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Narrowband Absorber Company P:VAD

Portable Variable Acoustic Device

Better Bass without tears

[Italian version here]

Product: Narrowband Absorber Company P:VAD
Supplier: Narrowband Absorber Company - E-mail: info@narrowbandabs.com
Price: £585.00 black or natural wood, £639.00 GBP with matching trolley
Reviewed: Summer-Autumn 2024
Dimensions: Size 525mm x 525mm x 360mm, 12.8kg inc trolley in black paint or natural wood
Author: Mark Wheeler - TNT-Audio UK
Published: November, 2024

What is your problem?

Your Old Scribe has been tinkering about with audio in various contexts for half a century. Trends have come and trends have gone in that time. Some, like the vinyl LP, have gone and come back all over again. The one thing that has remained constant throughout that time and in every listening space has been the planet earth‘s atmosphere. No atmosphere equals no music and without those jiggling nitrogen, oxygen, argon and CO2 molecules we hear nothing. Most of us listen in clouds of the stuff imperfectly contained in polyhedrons (usually rectangular cuboids) of plaster, gypsum board, brick, block, drywall, lath & lime plaster or wood panelling and an assortment of floor materials too. Therein lies the problem we intend to address with this product.

Those space boundaries are always selectively reflective and absorptive according to frequency. Hence within such a space there are peaks and troughs of loudness of different frequencies in different locations. If we play a familiar tune with a clear bass line that runs up and down the fingerboard while moving our heads around we will soon notice this effect. Stick our heads in the corners and notice the effect. We not only look really silly but we should feel very silly for spending all that money on equipment without allowing it to work properly. Your Old Scribe has used calibrated microphones and test tones to test home built loudspeakers for many years (since the Speaker Builder Mitey-Mike came on the market) but was more shocked at what it showed up about listening rooms. Thus the room described here with its lack of parallel surfaces was the first I fitted out after that revelation and made a massive difference to listening pleasure.

Real World Rooms

Most audiophiles have to adapt to an existing room that has many purposes. Recording engineers also have to contend with spaces not designed as recording studios. The same problems exist in these situations so products designed for the professional recordist might be useful to us. Enter the Narrowband Absorber Company P:VAD which has already been granted UK patents GB2592686 & GB2592762. The pictures illustrate both their prototypes under test and the finished plywood P:VAD as delivered for test and it should be obvious which are which.

Portable Variable Acoustic Device

The Narrowband Absorber Company P:VAD is designed primarily to control effectively bass problems in spaces ranging from the domestic up to public venues. The P:VAD is a narrowband lf absorber but also a broader band diffuser operating in 3 dimensions (unlike the popular 2d panels many audiophiles use behind their loudspeakers). Hence P:VAD may be positioned anywhere in the room where they are most effective for controlling low frequencies and orientated in whichever direction has most beneficial diffuser effect. Designer Anthony Frost says, "the initial idea I had for them was for use in studio live rooms, drum booths, vocal/guitar solo booths, studio control rooms, music listening and post production suites, mastering rooms, home HiFi setups and home cinemas."

Construction, Finish and Test Procedure

These are well constructed in two main finishes. Studio matt black is obviously available and for studio use some handles would be a good option. There is also excellent real wood veneer available too on all surfaces. This is a complicated shape and such veneering is therefore an achievement for a small company, especially at this price. During their time in the remote listening lair they underwent numerous experiments to test their effectiveness while adapting them for domestic harmony. This included mid wall, room centre and corner placement. Two were supplied and tested together and in different parts of the room. The P:VAD work exactly as described in the recommended positions. They were measured and listened to in every possible permutation and combination of positions apart and together, whether stacked or side-by-side. But hey, this is TNT-audio.com and we go further. We all live in real world rooms that have to serve multiple purposes so your Old Scribe investigated methods of domestic adaptation too.

The P:VAD boxes were tried with a tabletop perched on them to establish whether they would work when integrated into domestic furniture. They were tried stacked together both facing into the corner, then both facing out, then one in on top of one out, then vice-versa. The corner location is particularly effective and also relatively unobtrusive. The P:VAD were tried in both diffuser orientations mid wall: stacked; side-by-side and on opposite walls. Larger spaces will require more P:VAD boxes and being multi-purpose devices, your experience will vary with every room space. Anthony notes that Placement depends upon where in the room there are issues with specific frequencies. It may be the behaviour of sound in general or there may not be obvious issues but an opportunity to enhance the sound further. Some people may want to reduce some bass overhang. There may be a need to make sound crisper at specific frequencies or diffuse the sound to achieve improvements.

