## Wednesday, August 29, 2007

### How Much Power Do I Need?

Have you ever wondered how much power you will need from your amplifier to drive your loudspeakers?

Amplifier power is usually given in watts, which is the amount of energy expended in one second (1 joule per second). In electrical terms 1 watt is equal to 1 volt multiplied times 1 ampere. Not sure if that helps here, because this doesn't seem to directly relate to how much sound you can generate with an amplifier. We usually measure the loudness of something using decibels or dB. The dB uses the logarithmic (base 10) scale because that is how our ear/brain perceives sound changes. Theoretically, the smallest change in sound level the human ear can perceive is 1 dB.

The following chart shows the amount of dB per watts ((dBW), which will make it a little easier to relate the amplifier's power rating to the amount of sound it can provide:
 dBW Watts dBW Watts 17 50 24 251 18 63 25 316 19 79 26 400 20 100 27 500 21 126 28 630 22 156 29 795 23 200 30 1000

As you can see from this chart, an increase of 3 dB results in a doubling of power. So to handle an increase in dB from 23 to 26dB, you will need to double the power from 200 to 400 watts. To be able to notice the next incremental increase in loudness, you would need to go up to 500 watts.

Another factor that we need to consider is -- How loud do you need to go? That depends on your listening preferences. If you normally listen at fairly quiet levels, you don't need a lot of power, but if you like listening to rock music at live concert levels, then you may need a lot. Here's another chart (I love charts) to show how the dB relates to different sound levels:

 Decibel (dB) level Cause or Effect -80 (p) Underwater nuclear submarine microphones listening to shrimp chewing on food at 100 meters distance -30 (n) One human talking 20 miles away (60 db / meter at a distance of 20 miles) -4 to +4 (n) The ticking of an ordinary wristwatch at 1 meter 0 (n) Beginning of hearing, a mosquito 10 feet away, the ear drum moves less than 1/100 the length of an air molecule 10 (p) Absolute silence, AT&T - Bell Labs "Quiet Room" 13 (p) Ordinary light bulb hum 15 (n) A pin drop from a height of 1 centimeter at a distance of 1 meter 30 (p) Totally quiet nighttime in desert - impossible anywhere near city 35 (p) Anechoic hearing test room 40 A whisper 50-65 A normal conversation 80 Average city traffic noise 85 Beginning of hearing damage (8 hrs), earplugs should be worn 85-90 Lawnmower, food blender 100 Normal average car or house stereo at maximum volume 104-107 (p) The beginning of pain at the most sensitive frequency of 2750 hertz 110 Symphony orchestra 116 Human body begins to perceive vibration in the low frequencies 117-123 Home stereo system, a very loud and powerful 200-2000 watts 120-130 front row at a rock concert - up to 200 refrigerator size speakers and 50000-300000 watts of clean, full frequency sound 125 Drum set - only at the moment of striking, continous level 115 127 Human tinnitus (ringing in the ears) begins 128 (p) Human, loudest scream measured at a distance of 8 feet 2 inches, head hair begins to detect vibration, can begin to detect very slow “blast wind” of 0.124 meters/second 130 (n) Marching band - overall level at a distance, 100-200 members 132 Eardrum “flex” totally noticeable 133 (n) Gunshot- ear level, may vary greatly to size and type of gun, duration converted to one second, peak level may reach 140-160 130-135 (n) Large train horn 135 Human, a slight cooling effect begins to be noticed, from air expansion 137 Human body vibration is strong 137-140 Human ear all frequencies are painful 140 Extremely damaging to hearing no matter how short the time exposure, human throat and vocal cord vibration begins 141 Human body begins to feel nausea after a few minutes 142 Human body chest pounding is intense 143 Human body feels as if someone just football tackled your chest 144 Human nose itches 145 Human vision begins to vibrate making it slightly blurry, 1-3 degrees 148 Human vibration very uncomfortable and slightly painful 149 Human lungs and breathing begins vibrating to the sound 150 (n) Rock concert “The Who” two 10 story stacks = 144 double refrigerator sized speakers, actual level reached 120 db at a distance of 32 meters for this normalized reading of 150 db. Continuous level 114-118db (p) at 32 meters 158 Human body vibration is violent, nausea becomes more intense 153-163 N.H.R.A. Dragsters- 5000 to 7000 horsepower, liquid nitroglycerin fuel, earthshaking at 50 feet, humans find it hard to see, and breathe 140db (p) 163 (p) Glass breaking level, minimum, it is very hard to break glass windows. Many stories come from breaking glass but it is highly variable: it is easier to break if the window already has a crack, is very large or old and brittle and not car safety glass which can flex massively before breaking. An opera singer at 110 db may break a wineglass but it is an example of frequency resonance, and not high sound db level 145-165 (np) Common type of fireworks at professional pyrotechnic shows 172 (n) Boeing 727, 737, 747, 757, 767 cruising at 6 miles high mach 0.84, at the ground (sea level) loses an additional 6 db because air density is only half sea level at a height of 6 miles 180.5 Alan Dante reportedly set a new record in the world of in-car bass output by using four Stetsom 7KD amplifiers, 15 Power Master batteries, and a single Digital Designs 9918Z subwoofer. 183 (p) 6 p.s.i. Total destruction of all structures, particle velocity (blast wind) is 180 miles per hour. 0.9 miles from Hiroshima atomic bomb and 3.3 miles from 1 megaton nuclear bomb, less 0.1 % object survival 190.6 (np) Richter scale 0 (zero) earthquake 190-195 (p) Human eardrums rupture 50% of time 210 (np) Richter scale 2.0 earthquake 215 (n) Thunder, the largest positive giants. Ordinary thunder 165-180 db. Lightning strike on ocean surface 234db (p) at 2exp-5 newtons per square meter 240 (n) Tornado, Fujitsu 5, energy guess based on 300 mile per hour wind, 1 mile wide 257 (n) Nuclear bomb, 1 megaton (1 million tons of t.n.t.) 300 (n) Hurricane – average, extreme energy is “diluted” by covering 500,000 square miles. Energy = approx. 1000 nuclear bombs a second. 320 (n) Volcano eruption, Tambora Indonesia, 1815, ejected 36 cubic miles. Approximately equal to 14,000 megaton nuclear bombs or a 14 gigaton bomb based on ejected volume, change in megatons times 1.345 equals volume ejected change. If was a nuclear bomb it would create a crater about 12.4 miles wide and 1.33 miles deep. Internal pressure is believed to be about 47 million p.s.i. = 347 db (p)
(n) = Normalized total air power energy level sound plus any wind, watts or joules per second. These levels have been converted.
(p) = actual Peak pressure meter readings i.e. a force per unit area
(np) = Normalized Pressure used in explosive measurements, blast wind is not included
sources: Ultimate Sound Pressure Level Decibel Table, COPYWRITE WILLIAM HAMBY 2004, National Institute on Deafness and Other Communication Disorders.

