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Old 15th May 2012, 09:46 PM   #21
PRTG is offline PRTG  Latvia
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Quote:
Originally Posted by LafeEric View Post
A good example is the What is the ideal directivity pattern for stereo speakers? thread - 2200+ posts and counting.
I contributed a bit in similar thread where topic of directivity of dipoles. That was also quite a discussion until I jumped in with some dipole waveguide measurements. Have to work on them more elaborate, though.

Amazingly enough, audio gear seems to follow similar circular trend patterns as those of fashion industry. At the moment trend goes towards SET amps, hornloaded and waveguided speakers typical for nineteen 50-ties and 60-ties, and I believe also for 20-ties 30-ties. At 70-ties and 80-ties it was acoustic lenses and multi-angled drivers. So I wouldn't be very surprised if Karlson's folded pipe with that cute skirt-like frontal cut pops out again sometime soon as a major must-have issue.

Quote:
Originally Posted by LafeEric View Post

I too would be interested to see the results of this method - whether or not I had certain technical or editorial prejudi... err, misgivings.

PRTG - I also commend your patience and restraint.
LafeEric, thanks for your interest and friendly gesture. I was trained for patience at some point of my career, so no problem with that.. most of the time.
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Old 15th May 2012, 09:51 PM   #22
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Quote:
Originally Posted by Juhazi View Post
PRTG - are you going to create such a speaker? Please go on and show us your results!
Thanks Juhazi! All I needed was only one vote to go for it.

Ok, lets go with a minimalistic two-way speaker. Here is a plan.

I'll start with an easy (naturally matching) HF/LF speakers. Later as a side quest I'm going to do the same with a more difficult pair (only if it credible, clearly advantageous results are achieved with the "easy" speakers).

Now lets set target measurement values for the goal. Here is my proposal:

a) for phase-aligned method relative electrical phase shift should not exceed 7 degrees within 250Hz-12kHz range. No target for "typical" method is set here, still phase curves for drivers + filters are recorded for reference;
b) target f response to have maximum +3dB/-6dB on-axis deviation against ruler flat (in region mentioned);
c) Directivity will be measured with no target goals set. Results will be shown and analyzed after listening just to provide some food for thought;
d) Distortion values - same as c).

Measurement gear: licensed version of ARTA/LIMP + measurement box, Presonus FireStudio Mobile FireWire soundcard, Behringer ECM8000 mic, stereo gainclone "classic" amplifier (non-inverted), LCR multi-meter.

F response measurements will be performed outdoors with measurement SPL level 90dB @1kHz 3 meters away from speakers. Listening tests will be done at about the same SPL level but from 5m distance with distance between speakers being 2 meters and speakers turned at about 10 degrees inwards. SPL will vary from chosen material but will be kept within low-distortion range.

Now follows building plan for pair of test speakers.

1. First part of method (acoustical phase matching) will be done regardless of the second (filter building with and without electrical phase matching). First part involves creation of moderately wide baffle, HF speakers with waveguides, driver acoustic centers aligned vertically for first approximation).

2. Two different passive filters will be built by using different methods.

2.1 Phase-alignment method:

a) measure and study driver f response, impedance, and electrical phase curves;
b) add L-pad to match average sensitivity of drivers;
c) add resonance damping RLC notch to align the phase curves of drivers in range around HF driver's resonance towards set target phase alignment value.
d) add and tune Zobel or RLC filter for LF driver to align the phase curves of drivers at upper midrange and HF range towards set target values. Return to e) if d) makes negative impact on phase alignment made in c), re-tune both to achieve set target value;
f) re-measure f response and impedance curves of drivers;
g) choose crossover frequency at about half-octave above Fo of HF driver;
h) read driver impedance values at chosen crossover point;
i) calculate and apply 1-st order filters based on g) and h) values;
j) re-measure summed f response;
k) if response variation exceeds target value apply additional notch/shelving filter(s) to whole speaker;
l) make final summed phase adjustment by re-positioning of HF driver under pink/white noise.
m) re-measure summed f response to be sure it's still compliant against target values. If no, return to k) and tune parameters, if yes, proceed to blind tests.

