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Heat issue with SMV transmitters.


Todd Weaver

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An actress on a show I'm working on is a bit hot natured and wardrobe has her in skin tight dresses most of the time made of synthetic material. The usual location of the transmitter is her back. I'm padding the transmitter with foot foam to prevent burning of the skin, but the ambient heat is building up inside her wardrobe and causing her to sweat a lot. Has anyone found an elegant solution to this?

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An actress on a show I'm working on is a bit hot natured and wardrobe has her in skin tight dresses most of the time made of synthetic material. The usual location of the transmitter is her back. I'm padding the transmitter with foot foam to prevent burning of the skin, but the ambient heat is building up inside her wardrobe and causing her to sweat a lot. Has anyone found an elegant solution to this?

Hi Todd,

The SMv under any circumstances will not burn skin. I'll post a copy of FAQ #107 which you can read later when you are having a sleepless night.

 

We provide a hypoallergenic (non-allergenic) foam that you can place between the SM and the person. My guess is the tight fitting synthetic material is a much larger contributor to her sweating than the SM (0.75 Watt of heat). A resting human produces 75 Watts of heat equivalent and a lightly working person is 190 Watts. You and I both know telling someone this is not going to solve any problems.

 

If you can, get the outside of the SM as close to the outside world as possible so the heat is not trapped inside the wardrobe. The ideal is foam between her and the SMv and nothing between the SMv and the ambient air or at least as thin a material as possible. Air circulation around the SMv to spread the heat over a larger area inside the clothing facing the outside will help too.

 

Make sure the SMv is at 50 mW. Generally NiMh batteries generate a little less self heat than Lithium batteries.

 

I can send you some foam gratis with an address. It is good stuff but your shoe foam is probably doing the same thing.

 

I can tell you what needs to be done; maybe some others have got real world solutions.

Best Regards,

Larry Fisher

Lectrosonics

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Additional Keywords: faq, wireless, #107

Here is a RAMPS posting.

To the Group:

This post is in reply to an earlier post about "hot" SM transmitters. The SM puts out no more heat than a UM400; it just does it in a smaller volume. Since, despite the non stick finish, I'd never had any luck cooking omelets with an SM, I thought I'd run some crude tests.

I tested the temperature rise of an SMa transmitter, lying with its backside on a pad of paper with the temperature probe between the unit and the pad of paper. The air was fairly still with only the usual office air conditioning running. The pad blocked some air circulation to the backside and seemed to be equivalent to a unit on a belt. After 3 hours the temperature rise was 16 degrees, from 76 to 92 F. The battery was an Eveready lithium disposable, though the battery should make no difference. An SMQa (250 mW) under the same test rose 22 degrees from Seventy-four to Ninety-six degrees F.

I then firmly taped an SM transmitter to my leg with summer dress pants between the back of the unit and my leg. The probe was positioned between the pants material and the transmitter back. The unit was then covered in 6 layers of a Lectrosonics' jacket (polyester fleece) spread out over a 12 inch by 16 inch area around my leg. I think it is safe to assume that all the heat went into my leg. After the temperature stabilized with the transmitter off at 94 degrees F, I turned it on and at 45 minutes it was up to 104.5 degrees. At 66 minutes it was at 104.7 degrees and was effectively stable. The temperature rise (10 F) was smaller than the "belt" example (16 F) even though there was no heat loss to the air since heat was carried off by the circulatory system.

The 8 hr metal contact standard for Europe is 43 C or 109.4 F. and this correlates well with the fact that I never detected the smell of burning Larry. Another web tidbit was that oxygen gas sensors for neonatal units use a small metal plate warmed to 45 C (113 F) to increase the gas exchange rate from the skin of a baby to the detecting unit. These can be operated for up to 8 hours. 

The point here is that if the SM is not touching the skin, the heat rise exists but is moderate. If the surrounding air temperatures are very high or the unit is in the sun, the unit might be uncomfortable to touch but that is only if it is not in contact with a cooling device (human being) and if it isn't in contact then there isn't a problem. If it is in long term contact with a person, then the person will cool the unit so that there is only a small temperature increase. The skin on a healthy person is going to be less than 98 degrees to begin with or they've got much worse problems than the 0.75 Watt heat source of an SM.

In spite of all this, if the talent doesn't like the warmth, then a larger transmitter that spreads the heat out (UM400a) is one solution or a pouch or some thin foam between the transmitter and the talent.

As far as potential burns, the safe touch temperature for unpainted metal for 10 seconds is 132 F. Ten seconds is more than long enough to remove the offending object to a safe place. If they have a good arm, it can be removed 50 feet or so.

Best Regards,

Larry Fisher

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They shot many seasons of "Desperate Housweives" with ladies wearing tight dresses. They boomed it.

If you can't find a solution she's happy with, then she needs to be radio miked on rare occasions, and you need to chat with director and DP about solutions to record her dialog without putting a radio mic on. If she doesn't have the clout, then she needs to suck it up and do her job so you can do yours. Here's what you can do to help her.

