Author Topic: Sub strategy  (Read 18066 times)

Offline _Scotty_

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Re: Sub strategy
« Reply #45 on: September 11, 2015, 12:10:03 PM »
Having heard the open baffle subs at CAF, I would say that a servoed switching AMP like the Rhythmic AMP is a must. High SPL output at bass frequencies requires a lot of cone area. The three 12in woofers per side were a good match for the hotel room and the resulting bass had excellent definition and extension. Acoustic bass and drums had a real life quality and impact that I have not encountered before.
Scotty

Offline shadowlight

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Re: Sub strategy
« Reply #46 on: September 11, 2015, 03:56:30 PM »
@Scotty

No doubt about the servo sub.  I own one lonely 12" sealed GR Research sub and I am exploring options to add open baffle sub in similar 2 or 3 woofer fashion.  Will have to explore DIY options (get someone to cut the flat pack and I get to finish them off)

Offline HAL

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Re: Sub strategy
« Reply #47 on: September 12, 2015, 06:30:23 AM »
shadowlight,

Ruben is building OB H-Frame MDF flat packs for sale for both the 8" and 12" servo subs for the GR-Research drivers and Rythmik amps.  Not sure of price with shipping, but he will give you a quote.  If you need the tools, he can supply a set as well for an upcharge.  I did not have the clamps, so got him to get me a set for my builds, so I bought them.

The 3x12" OB H-Frames at CAF were driven by the Rythmik PEQ370 Class AB amps.  That is the amp they were developed for.  Same amps I have for the Super-V's. Brian makes bigger servo amps like the HX800.

I have built both the 3x8" H-Frames and the 1x12" modules and it was pretty easy the way Ruben marked them, with the tools and glue he supplied.     

Hope that gives you something to investigate. 

Offline shadowlight

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Re: Sub strategy
« Reply #48 on: September 12, 2015, 02:23:58 PM »
Thx Rich.  I will reach out to him when I am ready and will also look to see if local cabinet maker can help.

Offline richidoo

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Re: Sub strategy
« Reply #49 on: September 18, 2015, 11:58:29 AM »
A different article about DBA, translated by Google from German:
http://translate.google.com/translate?prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.poisonnuke.de%2Findex.php%3Faction%3DRaumakustik&sl=de&tl=en&history_state0=

This is interesting to me, because he says you need minimum 4 drivers per array to make a planar wave. Using only two at mid-height or two on the floor per array will make cylindrical wave with poor cancellation efficiency and will also create floor ceiling modes.  But I can see how the effect could still be positive because while it may not avoid as many modes the wave is roughly planar at ear height because there is a cylindrical wave formed with two horizontally spaced drivers. And side to side wall modes are still avoided.

This picture is interesting.

It shows how the individual spherical waves eventually combine to become planar waves. But this requires some distance. At zero distance, along the front wall, there are only standing waves. At several times the distance of the driver to the wall, and with help from side wall reflections (shown in red,) the spherical waves finally combine to become planar. This is true of front and rear arrays in DBA. I guess the planar formation is about 3x the distance of driver to wall, but planarity increases with distance as the waves naturally flatten with increasing radius.

It's important to note that waves do not have any replationship of affinity to each other. They don't know each other is there. They pass right through each other with no affect on each other. We observe the addition and subtraction at specific times and locations as modes, but there is no real interaction. It is the reflections from the sidewalls and floor ceiling that add more waves to the tank which add to the desired longitudinal wave to flatten out the observed planar wave faster than a single driver would by increasing wave radius alone. The planar wave in this case is not really a single wave, but a collection of spherical waves and wall reflections of spherical waves combining to make the appearance of a single wave.

I think this is why a true cuboid is so important to the planar wave phenomena. Angled ceiling will mess up the reflections to some degree. But I think this will have less affect at lower frequencies with more drivers in the array, since there will be more reflections also.

You want the listening seat and the cancel zone to be within the planar wave zone. There must be some distance between listening seat and the cancel zone where bass respone falls off. So a room needs to have enough length to allow the planar zone to be long enough.

I read in one description (maybe FoLLgoTT on avsforum?) that the number of drivers in the array affects the high frequency extension of the array because it allows shorter wavelengths to form planar waves coherently. But in light of the need for minimum length of the planar zone, adding more drivers to the array also shortens the distance required to form a planar wave at any freq. So in small rooms, increasing the number of drivers in the array will also create longer "planar zone."