2.2 "Typical" method:

a) measure and study driver f response and impedance curves;
b) add L-pad to match average sensitivity of drivers;
c) add Zobel for LF driver to achieve flat Z in HF region;
d) re-measure f response and impedance curves of drivers;
e) choose crossover frequency about 2 octaves above Fo;
f) read driver impedance values at chosen crossover point;
g) based on e) and f) calculate and apply 1-st order filters;
h) measure summed f response;
i) if response variation exceeds target values then correct LF Zobel to achieve the flattest f response. Restart at f) as we need to recalculate filter for LF to match impedance change at crossover frequency. Proceed further when target f response values are reached or changing Zobel/HF filter gives result that is closest to them;
j) Apply additional notch/shelving filter(s) to whole speaker if f response still doesn't achieve target values;
j) make final summed phase adjustment by re-positioning of HF driver under pink/white noise.
k) re-measure summed f response to be sure it's still compliant against target values. If no, return to i) and tune parameters again, if yes, proceed to blind tests.

So I'll leave the plan open for a week open for discussions and suggestions. Then I'll finalize it and proceed to the actual building.

Meanwhile I'll prepare similar plan on blind testing methodology.

Lets have fun!
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Old 15th May 2012, 11:08 PM   #23
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Quote:
Originally Posted by PRTG View Post
...Amazingly enough, audio gear seems to follow similar circular trend patterns as those of fashion industry.
That is because people seem to forget that the wheel has already been invented, refined, refined again, to the point where it is no longer recognized as a wheel. Thus, people come around and say, "Look what I discovered" and the process repeats itself. It's called short attention span and not learning from history.

Good luck with your endeavor, but it's all been done before, with varying degrees of success.
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Old 16th May 2012, 12:30 PM   #24
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Quote:
Originally Posted by sreten View Post
Hi,

The described "typical" way of designing a speaker is simply wrong,
its not the way its done at all. Neither is the "new" way of doing it.
Two wrongs don't make a right.

rgds, sreten.

So, it's a wrong, but not a new way of doing it? In other words, it is a persistant, but erroneous custom amongst loudspeaker designers? So, at least you are not blaming PRTG for introducing a new fallacy.

I am happy with everybody who is willing to invest time and effort in understanding how to design loudspeakers. I would like to commend again PRTG for his effort to put his thoughts on paper. He also invites critique -quo- That's about it! Questions, corrections and additions are welcome -unquo-. That's appropriately humble and almost scientific, to invite peer review.

I am disappointed with the tune adopted by some who consider themselves a step higher on the learning curve. I am convinced that loudspeakers designed by the method proposed by PRTG will come out all right. He may be overdoing it a bit with the design goal to have identical group delay of all drivers at all frequencies, but it will do no harm either.

Vinigar is nice to spice up a salad, but excreting it in public doesn't look good on anybody.

vac
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Old 16th May 2012, 07:01 PM   #25
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Quote:
Originally Posted by sreten View Post
Hi,

Quite frankly you are insulting those who have all been there and done
it before. Your rather large posts are are condescending / insulting to
those who have worked it all out before you, and much more, and
your perception of two separate approaches is just stunningly dull.
Personally I just don't get why would somebody be insulted if someone finds something already found and brings it up from debris of forgotten once again. If indeed somebody had described such method before and found it useful/useless, I'd be more than happy to drop the burden of building and testing and comparing. So please refer to the particular articles or threads so we can get into details and sort it out and eventually have happy ending for everybody

Regarding dullness - if you have found any errors already, please point them out. Remember that method two taken from reference (with minor improvement as I will use measured impedance values for x-over calculation not some predefined constants) in the beginning of the first post I personally find flawed and it is there for comparison's sake only.
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Old 16th May 2012, 08:23 PM   #26
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Quote:
Originally Posted by vacuphile View Post

....and almost scientific, to invite peer review.

vac
Hi,

Scientific peer review can be very vicious and can be very dismissive.

What is the crux of this thread when you sort the wheat from the chaff ?

