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Old 21st October 2006, 07:17 AM   #1
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Default Crossover nightmare......

Hi all.I am pretty good with wood, but when it comes to electrical stuff, i am a total IDIOT!!!!!!!!!! This is my nightmare.....So am asking you - PEOPLE WITH KNOWLEDGE AND EXPERINCE - if can someone help me with xover PLEASE....The drivers are Seas G18RNX/P (8L closed), SEAS 27TFFC (or T25FC001 Excel - still can not decide) and ScanSpeak 25W/8565-01 (76L closed).I would like to have the SS under 180HZ if possible.......Thank You in advance folks...........Hope U can help me.....



Danny
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Old 21st October 2006, 04:57 PM   #2
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In order for someone to help, the loudspeaker impedences need to be known.
Especially a graph showing the impedence vs. frequency.
You're likely to get some help then.

But crossovers are a *very* complex issue.
Help might still be limited.
Some issues are a matter of taste or philosophy.
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Old 21st October 2006, 09:40 PM   #3
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Quote:
Originally posted by myhrrhleine
In order for someone to help, the loudspeaker impedences need to be known.
Especially a graph showing the impedence vs. frequency.
You're likely to get some help then.

But crossovers are a *very* complex issue.
Help might still be limited.
Some issues are a matter of taste or philosophy.
Do-H.....ofcourse, the tweeter is 6OHM, bass/midrange 8OHM and woofer also 8OHM....i think that 2,5 way system should be tuned to 6OHM, but correct me if i am wrong........
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Old 21st October 2006, 09:59 PM   #4
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Quote:
Originally posted by myhrrhleine
Especially a graph showing the impedence vs. frequency.
This is important as the ratings you have listed are nominal and not actual. See what you can scare up on google.
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Old 22nd October 2006, 12:31 AM   #5
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Do you have the drivers allready .... or else why is it so important to use exactly those drivers ?
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Old 22nd October 2006, 07:31 AM   #6
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Danny,

Given your level of electronic experience, I wouldn’t recommend that you do a speaker project from scratch yet: And certainly not a 3-way. There are plenty of good kits around and if I were in your situation, then I would try one of those first. If you are careful and attentive and if the design you choose is well documented, then I am sure that you will learn many useful lessons that you can apply to future projects.

Personally, I would never start a crossover design without a complete set of measurements of each driver already mounted in the intended enclosure. Published data/curves are not valid because drivers behave differently in different enclosures, and the driver that you have, may not be identical to the one the manufacturer measured. Although, Seas and SS are among the finest for consistency and integrity, and therefore the driver that is measured is usually pretty close to the one that you will get. If the published curves for a driver were measured in a 12 litre closed box of unreported dimensions and construction, then the curve would only be valid if your enclosure were the same as that box – which you do not have sufficient information to duplicate. The best that you can do (without getting lucky) is close enough to useable that you would have to do a lot of tweaking to get a good result; you are more likely to get something not so serviceable. Sadly, many in similar situations (amateur and professional alike) suffer from hubris and “design” and build their speaker anyway. Of course, many would find it difficult or impossible to admit that their baby is Frankenspeaker and they try to rationalize their cognitive dissonance.

BTW: The Seas G18RNX/P is discontinued; is there a reason that you chose this driver? It is also a long throw driver being used as a mid above 180 or so; unless you are going to use all 6mm of X-max, I think that there are many more optimal mid-woofers (from Seas and others.)
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Old 22nd October 2006, 03:00 PM   #7
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Quote:
Originally posted by psych&sound
Danny,

Given your level of electronic experience, I wouldn’t recommend that you do a speaker project from scratch yet: And certainly not a 3-way. There are plenty of good kits around and if I were in your situation, then I would try one of those first. If you are careful and attentive and if the design you choose is well documented, then I am sure that you will learn many useful lessons that you can apply to future projects.

Personally, I would never start a crossover design without a complete set of measurements of each driver already mounted in the intended enclosure. Published data/curves are not valid because drivers behave differently in different enclosures, and the driver that you have, may not be identical to the one the manufacturer measured. Although, Seas and SS are among the finest for consistency and integrity, and therefore the driver that is measured is usually pretty close to the one that you will get. If the published curves for a driver were measured in a 12 litre closed box of unreported dimensions and construction, then the curve would only be valid if your enclosure were the same as that box – which you do not have sufficient information to duplicate. The best that you can do (without getting lucky) is close enough to useable that you would have to do a lot of tweaking to get a good result; you are more likely to get something not so serviceable. Sadly, many in similar situations (amateur and professional alike) suffer from hubris and “design” and build their speaker anyway. Of course, many would find it difficult or impossible to admit that their baby is Frankenspeaker and they try to rationalize their cognitive dissonance.

BTW: The Seas G18RNX/P is discontinued; is there a reason that you chose this driver? It is also a long throw driver being used as a mid above 180 or so; unless you are going to use all 6mm of X-max, I think that there are many more optimal mid-woofers (from Seas and others.)

