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Discussion Starter #1
Hi

Jack's IB thread raised some issues which I thought should be examined in more depth but I didn't want to muscle in on his thread.

My IB sounds great but has several problems which I have yet to address. How much these issues compromise my IB is hard to judge unless I had a direct comparison with a perfect IB in my own room.

A walk-in closet would have to be enormous to allow a 4 x 15" IB to work properly. At least one builder has taken the ceiling off his closet to allow it to breathe into the roof space. Or was it the room above? I imagine a closet open to the roof would get rather itchy from insulation fibres very quickly and be hopeless for storing clothes. It would also suffer from wild temperature swings in anything but a very mild climate.

I'm using 16 cu metres or 560 cu ft rear volume and this isn't quite enough for 4 x AE IB15s. I just happened to have a glazed gable end, in-roof balcony that almost perfectly suited my purposes. Besides it was my wife's idea rather than have me scrabbling about in the roof.

Muting any two of my 4 x 15" drivers made the bass almost disappear subjectively at the listening position. Whether this means you always need at least 4 x 15" drivers I am really not sure. I would certainly have been very unhappy with the results I get from only two drivers in my rather large 30 feet long open plan room. It would have been a waste of money and effort to only use two IB15s in my opinion. Perhaps using two better quality drivers with improved Xmax might have worked?

My IB needed loads of gain (+16dB at 20Hz very broad filter on the BFD) to lift the response low down from my 18Hz AE IB15 drivers. Without this extra gain the bass was very powerful in the 30-60Hz range but fell away below 20Hz. I really wanted to get a house curve more like my SVS. This huge lift at 20Hz was only effective below 20hz where amplifier power needs are falling with a true IB. Further filters above 30Hz cut that extra gain to almost nothing. Ths graph shows the raw IB response from the listening position without speakers or BFD. Crossover at a nominal 80Hz @ 24dB/octave. It is hard to judge precisely where 80Hz is on the CX2310.



I am still considering whether to build a manifold in the roof space centrally above my speakers to avoid the wall flexure I presently suffer from. Or even a manifold in the same space as my present vertical array. A pair of ceiling "outie" manifolds would be by far the easiest construction-wise. But cosmetically even more difficult to sell to my wife than me crawling about up in the roof to hide the manifolds. Which she remains dead set against.

I hope this link works: http://frappr.com/ib15

I do not recommend placing a baffle right beside old glazed double doors like mine. On REW it sounds as if the whole wall takes a sudden deep breath at the start of the test sweep. The sudden and violent vibration at 10Hz is so loud that it is really quite frightening! This awful racket at a nominal 75-80dB test level can't be doing the performance much good at even higher levels on typical programme material.

Even compromised in various ways my IB still sounds great. But given the amount of work involved. Not to mention the expense of 4 drivers, crossover, pro amp and loads of cables. I would strongly recommend that you do it right first time. Stick to the IB Rules. Or, like me, you will keep wanting to change things. Rather than knowing this is as good as it gets from day one. If you end up changing things later you are almost bound to meet resistance from your partner as the project gets more drawn out than either of you hoped, or feared.
 

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Discussion Starter #3
My listening room is in an attic within the roof space. There used to be a sort of sun room at one end open to the great outdoors but seperated from the listening room by double doors. (French windows)

I enclosed this open space with large insulated windows fixed at the gable end to make it into another room at one end of the roof space. This new room became my IB enclosure.

The silver metal panel you can see in one of the images is a louvered panel. I was worried about the sun beating down on my drivers through the glazed gable end.

Sir Thomas de la Cult was not happy at the idea of closing off the backs of the drivers. I calculated the actual open area of the louvers between the alumunium blades and decided it did not reduce the freedom of the backwave. Subsequent listening tests suggest it had no audible effect. It helps to add somes stiffness to the wall thanks to the frame and 6" long screws holding it in place. If I had to advise somebody building an IB I'd say don't enclose the drivers. It is much sexier to be able see and show off the drivers.
 

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Sounds like some good advice from learned experiences Chris... thanks.

I'm surprised all those windows have survived.
 

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Discussion Starter #5
I haven't noticed any problems with the windows in the end gable. It's the poor, old, glazed, double doors beside the array baffle that really flex sometimes.

It isn't my intention to put anybody off building an IB. Far from it. I'm just warning those who think they can get away with flimsy construction around an array installation.

Using opposed drivers in a manifold may be the safest way to go if there is any doubt about the stiffness of the structure which will be surrounding the drivers. Or what forms the enclosure for that matter. Things don't need much encouragement to start rattling or even get moving bodily when excited by very low frequencies at high levels.