Start with using rechargeable batteries and sleeping the SM whenever possible. Trim off the pouch part of a Neopak (or make your own neoprene pocket). It'll protect the pack from being irreparably damaged by sweat seepage, and works as a good barrier to keep heat off. If there's no air flow in the costume, it won't make much of a difference keeping it in the neoprene pocket.

The bra clasp can be a better spot if she has long hair. Less obvious too.

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They shot many seasons of "Desperate Housweives" with ladies wearing tight dresses. They boomed it.

When the SMV came out they ("Desperate Housewives" ) fought over the 2 available TX units as I was told by Lectro reps!

Aggie told us not to send any units until we could send all four. This was after the two beta units. Aggie preferred to boom but the SM's were used when booming wasn't possible and were out of the first production run.

 

Sharman's suggestion of putting the units in sleep mode is excellent. Just knowing the unit could be off a lot of the time might help the actress' attitude toward the units.

Best,

LEF

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They shot many seasons of "Desperate Housweives" with ladies wearing tight dresses. They boomed it.

When the SMV came out they ("Desperate Housewives" ) fought over the 2 available TX units as I was told by Lectro reps!

but why didn't they use Audio Ltd.s mini tx? It is still quite a bit smaller and slimmer than the smv. There are downsides zo the Audio range, but size isn't one
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My point being, radio mics were used as a very last resort on that show, and it sounded great.  Even when the SMs showed up, they were only put on when absolutely necessary.

 

In the case of the OP, it seems there's always on the actress, which has become common practice.  I'm just saying there is a solution other than making the existence of the pack less noticeable.  That's booming the actor.

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The SMs get hot.  Whether they are "too" hot is in the skin of the wearer, and neither my opinion nor that of the manufacturer means much at the point that there is a talent complaint about it--I have to fix it.  Have not had luck with moleskin or etc really, they do make the thing feel less hot but not enough less hot in the high-key set+tight dress situation.  We had to go with the thing outside where we wouldn't see their backs and not use them otherwise--the talent nixed any sort of thigh belt.  I have to say--they were VERY warm...

 

philp

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Constantin: " but why didn't they use Audio Ltd.s mini tx? "

because...

 

as for the solutions:

may I remind all that problem solving is a huge, a really huge part of our jobs.

I have, in the past, used the white packaging foam insulation that stuff sometimes comes in... with double stick tape,  I have also had wardrobe design and build pouches for the wardrobe...

but solutions vary, and it depends...

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Constantin: " but why didn't they use Audio Ltd.s mini tx? "

because...

And "because" is a brilliant explanation. One of my favourites. And my son's favourite, who is 2 years old.

Anyway, the miniTx would have been good, as it's very flat and with rounded edges so it's very inconspicuous. And it doesn't get hot. So on "Desparate Housewives" they aparently did wait, desparately, for the small Lectro TX, the Audio could have been a great solution.

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Thanks Larry and the guys for your input thus far. I have actually tried all of the above, using foam to keep it off the skin and placing it on the bra strap. Cotton pouches, noepax, 50mw, sleeping between setups. Unfortunately, we are still forced to wire due to stupid wide and tight situations, even though I have one of the best boom ops in the business, we are struggling with the situation. The main problem is not the transmitter burning the actress, it is the ambient heat building up inside the extremely tight and often synthetic wardrobe choices. The talent is not particularly receptive to us trying new mic placements or spending more than about 30 seconds with them in an attempt to make it better. None the less, we will prevail. Larry, maybe you guys should take a note from RED and add an extremely loud fan to future revisions. I'll look forward to that at NAB 2015.

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[snip]

Larry, maybe you guys should take a note from RED and add an extremely loud fan to future revisions. I'll look forward to that at NAB 2015.

Rats. You've just blown the 1 April 2015 product announcement.

Best,

Larry F

Lectro

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Also, are the AL minitx compatible with the lectro VRTs?

Venue wideband receiver frames (VRMWB, VRMWBL, VRMWBH) with firmware version 5.5 include compatibility mode 7 which works with AL transmitters in their 2020 & 2040 series. If you need to update your firmware for this functionality, you can download it here: http://www.lectrosonics.com/category/44-firmware?download=353

 

The update can be done with your VRPanel utility.

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Todd,

Your problem is no longer a sound problem but a production problem. If the actress is uncomfortable with a radio mic, and performance or "attitude" is affected, then get involved with director/producer about not shooting her wide and tight. I've done this before with actors who were reluctant to be radio miked. These were lead actors, of course, which I'm assuming yours is too.

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Venue wideband receiver frames (VRMWB, VRMWBL, VRMWBH) with firmware version 5.5 include compatibility mode 7 which works with AL transmitters in their 2020 & 2040 series. If you need to update your firmware for this functionality, you can download it here: http://www.lectrosonics.com/category/44-firmware?download=353

The update can be done with your VRPanel utility.

That is really useful information. Thanks. :)

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