Speaker Wattage Rating

[garyrc]

All seven channels are active and driven by the main receiver of 80 Watt RMS into 8 Ohms per channel.

Even if you ran the surround and surround back speakers directly, via speaker cable, would your main receiver really deliver 80 watts RMS into each of all seven speakers when all channels are operating? Many Home Theater receivers have fudged figures in this regard. The power is often measured with just two or three channels operating, and is often less when all 7 channels are going. Some magazine reviews are now pointing this out. It is sometimes assumed that as long as the SPL contributed by all speaker/amp channels add up to the desired SPL overall, that will be sufficient. That may be true with 99.99% of music disks, but these movie people can't be trusted! An explosively loud sound may be sent to the surrounds (see below).

I have Klipschorns for Front Left and Right, a Belle Klipsch from the center, and Heresy IIs for surround. I use 5 of the 6 channels provided by three two channel free standing power amps, rated at 150 watts/channel (really 120 wts RMS) for most channels, and 135 watts for channel # 5 (really about 110 watts RMS). The Klipsch RSW 15 sub has its own amp, naturally. While most of the music & movies I run do not use the available power, I still occasionally hear a bit of strain with sources like the SACD Mega Movies, with the vehicle crash from The Phantom Menace.

PWK used to say that you need brief peaks of 115 dB at your ears to simulate a symphony orchestra. He thought this could be done with good quality 20 watts RMS/channel feeding each speaker in a three channel "wide stage stereo" system using Khorns and a Belle or La Scala -- with the maximum SPL adding up to 115 dB for very brief time periods.. With today's program material, especiallly movies, I would opt for each speaker being able to produce brief peaks of 115 dB. While, according to Dope from Hope Vol. 16, No. 1 (January 1977), in a 3,000 cu ft. room, a single Klipschorn would only need about 2 watts to produce the 100 dB or so that conductors hear during the average part of a loud passage (Heresies might need 14 watts), that same passage may have the 115 dB brief peaks PWK was talking about. For those split seconds, a single Khorn would need about 63 watts, but a Heresy II might need almost 500 watts -- for that instant, only. I'm not completely sure that 21 wattts per Heresy will be enough --- although, I'm told, really good amps will pass 10 times their RMS power without clipping for the briefest (musical) time periods, that would be "only" 210 watts. Once again, those movie people ...

[Quiet_Hollow]

Here's a way to get an idea of how hard everything is working during movie playback:

Unplug the speakers, drop in a test disc, set the amp to -0 dB REF, play a 5.1 signal at -1 or -0 dBFS.

Measure the voltage across each set of terminals. That will be as loud as the channels can possibly get.

Then drop in a problem source, like a movie or SACD that has been know to give your system issues. Play the source and measure again.

The numbers will be lower, especially in the surround channels.

Finally, don't mistake a clipped source signal for a distressed speaker or amp. A clipped source signal will sound like junk regardless of the volume setting. It'll sound crunchy or bloated even at whisper levels.

[neo33]

My main concern here is damage to the surround speakers (drivers especially the tweeters) due to under wattages delivered by the wireless receivers during extended listening sessions.

Each of the two wireless receiver delivers a maximum of 21 Watts RMS into 8 Ohms per channel to a total of two channels. There is no clipping protection circuitry.

[Quiet_Hollow]

...due to under wattages....

You're concerned with something that doesn't even exist in an electrical circuit, or by technical definition. [^o)]

I highly encourage you to use a multimeter and stop fussing over "watts".

You're wireless receivers will not blow your Heresy speakers. They will be just fine....even at war volume. [8]

[neo33]

Someone told me that overamplfication and underamplification either way are bad for speakers. I just want to make sure in my case it is not.

[bobdog]

...due to under wattages....

You're concerned with something that doesn't even exist in an electrical circuit, or by technical definition.

I highly encourage you to use a multimeter and stop fussing over "watts".

You're wireless receivers will not blow your Heresy speakers. They will be just fine....even at war volume.

Too little power does ruin drivers when the amp clips. Usually the tweeters. An amp that clips at 20 watts will damage a Heresy if pushed beyond clipping.

[derrickdj1]

More headroom offers piece of mind.

[Quiet_Hollow]

Too little power does ruin drivers when the amp clips. Usually the tweeters. An amp that clips at 20 watts will damage a Heresy if pushed beyond clipping.

