Infinite Baffle and the Audiophile

[JonFo]

Hi JonFo,

This just looks like a lot of fun and not far removed from some ideas I kicked around as a Martin Logan franken-speaker I dreamed of concocting way back when I slaved for a Martin Logan retailer and after had the pleasure of hearing the Statement e2's in Gayle's home and later installing 2 pair. It is nice and encouraging to see such positive impressions even when using "lowly" pro audio gear to handle the crossover duties.

Hi Mark, Yes, its impressive what a good quality pro speaker processor can do. If one looks carefully, most 'high-end' active systems such as the JBL Synthesis use rebadged pro gear today. What they are not yet is consumer-friendly, which is why they tend to only appear in installer-only systems or in crazy geeks setups

... As to the "sound" of an IB, I have my own particular experiences and done my own investigations to see what really matters, and I do not feel it is any direct relation to the lack of a box behind the woofer, but rather the parameters and behavior which is commonly achieved when you have lots of displacement/capability and a very low Fb (driver + box resonant frequency) sealed box. There are some pitfalls in construction to watch for if someone is careless, but it is a very attractive solution I've heard in a handful of exceptional sounding systems.

Mark, good observation that it's more about the TS parameters of the system than any alignment. But isn't the fact that air resistance is both low and totally equal on both sides of the cone a large contributor to low THD at high SPL levels?

And yes, one does have to pay attention construction. For instance linear arrays like you are proposing are a bigger challenge to implement right than cube manifolds due to lack of balanced driver motion cancellation when they are all facing the same way. I've seen guys slap four 18" in a wall and have to redo because it shook the wall apart

I'm sure given your background, you'll do it right. Can you share how you plan to mitigate this challenge?

The biggest problem I see with IB subwoofers for most audiophiles and the market in general is that it doesn't lend itself to impulsive system additions, and you can't find extensive reviews of the exact setup you would be installing. IMO, the gradual acceptance and improvements in electronic room correction and related devices are what have started to make such options much more viable.

Indeed, this is not for impulsive cable-swapper people. It's more for the folks who understand the value of engineering a system that is the sum of the space, the gear and the setup. When viewed that way, a true SOTA system can be designed and executed using IB as part of the solution. For instance, integrating a Thigpen Rotary Woofer (the ultimate LF driver), one MUST be able to do an IB to house it.
I'm still analyzing how to integrate a TRW into my setup ...

 

[JonFo]

Anyone here been around the DIY community long enough to remember a rather impressive DIY system using BG75 ribbons, column/stack of dipole woofers and 8 12" ACI woofers in an attic IB? He was located in the NW Chicago area and I believe his first name was Tom...

Are you thinking of THE Tom, the Tom Nousaine who got a lot of us intrigued by this IB thing in the first place?

Here's a scan of his original article on 'The Subwoofer that Shook the World' - Navigate using the Page links at the top of the linked page.

 

[JonFo]

Sometimes one needs only one word to encapsulate the totality of one's thoughts. Stated another way, an idea is an emotion with roots. Jonathan: wonderful.

Thanks Ron, I appreciate the thought.

 

[microstrip]

As far as I could see, people with big speakers (Alexandria or Maxx3 type) cross their subwoofers typically around 39 Hz with a slope of 12 or 18 dB per octave, and all of them refer that subwoofer placement was vey critical. However, if we place an IB subwoofer in the front wall we are not able anymore to move it along the length or the room - in my case the largest dimension by far. Can it compromise the integration of the subwoofer in the system?

 

[FrantzM]

micro

subwoofer placement is always critical especially when you are using just one subwoofer whether you are using an X-2 or a Paradigm Atom That is why you determine the best position using a move-able sub .. Once this position is found you go cutting things... Looks like you would have to use your front wall ... The position may not be the best but once you have that limitation, that is that the sub will have to go there.. You must determine the best position for the manifold ... ( I prefer manifold)...What an IB allows you is the headroom.. It allows you to EQ the subs to the best sound you can get both objectively and subjectively.. You can use the same crossover you would have for a "normal" sub ...