Update 9/11/07: new entry for 180.5dB from Engadget post.

So, if you want to listen to your sound system at the same level as a symphony orchestra (I assume this is during a loud passage), you would want amplifiers with enough power to deliver around 110 dB. For rock concert levels, something between 120-130 dB. Most of the time you're probably not going to listen at these levels, especially for those of us who share their dwellings with other people, like wives, children, pets, plants, etc., etc. Maybe an amplifier that can provide 105 dB without clipping would be good enough, since you are probably listening between 85-90 dB most of the time. The dynamic range (the difference between the loudest and the quietest sound) for a good system should be from about 105dB down to maybe 35dB. This gives us a total dynamic range of about 70dB.

Now let's take this information and apply it to choosing the right size amplifier for your loudspeakers (if you like to do things ass backwards - you can also choose the right loudspeakers for your amplifier).
1. You need to find the loudspeaker's efficiency or sensitivity specification. This is the sound pressure level (SPL) at 1 watt from a distance of 1 meter, given in dB. My Precise Monitor 10s have an efficiency spec of 88dB/1 watt/1 meter. My Era D5s use those 5" long excursion drivers that provide good bass for a small driver, but they are not super efficient with a spec of 86dB. There are a lot of speakers out there today with higher efficiency, but that doesn't mean they will sound better.

2. Subtract about 10db SPL to account for the drop in sound level from the speaker to the listening position. (When you double the distance from the speaker, the SPL drops 6dB. The speaker's efficiency spec is based on a distance of 1 meter, and if the distance between the listening position and the loudspeaker is 2 meters, then the SPL drops 6dB. If this distance is 4 meters, the SPL will drop another 6dB for a total of 12dB. If the total distance is 10' (just over 3 meters) then the SPL will drop about 9dB.)

3. Add 3dB for each additional speaker in the room that will be playing music at the same level (so when you do this calculation for a stereo system you simply add 3 dB).

