Header Graphic
Dirty-South Blues Harp forum: wail on! > High vs low impedance - how it effects the sound?
High vs low impedance - how it effects the sound?
Login  |  Register
Page: 1

apskarp
4 posts
May 23, 2009
9:50 AM
As the amplified amp is becoming relevant in my "harpist career" I wonder what the high/low impedance means in practice. I searched the forum for this but didn't find any answers yet.

So, What does it mean in practise if the impedances of the mic and the amp doesn't match? Does it mean that it cuts some of the high or low end of the voice, or does it affect the volume, or what?

Currently I use SM58 with (home made) 15W tube amplifier (which I got from our guitarist) and it seems to sound pretty nice. Perhaps some more distortion could be nice. I don't have any impedance converters and I'm wondering how it might change the sound. Of course the converter isn't very expensive and I'll get one, but I'm interested to here some technical theory of that too. So I'd appreciate if some of you professors could explain it a bit.. :)
Greg Heumann
47 posts
May 23, 2009
4:57 PM
The short answer to your question - impedance mismatches deliver suboptimal performance from your mic/amp combination.

A low impedance mic into a high impedance amp like you describe will work, sort of, but frequently it is done with an XLR-to-1/4" cable that (believe it or not) only connects one of the low-Z mic's 2 signal pins (pins 2 and 3) to the "hot" or "tip" of the 1/4" connector, and then connects pin 1 to ground. (Ground is NOT part of the signal path in low impedance wiring.) In this case you get about half the possible signal from the mic. Even if the cable properly routes the full signal from the mic to the amp, the mic doesn't see the low ohms "load" it expects to see, and so all bets are off as far as the mic performing the way it is supposed to. The proper way IS to use an XLR<-->XLR cable and an impedance matching transformer. Now here's a more complete answer:


What's Impedance?

By definition, impedance is "resistance to an AC signal" - AC means alternating current - in this case the signal from your mic which is an electrical picture of the sound going into it. POWER in electrical terms is all that matters, but you can have the same amount of power with low voltage and high current, or high voltage and low current. Low impedance mics have a signal with more volts and less amps; high impedance mics are the reverse. But you don't need to know that. All you need to know is this:

1) Microphones and amplifiers work best with certain load or drive levels, respectively. For this reason, it is desirable to "match" the impedance of the microphone to the impedance of the device it is connected to - an amp, a foot pedal, or....

2) Impedance matching transformers are simple devices that can "match" a low impedance mic to a high impedance load, or vice versa.

3) Low impedance systems came later than high impedance ones, and were developed to enable much longer cable runs and better reject noise (like hum) that gets injected via the cable. 

4) There is no inherent difference in tone or feedback rejection between low and high. 

5) Low impedance systems are almost always wired with "XLR" jacks plugs. This is a worldwide industry standard. 

6) High impedance systems can be wired any number of ways, including use of XLR jacks. When XLR is used, however, the wiring is not the same. 

7) There's nothing wrong with connecting a high impedance mic with an XLR connector to a high impedance load (like an amp) with a cable that has XLR at one end and a 1/4" connector. There is something wrong, however, with using that same cable to connect a low impedance mic to the amp - because there is an impedance mismatch. Instead a proper low impedance (XLR to XLR) cable should be used, together with an impedance matching transformer.

----------
/Greg

http://www.BlowsMeAway.com
http://www.BlueStateBand.net

Last Edited by on May 23, 2009 11:39 PM
Buddha
485 posts
May 23, 2009
6:06 PM
That's great info Greg. Thanks!!!
apskarp
5 posts
May 25, 2009
4:02 AM
Thank's for the info Greg! This explains why the PA isn't responding the way it should when I use a behringer's V-AMP2 with SM58 without the impedance matching device. It feels to miss some of the tone. Somehow it still sounds pretty good when I use headphones with it..
Jim Rumbaugh
46 posts
May 26, 2009
1:17 PM
Greg said it all.

