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# Measuring Amplifiers - Page 39

Hi Mark,

"From an extreme mathmatic perspective, a sound source ALWAYS drops at a rate of 20*Log(D/Di)."

I suppose so; IIRC Terry Montlick pointed out that room gain is just the amplitude rising as the 0th mode (0 HZ) is approached.

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Quote:
Originally Posted by noah katz

Hi Mark,

"From an extreme mathmatic perspective, a sound source ALWAYS drops at a rate of 20*Log(D/Di)."

I suppose so; IIRC Terry Montlick pointed out that room gain is just the amplitude rising as the 0th mode (0 HZ) is approached.

Indeed. I suggested the alternate perspective of the exact same problem, which I believe may be more obvious to the casual observer. The smaller the room dimensions, the tighter the spacing of virtual sources, and the higher frequency below which they stop varying much with position.

The same can be said of a line source or planar source, just as they are studied in other disciplines such as charges or RF. The actual calculation of a line source is an integration of points. The reality is that while the initial observation is that the source appears to only fall only at 3dB/doubling of distance, further investigation confirms that this does not maintain at great distance nor at all frequencies. The real situation makes much more sense, as it does not defy the conservation of energy. An enthusiast doesn't need to know how to do the calculation (speaking to all here, not really Noah), but the concept is important...

The "line source," or even significantly sized planar source, does not drop off more slowly with increasing distance. Quite the opposite in fact. At great distance, the full power of the combined sources, or integration of the large source is observed. As we move closer, we initially find the level increasing at the square of the distance change, but at some distance related to array size and frequency we find an extended range/area of interference. In this interference range the level no longer continues to rise at 20*Log(D/Di), as the interference increases as you move closer.

While some will retort with "What's the difference?!?" I would argue this is a significant difference in understanding if you are trying to examine or predict the output, efficiency and sensitivities of a system.
Quote:
Originally Posted by Jack Hidley

Bosso,

Your quotes are discussing several different things, which I believe are all accurate, but which don't apply to soundfields or propogation in small environments (houses).
...

Sound energy is "lost" as it travels through the air. By lost, I mean that heat is generated. This does happen more at high frequencies, due to moisture, than at low frequencies. However, this decrease in sound energy is very small compared to the loss in SPL due to the inverse square law.

Bosso,

Jack is correct here, and your assertations are related to phenomena that require 100s of feet to be significant below 1kHz. Below 100Hz the effect is nearly nil at less than 1,000 feet. There are many more interesting things to debate about which ARE real problems in small rooms. This isn't one of them.

Quote:

Some of the other quotes (elephants) are dealing with sound transmission through solid matter, such as the ground. In acoustics, this isn't considered sound because it's not vibrations transmitted through air. I wasn't including it in my original comment because of this.

Having some indirect tie to these studies from previously working with Tom Danley at ServoDrive, the propagation is in fact acoustic through air. This isn't stomping, but instead very low frequency energy produced by the elephants. The low frequency energy is less easily affected by air losses and by terrain or temperature gradients, so it travels well across the terrain. This is exactly where Bosso's points come into play, but this is on the scale of miles, not feet.
Quote:
Originally Posted by bossobass

The discussion regarding THD in the first 2 octaves is an absolute non-issue. Noah and Mark are correct, but I have always said that, in either case, the harmonics of these frequencies are inaudible. They are inaudible. They have zero negative effect.

There is also the measurements that I've taken at 4Hz, 5Hz, 6Hz, all at the same dBSPL at the LP and all with extremely low HD showing up on the graph. If there was 100% THD, the harmonics peaks would be there on the graph.

Hi Bosso,

I would dissagree firmly with the statement that distortion is inaudible at low frequencies. It is most certainly audible. The question is how it impacts our listening, and at what point it becomes either objectionable as with higher harmonics and operational noises, or impactful on sound character as wtih coloration from harmonic distortion. The hearing sensitivity curves work against us here, but room gain gives us a fighting chance.

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I understand the theory involved, but I haven't seen any measurements that bear it out. The evidence suggests that ULF does indeed travel much farther at an intensity that contradicts the law. If the explanation is that higher frequencies are attenuated by refraction and/or absorption, the formula for the law is incomplete and has no application in HT discussions.

GP tests such as Ilkka's sweep of the LMS5400-18" L/T, expanded to 1Hz, could easily nail this one. A measurement at 2M and at 16M should show a perfectly uniform drop of 18dB across the entire BW. End of story.

To date, there is no such measurement comparison that I can find anywhere.

Myself and many others have done this measurement plenty of times and it correlates with theory quite well, making it rather un-interesting and unlikely to get published. The deviation which can be seen in some cases is within 2-4m where the size and configuration of the source can have a 0-2dB skew on what might be expected for different assumed origins (D=0).

Quote:

I suspect that this is the correct explanation. The room creates virtual sources and those virtual sources vary in intensity according to their refractive properties and are frequency dependent.

