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Multi-Way Conventional loudspeakers with crossovers

Metlako: A Small, Affordable Two-Way Unity Waveguide
Metlako: A Small, Affordable Two-Way Unity Waveguide
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Old 9th November 2019, 04:08 PM   #71
Patrick Bateman is offline Patrick Bateman  United States
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For the most part, I nearly always use this topology, or close to it:

http://www.melaudia.net/zdoc/jml_crossovers_etf04.pdf

Here's the math, from the presentation:

settings of a 2 ways system according the proposed method
1..........Only Butterworth 3rd order filters are used.
2..........The relay frequency Fr between the low-pass and the high-pass
is defined at -5dB.
3..........The cut-off frequency Fl (at -3dB) of the low-pass filter is
calculated by: Fl = 0.87 x Fr
4..........The cut-off frequency F
h (at -3dB) of the high-pass filter is
calculated by: F
h = 1.14 x Fr
5..........If the 2 drivers are aligned at the same distance of the listener,
then the low-freqeuncy loudspeaker has to be moved toward the listener
of a distance equal to 0.22 x wavelength at Fr
.
6..........The polarity of the high frequency loudspeaker has to be
reversed.


It's a great presentation, and I recommend reading the whole thing.

But if you want the short version, we're using 3rd order filters on the high pass *and* the low pass. A 3rd order filter introduces a delay. To compensate for that delay, we're moving the woofer closer to the listener. (This is done automatically, because the woofers on the waveguide are closer than the tweeter.)

Where things get tricky, and the reason I'd really recommend using active crossovers, is the fact that the response of the midbass and the tweeter ISN'T flat.

Because the response isn't flat, you have to use some strange slopes to achieve an acoustic filter that's 3rd order.

In Metlako V5, I used a 2nd order Linkwitz Reiley filter on the midbass, and a Butterworth 3rd order on the tweeter, along with some EQ.

In the UICW, I was able to get close to a 3rd order low pass with no crossover whatsoever! Basically the inherent filter that's caused by the midrange taps, was very close to the 3rd order filter needed by the overall design.

To make a long story short: I'd start with somewhere around a 1st or 2nd order low pass on the midbasses, along with a 3rd order highpass with the tweeter. This design requires EQ, and going active is highly recommended. The $80 cost of a MiniDSP will be cheaper than a passive xover.

Then again, if you're into tube amps, it will need a passive xover. (Unless you want to buy two tube amps!) In that scenario, a passive xover will be the way to go. But I haven't made a passive xover for any of the Metlako speakers, they're all active.
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Old 9th November 2019, 04:23 PM   #72
Patrick Bateman is offline Patrick Bateman  United States
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If you have a microphone, you can make a crossover for a Unity horn in about one hour. Here is how I do it:

Click the image to open in full size.

Click the image to open in full size.

I use a combination of EQ and crossovers to achieve an acoustic response that's 3rd order on the midrange and the tweeter. The reason that I can get away with these steep slopes, while keeping everything in phase, is because the midbasses are closer to the listener than the tweeter is.

In this design, Metlako V5, I *am* using a little bit of delay to make the crossover better. But the difference is subtle and probably inaudible, the delay makes things a *little* better. I'm too lazy to look up the settings, but IIRC, the delay on Metlako V5 is something like one tenth of a millisecond, which is equivalent to moving the midbass closer by about 3.4 centimeters.

Click the image to open in full size.

Here's the filters and the response of Metlako V1. This crossover is quite a bit different than Metlako V5. You'll notice that Metlako V1 is using a first order filter on the tweeter, and the xover point is much much higher than Metlako V5.

The reason that this works, is because the tweeter response isn't flat. It rises at low frequency. Because the tweeter response is not inherently flat, a first order filter way up at 3500Hz will yield something close to a 3rd order rolloff at 1350Hz. It's basically two ways to achieve the same acoustic filter.
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Old 19th November 2019, 10:36 AM   #73
KaffiMann is offline KaffiMann  Norway
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Metlako: A Small, Affordable Two-Way Unity Waveguide
Quote:
Originally Posted by jzagaja View Post
Simply printed in 5 pieces on Zortrax M200 using quality PLA, then glued using CA glue and metal pins, then filled with finnish putty then outsourced to experienced sprayer.

Now I an print in one piece on large printer in just one night. My next attempt will be printed mold and expanding polyurethane foam.
Very nice.

When I tried to fill gaps in a (much larger backloaded type for a 12") horn with PU foam I sprayed/misted a bit of water on the surfaces first, apparently helps the hardening process.

PB, What's the difference between v2 and v6?
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Old 19th November 2019, 12:35 PM   #74
Greebster is offline Greebster  United States
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One of the tricks we use in RC aircraft building is mixing PU with a small amount of water. It can be poured and foams nicely. It does not add strength and only helps expansion.
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Old 19th November 2019, 02:48 PM   #75
Patrick Bateman is offline Patrick Bateman  United States
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Quote:
Originally Posted by KaffiMann View Post
Very nice.

When I tried to fill gaps in a (much larger backloaded type for a 12") horn with PU foam I sprayed/misted a bit of water on the surfaces first, apparently helps the hardening process.
Yep, I should have mentioned that, I do it with all the multi-part waveguides. I mist it with a spray bottle.
Quote:
Originally Posted by KaffiMann View Post

PB, What's the difference between v2 and v6?
Click the image to open in full size.

I kinda lost track of all the variations. Off the top of my head, this was somewhere between V3 and V5. This was one was one of the poorest of the bunch. (Of course, this is relative, it outperformed a lot of commercial waveguides.) Basically the diffraction slot didn't work really well with that tweeter, and the response above 10khz was beamy and rough.

