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Audio Discussions
Topic: The Organic Bass vs. ULF Drivers

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Posted by Romy the Cat on 07-29-2018
My Placete preamp was sitting in Idaho for update for a long time, so there was not a lot of audio activity lately. Also, the last few month there was a lot of things going on in my life that severely compromised my audio rotation. It is summer and small kids spend a lot of time outside that request a lot if not my attention but at least presence. The property needed to be open for summer business and there was a lot of work need to be done. The idiot-landscaper destroyed grass at our lawn that required me to learn about the damn grass growing and fix it. I undertook a large construction project in our home that required a lot of planning and supervision, it is still going one and hopefully will be over in a week or two. I fired one of my long term helper and another good long term helper ended up in jail, so with a lot of property maintenance tasks I ended up to involved much more then I would like to. Our nanny tenure is expired and new one need to be acquired. I undertook a major transition from .Net to Golang in my professional life. Amy’s parents moved right next to us, which is blessing and curse. Amy and I decided to change to that dreadful “healthy life style”, whatever bloody thing it is, but hopefully it will keep us available for each other and to our kids slightly longer. I turn 50 years old in beginning of month, I can write a fucking book how I feel about it! Anyhow, there was zillion other things that made me kind of “busy” and there was not a lot of audio in my life during the last few month.  
Lately, I go my Placete back, the life looks straitening up and a few last time I had a long listening session in my listening room I recognize that I was so much missing these listening experiences.  The playback is a good shape, the extra 6dB from Placete made is even better. The way how I left playback before was a “smart” setting in my view. The playback do not go too low in term of overall balance, it has solid mid 30Hz, but it has also no “shit bass” when typically “wrong means” are used to squeeze bass out of wrong and bass-impotent topologies.  The lack of bass is not so notable in my current playback.  In fact the bass is quite good in my estimation. What is missing is the last feeling of “weight”, the very specific softness that usually introduced with sub 20Hz response, the softness that warms the whole sonic presentation and make is so fucking palpable!  I had in in my formal listening rooms, I call it ULF cannel (Ultra Low Frequency) and I do not have it in my current listening room. Here is how it was done in my last listening room:

When I said that that I left my playback in “smart setting” I meant that I did not go for ULF by wrong means. You cannot get any proper ULF by bumping room with LF distortions that come for a running a regular commercial subwoofer. You cannot put a large Sunfire-like topology with tweaked electronics in use. Well, you can and you will get the right SPL numbers under 20 but it will be sound that satisfy only your SPL meter but not you spirit.  
So, with this post I am starting to collect my thoughts about the ULF for my new listening room and hopefully as a result, I will have it implemented.
Rgs, Romy the Cat

Posted by rowuk on 07-29-2018
you have often advocated the ULF channel not having a sharp lower knee. Maybe something like the Thigpen rotary woofer with response to DC would be worth considering.

Posted by Romy the Cat on 07-29-2018
All thinking about ULF are usually centered on 3 subjects: drivers, topology and amplification. Even though these 3 subsets very much intertwined I still would like to talk about it separately. We do presume that we have the proper drivers for proper topology with proper amplification. When wrong type of driver used for a given topology or wrong amplification applied then there is truly noting to talk… 
The absolute majority of ULF solutions out there today are different variations of ported enclosures. It is know that I hate any ported bass, including is super expensive implementations. Still, in most of the cases implying bass I am taking about auditable bass that always to my taste has some foreign vowels in it. It is a valid presumption that is a ULF channel is crossed under 20Hz then the auditable port accent might not be heard. Years back Wilson Audio made the XS model with two 18” in a ported configuration that meant to run under the large Grand Slamms. That would be sub 20Hz setting and it something that might be aligned with what I am looking. Still, the large ported implementation similar XS takes a very large box and I do not want to invest my listening room with such a monstrosity. 
Also, I need to admit that I have no skills to make a ported design to sound better. Sure I can load the T/S in spreadsheet and circulate the necessary detention and to invest money into better peripherals but my hunch suggests me that it is not how good sound archived. I do not see myself to dedicate much efforts to learn about ported design decisions and its sonic consequences. 
Well, there is direction to buy a ready to go bass sections, so call subwoofers. Here is the problem. There is practically no products out there that might be used for ULF application. Most subwoofers meant to be used for auditable range. Let to look at the good commercial subwoofers. JBL for instance use to have a very good driver 2245H with resonance frequency 20Hz, QMS 2.2 and BL21. You can makes a very good sounding ported subwoofer with it serving very nice 30 or 40Hz. As you driving it harder or go lower in a larger room then with xMax 9 mm it is not so useful. JBL replaced 2245H with modern version 2269H, it has FS 28Hz more BL and xMax at sub 20mm. You can drive this beast much harder and JBL made number of new LB section around the driver: MD7, Sub18 and a few others. All of them are ported at low 20Hz and they can handle “some” power abuse at transition slope. This type of solution is also big and I would need to be very careful to enter an auditable range as the Fs is to close. 
The seals enclosure are foe sure the kind in my view but having 10-20dB lower out at RS you need a lot of drivers to get some SLP and VERY large box to avoid problem in case internal volume compression kick in. 
The horns also out if picture foe me. It might be a good idea to go for midrange horn and use my current LF section for midbass but I do not have in me stamina to unleash myself on another Midbass horn project. 
There is a direction that I am looking now – the Infinite Baffle (IB).  It was almost a cream de la cream topology, superbly hard to implement and very had to implement. The funny part is that my new listening room almost made foe IB. I have a very cool second sealing above my listening room and I am considering to put IB in there. With IB drivers need to be able to handle high exertion and a lot of power. I have in my storage 8 Aura 1808 drivers. They are 96dB sensitive, tunes for 25Hz and under 18mm Xmax, the most important is that 1808 undehung! So, I am considering to put 2-4 per channel, in IB configuration, loaded into an open triangle. There are some other options. The AeSpeakers have cool driver IB18HT. It is not underhang but with Apollo update it might be useful. It tuned for 18Hz, 18mm eversion, slightly less BL and less sensitivity. 
I will be exploring more IB options during the ways and weeks to come…

