Introducing the LM-1S

If you are looking for the simplest possible speaker project that is affordable, uses a traditional box, and provides very good sound for the money this may very well be it. Your total cost should be around $195 for the pair, assuming you have all the tools.

The S here stands for simple. The LM-1S uses the same size cabinet as the LM-1 but foregoes the multi-way / multiple driver design in favor of a single full-range driver. As a result we loose the absolute fidelity to the top three octaves the LM-1 has, but we cut the cost in half. Perhaps the S should stand for Surround instead, as these speakers would make ideal companions to a home theater system with the LM-1/LM-1C at the front. 

Compared to the LM-1, the LM-1S is MUCH cheaper, has only 1 driver and no crossover components at all.

The Italian made 4" FaitalPRO 4FE35 has good frequency extension up to 20 kHz and really quite decent off-axis response.

The treble response seems to be a bit peaky on-axis, but this can be adjusted by turning the speakers away from the listener. Compared to boutique full-range speakers, this little gem is really pretty awesome. With the large diameter cone acting as woofer and tweeter you may even find this speaker is unusually clear at a distance compared to more traditional speakers with normal 3/4" to 1" tweeters.

Ported vs. Sealed Cabinet

Visually, the cabinet is a little large for the driver, but that's how we get the 65 Hz cut off. 7L is actually a compromise volume, with WinISD suggesting twice that.

If you use a sealed cabinet, you could use a micro-cabinet of around 3.5L and get down to about 100 Hz.  If you absolutely know you'll use a subwoofer that's a great way to go, especially with a desktop system.

Specifications:

• Sensitivity 91 dB / 1m
• Frequency : 65 - 20 kHz 
• Minimum impedance: Approximately 8 Ohms.

The sensitivity is unusually high because there is no crossover. We pretty much get the full sensitivity of the woofer. 

Shopping List

Here is a list of materials you'll need:

• FaitalPRO 4FE35 8 Ohm Version
• Denovo flat-pack 0.25 cubic feet / 7L cabinet
• 41mm port cut to 57mm / 2 1/4" long
• Speaker terminals
• Wire - about 3' to 4' of  stranded 16/14 or 12 gauge (thinner is easier to solder) wire
• M5 wood screws
• Acousta-Stuf 

I specify the Denovo knock-down flat-pack cabinets ($50/pr) because they are much cheaper than the furniture grade Dayton cherry cabinets ($190/pr) but either will work similarly. If you want something very nice looking and don't feel like doing the finish work yourself the Dayton cabinets are worth the extra.


Tools and Supplies:

• Router
• Hole cutting jig to cut approximately 3 9/16" hole for driver
• Drill and bits
• Wood glue
• Clamps
• Soldering iron and solder
• Wire cutter / wire stripper

If you use the port you'll get an f3 of around 65 Hz, 100 Hz otherwise. Remember not to put the port directly behind the woofer! Not only could it be a tight fit, but you want to minimize high frequencies from exiting. If you never plan to put a tweeter into this speaker, then you could certainly place the port in the front underneath the driver, making this speaker easier to place in tight situations.

I also recommend the use of the 3/4" multi-layer Sonic Barrier products on the internal side walls to reduce cabinet resonances. Build your LM-1S first, and if you think voices are sounding a little "boomy" then I highly suggest adding Sonic Barrier.

Fill the cabinet loosely with Acousta-Stuf before final assembly, making sure to keep the area at around the end of the port clear.

Placement

With no equalization circuit of any kind these speakers will be best with close surface reinforcement. A desktop, bookshelf or entertainment center will work great. Hiding them in a bookshelf would also make them ideal for hidden surround placement. 

If you are using them as part of a HT setup the room calibration circuits will compensate for either stand or shelf use. Just make sure to set them to "small" with a crossover of 80Hz or higher so you don't overload them.