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[Jonathan E Lamb]

Hi,

I've been working on a whole bunch of projects recently, some of which may be of interest.

They've not been fully documented (partly time issues, partly tech issues), so to gauge relative interest before doing that I've compiled a brief summary, and archived up several gigs of raw/unsorted design documents, so as to open source their development.

All work is released under Creative Commons Attribution Non-Commercial Share-Alike 4.0 License, so you're welcome to use them accordingly - If you're not sure if your application is reasonable either PM me or e-mail jonathan at padr co uk.
 
You may need an up-to-date version of Photoshop or 3D Studio Max to open some of these files.
Autodesk 3DS Max 2018 30 day trial
Adobe Photoshop CC 30 day trial

Disclaimer: These are not production ready design files or anything close. They're flawed, work in progress designs in need of the attention of eyes and minds more expert than mine. They haven't been prototyped, only simulated. If you attempt to develop, modify, or assemble anything purely on the limited information provided here, I accept no liability for any WOFTAM.

Let me know if you're doing or thinking of doing anything similar to any of these. It'd be great to talk about it.


Projects
'Sunflower Stereo'
A high fidelity, high efficiency portable PA system.
Dimensions/Weight: 22x38x90cm, 14kg.
Tech specs: 250w 126dB SPL@1m -3dB points 58hz-20kHz 35w solar panel
Components used: 2x PHL 900 ND bass, 20x Sica 2,5 H 0.8 SL in stereo columns,
Materials / Manufacturing processes used: 10-12mm plywood core (6mm on the midtop modules), compression moulded rubber exterior, steel or aluminium perforated grilles, acoustic foam + steel bar handles.
Project links:
Dropbox
Torrent

 
'Aphelion'
A reference monitor.
Dimensions/Weight: 31x31x60cm, 24kg, 40kg including stand.
Tech specs: 250w/500w with DSP, 112/115dB SPL@1m, -3dB points 30Hz-40kHz
Components used: Seas L26RO4Y 10" bass, Tangband W4-1337SDF 4" midrange, Fountek CD3.0 ribbon tweeter.
Materials / Manufacturing processes used: 3D printed composite panel construction, steel stamped grilles with CNC milled aluminium sheet edging and compression moulded rubber baffle edge protection.
Notes: Makes use of a proprietary technique in development for 3D printing at a much lower cost, allowing for relatively affordable large format printing of complex shapes. Sealed tapered tube loading on the midrange (100cm long tapered tube covering the 100Hz-4,000Hz band), as seen in B&W Nautilus.
Project links:
Dropbox
Torrent


'Peapod'
A pocket sized, high output personal audio device with an expandable/modular design.
Dimensions/Weight: 15.1x7.3x3cm, 245g.
Components used: Sica 2,5 H 0.8 SL
Tech specs: TBA
Materials / Manufacturing processes used: Early versions will use 3D printed parts, later versions may use injection moulded plastics, rubber and cast aluminium details.
Notes: Design files lost in disk crash.
Project links: N/A


'MicroBass System'
A bass system to supplement the Peapod.
Dimensions/Weight: 33.5x20x13.5cm, 3.5kg.
Tech specs: 5.25" driver, 93dB/1W@1m, bass extension to 60Hz, 100w, 113dB SPL@1m
Materials / Manufacturing processes used: 3D printed composite panel construction.
Notes: Design files lost in disk crash.
Project links: N/A

'SystemLink'
A USB DAC and wired connectivity set.
Dimensions/Weight: 8x2.2x2.2cm, 20g.
Tech specs: TBA
Materials / Manufacturing processes used: Early versions will use 3D printed parts and laser cut/engraved metal parts, later may use injection moulded rubber (TPA).
Notes: For portable speaker link-ups. Based around an Android/iOS powered USB soundcard hub.
Project links:
Dropbox
Torrent


'Eightball / Eightball Duo'
A low cost, DIY friendly solar powered mobile party speaker.
Materials / Manufacturing processes used: CNC cut plywood or MDF, screwed and glued
Project links:
Dropbox
Torrent


