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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 11:42 am 
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Joined: October 21st, 2013, 6:53 pm
Posts: 263
hey Tom,

So if you want to hear my opinion, the biggest hole I can find in the experiment is this:

It sounds like your subjects were not intimately familiar with either the speakers, or the room they were tested in. Even the crossover itself was not familiar to them.

The best example I can give of the problem with this is that it's kind of like taking your grocery list to a new store you have never been to before, and expecting it to run as smoothly as your regular shopping trip to your local store. At best it is going to take you much longer, and at worst you will probably come out of there with several things on your list you just flat out couldn't find!

I think what is actually happening in your experiment is your subjects are being overwhelmed by a multitude of stimuli, other than the specific ones you are trying to test. They are too busy trying to make sense out of a situation they have literally never been in before, and they can't figure out what exactly they are trying to attend too.

My suggestion fur a slightly different experiment format is to find a fellow audiophile who has some speakers he built himself, including the crossovers, and has them set up in a room he is familiar with. Then run the same crossover swaps with all the familiar equipment, and see what happens.

Thanks,

Chris


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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 12:11 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 479
tomp wrote:
The objective is to see if the listener can tell the difference. By definition if they can detect no difference, they sound the same and therefore there can be no preference for the sound of one or the other. That is the basis of blind testing. If they sound the same, how can you have a sound preference. You may like other factors such as looks, fit and finish, peice, etc. but the sound is the same.

Tom


I feared you would say that. I will respond as soon as I can, tied up rest of the day....

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Last edited by Cogito on October 29th, 2017, 1:01 pm, edited 1 time in total.

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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 12:44 pm 
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Joined: February 28th, 2013, 3:31 pm
Posts: 964
Walt is correct that the devil is always in the details. I think it would be good for someone else to take up the mantra on this and run another test. However, as Jim said, even small differences in capacitance will change the ability to hear differences as the crossover point will change and that is audible. I have done enough of these that I do not wish to start all over again but I would be happy to provide someone with information on all the pitfalls I have personally fallen into trying to control all the variables in the test.

As far as the subjects not being intimately familiar with the speakers in this test, that may be a factor and as I said, results may vary test by test. Getting a null result in DB testing only says for the set of conditions not difference was found. Getting a positive result pretty much means that yuo can go to the bank that there is a difference. In this case, the only really salient point is that the claims of huge differences that anyone could immediately hear were not true.

Another case of trying to discredit a null test by someone who could not tell a difference happened to me when I lived in Chicago. This person built speakers and cables commercially and was raving about the quality of his speaker cables and all the extrodeinary characteristics of those cables. He brought them over to my house and listened. After the test, he could not hear any difference between his exotic cables and regular 12 ga zip wire. Totally frustrated he said that his inability was the result of using my speakers which were not as revealing as his and with which he was not familiar. So we repeated the test with his speakers and guess what he could still not hear any difference. Needless to say he never spoke to me again.

So, you can use DB testing as a tool to help you make decisiona or ignore it. It's your choice and each person has to do what they think is the right way to go. Having gone down the rabbit hole many times in the past with "exotic" components, I have learned to start with DB testing in many cases to shorten my choices before making the ultimate listening tests.


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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 12:59 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 479
Jim G wrote:
I don't know the crossover details either. I do remember assembling several brands of film capacitors @ 4.7uf. None actually measured 4.7uf however. There were easily heard differnces between the capacitors with slightly different values. Only 2 brands measured close enough to double blind test. I think they were approximately 4.4uf and within 1% of each other. No one was able to correctly identify the difference. I imagine few actually measure the competing capacitor brands they are comparing in this type of application to less than 1% and most of the differences heard are the varying values.

To be fair, the system was set up pretty hastily and not set up for optimum performance before starting. Hell, that could take weeks/months and require significant room treatment. I believe it may be possible there could be a difference between capacitors in spacial or atmospheric characteristics had the system (including the room) been capable of showing those characteristics. We really were only able to compare basic, but critical characteristics like toneality, and timbre.


Jim,

The tolerance of capacitance does no not account for audible differences.

Assuming a 2nd order Butterworth network was used, 4.7uF capacitor equates to 3000Hz crossover frequency. With a crossover frequency that high, it is most likely a 3 way system.

Let us look at few cap values within +/-5% tolerance

4.7uF gives 3000Hz crossover at -3dB
4.5uF gives 3072Hz crossover at -3.2dB (-5%)
4.9uF gives 2922Hz crossover at -2.78dB (+5%)

Suppose, we have two crossovers the caps of same make and mode at extreme ends of the tolerance, 4.5uF and 4.9uF, the difference in crossover is only 150Hz and .45dB at 3000Hz. I doubt any human ear can consistently detect that small difference of the signal crossover assuming neither of the drivers are rolling off near the crossover frequency. This is very important to understand because we are talking of same model and same make caps, so any differences we expect to hear should be strictly due to the crossover frequency and slope, both of which are fairly constant.