Only one thing I could change/add, and it's an electronics "nerd" thing, low impedance in low voltage high current, high impedance is high voltage low current. He just turned it around. See... a nerd thing. And like he said, "you don't need to know that"
rabbit
35 posts
May 26, 2009
1:35 PM
Thank you for this!
Casey
7 posts
Nov 10, 2010
7:34 PM
Can anyone tell me if a matching transformer like the Shure A95UF can be plugged directly into a low impedance mic (transformer with female XLR, mic with male XLR) then run a 1/4" stereo jack cable from the transformers female 1/4" end to your tube amp? Greg suggested using an XLR to XLR cable, but if you can plug the Shure A95UF directly into your low impedance mic, can't you just use common 1/4 cables, or do you have to use XLR all the way? If anybody can shed some light on this I'd sincerely appreciate it.

Thanks, Casey
Tuckster
769 posts
Nov 10, 2010
7:44 PM
You can do that-no problem. However it makes the mic become heavy and unweilding. Better to spring for an XLR cable and be done with it.

OOps I didn't read that thoroughly. You'd need 2 adapters. one for the mic and one for the 1/4". That X-former won't work as is. Or a 1/4' cable with a female end.That would save you one adapter.

Last Edited by on Nov 10, 2010 7:54 PM
Greg Heumann
873 posts
Nov 10, 2010
11:30 PM
Yeah - the A95UF does the correct impedance matching, but Tuckster is correct - it is nicer to unweight the mic end and use a transformer at the amp end of the cable. This also has the advantage that the cable portion of the run is low-Z, which means you can have much longer cables without much signal degradation.
----------
/Greg

BlowsMeAway Productions
BlueState - my band
Bluestate on iTunes
harmonicanick
998 posts
Nov 11, 2010
1:08 AM
Please can you tell me if my high impedance Fender BJ
will match with green bullet? I have a couple of Shaker mics as well would they be suited to the BJ as well?
Thanks for any info.
ridge
113 posts
Nov 11, 2010
6:02 AM
I want to throw my question in now too!

I am currently connecting using a low impedence mic with an xlr to xlr coupled with an IMT into my amp. I want to add an effects pedal in between (BOSS DD-3).

Would I just take my xlr to xlr with IMT and plug that in to the pedal and then use 1/4" cable out from the pedal to the amp?

PS - Greg I hope you're coming back to HCH in 2011!

-Dan Ridgeway
strawwoodclaw
121 posts
Nov 11, 2010
6:27 AM
if you use a low impedance microphone it will not make the tubes in your amp overdrive which gives you that fat raspy Chicago sound. a SM58 is a clean sounding mic

for that Chicago Honk you need a HIz mic & a amp that will take a Hi Z mic.

different amps sound better using different mics
strawwoodclaw
122 posts
Nov 11, 2010
6:28 AM
does any body know a transformer that will work with a medium Z Shure CM 99E86 to make it hi Z
5F6H
368 posts
Nov 11, 2010
6:29 AM
"I want to add an effects pedal in between (BOSS DD-3).
Would I just take my xlr to xlr with IMT and plug that in to the pedal and then use 1/4" cable out from the pedal to the amp?"

Yes you would. You would use the IMT to connect a lo impedance balanced XLR mic to any amp/PA/Mixer/effect unit that has a specific "guitar/instrument/direct/Hi Impedance" input. Boss are expecting owners to plug in a guitar direct to the DD3. The DD3 has a 1Meg (one million ohms) input impedance, anything measured in thousands of ohms, or more (kohms/megaohms) is hi impedance.

There are some lo & medium impedance cheapy karaoke type mics that can "work" into a hi impedance input, these come with an unbalanced 1/4" jack anyway.
ridge
114 posts
Nov 11, 2010
6:50 AM
5F6H, I appreciate your reply. I asked because I just won the pedal on eBay and don't have it in my clutches to actually try it out yet.