I like manifold because it affords you to place more drivers than the other method. 8 drivers on a front wall in line is feasible but take some real estates on the wall itself... The manifold looks to me like a more elegant option. You can also use 2 manifolds and go for Stereo subs.. with two manifolds symmetrically placed with respect to the mains... Some people simply drop the manifold in the center and because of the headroom equalize for best integration with mains. I think that is what JonFo has done... IB allows you that. When you have output up to 130 dB in the room .. and in an audiophile situation, knowing you will need much, much less.. You can EQ down 10 dB (!!) without any penalty in performance ..Ok let's EQ 20 dB down you still are hitting 110dB a substantial output and with amplifier-like distortion. IB brings displacement to another level.. You really , simply, add drivers, especially in a manifold ... the 4 sides allow you 4 subs to start with and you can 8 easily or 12 like Tom Nousaine ... with two manifolds where you are getting into the ludicrous territory at a more than sane price.. To match the output of such an IB you would need a plethora of Gotham-like subs .. Maybe 4 or 5, for less than $10 K ! ..... (Pro ) Equalizer., measuring gig (laptop, Calibrated microphone, Sound card with Phantom power) included !!! I am itching to start mine ...

 

[Mark Seaton]

Are you thinking of THE Tom, the Tom Nousaine who got a lot of us intrigued by this IB thing in the first place?

I've met Tom Nousaine a few times and he was actually at the now defunct PSACS group meeting that was held in the Chicago area at Tom Perazella's home, which is the Tom who's name I was trying to recall. If you do some digging, there is some info on his system floating around as I believe it was on the cover of an AudioXpress back maybe around 2001. In a very quick search I stumbled across this image:

The wall behind the ribbons had 8x 12" DV-12 drivers from ACI which was pretty extreme at the time, as they were installed in the early or mid 90s as I recall.

 

[Norpus]

2nd IB

Is there any acoustical advantage in using a manifold compared to drilling four speaker holes in the wall ?

BTW, Harman subwoofer placement white paper suggest using a minimum of two subwofers, centered and placed at opposite walls. Must one build two IBs ?

Hi microstrip

I realise this reply is rather late
But i thought i'd register just to say gidday. ( also hi to terryj and paul spencer)

I am fortunate to be able to answer your 2 questions above, having asked myself the same questions some years ago and then bitten the bullet to see!

1. I bought 2x avalanche 18s off a guy who had imported 6 from US to Australia. He built an array of 4 across his front wall (after structurally strengthening it substantially) and i went the floor manifold route, venting the backwave under my stumped house. Both are legitimate IB designs and both work well. Ken did say his front wall did vibrate more than my manifold does the floor, but his drivers are not opposed like my design. Mine is like jonfos, but buried flush with the floor. It is stealth and most people cant find it when i ask them to (odd)

2. I built the first, centred between the mains after checking locations with the old portable sub. Its performance was tremendous, and very pleasing for a diy. After reading the Harman paper, i decided to try the recommended 2 sub harman paper alignment- as you mention - the second hole being mid back wall floor.
I understood at the time noone at the Cult of the IB knew if this harman alignment IB config had been done before, so that was that.
Did it work? Absolutely, the bass envelops one just that more fully. But the overall experience only adds a little, maybe 10 percent? Not so much diff on music tbh, maybe more on movies

Now to your question - do you need 2?
Nope, i eventually mothballed the rear IB. (I must confess it was more to do with getting sick of visits from the EPA due to an unfriendly neighbour than SQ)
Do i miss the rear IB? Not really, i have more than enough SQ and output to satisfy my hedonistic needs with one IB. So no you dont have to have 2.

Hope that helps

 

[Gamb]

G'day Norpus I saw your post about your ib subs and I was thinking of doing the same thing during my renovations.

I'm in Melbourne and have a cream brick 1950's house on stumps. We're adding a additional living room on the back of our house and I would like to put a sorround system in. The IB approach appeals to me because of its hidden nature.

My main concern is that because the base of my house is unsealed with vents for airflow that the neighbours will hear as much bass as I do. My second concern is that it will shake my house and crack my walls. My plan is to build a manifold with 2 opposing 15's and vent it through two oversize ducted heating vents for a completely hidden look. Though I wonder if the openings will create some port airflow sound coloration.

