What prevents DIY speakers to become the ultimate?

I am talking about DIY companies (North Creek, Zalytron, GR research and so on)and possible real DIYers.

We can get the best drivers on the market (Scanspeak, Sears and so on) and Ultimate parts (Hoveland, Alphacore and so on).

Why the sounds of DIY is not the ultimate (or at least very closed to the up scale (say..>10K) speaker?

The total brain power (= total # people with good brain)of the DIY speakers may be less than the comercial speakers, but I don't think they are any less stupid either.

The only thing I can think of is the cabinets. Comercial one may have better access to get a better design (computerized and so on), but can't think of any other things.

I know one reason that DIY speakers are not as popular is probably the low resale value, but not sure if it has anything to do with the quality.

Also I have heard a lot about DIY speaker being good or excellent, but never heard the real comparison (i.e. DIY speaker model A is better than Thiel or Dynaudio (an so on) model B or something or at least price-wise. Is it just that they don't have a direct A/B access or just that they are in fact not really that good?

Love to hear more about this.

I think that DIY speakers COULD be the ultimate, but usually aren't because many of the folks interested in DIY are also interested in bang for the buck. Now if a DIY'er spent $10,000 on drivers, crossovers, cabinets, etc. it very well could be SOTA.
I don't think most people have access to an anchoenic chamber, Fast Fourier technology, and all the other technical goodies to check and confirm the development and results. Never mind the electrical/ acoustical/ mechanical engineering required. A good speaker is more than a collection of off the shelf parts.
Mvwine and Unsound have said it all. Outside of quality parts, technology and skill are required to make a killer product. In most cases, one or the other is lacking to some extent in DIY designs. Sean

I used to be a DIY'er...I worked at store where we sold drivers, X=overs etc. I tried my hardest to get a great sounding speaker (I was paying cost too and not retail) and never made it. It is very difficult. Also, because I was only making just one speaker there is no economy of scale. I had to buy the wood, make the cabinets, go buy my parts, kept testing everything...and came out with a nice speaker, but a not great one. In my case, I guess, talent is also an ingrediant that was hard for me to DIY. It was lots of fun though and my friends ended up with my creations for cheap.Wish you well.
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.
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.
I have been a DIY speaker builder for 20 plus years. I even worked at a small speaker kit company in college, making all of their cabinets. After college I kept building speakers and buying the best parts I could get my hands on. I am a trained cabinet maker and have tried just about all of the differnet types of cabinets and construction styles. I can build a very good "box" Many of them sounded good but none of them great.
Then a few years ago I build a set of Northcreek Rythem's and the whole DIY thing changed in a HUGE way for me. As it turns out the crossover was the key to way my speakers never sounding great. Granted Northcreek cabinet designs are excellent but their crossovers do set them appart.
I have now built many different Northcreek speakers and they all sound GREAT. I have a friend who owns a set of ProAc 3.8's and my Rythem sig. much better (I hope he doesn't read this) . I have another friend who has also built Northcreek speakers after hearing mine.
Also just to give you a refernce point my system is:
Sony AX777es CD/sacd, Ayre V1 & V3 amps, Arc LS25 pre, EAD Sig, processor and Cardas ref. cables.
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.
DIY speakers can offer superior performance at a reasonable cost. Subwoofers are a great place to start because nearly all commercial designs use less than optimal enclosure volumes and/or poor quality amplification and crossover. Try the Adire Audio Shiva in their suggested 5 cubic foot vented EBS alignment and be astounded by the level of performance achieved for about $200 in total parts cost. Add an amp and the Outlaw ICBM electronic crossover and you have a giant-killer for peanuts. Sealed box subwoofers are even easier to build and usually yield excellent results. Madisound also offers an array of kits with or without cabinets that are competitive with the best designs available commercially at a fraction of the cost. My current stereo system uses the new Thor speaker (based on SEAS Excel components) and it is superb in every respect.I have used their LEAP crossover design service with fine results on a number of "from scratch" designs of my own. Search the web for "DIY audio" and all sorts of other useful sites can be found to help with design and construction. Give it a try!
A while back I heard some extremely good DIY speakers. The guy had worked on them for years. He made the comment that had he paid himself minimum wage, he could have bought a fine new car. I believe he had about $1000 in the guts with a few $100 more in the cabinets. He told me he'd tried to get the crossovers right for over a year before giving up and using someone else's design.
If and when DIY speakers become the "ultimate", they will in all likelihood become "commercial" speakers. The art and business of commercial design is to manufacture a speaker with the cheapest quality parts, make it sound very good (better than DIY for around the same cost) and sell a ton of them. A $300 retail bookshelf (Triangle, PSB, Sound Dynamics, etc.) probably costs the manufacturer around $70 or less to make. But it will sound and look better than anything that the average DIY can make for $300 in parts and their time (at minimum wage). Of course there are exceptions to this, perhaps a Northcreek kit made by a DIY who is also an experienced woodworker.

