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 Post subject: Altec 511B Measurements
PostPosted: August 11th, 2016, 10:51 pm 
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Starting a new thread to present some measurements of the 511B provided by Bjorn Kolbrek, taken in anechoic chamber at NTNU, Trodheim, Norway. 902b driver.

Frequency response shows broad 5dB peak in presence region, 12dB rolloff below~800hz

Impedance plot shows serious dropoff in loading below 800hz, Various major discontinuities through frequency range. Blue is Resistive component of Z, Red is reactive Z.

FFT shows various nasty hangovers and delays. Check it out.

Hope this gives those who like to ground evaluations in empirical measurements something to cogitate on. I foreground subjective experience over measurements, personally, but I'll grant that a basis in physical phenomena exists and sometimes gross measurements do provide some insight.


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511B_CSD_on-axis.png
511B_CSD_on-axis.png [ 66.13 KiB | Viewed 10952 times ]
511B_ThroatImpedance.png
511B_ThroatImpedance.png [ 14.14 KiB | Viewed 10952 times ]
511B_FR_on-axis.png
511B_FR_on-axis.png [ 15.02 KiB | Viewed 10952 times ]
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PostPosted: August 12th, 2016, 9:51 am 
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The problem here is that the horn was tested with a horn driver that has the "Tangerine" phase plug and a loading cap. Neither of which have proven to be audiophile worthy when compared to the legacy 800 series horn drivers. Maybe start over.

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PostPosted: August 12th, 2016, 1:51 pm 
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Walt, get a PhD in acoustics then you argue with Bjorn.

As far as I can determine, his measurements bear out many of my assertions, which are based on 30+ years of extensive experience.

My job is to fly around the world demoing world class horn systems. Put 70k miles in last year. In the last year I have set up and deomoed several dozen top-flight horn systems. Hosted Jean Hiraga in Korea and Mr. Atarashi, the editor of a Japanese tube magazines and one of the very top guys in Japan, in March and we listened to 22 Western Electric, Lansing field coil, and Klangfilm systems in 8 days.

I help curate the most extensive collection of horn speakers in the world, which I have been working with since 2001

I just spent the day measuring 10 Western Electric theater horn systems along with Bjorn having a combined market value of several million dollars. but you will never find most of it for sale.

I'm somewhat opinionated , true, but with a bit of relevant experience to back it up.

Indeed, the tangerine models out measure the WE phase plug designs. I have owned both for at least 20 years, maybe longer, and find it hard to choose among them for sonics

But whatever anybody likes, they like. There is no true and false in preferences, but I must ask what have you heard besides 511s, Walt?

I post this empirical data for people who want to learn, that's all. Hope it is useful to somebody.


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PostPosted: August 12th, 2016, 2:01 pm 
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J-ROB,

Thanks for the plots.

I measured the freq response of the horn last night. This is my first attempt ever. Used Dayton Audio's EMM-6 mic with freeware AUDMES software. EMM-6 is not tracking below 70Hz, it could be defective. Returning it an d getting Berhinger ECM-8000. AUDMES is rudimentary software.

Measurement is taken with the mic about 1" from the mouth of 511B which is driven by 802D driver. Crossover was at 500Hz and the attenuator circuit was on. Disconnected the woofer for this measurement. I do not see the rolloff below 800Hz or in the HF ranges. It is pretty much flat within +/-5dB range all the way from 500Hz to 20kHz. Since the mic I used is entry-level and suspected to be defectivve, the +/-5dB band could be larger or smaller.

If Berhinger mike is better, I am thinking of investing in True RTA Level 2 or 3.

Any recommendations for budget mics and Software?


Attachments:
left_channel_horn_3_0att.jpg
left_channel_horn_3_0att.jpg [ 210.38 KiB | Viewed 10930 times ]

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Last edited by Cogito on August 12th, 2016, 2:59 pm, edited 1 time in total.
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PostPosted: August 12th, 2016, 2:13 pm 
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I've been using the Dayton UMM-6, which comes with a calibration file.

http://www.parts-express.com/dayton-aud ... e--390-808

Been using freeware, REW, Room Equalization Wizard, available from Home Theater Shack. They are pretty strict about language, you must agree to be a choir boy. At least on-line.

http://www.roomeqwizard.com/

Hope this helps.

Stuart


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PostPosted: August 12th, 2016, 2:31 pm 
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I could not get the mic input to work with REW. Using focusrite solo as USB sound card. Output thru focusrite is working fine. Maybe Dayton EMM-6 is not compatible with REW.

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Last edited by Cogito on August 12th, 2016, 2:56 pm, edited 1 time in total.

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PostPosted: August 12th, 2016, 2:35 pm 
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Interesting comment since I make a living going behind so-called "experts" including PhD and multiple PE types. BTW -- my professional experience also includes acoustics projects for Hilton Hotels and the Howard Hughs Medical Institute as just two examples.

Those horns are like a microscope -- everything is magnified - good or bad. The later Altec horn drivers with those damned plastic phase plugs and compression caps have a rep for sounding like crap when compared to the originals. Yet consideration regarding systems feeding the horns and crossovers seems to be missing from the dialog. If you want a reality check try the same measurements with Martin Logan electrostatics. You'll be surprised.

That's my six inches.

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PostPosted: August 12th, 2016, 2:55 pm 
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Cogito wrote:
I could not get the mike input to work with REW. Using focusrite solo as USB sound card. Output thru focusrite is working fine. Maybe Dayton EMM-6 is not compatible with REW.


Not sure about the EMM-6. My UMM-6 worked fine with a cheapo laptop, first try, no glitches.


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PostPosted: August 12th, 2016, 3:36 pm 
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Cogito wrote:
I could not get the mic input to work with REW. Using focusrite solo as USB sound card. Output thru focusrite is working fine. Maybe Dayton EMM-6 is not compatible with REW.


REW doesn't have a clue what mic you plug into the Solo. If you've got the EMM-6/Solo combination working with other software either REW doesn't like the Solo, or you're doing something wrong...

Roscoe


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PostPosted: August 12th, 2016, 4:54 pm 
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Plus one for trueRTA level 3, used it for years with Behringer mic, which I had calibrated and mark so I can always mount it the same way. BTW the fellow calibrated the mic gave me two cal files, one with mic in horizontal position pointing at source and one fle with mic held vertical pointing to ceiling which he told me was the preferred method.


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