In a typical domestic listening environment with speakers facing down the room, placing the boxes in the opposing corners of the room or centrally on the facing wall facing can have the desired effect. If room geometry or furniture is creating unwanted reflections between loudspeakers and listeners, placing them in between to interrupt the reflections may also be beneficial. Obviously, placing them between two hard parallel surfaces can help in a room suffering with flutter echoes.

"There is no medication for those suffering from flutter echoes" complain plebs misunderstanding the sentiment

The P:VAD are primarily designed for recording environments, so those audiophiles engaged in recording will find them useful to control the environment around vocal or instrument mics without overdamping the sound.

P:VAD Technology

Your Old Scribe prefers to see that products have been properly researched and tested and was therefore reassured to read that the P:VAD design has undergone extensive research and testing at the University of Salford. This is a UK university, in the engineering city of Salford. Your Old Scribe's actual measurements illustrated the frequency notch exactly as specified, the Q height and shape depending on room position.

Eschewing MDF (hooray) the P:VAD are constructed from plywood, measuring 525 x 525 x 360mm but fully 12.8kg mass. They're filled with natural sheep's wool, which your Old Scribe has measured as superior to polyester and glass based fillings in loudspeakers. This natural material is both more random and more sustainable. Compact and bijou, as filled Helmholtz resonators they offer absorption at what seem disproportionate wavelengths. A single P:VAD will affect frequencies centred as low as 63Hz with some effect lower. Multiple units will increase effectiveness especially at even lower frequencies. There's also an accessory vent extension to the front orifice (not a phrase the Old Scribe gets many opportunities to use) to lower the fs. The enclosed lid or bung can close the opening which extends their working range down to 40 - 50 Hz.

Having tackled the typical low frequency problems of small to medium rooms, the curious shape of the front face enables diffusion from 630Hz upwards. Anthony does not claim it, but these shapes in these dimensions will also create disruption and dispersion from about 300Hz up too, in theory. The University of Salford tests on six floor situated boxes demonstrated absorption at 80Hz, with and without 50mm thick sheep's wool placed in the box cavity. The addition of sheep's wool in the cavity increased the absorption coefficient. The overall absorption class for the product with sheep's wool placed in the cavity was Class C. Without sheep's wool in the cavity, the product behaved overall as a Class D absorber, which is of more relevance to professional acousticians but in our homes it means smaller things to achieve a similar effect. The Narrowband Absorber website has loads of graphs illustrating the changes in effect with changes of position and multiple units, which also affect the operating bandwidth due to the change in overal size of the acoustic treatment object. Four boxes arranged in the corner of the room in a column formation facing into the room. Absorption was evident in the frequency bands 63Hz, 125Hz and 160Hz. Those same 4 in a 2x2 configuration mid room has a clear and distinct high Q effect centred on 63Hz. A single PVAD diagonally in the corner has two high Q absorption peaks (or in room suckouts, depending on your point of view) at 63Hz with further second harmonic absorption at 125Hz.

Diffusion testing was conducted at Salford using 3D models at a scale of 5:1. Due to the size of the boxes, an anechoic chamber to undertake diffusion tests would need to have been the size of a sports hall. These tests were performed to BS ISO 17497-2: 2012 - A boundary plane method was used in a semi-anechoic chamber, using 37 microphones arranged in an arch shape. Seems pretty thorough to me, but how does it sound in a home audio setting?

In the Old Scribe's Secret Scottish Lair

The TNT-audio Derbyshire secret mountaintop lair, featured in earlier reviews, was a purpose built 4.5m x 5.3m x sloping ceiling, two clipped corners, acoustically designed space where any additional treatment would have resulted in a diminution of sound quality. In the TNT-audio Scottish lair the basic dimensions are 3.8m x 4.4m plus a deep fireplace (c1030 x c530mm rough stone), alcove (1070-1390 x 430mm) and window reveal (1150-1220 x 430mm). Being lime plaster on horsehair and laths, the walls are relatively inert and not exactly parallel. There is already standard corner bass-trap treatment and some treatment behind the loudspeaker plane. Pictures are all unglazed canvasses and local reflections are controlled above 2000Hz (tweeter x-over at 2400Hz). There is a heavy antique settee and the Ikea Hol bass trap in the window reveal.

