What prevents DIY speakers to become the ultimate?

I've heard my share of DIY desings in the past. Yes, it never ends up amounting to much, as it take more than just some good parts to make a good sounding speaker!(ALL AUDIO ENTHUSIESTS TAKE NOTE, AS THE SAME APPLIES TO THE THEORY OF GETTING GREAT SOUND WITH GREAT GEAR!!!...IT'S MORE THAN TNAT!). There is NO REPLACEMENT for experience when it comes to making a great sounding speaker. If anything, the crossover itself, as well as the sum of parts and geometry, etc, take a lot of years of skill to do right!...especially the crossover in a passive design! I've heard speakers with great drivers that didn't sound ANYWHERE NEAR AS GOOD AS what more COMPETENT and SEASONED speaker designers are making! (there's no replacement for experience, dedication, perserverence, knowledge, and skill!)....and that's with less expensive or equal parts no less!
When it comes to results, I'll take someone who's been dedicated to doing his or her craft for 20 years well, before I trust some fancy gear or parts to give me sonic bliss!!!
It's all fun though...

One of the exceptions is the Ellis Audio 1801, a DIY two-way monitor that can compete with the best of 'em.
http://www.ellisaudio.com

I have helped out an electrical/audio engineer friend on a
speaker project that turned out very well. We did not have access to an anochoic chamber and that is a serious handycap. But he had LEAP and another testing/modeling programs and went into the backyard to do the tests. He also spent two years blowing off college focusing on speaker design. It requires tons and tons of dedication and some natural talent. My opinion: for most people it would be better to build a pre-designed kit, you get most of the economic advantage and it's still fun and a learning experience. The other thing you could do is try to copy a design, more difficult but possible. Regular guys just don't have the access to equipment that the pro's do, and experince does matter! But who knows maybe your the next great speaker designer!!!! Someone will be?

In my experience, the one thing I would wish for is obtaining drivers which were matched very closely. For example, if a manufacturer specs a +/- tolerance of 1.5 dB, you very well could end up with 2 drivers which are up to 3 dB apart. Thankfully, North Creek offers perfect matched drivers. Have yet to try any.

Apart from that, I must say that while I agree that a DIY cannot achieve the ultimate, how many loudspeaker manufacturers do?

Most DIY designs can compete with most audiophile products. Start with the wisdom of those who came before us. Some simple, cheap tips that people a lot smarter than me have always stressed to me:
1)Remember that mid level drivers in a good box normally sound better than great drivers in a mid level box.
2) Instead of going crazy getting the "best" drivers, think about doing the little things that add up to good sound. - Use really good glue, lay a bead of glue or caulk inside all of the cabinet's outside joints.
- Always use a gasket in the driver/cabinet interface
- Don't put a lot of money in wire. Use good copper(cheaper than you think), and stay away from the cable companies
3) Crossovers are important...
- Despite what a lot of people say, it's harder to mess up a simple topology than it is to get a complicated one right. Keep it simple
- Series crossovers are very forgiving of the tolerances one finds in drivers, caps, and coils. Series crossovers also seem to have a coherence between drivers that is hard to match, glossing over a lot of what you or the component manufacturers did wrong
- If you don't feel comfortable designing a crossover, use a designer's. Nothing flatters them more

And finally, we are normally more critical of ourselves and our work than we are of that of others. When we do a project, we know the mistakes we make, and dwell on them always. When we buy something from others, we assume it is perfectly designed and put together. Not always so.

Wasn't most every speaker company once a DIY venture? I don't think Jim Thiel, etal, slapped their label on ready-made stuff and proclaimed themselves a "commercial" company.