'Ghostbuster Sub' (+ nested columns)A full output [SIZE="3"]PA system suitable for transportation by bike or handcart.[/SIZE]
Dimensions/Weight: Varies, but generally about half the weight for the equivalent sized wooden box
Tech specs: Varies
Notes: Part of an ongoing series of experiments into fibreglass shell and foam core composite construction methods for loudspeaker enclosures, as well as the nesting column and horns arrangement featured in the Sunflower Stereo. The name indicates the unusually light weight of the cabinets.
Materials / Manufacturing processes used: Foam core and fibreglass shell composite construction
Project links:
Dropbox
Torrent


'PA de Resistance'
Similar to the Ghostbuster system, only with larger events in mind.
Tech specs: In standard arrangement (two double bass bins, 7 splayed columns per stack), reaches 145dB per stack with bass from 35Hz.
Materials / Manufacturing processes used: Foam core and fibreglass shell composite construction or CNC cut plywood/mdf
Notes: Doubled up bass bins and large splayed column arrays for the mids and a central column for the high end.
Project links:
Dropbox
Torrent

'Li'l Jammer'
High fidelity, high output lightweight busking amp.
Dimensions/Weight: 32x16x9cm, 4.2kg.
Tech specs: 113dB total output, bass extension to 80Hz.
Materials / Manufacturing processes used: Early versions may be 3D printed, later injection moulded plastic. Rear panel in CNC routed aluminium sheet.
Notes: Design files lost in disk crash. Polemount receptacle for suitability as a personal monitor or compact PA system.
Project links: N/A

'3D Printed Coaxial System'
Installation friendly minimalist PA system.
Materials / Manufacturing processes used: 3D printed composite panel construction.
Notes: 8" Volt coaxials on rear ported tapered sphere enclosures and an optional 18" subwoofer to supplement the low end. A relatively easy project for anyone with access to an FDM 3D printer.
Project links:
Dropbox
Torrent

'One Sheet Solar Cinema'
A mobile PA system + cinema.
Dimensions/Weight: 15kg.
Tech specs: 250w, 100w solar panels, 35ah battery
Materials / Manufacturing processes used: CNC cut 6mm plywood or MDF, screwed and glued.
Notes: Powered through batteries and solar power. Incorporates subwoofer, two polemounted stereo tops, screen, and waterproof lockable transportation and storage box, cut from a single sheet of 6mm ply or MDF (doubled up to 12mm on the sub).
Project links:
Dropbox
Torrent


There's no documentation provided with this release. It just hasn't been practical at this time to put it all together as a presentation. There are more projects of interest not yet listed, due to a disk crash a couple of years back where several years worth of design documents were lost (a motor failed inside the disk). Recovery is possible, but expensive!
 
If you find this content useful or informative, and would like to see these projects developed further or see more like this in the future, consider donating to the fund for recovering that data, and for renewing/upgrading various software licenses and hardware so that work may continue. A more comprehensive and regularly updated description of these works along with further background info and image galleries is available on the funding page. https://www.gofundme.com/creativemaintenance

If you'd like to see more of anything in particular, or know more about any element of these projects, let me know specifically which and I'll expand as best as I'm able.

[Chris Grimshaw]

Interesting design work, but I've gotta say that some of the specs are, er, optimistic. In my view.

For instance, the 113dB claims for a single 5" driver.
I ran a simulation for a 6.5" mini-subwoofer that has 1/2" of one-way linear travel, and it will just about manage the sort of specs you're quoting, over a fairly narrow bandwidth thanks to a high-Q ported design. The particular PHL driver you've mentioned simply won't do it without turning itself inside-out. It might well have 93dB@1w sensitivity and 100w thermal power handling, but that doesn't mean you can put those numbers together and ignore the fact that the driver would be producing silly amounts of distortion when asked to produce low frequency content at those SPLs.

Next up, the claims of 145dB in the bass from the larger system. I ran another simulation, this time with a pair of high-power 21" drivers in 35Hz-tuned ~13cu.ft tapped horns. At 110Hz, there's a narrow peak that reaches 142dB with 1800w per driver. At 42Hz, the pair of cabinets can only produce 132dB before the cones run out of linear travel and distortion will be problematic. You'd need 16 of those drivers to produce 145dB across the operating range, according to Hornresp's Multiple Speakers do-dah.

The reference monitor looks okay, but I'm not keen on circular shapes around speakers because of diffraction (which prevents a convincing stereo image - see Earl Geddes' work for more). I'd probably use a decent dome tweeter (maybe in a waveguide) and try to keep the crossover frequencies so the drivers are within 1/4 wavelength of each other, which will minimise off-axis weirdness.