Thomas' suggestion to try a standard sub where the IB will be installed is a very good idea. Not just for checking sound quality and hoping for a decent response at the listening position or area. But also to check out the structure of the IB enclosure. If you were going to use a garage for your IB box for example. Then a big sub should be placed in the garage and wound well up. This will certainly help to find what will rattle when the IB finally gets installed and starts moving the back space and walls around.

Going outside will also tell you how much the neighbours are going to share in your free bass. Fortunately IB bass is so clean that most of the bass leakage is almost inaudible at any reasonable distance from the house. With a typical roof space installation the thick insulation probably helps to soak up some bass in the IB enclosure before it finally escapes.

Having a good look at the IB Cult installation images is a good way to see what works. A picture is worth a thousand words.
 

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I'd consider moving the IB location but it looks like yours was quite an ordeal to get set up as it is. It sounds like your listening position is in a huge null... I started with just two drivers in my 3,200 cubic foot room and had plenty of bass for casual listening and HT... when I upped it to 4 the improvement was more in low end reinforcement as you only gain 3db or up to 6db if you double the amp power at the same time.

Did you measure the location before you built?

I know you have probably already checked but could any of the drivers be out of phase with the rest?
 

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Discussion Starter #7 (Edited)
Darren said:
I'd consider moving the IB location but it looks like yours was quite an ordeal to get set up as it is. It sounds like your listening position is in a huge null... I started with just two drivers in my 3,200 cubic foot room and had plenty of bass for casual listening and HT... when I upped it to 4 the improvement was more in low end reinforcement as you only gain 3db or up to 6db if you double the amp power at the same time.

Did you measure the location before you built?

I know you have probably already checked but could any of the drivers be out of phase with the rest?
Thanks Darren. The present position was my wife's idea to avoid me scrambling in the rather cramped roof space above the attic listening room.

The SVS cylinder put in exactly the same place as the IB baffle was overwhelming. Which suggested an IB would work well there. Though I didn't do any test tone sweeps with the SVS in that position.

I may just try a battery on the driver cables at the amp end to confirm phase. (despite my confidence in the present situation)

If I can summon the courage I may try a temporary 2 x 2 opposed-driver manifold just to check how it would perform. I can throw some scrap materials together.

The manifold can have a very large opening into the room the size of the present opening covered by the IB baffle. About 6 feet high by 18" wide. This shouldn't spoil the sound quality compared with the array and I really don't want Thomas having any more sleepless nights on my behalf. :devil:

I just had another idea! I could turn the array baffle through 90 degree to make it work against the length of the wall rather than across it. Keep the same dimensions and box in one side, the back, top and bottom. That should kill the flexure problem. I could even use a 45 degree back to reduce the space it takes up in the enclosure.
This would be not unlike some of the door mounted manifolds in the Cult examples.
The drivers work against the door frame and the natural stiffness of the wall either side rather than trying to rapidly open and close the door @ 20Hz.
 

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Discussion Starter #8 (Edited)
My compromised IB is no longer comprimised! All I needed was more power!

I was running the drivers in 4 Ohm series pairs for 8 Ohms per channel from the EP2500. That equated to 125 Watts per driver. While most of those watts were going towards the production of acoustic power it really wasn't enough for true satisfaction.

Now I have the EP2500 working in bridged mono mode with the drivers wired in series-parallel for 4 Ohms. Power per driver has risen to 600 watts! The result of this simple change is quite incredible and all at no extra charge!

The IB now produces effortless bass as low as one could wish for [<10Hz]and as loud as one can physically endure [120dB+]. The original clarity has increased further and the interplay between deep organ notes has become markedly more complex. Beating between the large pipes is suddenly very noticeable with the frequency of the beating woven into constantly changing patterns as the pipes chuff or gently breathe themselves into life, change or hold pitch then die away again. The true timbre of the great pipes is now revealed with effortless clarity.

On the briefest of notes one can hear the attack, sustain and decay completely without conscious effort. On certain organ CDs the whole house shakes to incredibly loud and very deep bass. One senses that the audible organ is superimposed on a heaving sea of infrasonics. The inaudible tones of which manipulate the voices of the great pipes to an unwritten score. The IB manages all this with nothing more than a few small millimetres of cone motion. Usually cone movement is invisible and only touching the surround gives any sense of vibration.

Drums have become much more realistic with great depth and occasionally, real shock value. Electronic, electric and acoustic bass now have enough muscle to satisfy a hardened fairground ride operator or habitual head banger. From nowhere the IB thunders with massive authority, almost malevolent weight, to disappear into inky silence just as suddenly.