Hi psych.........well, i made couple of speakers before.butt the xovers were all standart items from catalog......Butt when it comes to fine tweeking te xo...I can build a XO either 1st, 2nd, 3rd. order, butt as i read about the "Zobels" or what the hell is it....U see, i have a book, where it is all writen, i mean the simple XO with some atenuation on the tweeter (if you want to take couple off dB lower).And i want to use each speaker from known project,say the SS from a project whoever used it and applay the enclosure volume and XO on this driver, then find a project with G18RNX/P and do the same (i hope U understand...), and its not a 3-way, its 2 way with integrated subwoofer....
And Your last Q, the Seas G18RNX/P were a gift, and i dont want to throw them away.I also heard a set with this drivers and was impressed by the sound.
If you have any suggestions, that would be wery appriciated.thanks guys.
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Old 24th October 2006, 07:30 AM   #8
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Danny,

Crossovers that are standard items from a catalog are not likely to get you a good result. Catalog crossovers assume that the drivers are some imaginary ideals with perfectly resistive impedance and perfectly flat and limitless bandwith – you know what happens when you AssUme. Not only that, these are usually made with iffy components….
Borrowing an aspect of someone else’s “design” is taking a leap of faith. You would be accepting on faith that the “designer’s” self-reported success of the “design” was unbiased, reliable, accurate, etc. In addition, one aspect of a “design” will not be the same in isolation or another application; you are talking about a system which will behave as a system.
Impedance compensation circuits are used to allow crossovers to behave closer to their theoretical transfer functions; but you must be able to accurately measure the impedance curve of the enclosure-installed driver in order to properly design a Zobel (impedance compensation circuit) in the first place.

Tweaking the “design” after building it like you are planning, is definitely not an approach that a well trained, experienced professional would take. What you are attempting is very much a hit and miss – time and labour intensive approach that will likely not result in as good a speaker as is possible with drivers of this quality. The approach that you describe will also require an extensive collection of quality crossover components and an ability to rapidly diagnose a “condition” and prescribe a corrective crossover change. And, how do you propose to do this? By ear? How much time do you have? How reliable (in the scientific sense) are you perceptual abilities? Personally, I wouldn’t count on my auditory perceptual apparatus to behave like reliable test instruments; they are required to enjoy music, but you can’t count on them – I never could get a NIST traceable calibration certificate for them. Before I build a crossover, I prefer to try a lot of educated “what-ifs” in the “virtual” domain – which requires a complete set of measurements. I think that time and money is better spent on learning the required basics and using a measurement and simulation set-up – which need not be expensive to be useful.

I’m afraid that you are just renaming roses by calling your speaker a 2-way with integrated sub – this is still a 3-way in my book.
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Old 24th October 2006, 05:34 PM   #9
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Psych:
U are right.A profesional would do it this way....But correct me if i am wrong......When you fine tuning your speakers, are you after a superflat response or likely it should be pleasant to your ear?Why should I tweek it to some specs, if I DONT LIKE THE SOUND OF THAT?Some like crisp heights, some powerfull low bass, some like mild midd tones.........that why I want to fine tune the speakers to my ear,because the speakers are for me, i have no intention to sel them, or make some business.....
Once i asked a profesional how would he name a speaker with midbass reaching to cca 70HZ with extra driver for 30-120HZ....and he said 2-way with integrated sub......
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Old 25th October 2006, 04:34 AM   #10
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If a super flat response were the only factor of interest; then loudspeaker design would not be a particularly interesting or challenging (a)vocation. Nor would you necessarily achieve a good loudspeaker. Without denying its importance, there is so much more to a good speaker than the axial frequency response. In fact, many companies design for a specific axial response curve that is not flat – e.g.: BBC monitors.

Commercial interest is something else altogether; I am talking about the first principle, i.e.: what is the job of a loudspeaker?

A loudspeaker, in my view, should not be a device to make a particular type of sound and be a collection of distortions – euphonious or otherwise. Tweaking a speaker to a personal preference is like having a preferred wine – I’m sure that you have heard the analogy. This is fine for wine tasting, where it is about personal preference and there can be no such thing as a universally indisputable perfect wine. But the job of a loudspeaker is to reproduce a recording of a sonic/musical event – one to which there is an absolute and indisputable reference – namely the original sonic/musical event. How well the loudspeaker approximates that event is the goodness of that loudspeaker. And the design of which has a lot more to it than the axial frequency response.

A device intentionally tuned to be a less accurate reproducer of the original event is no longer “designed” to be a good loudspeaker. If you prefer a type of sound, I suggest that you choose your music to suit your taste. I think that creating that music is the job of the recording chain (artist, producer, recording guy – rarely an actual engineer.) Choosing your music is more like choosing wines to taste. Choosing your loudspeaker is more like choosing eyeglasses to see; albeit, much more complicated and challenging. This is why I believe that there is no such thing as a good speaker that is good for this or that type of music and not good for another. This just means that the speaker is not so good, period.

Of course, all of this must be viewed within the constraints of the possible and the practical and the commercial and the personal. A speaker that gets close while being attractive and affordable is a good design. A lavishly expensive and grotesquely styled speaker that has a particular set of colourations that is prized by a small number of aficionados, and is common in some corners of the “high-end” or “audiophile” community, is to me a poorly designed loudspeaker: Although, it may be a superbly well designed money making machine for the manufacturer.

If your goal is to make your own DIY version of this machine, then I really have nothing to contribute to your odyssey.
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