New surround project-Tripole clone?

[pjpoes]

Hey guys, I just finished a surround speaker project. As many of you know, M&K went bankrupt, and before being reborn was liquidated. This meant many of their speakers, enclosures, parts, etc. were being sold at places like ebay for quite cheap. I ended living within driving distance of someone selling a bunch of their enclosures, so I bought them for 99 cents and drove to pick them up. I figured I would come up with something to do with them. I saw that ApexJR had a full range driver with neo magnet from M&K and looked right for the side firing full range drivers in these little enclosures I got. I then bought like 7 or 8 sets of those vifa tweeters for M&K, paid very little for them, I think 15 or 20 dollars for the entire lot. I also ended up with an odd bunch of Vifa TG9WD10-08 drivers, but was unable to make use of those drivers. Instead I purchased a Peerless 3" full range 830986 driver as my midbass to go with the Vifa tweeter. I then took some measurements of everything, and developed a sort of 12db per octave butterworth crossover for the midbass and tweeter, and basically ran the midrange drivers full range (Though with a bit of padding).

Biggest mistake I made was buying surplus polypropalene capacitors for the crossovers, they were around 5uf's each, making them quite large to fit into these tiny enclosures, but I managed. Anyway, here is some pics.

 

[pjpoes]

Here is another picture. Also, as for sound, they work well for their purpose. I mean, its a 3" driver in a tiny enclosure, bass rolls off at roughly 150hz. They are limited to probably around 25-50 watts rms, though I have done a little bit of testing, and they do play quite loudly. The front drivers actually sound quite good, and measured at 1 meter with the side drivers unhooked, I get a pretty nice flat response, would make a nice mini monitor. With the side firing drivers, wired out of phase with each other, the response becomes a bit messy, and having no experience with designing such speakers, I just got it as flat as I could without disrupting the effect. I made a few test crossovers by modeling it as a 2.5 way design, with the side drivers as the 2nd set of woofers, but run full range. I was surprised at how closely my real world results matched my models. The ones that worked best were when I measured the full range drivers in the enclosure measured roughly 30 degrees off axis. By the way, my next project is a larger set of these using larger M&K enclosures with 6" midbass drivers, their famous 1" tweeter, and I'm undecided on the full rangers, possibly the same. These will be built to a higher standard, since I will have more room, but if anyone has any advice on the best way to design the crossovers, let me know. I imagine that running the full range drivers full range in the larger ones will be a bad idea, so I probably will include a highpass crossover for those. Anyway, here is another picture.

 

[pjpoes]

I will try and get some pictures up of the insides, with the crossovers I built. I was in such a hurry, impatient and all, to get them together so I could listen and measure, that I forgot to take pictures. It's really nothing that interesting, as I said. I think I can post a picture of the modeled response, but I'm uncertain how to get a response from my Behrenger RTA to the computer at the moment (I have no midi connections), or from my Audiocontrol RTA (?).

 

[pjpoes]

ok this is the modeled response of the crossover network.

 

[pjpoes]

ah I was hoping someone would have some interest in this project. Those enclosures were so cheap, and pretty well made for what I paid, typically 99 cents, that I figured I would try and find something to do with them. I imagine some of you are in a similar boat, and I see plenty are still available.

I've actually gotten a tripole crossover now, so I'm going to draw a schematic of it and see if anything unique is done with the full range drivers at all. I'm thinking now for my next project that maybe I will make a timbre matched surround to my main speakers. Use a Focal W-cone 6" midbass driver, the TC90 tweeter, and a set of decent 3" full range drivers for the sides. I had avoided such a project in the past because of the expense, but with the success of this project, I think its worthwhile.

 

[Undefinition]

Those are cool!

Lately, I've been trying to figure out the best approach do to some sort of bipole/tripole or whatever you want to call it. I appreciate your experimentation with it.
Boy do I wish I could get some pre-built enclosures. You know, when I first started in this hobby (which wasn't even that long ago), I thought I just liked building the cabinets. But once I successfully did start designing my own crossovers, I'm wishing I had a patient woodworker who wanted to try building my strange ideas. Now, I know what some are thinking: "you can get pre-built cabinets from Parts Express and Madisound and whatnot" And those can be really nice, I admit. But building my own is still way cheaper.

What's your impression of that little Peerless driver? I was thinking it might be a good driver for just that kind of application, but I wondered if it might be better run full-range or used w/o a tweeter. How is the off-axis response?

 

[pjpoes]

I actually am really impressed with the peerless driver. I would highly recommended it for a small two way monitor. I would not use it full range without a notch filter though. There is a peak at around 10,000hz and also a bit of a bump at around 2500hz, which is a bit broader. Though its wide and probably less of an issue, I thought that run full range it sounded funny. It also sounds a bit sizzley with cymbals or other high frequency instruments. Also, it becomes somewhat directional past 3000hz.

Having said that, I'm using it crossed over at 3200hz, or so, and with the vifa tweeter, it sounds great. It is far less directional in this setup, with a much smoother sound. In the midrange and highs, this is a great speaker. I would say total cost for this project was around 75 dollars, and for that much money, I'm very impressed with the sound of the front drivers. Those side full range drivers are less impressive, but I don't have room for much else.

By the way, the reason, I believe, that M&K used the term tripole instead of bi or dipole is that instead of having two sets of drivers wired either in phase or out of phase, and typically facing in opposite directions. You have three drivers, could even be sets of drivers in theory, but they always used full range drivers facing to the sides, and mid bass/tweeter on the front. That way, you had direct radiation toward the listener that was timbre matched to the front speakers, while still having the enhanced ambiance and envelopment of a dipole speaker.

I've been finding that the crossovers are not that difficult to design, though no crossover program seems to give you the ability to tell it that a driver is angled 45 or 90 degrees from another driver. What I'm finding is that I can get a pretty flat response with good phase response while enhancing the ambiance simply by padding down the full range drivers. I will say that a smooth natural sounding full range is important I think, and I haven't found that yet. The M&K full range I have sounds thin and nasaly to me, I will have to study its response chart a bit to see if anything can be done, but for the sake of parsimony, I probably will find a different full range, such as one from Aura.

 

[chaswerner]

tripole crossover schematic

I am interested in building a similar project. You mentioned a crossover schematic. Is one available?

thanks,

charlie

 

[Undefinition]

You think those cabinets are still available? If so, where?

 

[pjpoes]

Hey guys, sorry, I missed the posts. If the enclosures are still available, check ebay. You can't buy them from the liquidation anymore, that was a one time only event, but lots of companies that bought up the liquidation are selling them on ebay.

As for the schematic, let me dig it back up and draw up a schematic, and I will post. The values I used need to be modified depending on the drivers you choose. There are something like three versions of the vifa tweeter floating around, not including the consumer one. All of the oem's are quite different in their impedance (Some are 4, 6, and 8 ohms), so the values need to change. I'm also redoing the side driver part. I wasn't happy with the sound, so I decided to reduce their output. First experiment has been to wire them in series (32ohms), but that wasn't great. I need to measure them on their own and maybe design a crossover, that or be happy with the sound, given how small they are.

 

[pjpoes]

Here is the promised schematic and response from Speaker Workshop

Here is the crossover schematic. I also have a somewhat simplified version. The side drivers are just connected to each other in series, and then parallel to the circuit with no other adjustments. You could of course insert an lpad or resistor, but I didn't bother.

 

[pjpoes]

Here is the response with this crossover setup, again, just for the front drivers, it will look a lot worse with the side drivers connected, but with drivers firing out of phase, thats what happens.