Inexpensive surround project, NS3-193

[joecarrow]

First a little background-

I recently built a pair of Modula MTs and bought a Panasonic SA-XR55 receiver to drive them. When I lived on my own, I listened to probably 80% movies and 20% home theater. In the time since I finished this stereo setup, that Netlfix and my girlfriend have reversed that ratio. It was a big step up from the TV speakers.

I walked into the local CompUSA to check out some laptops when I was stopped by an 80" flat panel TV with a surround setup. I never really thought about it before, but I sat down and listed while The 5th Element was playing. Those rear surround channels really did add to the immersion!

I had a couple of NS3-193 Aurasound speakers sitting around, so I walked over to the local OSH and picked up two 35" lengths of 4" ABS pipe for $4.50 each. I didn't have to cut anything myself, just clean them off to get the dust off.

I used a hole saw and then jig saw to cut some donut shapes out of some scrap HDF I had sitting around, and cleaned it up with a rasp. I held the HDF donuts on top of the pipes with black duct tape, and then got a good seal all the way around the NS3-193s with some clear packing tape.



The pipes were definitely boomy until I stuffed them with Polyfill, but once I tweaked that around they took on a nice neutral character from the midrange down through the bottom of their range. The really strange thing was that the treble sounded like someone was talking through a fan. It turned out that they beam straight up, and the ceiling fan was what was causing the problem.

I have them highpassed on the receiver at 200 hz, and I plan on experimenting with an inductor in series similar to how Linkwitz did with his surrounds.

[joecarrow]

By the way- I said they are "inexpensive" because they only cost $50 for the pair.

The next step is to get the girlfriend approval factor up high enough that I'll be allowed to keep them. Does anybody have any comments to offer on veneering a 4" diameter cylinder?

Also, does anybody have any opinions about the importance of the top octaves in a surround speaker? I read on Linkwitzlab that his surrounds were for "ambience", and too much treble would let your ear pick out the location of the speaker. At least, that's how I understood it. I'm not opposed to a simple crossover to 3/4" dome if there's much to be gained.

I hope this was interesting to someone. This hobby is a good time.

[morbo]

Well IIRC Linkwitz is using his surrounds in a non-standard way, so his requirements are not the same as for Dolby digital, DTS, etc, and thus I don't know that his approach applies to those applications, where discrete effects are mixed into the surround channels.

I have been looking at some ideas for surrounds myself. Because I have a small room, with listeners very close to the surrounds, I have been considering a wall mounted speaker with 4 x Aurasound NS3s, each mounted on one face, but with none facing the listener. So, I would have one firing up, down, left, right. They would be wired series/parallel to give a net 8ohm impedance, and my modelling shows they would be capable of significant clean output if highpassed at 100hz. The only question is how the 'quadrapolar' design would sound... I've seen some M & K surrounds that do the same thing only 'tripolar' (ie they fire only up and to the sides, not down), but have not been able to find many reviews.

[joecarrow]

Well, one thing to be aware of- the NS3-193 does not have "superior" highs. The highest octaves are quite directional. In short, tweeters just do it better.

I'll read up on exactly how Linkwitz used his surrounds. That's a good point- I seem to be getting a lot of highs out of these surrounds during movies.

[morbo]

I've used the NS3 before and know its limitations in the high frequencies, I certainly don't expect anything great in the top octave (whose importance is is overemphasized a lot IMHO). I am more interested in the radiation pattern and getting good output without distortion out of them...

Also, if you're running those with no filter, its no wonder you're getting so much highs, you need some BSC to balance them out, especially on that tiny baffle. I am hoping I won't need that since the speakers will be on-wall, and each pair of drivers will be 'dipolar'.

It would be interesting to mount your pipes on the wall horizontally, and stick another NS3 on the other side to make a small dipole in a pipe...

[JoshK]

I've thought about building some surrounds much like this with B&C 6NDL38s. I read a post by Dr. Geddes somewhere that said that if surrounds limit HF info they in turn sound further away and was considering whether HF content was even needed. I thought it would be easy enough to try out for myself. Some may disagree, that is fair but I've never been a big fan of DD anyway.

