Neutral, transparent, warm

Warm may mean more than one thing… you have to read the word in context. It can mean midrange and bass bloom (fully fleshed out midrange and bass). Or tipped overall tonal balance towards the bass, or attenuated high frequency.

Sound quality can be thin like from a small radio… as sound quality increases the presence of each of the frequencies is increased… in older electronics there was lots of treble and bass and thin unfleshed out midrange. So, a female singer has a thin high pitched voice. But in good warm systems a female voice will have heft and width… be hilly fleshed out. This is mid-range bloom… a great thing… putting the midrange in proper width and volume to treble and bass. This may not mean attenuation or a preponderance of bass.

To me warm and neutral are mutually exclusive. I think that transparent is also difficult to meld with warm. Perhaps a speaker can be both transparent and warm at different frequencies. I will use the Harbeth "house" sound as an example. Warm yes, neutral absolutely not and transparent perhaps but not to my ears. Warm=colored. 

Transparent pertains to the background and image specificy. Black/quiet background with images suspended on space… as opposed to “a wall of sound”..  

So, I find Harbeth to be slightly warm yet very natural/transparent. However I do not find it "Fast". I had Totem and KEF speakers and listened to many B&W's and found them to sound 'Fast" - but can I describe 'Fast" for you? Perhaps Lively is closest. I would suggest listening to as many speakers as you can and you'll eventually find adjectives that work for you.

For instance, I didn't understand a 'grainy' sound said about DAC's until I had heard enough of them and suddenly I heard one that sounded 'grainy". 

I don’t know if it’s still available, but at one time Stereophile offered a little pamphlet containing all the terms used (some coined) by the father of subjective reviewing, J. Gordon Holt.

Neutral and warm refer to frequency balance, transparent does not. Think of transparency like the pane of glass in a window between you and an object on the other side. If the pane of glass is absolutely transparent, removing it will in no way change your perception of the object. If you then install a not-completely transparent pane, the appearance of the object will be effected, to one degree or another. One effect can be the glass changing the color temperature of visual images passing through it. That is analogous to a loudspeaker being cold or warm---not neutral

A way to simulate the effect of transparency and lack thereof is to take a camera with an adjustable focus lens, and alternate between perfectly focused and just slightly out-of-focus. When perfectly focused the lens appears to be invisible---the image "tack sharp"; when slightly de-focused the image of the object becomes softer, a little "diffused" or smeared. In worst cases texture or grain will be added to the surface of the image. Also, the de-focussing can reduce your ability to see depth-of-field (front-to-rear layering, as in a symphony orchestra on a stage), and objects can be smeared together. All these visual terms, concepts, and observances apply equally to the high-fidelity reproduction of music.

If a loudspeaker isn’t perfectly ’neutral" (none are), it will change the "color temperature" of instruments and voices; it will change their inherent timbre. Since all loudspeakers are short of perfectly neutral, hi-fi consumers must pick the coloration they find least objectionable. That’s why loudspeaker preference is so subjective. Many audiophiles---while appreciating the transparency of ESL’s---find them a little "cold". ESL fans find dynamic speakers too warm. It’s been this way for a long time, and probably will for the remainder of our lifetimes.

In the early days of hi-fi (post-WWII and into the 1950’s)---when dynamic loudspeakers were really bad---audiophiles were astonished when they first heard an ESL design (the QUAD ESL hit the market in 1957). I know I was. The ESL’s sounded far, far more transparent than did boxed speakers (this was before Jim Winey in 1970 introduced his Magneplanar loudspeaker, itself a planar-magnetic design). Dynamic loudspeakers have been greatly improved over the past 6-7 decades, but ESL’s still sound more transparent (imo) than almost all box speakers. Magnepans are in the middle, still not as liquidly-transparent (a JGH-coined term) as ESL’s..

And then there are horns and ribbons. ;-)