This will be the first time in many years that I've used any effects. It will be the first time I've used them with a low impedence mic.

All you gear techs are the best! You've all helped me use the equipment I already own in a much more sensible and productive way :)
5F6H
369 posts
Nov 11, 2010
7:58 AM
@Apskarp "Does it mean that it cuts some of the high or low end of the voice, or does it affect the volume, or what? Currently I use SM58 with (home made) 15W tube amplifier (which I got from our guitarist) and it seems to sound pretty nice. Perhaps some more distortion could be nice."

I would suspect that running a lo impedance mic into a tube amp (based on my experience) will lead to you getting a less focussed, less dynamic sound, less edge, woofy. No matter how far you turn up the amp, it may get louder, but the tone is still loose, by comparison to a typical hi impedance mic.

The unknown (to us) factor here is your home made amp, if it has plenty of gain & sensitive power tubes (15W shouts PP EL84 to me) then it may be "workable"...if not exactly optimal. If you like the sound and you get the kind of projection that suits you, then you may well ask yourself, "do I have a problem?"...

A mic basically provides a voltage source, if that input voltage is not ideal, it still might get bumped up to a useable level by a high gain amp with enough preamp stages - each half of a 12AX7 can boost the signal voltage by a factor of 60, and sometimes by potentially more than x1,000,000, before hitting the power tubes ...this might be feedback hell for some big output hi impedance mics, so it's always worth trying combinations that you might come accross. I'm a big believer in trying what you have to hand, before lashing out with the credit card, but also consider the findings of those with wider experience in the matter.

If it doesn't work...then something in this thread will undoubtedly point to why not.

I'd still recommend getting the IMT, as you never know what you might be expected to plug into in the future.
Greg Heumann
875 posts
Nov 11, 2010
9:47 AM
@5F6H re: "I would suspect that running a lo impedance mic into a tube amp (based on my experience) will lead to you getting a less focussed, less dynamic sound, less edge, woofy. No matter how far you turn up the amp, it may get louder, but the tone is still loose, by comparison to a typical hi impedance mic."

Not true. Assuming the mic is impedance matched into the amp, there are simply no tonal concessions made to low impedance mics. The Shre SM57 is becoming one of the most popular harp mics, thanks in no small part to Jason Ricci's use of one, succeeded by his choice of an Ultimate 57. It is indeed MORE focused, dynamic and even edgy than MOST hi-Z mics.

----------
/Greg

BlowsMeAway Productions
BlueState - my band
Bluestate on iTunes
5F6H
370 posts
Nov 11, 2010
10:05 AM
Hi Greg, this is from Apskarp's original post, "Currently I use SM58 with (home made) 15W tube amplifier (which I got from our guitarist) and it seems to sound pretty nice. Perhaps some more distortion could be nice. I don't have any impedance converters and I'm wondering how it might change the sound."

Apskarp was asking about using a lo impedance mic without a transformer. My observations above are from experience.

Agreed, once a decent IMT/direct box is entered into the equation, preferences come down to specific mics, rather than similar models, or bullet vs wand etc. If all my old mics were stolen tomorrow, I'd just buy a SM57 & shure A95.
harpoon_man
6 posts
Nov 11, 2010
11:43 AM
Greg H (and others): this might be slightly off-topic but I’m curious to get your input. A lot of mics that you see for sale online are advertised as “hot” mics, “high-output” as if these are the most important qualities in a mic. Where would you rank these qualities in the hierarchy of important properties of a good gigging harp mic?

Here’s my quick take: When playing out, I tend to gravitate toward mics that are more middle-of-the-road in terms of output, such as my ceramic astatic element since “hotter” mics tend to introduce more potential for feedback (this even applies when using my Meteor, for which feedback is never a problem).