Posted by Paul S on 07-31-2018
The AE cited is said to be "designed for IB".  Since one does not "use the box" or a vent, etc. to jack up IB LF, it's going to be all about moving the 250g Mms through  the usual, steep, ULF filter.  Maybe a notch filter or anti resonance filter at 19 Hz?  Any readers out there running one of the AE IB woofers?

Paul S

Posted by Romy the Cat on 08-01-2018
Are any commentary from the folks who have done it before?

Posted by Romy the Cat on 08-01-2018
I engaged is a discussion about my IB project with some guys who do IB for a while:  , the My Projects Section, I think you need to login to get it… 
What is interesting is that they claim that “rubber and foam do nothing to decouple the manifold from the structure” because it will be “tremendous amount of vibration from the sound waves”. I certainly respect what they advise but it does sound not intuitive to me. I know that there are some builder at this forum, what is your take on the subject?

Posted by Paul S on 08-01-2018
Romy, does the area behind the drivers open into a sort of attic space?  If the parts of the structure are well fastened together, you get one major resonance.  Depending on the driver behavior it is sometimes possible to "spread" the resonance around some.  But at basically sub-sonic frequencies, expect the house to shake, according to what you're listening to.

Paul S

Posted by decoud on 08-02-2018
Low frequency damping is a huge problem in architecture, and that it is poorly solved tells you it is hard. Simplest improvement would be to use a viscoelastic material with better properties than rubber and to embed weights within it. Perhaps obtain a two inch thick sheet of Poron, fire lead shotgun pellets at it, and cut out your gaskets from the result.

Posted by rowuk on 08-02-2018
If one is using multiple in phase drivers, they are spread out over space and help reduce resonance by interference. Another possibility would be a B&W like lightweight matrix enclosure to move resonance UP, where it is more easily damped. A third possibility would be to mount the drivers in reverse and connect the chassis or magnets. This impulse compensation would dramatically reduce the transmission of energy to the structure!

Posted by anthony on 08-02-2018
 Romy the Cat wrote:
I engaged is a discussion about my IB project with some guys who do IB for a while:  , the My Projects Section, I think you need to login to get it… 
What is interesting is that they claim that “rubber and foam do nothing to decouple the manifold from the structure” because it will be “tremendous amount of vibration from the sound waves”. I certainly respect what they advise but it does sound not intuitive to me. I know that there are some builder at this forum, what is your take on the subject?

I did not bother signing on to that forum to see your thread, but no foam is going to decouple 20Hz, not even close.  Part of the design criteria of my my Bass Cannons project is to try to limit the transmission of low frequencies through the floor of my room down to the house below.  Speaker cabinets at those frequencies do not attenuate the volume very much and even with my rather inert, damped, very rigid and pre-tensioned Cannons sound leaks through like water through a sieve.  The transmission of sound causes vibrations in the cabinet walls which is then efficiently coupled to the floor which vibrates in sympathy which causes sound transmission to the rooms below.  I looked at all kinds of ways to isolate these speaker vibrations from the floor, but in the end I used industrial pneumatic isolators similar to those you have in you Vibraplanes (but much less expensive).  Part of the reason that I used those mounts is so that I can level the stack of Cannons, but there are other low frequency mounts that you may be able to use if levelling is not required.

