Seeking ribbon mic guidance

[WA2SQQ]

Some time ago I picked up an inexpensive ribbon microphone being sold at guitar center. The mic has an incredible low end, but severely lacks in the high frequency response. Not sure if this is a characteristic of ribbon mics or due to an inexpensive design. I have a Behringer DEQ2496 in line, so some processing is my next step. Can anyone offer some guidance? Is it better to attenuate the lows, or should I try pushing the highs?

[Todd, KA1KAQ]

You'll probably have to do a little of both. I run an RCA 77D given to me by WA2PJP. Stuffing it directly into the mic input gives a low/muddy sound. This is true of any ribbon mic I've heard or played with, due to impedance and other issues.

Not familiar with the Behringer, I ran mine into a little JoeMeek EQ/comp and from there into the 600 ohm phone patch input on my transmitter. Works great, gets excellent reports.

The best way to set it up is to monitor yourself and get it to where you like it. Then try it over the air with a trusted source who isn't just going to tell you it sounds good or is tone deaf. A quiet morning or afternoon locally works best. Then you should be able to fine tune it.

Otherwise, set everything mid-scale and work up or down with someone over the air. Just remember that everyone has an opinion about what sounds good, and many do not agree. Hence the need for someone whose advice you trust.

Once it's set, resist the urge to 'tweak' or otherwise improve or add more highs, bass, etc.

[WA2SQQ]

So, perhaps some impedance matching from 600 ohm to ~ 4.7K might decrease the need to use heavy EQ'ing? Appreciate your feedback!

[W3GMS]

In this case, impedance matching will not negate the need for some eq'ing.  The response of the mic is probably very flat.  You will need so eq'ing to give your signal some presence.  Its extremely important to make sure the transmitter audio is clean and the response is wide enough to respond to the frequencies your EQ'ing.   

Joe-GMS

[Todd, KA1KAQ]

Excellent point, Joe. Doesn't do much good to run a wide range of audio frequencies if your transmitter is lopping them off before they leave the box. Amateur transmitters tend to be a lot more restrictive than commercial audio equipment.

I forgot to add that the little box I use is also a preamp to boost the mic up a bit before it enters the transmitter. Also important on these mics, it seems.

[N1BCG]

Booming low end can also be a result of "the proximity effect" which occurs on many microphones when the user speaks closely. I have a Reslosound RBM ribbon mic that has a thunderous low end when close-talked, yet sounds far more sonically balanced at a distance of 9" or more.

So profound is the proximity effect that ElectroVoice set out to defy it in their RE-20 and RE-27 microphones by placing the transducer deep within the housing. This made the microphone popular for broadcast as it evened out the sound of the announcers and completely ruined the act of the overnight jock who liked to woo his female listeners by getting cozy with the microphone.

[Opcom]

An old couple of articles on making your own ribbon mic say to take a small audio transformer and replace the primary with about 10 turns, and it says the response is very good from the  deepest bass out to 7KC. The ribbon was to be 1/4 to 3/4 of a thousandth of an inch thick.

It makes sense. The fist thing that strikes me about a ribbon mike is that it looks like a current generator with a very low impedance. Indeed, the ribbon itself must have such a low resistance that anything else would be "hi-Z" and impede the flow of the minute currents.

I would think the wiring from the ribbon to the transformer should be heavy gauge, or perhaps insulated braid for flexibility, and the 10 turns ought be #12, or maybe a sleeved 1/8" copper strap or braid. Extreme maybe? Just thinking out of all boxes. how to maximize the energy transfer.

[DMOD]

Booming low end can also be a result of "the proximity effect" which occurs on many microphones when the user speaks closely. I have a Reslosound RBM ribbon mic that has a thunderous low end when close-talked, yet sounds far more sonically balanced at a distance of 9" or more.

So profound is the proximity effect that ElectroVoice set out to defy it in their RE-20 and RE-27 microphones by placing the transducer deep within the housing. This made the microphone popular for broadcast as it evened out the sound of the announcers and completely ruined the act of the overnight jock who liked to woo his female listeners by getting cozy with the microphone.

That and the proper transformer ratio can affect frequency response.

Here is one such transformer if the ribbon mike doesn't already have one.

https://www.edcorusa.com/rmx1

Go to the "specifications' button.



Phil - AC0OB

[AB2EZ]

A ribbon microphone can easily be shown to have a natural output voltage v. sound pressure frequency response that varies as 1/frequency*.

