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 11 
 on: February 14, 2019, 05:18:05 pm 
Started by mikezietsman - Last post by Kai
Many manufacturers use these MOV devices in their construction, it's a proven product...
...a Corcom IEC line filter is another good add on to any AC powered equipment...
It's not if, but how the mentioned parts are incorporated into a design.
E.g. the MOVs are often covered with extra glass cloth/silicon isolation.
It's important how these are mounted, as they can become extremly hot and can melt plastic and unsolder mains cables if simply soldered across the mains inlet sockets.
There needs to be a fuse in front that can swich off 2000+ Volts without turning into a light arc ...

I could go on an on.

This is not a power electricians DIY forum, people reading this often have minor or no skills in that area.
Telling people to "simply spend few cents and mod your device" leads into catastrophe.

I am skilled and would not mod an existing contruction, as because I am skilled I know about the consequences and know what (destructive!) testing would need to be done before I could call something safe.
 
The only exception if I see a definite faulty construction, mainly those from early US products where powerlines with only single isolation run all across the device in an unearthed cabinet (have you ever looked inside the famous Carver/Phase Linear amp constructions?).

My personal conclusion and last word on this topic:
Leave everything as it is as long as it's factory original safely constructed. There is not much that can be gained from mods in the power line section.
The more you do the more can go wrong which can cost a life at worse.

 12 
 on: February 14, 2019, 02:02:12 pm 
Started by Scott_Smith - Last post by Scott_Smith
Thank you all for your speedy responses!

Kai/David: yes, I am acquainted with the pitfalls of anechoic measurements.  Mostly, I was just trying to get a handle on how various manufacturers conducted their tests, so I can compare apples with apples (although, as David notes, there can be significant differences in the sound source). I have also used TEF systems in the past to make TDS measurements as well, which can be very useful, but I find it easier to do polars in a chamber equipped with a turntable.

When it comes to actually determining what mic to use for a specific application, I of course always depend on my ears, but I find measurements useful to corroborate what I hear with what the measured performance is, as well as to weed out mics that may have issues.

Regards,
--S

 13 
 on: February 14, 2019, 12:02:20 pm 
Started by mikezietsman - Last post by Jim Williams
Many manufacturers use these MOV devices in their construction, it's a proven product. Relying on the bean counters to look out for you is risky as you have determined.

Besides the MOV, a Corcom IEC line filter is another good add on to any AC powered equipment. Those cost a few dollars and provide extra AC line filtering.

 14 
 on: February 14, 2019, 03:56:28 am 
Started by mikezietsman - Last post by Kai
One can fit a MOV device (metal oxide varister) across the AC pins on the internals of the gear. Those clamp surge voltages and are effective and cheap.
Jim, I have long thought about your proposal here and it causes me headaches.

In my opinion it's no good idea to suggest doing modifications in the line voltage internals of any device.
The manufacturer has thought out, tested and got approvals on those parts and any changes here mess up the construction.
There are a too many things that can go wrong.

You buy a minor (and incomplete) improvement in surge protection on the expense of making the whole device unsafe in a lot of other aspects.
This can cause fire, injuries or death of persons.

If someone wants to go this cheap way a socket board with built in protection can be used to achieve the same or even better protective results.
Just don't expect wonders from that.

Professional overvoltage protectors don't rely on varistors only, they include spark gaps and a circuit breaker and are built to safely deal with the high energy amounts that can appear.
They even indicate a failure so you know that they have lost their protective effect after a very strong surge like from a lightning flash.


 15 
 on: February 13, 2019, 07:30:24 pm 
Started by Scott_Smith - Last post by David Satz
I've been in the anechoic chamber at Neumann in Berlin--but that isn't where they build their mikes any more.

At any rate, while a 1-meter effective measuring distance is a somewhat common practice, it isn't specified by any established standard. As I understand the IEC standard, frequency response curves shouldn't include any proximity effect at all. (At one meter there is some proximity effect for cardioids, more for super- and hypercardioids, and even more for figure-8 microphones--see the attached excerpt of an old Gotham Audio publication on the U 67, for example.)

If an anechoic chamber is used--as Kai mentions, there are alternatives--measurements are generally carried out at a somewhat greater distance, then "corrected" so that the published curves will show the low-frequency response that would be expected at the chosen distance, whatever it is. Even that is a generalization, since the geometry of the sound source--point versus plane or in between--is a major variable as well.

