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A force canceling subwoofer for implementing DBA's ( and Trinnov variant) around the periphery of a videowall based on the Purifi PTT10.0X04-NAB-01.

CINERAMAX

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This is a Quad Variant on the dual opposed concept. It is particularly useful in the new niche market, as the top videowall engineers are always extremely cautious regarding subwoofer placement. Videowalls resemble jigsaw puzzles, exhibiting a delicate sensitivity to vibrations that cause them to open up.

It is an-In bulkhead sealed design, the port is covered with wood lattice that is acoustically transparent to bass.
lattice work specs:
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The concept (based on dual opposing 12's) was enthusiastically endorsed by Arnaud Laborie at CEDIA. He even sketched it and offered a 10 % displacement variant that allowed for a larger cinemascope aspect ratio screen.
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POSEIDON ELEVATION KEF-PURIFI 181.png


The original design explored reaching 125 db @ 7hz with the 8 inch variant whose charts are here.
8INCH.png

The original plan with DSP, we make a Linkwitz Transform to give it more boost in the bass. Here I have boosted it down to 12Hz Q0.71 and shown the results with 2V peak on the speaker

EQ.png

Unfortunately, the 8-inch Purifi was found to be insufficient, as third-party peer review revealed. Additionally, we had neglected to consider room gain. German dBa experts suggest that room gain typically ranges from 7 to 9, while the English collaborator, associated with all Trinnov demonstrations and numerous dealer showrooms, indicated a room gain of up to 14.

A quick and dirty recalculation based on the 10-inch model indicates:

If the goal is still to achieve 125dB at 7Hz, then upgrading to the 10-inch model will be advantageous due to its higher excursion and larger cone area. Following similar calculations:

- A single PTT10.0X04-NAB-02 in a 35L enclosure, DSP corrected so that 7Hz is 10dB down, results in an SPL of around 91dB @ 7Hz within the driver's maximum excursion.
- With a 7dB room gain, this increases to 98dB. Therefore, an additional 27dB is required, equating to 4.5 times more woofers, or about 23 woofers. Consequently, it might be prudent to increase this number to 32 woofers, arranged in an 8 x 4 configuration.

Thus, it appears feasible to achieve the desired outcome with the 10-inch model.
 
I'm not an audio guru but how can PTT10.0X04-NAB-02 go to 7hz? I find it even more intriguing that it would work in a DBA/waveforming configuration
 
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Forget everything I said. I like it and I will make build as soon as the purifi 10" becomes available. It just looks awesome! Hopefully it will sound good as well. I have some concerns about its ability to dig that low and clean/without compression but we shall see...
 
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I'm not an audio guru but how can PTT10.0X04-NAB-02 go to 7hz? I find it even more intriguing that it would work in a DBA/waveforming configuration
One of the latest discoveries from Trinnov is that force cancelling effectively alleviates rattling that naturally occurs when subwoofers are mounted on walls. I implemented it for other reasons, including the structural integrity of the videowall's jigsaw puzzle nature. We even designed the mount to be anchored outside the isolated envelope, because although the quad subs cancel, there is always gravity-induced vibration that is addressed with the proper sub support structure. However, every countermeasure helps. You could use force cancelling, apply gravitational-born vibration dampening, mount the wall support outside the isolation envelope, and employ a fourth spring-isolated videowall mounting frame. These are four possible components of the ideal videowall mount.
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I'm trying to reduce the diameter of those coils...
 
Looks like a neat setup plan.
Is there a specific reason why you would use this purifi driver contraption instead of using just bigger sub drivers? Scan Speak drivers for example are really popular for DBAs here.

And is the second center channel really necessary?
If you're using a cinemascope LED wall that's on eye level then the upper/lower border of the screen is only about 12 degree off.
The center image shouldn't be that much off and Trinnov also has this position remapping AFAIK. A second center could potentially be even more harmful to useful.
 
IIRC the Purifi 10" is spec'd to have really low distortion, probably the lowest distortion of any plausibly-used-in-a-sub driver I've seen. And they tend to build drivers with high excursion, too. So I guess if you have an unlimited budget (and that goes for amps too) a 32x Purifi sub array makes sense...

By my lord is this build next-level. I think this is well over $32K just for the drivers. I hope you aren't building this in an earthquake zone, you might trigger something.
 
I thought my current build is crazy with some poor aluminium trussing but this is the real deal. Your renderings are greatly appreciated!

@juliangst I’m not the OP (obviously) but I think that one advantage of this config is that it provides you greater flexibility for the subwoofer placement as the cutout is only 10”. Not to mention that although the whole box seems to be 32” it’s still very shallow (~12” 14”)
 
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IIRC the Purifi 10" is spec'd to have really low distortion, probably the lowest distortion of any plausibly-used-in-a-sub driver I've seen. And they tend to build drivers with high excursion, too. So I guess if you have an unlimited budget (and that goes for amps too) a 32x Purifi sub array makes sense...

By my lord is this build next-level. I think this is well over $32K just for the drivers. I hope you aren't building this in an earthquake zone, you might trigger something.
32 Purifi 10s for the front wall and 24 for the rear wall, some of those 24 will contribute to LFE pressurization.
 