Thanks.

 

[Norpus]

G'day Norpus I saw your post about your ib subs and I was thinking of doing the same thing during my renovations.

I'm in Melbourne and have a cream brick 1950's house on stumps. We're adding a additional living room on the back of our house and I would like to put a sorround system in. The IB approach appeals to me because of its hidden nature.

My main concern is that because the base of my house is unsealed with vents for airflow that the neighbours will hear as much bass as I do. My second concern is that it will shake my house and crack my walls. My plan is to build a manifold with 2 opposing 15's and vent it through two oversize ducted heating vents for a completely hidden look. Though I wonder if the openings will create some port airflow sound coloration.

Thanks.

Hi Andrew

I can only say it is worth going for it
Best quality bass by far
Best bang for buck (andinexpensive)
Not too many fine woodworking skills required to build

Re your concerns
My house is 1920's on stumps and I am sure even leakier than yours - no probs. Just so long as the front and back waves are isolated which they are 99%
Shake the house? a little, but no more than another subwoofer with the same output if you crank it. Break the house - no.
I built two in the same room, no issues but have decommissioned the 2nd one as it was overkill

Neighbours? Yes they may hear a very low rumble but dB does diminish with distance and other stuff in the way (fences etc). Unless you spl race.... (which was what got me in trouble with one neighbour, who has since gone). I'd find boom boom bass from music by neighbours etc to be somewhat annoying but that is more 100Hz plus. Stuff around 40Hz and lower, especially without a natural beat such as with movies, is far less intrusive to the brain I find.

The vent size i understand should be at least the surface area of the two drivers, imo only. I have not tried it any other way, so cannot surmise.

If you wanna hear one and see one in action, you can view mine. PM sent

 

[JonFo]

Just to prove that geeks with too much gear can go absolutely crazy and solve corner-case problems with over-engineered solutions, I hereby present my solution to the following sub-related dilemma:

I wanted an easy way to adjust the Sub level across various recordings and to be able to run on/off the nifty Sub Harmonic Synthesizer (great for old 60's and 70's recordings).

Since I have the wonderful DBX DriveRack 4800 speaker processor handling the crossovers and speaker management for my front speaker array that includes the IB sub, I went to town with the HiQnet System Architect (PC software) and and created a 'panel' for their new iPad app called 'Motion Control'.
In SA I created a layout with controls for the Sub level plus buttons for Sub Harmonic synth on/off and a sub mute control.

Since so few controls would have looked really sparse on the iPad, I challenged my wife - an accomplished graphic artist, to come up with a suitable background that fit the look and feel of my theater. I think it all looks pretty cool:



I now can adjust the level on the IB, mute it and play with other controls from the comfort of my listening seat

Over the top?

 

[GaryProtein]

The DBX Subharmonic Synthesizer run through a processor loop does work well for recordings made prior to the 1970's where deep bass is simply not on the recording.

 

[GaryProtein]

. . . .My main concern is that because the base of my house is unsealed with vents for airflow that the neighbours will hear as much bass as I do. . . .
Thanks.

Don't worry about your neighbors unless they are right on top of you. The sound out of your basement dissipates as the distance squared. 6 dB for each doubling, plus your basement will absorb a good amount of sound unless your IB sub is right next to your basement exterior vent.

If you like your neighbors, invite them over for drinks, movies and tunes.

 

[mep]

The DBX Subharmonic Synthesizer run through a processor loop does work well for recordings made prior to the 1970's where deep bass is simply not on the recording.

I never heard one that didn't make pumping noises.

 

[GaryProtein]

I never heard one that didn't make pumping noises.

There are numerous adjustments you can make on the DBX unit. It probably wasn't set right. People often set it with too much boost in the 24-36 Hz or 36-56 Hz synthesis ranges. People also set the LF boost too high and set the subharmonics too high. Using it is like setting up a subwoofer. If used in moderation it will do a good job. If you try to take gross advantage of its capabilities, it won't sound good and you may well blow out parts of your system.

