Mazama

[GM]

[GM]

Originally Posted by Patrick Bateman

FYI -

I was pulling my hair out over this issue.

Good to know, thanks!

GM

[Patrick Bateman]

Mazama Unity Horn Thanksgiving 2020 - YouTube

Here's a video of Mazama 2.0 playing. On YouTube it doesn't sound particularly great, I hear a lot of mp3 compression artifacts and doppler distortion. But you get a general idea about how it sounds.

[Patrick Bateman]

I'll probably sell a few of these, if I can get it to work.

In the event of that, if you're buying one, you'll need to pay attention to this post to build the speaker.









Mazama 2.0 uses an HDF mounting plate for the MCM midranges. The mounting plate measures 5.25" / 13.3cm in diameter. The midrange tap is drilled right through the center of the mounting plate. The midrange tap is 1.125" / 2.9cm in diameter.

In order to glue the mounting plates to the waveguide, I used "Loctite Tite Foam."

The mounting plates are basically mounted so that the midrange tap is right at the edge of the waveguide. If you look at the pics you can get the general idea of where it's mounted. Obviously, the midbasses are not mounted on the center of the horn.

This is by design, to improve the polar response.









Here's some more pics that show how the midbasses are mounted.

[kipman725]

what is the model number for the mcm midrange?

It could perhaps be pushed higher with a small sealed rear chamber and an asymmetric tap closer to the throat? (although this would make low frequency operation impossible)

The N151M tweeter is great but it looks like it should be crossed at 1.8kHz due to the strongly rising distortion below that. I get that its not an issue at low levels but I worry about it quickly becoming an issue for me

[Patrick Bateman]

Here's the frequency response and distortion measurement. Pretty good I think. The compression driver has lower distortion than the midrange array, but what do you expect from $13 woofers?

https://www.newark.com/mcm-audio-sel...one/dp/39C2182



Here's the phase response. I can improve on this, but I intentionally refused to use DSP delay here. I can flatten out the phase by manipulating the crossover slope or by adding delay.

Having said that, this phase response is still pretty good I think. There's about 180 degrees of phase shift at the crossover point. I can improve on that by tweaking the crossover slopes, or adding DSP delay if necessary. Right now, the crossover slopes on the tweeter and the midbass are symmetrical, and due to that, there's some delay between the tweeter and the midbass. (Because the midbass is about three inches ahead of the tweeter.)



Here's the polar response. This is pretty darned good I think. I've been building speakers for over 20 years and this polar response is Top Ten I think, among my designs. Keep in mind, these measurements are very early. The speaker is mounted on a cardboard baffle and I invested a grand total of about 30 minutes tweaking the crossover. IE, these results will improve.

[Patrick Bateman]

To me, the Gold Standard is generally Genelec. From the measurements published at audiosciencereview and Princeton.edu, their directivity is about as good as it gets.



Here's my speaker

And attached are the polars of the $6000 Genelec 8351A

The parts cost on my speaker is about $500 per pair.

[454Casull]

Originally Posted by Patrick Bateman

For YEARS I have tried to make a two-way Unity horn. It's really difficult to pull off. Basically if you have a midbass that's beefy enough to play down to 80Hz, it will have too much mass to play up to 1500Hz on a Unity horn.

There's a formula for this:

the magic number = 2 * FS / QES

Basically you want the magic number to be around 500hz, which will get you a bandwidth of about two octaves, from about 250Hz to 1khz.

Couldn't you just go active and EQ the top end of the mid(s)?

[Kevmoso]

These results look really good. I look forward to seeing some crossover optimization if you don't end up throwing these away.

So is the 2 * FS / QES idea for a synergy midrange driver out the window?
This MCM's 2 * FS / QES, if it's listed specs are to be believed, is 215hz?
Yet this configuration works up to 1500hz?

Is the 'Suitable midrange cone, for bandpass mid in Unity horn' thread just outdated or should it be deleted?

How does one REALLY select a suitable midrange cone, for bandpass mid in Unity horn? Is that a new thread?

[Patrick Bateman]

Originally Posted by Kevmoso

These results look really good. I look forward to seeing some crossover optimization if you don't end up throwing these away.

So is the 2 * FS / QES idea for a synergy midrange driver out the window?
This MCM's 2 * FS / QES, if it's listed specs are to be believed, is 215hz?
Yet this configuration works up to 1500hz?

Is the 'Suitable midrange cone, for bandpass mid in Unity horn' thread just outdated or should it be deleted?

How does one REALLY select a suitable midrange cone, for bandpass mid in Unity horn? Is that a new thread?

Great question.

This has honestly been the culmination of at least a dozen projects. In particular, I spent most of the holidays of 2019 making phase plugs for tweeters. That taught me a lot about how to extend the high frequency output of a driver.

If you crunch the numbers on a tweeter, you'll find that it should run out of steam at about 3-4khz on a horn, based on the formula of "2 * FS / QES."

Due to this, the 'trick' to getting it to play out to 20khz is:

1) Smaller is better. Way easier to get a 3/4" tweeter to play to 20khz than a 1" tweeter.

2) Pathlength is king. Even a difference of a millimeter makes a difference at 20khz.

So I applied some of that here. In particular, using a single tap instead of two, in order to guarantee that the pathlengths are as close to equal as possible. If I'd 3D printed the entire thing I would've used a phase plug with slits, like a compression driver. But since this one was going to be combined with a commercial waveguide, I went with a straight hole.

I think I could extend the bandwidth even higher if I put some polyfill inside of the chamber. The idea would be to acoustically attenuate the radiation from the cone, while leaving the radiation from the dustcap untouched. Basically the idea is that the sound radiated from the cone will be around two inches out of phase with the dustcap, due to the longer pathlength through the midrange tap (aka phase plug.) A difference of two inches equates to a dip at 3375Hz, because the radiated by the dustcap is 180 degrees out-of-phase with the sound radiated by the loudspeaker cone. The "PDR" versions of the Bohlender Graebner drivers work on a similar principle. The stuff felt on the edges, sacrificing maxium output to increase high frequency extension.

But that last part is admittedly overkill and hopefully unnecessary here.



Side note: I need another project like I need another hole in my head, but one of the original variations on this project, was to use a bunch of 3" drivers. The Fountek FE85 in particular. Two of these won't generate much output, but if you stuffed six onto the horn you could get some real output. Similar in concept to how a 3" midbass won't be HiFi, but if you cram eight or sixteen of them into an array, it can really get loud. With a carefully designed phase plug, I'll bet the FE85 could reach as high as 2khz.