Mazama

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Did you ever take measurements of the 4552 on the QSC? I looked around and didn't find any posted.

In it's stock form, I don't see any issue getting down to 1350Hz or so. I've measured it with a single midrange on the waveguide, and I had to "pad" the Eminence down by about 15dB just to get it to match with the midrange.



It takes two watts for the N151M to hit THX levels.

It was actually the Jericho J7 that inspired me to start using the Eminence. In the pics of the Eminence, I thought it was mostly a clone of the BMS 4552ND, but the Eminence is actually quite a bit bigger. And my thought was that bigger might be better. For $90 they're a steal.

Side by side:
 
Member
Joined 2007
Paid Member
My waveguides arrived, how are people going about measuring the curved walls to make adapters?

I was thinking of sticking as much woofer as I could cram onto the waveguide and using it as an ultra compact PA top, I would need to do some simulations but I was thinking of mounting a woofer directly behind the compression driver (small BMS) and using 3D printed tubes to route the output of the woofer into the waveguide. Am I right that if the tubes are continuously expanding from the woofer to the horn I will avoid a pipe resonance mode?
 
This was one of the things that became an issue for me.

Basically my adapters have a flat face, and the walls of the waveguide aren't flat.

So I had to use a TON of liquid nails to fill the gap.

Ideally I'd like to minimize that space between the midrange adapter and the waveguide walls. Because the longer that the midrange taps are, the lower the crossover is. (Which is BAD.)

Because the air under the cone, and the length of the taps, it acts like a bandpass. Ideally, the length of the holes would be as short as possible.
 
Founder of XSA-Labs
Joined 2012
Paid Member
I cut thin sheets of cardboard templates to match the walls at several intervals (4 or 5) and then digitized the shapes as jpg images which were then fit with a 2-3 point spline, and used as profiles for doing a loft operation in SolidWorks. It’s a lot of work vs having a 3D scanner - but works if you don’t need to do it all the time.
More here:

A Bookshelf Multi-Way Point-Source Horn

I used PL Premium to glue it in place.

Or you can do what Bushmeister did: use a lot of Bondo auto body filler putty :)
 
Last edited:
Member
Joined 2007
Paid Member
I have ordered one of the comb things to aid with making the models. Thanks for the tips.

I have attached a picture showing my proposed mounting arrangement with a 12TBX100 I had lying around. I would use a lighter weight driver as I would only aim to play down to 100Hz and would prioritize efficiency. The plan is to make some kind of 3D printed or machined plate* that volume fills the 12" driver and routes its front volume to holes in the wall of the wave guide.

*might be easier for me to make this out of aluminum than 3D print
 

Attachments

  • woofer_on_horn.jpg
    woofer_on_horn.jpg
    479.8 KB · Views: 362
Oddly enough, this entire project nearly got cancelled because of Microsoft:

I 3D printed the adapter, and put everything together, then measured it. Looked really bad.

Put it back on the shelf.

A few days later I came **this** close to putting it in the trash. I have a really bad habit of never finishing anything, and it doesn't take much to convince me to throw a project away.

But I decided to give it another go, another round of measurements. I started to notice that they just looked inexplicably bad. For instance, there were was way more echoes in the measurement than you'd expect with a proper gate.

I tried different USB ports, different volume levels. I came really close to disassembling my microphone, but decided that would probably break it.

I upgraded the drivers on my sound card. Rebooted a few times. Still crummy.

Finally, as a last ditch sanity check before buying a new mic, I tried a different computer.

Everything worked fine.

So it looks like the geniuses at Microsoft have added some type of new "feature" to Windows ten that's trashed my ability to use the microphone.

A long, long time ago, like 20 years ago, I had the same problem with Windows XP: Microsoft would randomly make changes to the microphone and sound card settings with no rhyme or reason. For instance, there were some "features" that would screw up the microphone input in subtle ways.

Windows 10 barely has any user accessible settings for the mic at all, so this is really irritating.

I think I may have to install Windows 7 just to get this stupid PC to behave properly. Or possibly get an external sound card.