Most DIYs don't design their speaker projects, but rather use a proven design (Proac clone/ Lowther horn/pipe) or build a kit. This is the safest approach, but don't expect the "ultimate" sound.
I'm interested in making my own speakers as well. I'm not interested in engineering my own- nor am I interested in re-inventing the wheel. I understand that the Thor is a solid design, are there others? Is there a short list of Best DIY kits or designs.
Northcreek notwithstanding, a non-dedicated non-OEM can't buy tight-production tolerance drivers required for superb-imaging, ultranatural response. As alluded above, the best manufactures have custom-made drivers specced within a tight sensitivity window, and even then sometimes pair-match them. (Verity even jeeps a response curve on each midrange for replacement if needed!)
It's a given that Madisound, Solen, etc, get the outer 2/3 or so of a given driver run! I've built a couple of 2 and 3-ways, and once I heard a midrange voicing change of only 1/3dB over 1.5 octaves during a crossover massage, I gave up, knowing that I'd NEVER be able to afford drivers that well matched! This is by far the largest impediment to DIY
ULTRA-high quality production. Though a reseller can sit there and wade through a box of drivers, sorting their sensitivity with a Radio Shack SPL meter, and then selling so-called "matched pairs", that's only going a short way to providing yje standardization required, 'cause you gotta do it with the crossovers next!
Tweeters and caps are notoriously wayward in spectral response. When I heard Verity Audio's midrange, I cried, and now have a couple crates of nice big inductors, caps, resistors, etc., if anyone wants 'em for a dime on the dollar! Spendor, Revel, Snell, and even Boston (!) do a VERY creditable job of pair-matching and building to a target reference with decent precision. Who's going to build us DIY'er some clones to work with? I'll stick to power cords and other non-transducer components....
My hatsoff to those still trying!
Although tempting,I passed on DIY kits...it is hard to justify spending $500-600 on a pair of DIY monitors when you can buy a very good pair of used monitors for that kind of cash...such as the SPendor 3/5,QUad 11L,etc...and be certain of the outcome.. today even $500-600 new will still get you very good sound... w/ alot less headaches...
I spent about $1400 on a pair of DIY speakers, and am extremely pleased with the outcome. I built a set of Voigt Pipe cabinets from oak, and loaded in a set of Lowther EX3 single drivers. The sound is exactly what I was looking for, and the job was quite easy. Didn't have to worry about building a crossover, because I didn't need or want a crossover in my speaker system. Just one, fullrange driver per channel, with point source radiation. No problems, very happy, saved money.
In my experience (twentysomething years of amateur speaker building), crossover design is what primarily separates the men from the boys. Other significant factors can include custom-tailored drivers and exotic cabinet materials.

Note that in my twentysomething amateur years I've amassed perhaps as much experience as a professional does in his first year or so. And I don't have the engineering background that a professional does.

The main practical advantage of DIY is that there are no layers of price markup, and the labor is free (or nearly so). This means that DIY speakers can include a lot of painstaking detail work (especially on the cabinet) that would be prohibitively expensive for a manufacturer.

For me, the appeal of DIY is the joy of creating something that no one else has ever created before. I'm tweaking a high efficiency monster in my living room right now. Yup, it's R&D for a (hopefully) commercial product, but it's also a lot of fun. Assuming my prototypes validate the concepts I'm exploring, I'll engage a professional designer before going commercial.

So, can a DIY design be the ultimate? In 1998, a first-generation commercial effort by longtime amateur designer Siegfried Linkwitz walked away with Stereophile's "Speaker of the Year" award. The Audio Artistry Beethoven was essentially a commercial incarnation of a DIY design, and in fact you can go to Siegfried's website and learn how to build your own Beethoven equivalant, called the Phoenix. I would suggest that amateur speaker builders in the same league as Siegfried Linkwitz have a shot at designing and building a truly "ultimate" loudspeaker. The rest of us are somewhere farther back on the learning curve.
Some folks prefer the Scan-speaks design, Northcreek. Like Njoy, I prefer the Seas Excel design, Thor, an MTM. Thor at under $2K! audiokenesis summed the difference quite well DIY vs commercial. Linkwitz has finally answered the big commercials with his Orion, an open baffel, dual Peerless XLS + Excel W22 (crossed at 1500hz to the tweet) + Excel tweet. The only problem here is that you need to use a ss multichannel amp. Its active xover. So if you love tube amps, won't go. But you can use a tube pre with these. There is not a commercial alive that can touch them, well maybe the big Burmesters at $50K! So as I see it DIYer kits are the ultimate. Now can anyone predict if the commercial market share will take a small hit or big hit from Northcreek or Seas, and will this be soon or much later??? I doubt if anyone wants to take a stab, but something to think about for sure.