Of course, again, the evidence shows that this theory is also suspect. ULF appears to be less affected by walls and in fact travels better through the earths crust than it does through air. This makes it hard to understand how a 4" wall in a typically constructed home offers any sort of refraction as frequency decreases, much less offering more refraction.

Vibrations, be it airborn acoustic energy or SONAR through water, will alwasy travel faster through a higher density medium. The incorrect part above relates to the transfer from air to that higher density medium. In general the transfer is very inefficient between mediums of greatly differing density.

Refraction is different from reflection, and it is the reflected energy we are concerned with. If you look at the problem from a virtual source perspective, it makes sense that you need a reflected energy of less than 50-70% to have significant impact on the total summed result. I only wish we could build walls that lossy, as our room mode problems would be much less severe.

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In the end, I am less interested in the precise mathematical formulae involved and much more interested in the results. I'm not a physicist. I'm a HT enthusiast who has a library of source that has content that's intended to be reproduced as part of the A/V presentation.

Agreed. My intention is to convey the concept, not the math. If we remember that every large source can be viewed as a tightly spaced cluster of discrete points, we can save much confusion when we consider less common or new ideas.

Quote:

I continue to be taken to task over this by the weakest arguments imaginable. "It's impossible with conventional drivers. Flat isn't loud enough. There's too much THD. The source is mistaken, it's just artifacts. It adds nothing to the experience. There isn't enough juice in a 20A circuit. The signal chain rolls off. GP measurements to below 10Hz won't offer any useful information. There was a bus driving by. The HVAC skewed the measurements. It's one of the walls. The box is too small. Ported is better..."

There is plenty of room for argument as to the subjective benefit, usefulness and pitfalls of greatly extended VLF response. Let's not confuse these issues with the physics of what is actually occurring. There is plenty of ammunition for argument already!
Mark,

Very interesting read.While this thread is a bit out of its path it is one anyone interested in more serious DIY should read.
The inside of a Crown XTI 4000.

And the partial software "System Architect" displayed on a laptop.

And the EQ settings available on one screen

Here is an Audiosource amplifier, model Amp ONE/A that jvgillow has sent to me for measurement. Here are the manufacturer specifications.

Specifications: *Power output: 80 watts per channel @ 8 ohms, 100 watts per channel @ 4 ohms, 200 watts bridged mono @ 8 ohms *Total harmonic distortion: <0.04% *Frequency response: 20-20,000 Hz *Signal to noise ratio: 110 dB *Inputs: Line in (RCA) *Outputs: Line out/Thru (RCA) *Speaker connection: 5-way binding posts *Dimensions:16-1/2" W x 2-3/8" H x 11-5/8" D.
Large torrodial power supply
80 watts per channel
200 watts bridged mono
2 ohm stable

And here are some pictures:

Here are the results of 8 ohm stereo and 4 ohm stereo testing.

This amplifier pretty much, kinda sorta meets its specifications. It will run at 2 ohms but it does not like being tested at 2 ohms. Same goes for mono/bridged operation. I went through 4 6 amp fuses from the power supply when trying to bring up the amp at 2 ohms or bridged. I also noticed that distortion rises drastically as the heat builds up. I had to stop and let it cool down several times. In everyday use none of this would matter and it would work just fine.

Chuck
It's an inexpensive amplifier at \$209 (@ PE) and like you said makes it's claims, kinda sorta. It doesn't advertise itself as the end all and doesn't get there with it's performance either.
If there were a DIY old widow who liked a little bass with her stereo, she might buy this one.
Thanks for the test data Chuck, you are da man

I'm glad to see it didn't test too poorly, at least it meets/exceeds rated output at 4 ohm; I use mine bridged at 8 ohm per for mains. Not sure what it was doing with the 8 ohm stereo @ 20kHz but interesting nonetheless. I've never had a fuse blow on me but I never have pushed them as hard as Chuck does in his tests. For a few weeks I was using one bridged to drive my SVS CS-Ultra (4 ohm) and it never even got very warm.

Buy.com has them cheaper than anyplace I've seen recently, but I got mine back during the Ubid refurb sale so they were I think \$85/ea delivered. Not very interesting as a sub amp but they were the cheapest option for me at the time I wanted to go separates.
Quote:
Originally Posted by jvgillow

Buy.com has them cheaper than anyplace I've seen recently, but I got mine back during the Ubid refurb sale so they were I think \$85/ea delivered. but they were the cheapest option for me at the time I wanted to go separates.

Now wait a minute . . . . for 85 bucks I for sure, wouldda bought one too! That toroid transformer alone is worth 85 bucks.
We have a Techron 8506 'Gradient Drive Amplifier' provided by Ricci. For those of you that don't know or are unaware Techron is/was the industrial/laboratory division of Crown International. These amps are huge! I estimate that one of them weighs close to 100 pounds. The manual provided with the amps is for a 7560 but the labal on the amplifier states that it is an 8506. So, I set them up and measured them (there are 2 mono units).

