Comparison between Brass and Stainless Steel reeds of low-pitch diatonics in the key of LLF:

Frequency analysis (FFT) of the octave F2-F3 (1 and 4 blow) for sound and volume comparison: same distance to the measuring microphone, identical playing pressure: The 1847 Low plays louder and sounds fuller (blue curve) - the peaks at 355 and 532 Hz (fundamental frequencies) are stronger compared to the the Favorite (black curve); refer also to the envelopes.

Listen by yourself: small:1 & 4 blow on LLF Harmonicas - Comparison: Brass reeds vs. Stainless Steel reeds

FEEL THE POWER OF STAINLESS STEEL REEDS.

Nearly all musical instruments have their own resonance chambers. High-pitched instruments (for example, alto and soprano) require a smaller resonance chamber whereas low-pitched instruments (for example baritone and bass) require a larger resonance chamber. The harmonica has no built-in resonance chamber for amplifying sonic waves.

How is a full and loud tone produced with a harmonica?

Harmonicas produce sound by a free-reed system. As you introduce air to the harmonica, either blowing or drawing, the reeds are actuated, rapidly moving up and down, cutting the airstream and produce the sound you hear. Higher-tuned reeds move faster producing the higher-frequency of sound. Low-tuned reeds move more slowly, cutting the airstream at a lower frequency, producing the low, sonorous tones. The resonance chamber in the case of the harmonica is the provided by the player. The player’s mouth cavity forms the resonance chamber creating a functional unity between player and instrument. For this reason, the shape of the player’s mouth cavity is crucial to the tone produced by the instrument. An expanded mouth cavity and deep, diaphragmatic breathing combine to produce strong, fat tones. The principle of opening the jaw to form a larger resonance chamber is also used by singers who produce loud sounding low notes (like vocalizing the low-sounding vowel "Oh").

The SEYDEL 1847 Low-series (LLE to LF#) incorporate a thicker comb with deeper coverplates. This encourages the player to adopt the wider embouchure and form a larger resonance chamber (mouth cavity). Additionally the new coverplate design has a very positive influence on sonority and volume by creating greater sound projection towards the audience through the wide-opened back of the instrument.  

These fundamental improvements help to make the low notes sound fuller than on other low-tuned harmonicas without this special baritone design.

Comparison: Brass- vs. stainless-steel-reeds

Both tones where produced with Bb harps (2-draw, F = 349Hz = 3.49 on the x-axes), at the same pressures and 40 cm distance from a condensor microphone with no cover plates in order to make it more comparable.

You can hear and see the difference!

Any tone consists of the fundamental frequency plus harmonious and disharmonious overtones.

There are much more overtones produced with stainless steel reeds (see range 1600-4000 Hz). This is one of the reasons for the fuller (or more bluesy) sound of stainless steel reeds!

Fig.1: Power spectra: 2-draw (fundamental frequency of is F=349 Hz, mean of ca. 1/3 second, see envelopes below)

Sound examples:

small:Session Bb vs. 1847 Bb, 2-draw, no covers small:Session Session Bb vs. 1847 Bb, no covers

Envelopes:

Fig. 2: Signal on the left: Brass-reeds (blue in the upper panel), signal on the right: stainless steel reeds (red in the upper panel)