4. For my example with the Era D5s, I would get:
86dB - 10dB + 3dB (for stereo music) = 79dB.

5. Next, I need to calculate how much amplifier power is needed to get peak levels to 105dB without clipping.

So I take the difference between the peak level and the loudspeaker value:
105dB - 79dB = 26dB, which gives me the amount of power needed from the amplifier.

6. Using the first chart, you can see that I will need 400W of power to get 26dBW.
Using this method, I would need about 250W to power my pair of Precise Monitor 10s. It gets a little more complicated when you try to calculate power requirements for multichannel 5.1 or 7.1 surround sound amplifiers. That's because the amount of sound from the surround speakers is usually less than the front right, center and front left channels. If you use bass management to send all signals below a certain frequency to a powered subwoofer, that will also decrease the power requirements of the multichannel amplifier. If I find a little more data on the most common multichannel surround mastering methods, maybe I will try to tackle this problem in a future post.

Here's a handy dandy dynamic slide rule that you can also use to perform these calculations.

Update 4/8/08: I discovered that Crown has a good article on their website to help you determine how much amplifier power is needed for your loudspeakers.

## Tuesday, August 28, 2007

### 1/3 of Home Networks Used for Entertainment

This was reported awhile ago in ars technica, but I thought it was significant enough (at least for our business plans) to post here.

A study by Forrester Research found that 27% of online adults in the U.S. have a home network. One third of all these home networks are now used to stream music, movies, TV shows, and other media throughout the home.

Some of the numbers used in our business plan to estimate potential market size are based upon a typical user who is tech savvy, etc. If the user has a home network, specifically used for entertainment purposes, they are more likely to be interested in a product like ours, as opposed to someone who doesn't. It is interesting to note that one of the biggest reasons given for using their home networks for entertainment uses was for streaming music.

It's nice to know there is an actual study that shows how many people who fall into this category.

## Monday, August 27, 2007

### Microsoft Responds to Vista Audio Problems

Last week's post, 'Networking problems when Vista Audio is Active' linked to reports from the 2CPU forums about networking problems in Vista during audio playback. Adrian Kingsley-Hughes in his "Gear for Geeks" column for ZDNET received a response from Microsoft regarding these problems. You can just read his article, but I might as well provide his list of Microsoft responses here:
• “We have been looking into this problem and are working on a doc that will go into the technical details of what we have found.”
• “Please note that some of what we are seeing is expected behavior, and some of it is not. In certain circumstances Windows Vista will trade off network performance in order to improve multimedia playback. This is by design.”
• “The connection between media playback and networking is not immediately obvious. But as you know, the drivers involved in both activities run at extremely high priority. As a result, the network driver can cause media playback to degrade. This shows up to the user as things like popping and crackling during audio playback. Users generally hate this, hence the trade off.”
• “In most cases the user does not notice the impact of this as the decrease in network performance is slight. Of course some users, especially ones on Gigabit based networks, are seeing a much greater decrease than is expected and that is clearly a problem that we need to address.”
• “Two other things to note. First, we have not seen any cases where a users internet performance would be degraded, in our tests this issue only shows up with local network operations.”
• “Second, this trade-off scheme only kicks in on the receive side. Transmit is not affected.”
Seems pretty strange to me. Slight degradation? Some people have reported network performance throttled to 5-10% when playing audio. Heck, when using Windows Media Player the network performance is reduced even when the audio is paused (using other media players like Foobar2000, the network performance is only throttled during playback). Anyhow, I never had any pops, clicks or skips when playing audio on my old Pentium III or IV hardware running Windows NT while connected to a network back around 1999. So I still don't understand why they are having this problem with today's hardware. Hopefully this will be fixed in a future patch or something.

## Friday, August 24, 2007

### HTPC Help Is On the Way, Go Troy Go!

If you've recently tried building an HTPC that can do all the basics, like play music, DVDs, plus play the latest HD formats like HD-DVD and Blu-Ray and have been frustrated with the incompatibilities between hardware, operating systems, drivers and A/V codecs, there might be some help in the very near future.

Troy, aka "pcCinema" on the AVS Forums, is offering to help everyone out. Troy started a thread titled, "Suppose I make it easy for all the newbies and budget folks?" back on August 16th to first announce his intentions and gauge interest. Troy is a former MCSE Senior IT Consultant who was responsible for the large scale automated rollout of PCs to corporate clients. He specializes in writing scripts or deployment tools that would make building high performance HTPCs easy for every newbie out there. He plans to maintain a website that would provide a list of high quality software and hardware components that have been fully tested for performance and compatibility with the required HTPC applications. Best bang-for-the-buck components would be included to make sure systems built from the recommended hardware list would also be affordable. Whenever, newer more advanced hardware or software is available and passes the necessary testing, the list will be updated.