And is the second center channel really necessary?
If you're using a cinemascope LED wall that's on eye level then the upper/lower border of the screen is only about 12 degree off.
I am not a fan of remapping; however, using the 4-way crossover feature, it is best to use two centers with Trinnov. This project, nearly derailed by COVID delays, was visited by an AI expert who had seen multiple theaters. Additionally, this client, who operates on the spectrum and has an extraordinary ability to determine the room's RTA within 15 milliseconds, visited many top-of-the-line theaters. He remarked that the two centers are highly effective, an inconvenient truth for aficionados of multi-row theaters, as it only works for one row and the back bar. However, presets can be used to adjust the center channel for convergence on the front row, which is why the main row in this new 2024 Purifi &Trinnov Waveforming™ KEF Wallscreen Immersive Lounge is very long.

His words not mine....
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Some More pics, we handed over the shop drawings and then the client had some not so trivial changes Lol.

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The videowall mount and the subs, there are 4 isolation tricks possible, anchoring the mount outside the Iso Envelope, The Force Cancelling Sub, gravity induced Vibration Damping struts, and the coiled wall frame.

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i spent 2200 euros for 2 BMS 18n862 add 2 of them 4400 , add 2 Inuke and you go to 6000 euros , you don’t have super low frequency extension but you are safe till 25hz and up having insane spl
 
Only 32 Purifi drivers? Just one question, why? OK, I know the answer...because you can....
 
This is a Quad Variant on the dual opposed concept. It is particularly useful in the new niche market, as the top videowall engineers are always extremely cautious regarding subwoofer placement. Videowalls resemble jigsaw puzzles, exhibiting a delicate sensitivity to vibrations that cause them to open up.

It is an-In bulkhead sealed design, the port is covered with wood lattice that is acoustically transparent to bass.
lattice work specs:
View attachment 340737
View attachment 340739
View attachment 340741

View attachment 340729

The concept (based on dual opposing 12's) was enthusiastically endorsed by Arnaud Laborie at CEDIA. He even sketched it and offered a 10 % displacement variant that allowed for a larger cinemascope aspect ratio screen.
View attachment 340742

View attachment 340725
View attachment 340726

The original design explored reaching 125 db @ 7hz with the 8 inch variant whose charts are here.
View attachment 340727
The original plan with DSP, we make a Linkwitz Transform to give it more boost in the bass. Here I have boosted it down to 12Hz Q0.71 and shown the results with 2V peak on the speaker

View attachment 340728

Unfortunately, the 8-inch Purifi was found to be insufficient, as third-party peer review revealed. Additionally, we had neglected to consider room gain. German dBa experts suggest that room gain typically ranges from 7 to 9, while the English collaborator, associated with all Trinnov demonstrations and numerous dealer showrooms, indicated a room gain of up to 14.

A quick and dirty recalculation based on the 10-inch model indicates:

If the goal is still to achieve 125dB at 7Hz, then upgrading to the 10-inch model will be advantageous due to its higher excursion and larger cone area. Following similar calculations:

- A single PTT10.0X04-NAB-02 in a 35L enclosure, DSP corrected so that 7Hz is 10dB down, results in an SPL of around 91dB @ 7Hz within the driver's maximum excursion.
- With a 7dB room gain, this increases to 98dB. Therefore, an additional 27dB is required, equating to 4.5 times more woofers, or about 23 woofers. Consequently, it might be prudent to increase this number to 32 woofers, arranged in an 8 x 4 configuration.

Thus, it appears feasible to achieve the desired outcome with the 10-inch model.

You provided a bunch of "box model" results above. But this only captures what the system will do from the perspective of its TS parameters. As such, this type of modeling completely misses one important aspect of this design: the tunnel resonance.

The tunnel resonance is an acoustic consequence of pushing air in and out of the "box" into which your four opposed woofers will sit. The box forms a short tunnel or cavity that is open to the room, and there will be a quarter wave resonance that forms within it. This resonance (a peak not shown in your simulations) can easily be measured once the box is installed and a PEQ band used to zero it out, but it is good to guesstimate the frequency where this will happen. Note that the resonance does not need to be "in band" to occur, and any air movement can inject energy into the system and stimulate the resonance. The frequency of this resonance is calculated as if it is a pipe with one end closed, as described on this page:
The wavelength will be about 4*L where L is the depth of the cavity, and the frequency will be the speed of sound divided by 4L, e.g. in meters about 0.25*344/L. But in reality the length "L" will be a little bit longer than the depth of the cavity due to end effects, so you could use 1.1*L as the depth in these calculations. As an example, for a 12" depth if we correct for the end effect we can use 13.5" as L and this gives a frequency of about 250 Hz. It could be at a lower frequency depending on the exact nature of the end effect. The Q of the resonance depends on the aspect ratio of the cavity, with a long tube having a higher Q compared to a shallow or short cavity, and in this case the Q might be around 3. Keep this in mind when you are tuning the installation. Just make a mid measurement of the frequency response right at the plane of the opening or within a couple of inches and you should be able to see the response peak pretty easily.
 
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