Eightball looks like a half-Boominator (see www.diyaudio.com). The many versions of that design all seem to have good reviews. You run the risk of reinventing a perfectly good wheel.

I don't mean to just tear you down, but it seems like you haven't finished your homework just yet.

Chris

[Jonathan E Lamb]

Fair criticism Chris - A lot of my work is sloppy and needs work. I don't have a solid foundation in some of the fundamentals which does lead to errors.

The particular PHL driver you've mentioned simply won't do it without turning itself inside-out. It might well have 93dB@1w sensitivity and 100w thermal power handling, but that doesn't mean you can put those numbers together and ignore the fact that the driver would be producing silly amounts of distortion when asked to produce low frequency content at those SPLs.

Well, PHL publishes some detailed specifications relating to the xmax of the 900 ND. They used to cite the xmax as 5mm, they recently revised the specification to 6.5mm, but even that is a very conservative figure. They used to have a graph published which they've removed from their website so I can't show it, but it basically showed that per the methods most big PA driver manufacturers measure their xmax, it would actually reach 9mm.

It's the 9mm xmax figure that I used to calculate the 113dB SPL. It certainly wouldn't be hifi levels of distortion, but it's perfectly adequate for the suggested application. The main downside is the price. It's a very expensive driver with a MOQ of 6 pieces.

Next up, the claims of 145dB in the bass from the larger system

To be honest I pulled up that number from memory as I haven't got the details of that design to hand, I need to sort through some old files. It may have been lower, but the driver used in that simulation was a very chunky 21. It could have been the Eighteensound 21NLW4000 with 15mm xmax. It looks like it from the picture. That might do it eh?

I'm not keen on circular shapes around speakers because of diffraction

You're the second person to mention that and it's a definite point of concern in that design and one that I'm thinking about at the moment. The same was pointed out by xrk971 on the DIYAudio boards, he referenced the research on the effects of round baffles on tweeters from Linkwitz Labs

It's looking like the original specification of the Fountek CD3.0 ribbon tweeter may be ruled out for that reason, so your suggestion of a dome tweeter makes a lot of sense.

From what I gather, there should be no issues for the bass or midrange as specified. A sphere shaped midrange enclosure is well regarded for providing a flat frequency response, although I've not considered the stereo imaging effects you mention.

Do you have a link to Geddes' work on that?

Speaker baffle design, diffraction and baffle step - Audio Judgement

The study included very odd shapes, like a double pyramid and we are going to list the shapes and SPL variations that make sense in the real world :

Sphere ± 0.5 db.
Rectangle ± 3 db.
Beveled rectangle ± 1.5 db.
Cube ± 5 db.
Beveled cube ± 1.5 db.
Cylinder ± 2 db.

As you can see, the sphere is the shape with the least amount of diffraction.

There are loads of high end designs using sphere shaped enclosures for their midrange, including many by B&W, but they always separate their high frequency bands out to one or two levels above the midrange, presumably to minimise the baffle diffraction issues you mention. The smaller the tweeter, the smaller the baffle. A good dome could be as little as 1.5" total baffle width.

The Fountek CD3.0 will probably be ruled out as it will require a 4.5"+ baffle.

From the Linkwitz article:

The grey line indicates the 1.5" dome without any baffle at all, and that's would essentially be the target.

I'm keen to keep the design balance with the 3 equisized grilles, but A 1.5" OD dome could still be suspended behind a larger grille with a mostly acoustically transparent surround on all sides.

Eightball looks like a half-Boominator (see www.diyaudio.com). The many versions of that design all seem to have good reviews. You run the risk of reinventing a perfectly good wheel.

I'm very familiar with the Boominator and I know there's little can be done to improve on it. That isn't the aim of the Eightball.

I think the design goals are sufficiently distinct to warrant a reinvention. When people build the Boominator it's typical to spend 300-400 euros on parts, and ~200 for a Halfinator. That might not sound like a lot, but for some people it certainly is, and there is often the urge to 'pimp out' the basic model with extras like solar panels, and a cart for transportation. That can bring costs up to 500 Euros, or 300 for the half model, which is a significant investment, and doesn't include wood/cutting costs.