Offline _Scotty_

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Re: Sub strategy
« Reply #50 on: September 18, 2015, 03:59:05 PM »
There are certainly optimal conditions for achieving very high cancellation of standing waves in the listening room and then there are going to be situations, while sub-optimal, where it is still worth implementing a CABS array as it will still likely be quite effective and will have the added benefit of much improved imaging and flatter bass response. The wave from the front doesn't have to cancelled out until the last millisecond.
 It's also hard to argue with Celestinos real world measurements.
 I wonder if the other people playing around with this concept are aware of his thesis.
Scotty
« Last Edit: September 18, 2015, 05:14:51 PM by _Scotty_ »

Offline richidoo

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Re: Sub strategy
« Reply #51 on: September 18, 2015, 08:53:51 PM »
Yeah you're right Scotty. Thanks

Offline Werd

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Re: Sub strategy
« Reply #52 on: September 19, 2015, 10:03:58 AM »
There are certainly optimal conditions for achieving very high cancellation of standing waves in the listening room and then there are going to be situations, while sub-optimal, where it is still worth implementing a CABS array as it will still likely be quite effective and will have the added benefit of much improved imaging and flatter bass response. The wave from the front doesn't have to cancelled out until the last millisecond.
 It's also hard to argue with Celestinos real world measurements.
 I wonder if the other people playing around with this concept are aware of his thesis.
Scotty

The problem with that Cabs paper. Like i said, I like it for the theoritcal numbering. The problem with it (people seem to overlook) are the drawbacks listed at the end of the paper.  The one i have is the diminishing returns in a furnished room. That paper which uses a smorgasboard of numbers and figures to show a problem solved. When it comes to it's own stated drawback... Nothing. No examples or anything just a statement. As a work of science with the intent to apply practical methods would then apply and show work to the diminishing returns. Its not there so what does that tell you. Its a theoretical work that isn't meant for house hold use or the diminishing returns are so bad that it destroys its own paper. Which one is it?

I only say this because you mentioned it. That other paper won't load on my ipad  :cry:

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Offline richidoo

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Re: Sub strategy
« Reply #53 on: September 19, 2015, 01:15:23 PM »
Very low frequency wavelengths will not be diffracted by room furniture because furniture bits are too small to affect the long wavelengths. With only two subs per array, the bandwidth of the array will not be high into the upper bass range where furniture will be a problem, methinks. Try it and see...

It is a valuable resource because it gives practical advice and provides measurements proving the concept works. Of course one can find faults in anything. 

It was his PhD dissertation afterall so you can't expect him to hype the problems. ;)

Offline Werd

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Re: Sub strategy
« Reply #54 on: September 19, 2015, 02:30:59 PM »
Very low frequency wavelengths will not be diffracted by room furniture because furniture bits are too small to affect the long wavelengths. With only two subs per array, the bandwidth of the array will not be high into the upper bass range where furniture will be a problem, methinks. Try it and see...

It is a valuable resource because it gives practical advice and provides measurements proving the concept works. Of course one can find faults in anything.  

It was his PhD dissertation afterall so you can't expect him to hype the problems. ;)

The applications on the paper into a bare rectangular room are excellent. You can't make me not like it... :thumb:  :rofl:. It is a theoretical exercise and an excellent learning tool. Couches and heavy curtains do sink bass including other speakers. What they (furniture,etc) are good for is not allowing bass nodes sound audible back at the sweetspot. If you want the room to low freq. sound the same at different  spots Like a a sitting chair in the corner then CABs is what you want. If you don't care about that and only care about the sweet spot then it might be chasing over kill and can be accomplished doing other things.

Mind you the cost of a decent sub stand is probably more expensive than a delay.  :duh so maybe not   :lol:


« Last Edit: September 19, 2015, 02:33:28 PM by Werd »
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Offline Werd

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Re: Sub strategy
« Reply #55 on: September 19, 2015, 03:01:02 PM »
   IMO most of the issues of sub placement is most subs are in a box. Open baffle is a huge advantage over seled or ported subs IMO.
   Add servo drivers with a plate amp designed for such will change your sub opinions.
    We recently showed at Capitol Audiofest using three per side servo open baffle subs with great success.
     Using servo controlled drivers eliminates any box coloration from the back wave. All drivers are designed to act as one with a computer controlled coil on the drivers.
    Tight articulated bass wit zero boom or or overhang. tone with harmonics. One is easily able to discern foot pedal action on organ as never heard before.
    After hearing open baffle design done right it would be impossible for me to listen to a sub in a box.


charles

i like how an enclosed subs work with OB mids and tweets.  :thumb:
Nola Viper Reference iii, Nola Blue Thunder Subs, Chapter Couplet 400s, Chapter Précis 250 integrated set to pre, Bryston BDA2/BDP1.
Torus RM-20 240v

Gutwire, TWL, Wywires,