The sense of incredble weight is the hardest thing to describe about the sound quality of an IB. A small fraction of a second is enough for single deep note to convey a huge mass rising and falling instantaneously but with stupendous gravity. The IB does this regularly on pipe organ and electronic synthesised bass. Not only does the IB manage this in a fraction of a second but it speaks to you with great clarity how the note began and how it swelled and was sustained. Whether the sustain was level, or dipped and rose again. Before dying back to decay into nothingness. Nonsense! (You say to yourself) How can such a short note produce this strange effect of immense weight? I'm afraid the only way you will hear it for yourself is from a True Infinite Baffle Subwoofer.


http://ibsubwoofers.proboards51.com/index.cgi?

http://frappr.com/ib15
 

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Discussion Starter #9
Most of you who have reached this far must be wondering what I am struggling to say about TIB bass. Many of you won't care anyway.

Here is a reference level recording to help you understand:

"Tsar of Instruments" (organ music from Russia) Chandos CHAN 10043 (2003)

Track 17: Credo: Music from the film "The Gadly" by Dmitri Shostakovich Op. 97.

This track in particular has very low, very loud and incredily heavy bass almost throughout. The organ writhes above and behind this massive foundation.

You should be able to feel this easily through a boarded floor, though your chair and through your body. Then note how the speed of the beating changes constantly as other great pipes are superimposed or underpin the foundation notes. Giants are at work here.

The constantly changing pitch of the enormous pipes should be perfectly clear cutting through the heavy foreground with great clarity and precision in their positioning in the soundfield. As should the timbre or tonal colour of each towering pipe played. Soft or hard edged, nasal or fluty. How it starts and how it stops should be clearly heard without any effort on the part of the listener.

One can almost feel how tall these huge ranks of pipes are as the organist tiptoes nimbly across them. Sounding like some gigantic, long-forgotten colossus. Looming over a vast set of panpipes in the subterranean gloom. As he expresses his agony and hopeless longing for freedom and the light.

A truly superb and uniquely dark piece of music beautifully recorded. But then, you may not be able to hear any of this without an IB. (or the CD of course) :)
 

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Doesn't Chris have a way with words... I think he should be a journalist.

Glad you figured out the power requirement issue Chris... :T
 

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Discussion Starter #12
If I can't describe it satisfactorily then I don't feel I can "sell" the benefits of an IB to anyone else. I find my vocabulary frustratingly limited when trying to adequately describe the IB's unique sound quality and power. While at the same time I want to share my enthusiasm for the IB.

Perhaps "IBs ROCK, OKAY?" works for everybody else? :D
 

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I'm just glad you got your problems worked out. Sounds like you are really happy with the IB. I'm still dialing mine in and am hoping my new amp will help things out on Wed. I love mine as well but there are issues that still have to be worked out of mine.
 

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Discussion Starter #14
Darren said:
I'm just glad you got your problems worked out. Sounds like you are really happy with the IB. I'm still dialing mine in and am hoping my new amp will help things out on Wed. I love mine as well but there are issues that still have to be worked out of mine.
Thanks Darren.

I shall have another look at the BFD myself and play around with some more filters using REW.

I'm listening to some Vierne Organ Symphonies while I'm browsing. The deep and powerful rumbles are very satisfying. My computer is in a bit of a bass hotspot about 12' from the array! :)

I've waited 40 long years for the bass to finally catch up with the rest of the music! Nothing else even comes close to an IB, does it?

Not tempted by 8 of these inexpensive 18" drivers then? :D
 

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Oh, I'm tempted but the low XMAX and super high Fs keep me satisfied with my choice of driver. I figure my 4 RL-P 15's will have more displacement than 4 of those 18's. If I had the option beforehand though it would have been a huge decision... $~350 for 4 18" drivers or the $1000 I spent on the 15's... I'm very happy with my choice though. They will give me more than I could ever need.
 

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Discussion Starter #16
Darren said:
Oh, I'm tempted but the low XMAX and super high Fs keep me satisfied with my choice of driver. I figure my 4 RL-P 15's will have more displacement than 4 of those 18's. If I had the option beforehand though it would have been a huge decision... $~350 for 4 18" drivers or the $1000 I spent on the 15's... I'm very happy with my choice though. They will give me more than I could ever need.
Difficult call when you only have 4 x AE IB15s.

VAS for the 18" is half that of the AE IB15.

4 x 18" should slot right in place with improved sound quality.

IB willy waving takes on a whole new meaning when you can boast 4 x 18". :hail:
 

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Chrisbee...

