Wikipedia:Reference desk/Archives/Science/2023 May 22

= May 22 =

Desk microphone
In situations where there was once a desk microphone (parliaments for example), it seems usual nowadays to have two, each with its own gooseneck, an inch or two apart. Our articles don't seem to mention the fact, let alone give a reason. Doug butler (talk) 05:51, 22 May 2023 (UTC)
 * Uses of dual microphones could be explained better in the article about Microphone practice. PA (Public Address) system engineers can use dual microphones in several ways:


 * The two microphone signals can be distributed to different listener groups such as local and international broadcasters, journalists, translators, recording equipment, etc. (saving on the simple expedient of using a signal splitter, see example) with assurance that each channel is unaffected by any filtering, switching, intrusion or censoring applied to the other channel.
 * For music performance where room acoustics are relevant, two near-co-sited microphones can serve in a stereo recording technique though this is not usually done for a parliament speaker.
 * Adding two microphone signals with equal gains but in antiphase results in cancellation of sounds (nulls) in some directions, see . This can be useful both to reduce ambient noise and to allow higher voice amplification at public events before Audio feedback occurs. Philvoids (talk) 10:13, 22 May 2023 (UTC)


 * And if one fails, probably the other one will still function.
 * If there are two speakers (eg an interpreter or an interview situation), Each speaker can use a different microphone.
 * If people of different height are using them, they can be adjusted to point to the speaker's mouths. Graeme Bartlett (talk) 10:48, 22 May 2023 (UTC)


 * I'd assumed it was so they were free to move their head from side to side without the volume varying much. People who are not used to microphones are always fading in and out. NadVolum (talk) 12:19, 22 May 2023 (UTC)
 * NadVolum's suggestion is the most compelling so far. The antiphase trick works to reduce ambient noise pickup, though it relies on the performer being closer to one or the other; if midway it's the politician's voice that gets canceled, which can be a problem for the Hansard staff if for no-one else. I had several other thoughts, like deterring the speaker from "swallowing the mike" or even reducing the "spitting" on sibilants and "popping" on plosives, but the mikes are usually paired up too closely for that to be a factor. I peeked at a few microphone companies' websites, but they are strangely silent on the matter, though it must result in greater sales :) Doug butler (talk) 14:09, 22 May 2023 (UTC)
 * A young or very inexperienced speaker may find it stressful and unnatural to be instructed to "speak into" a single object microphone. With dual microphones one speaks more comfortably into open space between the microphones. Philvoids (talk) 13:17, 23 May 2023 (UTC)


 * I had assumed that it was for backup (as with the President of the US at the podium), but the anti-phase makes sense. I fact, decades ago the Greatful Dead had a large set of amplifiers and speakers behind them and they used two small microphones, out of phase, to sing into, too keep from causing feedback.  Bubba73 You talkin' to me? 01:52, 27 May 2023 (UTC)
 * That was the famous Wall of Sound system, created by LSD manufacturer Owsley Stanley when he was the sound engineer for the Grateful Dead. Here's a photo of the dual microphones. CodeTalker (talk) 20:04, 27 May 2023 (UTC)

mp3 file on apple music
is there a way to play a rare recording i only have in mp3 on my apple music app along with all the songs i paid for i have an iphone x and on os 16 or so 2600:1700:9758:7D90:C5BF:5F1C:A46C:C83A (talk) 07:23, 22 May 2023 (UTC)
 * I expect there are other ways, but one way is to put it on an audio CD, and then let iTunes rip it off (like it used to do whenever I played a CD on my computer!). Graeme Bartlett (talk) 10:50, 22 May 2023 (UTC)
 * On desktop (including laptop), you should be able to just drag the mp3 onto the Music app's icon in the dock, and it should start playing it and add it to your library. To get it onto your phone, you'd have to sync your phone with the desktop computer.  -- Avocado (talk) 00:35, 24 May 2023 (UTC)

