I've got into the habit of doing singing exercises in the morning and evening.
In the evening I'm often struggling to reach A110Hz. However in the mornings I can get down to E and beyond, sometimes even Bb (a disparity of nearly an octave -- 10 semitones!).
It's lovely, but if only it lasted! Is there any specific training for this? What sort of disparity might a trained singer expect.
I notice a related question: Why is my voice lower pitched when I get up in the morning?
Our voices are lower in the morning because the vocal cords and the subtle musculature which surrounds our larynx are in a state of relaxation from resting the voice overnight.
In my case I used to sing professionally as a bass in a nine a.m. choir then as a tenor, my legitimate range, at the 11:00 service. In order to have the bass notes for the 9:00 a.m. service I would go straight to the gig without warming up. By the time I'd sung an hour as a bass (baritone really) my voice had crept back up to it's normal range of tenor.
If you want to improve your lower range, practice singing as relaxed as possible with a full breath throughout, probably more breath than you think you need. Keep breathing but don't push on your voice. It will gradually become more adept and full in the lower register through relaxation. Think of a guitar string which vibrates at a higher pitch when tightened, lower pitch when loosened.
It is true that you can lose the lowest notes throughout the day, but 10 semitones is quite dramatic! It makes me wonder if you are straining your voice during the day. If you are, it would help to address that.
Aside from that, the best thing I can suggest is spending some time practicing low notes specifically. Lower notes are generally easier for people to hit than higher notes, but the lowest notes can actually be quite tricky. At a point it's like they require their own technique. Some things to pay specific attention to:
Breath support -- obviously, all singing requires good breath support, but I would expect you to need much more breath support for the E than for the A.
Posture -- In my opinion, it can be far from perfect for most singing as long as you have the breath support... but for me it makes a difference on the lowest notes.
Larynx position -- the larynx naturally raises a little as you go up and lowers a little as you go down, but you want to make sure it's relaxed. Make sure not to push. Pushing the larynx down as you sing lower is a way of getting a bigger sound (probably unconsciously), but it limits your range.
Volume -- the lowest notes can get pretty quiet... which you might not notice first thing in the morning, but then after a day of hearing louder sounds and singing higher passages at much louder volume, it's natural to come back to those low notes and try to push them out. (Well, it is for me at least. It's not something I'd do on purpose, but reminding myself to shift gears when going lower has helped.)
Additionally, when practicing low notes, focus on getting a clear tone first, even if it's barely audible. When you get better at producing a tone consistently, then it is much easier to make it a little bit louder. (It'll still be quiet, but it'll be better than "barely audible.")
When you're doing exercises, make sure to visit your lowest notes before your highest ones... and if you go back down to low notes throughout the warmup, it helps retain them (even though you still lose a few semitones... 10 is much more than I would expect). The rest is just practice and attention to that part of your range.
Just keep doing the exercises. At least you then have the proper reflexes and control and vocal cord resilience for the time when the depth is there. Which may eventually lower the barrier when it isn't readily.
I'm a bass singer. A few things I've noticed is my voice is always best while fasting. Sleep and fasting happen at the same time. If you plan to sing, give yourself about 4 or more hours after your last meal. Also, never over eat. Hydration is important too. Don't sing when you're not properly hydrated. The foods you eat affect your ability to sing. Non singers might not notice a problem with chocolate, sugar, or tomato, but singers who are in the bass range have probably more sensitivity to foods that commonly cause tissue inflammation.