Now that you've alterred your setup so the LFE signal runs through your IB, have you had to change your filters? Futher up on the thread you stated you have +16 dB boost at 20 Hz with an ultrawide bandwith (120 I believe)... has that become too much? Do you still have 600 watts powering each of your 4 drivers? I would think all that boost with all that power would shred you 15's despite the stiff suspention they are known for. I asked very similar questions on your thread at the cult (and you discussed the changes a little on the crossover thread), but an in depth/theoretical answer is probably more appropriate here. If you can, please show your most recent/accurate plots on REW. I'm looking forward to your response.

BTW... Here's my thread on my EQ process. The last post is the only one of interest now that I'm done (the rest were just my documented struggles with getting REW to work). I only have +3 dB boost at 20 Hz with the bandwith set to 120... maybe I should increase it!!!

I was just thinking that maybe you can have that much boost because you have so much power. That is, you don't have to risk clipping and thus the only real problem would be over-excursion. Still, I have to think it would be easy for you to bottom out your bad boys.
 

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Discussion Starter #18 (Edited)
Hi jagman

I have only just discovered DTS + LFE in my system.I quickly found that the bass level was comparatively too high compared with my DD settings. I have reduced the IB bass channels to 0dB (flat with the Mains) from my previous +6dB to compensate. The BFD bars are lighting up for the first time on bass peaks. No sign of clipping though.

My dislike for the SQ from my Yamaha processor has denied me LFE & DTS until now. DD offered very limited dynamics compared to DTS + LFE. To overcome this I had been cranking the bass just to get enjoyable levels on bass peaks. Cone movement has never been very visible, until now. At first I would rush over on every loud bassy sequence to feel the IB cones. They are in deep shadow so difficult to see from the listening position. The Front Mains signal was rarely dynamic enough in DD to really get things moving even when overall sound levels were very high. I have always used my DVDP stereo out connection with no center speaker. This has killed the dynamics and denied me LFE. Bass simply was not being redistributed to the mains as I'd expected. It was certainly impressive but the lack of dynamics was a serious problem.

At last I am beginning to sense the true capability of my system! It has been a long but interesting journey. My insistence on sticking to a slowly evolving stereo system has been the problem all along. Had I grabbed a mid-priced AV receiver for films and just worked with that I would have been more successful from the very start.

My new soft-look RS meter has finally arrived after a total cockup by the dealer. I planned to retest the IB anyway to see if there was a measurable change over time but had been putting off testing until I received my new meter. Now I can confirm or deny the accuracy of my original REW curves using the Shack's analogue correction factors. Naturally I shall have to load the appropriate correction factors for each meter when testing.

Give me a few days and I'll post some comparison graphs.

BTW: The EP2500 has a claimed output of 450 wpc into 8 Ohms. That's only 225 watts per driver. Still enough for some (very) serious SPLs. 120+dB(C) has never been any problem at all. :T
 

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Hi jagman

I have only just discovered DTS + LFE in my system.I quickly found that the bass level was comparatively too high compared with my DD settings. I have reduced the IB bass channels to 0dB (flat with the Mains) from my previous +6dB to compensate. The BFD bars are lighting up for the first time on bass peaks. No sign of clipping though.

My dislike for the SQ from my Yamaha processor has denied me LFE & DTS until now. DD offered very limited dynamics compared to DTS + LFE. To overcome this I had been cranking the bass just to get enjoyable levels on bass peaks. Cone movement has never been very visible, until now. At first I would rush over on every loud bassy sequence to feel the IB cones. They are in deep shadow so difficult to see from the listening position. The Front Mains signal was rarely dynamic enough in DD to really get things moving even when overall sound levels were very high. I have always used my DVDP stereo out connection with no center speaker. This has killed the dynamics and denied me LFE. Bass simply was not being redistributed to the mains as I'd expected. It was certainly impressive but the lack of dynamics was a serious problem.

At last I am beginning to sense the true capability of my system! It has been a long but interesting journey. My insistence on sticking to a slowly evolving stereo system has been the problem all along. Had I grabbed a mid-priced AV receiver for films and just worked with that I would have been more successful from the very start.

My new soft-look RS meter has finally arrived after a total cockup by the dealer. I planned to retest the IB anyway to see if there was a measurable change over time but had been putting off testing until I received my new meter. Now I can confirm or deny the accuracy of my original REW curves using the Shack's analogue correction factors. Naturally I shall have to load the appropriate correction factors for each meter when testing.

Give me a few days and I'll post some comparison graphs.

