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(flat) Voxel under cabinet
(flat) Voxel under cabinet
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Old 1st November 2019, 01:03 PM   #1
Stefaantje is online now Stefaantje  Belgium
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Default (flat) Voxel under cabinet

Hi all,


In addition to the Overnight Sensation's (TM) I'm currently building, I am planning on adding a variation to Paul Carmody's Voxel to support LFE (30~60 Hz).

As I'm planning to make the OS's look nice, they will be allowed a spot on top of the tv cabinet. A subwoofer however, is very unlikely to score a high WAF...
That's why I would like to modify the Voxel design, so it can be completely hidden from sight, under the cabinet.

I had the idea of making a triangular enclosure in MDF (1/2"), with the w5-1138 being angled towards the floor. The width I can choose freely, to achieve the internal volume of the standard Voxel design.
See some dimensions on the attached picture.
For the port, I would run a length of PVC pipe outside of the actual enclosure.

Does all of this make any sense?


- With the subwoofer being located under the tv-cabinet, against the rear wall & very close to the floor, should I expect fantastic or rather terrible "corner loading"?

- Does the external port behave any different from a regular internal port?
Is it ok to have the port placed along the corner between the rear wall & the underside of the tv-cabinet?

- Can I add a grill over the subwoofer driver without impacting sound quality? (we have two toddlers, who might have some pokey fingers...)


Best regards,
Stefaan


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Old 1st November 2019, 01:41 PM   #2
grahamgraham is offline grahamgraham  United Kingdom
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Hi,

Personally, I don't think much of the Voxel design. It's pivoted around the availability of a particular (undersized) port available at parts express, I think.

What might be a good idea is to make longer, slimmer box with a long 50mm diameter port and model them it Hornresp. You will have the ability to play with driver offset and control where the port resonance falls.

This will address the issue of undersizing the port in order to shift the port resonance up. You can use quarter-wave phenomena to do it instead.

I did this with a Reckhorn D165 driver which would have a very similar alignment to the TB W5.
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Old 1st November 2019, 04:59 PM   #3
weltersys is offline weltersys  United States
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Quote:
Originally Posted by Stefaantje View Post
1)For the port, I would run a length of PVC pipe outside of the actual enclosure.
Does all of this make any sense?
2)With the subwoofer being located under the tv-cabinet, against the rear wall & very close to the floor, should I expect fantastic or rather terrible "corner loading"?
3)Does the external port behave any different from a regular internal port?
4)Is it ok to have the port placed along the corner between the rear wall & the underside of the tv-cabinet?
5)Can I add a grill over the subwoofer driver without impacting sound quality? (we have two toddlers, who might have some pokey fingers...)
Stefaan,
1) Yes.
2) Nothing "fantastic", but the location will certainly change the response compared to other locations in the room.
3) Other than not reducing the internal cabinet volume by the volume of the port tube, there will be little difference. The port not directly terminated on a baffle will affect (reduce) output slightly, but as the wavelengths of the port output compared to the distance from the surrounding boundaries are quite small, that effect is almost none.
4) Yes, though the cavity under the cabinet will affect the response somewhat-it is a "resonant chamber" of sorts. That said, the room itself is also a "resonant chamber", response varies throughout depending on the listening and sub location.
5) Any grill that is "breathable" will have no impact on the sound quality of sub frequencies. Open weave, non-organic fabric can be purchased from any fabric store to fit your decor. Decent grill cloth has little affect (less than 1/4 dB) even on frequencies as high as 20kHz.

Grahamgraham's comment about the port being undersized is valid, with an external port there is no need to have a small port diameter and the chuffing (wind noise) and "port compression" associated with small diameter ports.

Cheers,
Art
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Old 2nd November 2019, 01:40 PM   #4
grahamgraham is offline grahamgraham  United Kingdom
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Heres a thought.

If budget would allow perhaps buy two w5 drivers and run them sealed. Very small cabinet with a low profile that wont be seen. Also the LF roll off might be a bit kinder in respect to the boundary loading of being up against a wall.

The second driver will make up the gain you would have with a vented system in respect to xmax. You also benefit from not worrying about port turbulence and resonances. You may need a little more power but I have used the w6 sealed to great effect.

Kids cant put toys in ports that dont exist.

Last edited by grahamgraham; 2nd November 2019 at 01:43 PM.
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Old 2nd November 2019, 02:44 PM   #5
Stefaantje is online now Stefaantje  Belgium
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Looks like I'll need to learn how to use WinISD and/or hornresp...
I'm not after the biggest SPL, I would be happy to trade in some dB's for some extra Hz lower. Would 2x sealed still be preferred then?

Regarding ports:
At what point is a Port no longer a Port? E.g. a Port diameter of 80mm at 1m long, wouldn't that start behaving like a cabinet with one baffle missing?
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Old 5th November 2019, 09:00 PM   #6
grahamgraham is offline grahamgraham  United Kingdom
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Quote:
Originally Posted by Stefaantje View Post
Looks like I'll need to learn how to use WinISD and/or hornresp...
I'm not after the biggest SPL, I would be happy to trade in some dB's for some extra Hz lower. Would 2x sealed still be preferred then?

Regarding ports:
At what point is a Port no longer a Port? E.g. a Port diameter of 80mm at 1m long, wouldn't that start behaving like a cabinet with one baffle missing?
How will it/they be powered?

Two drivers sealed with lots of watts and dsp would be ideal. A minidsp and class d amp maybe.

A port is always a port but will start to have quarterwave characteristics within the pass band if too long and make the crossover region a no mans land of poor response. The longer it is the lower in hz the disruption will be.

You can deal with it a number of ways, here are my thoughts:

1. Use two drivers sealed - the second SUb plays the part of the port in terms of xmax relief. Dsp to boost the lows.

2. Get the TB sub and passive radiator kit. No nasty port velocity or resonance to deal with.

3. Design the enclosure as I mentioned initially with the intention of pushing the resonance higher out of the pass band. This ties in a bit with your question about the port as it becomes a transmission line of sorts and the behaviour can be manipulated.

I'm not an expert but I see any if these solutions as valid depending on budget and how much you want to get your hands dirty in designing.
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Old 5th November 2019, 09:04 PM   #7
grahamgraham is offline grahamgraham  United Kingdom
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The w5 was my first Sub and was a terrific crash course in demanding and restrictive design. Small, low and loud us a tall order but achievable.
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Old 8th November 2019, 09:56 PM   #8
Stefaantje is online now Stefaantje  Belgium
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[QUOTE=grahamgraham;5966067]How will it/they be powered?./QUOTE]

I would love to power the w5-1138 by a class D (china) amp. Unfortunately, I can't find any with an auto-on/off feature, which is a must for me.
So I guess a 100W - 200W plate amp will be my go-to. Any recommendations? (or an auto-on/off solution?)


Quote:
Originally Posted by grahamgraham View Post
You can deal with it a number of ways, here are my thoughts:
2x sealed + miniDSP (too expensive) or Passive Radiators (too big for my limited space constraints) are not an option, so Ported seems like the most obvious choice...
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Old 9th November 2019, 07:33 PM   #9
GM is offline GM  United States
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Curiosity question; with as much length there is underneath, why not a full size ~30 Hz/112" long TL?

GM
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Old 14th November 2019, 06:19 AM   #10
Stefaantje is online now Stefaantje  Belgium
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I'm looking into a TL design for my sub, but I can't figure out whether a longer straight pipe (the only achievable form factor in my case) is as good as a tapered design.

I'm also in doubt on how usefull stuffing is for sub-applications & the effect on driver offset within the transmission line.

So there are suite some things about TL's I can't fully grasp yet...
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