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Author Topic: Combiner quality  (Read 14327 times)

Jason Glass

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Re: Combiner quality
« Reply #30 on: April 18, 2018, 02:41:06 pm »

Again, I still don't understand how the 8ch devices are over $5k each and the 4-channel devices that are sub-$1k? The Sennheiser AC-3 and RF Venue Combine-4 are 6-8 times cheaper.
What are the "real-world" differences that justify the huge increase in cost?
If you're only using 4 channels, do they perform the same? If you use 2 of the 4-channel units for 8 channels with antennas spaced apart, does that work as well as a single 8ch?
The AC-3 can only handle 50mW input and the RF Venue handles 100mW. The PA821A, AC3200, and TX-8 can handle 250mW. Higher headroom, lower noise (IMD), and higher isolation are more expensive per channel because they require more components per channel and higher tolerance and performance spec'd components per channel. Then multiply by 2 to go from 4 to 8 channels and account for higher gain amps on each channel to overcome 3dB more splitter loss.

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frank kayser

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Re: Combiner quality
« Reply #31 on: April 18, 2018, 03:12:08 pm »

So, there has to be something other than a $5k solution


The Shure manual



https://522bb370f5443d4fe5b9-f62de27af599bb6703e11b472beadbcc.ssl.cf2.rackcdn.com/publication/upload/981/us_pro_antenna_setup_ea.pdf


on page 12, diagrams an 8 channel setup with 2 active splitters, then combined with passive splitters into a single set of antennae.


So, in theory, this setup would be less than half of the $5K 8-into-1 single active combiner.


Of course, something will be lost. Yes, 3dB loss in the passive splitters.   
Shure seems to think it is OK.


What problems does this configuration create?  What is missing?


frank







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Andrew Broughton

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Re: Combiner quality
« Reply #32 on: April 18, 2018, 04:42:35 pm »

Thank you, Jason.

The AC-3 can only handle 50mW input and the RF Venue handles 100mW. The PA821A, AC3200, and TX-8 can handle 250mW.
I can imagine there are situations where that matters, but if I'm using it for IEMs, I'm not going to be sending it more than 50mW. The TX-8 can amplify the output anyway, so why would you need to hit it with a higher signal?

Quote
Higher headroom, lower noise (IMD), and higher isolation are more expensive per channel because they require more components per channel and higher tolerance and performance spec'd components per channel. Then multiply by 2 to go from 4 to 8 channels and account for higher gain amps on each channel to overcome 3dB more splitter loss.

Is there a way to quantify these differences?
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-Andy

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Lyle Williams

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Re: Combiner quality
« Reply #33 on: April 18, 2018, 05:14:00 pm »

Solid state transmitters will retransmit received signals as intermodulation products at about 16dB down from the received signal.

So port isolation is critical to reducing intermod problems.  Doing the maths to work out the level of intermod products isn't hard.  Working out the impact in the real world on paper can be hard.

Better is better, but when is sufficient suffiicient?
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Ike Zimbel

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Re: Combiner quality
« Reply #34 on: April 18, 2018, 05:38:59 pm »



Better is better, but when is sufficient suffiicient?
When it works for your situation. On the gigs that I'm usually doing, the game is all about minimizing un-wanted artifacts (in this case intermod products, ie: unwanted occupied frequencies) because they will start to build up. Go with something that is "good enough" here and something that "oughta' do" there and before long you have created a hostile RF environment. Especially lately, when packing a lot of channels into less bandwidth has become the order of the day. Bottom line, if you have a handful of in-ears and they work for you every night with one of the less expensive combiners, go for it.
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Andrew Broughton

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Re: Combiner quality
« Reply #35 on: April 18, 2018, 05:51:02 pm »

Working out the impact in the real world on paper can be hard.

Better is better, but when is sufficient suffiicient?
When it works for your situation. On the gigs that I'm usually doing, the game is all about minimizing un-wanted artifacts (in this case intermod products, ie: unwanted occupied frequencies) because they will start to build up. Go with something that is "good enough" here and something that "oughta' do" there and before long you have created a hostile RF environment. Especially lately, when packing a lot of channels into less bandwidth has become the order of the day. Bottom line, if you have a handful of in-ears and they work for you every night with one of the less expensive combiners, go for it.

Still hoping to eventually get some quantitative information. I've no doubt that the more expensive devices are "better", but how much better exactly?
Will the more expensive product make a difference in my environment? How will I know before I buy? Where does one find non-anecdotal evidence and information that shows the real world benefit of the additional quality components?

This currently feels like the kind of discussions that happen on audiophile forums. "It's better because it's more expensive". "Ok. Prove it."
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Scott Holtzman

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Re: Combiner quality
« Reply #36 on: April 18, 2018, 08:20:48 pm »

Still hoping to eventually get some quantitative information. I've no doubt that the more expensive devices are "better", but how much better exactly?
Will the more expensive product make a difference in my environment? How will I know before I buy? Where does one find non-anecdotal evidence and information that shows the real world benefit of the additional quality components?

This currently feels like the kind of discussions that happen on audiophile forums. "It's better because it's more expensive". "Ok. Prove it."

If that 6db you need to maintain your BER is lost due to a IM product then the answer is far more than semantics.  You chip away at your S/N ratio with every signal that gets into the front end of the distribution amp and comes out the other end with amplified harmonics.

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Andrew Broughton

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Re: Combiner quality
« Reply #37 on: April 18, 2018, 10:35:32 pm »

If that 6db you need to maintain your BER is lost due to a IM product then the answer is far more than semantics.  You chip away at your S/N ratio with every signal that gets into the front end of the distribution amp and comes out the other end with amplified harmonics.
I get that, but are there actual numbers? I suspect nobody has done any head to heads between these devices in a controlled setting so itís very difficult to quantify the real world differences I expect.
Wish I had the time and RF chops to do it!


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-Andy

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Lyle Williams

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Re: Combiner quality
« Reply #38 on: April 19, 2018, 08:02:03 am »


The level of the intermod products depends on the port isolation and the number and power of input signals.

The frequency location of the intermod products depends on the choices you have made for transmitter frequencies, as well as the frequencies of other transmitters in the area.

The succeptablity of your receivers to interference depends on the quality and qualities of the receivers.

As just about everything can vary, results can vary.  If you have a situation where intermod is starting to be a problem, then a combiner with better port isolation will probably fix it.

It is easy to heckle and say it sounds like audiophile garbage.  Some reading on the basics of RF technology may help.

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Jason Glass

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Re: Combiner quality
« Reply #39 on: April 19, 2018, 03:30:37 pm »

I get that, but are there actual numbers? I suspect nobody has done any head to heads between these devices in a controlled setting so itís very difficult to quantify the real world differences I expect.
Wish I had the time and RF chops to do it!


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ProSoundWeb Community

Re: Combiner quality
¬ę Reply #39 on: April 19, 2018, 03:30:37 pm ¬Ľ


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