RCA (in its original ribbon microphones) and others counteract his effect by placing the ribbon in an acoustic cavity that rolls off the net sound pressure (net of: front sound pressure - rear sound pressure) on the flat part of the ribbon at low frequencies. This rolloff follows an approximately "f" pressure v. frequency characteristic.

Therefore, if all goes well, the net frequency response is: output voltage v. incoming audio sound pressure = A x f x (1/f) = A, where A is a constant having the units of volts per pascal.

If the acoustic cavity is not providing the needed "f" shaped response (i.e. of: net pressure on the ribbon v. incoming sound pressure), then there will typically be a residual low frequency rollup. Close talking the microphone can reduce the benefits of the acoustic cavity.

The output load impedance, across the ribbon, should be high enough... so that current flowing in the ribbon produces very little opposing force (Ampere's law) to the ribbon movement being caused by the sound pressure. Nevertheless, one still typically benefits from the use of a step-up transformer between the ribbon and the preamplifier. The preamplifier should have a high input impedance (50k ohms or more)... so that, even with the step up transformer, the load on the ribbon is still a high enough impedance.

Remember, we are not trying to maximize power transfer to the load (as in a generator). We are trying to maximize the signal-to-noise ratio at the output of the preamplifier. Using the step-up transformer increases the signal before it enters the cable between the microphone and the preamplifier. This reduces the effect of hum ingress (induction) into the cable, and also reduces the effects of thermal noise associated with the preamplifier (the preamplifier's equivalent rms input thermal noise is approximately fixed by the characteristics of the preamplifier's first stage FET; but the signal across the secondary/output of the transformer increases in proportion to the turns ratio).

*The net acoustic force (on the ribbon) accelerates the ribbon... but the peak velocity of the ribbon (for a fixed acoustic force level) will be higher at lower frequencies (i.e. v(max) = the integral of the acceleration... and, since F=ma,  the acceleration of the ribbon is proportional to the force). The voltage produced across the ribbon is proportional the velocity of the ribbon (Faradays law)... because the total magnetic flux enclosed by the ribbons goes up and down as the ribbon moves in and out.

Once the signal passes through the preamplifier, you can provide additional equalization (low frequency roll off and/or high frequency roll up... as needed. It shouldn't matter whether you roll off the low end or roll up the high end... provided you have enough flat gain.

Stu

[WA2SQQ]

Never expected so much great info - Thanks! Now I'm all psyched up to get home and start playing! Using this with a Flex 6500, so I can open it up wide. I'll see if I can get it going and try to check in on 75M this evening. Already added a switch to my preamp to disable the 48V phantom power.

Thanks again!

[N1BCG]

If headphones were used in this test, it's possible that the phase may have been wrong, which would muffle the high frequencies due to bone conduction. I get a lot of use out of a phase-flipping cable made from two XLR connectors and a DPDT switch in between. Just throwing out another possibility...

[WB5IRI]

Ribbons can be great if used correctly. First, every musician will tell you to use a pop filter, but then they are singing into the darn things, and they get really loud and emotive. If all you are doing is speaking normally, I don't thinbk you'll need the pop filter -- monitor yourself or have someone listen to your signal, to see if you need one. Second, as has already been pointed out, you can use a ribbon from several feet away and it can still sound good -- they are very sensitive, and they don't get all weird sounding from a distance like so many condenser mics tend to do. They will also pick up lots of extraneous noise, though, so you might want to get close and turn the gain on your preamp down. Third, yes you need a preamp and EQ so you can adjust for things like gain and low-end. Cut the bass and up the treble, monitor yourself or have someone else do it, and you will be pleased. Ribbons sound best with preamps that have a transformer input, such as the GAP PRE 73. Try it with the preamp you have, but if you can't make it sound right, going to a transformer input might help, as has been pointed out above. Oh, and if you purchase the GAP PRE 73, note that it isn't a stand alone unit but has to be plugged into a "lunchbox" that provides thje correct voltages and connections for it to work. Ask me how I learned that lesson!

Once adjusted correctly, you will love your ribbon mic. But do note that they are very fragile. Don't drop it or it's likely to be toast. The ribbon is extremely thin. Also, NEVER blow into a ribbon mic to see if it's working -- that blast of air can damage the element as well. Michael Farrabee of RestoMod Mics can rebuild your element if disaster strikes.

Doug

[W3GMS]

Never expected so much great info - Thanks! Now I'm all psyched up to get home and start playing! Using this with a Flex 6500, so I can open it up wide. I'll see if I can get it going and try to check in on 75M this evening. Already added a switch to my preamp to disable the 48V phantom power.

Thanks again!

Flat audio systems seldom sound good on the Ham bands.  Remember mostly everyone on the receive end has bandwidth limitations on their receivers.   

