Originally Posted by: dlwalke

Just an observation really, but the dom7 chord is famous for having that rough coarse bluesy sound - due mostly, so I am told, to the fact that it contains what is widely regarded to be the most dissonant interval in all of music - the tritone.[/quote]

As Carl pointed out, the musical context is very important. It can make all the difference. In addition, the musical timbre can also make a great deal of difference in how consonant or dissonant some musical event sounds.

Compare a dom7 chord played with a modern high gain guitar tone with a piano playing a perfect authentic cadence moving from Vdom7 to I.

The former is going to sound pretty crazily dissonant no matter what while the later is going to sound very natural & commonplace.

Originally Posted by: dlwalkeAnd yet, the major 7, in effect, trades in the dom7's extremely dissonant tritone for what is generally regarded as the second most dissonant interval in all of music, the minor 2nd (i.e., between the root and the 7th). So it surprises me that the dom7 and maj7 have such a different type of feel.

That depends on how you voice it. Most maj7 voicings do not have a minor 2nd, they only have a major 7th.

This is one of the easiest ways to voice a major 7 chord. Cmaj7 with no minor 2nd.

c-e-g-b

|------------------------|[br]|--0--------------------|[br]|--0--------------------|[br]|--2--------------------|[br]|--3--------------------|[br]|------------------------|

Now let's change that to this Cmaj7 (no5th). In this case we drop the 5th, but add a second root note. This voicing does have a minor 2nd between the high C & B. But it's very lovely through a clean tone or on an acoustic guitar.

c-e-c-b

|------------------------|[br]|--0--------------------|[br]|--5--------------------|[br]|--2--------------------|[br]|--3--------------------|[br]|------------------------|

Now just play the minor 2nd interval by itself.

|------------------------|[br]|--0--------------------|[br]|--5--------------------|[br]|-----------------------|[br]|-----------------------|[br]|------------------------|

Yikes. Now try turning on some gain & playing either that interval or either Cmaj7.

Now let's try an inverted maj7. In this case we have a 3rd inversion because the major 7th scale degree is on the bottom. So we get a minor 9th interval from the b to the c.

b-e-g-c

|------------------------|[br]|--1--------------------|[br]|--0--------------------|[br]|--2--------------------|[br]|--2--------------------|[br]|------------------------|

Context is everything.

[quote=dlwalke]Just after I typed that, I looked more closely at the other intervals in these chords and can offer a provisional hypothesis. It seems that the maj7 chord has TWO of the most consonant interval - a perfect 5th (i.e., between the root and the p5th, and also betweern the 5th and the maj7th) whereas the dom7 only has one. I wonder if that could explain it.

Yes, it helps to consider all the intervals & voicings in any given chord. But it also helps to consider the musical context. What happens before & after the chord provides context. How do the voices move from one chord to the next? And timbre also plays a big role!

Fun topic!