The Eightball cuts corners on costs considerably but hopefully not unacceptably, for people on a budget, by using the GRS-8FR 8" Full Range Driver, which by all accounts is a very serviceable bargain woofer at $11.46 each. The version pictured has a dome tweeter but the idea is for that to be an optional expansion. You should be able to build it with the full range woofers alone, cutting costs and complexity.

Someone measured the GRS woofer with a $2.50 piezo on top and came up with this unbelievably flat measurement:



I don't know how accurate that is, or how it looks without the piezo, but anecdotal feedback on the driver suggests it's good enough. I've tried to incorporate wheels, a retractable handle and a solar panel into the design. Total cost of parts including everything could easily come in at under $100/100 Euros before wood, so potentially looking at less than half, or even 1/3 the overall cost for a hit of quality, but not a hit of output levels.

The project with the unconvincingly flat measurement is on this page by the way -
 scroll down a couple of screens: https://cockrum.net/cnc_projects.html

Someone on PartsExpress has reported using it in a very fancy hifi design with good results as well:

[Chris Grimshaw]

Having looked at the BL(x) and Kms(x), I'd guess at around 5mm one-way travel for the 5" driver.
To produce 113dB at 60Hz, a 5" cone would need to move 2" one-way. Note that the PHL driver might have a cone that's more like 4" across. That sort of SPL in the low end simply needs more cone area.

How did you do your calculations to find the 113dB figure?
I use this: http://www.baudline.com/erik/bass/xmaxer.html to get a rough idea of what needs what. Of course, ported cabinets help at some frequencies, but even producing that SPL at 80Hz would still need 30mm of one-way cone travel. Some kind of horn or bandpass might help, but then your cabinet size is increasing rapidly.


The 21" driver I simulated with is a P-Audio SD21-1800N. 1800w continous, 10.5mm Xmax. With the 18Sound unit's greater Xmax, you'd need about 10 drivers to match the 16 of the drivers I simulated. Either way, we're well outside of what any pair of sensible-sized cone drivers can realistically do. A couple of those 40"ers would probably be able to produce 145dB, but anything smaller just won't move enough air.


I believe Geddes has posted about edge diffraction on diyAudio (I'm also a member there). I'd have to do some digging to find it, might be on the long thread about waveguides. All of his speaker designs seem to point towards a systematic approach to killing off diffraction as much as possible.

My problem with ribbons is that they tend to mandate high crossover points, so the polar responses suffer. A good dome is capable of all the HF extension anyone could need, so why compromise the audible range?


That 8" two-way has an unfeasibly flat response. I do wonder if he was clipping something so all the peaks got chopped off. It's in a reflective room, too, and no floor bounce. Hmmmm.

Chris

[Jonathan E Lamb]

Having looked at the BL(x) and Kms(x), I'd guess at around 5mm one-way travel for the 5" driver.
To produce 113dB at 60Hz, a 5" cone would need to move 2" one-way. Note that the PHL driver might have a cone that's more like 4" across. That sort of SPL in the low end simply needs more cone area.

Okay, well I just simulated the PHL 900ND in WinISD in a bass reflex cabinet, 6.5 litres tuned to 92.5Hz. 110w signal yields 113.83dB SPL at 108.36Hz, 110.5 at 200Hz, 109.85 from 400Hz and up, and 106.85 at 80.2Hz (making 80Hz approximately the -3dB point as suggested).

Cone excursion 4.666mm peaking  at 120.28Hz, 4.546mm at 80.2Hz, 9.086mm at 62.73Hz.

So whether the driver actually can produce 18mm of peak to peak excursion as the charts PHL provided in their old datasheet suggested isn't exactly relevant to the viability of the design. If it can do it, great. If not, high pass at 80Hz, no problem.

PHL's datasheet lists the xmax as 6.5mm.

Obviously that's quite a bump in the frequency response that no one could claim to be hifi, but it's not supposed to be. It's intended to be a busking amp, primarily. It should be able to reproduce bass outdoors, so that bump around 120Hz is really necessary. You could tune it to 88.1Hz and yield 112.492 at 105.73 and 107.956 at 80.2 if you preferred a flatter response.

The 21" driver I simulated with is a P-Audio SD21-1800N. 1800w continous, 10.5mm Xmax. With the 18Sound unit's greater Xmax, you'd need about 10 drivers to match the 16 of the drivers I simulated. Either way, we're well outside of what any pair of sensible-sized cone drivers can realistically do.

