in the bookshelf, around 89 dB, and that the crossover excludes most baffle-step compensation.Had we designed this blindly adding baffle-step compensation we would have ended up with a pair of speakers that were boomy, much less sensitive (83 dB or so) when placed in a bookshelf. Conversely, if we had tried to use this woofer in a stand mount we would never have this much bass. We would probably loose at least an octave.
Impedance
This is a very easy to drive speaker. The impedance stays well away from 4 Ohms at all frequencies and in fact stays closer to 6 Ohms for most of the plot. I would easily call this an 8 Ohm speaker based on this and how commercial speakers are rated. Here we have the simulated impedance charts for both versions of the speaker. The green line is of course the ported version:
These are just simulations, but the actual Z is very very close. I'll try to post them before 2017, but no promises.
Notice also the impedance below 200 Hz stays above 8 Ohms! Oh my Dark Goddess of Espresso Coffee Beans, this is a dream speaker for most amplifiers. You could practically drive them from an iPod. Any receiver or integrated amp will be absolutely over-joyed to play these speakers.
Raw Files
The XSim files are available, letting you play with the crossover design yourself. Please join us at the DIY forums here.Step Response
I don't have any tools right now to allow me to measure the step response, but I can simulate it using XSim. It's perfect for a 2-way that is not time aligned. The tweeter starts in a positive direction with just a touch of pre-ringing, and the bottom of it's response blends seamlessly into the rise of the wide-bandwidth woofer whose output is almost perfectly triangular. Outstanding!!
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