The HOMster! (or How I Learned How to Fix a Horn)

[gedlee]

Originally Posted by winslow

Dr. Geddes, how would you do such testing in amps? Is it something that you would need AudioPrecision hardware, or could the average guy measure these things with something more available?

I have a few for my car and want to put the best one on my horns. The only one I have that I know doesn't have crossover distortion is my BIG heavy class A all tube amp (yeah, it's made for automotive applications).

I posted the technique some time back, it would be good if someone dug that up. Basically there is a trick that you can do with some measurement software that is called sychronous averaging. You need to generate a "near" 1 kHz tone that exactly fits a 1024 window. Then you send this into the system and average the time signals at the output on exactly the 1024 (or 2048 etc.) samples. The signal will average to a sationary signal but the noise will average down. This allows you to find the harmonics of this signal well below the noise floor of anything in the system. You then drop the signals input level until it gets lost in the remaining noise. You are now looking at the actual nonlinearities of the system at very low signal levels and NOT the signal + noise. An amps with crossover distortion will show a rapid rise in the higher harmonics as the signal level falls. This is very very bad!

Chip amps have a serious advantage in this test since being all on one substraight the components match and track much better for a smoother transfer at the zero crossing.

[winslow]

Found it in the amp section-

Geddes on distortion measurements

[MisterTwister]

Excellent thread! thanks for sharing Patrick.
does anyone know where I can buy this type of horn, with side mount for compression driver.

[Patrick Bateman]

Originally Posted by MisterTwister

Excellent thread! thanks for sharing Patrick.
does anyone know where I can buy this type of horn, with side mount for compression driver.

I bought mine off Ebay... Here's a similar set.

http://cgi.ebay.com/Image-DynamicsCD...4#ht_500wt_958

If I'm not mistaken, Bruce Edgar of Edgarhorn fame contributed to improvements in the designs from Image Dynamics.

The ones that I am using are from a competing company... They're an older design.

Here's their current offering:

http://www.usdaudio.com/products/wg-a700.php

[freddi]

are their current equivalents to the "clean" Pioneer receiver tested by Dr. Geddes?

[gedlee]

Originally Posted by freddi

are their current equivalents to the "clean" Pioneer receiver tested by Dr. Geddes?

Personaly I'd like to know the answer to that question too. Does anyone know if current Pioneer receivers also use the same chip amps as the older ones? The older receivers use a chip that said "Pioneer" on it. Don't have the part number handy.

[soongsc]

Originally Posted by gedlee

Hold whatever opinion you like, but I always back mine up with data. The point is that I bought a $200 receiver that is as good as any amp that I have ever tested and certainly not a limitation to sound quality in my systems. (Ask anyone who has heard them.) Problem solved, end of study, and time to move on. You should too.

I'm almost sure you only measured with a constant resistor load, which is what most people do. Distortion will vary quite a bit with speaker loading due to back EMF. There are also many other aspects that effect audible performance not viewable in distortion measurements. So it's a good idea to keep an open mind in the process of system improvement.
I also realize that you do make great effort to back you optinion with data; however, it's not possible to do 100% of the time.

[dantheman]

I think he is saying amps and electronics matter...to a point. Once you get to that point, then other things clearly matter more- like speakers and the room. I can believe that...but I also know that personal preference can dominate the argument. What is "right" may or may not always be what you find as "good."

This is sort of a quibble and not intended to start an argument. I think this is a bit closer to what Dr. Geddes means. If not, it's what I'm saying from my own experience: Actually I think he's saying that the speakers and rooms matter the most and that there is very little to be gained from an amp after a certain point in design. I more than tend to agree. Whenever I go to Tokyo I also go and listen to all the latest HiFi and otherwise gadgets I can in the Akiba district. A few years ago my wife and I did some listening to many amplifiers--roughly a dozen--all in the same room through the same speakers and same song. The difference is incredibly small and indiscernible even during honest (as can be) sighted listening at the same SPL. The only ones we heard that sounded audibly different with a normalized volume were Rotel models--a bit smoother, and it was only slight. All these were SS designs. There were no Sony, Pioneer, etc... receivers in the room so I can't comment on them. I just had a similar experience at Burning Amp. Of course the set up there wasn't that good for evaluating amplifiers. Seemed that speakers got switched with nearly every amplifier switch. In any case I didn't hear any amplifier that sounded bad there. The tube amp definitely had a unique sound, but it was playing through speakers that were not "tube friendly" at all. Even in that case the difference was not as large as a speaker change.

Dan

[454Casull]

Originally Posted by soongsc

I'm almost sure you only measured with a constant resistor load, which is what most people do. Distortion will vary quite a bit with speaker loading due to back EMF.

Out of curiousity, who measures this?

[gedlee]

Originally Posted by dantheman

This is sort of a quibble and not intended to start an argument.

Dan

Dan

Mostly agreed as long as you realize that "different" does not imply "better". Thats a whole other level of complication.