Some interesting 60's? speakers I picked up...

[ValvTubeHead]

So, by happenstance I've come into possesion of a pair of John Muska Co boxes via sfbay craigslist. Mine were loaded with EV 12trxb's...which drew me to them to begin with. The condition of my pair quite a bit more weathered than mxlews starting point, minus tuned toilet cleaner reflex plumbing...really overflowing modesty though. If these dang things didn't sound so pleasing I'd be using this thread as a gps map. A few wipes with Howard restore-a-finish, mmm...done.


swapped the Muska's up onto the stands after this pic shot:

 

[willyrover]

Ok. You have to tell me what that thing with the meters is on top of your EQ. I want one!

And is that a Radio Shack Genexxa EQ? I had one of those and found it pretty noisy. Do you have it in the loop or are you just using it for the display?

 

[Zilch]

Bring them over and let's measure them and compare the sound to that of the project speakers. :yes:

 

[ValvTubeHead]

Ok. You have to tell me what that thing with the meters is on top of your EQ. I want one!

And is that a Radio Shack Genexxa EQ? I had one of those and found it pretty noisy. Do you have it in the loop or are you just using it for the display?

Meters? ...Logitech/Slimdevices Squeezbox screensaver; digital delight with an analog twist.

yes? Optimus 31-2030
noisy? no
in the loop, yes...I'm waiting for my trends audio TA10.1 to show up, I'll be splitting through eq's tape monitor feeds to drive my corner speakers.

 

[ValvTubeHead]

Bring them over and let's measure them and compare the sound to that of the project speakers. :yes:

Sure...why not.
Not sure about gravenstein boxes v. pippin boxes make a fair comparison, but I'm game. PM me
My ear's probably not as discriminating as most here at AK, but like...I guess I know what I like.:stupid:

 

[ValvTubeHead]

warning, nudity

I did say modest, right?

 

[mxlews]

Sweet. Nice find. :thmbsp:

 

[Zilch]

Shootout pending. Heh, heh....

 

[Brian]

The cabs look pretty decent. Maybe do some looking and see what it will do to get them to work with the drivers. Years ago Jayell used to make cabinets that included a precut round and rectangular port. You were to cover whichever was not needed. It may be the case with this box. In fact, from the photos does not look home brew and could be from the company or another such as Barzilay that also made stock empty cabinets.

 

[Zilch]

Look like John Muska Co. boxes to me.

[I'd recognize them anywhere.... : ]

 

[Zilch]

12TRXB in Muskas

VTH brought his nice Muska bookshelves by today for measurements.

1) Full range unwindowed MLS response of both units, tweeters full on. Nice flat response from 100 Hz to 2 kHz, but they are poorly matched above that. The typical rolloff of the T-35 tweeters is apparent in the VHF. Bass response is lacking in these too-small vented cabinets.

2) Unit #1 showing full range, windowed (quasi-anechoic) high frequency response, unsmoothed version of same, and midrange response of the woofer (tweeter off). There are major notches in the response at 2 kHz and 4 kHz, which may be coming from the mechanical crossover of the whizzer cone, or diffraction artifacts. More study would be required to ascertain the source.

3) Unit #2 showing the same. Well, not quite. The notches appear at different frequencies, the major one 1 kHz lower on this unit, @ 3kHz. This certainly supports the suspicion of a mechanical origin.

4) RTA plot of Unit #2 before and after equalization. Correcting the responses would require different passive coutouring filters for each unit, so we moved directly to AutoEQ. We chose a slightly downward tilting response due to the tweeter response limitations, and disabled EQ below 100 Hz, as there's nobody home down there to work with.

5) What AutoEQ did to accomplish that, +7.5 dB @ 3150 Hz and -8.5 dB @ 6300 Hz are the extremes. There's clearly a transition in the requisite EQ at 2 kHz.

VTH will tell you how everything sounded. We DID listen to my copies of the Mxlews project speakers for a bit, as well....

[Béla Fleck RULEZ.... : ]

 

[ValvTubeHead]

Well folks...
I left Zilchlabs a little slackjawed and a wiser man for the experience...kindof knew I would be. We began with a listening session of his very sexy, hotted-up cabs; btw, jealousy is still a deadly sin... right?
Popped in a few cds for a quick spin: Bela Fleck - Flight of the Cosmic Hippo, followed by a Jazz pop sampler -Bruebeck, Sachmo and Weather Report, next Toni Price's - Born to be Blue, a few DJ Zilch selections and finally a candid Hendrix slowhand blues "I once had a woman"
Short critique: "Zilch's cabs have stunning legs!"

I had few misconceptions about what was to follow; sobering...yet very enlightening. The objective RTA peaks & valleys speak clearly to the Muska and 12trxb's shortcomings. The holes at 3 and 4kHz respectively, rapid hf drop-off and poor efficiency lows aren't pretty and relative to reference cabs like Zilch's...not much to gloat over here, but not is all lost. Happily, some digital wizardry by way of Zilch's Behringer DEQ2496 / ECM8000 combo, inadequacies were smartly shored or patched with some auto-EQ processing. Wide eye'd...I remarked something to the effect..."yeah, but that's cheatin', huh?" heh, a not so tough call, but my complaints are few. A listening to more of Bela Fleck dynamics through both EQ'd and bypass showed headway had been made. After returning home, I've made tweaks to my 10-band settings, and am enjoying listening with new appreciation, enthusiasm and perspective.