Look for the resonant frequency of the mount (Fs) that is sufficiently below the frequency that you wish to isolate above.  Multiply Fs by the 1.41 and that is the frequency from which the isolator will start isolating:  so if Fs = 5Hz then isolation begins at 7.07Hz.  

Have a look at these mounts.  Note that they have specidfied a minimum and maximum load:  to get best isolation you have to load them near their maximum (same with all of these mounts I will link you to).  These are the pneumatic mounts that I used.  Under the DSET power supplies I needed something that was relatively inexpensive but capable of isolating reasonably low frequencies so that I could keep floor vibrations out of the power supplies:  I used these.

I hope this is of some use Romy.

Posted by N-set on 08-05-2018
As a practitioner of vibration decoupling (, I second the idea. No gel, foam, rubber, etc will work on ULF as high mass + pneumatic mounts do. Pref. pneumatic damped too. I can assist with the design of the suspension.

Posted by Romy the Cat on 08-07-2018

Posted by Paul S on 08-07-2018
It is not clear to me, when looking at the sectional elevation, are we seeing an "exit hole" that is smaller than the sum of the driver diaphragms?

Paul S

Posted by N-set on 08-07-2018
How heavy is the structure to be suspended?

Posted by Romy the Cat on 08-21-2018
My contractors who built for me the 40Hz midbass horn in my former listening room is doing currently my infinite baffle manifold. The deals was changed, it is not what depicted above and there is no compression chamber in there anymore. It make with 1.5” Baltic birch and it is heavy like hell. If everything will be fine then we will be opining the attic next week and begin to cut the joists to mount the thing in time-aligned position. H, the 4 Aura 18 drivers in that room with half dropped Fs… it will be interesting. Frankly I do not know what to expect from sound…

Posted by Paul S on 08-21-2018
Is it too soon to talk about amps and X/Os, line or speaker level, active or passive, etc?  If nothing else, it might save years to use a "board" to establish profiles, especially since the speaker positions will be fixed, and there are (almost) always sum and difference issues.

Paul S

Posted by Romy the Cat on 09-03-2018
Ok, my carpenter brought today two large manifolds for 4 Aura drivers and this week will be installing them. Can’t wait how it will end up sounding...


Posted by Romy the Cat on 09-06-2018
OK, the first assembly is there. It sits on 3 joists and with the joists are cut, blocked and warped up. The exit is 30.5 inch by 24 inch. It is 1.5” birth plywood.



Posted by anthony on 09-06-2018
Although difficult to tell from the photos, they look pretty close to being time aligned too Romy, by the time you allow for the height of the baskets in the ceiling and their overall height above the horn stack relative to your sitting position.  

Posted by Romy the Cat on 09-07-2018
That was a subject of long consideration for me and I ruled not to go for time alignment. You see, my current listening position is 8.5 feet from the diaphragms and my ceiling height is 14 foot. Let pretend that I am siting at 4 feet at my listening chair then it still not enough distance to get a true time alignment. There are more complications then this. I have 100 inches ceiling fan above me that I would like to keep, I would like do not have IB exit juts above me, I would like the IB exists were separated between R and L channels, I would like the IB exists were not in the middle of the room but rather closer to walls and to be loaded to the walls. And there is another huge reason: above the ceiling in the attic I have a LOT of things going on. I that’s the exhaust pipes from bathroom fans, I have center HVAC in there, lightings, security and a few other systems are running in there and my carpenter spent a LOT of time to reposition the thing and to clear the space for two manifolds. So, we end up with 2 locations that are a good compromise to the are equidistant from my listening position and to be visually agreeable in the room (my listening position is not symmetrical in the room). So, it is not time aligned. I am planning to cross it at 20Hz and it will be indirect hitting my listening position, if we can call “indirect” about pressure wave propagation… 
So, in a way it is a compromise and “a bad design” to begin with but it is what it is. When I divorce my wife and built my next house explicitly for listening pleasure then I will factor the time alignment of IB into the room design but for now it will be as is. I wonder if I will be able to get from IB the overall quality of the sound I was able to get from the system with midbass horn. I know that IB and midbass horn are different animals but I am taking about the overall Sound….

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