Shure's PSM900 vs the Best IEM System in the World

Langston Holland

Sophomore
Jan 13, 2011
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Pensacola
I just made a post on the wireless stuff we use where the batteries go in part that talks. This is a look into the wireless stuff where the batteries go in the part that listens. The former is posted to the new PSW forum in deference to the amazing kindness Craig showed me after I kept the Line 6 road test system for several months too long.

So, since I had the test rig fresh in mind, I went ahead and measured the two IEM systems I own; Shure's PSM900 and the wired PSM600. Funny how easy and inexpensive it is to achieve the best possible sound by using a bit of copper, but instead we have to supply wireless to the majority of folks that never move more than the radius of half a mic cable during their whole performance. I really enjoy the rental revenue though and it does seem popular spending money to make something worse. In more news that you can use, have you ever read the box that Shure's IEM systems come in? It says "Personal Monitor System". So why then do all the model designations start with "PSM"? Oh, never mind...

Conclusion:

The PSM900 is an absolute joy to use. Its feature set is excellent when used in smaller herds, iPod simple, dead quiet and very well built. Battery life is great. Price is rational. Everyone seems to be very happy with the sound - likely due in a large part to how quiet it is.

I do have a small beef with this system though - its use of companding results in up to 4dB of compression with a threshold of approx. -30dBu and smoothly increasing until its input clips around +18dBu. I was hoping that the system would be like the UHF-R with its complete absence of compression. I know of one young (still has hearing), good (and picky) musician that never complained when I supplied Sennheiser G3's to him. He did notice some "dullness" in the PSM900 and asked me if I'd committed the unpardonable sin and used compression on his ear mix. I didn't of course, but this did make me scratch my head a bit.

The following measurements reveal the compression which is likely the issue. I'm sure the G3's use companding as well and my theory at present as to why it's not as noticeable is related to how quiet the PSM900 is. The quieter something is, the better you can hear stuff. You heard that here first folks.

Oh yeah, the wired PSM600. Did I mention it's wired? Perfect sound. Perfect feature set. Makes an iPod look hard. Inexpensive. Laughs at being used on a crash dummy.

Shure PSM900 Wireless:

In most cases, when measuring at various input levels, I started with -50dBu and increased levels in 10dB steps through 0dBu (.775v) if the unit could handle that much level before clipping. If the unit could handle more than 0dBu, I added one more trace at the higher level.

You'll notice that the output is progressively lowered by a maximum of 4dB without changing bandwidth (tone). The lower traces are the higher input levels with increasing compression.

ShurePSM900(PinkNoise).png


Now you'll note the tell-tale sign of classic wireless companding - which is a variable sensitivity to a sine stimulus based on frequency. Since the system is reasonably expecting a fairly broadband signal, if you use a slow sine sweep (or worse, one frequency at a time via a stepped sine measurement), you'll find that the passband will exhibit varying amounts of compression. The application here would be that monitoring the impulsive LF energy of a drum kit or bass would be somewhat suppressed relative to vocals, guitars and keys. Sounds like a good engineering compromise to me… Finally, distortion measurements are only practical on systems that can tolerate swept (or even better - stepped) sine stimuli and the PSM900 is borderline here IMO.

Swept sine stimulus. Notice how -50dBu and -40dBu measure the same as pink noise. Higher input levels confuse the companding - but in a musically useful way.

ShurePSM900(SweptSine).png


Pink noise stimulus. Notice that even at the "flat" setting we have a HF boost of +1.5dB. Turns out I'm not the only one that's used a bit of HF boost to mitigate the effects of single band compression. The "+2dB" setting adds another 2.5dB and the "+4dB" setting might not sound as bright as the "+2dB" setting in some cases.

ShurePSM900(HFBoostPN).png


Shure PSM600 Wired:

The world standard. What you put in is what you get out regardless of level. Gentle roll offs which dictate gentle phase curves.

ShurePSM600HardWired(SweptSine).png


The CLIO measurement system has a very accurate, very short term gated stepped measurement feature - only 6.5ms down to 300Hz or so where the wavelengths get long enough that you have to open the "meter on time" enough to get at least a couple of sine periods in to make a reliable distortion measurement. These very short term sine bursts allow peak measurements of loudspeakers and amps without melting things. In the case of wireless measurements, it'll reveal which systems can pretend to be hardwired and which cannot - the wired PSM600 has no need to pretend. Vanishing distortion at maximum input, pad not engaged.

ShurePSM600HardWired(GatedSine).png


The HF boost is simplistic and effective. You'll not be sending the muso's ears 40kHz, so the engineering compromise here is harmless.

ShurePSM600HardWiredHFBoost(SweptSine).png


Engaging the pad pushes the input voltage down 14dB and adds this same amount to the non-padded 3dBu clipping threshold.

ShurePSM600HardWiredPad(SweptSine).png


The effect of the limiter relative to input level. These types of limiters are simple on/off affairs that are a shot in the dark as far as protecting your hearing. The result depends on the sensitivity of your earphones relative to the voltage the limiter allows as to how much pressure your tympanic membrane is exposed to. Something simple like the adjustable limiter on the PSM900 makes sense, assuming the musician has some and uses it. Am I the only one that's never met a musician that makes use of IEM limiters?

ShurePSM600HardWiredLimiter(SweptSine).png


A mic cable! A mic cable! My kingdom for a mic cable! (Richard III, soundman for William Shakespeare)
 
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Re: Shure's PSM900 vs the Best IEM System in the World

Thank you. This was a very interesting read. I think the bandwagon effect of musicians moving to in ear monitoring has created a number of bad stage habits due to misunderstanding what is really needed to perform and how monitors are mixed.

One musiciam I know managed to blow the drivers on three sets of ear buds in just under 2 years, even with the limiters in place.