-Rusty
MP
983 posts
Nov 11, 2010
11:56 AM
@harpoon_man,

i like middle of the road output myself. poster mojokane has shown me mic elements that have so much output you can't turn up the amp, any amp, very much at all.

if they say high output crystal or ceramic the chances of overkill are greatly reduced. possibly because most crystals and especially ceramics don't have high output.

of course a mic VC would help but then you can't run the mic wide open.
----------
MP
hibachi cook for the yakuza
doctor of semiotics
superhero emeritus
5F6H
371 posts
Nov 11, 2010
12:16 PM
My take is that a good mic is a mic that works well in that particular application (like there are tubes and speakers that work better in some environments than others - if there's a "magic" mic/tube/speaker I haven't heard it). It's worth having a few because you never really know, without trying, how a mic will work with a particular amp. Kim Wilson, for one, has used mic subbing to find the best deal with pick up amps during a sound check. Whether they were his "go to" mics when playing his own amps is another matter.

Hi output mics can sound great, but sometimes you might get more flexibility from a moderate output mic, in a situation where the high output mic has little sweep before feedback, or has a very driven tone before you get to the headroom that you need. In a very high gain, stiff amp, a lower output mic can be good to give you a little more leeway in settings.

A wide variety of mics can be made to work with one amp, if you are in situation to do a bit of auditioning, but if you are plugging into someone else's gear (sit in/jam/pick up amp) your "killer" mic, with your rig, might not be the best thing in that particular situation, at that time.

Variety can be the spice of life in this case.
5F6H
372 posts
Nov 11, 2010
12:26 PM
@MP "if they say high output crystal or ceramic the chances of overkill are greatly reduced. possibly because most crystals and especially ceramics don't have high output."

There are a few crystals with a whopping output, Shure made one with a -33 or -36db output (in old money) whereas a regular output hi-Z mic might be between -55 & -52db. I have even come accross a few 151 with a huge output. Ceramics should always have less output compared to a similar design crystal, the ceramic element simply can't generate the same voltage as a properly functioning crystal. Ceramic mics were typically rated around the -60+ mark. Unless you are comparing to other ceramics, you are unlikely to find a "big output" ceramic.

Even between mics of the same design, there will always be a significant variation in output & tone. There's no substitute for actually trying them out.
Greg Heumann
877 posts
Nov 11, 2010
10:02 PM
High output mics CAN be great coupled with amps that aren't too gainy - but the combination of a gainy mic AND amp will be a feedback nightmare. My amps are generally feedback friendly, and the hotter elements sound great with them.
----------
/Greg

BlowsMeAway Productions
BlueState - my band
Bluestate on iTunes
hvyj
824 posts
Nov 12, 2010
2:31 AM
per Greg: "Assuming the mic is impedance matched into the amp, there are simply no tonal concessions made to low impedance mics. The Shure SM57 is becoming one of the most popular harp mics, thanks in no small part to Jason Ricci's use of one, succeeded by his choice of an Ultimate 57. It is indeed MORE focused, dynamic and even edgy than MOST hi-Z mics."

While I don't have Greg's expertise, what he is saying is certainly consistent with my experience. I don't pretend to be a great player or anything like that, but I do play out a lot.

True story: I was at a blues jam a couple of weeks ago. There was a harp player there with a Blues Jr. playing through a Green Bullet and a Lone Wolf Harp Octave. I had my Princeton Reverb Reissue set up right next to his amp and was playing through a lo-z Shure 545 Ultimate with an IMT. No pedals. No mods or tube swaps in my amp other than the stock tubes having been replaced with a set of JJs and a set of tilt back legs I put on the amp because i think the tone opens up when it's tilted back.

Anyway, before the end of the night, the other harp player was asking if he could play through my rig because he liked the sound/tone better. (So did I.) And this other harp player has a fetish for bullet mics.


Post a Message



(8192 Characters Left)


Modern Blues Harmonica supports

§The Jazz Foundation of America

and

§The Innocence Project

 

 

 

ADAM GUSSOW is an official endorser for HOHNER HARMONICAS