After the user purchases his components based on the recommended hardware and software list, Troy's scripts would be used to assist with the process of assembling and installing all the hardware and software to create a trouble free HTPC. No more driver or codec conflicts. Finally, HD DVD and Blu-Ray playback will be stutter-free without all the hassles many people currently deal with today to get the correct combination of hardware and software to work together.

It's also interesting to note that Troy doesn't plan to charge a penny for any of his services. Troy doesn't sell any of the hardware or software, the user will have to shop for everything on his/her own. This is something he plans to do out of the goodness of his heart. Actually, it sounds very altruistic (it is), but he's also doing this out of self preservation. Troy explains that he is disabled and unemployed, waiting for Social Security benefits. He says he has nothing better to do with his time and since this is something he is very good at, he might as well do something he enjoys and allows him to be productive.

"It has been good for me to have a purpose again. I actually feel better physically and mentally now that I have this to focus on," Troy writes. "I've said it before that I've been going out of my mind with boredom, etc. I also want to make it good for the volunteers, and the community at large, and not just those that benefit from the plans directly. What's that they say about how people live longer if they have work to do? And the number one killer of retired people... "

Troy is hoping enough people will donate to his non-profit organization to help pay for the latest hardware and software that will be used to test for performance and compatibility with a high quality HTPC.

Interest in his proposal has been pretty positive. Of the 149 responses so far, it looks like more than 95% have been very encouraging. People are even willing to volunteer their time to help build a website (this one was thrown together pretty quickly by someone with the user name "pc1984" to demonstrate what he can do with a content management system (CMS) based website), help with the legal issues regarding setting up a non-profit organization, writing more advanced automation scripts, writing how-to guides and testing systems.

Well, I hope it works out. Personally, I'm pretty annoyed by all the hassles we have to deal with to get an HTPC to play all the high definition formats today. The latest dual/quad core CPUs from Intel or AMD and video cards from ATI or NVIDIA show promise, but sorting out the right combination of drivers, codecs and applications is enough to piss off an experienced HTPC builder. It will be interesting to see where this leads. I'll be paying close attention.

Good luck Troy!!

## Wednesday, August 22, 2007

### Networking problems when Vista Audio is Active

Just thought I'd relay some news about Vista audio that has been spreading around the last few days...

People have reported on the 2CPU forums that network performance is throttled whenever they play audio in Vista. It looks like more of an annoyance that a critical problem. Hopefully Microsoft will respond with a bug fix in the near future.

## Tuesday, August 21, 2007

Constantin Gonzalez posted this excellent article: "So, where's the future of HD Audio?" in his blog a few days ago.

He explains that the music industry has 2 major problems with high definition audio:
1. most fans, retailers and music publishers don't care about HD audio
2. those that are interested in HD audio are a small niche scattered across many competing format choices
The first problem is due to the fact that most people have been told CD quality audio is good enough. Heck, most people are perfectly satisfied with less than CD quality - lossy encoded MP3s or AACs they either download from peer-to-peer sites or purchase from iTunes or other online music stores. Constantin explains that the human ear/brain is much more accurate and capable of hearing a higher dynamic range of audio and phase differences than is possible with CD recordings.

He's right. If only people knew what they were missing, maybe there would be more interest in HD audio. Some may argue that DVD quality video is also good enough, but the fact that more people are purchasing HD televisions, obviously they must believe there are added benefits to the higher resolution video images. Otherwise, why bother spending a few thousand dollars on a new screen when the standard definition screens are only a few hundred bucks and they work fine for watching DVDs. Now that they own a nice HD monitor, maybe they'll want to match it with a sound system capable of reproducing the audio tracks in all their higher resolution surround sound glory. If they appreciate the improved quality from the movie's sound tracks, maybe they will demand higher quality audio from the artists that provide rock, jazz, classical, etc., recordings.

Constantin says the second problem is really a mess and it is really about how the companies in the music business are competing to control the next popular format(s). The combination of competing media like SACD, DVD-Audio and now HD DVD and Blu-Ray, along with competing encoding methods like DSD or 24bit PCM with compression schemes from either Dolby, DTS, Meridian, etc., etc., AND the DRM methods employed to restrict copying resulting in a variety of hardware incompatibilities have just made the transition to HD audio very difficult.