So don't drive it into clipping. It'll sound like junk well in advance of causing any trouble, if that's the case. Taking into account the OP's scenario, that's very unlikely.

More headroom offers piece of mind.

So does a good multimeter, knowing where to use it, and understanding how the system works as a whole.

An expensive meter is still cheaper than an over-sized power amp. []

[Chris A]

Someone told me that overamplfication and underamplification either way are bad for speakers. I just want to make sure in my case it is not.

So have you determined your answer?

Chris

[neo33]

Based on Quiet_Hollow reasoning, it is safe to say that I am okay. Another word is that, my current set up will not cause damage to my surround speakers in the long run.

[derrickdj1]

An expensive meter is still cheaper than an over-sized power amp.

I hear ya![:#]

[neo33]

I did some measurements on my main receiver to see what kind of numbers I would get.

At full power outputs of 80 Watts RMS / channel with all 7 channels active at reference level, 90dB is registered on my sound meter from the listening position (10 feet from the screen) during highly active seen with no explosion. I don't normally listen at reference level so I set at my usual listening level to -20dB and saw 75dB registered with the same scene. What do you think of these numbers?

[neo33]

I've been re reading the entire thread and thought about the original question over again and have a feeling that it has not been answered. So let me reprhrase the question in a different way. I need to ask the following questions first:

1) What is the ratio between the surrounds output levels and main output levels?

2) Why is wireless receiver outputs are so low compare to main receiver outputs?

My main receiver can support 7 channels at 80 Watt/Channel with circuitry to prevent clipping. My wireless receiver can support 2 channels at 21 Watt/Channel with no circuitry to prevent clipping. The output of 1 channel on the wireless receiver is about 1/4 of the output of 1 channel of the main receiver. To connect the surround channels for wireless operation, you connect the left and right surround channels outputs of the main receiver to the left and right channels inputs of the wireless transmitter. Then you connect the left and right channels outputs of the wireless receiver to the left and right speakers.

Now, during highly active scene full power is fed to the surround channels from the main receiver to the wireless transmitter. But only 1/4 power is going into the speakers from the receiver channels. So, if the transmitter channels peaked, would the receiver channel clipped? And if so, would this clipping cause damage to the speakers (most likely to the tweeters) since there is no clipping protection circuitry in the wireless receiver?

And this is what I mean when I said receiver underamplification.

However, can this even be possible? I don't know how wireless audio trasmitter/receiver work. But I assume that the wireless trasmitter can transmit a voltage higher than the wireless receiver can handle.

[garyrc]

I did some measurements on my main receiver to see what kind of numbers I would get.

At full power outputs of 80 Watts RMS / channel with all 7 channels active at reference level, 90dB is registered on my sound meter from the listening position (10 feet from the screen) during highly active seen with no explosion. I don't normally listen at reference level so I set at my usual listening level to -20dB and saw 75dB registered with the same scene. What do you think of these numbers?

Gee, I've seen the needle on my Radio Shack meter (C weighting , "fast") hit 100 dB fairly often in loud passages (e.g., "Fanfare for the Common Man" on Crystal Clear direct to disk), and 110 dB once in a while. Analog meters using a needle (due to needle balistics) can lag 13 dB behind the instantaneous peaks measured by digital read-out peak reading meters, so the 100 dB reading could be 113 for a sliver of time, and the 110 dB reading could be 123 for a split second. I've seen similar readings (110 dB with a needle meter) when measuring orchestra rehersals (from about the 5th or 6th row) at SFSU. Even a single visiting violinist in our living room hit 86 dB .. I was surprised.

As to reference level, it depends on what you mean. With normal speakers, Audyssey says each seperate speaker must be adjusted (e.g., automatically by Audyssey MultiEQ) so that - 30 db band-limited (500 Hz - 2000 Hz) pink noise produces 75 dB -- coming from only that single speaker, I think -- at the main listening position. Then, when the volume control is set at 0, modern movies (but not music CDs, for which there is not a level standard, bless the commanders in the Loudness Wars) will be at refernece level, i'e, will be at the level at which the mixers heard it in the control room. That level can have ff levels above 100 dB, easily. The old THX set up book for actual movie theates reported SPLs up to 110 dB in the bass, and 108 dB in the midrange, for The Empire Strikes Back. I'm fairly confident that modern movie sound touches 115 dB every so often. Some old movies can churn it out, too, e.g., the sound of the galley ship splintering, or the thunder/earth tremor near the end of Ben Hur (1959). In the 70mm/6 track Coronet theater in San Francisco, the latter sequence shook the concrete floor, and created a breeze in the theater. Didn't we hear that BH blew out the speakers in Ted Turner's screening room?