I never said the 145dB calculation was for two drivers. That's four drivers in a stack. I don't have the sims to hand but as you can see my memory of the PHL in a bass reflex was more or less spot on, so I wouldn't be surprised if 145dB is the actual figure.

That 8" two-way has an unfeasibly flat response. I do wonder if he was clipping something so all the peaks got chopped off.

Clipping mostly affects loudness not frequency response though. A clipped 100Hz signal is still a 100Hz signal, clipped 1000Hz is still 1000Hz etc.

For what it's worth, I've seen plenty of responses that flat with smoothing applied to that level, from real measurements of drivers, but not generally from such a cheap woofer admittedly. I'm not convinced by it either but it's not so important to be convinced that it's some sort of crystal clear hifi driver. It's $11.

The target as mentioned is ultra-shoestring. People spend $100 on little dinky bluetooth speakers all the time. If you want 'event' level of sound for under $100 your options are  severely limited. I'm just attempting to suggest a possible option for someone on that sort of budget. For every application and budget there's an optimum to be found, and my suspicion is that may be close to the optimum in that case.

Edit: Having looked at the calculator you linked to, I think you missed a couple of notes.

This calculator is only valid for sealed box or infinite baffle alignments.
Vented alignments will typically have double the driver's Xmax values at F3, this shows the efficiency inherent in the vented alignment.

[Chris Grimshaw]

Okay, well I just simulated the PHL 900ND in WinISD in a bass reflex cabinet, 6.5 litres tuned to 92.5Hz. 110w signal yields 113.83dB SPL at 108.36Hz, 110.5 at 200Hz, 109.85 from 400Hz and up, and 106.85 at 80.2Hz (making 80Hz approximately the -3dB point as suggested).

Edit: Having looked at the calculator you linked to, I think you missed a couple of notes.

Sorry, your original post said bass down to 60Hz, so I assumed a port tuning there. Above the port tuning, the port is relatively inactive and the driver has to do the majority of the work. I do account for what happens when you put the driver in a cabinet. It's just a useful tool for order-of-magnitude work.
What does your port airspeed come out as when you put some power in? It might be worth looking at passive radiators since I often find pushing a lot of air through a small port can lead to problems.

Looks like I did mis-read your original post with regards to the big PA system, though. Two double cabinets per side. Eight cones total. I re-ran the sim allowing more Xmax, it'll do 145dB at 75Hz, but nowhere else. Again, I've tuned the bottom cabinet frequency to 35Hz.

I suppose it comes down to how you spec your cabinets. You could honestly say you can get 145dB and also bass down to 35Hz, but it won't do those two numbers at the same time, which is the bit I take a small issue with.


I think you haven't understood my meaning when I said the measurement system might be clipping. If the mic/soundcard input is clipping at, say, 90dBSPL, and the speaker has a response that starts at 90dB and goes up to 100dB in places, the meter will still only read 90dB. There's no evidence of any reflections at all in that measurement, while the author claims that it's in-room. I'm taking it with a spade of salt, since even good speakers in an anechoic chamber would struggle to measure that well.

Chris

[Jonathan E Lamb]

Sorry, your original post said bass down to 60Hz, so I assumed a port tuning there.

We're talking cross purposes here, sorry! There are two designs using the 900ND which both achieve a 113dB SPL, just to confuse things. One extends to 80Hz (bass reflex - which has about 35m/s peak port velocity at max input with a straight port. Could be reduced with a folded port) and the other does extend to 60Hz, but it uses a different sort of loading, similar to this design:



That enclosure has a much more even 113dB and then a gentle roll-off to F3, while the reflex is much more peaky, with an average closer to 110dB, so it's a significant advantage in overall efficiency and bass extension for a small increase in enclosure size, hardly bigger at all as I recall. Kind of a tapped horn/bandpass box, as you suggest, but without the dramatic rise in enclosure size.

You say you've adjusted your simulation to include more xmax. I don't see the value in that sort of rule of thumb estimation. You mentioned simulating a 13 cubic feet tapped horn but you didn't simulate the horn design in question, and if you're just plugging more xmax into your sims it sounds like you didn't model the correct driver either.

The 145dB is quoted 'per stack' so I think that's the number for four drivers.