The reason the D-104's can sound so good is the mid-range presence rise.  Even the low end is impressive when terminated properly.  So flat mic's need some help.  Based on your voice,  you may have slightly different setting as compared to someone else's settings.  For my voice which has lots of low end response, I do a deep notch around 250 HZ and then some slight boosting between 2 and 4 KZ.  That EQ works with both my Shure SM-7B and my RE-27 and my RCA 77D.   I like to EQ while recording off a nearby receiver set to a 6 KHz bandwidth since that is probably the most common BW that stations copy at.  As far as gain buildup with a preamp, I like the Symetrix 528E although there are many choice to go with.   The 528E has a parametric EQ although I like my ART graphic equalizer better. 

Like pictures on the wall, you have to settle on what you like and proceed accordingly. 

Joe-GMS

 

So do your own listening through recordings and set it up the way you like it and then leave it alone. 

Joe-GMS   

[W9ZSL]

From my recording studio experience (among them founding Full Compass...blow that horn) the BEST results when miking an upright bass were attained with a ribbon mic.  They don't have to be exposed to a lot of sound pressure and have a nice bottom end.  During the Big Band era, RCA 44BX's were essentially flat from 50-15,000 CPS and were widely used in both broadcasting and recording.  They were used for solo vocalists who actually stood back 2-3 feet from the mic in order to eliminate any proximity effect.  The 77DX was also important.  It was multi-pattern and actually had a movable mechanical baffle inside to adjust the patterns to make it poly-directional.  It wasn't quite as flat as the 44 but was good for 30-20K!  It's no wonder such great recordings were being made back in the 40's with three or four mics max.  There was no such thing as close miking as you find today.  The Western Electric / Altec 639A had both a ribbon and dynamic element.

Electro-Voice made several types including the famous "Johnny Carson" type but discontinued them in the mid-60's.  Beyer manufactured them but for some reason, very few were manufactured and used during the 70's-90's.  Unless you bought a rugged version like the RCA's designed for rough handling in radio, TV and recording, they tended to be on the fragile side.

Now ribbons have come back into use because technology has made them more solid.  Russia has built some which would blow anything away but are expensive as hell.

Getting back to the Behringer.  ANY microphone will be bass-heavy the closer you get to it and ribbons are ESPECIALLY prone to the proximity effect because the surface area of a ribbon, while great for higher fidelity, have to have some distance between the sound source and the ribbon to maintain a flat curve.  Try backing off a couple of feet, work your way closer to the mic and then adjust your EQ.  I'd roll off above 5 or 6K and under 100 CPS.  If you boost around 2-3K that should get you in the ballpark provided the mic isn't defective.  ANY mic's sound depends upon how far or near you place it.

By the way, as far a tooting horns are concerned, go for the Sennheiser MD-421.  For voice work, EV RE-20.  Standard for broadcast announce.

[Opcom]

I guess the old articles were wrong. Feb 33 and mar 38.

[W9ZSL]

I don't get into the math and theory.  I'm relaying 53 years of practical experience. Where are those posts Op?  Oh, wait.  No such dates.  Almost got me there!

[W9ZSL]

When I worked for KSTP in Minneapolis in the 80's, we used a mic that was like a RE-20 on steroids.  You could unscrew the back of the mic where there was a mini patch panel complete with tiny plugs to change impedance and modify the frequency response.  That was a killer mic.  I don't remember the model number but they were incredible.

[ve7xf]

>When I worked for KSTP in Minneapolis in the 80's, we used a mic that was like a RE-20
>on steroids.  You could unscrew the back of the mic where there was a mini patch panel
>complete with tiny plugs to change impedance and modify the frequency response.
>That was a killer mic.  I don't remember the model number but they were incredible.

E-V 667 or 668.
The design became the RE-20.

VE7XF

[Opcom]

I don't get into the math and theory.  I'm relaying 53 years of practical experience. Where are those posts Op?  Oh, wait.  No such dates.  Almost got me there!

No excuse me please, I meant to indicate they were QST construction articles and must have become distracted while posting.

There are two with permanent magnets and one using an electromagnet. The articles are in QST February 1933 and March 1938. Do you have access to them?

With that much experience, your comments about the ribbon mikes in the articles would be very valuable, since they appear to be examples of the same kind of equipment. I would certainly like to know more about the subject.