Its being implied there is something sour in my attitude, perhaps there
is, that is because the presentation, full of assumptions and rules of
thumb, doesn't lend it self to simple useful comment.

AFAICT some alleged "typical" methodology of ignoring the tweeter Fs
impedance peak and choosing a x/o point of 4 x tweeter Fs is to be
replaced by a "new" methodogy of compensating the tweeter Fs peak
and using a x/o point of 1.4 x tweeter Fs as a better methodology.

It might be a better way of doing it if the "typical" methodology is
true, but it simply isn't, speakers aren't designed that way. Baffle
step is accounted for in the x/o, zobels are only used if needed,
mid and treble Fs impedance peaks are compensated if needed,
and x/o points are not chosen simply based on driver Fs's.

The holes in the assumptions are there to make the conclusion seem
reasonable, and that is simply not how it actually works scientifically.

rgds, sreten.
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Old 16th May 2012, 09:54 PM   #27
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Quote:
Originally Posted by sreten View Post
AFAICT some alleged "typical" methodology of ignoring the tweeter Fs
impedance peak and choosing a x/o point of 4 x tweeter Fs is to be
replaced by a "new" methodogy of compensating the tweeter Fs peak
and using a x/o point of 1.4 x tweeter Fs as a better methodology.

It might be a better way of doing it if the "typical" methodology is
true, but it simply isn't, speakers aren't designed that way. Baffle
step is accounted for in the x/o, zobels are only used if needed,
mid and treble Fs impedance peaks are compensated if needed,
and x/o points are not chosen simply based on driver Fs's.
Thanks Sreten, I found your comment very useful. "Typical" methodology was actually hard to describe as there are a lot of general recommendations floating around that are correct only to some degree. I'd re-define that "typical" approach states that flat F response is the only things that matters for good sounding speaker.

- BS is omitted intentionally because wide-enough baffle is used to get room help as already stated in introductory part;
- In my version of "typical" method Zobel is used along with its tuning against target frequency response flatness, so it also contains possibility of omitting it completely;
- Mid and treble Fs impedance peaks are compensated if needed - we need some criteria of why would we do it if flat F response is the only that matters;
- Sure, filter's x/o points cannot be chosen simply based on driver Fs's, but see my comment about general recommendations. But I see your point. So to have less degree of "apples to oranges" I'm going to change "Typical" so that x-over point will be chosen at the same F as for phase-aligned method.

How does that sound?
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Old 16th May 2012, 10:11 PM   #28
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Regarding recent cross-accusations my call is to keep the focus on topic. I don't see need to argue on why who wrote whom what way ago. We are underreacting and overreacting on lots of things everyday and for very personal reasons, so i'ts barely enough to think about our own attitude which gets easily missed when we start bothering about other's (like I'm doing right now). If somebody will be interested in outcome of this thread lets make it shorter to read, so we'll be saving a lot of time (most valuable asset for a life). Thanks!
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Old 16th May 2012, 10:25 PM   #29
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Quote:
Originally Posted by PRTG View Post
Regarding recent cross-accusations my call is to keep the focus on topic. I don't see need to argue on why who wrote whom what way ago. We are underreacting and overreacting on lots of things everyday and for very personal reasons, so i'ts barely enough to think about our own attitude which gets easily missed when we start bothering about other's (like I'm doing right now). If somebody will be interested in outcome of this thread lets make it shorter to read, so we'll be saving a lot of time (most valuable asset for a life). Thanks!
So sorry PRTG. I don't mean to appear argumentative, but I am genuinely curious just what sreten was on about. It must have been VERY important - it certainly sounded like you were hammering a stake into his soul - and in the interests of avoiding his cross hairs in the future, if that is possible, I thought I would make some inquiries.

I'm sure the normal bedlam will quickly resume after sreten clears this all up.
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Old 16th May 2012, 10:45 PM   #30
sreten is offline sreten  United Kingdom
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Hi,

Yes there are "typical" design approaches, differentiated by their
stupidity, and that is essentially my point. Proper speaker design
is now easy to do armed with the right tools and knowledge.

rgds, sreten.
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