You could honestly say you can get 145dB and also bass down to 35Hz, but it won't do those two numbers at the same time, which is the bit I take a small issue with.

That's a very standard way to describe a speaker. The peak SPL figure and the F3. Some would stretch the definition to the F10, but that I would take issue with as well. Peak SPL and F3 is standard practice. I should have made that more clear though.

[Chris Grimshaw]

The BassPod is neat. I'd suggest, if possible, using some dynamic EQ to prop up the 60Hz content at lower volumes. Looks like a decent amount of noise from a smallish box.

You say you've adjusted your simulation to include more xmax. I don't see the value in that sort of rule of thumb estimation. You mentioned simulating a 13 cubic feet tapped horn but you didn't simulate the horn design in question, and if you're just plugging more xmax into your sims it sounds like you didn't model the correct driver either.

Using the exact driver isn't strictly necessary. A 21" cone can move a given amount of air. A different driver might have a different response shape, but when you're looking at mechanical limits, what matters is the cone area and Xmax (and ensuring you've got enough thermal power handling to make sure you can use all of the mechanical capabilities of the driver). I do see your point, though.


If you've got any drawings of the internals of your designs, I'd be happy to run some simulations and make suggestions.
For instance, you might find a carefully-tuned Helmholtz resonator would take out the 200Hz notch on the BassPod, which opens up a wider range of crossover frequencies.

Chris

[Stephen Kirby]

Ghostbuster looks remarkably similar to my Cubo subs.  Which are kind of peaky around 60Hz.  Not sure where the bump would be with smaller dimensions.

[Jonathan E Lamb]

Ghostbuster looks remarkably similar to my Cubo subs.  Which are kind of peaky around 60Hz.  Not sure where the bump would be with smaller dimensions.

It was based on the Beyma SB series (SB12, SB15, SB18). If you look in the design files I think you can even see the artifacts of the SB12 diagram overlaid in the file as reference!



I think the main difference between the SB series and the Cubo series is there's a little bit of extra path length that comes after the woofer. The woofer in the Cubos goes more or less to the edge of the horn mouth. I found in the sims that moving the driver back further had a beneficial effect with certain drivers, so I tried to accentuate that.

As mentioned, the suggestion is that a thin wall composite technique may be used, which would allow for a lot more flexibility in the shape of the cabinet walls. I know it's generally advised that precisely accurate walls are of no importance in the design off bass horns, but I figure if the potential exists with an alternative manufacturing method, may as well try it and see what happens. So all internal corners are fully rounded, and I tried to account for the impact of the cone shape on the horn path.

That thin wall composite might be foam core and glass as suggested, but there may be other options opening up with the advent of affordable large format FDM 3D printing. A 55x70x90cm cabinet, for example, if you printed it with 1.75mm cavity walls with 20mm cavities, and you then filled those cavities with something lightweight (expanding polyurethane foam, perhaps), could be achieved with a total of 12kg of printed materials. If you capped off that printed profile with 18mm ply and used a 10kg driver you would have the potential for a 30kg cabinet that might otherwise have weighed 50kg, with the added advantage of complete freedom of form on the internal panels, and massively increased ease of assembly.

FDM 3D printing services are available for as little as $0.10 per cm3 of printed material (which is unusually low, and hard to source at the moment), but prices fall all the time, and if you had access to your own printer, you could possibly cut that price in half. Spools of material are as low as $15 per kilo, the rest goes into electric/machine operating and servicing costs. If you get the costs to $0.05 per cm3 then 12kg comes in at $600.

That's a huge chunk of change to put in to printing a speaker so it may be that this method never becomes economically viable, but it could conceivably drop at some point to $300-400, and there might be some design not yet conceived that would make very effective use of the freedom of form and low weight of enclosure afforded by that method or something like it.

I had an idea today for a design using that method, it's just a little one using less than 1kg of printed material, so it may already be viable: http://forum.speakerplans.com/3d-printed-jvc-kaboom-clone_topic98848.html

[Stephen Kirby]

We use a lot of printed parts in the tech world for prototyping but it's far too slow to be cost efficient compared to casting/molding and assembly.  Cosmetics are also poor.  Maybe for interior parts.  Might be able to come up with phase plugs that aren't achievable any other way.  That could have some audio benefits.

[ProSoundWeb Community]