'Optimus' PZM/boundary any good ?

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51 years 4 months
Submitted by Anonymous on Mon, 02/09/2004 - 01:37

Sorry for this budget-question, but how useful is the boundary ('PZM') mic that Radio Shack has for US$39.99 ?
It's the Optimus #33-3022.

Since someone here will be visiting the US soon I was thinking about asking him to get me a pair.

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=&product%5Fid=33%2D3022

Applications will mostly be for loud sources, like room for drums or guitars.
(Will add the 'usual' PZM-mods)

Any good ? At least usable ? Or just a cheap mic with a bad capsule ?

Thanks,

Peter

Peter, I own one (haven't used it in quite a while to be honest). I think I remember some one telling me the capsule is made by Crown, but it's nowhere near their PZM. This one is unbalanced and has a battery compartment in the mic cable attached for two size AA batteries. If it could be modded to use with regular phantom power it would be more useable. I used to use it with a Portastudio for doing guitar/vocal rough sketches, fine for that. Actually, I'm doing some guitar tracks today and will plug it into my board for research and let you know what happens.

Sounds like you're already aware of this, but just in case...

Jensen transformers has this app note for connecting phantom to the PZM in conjunction with one of their transformers.

http://www.jensentransformers.com/as/as070.pdf

Never tried it so I can't comment on its effectiveness, but coming from Jensen, it should be cool. Of course you'll probably spend more on the transformer than you do on the mic, but that's another story...

Thanks all for the responses, I'll sure ask the person to get me two of these mics.

Last question: they're reasonably sturdy, right ? Saw the total weight (including cable) is 10.93 oz. (310 g) so I assume the mic body itself is from metal, not plastic.

from riversedge:

Actually, I'm doing some guitar tracks today and will plug it into my board for research and let you know what happens.

Thanks ! Will that be electric ? Other PZM's I tried turned out to be somewhat noisy; if your recording happens to be of an acoustic instead of elec. I guess an eventual noisy side would show up.

from RecorderMan:

it's a good deal

Trusted source ! ;) Thanks.

from Old House Scott:

Jensen transformers has this app note for connecting phantom to the PZM in conjunction with one of their transformers.

http://www.jensentransformers.com/as/as070.pdf

Never tried it so I can't comment on its effectiveness, but coming from Jensen, it should be cool.

Thanks. I'll definitely mod them to balanced and preferrably phantom as well. 1/8 Inch (3.5 mm) plugs :td: and XLR-3 :tu:

Of course you'll probably spend more on the transformer than you do on the mic, but that's another story...

I'll probably go for an active circuit, so that'll keep cost comparable to the mics themselves.

Bye & thanks again,

Peter

Peter, Just finished the session, electric through a vintage Fender Deluxe amp. I close mic'd with an ATM29HE ($200 vocal dynamic, much like SM57 tonally) and the PZM on wall about 2 ft away. The PZM won hands down. I connected it with a passive DI box, had the mic pre at about 75%. It sounded exactly like his rig. I may buy another! I doubt it would have eough gain for acoustic unless I cascaded through two channels on an outboard pre, and then noise would probably be an issue. The body is metal. Happy shopping.

The secret to the pressure zone microphones is how they are mounted. The sound bounces off of the surface around the mic into the mic(the capsule recieves no direct sound). You can get different sounds by changing how and on what it is mounted to. Mount one on a 4x4 plexiglass sheet and suspend it from the ceiling for room miking. I have heard of it being used for drums. Mount it to the inside of the lid of a Piano. If the area it is mounted too is too small the low end response drops off. You probably already knew most of this but thought I would mention it anyay because it is such a different type of mic and fun to experiment with.

Thanks all again, this really exceeds the expectations I had - expecting something like "no the present-day Optimus model is no longer the real deal".

Good to hear it's made of metal, would not live long otherwise I'm afraid. :( Our guitar player has a pair of another brand, for recording band rehearsals we usually put coloured paper between the wooden floor and his PZMs to avoid stepping on them.

Riversedge, your Optimus-mic is still unmodified ?

Kent, about mounting them on large surfaces, yes I knew but good to hear they can be used up in the air as well. The 4x4 plexiglass you suggested, that's four by four foot ? (the Netherlands here)

About experimenting, sounds like it'll be usable both for closer micing (say on the floor a few feet from a drumkit or guitar-amp) - or for more room-sound as well when moved further away.

I've those various Crown-pdf-articles around; now that actually a few of such (related) mics are upcoming I'll get those files out again.

Bye & thanks again for the good info I got on these mics,

Peter

Peter, Mic is unmodified. I'm sure I got some noise rejection from going through the direct box to a balanced line. The gain required was a little more than a decent dynamic, but not much. Try close mic on guitar amp from the wall, I think you'll get better balance of tones than from the floor. They're often used on a large table to record business conferences as well.

from Riversedge:

Peter, Mic is unmodified. I'm sure I got some noise rejection from going through the direct box to a balanced line. The gain required was a little more than a decent dynamic, but not much.

That's good news, already good results from the unmodified unit.

Try close mic on guitar amp from the wall, I think you'll get better balance of tones than from the floor. They're often used on a large table to record business conferences as well.

So that's the amp facing the wall ? Hmm, would
quite suit the setup I sometimes use at rehearsals for making guitar a bit less spikey in the room: Twin Reverb tilted back on its legs upward - facing a wall.

from Kent:

Sorry I didn't notice where you were. Yes 4 feet x 4 feet you can play with the size but that size will give you a good sound field. Try different surfaces for sound shaping.

