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 Post subject: HMV 5A & 5B soundbox differences
PostPosted: Mon Mar 19, 2018 3:53 pm 
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Victor O
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Joined: Mon Dec 18, 2017 2:51 am
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Location: Madrid, Spain
After much careful observation and comparison between well restored examples of both soundboxes, performing at their best on a big reentrant horn (the 194) and on a smaller exponential (the 102), I've lately been thinking that the only difference between the HMV 5A and the 5B lies in the sound, and the true difference between these two is the diaphragm geometry alone. And it seems an intentional designer's purpose. The 5A has a compliant border crown of corrugations that run diagonally to the edge. The center part of the diaphragm is stiffer due to the concentric ridges, and when vibrated by the spider it plunges back and forth thanks to the compliance of the corrugated crown.
The 5B has a different arrangement of the corrugations, which are shaped as small pyramids, with ridges and valleys much more perpendicular to the diaphragm edge. This crown is noticeably stiffer than that of the 5A. When vibrated by the spider, this configuration makes the diaphragm vibrate as a whole, and the difference in displacement between the center and the border is not as marked as in the 5A. This can be clearly noticed when you move both diaphragms forcing them with the needlebar or with a finger.
I believe this is the reason for the different sound. In the 5A the center acts as a true piston, while in the 5B it bends alongside the rest of the diaphragm. It's clear that the sound of 5A has a much stronger resonance in the bass, while in the 5B that resonance is absent. It vibrates the same to all frequencies. The sound seems to lack the bass power that the 5A has, but this is only an illusory contrast. The sound of 5B is much more equilibrated, while in the 5A, the bass masks completely the trebles. The bass in the 5B is truer, more in equilibrium with the rest of frequencies, and the sound definition results much clearer than in the 5A.
It is a case of clear improvement; HMV engineers launched the 5A which was an English version of the no. 5 (orthophonic) which sounded the same, but later they continued experimenting and finally launched the 5B, a definite upgrade of the boomy 5A. The 5B lasted many years, while the 5A is much scarcer.
Said this, I don't mean to condemn the 5A; for certain records it's an advantage, and sounds very well. But as a whole, the 5B is better.
Maybe if you see the YouTube video of my 102 performing with the 5A at https://youtu.be/NLs17N_3CIM you may notice what a deep bass it gives to such a small horn. But you also may notice the very apparent lack of treble. The needle is bamboo. In the other hand, the 5B performing in the 102 with steel needles has always sounded a bit shrill to me. This sounds good when using bamboo. Usually the bad tracking angle of the short tonearm breaks the bamboo soon, if the recording is strong. With softer recordings they work fine.
Yesterday I tested both soundboxes with several records on the big reentrant horn of the 194, using bamboo needles. And for such big air column, the 5A sounded well with softer recordings, but resulted somewhat boomy on others. The 5B at first seems to have less bass, but the bass is there indeed. The treble is better, and it sounds much more natural. The 5B in the big horn with steel needles sounds also well, with more treble, but it doesn't give a sense of shrillness as in the 102 shorter horn.
It might also affect the sound the smallest difference in size of the air chamber within the soundbox, as the diaphragm joints in both soundboxes (mine) are not equal, slightly thicker rubber ring in the 5A, and the original thin felt joint in the 5B. I've concluded with other experiments relaxing the pressure on the diaphragm edge, that a thicker air chamber and relaxed pressure on the diaphragm border also produces a deeper sound.
Still I must do again the comparison with the 5A using the same thin felt joint on the diaphragm.
But by now, the conclusion is that definitely the 5B was an improvement both in treble response and overall flat response over the 5A, and the difference resides in the compliance of the border and the different way it makes the diaphragm vibrate.
Inigo


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Mon Mar 19, 2018 4:22 pm 
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Victor IV
Joined: Mon May 13, 2013 2:04 pm
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Amazing analysis ! I have to say they ( 5A , 5B ) sound remarkably similar to me but then I probably have cloth ears :lol:

Can't you record each soundbox on each machine and post a picture of the sound easily done with https://www.audacityteam.org/


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Mon Mar 19, 2018 4:59 pm 
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Victor O
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Yes, Mike. I am planning to do similar recordings with my mobile phone, which seems to work finer that I suspected, judging by the YouTube vídeo. I will prepare recordings of the same record with the 102 and 194 using both sound boxes. A true video for comparison. Of course the mobile phone must be held in the same position all the time, for when you move it around the gramophone the sound changes a lot. This weekend I'll do it.
Inigo


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Tue Mar 20, 2018 5:34 am 
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Victor II
Joined: Tue Jun 30, 2009 8:17 am
Posts: 351
Here is a link to Graham Barber's site.(RIP, a very helpful man, who will be missed).
http://www.graham-ophones.co.uk/hmv-page-2/4580358062


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Tue Mar 20, 2018 8:41 am 
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Victor III
Joined: Sun Mar 15, 2009 6:18 am
Posts: 836
Interesting comparison!
I have the 5, the 5A and the 5B, and I admit that I never noticed any acoustic difference between the 5A and 5B. The 5 (the HMV copy of the orthophonic) performs better than its successors, but it is very hard to find one in good condition - it was made in pot metal of lower quality than the Victor counterpart, and most nr 5's that can be found today are cracked. I have exchanged the 5A and 5B in a number of machines with no noticeable difference in casual listening, but I never tried to make a systematic comparison like you did.


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Tue Mar 20, 2018 9:59 am 
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Victor III
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F. Depero, "Grammofono", 1923.
Joined: Thu Feb 24, 2011 4:19 am
Posts: 709
Location: Italy
chunnybh wrote:
Here is a link to Graham Barber's site.(RIP, a very helpful man, who will be missed).
http://www.graham-ophones.co.uk/hmv-page-2/4580358062


Oh Lord, did he die? :shock: How happened? I'm so sorry, I was in contact with him as he was one of the few interested also in portable gramophones! :cry: How sad!


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Tue Mar 20, 2018 12:14 pm 
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Victor V
His epigrams are all his own, the man's an epigramophone!
Joined: Mon Oct 24, 2011 1:21 pm
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Location: The Somerset Levels, UK.
viewtopic.php?f=11&t=34469


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Tue Mar 20, 2018 4:27 pm 
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Victor O
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Keep'em well oiled
Joined: Mon Dec 18, 2017 2:51 am
Posts: 63
Location: Madrid, Spain
Still I have to remind you that my current 5 - A diaphragm is somewhat tired and mistreated, and this may be the cause of an extra sensitivity to the bass and lack of treble. Anyway I remember the former 5a diaphragm it had installed before sounded more or less the same. I changed diaphragms with a 5 - B years ago, when I noticed that the sound was then more natural. This issue has been raised again because I still had the old 5 - A diaphragm and an empty sound box and simply I decided to recovery it. I'm always doing experiments with diaphragms and sound boxes...
Inigo


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 Post subject: Re: HMV 5A & 5B soundbox differences
PostPosted: Wed Mar 21, 2018 12:32 pm 
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Victor O
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Keep'em well oiled
Joined: Mon Dec 18, 2017 2:51 am
Posts: 63
Location: Madrid, Spain
Yesterday I was playing several records on a 194 with the 5A and the 5B. And finally the 5A didn't sound so boomy to my ears as it did on days before. Of course, the bass is better with the 5A.
Maybe it's the difference of horn sizes among the 102 and the 194. Maybe I'm getting used to the 5A sound... One never knows!
I fell in love completely with the repaired 5A... So I'm going to gold-plate it, and it will be my official 194 soundbox. I'll keep the golden 5B at hand too, for certain records it could be better...
Inigo


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