Secondly,
Not all capacitors sound drastically different, irrespective of their cost. If the caps in the test are "similar" sounding, it would be hard to detect the difference in double blind testing (thats another subject which I will try to address shortly).

Moreover we need to know exact crossover topology and the caps changed. In our example, if only the HF capacitor is changed, frequencies below 3kHz remain fairly unaltered which makes it extremely difficult to detect the sonic differences of the capacitor of interest.

IOW, there are more questions about this test than information to postulate any inferences.

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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 1:56 pm 
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Joined: February 28th, 2013, 3:31 pm
Posts: 156
Shashi,

Even though the caps were 5%, the swing over the group was more than 10%, but it's only a fair test if the 2 brands (or more) being used are (essentially) identical value. I'm making 5% value changes to capacitors attenuating the tweeters in my current system that are easily noticed.

Continue to tweak your Altec crossover build until you are satisfied it's spot on, and you've gotten comfortable with it. Set up your external network with screw terminals for the capacitors and we'll do a test there if we can find other film caps that measure within 1% of yours, assuming you're using film caps of course. You may be able to differentiate the 2 brands of like value caps in your system, or someone else might. I'm guessing that if 10 members of this group did the test one at a time sitting in the sweet spot, only 1 or 2 at most would be successful.

Don't fear the DB test. I didn't think it was useful until I did one with Tom/Dave and picked 15 of 16 correctly when no one else in the room could hear a difference. We did that test on a system I was unfamiliar with. It was an interesting moment. We all hear differently.


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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 2:01 pm 
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Joined: July 8th, 2016, 4:34 pm
Posts: 228
Why not pad the capacitors with small value caps in parallel to match capacitance?


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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 2:46 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 479
Jim,

Quote:
Even though the caps were 5%, the swing over the group was more than 10%, but it's only a fair test if the 2 brands (or more) being used are (essentially) identical value.


Ofcourse, in a controlled test capacitor values should be constant. My exercise is to justify or cast doubt on this interpretation of your post (my interpretation too).

Quote:
However, as Jim said, even small differences in capacitance will change the ability to hear differences as the crossover point will change and that is audible.


All I am saying is, with 10% variation in the capacitance, there is a difference of less than .5dB at the crossover point. Human ear cannot detect .5dB variation. Hence, attributing the difference in caps to solely to capacitance values is very likely to be false assumption.

Quote:
I'm making 5% value changes to capacitors attenuating the tweeters in my current system that are easily noticed.


In a standard crossover, capacitor values DO NOT alter the frequencies responses on either side, ie: the slope remains flat.

In an attenuation circuit, I believe 5% change in values would be audible because the slope of the frequency response is altered.

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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 4:05 pm 
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Joined: February 19th, 2017, 9:43 am
Posts: 221
I suspect that the more audible difference of varying capacitor values by a small amount is more in the phase difference with the adjacent driver as opposed to small shifts in frequency response. By adjacent I mean crossover wise, not physically.


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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 4:12 pm 
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Joined: February 28th, 2013, 3:31 pm
Posts: 156
Quote:
I'm making 5% value changes to capacitors attenuating the tweeters in my current system that are easily noticed.

Cogito wrote:
In a standard crossover, capacitor values DO NOT alter the frequencies responses on either side, ie: the slope remains flat.

In an attenuation circuit, I believe 5% change in values would be audible because the slope of the frequency response is altered.

Sorry, that could be a red herring, and possibly a bad example that doesn't apply to the DB test.

Let us know when you're ready to try it. It's a worthwhile experiment and I would like to hear differences between them. Believe me. #Failing ears #SAD!


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 Post subject: Re: Passive crossovers
PostPosted: October 29th, 2017, 4:57 pm 
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Joined: July 17th, 2016, 6:24 am
Posts: 479
Jim,

Those two statements of mine you quoted are scientific facts, nothing to do with DBTs. If you wish I can post spice models once I get back home.

I will create a new thread about blind testing for audio when I get a chance.

Right now, my system is so transparent every little change is effecting the system so much I keep remembering your statements about Charlie’s system and how a simple cable change effects it.

I don’t expect to settle on the crossover for few more months. My main focus will be on the notch filter for the horn. Recently, I got the tubes recommended by Walt on the preamp which significantly increased the HF energy.

And finally, don’t worry about ears. Ears do not determine how much you enjoy music and audio system.

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Shashi


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