Any way to mod the TAD-803's ?

Well, I took out the drivers and found that this is actually the crossover version. However, as they don't seem overly bright to me (with a tube amp), this is probably the better situation.

Do the SD units (the ones without crossovers) have better drivers? Or is the crossover simply removed. On the website it seems to imply that it uses a very similar albeit different driver.

Basically, do you think I could simply install a switch like the new 2007 models?

Cleaneduphippy - I actually did e-mail Paul and asked why the moon-rocks would fix the problems, and asked what else could be done. I've done some speaker design before, so I was curious as to how decreasing the volume would improve bass response, unfortunately I was thinking of sealed containers. (I might go to home depot and get 20 lbs of white marble then roll it in flour =P, just kidding on the flour).

He responded- "Moon Rocks are a specific material with real science based audio properties. (marketed like snake oil for fun!). They eliminate the cabinet side wall sound - place you ear against the 803 - you will hear eerie distorted midgange that comes off the cabinet walls (all speakers have some of this), mixing smearing the driver sound from behind. The rocks deaden this cabinet noise plus the rough sound absorbing rock mass stays piled at a 45-degree angle leaning against the back wall (other materials settle to the bottom, moon rocks stay in place). This rough slanted heavy back wall behind the port helps deaden cabinet noise. Moon Rocks will definitely aid the rock music cone confusion you mentioned. The bass from the 803 is relatively flat with a slight bump up. This bump up when driven hard competes with single driver midrange. Moon Rock cabinet volume reduction behind the port eliminates this bass bump - flattening it further, the cone stops gyrating out of control from cabinet noise backlash."

I'm not sure how it would deaden the cabinet noise, and he stated that it was not intended to couple the speaker to the ground better. I'm assuming the biggest effect is probably a cabinet volume reduction. It's possible that the speakers were originally designed with a box that was too big. Reducing the volume would reduce the qts and cut out a hump if there was one there. Unfortunately, unless the port length was also increased significantly, I'd think that this would effectively drop out a lot of the bass originally provided. With a subwoofer integrated, this may not be a real issue, but he didn't mention where the hump was located. If the bump is in the 85-90 hz region then there may still be a problem.

I opened the cabinet and noticed a few things.

A) There are two large wooden disks glued to the bottom of the box. I'm assuming that these were placed there for one of three reasons. 1) Perhaps this was originally a tweak to reduce cabinet volume after noticing the hump. 2) Perhaps simply to add more weight to the bottom of the box. 3) maybe an attempt to fix a resonating node on the bottom of the box.

B) The walls are very thin and corrugated to some extent. I'll probably try to add more structure to this using the putty advice previously mentioned. The walls are also made out of particle board as opposed to MDF board, this will naturally induce more resonance.

C) The driver isn't coupled to the cabinet very well. First off the screws were very loose (most likely so as to not strip the thin particle board wall). Secondly, there is no seal whatsoever, the metal backing of the driver is coupled directly to the laminate/particleboard. This might not be a big issue in vented designs. But it's probably better to over-design than to risk some weird leaks or vibrations. I'm assuming that the lack of any foam also transfers a lot more vibrations directly to the cabinet. (which I mentioned was very thin and resonance prone)

D) There are air leaks in the back binding post plate. Once again, this may not be a huge problem in vented designs; but it will change the frequency response somewhat, and may cause some noise.

Further Testing:
After doing some simple frequency analysis, it seems like the hump occurs at 90 hz with a slight recession at 100-110. Meaning a subwoofer won't do much to remedy the situation unless the crossover point is set to 100 hz (probably not a good solution). Presumably because I have the crossover design there is also a moderately large hump at 3khz, there's really nothing that can be done to fix this aside from changing the crossover manually or equalizing the original signal.

Some of these results may be skewed slightly by room acoustics, I'm simply reporting what I found in my specific case.

I purchased some putty, a little weather stripping and 50 lbs of gravel for $10 total at home depot. Let's see what happens.

After putty-ing the inside with special attention to the corners, weather stripping the basket ring, and filling each with 10 lbs of gravel... I can say that there's a decent difference in sound.

First off, contrary to what I thought would happen the bass was extended deeper... Now I can't attribute this to the gravel as more should have rolled off the bass but fixed the hump. Before the bass began to roll off at 70-75 hz.. now it begins to fall at 50 hz... This may be due to added weight, mechanically decoupling the driver a little with the weatherstripping, sealing off all extraneous air holes, or decreasing energy lost to the cabinet using the putty.

Secondly, the speakers can play a bit louder before breaking up. Not too much more, but it's still noticeable.

Thirdly, there's something different about the sound.. almost like it's a little thicker or richer, a bit less airy than before. This is the change that I don't welcome quite as much. It's not a big difference though, and I may grow to love this new sound, who knows.

Finally, heavier pieces have been cleared up a bit, most likely just due to the solidifying of the entire design, and possibly due to the hump at 90hz getting fixed (which tended to muddle the mid-range.)

I'll give it some more listening tomorrow once the putty has completely dried.

Rob,

Thanks for posting this; I just got a pair of the 07 version; just couldn't resist to try them at that price :)

Looking forward to your impressions after listening a bit more.

I've had mine for a week or so and they have broken in nicely; fq. range does not reach too low, but I am impressed with the accuracy and details in mids/highs. For strings, piano, and percussion instruments, this speaker is amazingly real. With a nicely blended subwoofer these things will sound as good as speakers costing much, much more.
The 2007 version is internally covered with some kind of foam. No moon or mars rocks added yet; I'll give it a try with gravel and see if the lows can be extended as Rob says.