The P:VAD boxes were tried with all this in place and with various permutations of them removed. Removing existing extensive lf treatment (that takes up more space than two P:VAD) and substituting the P:VAD confirmed that in this room a broader Q of control is required centred on a slightly lower frequency. The Narrowband Absorber Company can supply a port extender to achieve a lower frequency but your Old Scribe cobbled together this arrangement with the port cap and some acoustic foam to achieve exactly the desired effect. Usually this level of lf control in this room requires two 1.5m x 0.5m x 0.5m and one 0.75m x 0.5m x 0.5m corner foam bass traps to achieve a flat lf response in room over a large listening area. With two P:VAD (one configured as illustrated) the room was balanced with just one 1.5m x 0.5m x 0.5m corner absorber.

Several configurations were tested in your Old Scribe's room and the corner result was identical to the lab test graph. Two PVADs in the centre of the room also created the same high Q 63Hz effect but also removed the well known primary floor reflection cancellation mode familiar to hifi loudspeaker designers and installers. Tests using two well reviewed calibrated microphones and software confirmed the lab results. There is a clear high Q notch wherever the two P:VAD boxes are placed. Varying the primary frequency affected is easy using obvious modifications to the Helmholtz resonator port. Changing the Q with adjacent P:VAD boxes with different port treatments is also possible.

In a room already well controlled for overhang (tested by waterfall plot) the P:VAD absorber/diffusers still had beneficial effects, Especially noticeable was when placed on their backs. Firstly, on top of the filled Ikea Hol absorber.

Sound Quality

Your Old Scribe has never attended any Grooverider sets but remembers tuning-in to London pirate stations in Grooverider's more junglist days. Buying Mysteries of Funk in 1998 was one of those seminal moments of transition. After hearing Grooverider from nearly 10 years previously on those ever-fading tower block stations while travelling South of the river from the family familiar Hackney to attend events, it seemed like the wrong place to see a Grooverider box set upstairs in Nottingham's Selectadisc. When Raymond Bingham aka Grooverider (the perfect analogue name) began to fuse jazz with jungle it was like another British step along from dancehall and dub. The first time one notices a genre is the reason we go to gigs and surely the best reason to own a stupidly expensive audio system. Your Old Scribe is trying to concentrate on this review while being transported back but simultaneously forward while listening to this seminal, indeed one of a kind, recording through from the Decca London cartridge to mostly valve (tube) active system. The Narrowband Absorber Company P:VAD acoustic devices, currently sitting face-up, simply elevate the experience further. 8 LP sides of stunning innovative Drum'n'bass that really test whether a system-room interface is plagued by peaks and troughs. The word "Ooh" was most often used by visiting members of the plebs chorus.

After numerous tests and experiments, all of which confirm the objective claims of the manufacturer, a wild excursion of ludicrous experimentation proceeds. Every possible combination and position (including atop a high shelf) is tried to ensure that all the domestic listening room possibilities are explored. All positions have different effects. Finally is identified the best combination of P:VAD for this room, without 8 of the 11 acoustic treatments usually present. Only one corner foam absorber 1.5m x 0.5m x 0.5m remains and the absorption filling the 50mm gap behind a hard backed shelf unit remains. One P:VAD is positioned diagonally in the corner behind the right hand loudspeaker on the floor. Another P:VAD is positioned atop the Ikea Hol table in the window.

The bass is tight and clear which also enables the mid and treble to be better heard. When the P:VAD was on the floor face up between the loudspeakers, contrary to expectations, the soundstage became clearer and larger and vocals carried better. This seems contrary to all we read about early reflections and the LEDR test was almost unaffected.

Conclusion

Audio bliss is most often more closely approached by acoustic interventions than by bits of wire or esoteric incantations. The Narrowband Absorber Company P:VAD offer a simple, easily reversed, cost effective bass control and dispersion device.

Two P:VAD devices plus a trolley (exactly as tested) amount to £1224. Received value is high: it is a lot of plywood and real wool for the money. Audiophile value is even higher because that is the price of a new set of ordinary valves or a pair of NOS fancy power triodes; it is the price many pay for a set of interconnects or speaker cables; it is an entry level moving coil pickup cartridge. Room treatment upgrades the whole system forever.

Fortunately your Old Scribe already owns a lot of acoustic treatment solutions, optimised over a long period using calibrated mics and software, otherwise the Narrowband Absorber Company P:VAD would have been an immediate purchase.

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Copyright © 2024 Mark Wheeler - mark@tnt-audio.com- www.tnt-audio.com

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