Click the image to open in full size.

Metlako V6 (or was it V5?) is probably one of the best "bang for the buck" waveguides I've ever made. Really nice performance, but also fairly easy to print. I was honestly surprised that I was able to fit two 5" woofers onto a waveguide that fits onto a print bed that's 8" x 8". I'm not entirely sure how I pulled that off. This waveguide is a straight up clone of the 18Sound XT1086, but it's about 80% as big. I really need to post some pics and upload the STL files to github. It's a nice one.

Probably the only reason I didn't wind up using it, is that I've been kinda obsessed with using curved baffles to extend the F3. I made another waveguide that fits into a cylinder, similar to Metlako V3 (or is it V4?), and that waveguide simply knocked it right out of the park. Really REALLY great performance, and though I shy away from subjective analysis, it sounds FANTASTIC. Of course, I've been too busy building waveguides to document anything... I put the kibosh on that one because it's incredibly difficult to print, and mounting it in a cylinder is a complete p.i.t.a. I'm working to come up with an enclosure shape that will mimic what a cylinder does, but is easier to build along with a waveguide that will take advantage of the baffle shape.

Basically the idea is to have a waveguide that's small, like 8" x 12", but that behaves as if it's twice the size. This is doable when you put the waveguide in a cylinder, or you use a big roundover.

Click the image to open in full size.

To give you an idea, here's a polar response of the waveguide in question. This waveguide is 8.5" wide. But note how the directivity control goes about as low as a 17" waveguide, and it also collapses in a really benign way. IE, some of the big waveguides have a habit of collapsing poorly, basically they have a narrowing in the midrange and then they widen abruptly, and suffer from pattern flip. (This one DOES suffer from pattern flip on the other axis, which is part of the reason I'm redesigning it...)
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Old 19th November 2019, 03:39 PM   #76
kipman725 is offline kipman725  United Kingdom
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That last set of polars looks fantastic Patrick. I think if you can get the performance of a 17" wide wave guide in 8" wide you are onto a very commercially viable product as there is a strong preference among more normal people for narrow baffled speakers.
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Old 19th November 2019, 03:48 PM   #77
Patrick Bateman is offline Patrick Bateman  United States
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Sound really seems to HATE symmetry. Here's an example of what I mean:

Click the image to open in full size.
Click the image to open in full size.
Unsmoothed polars
Click the image to open in full size.
Smoothed polars


Here's a waveguide that I kind of made on a goof, 2.5 years ago (Synergy Beolab)

Click the image to open in full size.
Click the image to open in full size.

Here's the new 'Bend it Like Bateman' waveguide, that I made a week ago.

The performance isn't quite as ridiculous as the one from 2.5 years ago, but it's interesting that the asymmetry of the waveguide seems to be having a beneficial impact on the frequency response and the polars.

Last edited by Patrick Bateman; 19th November 2019 at 03:51 PM.
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Old 19th November 2019, 10:09 PM   #78
KaffiMann is offline KaffiMann  Norway
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I'm not surprised. It's the same as many other things, imperfections make it more perfect. Complete symmetry never works out well.
What about doing the "pinch" thing on just the upper or the lower side of the horn? perhaps on one side as well? And what about more aggressive curves towards the corners of the horn?
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Old 22nd November 2019, 05:44 PM   #79
1hiep0 is offline 1hiep0  United States
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[QUOTE=Patrick Bateman;5928419]
Quote:
Click the image to open in full size.

If I was going to put a coax on a Unity horn, it might look like this.

Click the image to open in full size.

The depth is 3.5". The depth is largely dictated by where we want the midrange taps to be. (See the beginning of this post.)

Click the image to open in full size.

Here's where your coax would go. The tweeter fires through the throat of the horn, and the output of the midrange fires through that ring shape.

Click the image to open in full size.

Okay, this diagram is super important.

It is *critical* that the area of the midrange tap is expanding.

Here's a few reasons why we want that midrange tap to expand:

1) this is still a horn. If the area of the midrange tap is constant, we're going to get a resonance. In the original Unity horns, from 20 years ago, the area of the tap was constant. The reason that it worked was because the taps were short. For instance, if your midrange taps are only one inch deep, it's ok if they're straight. But if your midrange taps are three inches long, or six inches long, or TWELVE inches long, you want the area to expand. If not, you're going to get a big ol' resonant peak and that's going to ruin your speaker. Long story short: you want those midrange taps to be expanding. If you're a complete madman, you can mass load the ends of those taps. That's a story for another day.

2) If the area of the midrange taps are expanding, the horn behaves a lot more like a horn. If the area of the midrange taps are NOT expanding, you're going to maximize diffraction off of the slots, and you'll probably get some reflections off of the transition from the midrange taps to the rest of the horn. Also known as "higher order modes."

If it's not clear from this post, the reason that the AREA of the midrange taps is growing, is because the diameter of the midrange taps at the throat and at the exit of the taps is higher.

For instance, at the entrance of the midrange taps, the diameter of the midrange taps is 2". At the exit, the diameter is something like 4". This means that the *area* at the exit of the midrange taps is 4X higher.

Click the image to open in full size.

Here's a cutaway giving a better idea of how the area of the midrange taps is constantly expanding.

Click the image to open in full size.
Any development on this? I am eager to find out. Thanks,
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Old 22nd November 2019, 05:59 PM   #80
Patrick Bateman is offline Patrick Bateman  United States
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yes, I'm measuring it today, thread is here : Synergy Eggstravaganza
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