[W9ZSL]

OH!  I see.  When you consider mics started out as being carbons similar to those in telephones and evolved from there, early types of ribbons went through their own changes.  I'm not familiar with earliest types but have used the RCA's and W.E. Altecs.  Until technology caught up, they were still relatively fragile compared to other types like dynamics and there are instances where you wouldn't even consider using them such as on a kick drum, amplified bass or close-miking a screaming guitar amp.  It all boils down to SPL (Sound Pressure Levels)  

If you used an older ribbon in front of the sound hole of a kick drum, you would likely get distortion and run the risk of damage.  For that application I use a dynamic with a large diaphragm to handle the high SPL.  There are some dynamics specifically designed for use on a kick and for high SPL, but using them elsewhere, they become pretty useless.  I have a drum kit with four mics each designed for specific drums: Kick, Snare and two for Toms.

Condensers are another story.  They are great for strings because of their high-frequency response, but they are best used in a lower SPL situation also such as pickups for a grand piano.  Overall, dynamics are the way to go for close miking and high SPL, but again ANY mic will have that proximity effect emphasizing the low frequencies the closer you get.

Microphones can be frustrating because each model has it's own sound and unless you can afford to buy a huge variety like major studios do, you're shooting in the dark.

I can safely say, if you want a GREAT mic at a reasonable price for voice/vocals, check out the Audio Technica 2050 large diaphragm, side-address condenser.  I heard one in action two weeks ago.  A bluegrass band used the one mic for 3-4 vocalists who gathered in around it to sing and it was fantastic. Reminded me of what you might get from an old RCA 77.

[WA2SQQ]

Just wanted to says "Thanks" again for all the great feedback. This weekend I decided to try again. Pulled everything from 100 hz and below down by about 6db, and kicked up some parts of the high end. With about 20 minutes of testing I got this relatively inexpensive ribbon mic (MXL R144) to sound nearly as good as my Heil PR40. The highs are not quite as brilliant but I think with some additional shaping it will make for a good "guest mic". I also found that the deep nulls of the sides of the mic eliminate the washing machine noise when the wife is doing her thing in the next room!

Just saw that B&H is selling it for $84

http://www.bhphotovideo.com/bnh/controller/home?O=&sku=642524&gclid=CjwKEAjws5CrBRD8ze702_2dyjYSJAAAJK9yZA0Jsm2o6Asxn_tGzraQqKT9YUGhojoSdOZFbfJ8DxoCs4vw_wcB&Q=&is=REG&A=details

[W9ZSL]

The ribbons aren't as crisp on the high end like condensers that's why they were used extensively as broadcast announce mics.  They were fine for big bands also because the top end response was well-suited to the high-end of around 12 KHz of the transmitters.  Then you have to remember that little or no EQ was used in the audio chain for flat response. In fact more recent processors, especially those for FM, actually were/are multi-band with EQ/Compression/Limiting dividing the audio spectrum up and treating each separately to provide more "punch" across the spectrum.  I believe Orban was one of the first companies to sell such a device.  

Rather than mess with the high end, you would probably be better off boosting mid to high mid up to maybe 7 KHz to accent the frequency range of the voice. Anything above that would be mostly harmonics and over-tones which, if used with an instrument such as a violin adds "air" but not punch or presence.

If you have some 45 RPM records cut in the 60's, some have a lot of highs and mids but relatively little on the low end.  That's because when played on AM radio, which used a lot of compression and limiting to sound "loud", those highs sounded great when played back on radios with smaller speakers since the compression squashed things enough to make them sound "balanced".  Listen to some of Phil Spector's early 60's stuff on a good stereo system, and you wonder what happened to the bass!

I did a collection of tunes to CD in my studio and many drove me nuts trying to get them to sound good on digital.  I virtually had to process the heck out of them to "undo" mixes that were made with AM radio airplay in mind.

[Steve - K4HX]

A few points:

1. Most often, anything above about 6 kHz is irrelevant for AM Amateur Radio applications. Receiver bandwidths will not allow one to hear anything above these frequencies.

2. I think the Dorrough processors were the first multi band (more than two) units for broadcast use.

3. Most any mic that isn't a total POS, like a busted crystal or a carbon type, can be made to sound very good in an AM Amateur Radio application, with judicious use of an equalizer.

[W9ZSL]

The Optimod AM unit was the 9000A and I believe it processed 100, 450 and 700 Hz along with 1.6, 3.7 and 6.5 Khz separately.

[DMOD]

I set up many of those for Mom'nPop stations.

The Inovonics 235 was a three-band processor and worked well for those on a budget.

Ahh, the good ole days of AM Analog Stereo.

Phil - AC0OB

BTW, if anyone needs manuals for either the Inovonics 235 or the Optimod 9000A, send me a note with your email address to spf@Reagan.com