It's seriously aggravating because I didn't make any changes to my PC, it just upgraded itself, like it constantly does. (Yes, I know you can turn off updates, but I kinda like having the O.S. up-to-date.)

TLDR: I can't do distortion or polar measurements at the moment, unless I drag another PC to the garage.

FYI -

I was pulling my hair out over this issue. I tried everything you can imagine:

1) instead of using my motherboard's sound card, I tried using the HDMI out supplied by the video card. (HDMI includes audio, and you can get that stream from the audio out of your TV.) It didn't help any.

2) I noticed that Windows was *refusing* to use the drivers for USB chipset. I even uninstalled and re-installed the drivers, it just flat out refused to use them. My motherboard is about six years old, and the newest drivers available for it are five years old. So I'm guessing MSFT is blacklisting the drivers in Windows 10.

But I noticed something funny; my MiniDSP USB mic, which worked perfectly fine six months ago, now it only works when plugged into a USB1 port. In a USB3 port, it absolutely *refuses* to work.

So I replaced the USB cable.

Voila!

I am back in business.

It's really ridiculous if you ask me; this issue was 100% a software issue, and appears to be caused by some Microsoft-inflicted driver issue. My hunch is that my old USB cable is a USB1 cable, and MSFT fubar'd the USB1 ports on my system somehow. You can plug in a mic just fine, but the measured data is no good. With the new USB cable, I can plug the mic into the USB3 ports and things work great again. (With the old cable, when I plugged the mic into a USB3 port it wouldn't work at all, it didn't even show up as being plugged in.)

TLDR: if your measurements in Windows have gone south, take a look at getting a new USB cable.
 
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.

See: Suitable midrange cone, for bandpass mid in Unity horn.

I spent a couple weeks trying to make a phase plug for some one inch aluminum tweeters, in the hope that I could cross them over at about 800Hz. This would allow me to make a two-way Unity. The idea was to lower the xover on the tweeter to a point where I could use a beefy midbass.

That didn't work too well.

So then I bought some compression drivers with aluminum diaphragms, as detailed here:

Annealed Aluminum

That worked really well, better than expected.

So I revived "Mazama" with the intent of making it a two-way instead of a three way.

Lo and behold, the phase plugs that I made for the midbasses work so well, it looks like Mazama won't even require a super-expensive tweeter:
My flashy new phase plugs seem to get my midbasses to play all the way to about 1500Hz.

BNERVh0.png


Here's a measurement of the midbasses and tweeter on the QSC horn with a very basic xover and no EQ. I haven't built a box yet, this is just a dipole.
 
5H8YHr5.png


Here's the response of the Eminence N151M on the QSC / B52 waveguide, with some EQ added. Efficiency is crazy high and distortion is well controlled. The QSC is a really good match for this compression driver.

There's some distortion in the midrange, due to me lowering the crossover down to 1500Hz (second order LR). But the distortion is buried, and it's second order. The 3rd order distortion is basically inaudible. It sounds clean.
 
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.

Q3oinNK.jpg


TcmbllK.jpg


M5Fjgx8.jpg


vo9zaNK.jpg


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.

bns8tpF.jpg


dulS4aZ.jpg


1C9rCVt.jpg


BVrfcyc.jpg


Here's some more pics that show how the midbasses are mounted.
 
Member
Joined 2007
Paid Member
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
 
eU8xrQB.png


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-select/55-1870/woofer-5-aluminium-cone/dp/39C2182

qrM6tPL.png


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.)

Gr5ywh1.png


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.
 
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.

Gr5ywh1.png


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.
 

Attachments

  • Genelec 8351A H Freq Resp Plot Q1.png
    Genelec 8351A H Freq Resp Plot Q1.png
    190.2 KB · Views: 89
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)?
 
These results look really good. I look forward to seeing some crossover optimization if you don't end up throwing these away. :rolleyes:

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

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.

images


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.
 

Attachments

  • s-l1600.jpg
    s-l1600.jpg
    182.6 KB · Views: 60
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.