Octane rating
Why is gasoline/petrol sold with much higher octane rating in the UK than the US? 135.180.146.84 (talk) 16:28, 22 May 2023 (UTC)
 * See Octane rating. Two different rating systems. AndyTheGrump (talk) 16:31, 22 May 2023 (UTC)
 * There's a bit more to it than that. I've extracted the US and UK relevant entries:


 * so there does seem to be a slight difference. Historically US made cars had larger, lower compression ratio engines than European (and Japanese) made engines.  I don't know if this is still the case, but it might explain the differences. Martin of Sheffield (talk) 17:03, 22 May 2023 (UTC)
 * In Australia at least teh car manufacturers pointed out the the poor fuel quality historically made it far more difficult to reach emissions targets. Low octane low temperature fuel is cheaper than high octane fuels for high ambients. Greglocock (talk) 22:29, 22 May 2023 (UTC)

What has five leaves and looks like poison ivy?
I don't know how to find the question I asked earlier but I have more information.

Although it looks like poison ivy and sometimes there are three leaves, this plant has a leaf on the end and two pairs of leaves. The first pair, of course, looks like the pair of leaves in poison ivy.

Sorry, I don't carry anything I could use as a camera. But last week I was walking on a trail where this plant was very, very common, and I made a new discovery. It eventually becomes a full-grown tree, and there are many trees of this type on the trail, with the same leaf pattern--five leaves on each small branch.— Vchimpanzee  •  talk  •  contributions  •  22:38, 22 May 2023 (UTC)


 * Virginia creeper? --Amble (talk) 23:41, 22 May 2023 (UTC)


 * No, that's a vine and the five leaves are in a different pattern.— Vchimpanzee  •  talk  •  contributions  •  16:10, 23 May 2023 (UTC)
 * Just to note that poison ivy is absolutely a vine, especially as a mature plant. Like all vines, the young shoots may not be vine-like until they find a substrate to crawl up, but mature poison ivy can grow absolutely massive vines that are many years old.  -- Jayron 32 17:19, 23 May 2023 (UTC)
 * Sweetgum, Buckeye, any Juglans sp.?  Eve rgr een Fir  (talk) 16:16, 23 May 2023 (UTC)
 * None of those.— Vchimpanzee  •  talk  •  contributions  •  16:56, 23 May 2023 (UTC)
 * Found it. I decided to see what would happen if I did a Google search with the same question. This time a photo came up that looked like what I saw. Acer negundo. Wikipedia doesn't have a photo that would allow me to see the similarity, but there was one in the Google search results, and this site says "Box elder" beside the same photo.— Vchimpanzee  •  talk  •  contributions  •  17:04, 23 May 2023 (UTC)
 * Ah, yes. Box elders are interesting in that, unlike most maple trees, they have a compound leaf, similar to many ash trees.  I've never heard them called this, but the Wikipedia article notes "ash-leaved maple" as another name for box elders.  The way to recognize a compound leaf, by the way, is that each leaflet is attached to a central rachis, which in the autumn will detach from the plant; this is not a proper branch of the tree, rather it's part of the leaf structure itself.  While most notable on ash trees, you also find such compound leaves on other trees such as the box elder (you've already found) and mimosa trees, which are doubly compound leaves, and moringa, which are triply compound.  -- Jayron 32 17:37, 23 May 2023 (UTC)


 * ""Ash-leaved maple" is the name generally used in the UK, where it is a fairly unusual specimen tree, sometimes found in parks and gardens. Maybe because the common ash is a well-known native here. It's not actually a true elder, although the leaves are similar. Alansplodge (talk) 17:10, 24 May 2023 (UTC)
 * Interestingly, the box elder's leaves more closely resemble the green ash (a common North American tree with a range overlapping the box elder) than they do the common ash, which is not well known on this side of the pond. Compare  and .  Regarding North American species which are unrelated to similarly named Eurasian species.  It's a common problem.  -- Jayron 32 18:26, 24 May 2023 (UTC)