Pictures of my new speakers

[Saurav]

The prototypes are up and running. Everything is "bare bones minimum" right now, so the frequency response is fairly lumpy. I just wanted to put the thing together to get a feel for how the concept sounded.

Here's my living room, after I've cleaned up most of the parts lying around. Till this evening it looked like a hurricane had been through here:



A closer shot of the veneered cabinet. The camera can't capture any of the grain, I think it actually looks pretty nice. I still need to do the other one. Or if I get lazy I might keep them this way and say that this is my "black & gold" design:



When I said prototype, I meant prototype This is the active crossover that divides the signal between the subwoofer amp, woofer amp, and midrange+tweeter amp. This still needs a lot of work. Slopes are 2nd order right now and need to be 4th order, I don't have any BSC correction, and so on. Also, moving this even slightly causes some wire to come undone and makes my speakers hum loudly. This will all be soldered down once I've finalized what the circuit will look like:



The SET tube amp that's driving the midrange and tweeter:



Part of the passive crossover between the midrange and tweeter:



And finally, the chip amp that's driving the woofer:



Background - I went and listened to a pair of Bottlehead Straight 8s recently, as well as some VMPS speakers, and it really made me notice what needed improving in my speakers. I had been listening to heavily modified Adire HE12.1s, to which I'd added a different tweeter and slapped together a crossover that I thought would work with that tweeter. That gave me the more extended treble I was looking for, but the tweeter was a poor match for the woofer, and my crossover was... well, let's not talk about that.

Anyway, I decided to keep the woofer from my 12.1s but run them up to a much lower frequency, and add a midrange and tweeter. I also decided to try those on an open baffle, just to see what the fuss was about ("get rid of the boxy sound" and all that). I spent some time with books and modelling software, and a lot of time on this forum. I think this time my crossover is a little better than what I had before, and more importantly, my drivers are better suited to work with each other. The cardboard baffles are definitely temporary, the drivers aren't even screwed down to them so they're providing zero rigidity and support right now. They's just for testing diffraction and dipole cancellation issues in order to pick positions for the drivers. The final baffles will be plywood or MDF (probably 1/2", whatever's easier to cut with a jgsaw).

Sound - I think these are sounding great. The imaging is kinda off, since my midrange is dipole and my woofer and tweeter are monopole, that'll get fixed soon. But other than that, these sound a lot better than what I had before. Open, airy, room filling sound. Much more resolving of nuances and subtle cues. The treble still isn't quite as smooth as some other speakers I've heard - maybe I just don't like the sound of horn tweeters? Which would be funny, since I always considered myself a big fan of horn loaded designs My tweeter isn't the best match for my midrange driver anyway, the overlap is a little less than I would have liked. I might try one of the high efficiency dome tweeters instead.

Thanks for looking.

Saurav

[Timn8ter]

I need a nice SET like that. Did you happen to try the 12.1 in OB? Whatever happened to the Adire XO?

[Saurav]

Didn't try the 12.1 OB. I built one set of cabinets, and that was more woodworking than I want to do again

The original XO of the 12.1s has been cannibalized for parts to build the new midrange - tweeter passive XO. Or were you referring to something else when you said "Adire XO"?

I need a nice SET like that.

They're not that hard to build if you stick with a proven design and be careful with the high voltages

[5th element]

Nice to see and hear? that they are working well. You do not need any baffle step comp on the mid/tweet bit because its dipole. If there are any problems there you will need an open baffle compensation circuit, linkwitz describes how he uses his on the web site.

The bass may or may not need baffle step compensation, although looking at baffle dimensions I would imagine it does.

Also IMO dipole to monopole in a speakers doesnt mess up anything with reagards to sound stage it just sounds as if your xover needs sorting out

Also im not sure how dipole cancellation works if the woofer is offset like yours is, to simplify things id mount the woof and tweet both central and make the baffle as wide as the bass bins. I cant say a cardboard frame would help with regards to sound.

Good luck with getting it sorted mind you

[Saurav]

Thanks for the advice.

You do not need any baffle step comp on the mid/tweet bit because its dipole.

I know, the dipole cancellation cancels the BSC, or something like that. I was talking about BSC on the woofer. The cabinets are 14" wide, which puts the BSC corner at around 325Hz, and I can definitely see the output go up from 200Hz to 500Hz on the woofer. I'd though of putting the woofer - midrange XO at 325Hz, and just adjust levels to compensate for BS, but 500 looks like a better XO point for power-related reasons. I'll be adding a BSC stage to the woofer's active XO, with the circuit taken from the Linkwitz site.

Also IMO dipole to monopole in a speakers doesnt mess up anything with reagards to sound stage it just sounds as if your xover needs sorting out

That is definitely a possibility The Beta 12CX woofer has a rising response above around 800Hz, so my 2nd order XO isn't quite good enough. The XO is at 500Hz, but the woofer's output is almost flat out to 1kHz. I'm pretty sure that that is messing up the midrange too. Things sounded a little cleaner when I was running the midrange driver down to 100Hz with the woofer disconnected, which means my woofer is going up too high and messing with the output of the midrange driver.

Also im not sure how dipole cancellation works if the woofer is offset like yours is, to simplify things id mount the woof and tweet both central and make the baffle as wide as the bass bins.

That was the original plan - drivers offset by maybe 1". I just ended up building this baffle to see how it works. When modelling this, the rise in response just before the drop off is higher with the drivers centered, and smoothest when the driver is all the way over on the edge of the baffle, which is why I decided to try this. I will be changing this though, I have a suckout around 2kHz, which seems to match the 2-3" I have between the driver and the baffle on one side.