All of this has created so much confusion with the average consumer that they are more inclined to just wait it out until a clear winner emerges so they don't mistakenly invest a lot of money in a bunch of discs or equipment that aren't supported in the future. Besides, the latest technology is always pretty expensive. Look at the historical prices of any consumer A/V products. Early VCRs were over \$1,000, as were the earliest DVD players. Now look at how much they cost. Nobody wants to repeat the mistake of purchasing a \$1,200 Beta VCR, like I did.

So, combining these problems we have the old chicken and the egg dilemma. Most people don't care about HD audio, but why should they? There's really not enough HD content out there to make it worth while on any single format. Maybe the big record labels are unwilling to produce albums on HD media until they are confident a secure HD format is popular enough to make it worth the necessary investment. Since most of the current HD audio content is offered through many small niches on either SACD or DVD-Audio and possibly HD DVD or Blu-Ray in the near future, there obviously is no clear winner. From a business perspective, compared to regular CDs and DVDs all of these higher quality formats are huge losers.

Oh, and to add to the confusion... Interactive MVI discs are the CD's newest rivals.

I guess this is one of the reasons why I think PC audio is the way to go. With a PC, you can play almost every media type and encoding method out there. You might not even have to deal with multiple media types if you choose to download from online music stores that offer HD audio albums.

## Monday, August 20, 2007

### I Got a Rocket in My Pocket

I found this great NRBQ clip on YouTube. I also got a kick out of some of the comments following the clip:

Huzzab: "Before I ever heard these guys, I read two reviews. One was "Good music to get drunk to." The other was "NRBQ doesn't let their exceptional musical ability get in the way of their playing". They certainly didn't let me down! Terry Adams is the devil incarnate."

seantgould: " best American rock and roll band EVER...u can't name any band with keyboard and guitar solos as cool as the Q...sorry, just my opinion"

chalkdavid: "Outstanding. Al and Terry solo their asses off and Joey and Tommy are about the most inventive rhythm section around."

## Tuesday, August 07, 2007

### What is HD Audio?

I just read a response by Mark Waldrup, Ph.D., to an article on HD Audio that appeared in SmartHouse News. Mark is the chief engineer at AIX Records. He's also the founder and director of the High Definition Surround Music Association (HDSMA), a non-profit dedicated to supplying accurate information and demos of HD Audio.

Here's the definition the HDSMA prefers - "HD Audio is music or sound that is captured from the acoustic source at or near the fidelity of human hearing."

Mark explains that this means recorded/reproduced sound that has a frequency response of at least 20 kHz and a dynamic range of around 124 dB or more.

He goes on the say that the only consumer formats capable of supporting HD Audio fidelity are SACD and DVD-Audio. However, most of the SACD and DVD-Audio discs released are not true HD Audio because they are performances that were recorded before HD recording equipment was available. The analog tape equipment is only capable of a frequency response of 18 kHz and a signal to noise ratio of 72 dB, which is equivalent to a sample rate less than 44.1 kHz and a bit depth of 12 bits. Mark explains that even though you re-record it at 24 bit/96 kHz, it won't sound any better than the original analog master tape.

Mark also mentions that the HD in HD Radio doesn't stand for high definition, but is instead something like "hybrid digital." I agree that this is only adding to consumer confusion, especially when you consider that the resolution of HD Radio is only 64 kbps, which is half the bitrate of the worst quality MP3 or iTunes downloads available today.

Personally, I think the marketers have really screwed things up. It probably started when the marketing folks at Microsoft referred to the quality of their WMA encoder as "CD quality" when the bitrate was set to 128 kbps. The marketers probably know that if this kind of thing is repeated enough people will just accept it as fact (hmmm, that sounds familiar). Other companies simply play along. Now MusicGiants refers to their losslessly compressed tracks, which are really CD quality, as HD audio to distinguish it from the lossy encoded tracks available from the big music services like iTunes. Their 24 bit/96 kHz tracks are now referred to as "Super HD Audio". According to Mark, MusicGiant's "Super HD Audio" isn't even HD Audio because it was re-purposed from the original analog master tapes instead of recorded with actual HD equipment.

I have listened to 24 bit/96 kHz recordings (both 2 channel and 5.1 surround) from MusicGiants and they do sound better than the same recordings that I already owned on CD. However, I haven't had a chance to listen to the HD Audio offered by AIX Records. I first read about Mark (Dr. AIX) last Winter and am still waiting for them to launch their itrax.com website, which will offer HD Audio downloads. I thought their website was going to go live in June. I wonder what is holding them up... Anyhow, I am looking forward to hearing what Mark calls True HD audio. Hopefully they will have a diverse catalog with a lot of great artists to choose from.