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Speaker 'burning in' - debunking the debunk?

Discussion in 'Monitoring' started by paulears, Jan 29, 2020.

  1. paulears

    paulears Well-Known Member

    Joined:
    Feb 7, 2014
    Location:
    Lowestoft - UK
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    Cards on table - I have very little support for the hi-fi fraternity with their anti-physics viewpoints on all kinds of crazy thing, including the need to have to burn in loudspeakers.

    I'm now having to think very hard to explain a recent experience. I thought I'd share it to see if anyone else has views on what is happening here.

    Not studio speakers, but JBL VRX932LA-1 PA speakers. This design is not really a line array, although most people talk about them in this way, but they're a constant curvature speaker. Our small business does a lot of theatre work, and for one venue we work in frequently, it's not very tall, but very wide and very deep with over 1000 seats on one level. We have no need for mega loudness, but being able to manage the throw is vital. We can't use delays because there's simply no way to hang them because in 50% of the space the ceiling is far too low and the people would be able to touch them. So a speaker position near the pros arch is the only possible place for speakers. These JBLs can have their HF adjusted to add 3dB for the distant seats and pull it back 3dB for the close ones to avoid taking their heads off with cymbals etc.

    Trouble is, our budget didn't cope with the purchase price for 2 subs and 6 tops. I searched worldwide, as they're not very popular and a ten year old design product probably in it's last stages of availability. I found a couple of dealers with a mix of brand new, and customer returns and got what I need from them, in total. It's arriving slowly and just waiting for the subs and 2 more tops, but I have a strange problem.

    Three boxes (2 from dealer A and one from dealer B) do show signs of having been used - which is fine. Tiny marks, and one has had a bit of touch up paint on a deepish but small gouge. They told me about it, and it's OK with me. The last box was still in the original wrapping and the box showed no signs of being opened. This is/was the problem. To check how the switches function on the -3/0/+3dB settings I played my usual test tracks and the 'virgin' box sounded a bit thinner? I switched from music to pink noise, and all of them do the same things with the switches, but the unopened speaker sounded different. Pulled out a mic and looked at the response on the pink noise and a tone sweep. The different speaker has less output at just above 500Hz, and then another trough although a bit smaller at 1200Hz. Using a 32 band EQ, I could quite easily restore the response to match the others. I had a think. These speakers can also be bi-amped, and I realised that if I switched the speaker to this setting, then with no connection to the 3 HF drivers, it would just be the LF driver working, and this confirmed the driver was the problem, not the HF units. I sent it some music and did some more tests and tried it at various volume levels. In my studio it was too loud for comfort so I threw some blankets over it to tame the volume a bit. Then I had a phone call and had to dash off to fix something for a client. When I got back, I forgot the studio, and with the doors working fine, I didn't hear it and forgot.

    This morning, I remembered - 24 hours later the music on loop and the thing still blaring away.

    It now sounds exactly the same as the others!

    I have always discounted the burning in theory as rubbish, and couldn't find any sound reason why blasting a speaker for a bit changed the sound - but it has. A 100% fact. The response on screen now is so close to the others I cannot compare them?

    I wonder if perhaps the voice coil was perhaps rubbing a bit in the slot, or maybe the surround rubber was a bit stiff, but I don't know? I now have 4 matched speakers.

    Has anyone else had something similar? I've always been content my opinion on burning is was solid, but clearly I was wrong. I'm assuming whatever the loud music for 20 hours or so did was fix something?

    Any opinions on what's happened?

    I'm more than happy with the speakers now, and we've got a good system for around half the normal price and that's included the shipping. My remaining speakers are on a ship somewhere. I accepted the sea freight option rather than air freight because of cost, and time isn't a problem ..... but it has been at sea a fair while now from Mexico!
     
  2. Makzimia

    Makzimia The Minstrel Well-Known Member

    Joined:
    Aug 20, 2014
    Location:
    Keighley, England
    Home Page:
    Great story Paul. I’ll be waiting to see more learned responses:). I sold hi fi gear at one point, and a friend of my mother’s in the 70s had a very expensive system. I do recall such things in discussions. Go figure hey :).

    Tony
     
  3. dvdhawk

    dvdhawk Well-Known Member

    Joined:
    Dec 18, 2008
    Location:
    Western Pennsylvania, USA
    Like you, I'm also skeptical of most of the exorbitantly priced, voodoo, nonsense that some audiophiles seem gullible enough to buy.

    I think that the speaker burn-in theory is within reason and can hold up to your 'physics viewpoints'.

