Why are double consonant ‘r’ sounds transcribed as a single phonetic sound

Question

Take the words ‘irregular’ and ‘erectile’; the ‘r’ sound in the first one is clearly different from the second (at least to my ear). In ‘irregular’ we have a double ‘r’ sound: ‘ir-reg’, while in 'erectile' we have a single 'r' sound ‘i-rec’. Yet dictionaries show identical phonetic transcription for both; in Oxford for example: /ɪˈrɛɡjʊlə/ and /ɪˈrɛktʌɪl/, and in Cambridge: /ɪˈreɡ.jə.lər/ and /ɪˈrek.taɪl/.

Contrast with a pair like ‘dissatisfaction’ vs ‘disambiguate’. In this case, we have ‘dis-sa’ and 'di-sa’ sounds, and dictionaries distinguish between the two cases by transcribing the first with a double ‘s’; again in Oxford: /dɪssatɪsˈfakʃn/ and /dɪsamˈbɪɡjʊeɪt/.

Edit1:

Pronounce to yourself 'erectile' by doubling the 'r': /ɪrˈrɛktʌɪl/ (ɪr-rɛk), the way 'irregular' is pronounced. Surely it's different from /ɪˈrɛktʌɪl/ (ɪ-rɛk). Also pronounce to yourself 'irregular' by dropping the double 'r': /ɪˈrɛɡjʊlə/ (ɪ-rɛɡ) , the way 'erectile' is pronounced. Surely it's different from /ɪrˈrɛɡjʊlə/ (ɪr-rɛɡ).

My question is very specific: are the two sounds in the first segments of the words pronounced exatly the same or not? And if they're not the same, why isn't this reflected in the phonetic transcription.

Edit2:

When I say a double 'r' sound, I'm not referring to repeated flapping or vibration of the tip of the tongue against the hard palate in heavy rhotic 'r' sounds, as is the case in Arabic. Sure, an 'r' sound with a repeat flapping of the tongue would most likely indicate a non-native pronunciation.

The double 'r' sound I'm talking about can occur with a non-rhotic 'r' too, where the tongue is pressing against the air flow between it and the hard palate for a longer time than it would take to pronounce a single 'r' sound. What I'm suggesting is that the 'r' sound in 'irregular' takes longer than the 'r' sound in 'erectile', whether or not we're using a non-rhotic 'r' pronunciation; hence this should be reflected in phonetic transcription.

Edit3:

1. American pronunciation:

My original position was based on the British accent. After listening carefully to the american pronunciations in a bunch of dictionaries, I accept that the pronunciations of both words seem to similar. To my ear, Americans seem to be pronouncing them both with a double 'r', which is the same way tha 'irregular' is pronounced. So the American pronunciation is 'ir-rec-til', rather than 'i-rec-til'. Of course the last syllable is not a diphthong like in the British pronunciation.

2. British pronunciation:

The only dictionary with full sentence pronunciation I could find was Longman. While the entry for 'irregular' has many sample sentence, 'erectile' is not listed, so I used samples from 'erected' and 'erection'.

I provide now direct links to the sample sentence pronunciation, where the reader can listen and compare for themselves:

irregular:

1. http://www.ldoceonline.com/media/english/exaProns/p008-001392428.mp3
2. http://www.ldoceonline.com/media/english/exaProns/p008-001724213.mp3
3. http://www.ldoceonline.com/media/english/exaProns/p008-001724234.mp3

erected:

4. https://www.ldoceonline.com/media/english/exaProns/p008-001501950.mp3

erection:

5. https://www.ldoceonline.com/media/english/exaProns/p008-001501986.mp3

Next I provide three screen shots of segments from the audio patterns for either words in some of the sentences above as shown in Audacity(audio software). I will comment on these patterns below:

1. 'irregular' in example 1 above (ir-reg ends between 1.5 and 1.6 time marker):

2. 'irregular' in example 2 above (ir-reg ends just before 1.20 time marker):

3. 'erected' in example 4 above (i-rec ends around the 1.70 time marker):

What we can observe in these patterns, is that the segments till the end of the first consonant after 'r' ('i-rec' or 'ir-reg') generally form two humps. We can see clearly that for the 'ir-reg' cases (patterns 1 and 2), the first hump (representing the 'r' sound) is more extended than the second hump, and this difference is more pronounced in pattern 2. While in the 'i-rec' case (pattern 3) we can see that the two humps are of equal length, indicating a shorter 'r' sound.

Of course this is not an extensive analysis, but at least it's a case in point.

Answer 1

Generally, double consonants are not pronounced distinctly in English, unless they are part of different syllables and the emphasis is on the second syllable.

A word like dissatisfied is formed by adding a prefix dis- to the word satisfied. It starts off with two s in separate syllables, and can be pronounced like that- one at the end of the first syllable, one at the end of the second syllable.

A word like irregular is formed by adding a prefix in- to the word regular. The n-r combination is difficult to say, so we replace the n by another r. The same thing happens with the letter l, so in + licit becomes illicit. According to Cambridge Dictionary, the first l is not pronounced, likewise with in + modest. Note that this conversion only happens with word that passed through medieval latin: more modern words like inroad (1540), inlay (16th C) and inline (1913) are unaffected.

The same kind of conversion happens in arabic for sun letters (il+r -> irr). In arabic double consonants are always clearly pronounced, and this applies to sun letter conversions too.

In a non-rhotic dialects there is an identifiable reaason for not pronouncing the first r, because in non-rhotic dialects (England english, for example) an r followed by a consonant is not pronounced.

In rhotic dialects such as US english, the pronunciation of the n-become-r is, according to Merriam-Webster, optional.

I am a native of England (non-rhotic) and I do not pronounce it as a double r. I can and do double the r when speaking arabic, so I do understand the difference. Other natives of England do not pronounce the double r. If I heard somebody pronounce it with a double r, I would assume that they were foreign. I believe that I have heard natives of Scotland (rhotic) pronouncing it with a double r. I cannot comment on US english.

Here are recordings of me saying irregular and erectile:

And here I say irregular again, pronouncing the two r's separately.