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. :-)