Good luck with getting it sorted mind you

Thank

[5th element]

You seem to have everything under control everything which you said in the last post made sense, id just try 4th order electrical slopes on both the mid and bass and see if that helps.

I was crossing a bass driver 1st order electrical at about 300hz and this did give too much output and was clearly audible in its doing so, increasing to 4th elec sorted it out greatly.

[Saurav]

I'll definitely go 4th order on both drivers when I move this to the PCB, I've run out of space on my breadboard

[CeramicMan]

Remember that a cardboard mock-up of the baffle isn't any good at isolating sound between the front and rear. It's only about as good as, well, cardboard . It's almost like having no baffle at all for the midrange, and I'm guessing that it's worst at those 1-3kHz midrange frequencies where the losses happen but touch-testing doesn't reveal any vibrations.

A solid baffle will probably sound completely different, and better of course. I've got a large off-cut of 12mm polypropylene plastic sheet at home, and I suggest that it would be a really good material for open baffle speakers. It's quite tough and heavy, and tapping on it reveals very little of those "wooden" resonances that MDF has. If you can get some from a plastics supplier, then it would be the perfect material for that box-free sound. The only catch is that it's an absolute pain to cut.

If you want to go all-out with BSC, then I'd definitely consider the effect that floor-coupling has on the woofer. That naturally provides a 3dB boost below frequencies like 200Hz, depending on the height of the woofer above the ground. For the most balanced sound you'll probably only want BSC to fill out the low-midrange.

CM

[Saurav]

Thanks for the advice.

Remember that a cardboard mock-up of the baffle isn't any good at isolating sound between the front and rear.

I was wondering about that I definitely have some pretty weird output swings in the 1-3kHz region.

The only catch is that it's an absolute pain to cut.

That doesn't sound good. All I have is a jig saw, and I'd prefer not to invest in tools that I'll end up using only for this one project.

If you want to go all-out with BSC, then I'd definitely consider the effect that floor-coupling has on the woofer. That naturally provides a 3dB boost below frequencies like 200Hz, depending on the height of the woofer above the ground.

I do have a boost below 200Hz, the 100Hz tone is quite a bit louder. I was thinking of dealing with that by moving the woofer - sub crossover point higher on the woofer (say 100 or 120Hz, 4th order LR), and keeping it lower on the subwoofer (80Hz 4th order LR). Maybe that'll help me get more even response, I'm not sure.

For the most balanced sound you'll probably only want BSC to fill out the low-midrange.

And that's a good option too. Any idea how I could do this? Can the standard active BSC circuit control how far it has an effect? I know it's supposed to be a shelving filter so it should flatten out at both ends, but is there a way to control both the width (frequency range) and the height (gain/attenuation) of the filter?

This would require that my 100Hz is about the same SPL level as my 500Hz, and then I could just fill in everything in the middle. Hmm.. maybe just a small bandpass filter with gain?

[Saurav]

New pictures.

Room (still a mess):



Speaker closeups:





Veneer closeup (as best as I can do with my camera and this light):



The color is off since this is indoor lighting, but it does kinda look golden in this kind of light. Since the light source is to the side, you can really see the gap where the open baffle meets the enclosure, from the seating position that's not that visible, nor is the color difference between the top and bottom portions.

This is sounding really good now, and I've still got several crossover wrinkles that I need to try and smoothen out over the next few weeks/months. I think this now counts among the more musically satisfying systems I've heard. It seems to do a good job of conveying musical changes, like how a crescendo builds up to a peak and then tapers off, like a wave breaking on a beach (corny, I know )... things like that. I find myself listening to my music collection in a different way, which is hard to put into words. It's definitely higher resolution than anything I've owned before, that midrange driver is something special. These are not the most resolving speakers I've heard, that's too much to ask for less than $500 in drivers

The bass response is pretty smooth (my BFD is still doing it's thing), though I can hear overhang at certain frequencies even though the frequency response is pretty flat. No way to fix that without room treatments or complex processing circuitry. The integration around the woofer (bass to midbass to lower midrange) still needs a bit of work, I think, though putting a solid state amp on the midbass certainly added a lot of life to the system. I thought 97dB on 4W was lively, well, 97dB on 25W is a lot livelier And I'm discovering that midbass/lower midrange dynamics seems to play a pretty big role in the overall sense of PRaT in the system.

With regards to the woofer, I have a pretty interesting situation here - room gain and floor bounce and baffle step correction all come into play within a couple of octaves. I'll have to handle that in the crossovers. I tried setting it to measure flat on the SPL meter at 1m distance, and it sounded pretty bad at the listening position.

The midrange is nice, I'm happy with it. Not as clear as planars/ribbons, not as dynamic as horns, but IMO a very nice mix/compromise of both. If someone knows of a ribbon midrange driver that's 97dB or higher, please let me know

The treble could be better, maybe I'll save up and try the Aurum Cantus ribbon tweeters. My current tweeter isn't the best match for my midrange, so I might try out something different there in the not too distant future. I've heard smoother treble, and I could use a little more room to play with the crossover to get a better blend between the drivers.

The soundstage/imaging is also different from anything I've experienced before, which I guess is due to the open baffle/dipole nature of the midrange. I don't think I've heard any speakers outside of planars that have dipole OB mids. The imaging is more diffuse than what I had before, and the sound seems to fill the room without a precisely identifiable boundary to the stage. It's different, and interesting, and I like it.

Long writeup... did I hear someone say "ego"? These aren't "done", and won't be for quite a while (maybe never?), but I think they're more or less presentable, so anyone in the bay area who's thinking of making a weekend drive up to wine country is welcome to drop by. A second pair of ears is always a good thing.