    There is only one major moving part of a 12" that I could reason needs to limber up before it can perform at peak - the cone. In your specific case, the 12" driver has 2 voice-coils floating in 2 magnetic gaps. Barring a catastrophic failure, I would expect the physical properties of the copper winding and magnet to be pretty stable over a very long time. Magnets may lose some degree of magnetism over the years, but not within 24 hours. The pure copper in the voice-coil windings is enamelled and also unlikely to change properties.

    The rigid paper cone, and in particular the 'surround', are the things I can easily believe would change their properties in short order. The accordian folds of the surround are often coated and I don't have any trouble believing that would all be excessively stiff at the time of manufacture and flex more freely once they're used for a while.

    My biggest question in all of this is, why don't the manufacturers burn them in. If I made Brand G audiophile headphones - that reportedly sound better after 100 hours of pink noise, I would burn-in every pair at the factory before I shipped them out the door.
     
    kmetal likes this.
  4. Boswell

    Boswell Moderator Well-Known Member

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    Apr 19, 2006
    Location:
    UK
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    In my hi-fi rig, I have a matched pair of Spendor BC1s, bought new in the early 1970s. The BC1 is a BBC design, originally manufactured under licence by Spendor, Rogers and others. Some years ago, the suspension of the LF unit on one of the speakers weakened to the extent that the voice coil started to scrape on the magnet. I looked at getting this unit re-coned, but was told that it would be cheaper to buy a whole new drive unit. I was worried about the sensitivity matching between the stereo pair of units, even if I could get one with the same code of colour paint dabs on the speaker magnets. In the end, I did manage to buy a new, unused one made in about 1980 that had the same colour code.

    I replaced the failed driver and gave it a critical listening test. About the only thing I could say about the two speakers that was the same to the ear was the sensitivity. The sound was astonishingly different. I remembered the burn-in story, so left the new one on acoustic pink-noise soak while I was away for the weekend. When I came back, I had two speakers that sounded the same. It's not a myth.
     
  5. paulears

    paulears Well-Known Member

    Joined:
    Feb 7, 2014
    Location:
    Lowestoft - UK
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    Boswell - thanks for the duplicate story, now they sound the same - just amazed that it's taken me a very, very long time to change my opinion on this one. Clearly, like you - it worked. I think the idea that it's the cone makes sense rather than the surround.
     
  6. kmetal

    kmetal Kyle P. Gushue Well-Known Member

    Joined:
    Jul 21, 2009
    Location:
    Boston, Massachusetts
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    Ive experienced the burn in with several pairs of speakers.

    I take it one step further and also feel like amplifiers have a burn in too. I think all the electrical components round out a bit after some initial usage. I have no proof but it seems to be the case that the tone smooths slightly and the volume sweet spot requires an extra click after a little bit of use.

    This could be my ears, or maybe just the speakers, not the electronics.

    Probably because a bean counter said it would cost .0000000000000000000001 cents more per pair.
     
  7. cyrano

    cyrano Active Member

    Joined:
    Feb 4, 2018
    Location:
    Brussels
    Considering how a speaker is constructed, I've always felt you should expect some burn-in effect with new speakers, especially woofers.

    I's not that I really burn-in new speakers, but they always sound better after a few days of use. Part of that "better" might be psychological, but the lower end part of it can be measured.

    For a long-lasting :D project, I've tried to get eight vintage active speakers that sound the same. I've abandoned the idea. Besides the hardware revisions, I can still identify pairs by ear. But I can't get even four speakers that sound reasonably identical.

    I've got four identical ones now. Four NOS KEF's I almost found by accident. It seems I bid on them ages ago and completely forgot about it. It was like an online yard sale. A few weeks ago, I was contacted about them and they simply accepted my next-to-nothing offer. When I picked them up, another six pairs of vintage speakers (Wharfedale, B&W...) were offered. Fortunately, I was able to restrain myself :D
     
  8. cyrano

    cyrano Active Member

    Joined:
    Feb 4, 2018
    Location:
    Brussels
    Well, at least you did change your mind about it. I know some who would lie to keep their audio belief.

    With woofers and some mid-range speakers, I suspect the spider to have some influence too. But I don't see an easy way to measure it. And magnets can be considerably weaker with vintage speakers. Especially with some high-power PA woofers as these tend to run hot. One of the reasons why some PA companies change woofers/speakers on a yearly basis.

    Besides, the error margin on my measurements might be somewhat larger than the effect itself.
     
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