The beast is loose at last!

*
Mixing in the LFE has released a violent monster. We have just watched "The Last Air Bender" with terrifying levels of bass suddenly unleashed from nowhere.

After the first warning, when the whole house shook like a leaf, I turned the EP2500 controls right down from 12 o'clock. When the house was still about to collapse I turned the LFE right down on the mixer control. A cut of about 10dB. I was till getting occasional red flashes on the BFD with every surface vibrating violently. I have never experienced anything like it before.

Years of messing about with downmixing had not prepared me for this. The highest I ever registered (during a film) before, was about 111dB(C) on the Galaxy SPL meter. It was brutal and certainly impressive but almost a whimper compared with the present performance.

Being completely dark at the time I had no way to tell what the cone excursions looked like. Eight 15" drivers moving in unison never felt so dangerous as they do now. I know the IB can do 135+dB on sinewaves above 30Hz without much sign of anything happening at all.

That seemed like mere child's play compared with what we just experienced. The walls, ceiling, floor and windows were shaking so hard I feared for the safety of the structure. The vibration through the floor was literally painful. The air around us was being shredded by an incredibly forceful shaking.

Every moment of film watching, prior to mixing in the LFE, feels as if it has been completely wasted. I hadn't a clue what I had been missing even on DTS. I had sound quality aplenty but the infrasonics were almost absent. My wife kept saying that the SVS cylinder was far more impressive. I am ashamed to admit she was right. I had been fooling myself that SQ was more important than the physical violence of which a large subwoofer is so easily capable.

I was so keen to believe that my IB was impressive that I shut out the memories of rattling eyeballs. The weird, slow waves of bass which passed eerily through the room. The terrible shaking of dragon's wings on LOTR. All this from a puny 12" driver in a cardboard cylinder covered in a thin rug.

Not even a better model either. My SVS was the cheapest (though tallest) of their range when I imported it.  No wonder it had turned my wife onto serious bass and infrasonics. We were both incredibly impressed right out of the box. We went around with a silly SVS grin for literally ages.


Then came the demand for more. For greater safety on the really serious peaks. The SVS seemed to peak at about 107dB on the meter when there was a loud bass roar. The IB seemed like the obvious answer at the time. It went a bit louder than the cylinder but was hampered by very non-spec drivers and a flimsy baffle wall.

Then the array gave way to a manifold and a serious gain in output and drop in vibration. Then newer drivers arrived to replace the old ones. Then I built all eight into a box taller than myself. Quite honestly it was all a complete waste of effort for films! We watched literally hundreds of films without the bass which the director had intended.

I was  very seriously handicapped by the lack of LFE. On music the IB went loud and deep. Only fear kept levels reasonably modest. On films the bass only went loud when the dialogue and everything else was far too loud. I read other people's descriptions of film bass and buried my head in the rock wool lining of my enclosure. I was in serious denial.

The weird thing was that I could easily make myself nauseous on organ music. Films were a loud disappointment. The bass was certainly there but not like it should and could have have been. It was exhausting sitting through an action film at reference level without the special bass sound effects.

Now I don't know whether to feel like a complete fraud or a complete chump. So much potential was just sitting there with so little reward. Until now. The mixer has finally allowed me to inject the LFE into the front channels.

The IB must have hit 130dB (briefly) on the effects at the start of the film we watched last night. "The Last Air Bender".  Without any exaggeration the vicious vibrations were really very frightening. My arm shot out to cut the bass on the mixer. Then I went out to the EP2500 and cut that to zero on both controls. I was still seeing occasional red (clipping) lights on the BFD. The air, floor and every surface in the room were still shaking incredibly violently at times. It sounded as if everything was literally going to come apart. An odd film with good points and bad.

I shall have to go back to the beginning and recalibrate the bass channels and the IB relative to the speakers. I remember leaving the IB/speaker calibration flat on "The Calibrator" DVD after discovering it was a a few dB "hot". The speakers didn't sound as loud as usual when we started watching the film and I turned up the volume to get clearer dialogue. That may be where the problems started.

Another update 26/2/11. Just watched XXX with Vin Diesel on DVD. The avalanche scene hit 117dB(C) Max hold on the Galaxy 140 with no red lights on the BFD. It sounded strong without the imminent threat of damage. The mixer BFD control was at 12 o'clock. I should have measured the explosion at the earlier drug bust helicopter scene. I think it was a bit louder. Exterminator Salvation played at up to 111dB(C).

March 2011 RED and Takers both peaked out at around 115dB with no red lights on the BFD. The hotel gunfight on Takers was spectacular. It was this scene I checked on the Galaxy 140 SPL meter afterwards. Both films were good fun.