BTW: The EP2500 has a claimed output of 250 wpc into 8 Ohms. That's only 125 watts per driver. Still enough for some (very) serious SPLs. 120+dB(C) has never been any problem at all. :T
Chrisbee, great to hear the LFE setup advice and extra behringer have assisted you. I was just reading this for the first time from the start today, and it really doesn't make any sense that extra power gave you so much more when 500w gave you almost nothing before?? 125w x 4 is still a lot. It really does point to VC set up IME. And as your driver wiring has now been changed, this makes most sense to me you are getting way different response. 4x15 is a lot of cone area and even if the cones aren't visibly moving much you should have had plenty of bass before with 500w. I did when I only ran 230x2 of behringer A500. I too would love to see the new REW and I'll be surprised if you don't achieve way more VLF. I must say extra grunt is a nice to have tho. :)
Good news anyway, well done!
 

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Discussion Starter #20
Chrisbee, great to hear the LFE setup advice and extra behringer have assisted you. I was just reading this for the first time from the start today, and it really doesn't make any sense that extra power gave you so much more when 500w gave you almost nothing before?? 125w x 4 is still a lot. It really does point to VC set up IME. And as your driver wiring has now been changed, this makes most sense to me you are getting way different response. 4x15 is a lot of cone area and even if the cones aren't visibly moving much you should have had plenty of bass before with 500w. I did when I only ran 230x2 of behringer A500. I too would love to see the new REW and I'll be surprised if you don't achieve way more VLF. I must say extra grunt is a nice to have tho. :)
Good news anyway, well done!
Sorry. I have just changed my post but can't change your quote. The EP2500 actually produces 450 watts per channel. That's 225 watts per driver.

The history of my system is burdened with small discoveries which corrected what was wrong beforehand. By surfing the AV forums and asking direct questions I was able to find out what was actually wrong with my system.

When I started on the IB I had almost no surround sound experience and none whatever with pro-gear. Getting the required information to make my hybrid system work properly took a remarkably long time! The downmixing thread was a case in point. Had I not seen it I would never have discovered I needed DTS and LFE for bass dynamics.

Most of my early problems were due to my EP2500 being starved of signal by the stereo preamp feeding it. The twin volume controls on the EP2500 are no such thing. They are attenuators. Decades of hifi experience told me not to turn them up too far. In fact it is perfectly safe to do so. If they need to be turned up full then that's fine.

I even tried the EP2500 bridged and then with the drivers in parallel. This hunger for signal was finally corrected by a chance discussion with a sympathetic electronics engineer. Which meant I could go back to 8 Ohms series pairs without loss of performance.

Then I was suffering dynamic compression due to my sole use of the downmixed, front main speaker channels to drive the IB. I was expecting proper bass redirection by my DVDP. Unfortunately the DVDP didn't redirect the bass as expected. So I was suffering from lack of LFE and the dynamics were very poor.

There was no lack of bass! I could hit 120dB any time I liked. It was the lack of bass dynamics and in particular the lack of LFE which was throttling my system. Bass was screwed up far too high to compensate for the lack of LFE. I wanted to enjoy the bassy scenes that everybody raves about, but couldn't! But I didn't know any of this because I had never built an IB before. I had nothing to compare it with because my SVS was so completely outclassed and I had never had that running on LFE anyway.

Finally, I have used the processor as intended to give me LFE and bass redirection. All is now well with my IB.
(As far as I can tell. Because somebody keeps moving the goalposts) :D

The speaker SQ isn't up to scratch yet because I'm still using the Mains out sockets on the Yamaha processor. I'm still waiting for my special Naim 4 Pin DIN to 2 x jack cable. So I can't use my mixer. When the cable arrives I can then start experimenting with the stereo analogue out from my DVDP. I still hope this will give me back my superb speaker SQ on films + some serious LFE wallop on top via the mixer!

If this thread (and this lengthy monologue) saves somebody else the hassle of struggling with a hybrid stereo/surround system then it will not have been in vain.

Things I have learned the hard way:

Rule 1) Don't rely on downmixed stereo for your IB feed.
Rule 2) Don't use a DVDP as your processor. It isn't one.
Rule 3) Don't starve your pro power amp of input signal. An extra +6-9dB is needed from a typical stereo preamp.
Rule 4) You need LFE and all your bass properly redirected. But is it?
Rule 5) Check you aren't using dynamic compression anywhere in your system by default or otherwise.
Rule 6) DTS is more forgiving than DD5.1 when you are struggling for dynamics.
Rule 7) The controls on the EP2500 are attenuators. Turn them right up if you need to!
Rules 8-10) IBs rule! :T
 
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