I really appreciate Zilch for welcoming me into his laboratory/wonderland and taking time to measure my cabs, offering conservative advice; options are always plentiful...wheels are spinning.

jealousy is still a deadly sin...:thmbsp:

 

[BrocLuno]

What happened to Utah's ?

Sweet. Nice find. :thmbsp:

OK, Just curious - what happened to the Utah's?? Did you ever find the tweeter cap? Did they ever work?

I played my Axe through a full range speaker with X-O and tweeter driven by a PV amp. Sounded nice - just needed more build to be able to bang it around in and out of the truck, etc. Thought about building an industrial strength cab with casters, but sold the Axe instead and went back to acoustic.

 

[Zilch]

Thank you VTH for your excellent review, and the opportunity to study your 12TRXBs.

AutoEQ's no panacea, of course; I use it primarily as a development tool. It does illuminate a path to design optimization, and tells immediately what to pursue and how it will sound.

As example, it was quite aggressive in going after the major notch, but I think I'd step back and say, "7.5 dB of boost in a single band? Clearly, that's going to color the sound, so we'd better look harder at fixing whatever is causing that with something other than EQ." :yes:

Contour filtering the HF is commonly used with compression drivers on constant directivity horns/waveguides, but I'd probably do a bunch more testing and listening before concluding it was applicable to T-35B as well. EV did do it with subsequent derivative tweeter designs so this is not entirely unexplored territory, but it does comprise a defacto "boost" of the VHF, which might not come without consequence.

With respect to the low frequency response, I believe the answer is clear -- bigger boxes, and corner horn loading, perhaps. The woofers were obviously trying to make bass, but to little avail. There are other projects to explore using the Muska cabinets. :thmbsp:

Edit: An earlier look at 12TRXB bass response appears here:

http://audiokarma.org/forums/showthread.php?p=1159362#post1159362

 

[mxlews]

OK, Just curious - what happened to the Utah's?? Did you ever find the tweeter cap? Did they ever work?

I played my Axe through a full range speaker with X-O and tweeter driven by a PV amp. Sounded nice - just needed more build to be able to bang it around in and out of the truck, etc. Thought about building an industrial strength cab with casters, but sold the Axe instead and went back to acoustic.

Yes, I found the tweeter caps behind the woofer magnetic shields. I removed the tweeter from one and am using the woofer in an Altec cab for guitar. I'm thinking about building a box for both woofers and a head.

 

[ValvTubeHead]

Thank you VTH for your excellent review, and the opportunity to study your 12TRXBs.

AutoEQ's no panacea, of course; I use it primarily as a development tool. It does illuminate a path to design optimization, and tells immediately what to pursue and how it will sound.

As example, it was quite aggressive in going after the major notch, but I think I'd step back and say, "7.5 dB of boost in a single band? Clearly, that's going to color the sound, so we'd better look harder at fixing whatever is causing that with something other than EQ." :yes:

Contour filtering the HF is commonly done with compression drivers on constant directivity horns/waveguides, but I'd probably do a bunch more testing and listening before concluding it was applicable to T-35 as well. EV did do it with subsequent derivative tweeter designs so this is not entirely unexplored territory, but it does comprise a defacto "boost" of the VHF, which might not come without consequence.

With respect to the low frequency response, I believe the answer is clear -- bigger boxes. The woofers were obviously trying to make bass, but to little avail. There are other projects to explore using the Muska cabinets. :thmbsp:

You're making a lot of Zilch-sense. I think a bit of soul searching is prompted ...which path to follow or forge. I don't find my speakers arrogant or obnoxious, but they do certainly lack acrobatics of those granted purpose-minded optimization. I can tell...good, clean fun is to be had up ahead :stupid:

 

[Zilch]

I think a bit of soul searching is prompted ...which path to follow or forge.

Science, friend.

You KNOW where the next $300 must be invested to move forward.... :thmbsp:

 

[mxlews]

Pics

A few decent pics of the speakers. Yes, I have to fix the bulging grills.

 

[cuthien]

Hi Zilch,

I now have the JBL Wave Guides, the BMS 4550s, and the crossover parts. For woofers, I have 2 JBL 126A and 2 vintage RCA 15" woofers that I can use for this project (instead of the 123A). Can I use these woofers that I have (the RCA are highly regarded and they sound really awsome to my tin ears) and use your schematics that was posted previously here without any other modification. Thanks.

 

[Zilch]

Yes, possibly, but you'll have to tune your boxes for either of those.

123A is a closed-box driver, and the box alignment is set up for them.

The other major issue is the ability of either of those alternatives to play nicely up to 1.2 kHz.