Another update at the end of March 2011: Instead of previous attempts to balance the drivers I am trying balancing the orange lights on the EP2500. Previously I have tried to match the frequency responses of the two very different sets of AEIB15 drivers. This didn't work too well because it robbed the drivers of energy in their respective power bands. This greatly reduced impact and had me searching for alternative ways to get it back. OBs and small sealed boxes were tried but discarded on SQ and other grounds.

I am now using only one filter on the BFD. +16dB @ 20Hz with 120BW on the older 32Hz, vinyl coned drivers. They don't do deep bass without massive boost. Now both sets of drivers are still very different. The older 32Hz drivers are stronger higher up. The newer, paper coned, 13Hz drivers roll off early at the top end. How best to match them so they share their output to best effect? I have tried matching their excursions on programme material but this isn't ideal as it is so frequency dependent.

One day I was watching the orange lights on the EP2500. Just checking for clipping on very loud LFE effects. It was obvious that one channel had a continuous orange light while other only flashed on now and then. I have yet to see a red clipping light despite all my audio games. The two sets of drivers not only have very different physical characteristics but also different impedances. It occurred to me that I should try to match these orange lights on broadband LFE effects. The EP2500s controls ended up at 90 degrees to each other. I then physically checked the excursions with my fingertips on the outer suspensions of each set of drivers.

On bassy music (like Bass Outlaws) the drivers show quite serious variations in excursion. This is unavoidable. On deep and continuous LFE "roars" the drivers are much better matched. This suggests (to me at least) that they are now sharing output duties more evenly. The sound and feel very strong on films now. With some amazing infrasonic effects on recent films. I must find time to try some of the old bassy film classics like LOTR. I have never heard them played properly on my various IBs.

Of course nobody sensible would use two very different sets of drivers in one IB. I had no choice in the matter. I was originally supplied with a set of four very poor quality, very badly machined and cosmetically unfinished IB 15s.

After much fretting about the missing infrasonic bass I discovered they had a totally non-spec Fs of 32Hz instead of 16hz. I had followed a thread on an audio forum where another owner was complaining about his IB15s. So I tested my drivers myself. Using REW, a small amplifier and a series resistor I discovered Fs averaged nearly 33hz instead of the claimed 16Hz.

Later, when John H @ AE offered me four of his latest 16Hz IB drivers I discovered these were non-spec too. Measuring at 13Hz average Fs. He must have dumped some of the pre-production prototypes on me. At least they were properly finished this time. They cost me a lot of money to get delivered and cleared by the freight company.

John had originally told me he would pay my costs but didn't. After posting a favourable review on his AE forum I have now been banned. Presumably for speaking up about his non-spec drivers on another forum. It seems supplies of his excellent IB drivers have now dried up. He seems to be incredibly unlucky in his choice of workers and suppliers. Last I heard he was working alone to catch up on backlogs of unfilled orders going back for over a year! Dé jà vu!

Ironically, Fi, the only other supplier of specialist IB drivers, is restructuring. Henceforth production of all their HT drivers will be under the Blueprint name. It seems too many customers were using their HT drivers in car audio applications and breaking them. Several months without any IB drivers being available is causing some disquiet in IB circles.  Blueprint hasn't made any public announcements for several months.

If there is any doubt about the latest boost in performance of my IB you may find the following amusing: My wife had gone downstairs while I set up the system for a new hired film. She came back up with a bowl of yoghurt just as an LFE moment hit. She was so shocked she poured her yoghurt all down the front of my system rack! Of course I switched everything off as quickly as possible. Then there was an intermission while everything was cleaned up again. No damage was done but it is revealing of the incredible shock value we are now getting from the IB. :-)

*

The mutual benefits of a constructive forum

*

Forums are strange places. There are those who thank the regulars for their input. While completely ignoring the fresh ideas they themselves brought to the floor. Their own potential impact on the subject may be far greater than the safe council of those who regularly offer basic constructive advice. 

The benefits of any constructive discussion are always mutual. Provided the exchange of ideas continuously redefines the possible within the flexible framework of the already known.

Hierarchical battles for supremacy are infinitely wasteful of time and energy. The pedant, dictator and bully block all progress until they can be finally overthrown. Their egos are all that they have to offer and this is poor sustenance for any form of true creativity. Their only purpose is in building their tinpot armies. With marching bands rigidly goose-stepping across their ego's empty parade ground.

The finest teachers are those who allow others to expand to fill their own potential. Thereby increasing the sum of human knowledge by facilitation and open questioning. Rather than forging endless bottlenecks and hurdles to overcome.