No problem ! I'll try wood first, but have seen PZMs used as drumoverheads (actually more 'sideheads') mounted on plexiglass.
I'll experiment.

Thanks,

Peter

Thanks Riversedge, I thought the Jensen schematic used something like 110k resistors (so 55k 'effective'), so the full 48 V won't reach the capsule - but you've got a point there - depending on the currentdraw of the capsule a proper resistor value should be chosen. Or another circuit topology wuth for instance a zener etc.

Those capsules can have more than 1.5 V but I don't know what the actual limit would be. It's indeed good to be careful here.

Bye,

Peter

Peter,

Seems that you have this worked out but FYI there is also a step by step set of instructions for modding the PZM on this page.

http://www.itrstudio.com/pzm.txt

The Radio Shack PZM is actually just an omni electret capsule mounted close to the metal plate on the inside. I am pretty sure that you can build your own using those cheap panasonic omni capsules. Not that the RS mics are going to break the bank! But it may be worth playing around with down the road... those panasonic capsules are only a few bucks and i doubt the capsules in the RS mic are any better... it is something i've been meaning to try... as soon as all my other responsibilities magically fall away and i have oodles of free time.

cheers,
greg

hallo peter,

i got two older 'tandy/radio shack' pzm's (always nice to record in stereo). i use 9 Volt batteries (taped to the side) with good results. it gives you more bass (and less noise, i think), wich you'll need!
i use 'm to record rehearsels and gigs and they are amazing for it.
it took me some time to get used to the fact that they are not directional. ideal for 'room'-recording.
i even saw them taped inside a piano in a theater in Naaldwijk (nl!).
i love 'm.

grote groeten,
will

Thanks again all,

from Greg:

Seems that you have this worked out but FYI there is also a step by step set of instructions for modding the PZM on this page.
...
The Radio Shack PZM is actually just an omni electret capsule mounted close to the metal plate on the inside. I am pretty sure that you can build your own using those cheap panasonic omni capsules. Not that the RS mics are going to break the bank! But it may be worth playing around with down the road... those panasonic capsules are only a few bucks and i doubt the capsules in the RS mic are any better...

Thanks for the additional info. Yes, stumbling on those PZM-mods was what drew my attention and now a few years later the opportunity comes along to mod a pair (if all goes well, depending on 'my US-contact' :-)

I've seen alike suggestions that omni-mics can be placed near a wall (a few mm) for the 'PZM-effect' but ready-made is indeed nice for convenience and that one doesn't have to take care that the small distance is not disturbed by mic-stand movement etc

it is something i've been meaning to try... as soon as all my other responsibilities magically fall away and i have oodles of free time.

Sounds like we're living in the same imperfect world ;)

from Will somewhere else in the Netherlands:

i got two older 'tandy/radio shack' pzm's (always nice to record in stereo). i use 9 Volt batteries (taped to the side) with good results. it gives you more bass (and less noise, i think), wich you'll need!

Having tried someone else's PZM-like mics (forgot which brand) this sounds familiar - got the impression they can be somewhat noisy for some applications.

Thanks again all & bye,
(bedankt & grote groeten as well !)

Peter

Radio Shack no longer carries PZM mics. Crown pulled the license from them. Crown NEVER made the Radioshack PZMs, they were outsourced by Radioshack. They were garbage, and still are, thats why Crown yanked the licensing.
The boundary mics "by Radioshack" are now cheap electrets mounted close toa boundary, not even close to the PZM concept.

Do yourself a favor, amd locate a real Crown PZM, or better yet find one made by Ken Wahrenbrock, prior to selling his license to Crown.

Radio Shack no longer carries PZM mics. Crown pulled the license from them. Crown NEVER made the Radioshack PZMs, they were outsourced by Radioshack. They were garbage, and still are, thats why Crown yanked the licensing.

Do yourself a favor, amd locate a real Crown PZM, or better yet find one made by Ken Wahrenbrock, prior to selling his license to Crown.

Thanks for the info - hmm, quite something else. Since the pair I asked someone to buy will have been bought by now, I'll just fiddle around with them and see what they can do for me.
Indded is there quite a difference in price between 'serious manufacturers' of PZM-like types and the RShack-models but I guess this is partly a name thing - and of course also partly better materials, design and quality control.

The boundary mics "by Radioshack" are now cheap electrets mounted close toa boundary, not even close to the PZM concept.

This _is_ the PZM-concept, not ?

Thanks,

Peter

The Crown is a fabulous mic, but after Peter's inquiry (my RShack PZM is about 15 yrs old) I decided it was worth plugging in, now that I have decent gear. I'll be using the track in the mix with no EQ, not bad for $40. I'm willing to get a new one just to see what the diference is. You never can tell what result you're going to get until you try. A friend came over with his upright bass a few months ago, and the best sounding mic to capture the "growl" was a $50 Audio Technica semi-pro vocal dynamic. Go figure.

The boundary mics "by Radioshack" are now cheap electrets mounted close to a boundary, not even close to the PZM concept.

This _is_ the PZM-concept, not ?

Yes, that IS the PZM concept as i understand it...

I understood that the difference between the Radio Shack mics and the Crown mics was not the actual acoustic principle but the quality of componentry,design and manufacture...

greg