I see a lot of DIY MTM speakers are of a transmission line design. My concern is the bass. It seems from some of the reviews and such on TL speakers that the bass is "different". I've never heard any TL speakers before so I don't know what this "different" is.
I guess if I tell you what I want from a speaker you can tell me if a TL is the answer. I like solid, tight, punch in the chest type (double) bass. Not boomy, rattle the license plate frame, rollin' the dubs kinda bass.
The short version of my answer is YES, I think you'll like the sound of TL bass. To my ears, it does all that you describe.
I've been listening to TL speakers for about 10 years now. First the Salk SongTower, and more recently the Salk Veracity ST. The ER18 MTM shares the same cabinet designer (Paul Kittinger) as do all the other Salk MTM tower cabinets. My first reaction to hearing the SongTowers for the first time was that I couldn't believe how potent and clean sounding the bass was. It was not exaggerated, boomy, or muddy sounding at all. Without the exaggerated boominess, there was more bass detail than I'd heard with other speakers. The bass was all there while remaining relaxed sounding – as if the speaker & amp were not straining at all. I've known the bass sound of sealed cabinets (tends toward over-damped, kind of lean & dry sounding) and ported cabinets (tends toward under-damped, more potent, less lean & dry sounding – the opposite of lean & dry is fat & wet, but that makes no sense at all). So I decided the TL sound was something totally different. Basically, I think Paul Kittinger gets the balance between over-damped and under-damped just right for bass, and he could achieve that same balance for TL, sealed, or ported designs.
The ER18 MTM design achieves an F3 frequency of 35 Hz. (F3 is the frequency at which the bass response has rolled off by 3 dB from the sound above that.) For music, that is good. For the bass effects in movies, you'll probably want a sub-woofer as well.
Also, I seem to have a sensitivity to the 1k range so if there is a mid-range adjustment or equalizer involved I usually knock that region down a bit. I guess I like bright, but not "bitey" top end. Basically I would describe what I'm looking for is distortion-free, smooth, yet hard-hitting. So, would I like a TL or do you think I would like your basic ported design.
The TL bass has no effect at 1000 Hz. In the ER18 MTM, that range is entirely due to the ER18 mid woofer. It's frequency response is very smooth across the whole mid-range. It crosses over to the tweeter at about 2200 Hz for the dome tweeter version, and a bit higher, about 2600 Hz for the ribbon version.
BTW, I have a $400-$500 budget. I've been considering the Parts Express TriTrix but I'm leary of the TL design. I could be persuaded to spend a little more on the Murphy/Kittinger ER18s found on this forum if you could convince me that their sound is for me.
The ER18 MTM is definitely in a class level above that of the TriTrix. Maybe two class levels above it. I think it's well worth the extra cash.
By now you have read the write up and realize there are two versions of the ER18 MTM, with different tweeters. One has a ribbon tweeter, and the other has a very good quality dome tweeter. The ribbon version is a bit more expensive. But you can save a bit if you get the dome tweeter version.
Meniscus Audio has done a good job with these.
https://meniscusaudio.com/product-category/speaker-kits/page/2/ . They offer a variety of 'bare bones' and 'full kit' versions for both the ribbon and dome tweeter designs.
If you can build doors, you can probably easily build these cabinets. The trick is getting the cabinet edges to fit with the joints all tight and at right angles. I made the cut list with that in mind. I bought 4'×8' MDF sheets at Lowes' and had them cut at the store into 4' long×12" wide strips. Their panel cutting saw made that work easily. From those 12" wide boards, I used a sliding miter/chop saw to cut all the side pieces, tops, bottoms, and braces. Because they were all the same 12" width, I think things fit together more easily.