That "chosen distance" has been 1 meter for several of the most respected manufacturers, including Schoeps and Neumann, for a long time. For other manufacturers (DPA among them) it is less, e.g. 30 cm. There also are manufacturers who choose the measurement distance on a product-by-product basis according to the intended use, e.g. if a microphone is designed for close speech pickup it will be measured at (or "corrected to") a smaller distance than if it is intended for general studio use.

Of course when you "correct" to (or actually measure from) a point that's closer than another manufacturer uses, you raise the apparent bass response in your curves relative to theirs. Most manufacturers don't say what their measurement distance is--and even if they did, it's not exactly obvious how to use that information when interpreting the low end of two published response curves if they were made at different effective distances. This makes it difficult to compare the low-frequency response of directional microphones between different manufacturers, which I find unfortunate.

--best regards

 16 
 on: February 13, 2019, 05:52:12 pm 
Started by Scott_Smith - Last post by Kai
I can't comment on what Neumann currently does, but I have first-hand information from Schoeps, being located in my hometown.
They do not use an anechoic chamber, but a long tube to generate a clearly defined sound field.

Unechoic chambers have certain disadvantages:
- There is a lower limiting frequency connected to the chambers size and kind of damping.
- They are not perfectly free from reflections, for example you need something to walk on which is usually done with steel net, and the damping materials cannot be made 100% unreflective too.

There are other techniques for microphone measurements that can exclude reflected sound.
One of the most popular is named Time Domain Spectrometry, TDS. 
The idea behind these types of measurements is, that reflected sound takes longer to reach the device under test than the direct sound stimulus.
So reflections can be excluded by using a very narrow band sweeping filter that has swept out of their way at the time the reflection arrives.
The stimulus would be a swept sine wave in this case, as usual.

I have used TDS with great success in absolutely normal rooms, and the other advantage is, the room does not even need to be very quiet, as noise is filtered out by some amount too.

Cardiod mic's frequency response measurements are usually referenced to 1m, except for special types that are made for close up use only.
These measurements only show a small window into the real situation, as going closer to the source will boost the lower frequencies up to 20dB due to the proximity effect, and going further away will leave a roll off in the range below ca. 100Hz.
The rolloff is partly compensated by room reflections in real recording situations.

BTW, LDC (Large Diaphrag Condenser) cardioid mics are not better in this regard, just different.
Usually their proximity effect is less pronounced, as they tend to go into omni characteristics for lower frequencies.

This all is purely academic, finally your ears needs to judge the result.
I would go so far to say that studio microphones all have quite similar published measurements and sound much more different than the measurements would suggest, on the other hand.

 17 
 on: February 13, 2019, 03:56:19 pm 
Started by Scott_Smith - Last post by klaus
I asked David Josephson to chime in. He is the expert on measuring protocols for condenser microphones.

 18 
 on: February 13, 2019, 03:51:57 pm 
Started by mikezietsman - Last post by klaus
I guess you misinterpreted my sentence, clumsily written:
("Keep the M269 head in cardioid when testing on the U67 body. That's the only pattern that will work in this combination."
I was referring to the ONLY combination that will work without modifying mics or heads: M269 head on U67 body, and it will only work in cardioid.

 19 
 on: February 13, 2019, 02:25:29 pm 
Started by Scott_Smith - Last post by Scott_Smith
Klaus:
I've searched for this information elsewhere, bu am not finding anything definitive. Can you enlighten me as to whether Neumann used a standard distance from speaker source to mic when performing response plots and polar plots? I have seen the distance of 1 meter bandied about, but don't know if that is in fact correct. Has the distance varied over time? Is it the same for all microphone types?

Also, are the polar plots typically conducted with the diaphragm located at the 0 degree axis point, or with the front of the mic grille located at 0 degrees?

I would also be interesting to know what the termination impedance is of the mic preamps typically used. (I am assuming about 1.2K ohm).

S. Smith   

 20 
 on: February 13, 2019, 11:56:55 am 
Started by mikezietsman - Last post by mikezietsman
Just a quick follow up...

It would appear that a u67 head does not work on an m269 in cardioid mode. Luckily it also appears to have not done any damage. (there was just no output)

Thank you so much to everyone for their advise on the power variations...

My current strategy until I can get something like Uwe's reccomendation, is to be powered down before the blackouts (we have a nationwide schedule) and to make sure I stay powered down for a good ten minutes after the power comes back on.

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