And a size comparison picture..............

Rear view.

PS: The date on the manual is October, 1988.
Can we expect the Face amp tests later today?

And good FR, pretty solid power output from that Techron. What are its manuf specs?
Hey...not bad! I'm kind of surprised that they did so well. Pretty much matches the specs for it which I think were 600 / 8ohm, 1000 / 4 ohm and 1250w at 2ohm. FR and distortion looks decent too with a bit of deviation at HF. SN ratio isn't the best though. This is the old school, overbuilt , brute force kind of amp.

Chuck,
Did you test both and they were really close, or just one? Any hiccups during testing? Blown fuses, etc? How bad was the amp sucking the line voltage down?
Anyone ever do a test of a Crest CPX 2600?

Here's the specs on the AETechron 7560. I can't find jack from either Crown/ Amcron/ AETechron about an 8506 model

http://www.aetechron.com/7560.html
Quote:

Anyone ever do a test of a Crest CPX 2600?

Send it to chuck!!
Quote:
Originally Posted by Ricci

Here's the specs on the AETechron 7560. I can't find jack from either Crown/ Amcron/ AETechron about an 8506 model

http://www.aetechron.com/7560.html

Since the amp doesn't seem to be directly badged as AE/Techron, that model number 8506 might be a custom number for the Picker International branded unit.
Not much under Picker International either. They got sold too many times! Probably just a 7560 or 7570 rebranded for Picker anyway. As far as I can tell the pair were probably originally used in a medical setting for an MRI system, or an X-ray system. Hopefully they will impart holographic MRI like resolution to any audio system they may be connected to. I paid \$600 for the pair. Thilo from TC apparently liked them for subwoofer useage. At about 1min 20sec in you can see one in this TC3000 excursion video. It's slamming the hell out of that TC3K too. Dang those TC3000's could wang!

Chuck,

And a big thank you for all the testing you do.
Can we see the inside of that big sucker?
Chuck,

Thank you for your superb contributions to the community! My, that Techron is a massive beast; I'm curious to see pics if you've looked under the hood.

Like others have requested; I'm really looking forward to the F1200-TS testing - I have two of these guys, and may add yet another.

Regards,

Larry
Dying to see the Face Audio results.

I have an observation about the output between lower comparable models in the TS and the TX lines.

F500TS:

Stereo / 330 W
Bridged / 700 W
Stereo / 500 W

Stereo / 950 W

F520TX:

8â„¦
Stereo / 300 W
Bridged / 800 W
4â„¦
Stereo / 520 W
Bridged / 1200 W
2â„¦
Stereo / 650 W

Why does the F500TS have more power at 2â„¦? It seems like the F520TX has a harder time doubling down to 2â„¦ in stereo than the F500TS even though the TX line is supposed to be more substantial in build. I would love to see pictures of the TX internals to see the difference.
I would like to see a test of the Crest..2600 cause the specs seem a little off to me...

Power Rating 2 Ohm Stereo: 1100 Watts
Power Rating 4 Ohm Bridge: 2200 Watts
Power Rating 4 Ohm Stereo: 900 Watts
Power Rating 8 Ohm Bridge: 1550 Watts
Power Rating 8 Ohm Stereo: 550 Watts
Quote:
Originally Posted by Willd

Can we expect the Face amp tests later today?

And good FR, pretty solid power output from that Techron. What are its manuf specs?

The Face will be done later this week. I am about half way through the testing and recording of the measurements.

I have a manual with one Model number on it and an amplifier with another Model number on it, so I am not sure what the specs are.
Quote:
Originally Posted by Ricci

Hey...not bad! I'm kind of surprised that they did so well. Pretty much matches the specs for it which I think were 600 / 8ohm, 1000 / 4 ohm and 1250w at 2ohm. FR and distortion looks decent too with a bit of deviation at HF. SN ratio isn't the best though. This is the old school, overbuilt , brute force kind of amp.

Chuck,
Did you test both and they were really close, or just one? Any hiccups during testing? Blown fuses, etc? How bad was the amp sucking the line voltage down?

Yes, both were tested and both measured almost identical. No hiccups at all. They are rock solid old time big heavy iron amps. No blown fuses, but a bunch of heat out of the top and the fans would kick in regularly. Voltage was not sucked down, but they were running on a dedicated 30 amp circuit and would draw close to 20 amps.
Quote:
Originally Posted by Ricci

Here's the specs on the AETechron 7560. I can't find jack from either Crown/ Amcron/ AETechron about an 8506 model

http://www.aetechron.com/7560.html

Physically, the amps I have look close to the amp pictured in the drawing. The specs are probably very close to the amps I have and they only vary in minor ways such as (1) No meter or provision for meter on the front panel, (2) 1/4" jack instead of BNC on rear.
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