More rumblings

The largest subwoofer in the world is limited by the speakers with which it is associated. This may not hold true for all systems but, in genral, it makes sense to me. Moreover, the limits of average system loudness lies with the dialogue. Turn up the volume too much and the dialogue takes on the qualities a deaf old granny listening to her TV! No offence to grannies. Just making a simple analogue. Having set our steady state upper limit on dialogue SPLs one cannot just turn up the subwoofer alone. Or it all becomes too bottom heavy. The dialogue would be simply drowned out by the bass. Running the subwoofer hot to get a bit more excitement into the LFE is quite commonplace. The human ear actually seems to prefer a rising "housecurve" into the deep bass. This is probably tied in with the equal loudness curve. The human ear is insensitive to low frequencies. So the lower the frequency the higher the level needed to make it sound equally loud as higher frequencies.

You can't turn up the mains and surrounds either or the dialogue is lost in a sea of exaggerated environmental sounds. Though I often surprise myself how loudly my system is playing if I leave the room during a film then return armed with coffee and ice cream. I can still remember this being the case with cinemas. Though it must be decades since I last entered one. So a degree of over exaggeration in sound levels is acceptable and even expected. If only to add excitement and to drown ot the rustle of snack bags. This exaggwration of loudness is rather odd when one thinks about it. Because ordinary speech is not usually very loud in real life unless the person is "talking too loudly". Speech is only usually around 60-65dB(C) measured indoors where there is no distracting background noise, traffic, music or kids screaming. So whacking the master volume control up to give a constant 80dB(C) on ordinary dialogue is a bit of a distortion on everyday reality.

The answer to our sound level problem is wide dynamic range. It is the contrast between the soft parts and the loudness of noisy parts which makes the film exciting without singing the hair on (and in) your ears. The difference between peak loudness and quiet moments should be possible at all frequencies without audible distortion. It's no use having an IB to bellow out the bottom end if your speakers aren't up to their respnsibility for the higher frequencies. Otherwise the bass becomes too dominant on peaks of loudness too. Which may be a good thing if it protects the ears for suffering damaging peaks at dangerous SPLs at higher frequencies. Low distortion means fewer false harmonics are produced. So speakers capable of large dynamic peaks should actually be safer than those which struggle when pushed too hard.
Simply becauase they produce less distortion.

The response from those who value low distortion ansd wide dynamic range seems to parallel the IB. More drive units are brought in to allow them to coast along even when they are playing much louder than "normal" domestic stereo speakers. Usually they also have the advantage of being rolled off with active crossovers. Since they no longer need to produce high levels of low frequencies they are easier to drive which means the ampifier has an easier time too. Many of these multi-driver speakers use open baffle arrangements to avoid colouration.

Introduction

*THIS IS THE START OF THE ORIGINAL IB BLOG.*

Posts run forward in time from this point.




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By the way: The dates of all posts are completely fictitious. I deliberately date each new post so that it follows a logical chronological order. When I started blogging it was impossible to run a blog "backwards". i.e. So that new posts appeared at the bottom of the chapter list rather than at the top. Dating posts backwards into the past to achieve my aims has continued.

If you find yourself running out of new chapters to read try clicking on "Home" at the bottom of the page. Clicking on"Older Posts" will usually provide the next chapter or chapters.

I chose the blog format because it is so flexible, provides enlargeable image hosting and can be continuously updated and corrected. It is also free. It's strange editing problems are a trial but beggars can't be choosers.

Blogging seems unlikely to suffer the sudden death common to ISP's free web pages as more avaricious companies buy them up. I lost 5 websites to changes of ISP ownership ending in a final toxic dose of agent Orange.

Although it doesn't seem very likely this blog actually gets more interesting as it goes backwards in time! If you have already dismissed March '07 as out of date then you may like to know that this was written in mid summer '09 just as I doubled the size of my IB to 8 x 15".

If you are regular visitor do remember to reload the pages regularly. I go back and change things all the time. Often adding new images as appropriate.
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The IB Array

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My first attempt at a True Infinite Baffle Subwoofer proved to be slightly flawed. It performed incredibly well compared with my large commercial SVS cylindrical subwoofer. It was just that the array seemed to lack the giant-killing power that I had read about in posts from other delighted IB subwoofer owners on The Cult of the Infinitely Baffled. (A specialist Internet forum dedicated to True Infinite Baffle Subwoofers)

The major problem was the flexibility of my baffle wall. This old planked-over-vertical-studs wall forms part of an even older timber-framed house with later additions. When the four big 15" driver cones moved ... the wall moved the opposite way! Newton's Law of action = reaction was biting back with a vengeance.

The original array had a remarkable performance but had shaken the wall and adjacent double doors far too much for comfort. In fact the whole house seemed to shake from the mechanical vibration of the drivers. The bass sometimes made me feel nauseous in the bathroom below the IB enclosure! Yet despite the available power and four large drivers the output on programme material was just a little disappointing. It failed to vibrate the floor on films no matter how much I played with BFD filters. Despite an easy 120+dB capability and 8Hz extension on test tones the IB just did not deliver quite as expected. I also had absolutely no headroom to play the subwoofer louder ("hotter") than the speakers on programme material. Something had to be done!
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