I was thinking of doing something very similar to your project with a PVC pipe and mounting the driver upwards to gain an omnidirectional surround. If HF content is wanted you can always add a small neo tweeter like SL did with his Pluto or add it a little lower than the top of the pipe facing towards the listener.

To avoid beaming HF content as in your case, you could roll it off with an inductor of appropriate size. It would be a very easy experiment to try out and see if you like the result.

[joecarrow]

Guys, thanks for the thoughts. I think this will be an experiment in stages.

I re-read Linkwitz's section on his surround speakers, and it did sound as though he'd advocate high frequency sound if the original recording includes it. However, the "diffuse" sound is kind of close to what my ideal would be. I don't know if I want to be able to say "Hey, there's a monster three feet behind me, and two feet to the left!", because that might be distracting. Instead, I think "There is a monster behind and to the left!" is sufficient.

First, I'll try an inductor to roll off the top. That's cheap and easy, and if I like it better than what I have now I might call it a day.

Next, if it's too much and I feel like I'm losing out on the creepy sound effects (just saw the movie Saw last night!), then I'll try a tweeter with a real crossover. I'll need to really investigate what's up with baffle step for something like this. It seems like the baffle step would be high enough that by the time you hit that frequency it's already beaming. I'll have to check and see.

[cjd]

Movies that really use surround well do indeed have high frequency content - not having it will reduce your sense of immersion.

The ~$5 "neo" tweets at PE (ND20 for example) would be an excellent match IMHO.

And, sensitivity is going to be low indeed if you roll baffle step into these. You'll already have a fairly sharp knee since you've gone and put these on a round baffle, perfectly centered... tough to work with.

C

[joecarrow]

Thanks C, I was thinking of exactly the same tweeter.

The sensitivity isn't too much of an issue, since I can throw 100 watts at them, I don't listen that loud, and my receiver can increase their level relative to my Modula MTs by something like 10 db.

The baffle isn't set in stone. It's made out of scrap HDF, so I would be able to whip up an offset woofer with tweeter at the edge without an major hassle. I need to redo it anyway to veneer the thing and get it looking nice enough for my girlfriend.

Diffraction/baffle step simulation, here I come!

[cjd]

These would be interesting to continue the omnipole concept, and fire the tweeter up as well. The bottom of the tweeter mount could be "coned" facing down...

C

[JonP]

By the way- I said they are "inexpensive" because they only cost $50 for the pair.

The next step is to get the girlfriend approval factor up high enough that I'll be allowed to keep them. Does anybody have any comments to offer on veneering a 4" diameter cylinder?

Very cool... get an idea, grab available materiels, throw it together...
True DIY spirit!

Thoughts on the veneering... better check that the contact cement isn't going to eat your ABS pipe!! :E Possibly PSA might work, or some other kind of glues, you would need something that would "wet" the plastic surface, but not dissolve it. I'd guess wood glue would want to bead up and not wet it well. Sanding with coarse paper to rough up the surface will help with the bond.

I've seen pics of a 6.5" Tangband Sonotube sub... think it was 8" in dia... he had endcaps and had done a wrap of oak or something. It looked very nice!

There is sanding the ABS... though that has a kind of unfinished look, and then there's some kind of texture coat, or plain paints. Look at the Pluto gallery, there's several approches there on what to do with a long tube!

[Bent]

Hehehe, the pluto gallery?/

[JoshK]

Hehehe, the pluto gallery?/

http://www.linkwitzlab.com/Pluto/photos.htm

[Bent]

I see,
my bad.

[joecarrow]

That art piece from Brazil is insane, I love it!

Once I figure out 90 degree off-axis diffraction and baffle step, I'll decide where to put the tweeter. Should be a few days, at least.

