Biamp: Wich fc ?

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Hi, guy´s
One year ago I finished to build my first 2 way-speakers with XOP with fc=3Khz.
I used a titanium tweeter which It reaches 2Khz.
Presenty, I´m building an amplifier and, in the future, a XOA. Then I´m thinking in bi-amp.
For 2 way-speakers with the same tweeter that I described before, what is the optimal cut frecuency if I use a XOA? Could I use the same (3Khz)? I was reading the article
about bi-amp in Elliot Sound, but I´m little confused, `cause He uses 3 way-speakers.
Any advice will be appreciated
Thanks,
Marcelo.
 
Normally two way speakers would be bi-amped to the sub or subs at a frequency in the bottom range of the lower part of the two-way.

Usually, if you are using line level crossovers ( after the pre amp but before the power amps) up in the 3k range, that system is being tri-amped with a pair of amps for each range of lows, mids and highs -

Think about it along those lines and that will probably put you on track


Later

Ken L
 
Konrad said:
2 Way system with 8" to 3Khz. Consider the transfer-funksjon in your speaker filter before making line level filter, then it should bee possible to make near ore equal to your 'ideal response' (u know youre speaker data's i supose?):rolleyes:


Yes, I know the TS parametes of my woofer, `cause I have to measure them to design the box :) :) (They are not Vifa or ScanSpeak, they are made for a argentinian company and, in the beginnins, I didn`t trust very much in them until I visited the factory.... ;)
Anyway, I don`t have the data here, rigth now. Tomorrow I`ll show a picture of mi speakers, the TS and the filter that I buid.
See you
Marcelo
 
Well, I post all the information that I have:
Woofer 8":
SLP 90db/80W/8ohms
Qms 2.84
Qes 0.82
Qts 0.64
Fs 46Hz
Vas 49
I measured all this values. I found very good response from 80 Hz to 3.5k.
I used second order Bessel filter with:
Fc 2500hz
C 4.7uF
L 900mHy
Zobel Re 6.8 ohms and C 10uF

Tweeter:
3.75" Aluminum Bullet Horn with 1" Super Tweeter
SPL: 99dB/120W/4 Ohms
Frequency Response: 1.5k-25kHz

I use second order Bessel Filter (same values as above) and L-pad with
R1 5.6 ohms
R2 8 ohms

I had the frecuency response in my PC, but unfortunatly I had a problem and It dissapeared...

Anyway, I know that this speakers are more suitable for car audio use,but It`s the better that I can find here. Importation It`s almost imposible, `cause the economical situation`s of my country (2 years ago I earn u$2000, presently only u$700...devaluation). I have a pair of Audax Tweeters (AW01E01), but I`m going to use them with a 6" midwoofer.

Well, Dou you think that I can use 3K for XOA?
Or It will be better if I change the configuration to 3 way system?
Any advice will be appreciated.
Thanks,
Marcelo
 
Higo,

Theorically, the three ways seems to be the way for a fully optimized active system. I am in the same stage like you are, and I'm decided to build also a two way active crossed over in the same range of frequency (but 6" woofer). Most of the advantages of the biamping would appear, i hope, but seems to be that the 3ways are the way here. Which xover do you plan?
 
frugal-phile™
Joined 2001
Paid Member
Bill Fitzpatrick said:
Unless extenuating circumstances prevail, a passive network is the most practical and cheapest way to go.

Adding a separate amp for the tweeters still has the best potential for best sound...

Unless well planned and speakers well picked, a good passive XO is one of the hardest things to get right, and can present a really ugly load to the amplifier. With a complex passive & the low cost of some decent amps we are seeing, active can actually be cheaper in some cases.

I heartily recommend going active all the way.

dave
 
Cheaper my foot. The extra amp needed makes it more expensive and that doesn't count the crossover.

And it's just as hard to come up with the correct transfer functions with an active network as with a passive.

The load presented by a passive crossover is not that ugly.

I only use active for the high frequency crossover if I need to level match, tailor the curves in an unusual way or need a differential circuit.
 
frugal-phile™
Joined 2001
Paid Member
Bill Fitzpatrick said:
Cheaper my foot. The extra amp needed makes it more expensive and that doesn't count the crossover.

Certainly sometimes it can. But when you can build a gainclone, a simple Class A amp, or a nice little 6BM8 amp for <$100 compared to good inductors & caps that can easily top that price wise. With clever engineering the XO won't add much to the cost. And you also have to factor in that you can get away with a less costly midrange amp.

And it's just as hard to come up with the correct transfer functions with an active network as with a passive.

But it is a lot easier to get the active one working right because you have a nice resistive load to work into and not a reactive speaker with back EMF and such. I'd say getting an active XO tuned right is probably 1 or 2 orders of magnitude easier. The tuning of an active XO can also be a lot cheaper then tuning a passive XO... a small cap & resistor vrs a big inductor & cap...

[QUOTEThe load presented by a passive crossover is not that ugly.[/QUOTE]

Any crossover is uglier than directly into the speaker. Unless you are using something like a simple cap in series with a well-behaved tweeter, i'd consider active the way to go, and even then if quality is your main concern.

dave
 
Raka:
I`m planning to use second order Butterworth in Sallen - Key topology.

According to Rod Elliot article about biamp and your comments I think that I have to change my speakers. I mean rebuild them from 2 ways to 3 ways.
I have to change the box or do you think that I can use the same? I never design a 3 ways system... :scratch:. Any advice??

The tuning of an active XO can also be a lot cheaper then tuning a passive XO... a small cap & resistor vrs a big inductor & cap....

I`m totally agree with this. It`s easier to tunning the XOA

BR.
Marcelo
 
I think we know start system design... triamp and aktive all the way. Personaly i belive IC amps in an fully aktive design beats amplifier and passive x-over speaker's.
The main reason i think is that speaker element's parameter varies with motion and is therfore a komplex load and have more than frequensy as a variabel to the filter. And that an amplifier is more suited for that job than any passive filter output ever can cope with.:mafioso:
 
i think that there are few things which benefit sound more than bi-amping or tri-amping. i have bi-amped Linn Kelidh's driven by a Linn Majik and a Linn Power Amp -- I was able to audition both the passive xovr version of the kelidh's and the active xovr version before I decided to go with the biamped version -- I also biamped a set of the KEF reflex speakers (KEFB139/B110 and Audax Tweeter) -- now disused collecting dust in the basement/laboratory. The quad GC I was building was to use active XO but I haven't gotten around to finishing it.

Speaking of designing XOVR's I again refresh the list with the link to the beta at Analog Devices:

http://www.analog.com/Analog_Root/static/techsupport/designtools/interactiveTools/filter/filter.html

This is much more comprehensive than the design tool at Texas Instruments.
 
Made up a stat-var filter. Also made lovpas(30-600) and highpas (600-10K)freq adjustable. Then bass gain and mid Q adjustable. :nod:
At the end i figured it vise to add inverters at the same time. Then phase switch or balanced output is possible. Only one channel without power suply shown:
 

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