 

[JonFo]

There are numerous adjustments you can make on the DBX unit. It probably wasn't set right. People often set it with too much boost in the 24-36 Hz or 36-56 Hz synthesis ranges. People also set the LF boost too high and set the subharmonics too high. Using it is like setting up a subwoofer. If used in moderation it will do a good job. If you try to take gross advantage of its capabilities, it won't sound good and you may well blow out parts of your system.

Absolutely, it's in how you tune the settings. I run fairly moderate settings in the Sub-harmonic synth block inside the 4800. When first turned on, you can hardly tell it's doing anything. But play 10 minutes of an old rock recording with it on, then turn it off, and you immediately miss it. That's when you know it is about right.

Here's my current set:

 

[bwraudio]

I hope you are successful in the future of integrating a Thigpen Rotary subwoofer into your system.
There is, simply put, nothing like this sub.

One has to have a lot of space behind the rotary for it to work properly, (I vent it into my basement,
which is very large). The enclosure should be large enough with lots of thick insulation on the interior
walls to reduce the fan noise (4' wide x 8' long x 4' high, is what I use.) The opening into the room
should be at least 3' x 4' for good results (I use a 4' x 4' opening. Location is also very important
to getting great coherence with mid bass and upper bass, as well as perfect transient response.

I also agree that electrostatic speakers are difficult to get bass to to be coherent with cone bass
speakers (I use Magneplanar Tympani IV bass panels for the mid bass and the rotary takes over
below 25 hz.

The result is stunning and worth all the time to get it right.

No equalization needed, efficient (200 watts needed to pitch the blades),
one does not need to worry about over driving or damaging
the rotary. This sub handles anything one can come up with.

I use half the total output with amazing results.

Good luck with your efforts, Thanks

 

[JonFo]

Hi bwraudio, yes, the Rotary is in my future. I have some drawings of a re-do of my current space to not only integrate a rotary , but to also go full Infinite baffle for the main speakers as well.

While all the attention in IB-land is paid to subwoofers, there is actually an application for IB in terms of large dipole line sources. So I plan to build out an in-room IB chamber for the front mains, inserting three MartinLogan CLX into the dividing wall.

By killing all interference from the rear wave, I expect to obtain outstanding ESL mid-bass performance and razor sharp high-frequency performance thanks to the removal of all the comb-filtering in-room dipoles generate.

The IB chamber will be absorbent to minimize any reflections back into the panels, and listeners should only hear the 'front' of the three CLX speakers. To my mind, that should be one of the highest performing ESL rigs around.

So IB for audiophiles is more than low frequencies, it can apply to the entire range. It just requires you build the room around the principle

 

[ribbonmicsrus]

I built the Monochord Sub woofer by JB Lord, used slightly bigger cabinet and it was flat down to about 16Hz, my mains came in at 45Hz so the unit was set to come in under that point. Used a 100watt mosfet amplifier I built to drive it along with JBL's adjustable LPF.
Most impressive sound, apparently, I was one of only two people he heard who had built it. Using test CD with Tornado aircraft flyby, put the plane firmly in the room and terrified the neigbours!!. Room was 40 feet x 15 feet x 8 feet high..
Andy

Very nice sub. The biggest speakers I have built in the late 70s was a 150 lb transmission line speaker using the oval KEF B139. Much later I considered the Monochord design, using a 12" speaker, but as at time I was living in a condominium, I wisely gave up the idea of having a great bass ...

Curiously, already at that time some people claimed that the best type of sub to complement dipole speakers was the transmission line. The DTS-10 is awakening the DIY person in me. Wood is softer than stone!

 

[rugyboogie]

Looking to possibly integrate an IB into my dedicated 2 channel music room in my retirement home.
Still a bit to go in construction of the home so would need to plan for it now.
My room size is 24x16x10.
24' walls are 8" cast in place concrete.
Speakers will be on SOG concrete slabs and back of room is a 8" suspended concrete slab.
Any good sources on planning and placement ?
Ceiling is constructed of 5x12 " fir beams with 3" fir t&g for the ceiling.
Can I have the opening of the baffle on the ceiling behind the sitting location or this just a bad idea ?
Thoughts or ideas, opinion would be welcome please.
Thanks