Your last post came in while I was writing this. In answer to #1,although, in my experience, surround channels usually are not as loud as the mains, but they can be as loud, or even louder, from time to time in a movie. There is no fixed ratio, except in set-up they need to be adjusted to the same SPL as every other speaker you are using -- if you want to get what the filmmakers intended. Someone else mentioned peace of mind ... I would turn down your surrounds temporarily, untill you can afford more powerful amps for the surrounds. Does the manufacturer of the wireless receivers make ones with more powerful amps, say, 80 watts? That would give you about 6 dB more headroom. Do I remember that you are going to replase the Heresies with Cornwalls? That would get you a few more dB.

[Quiet_Hollow]

90 dB SPL @ -0 dB REF and 75 dB SPL @ -20 dB REF sounds a little warm, but in the ball park.

The numbers point to the system scale off from reference just a bit , 5 dB to high side.

[derrickdj1]

Reference level sound 85db with peak to 105 db from speakers

Subwoofer peak should reach 115 db max film industry standard

-30 db on avr should be 75 db

[Quiet_Hollow]

My bad. [:$] 90 is about just right.

[Quiet_Hollow]

It's great to hear you've got an SPL meter at your disposal. [Y][H]

Got access to a multimeter too? Maybe even one you could borrow?

Also,
knowing what you've got for equipment, in particular the AVR and the
model of wireless surround amp, would help everyone here get on the same
page.

1) What is the ratio between the surrounds output levels and main output levels?

SPL levels are set the same when using test tones. However, the power they actually use is dependent on how they're high-passed, and most importantly, how the source is mixed.

2) Why is wireless receiver outputs are so low compare to main receiver outputs?

With all the speakers highpassed, they're using a fraction of the power they would if being run full-range. Surround speakers are almost always high-passed, so the amps are sized accordingly.

So, if the transmitter channels peaked, would the receiver channel clipped? And if so, would this clipping cause damage to the speakers (most likely to the tweeters) since there is no clipping protection circuitry in the wireless receiver?

This scenario requires a setup technique called "gain staging" that requires the use of the receiver's test tones (if it has that feature) and a multimeter.

[neo33]

To answer some of the questions:

1) I have a Radio Shack digital sound meter.

2) I have a Fluke digital multimeter.

3) My main receiver is a Pioneer model VSX-1020-K. (7 Channels with 80 Watts / Channel @ 8 Ohms.)

4) My surround wireless audio transmitter/receiver is a Rocketfish model RF-RBKIT. (2 Channels with 21 Watts / Channel @ 8 Ohms.)

A 2 to 4 Channels with 50 Watt / Channel @ 8 Ohm surround wireless audio transmitter/receiver is virtually non-existent. It is impossible to find a surround wireless audio transmitter/receiver that match the per channel output of your main receiver. Hence, my question about the ratio between surround and main outputs. And my question about why surround wireless transmitter/receiver is so underpower.

[garyrc]

A 2 to 4 Channels with 50 Watt / Channel @ 8 Ohm surround wireless audio transmitter/receiver is virtually non-existent. It is impossible to find a surround wireless audio transmitter/receiver that match the per channel output of your main receiver.

I wish I could find my theatrical THX packet. Maybe later. If they say that midrange peaks can get as loud as 108 dB, wouldn't that be about 90 watts (or about 27 volts ???) into a high passed Heresy from listener position in a 3,000 cu ft room, for just an instant? The high pass frequency most recommended for HT is probably 80 Hz. For music, the SPL distribution generally has the highest SPL at from about 100 to 500 Hz (surprising, but I've seen this several places, first in the old Martin Mayer book), and the 115 dB peaks PWK was refering to were in music. The Heresies claim to be able to take more than the aforementioned 90 watts, especially on peaks, but I don't know if your 21 watt transmitter/receivers can put out 90 watts without clipping during those brief peaks. Do multimeters vary in their ability to measure brief voltage peaks, the way SPL meters vary in their ability to measure SPL peaks? I honestly don't know.