Since the 1/4 inputs on all the current products are mono, can someone confirm that I should have no problem running this cable to connect my laptop to a single channel of a L1, F1, or T4s mixer. This way, I don't have to use takeup two inputs. It has a stereo on the 1/8 end (laptop) and 1/4 Mono on the other side that plugs into the Bose input.
The cable you refer to will work as far as the Bose equipment goes, however -- it is not a proper method to convert stereo to mono. It is hard on your laptop's output stage and may cause it to overheat and permanently damage it. The 1/8" TRS connector is wired to simply short the L and R signals together.
There are several devices designed to do what you want. They properly convert a stereo signal from a "consumer-level" device (laptop, tablet, phone or MP3 player) to a "pro-level" balanced mono signal suitable for any of the devices you mentioned.
RapcoHorizon makes a couple of devices: the LTIBLOX (mono output only) and LTI-1 (mono or stereo output).
Whirlwind makes several as well: The ISOPOD (mono output only), the pod-DI (mono output only), and the PC-DI (mono or stereo output).
I'm sure there are other manufacturers as well. You can find them on Amazon or a lot of music equipment websites. These devices provide the proper circuitry to sum the two separate stereo left and right unbalanced signals to one mono signal. (The LTI-1 and PC-DI can provide either one or two mono signals or individual left and right signals.)
As far as the T4S goes, I would highly recommend connecting via USB instead of an analog cable. You can route the left and right signals directly to main or channels 3 and/or 4 (to take advantage of the ToneMatch presets and individual volume control.) You can route both the left and right USB signals to one channel (either 3 or 4) to sum them to mono. (I know you're looking to use only one channel on your T4S, but for others reading along -- if you want to maintain true stereo output you can route the USB left signal to channel 3, panning it left, and the USB right signal to channel 4, panning it right.)
Also, I know that all the Bose product's 1/4 is mono, but how often do other manufacturers have a stereo 1/4 input. I would assume only on an older home or prosumer stuff or are there plenty of popular professional devices with 1/4 stereo?
Could one use a stereo cable like this, and just set the computer or mp3 player that has the 1/8 connection to Mono or is this a no-go, b/c the 1/4" connection is still stereo going into the L1 and or T4s?
I can't remember seeing any pro devices where the 1/4" inputs are stereo -- not to say they don't exist, but they're probably pretty rare. One the other hand, 1/8" inputs are very often use TRS connections wired for stereo (the Sennheiser bodypack being a noted exception.) 1/4" outputs are a whole different story -- lets of headphones use 1/4" TRS wired for stereo, and newer ones use 1/8" TRS wired for stereo. Then throw in the use of 1/4" TS connectors, XLR's, RCA's, splitter cables and everything else and you have a real connector salad!
I came across a handy web page that is a condensed version of balanced vs. unbalanced at this link from Datapro: DataPro's Guide to Unbalanced vs Balanced Audio It also lists the common usages of all the connectors. Add to this the fact that TRS connectors can be used for either balanced or stereo, and confusion can abound.
That's why manuals or diagrams explaining the exact specs of every jack or plug are very important when connecting one piece of equipment to another.
So I just want to confirm that the little adapter posted above which converts 1/8 stereo to 1/4 Mono isn't really any different than the cable I originally posted as it could still damage my equipment.
Are you able to confirm if I use a stereo cable (1/8 to 1/4) and set my device's settings (laptop, phone) to MONO that it still won'twork bc the cable is wired for stereo on both ends, although it would technically be dual mono with the setting engaged) but still going into a mono input (L1, F1, T4s)
1/8" TRS to 1/4" TRS from a device set to MONO to an L1, F1, or T4S probably still won't work. Even though the sending device is set to MONO, it still sends that mono signal to both the Tip and Ring connectors on the jack. The receiving device sees activity on the Tip and Ring, thinks it's a balanced connection, and flips the Ring signal's phase causing the two signals to cancel each other.
This does raise a question that I don't know the answer to: I don't know how your laptop behaves using the 1/8" TRS to 1/4" TS cable from your original post when it's set to MONO. I don't know if having the Tip and Ring shorted is still bad for your laptop if both signals are identical. I'm leaning towards "still bad" as the L and R signals are still being amplified separately (even though they're now the same signal) and shorted together.