[dlneubec]

Hi Joe,

I've been thinking of doing something omnidirectional, but perhaps on a larger scale. I found these and thought they might be worth trying to reverse engineer for a DIY version. This concept might work great for your smaller surrounds also. It could be adapted to a single driver or a 2-way as shown in here:

Duevel Venus
Duevel Planets
Duevel Bellaluna Diamante
Deflector/horn detail

You would probably need someone who has a lathe to make the deflector/horn part.

I'd like to do a full range system like the Venus or Bellaluna, maybe even a 3way by adding a downfiring woofer at the base and another deflector for a deeper bottom end. This would make them omnidirectional thoughout the full range.

The planets might also be adaptable to surrounds. You'd simply have to find the appropriate sized balls. :rofl:

Any thoughts?

[JoshK]

I've heard the Bella Luna. A friend of mine owns them along with a seriously high end system (Sakuma san PP845s & KR PSE monsters with the T16xx tubes and ultra high end analog front end). They are quite amazing in their dynamics and the sound stage is pretty large while imaging is still sharp but natural. Of course you have to have the right kind of room IMO for these to be your main speakers. A very worthy klone/inspiration project if you ask me.

Maybe one of these days I'll get a lathe and learn to spin wood so I can make nice horns, guides and the like. For now, I like the idea of the omni-directional surrounds. I haven't decided whether to deal with HF content or to roll it off. I think a switch to choose either would be a cool feature to add.

[dlneubec]

I have a son-in-law who is getting a master's in fine art and has access to a shop at Indiana University where he works with all kinds of materials and an impressive set of power tools. I haven't talked to him, but I bet he would make me some deflectors/horns like those on the Venus or even the Bellaluna, at least out of wood, maybe out of aluminum or something.

As far as a DIY clone of those, I would think something like the Bella Luna cabinet shape, but maybe more like the Venus top, so it would be simpler to make and you could probably use pretty standard drivers like those used in many of the projects here.

I wonder if there would be enough room, or if it would be beneficial to do a downfiring woofer also, perhaps a 2.5way or 3way configuration. Unfortunately, I don't have the knowlege or ability to do my own measurements yet, which keeps me from jumping into it on my own. Something like this would take some serious design skills I would think.

I do have 4-RS180's, 2-RS225's and 2-RS28a's from an old project that I'm itching to do something with, however! :B

I could also see it working quite well for floor standing surrounds also, with small drivers and limited freq. range, maybe down to 100 or 120hz. The HF switch sounds like an interesting idea too.

I agree that a Bella Luna/Venus DIY would be a very worthy "klone/inspriation project". Maybe I'll post it as a subject on the main board to see if anyone else is interested.

[joecarrow]

Part of the beauty of the design is that the woofer has an extremely rigid container for the rear wave that is well suited to dissipating the energy as heat. There's very low coloration from the cabinet, very low stored energy beyond what is inherent in the driver.

The down-firing woofer reminds be of the flagship Bang and Olufsun Beo 5. I had a chance to listen to those, and they are really quite amazing. Good dynamics, good... everything. The part that surprised me the most was that they could hang together at reasonably high volume and have maintain impressive dynamics.

My goal for this whole project is to keep it under $125 for the pair (would be under $100, but I haven't shopped for veneer yet). If you guys start one of these higher end projects I'd love to see more, but I'm afraid I can't participate without outspending the front speakers. That just wouldn't do!

[JoshK]

You know, suspending a ball over the Aura driver could work for dispersing the HF content. Maybe you should try it.

[joecarrow]

Not a bad idea... if I can find a billiard ball, it might be cheaper than an inductor.

[dlneubec]

Hey Joe,

I would think you could find some tipe of wooden balls at a Lowes/Home Depot or a craft type of store, though I've never looked.

Maybe something like a styrafoam ball that you could cover with something to harden the surface could work. They would have the benefit of being very light.

This place has wooden balls. Most you have to buy a bag of 10, but they show some 3" ones that are slightly out of round or have slight blemishes that sell for $2.75 each.

Wooden balls

[ThomasW]

As exemplified by the B&O system, look for a cone instead of a ball..

[Dennis H]

Maybe a plastic funnel from the housewares or automotive isles?