The best advisers do not dictate rigid rules. Instead, they allow others to answer their own questions in a creative way. The safety net only remains in place should they stumble. Or lose their nerve while scaling the heights. While still unfettered by dragging ropes.

Criticism and negativity do not fan the spark in the kindling of human endeavour. The freedom to explore new ideas should be a universal right. We learn far more from our mistakes than we ever do by slavishly following the footsteps of those who went before. That way lies the tyranny of countless rigid rules and regulations and stifling conformity. The chronically septic appendix of religion and dogma. Which sap the energy of all human society at present. Crippling its victims and all those they lock into their self-built, universal asylum.

A strong framework is still vital to avoid repeated, easily predictable failures through ignorance of what went before. Though the accepted forms should always be flexible enough to allow our minds to soar free. To continuously push the boundaries of the possible. This is the only real way forwards without extravagant waste. To dare to be different is the root of all human creativity. Not merely for its own sake but to add to the sum of the whole. Fear of failure must be the most common and contagious of human weakness.

Decoration has its place but never at the expense of fitness for purpose. The triumph of pointless detail over function is never a useful goal. This path leads to ostentation and finicky gargoyles. Mere competence only delays damnation by faint praise. Does an ark really require a gilded figurehead?

The finest creations are those which beguile us with their staggering simplicity. Those things which make us ask why nobody thought of it before. It seems so obvious that it was unthinkable. To have dared to have tried was all that stood in its way. These things have a unique beauty which does not jar. They leave us in awe at the genius behind it.

Perhaps the opposed driver, infinite baffle manifold should be included in the list of apparent simplicity concealing true genius? The manifold offers cancellation of reaction forces and the compact application of huge driver cone area. While maintaining coherent phase at the mouth. All without raising the free air resonance of the multiple drivers and achieved with the simplest of inexpensive and commonplace board materials.

No doubt further slight improvements are possible using more rigid materials. Though at the risk of greater complexity in manufacture. Moulded concrete, for example, offers far greater mass and rigidity at the expense of intricacy in producing a suitable mould which will safely avoid voids. Reaction forces are not the only drivers of sympathetic vibration in our building structures. Cyclic air pressure waves can set walls and even concrete floors into movement. Colouring the sound by spoiling the frequency response by addition and subtraction, cancellation and delayed output and phase changes.

Who knows what changes in manifold geometry might offer? Would a suspended (ABR?) diaphragm provide improved SQ or further reach into the deep infrasonic region? An entire wall could become a suspended diaphragm. Driven by multiple manifolds for uniformity of drive and massive pumping force. Several walls might be so treated at the expense of requiring more adjacent rooms as enclosures. Though the ceiling and attic/overhead rooms could be utilised. With ducts to the rear of the wall diaphragms. New 'miracle' carbon based materials are constantly being hyped in the media. Could these become our desired low mass, ultra-lightweight and completely inflexible diaphragms?

The sub-10Hz region seem to defy accurate reproduction with low distortion at suitably high levels in comparison with the rotary subwoofer. Is there any limit to the number and size of drivers which might be brought to bear on the problem of ULF reproduction? Apart from expense, of course. Would pumping losses between the listening room and enclosure eventually inhibit the potential for true ULF output? Is there an asymmetric arrangement between listening room and enclosures which would change our present knowledge of ULF reproduction? Has anybody mathematically modelled the IB in all its variations?

Several people have tried porting huge boxes. Port noise seems to be a common feature of their efforts. The vast flares required for equally large ports have yet to be applied to the efforts I have heard of so far. We have had little feedback as to the bandwidth and phase relative to the driver cones. One imagines the maths of the common reflex enclosure are not much affected by a huge leap in scale.

The most common drivers used for IB have a rather high natural resonance. Will steady improvements in drivers bring new fare to the IB table? Or will some new technology sweep all dynamic drivers into the bin of obsolescence?

I once imagined large numbers of SEDs (Sound Emitting Diodes) embedded over the listening room's entire wall surfaces to provide truly enormous piston area. Reproducing ULF at high levels with only microscopic  linear movements per unit. All thanks to the vast total area in comparison with coned drivers.

It would probably need a wireless system to drive each SED without the near-infinite complexity of wiring each and every unit. Built-in battery power per SED unit could be "flashed" with light or an EMP to recharge all the units at intervals. A "wallpaper" type backing material with billions of printed SEDs would seem the most obvious means of applying the sound reproduction system to the walls and ceiling. Though spraying in a support/adhesive medium might be possible if SED unit orientation was irrelevant to function. A spherical expanding/contracting flexible SED shell would make this possible. All a long way off and highly dependent on developing new technology.

*