The volume is a little too low, could you turn it up a little?
Can you turn up the volume a little?
Can you make it louder a little bit, it’s hard to understand.
Kenshinさん
ご質問どうもありがとうございます。
様々な表現があると思いますが、いくつか自然な表現を紹介します。
そのI. 先生がマイクを使ってお話している場合は、下記のフレーズがいいと思います。
1. The volume is a little too low, could you turn it up a little?
音がちょっと小さいんですが、少し大きくしていただけないでしょうか？
2. Can you turn up the volume a little?
少し大きくしていただけないでしょうか？
3. Can you make it louder a little bit, it’s hard to understand.
少し大きくしていただけないでしょうか？聞き取りし難いですので。
_______________________________________
そのII. 先生の声が小さい（マイクを使わない場合）
4. Mr. Smith, do you think you could speak up a little? Thank you.
Smith先生、少し大きい声でお話していただけないでしょうか？
P.S. speak up は、より大きい声で話す、という意味です。
では、お好みに合わせて使い分けてみてください。
ご参考にしていただければ幸いです。
『先生の声の音量が小さいのでおっしゃっていることは聞き取るのが難しいです』
Because volume of your voice is low, it is hard to listen and understand.
The volume of your voice is too low to listen and understand,
で、先生に理解していただけると思います。
お役に立てたらうれしいです。
Well, if you can't hear your teacher, the chances are, it is a deficiency in your sound system rather than your teacher's - probably you need to adjust your settings and volume control! However, either sentence one or two will suffice in this situation.
When the volume is too low, you can say "I am having trouble hearing you" or "It is hard to hear you". You can then say "Please turn up the volume on your microphone" or "Please speaker louder".
音量が低すぎる時は：
"I am having trouble hearing you".（よく聞こえません）
"It is hard to hear you".（よく聞こえません）
その後：
"Please turn up the volume on your microphone".（マイクの音量を上げてください）
"Please speak louder".（もっと大きな声で話してください）
If you believe the teachers technology is at fault rather than your own you can can say "Your microphone is very quiet" and this lets them know they may need to increase their microphone sensitivity so that you can hear them.
"I can hardly hear you" - This tells the teacher that you are having trouble hearing them. The word 'hardly' has the same meaning as 'barley'. It implies a small amount of something. It tells the teacher you can hear them, but only just.
こちらではなく先生の設備に問題があると思うのなら：
"Your microphone is very quiet"（そちらの音がすごく小さいです）
と言えます。音量を確認するよう促す言い方です。
"I can hardly hear you" - 先生の声が聞こえづらいと伝える言い方です。「hardly」は「barley」と同じ意味です、量が少ないことを表します。先生の声が少ししか聞こえないと伝えています。
Can you turn the volume up please, I can hardly hear you
I can barely hear you, can you turn the volume up a little please
Your voice volume is a little low
When telling your teacher about the volume then it is also good to ask/say this politely, you can add please to do this
to barely hear - means the same as hardly being able to hear so you can hear very little
Excuse me but I can hardly hear you. I think your volume is too low.
I can barely hear you, can you check to see if your volume is too low?
The two sentences you see provided above are terrific ways to express to your listener that their volume is too low and you are not able to hear them. In the first sentence you will notice the word hardly and in the second sentence you will notice the word barely. Both of these words mean not easily. These words would make great additions to your vocabulary.
おっしゃられている内容は、以下のようにも表現できると思いました(*^_^*)
The volume of your voice is low.
「あなたの声のボリュームが小さいです」
I can't hear you clearly.
「はっきり聞こえないです」
以上です。
少しでも参考になれば幸いです(*^_^*)
ドイツ 
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