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Pre-Amplifier with Active Crossovers

Wharfedale Linton Heritage Speakers

sridhar-v

Active Member
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Sep 26, 2009
Messages
145
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Location
Pune
Hi All,

I had done some research & amps/speakers auditioning & came to the conslusion that i need to make the setup to suit my requirements.

My thinking is as follows:

System will be basically a 2.1 or 2.2 stereo with provision for occasional 5.1 type use.

Likely sources are DVD player(movies & music), Ipod, Laptop (for music & movies including HD) & later on a BD player.

The inputs that the unit will have are 2 optical, 2 Digital co-axial (RCA), 3 stereo inputs.
The digital signal will be decoded by a DAC chip & the Front Left & Front Right signals will be forwarded to the crossover module. The centre & surround signal will be directly forwarded to the amplifier inputs.

The crossover module will have a 4 way filter as follows:
0 - 100 Hz for subwoofer
100-800 Hz for mid bass
800-4000 Hz for midrange
above 4000 Hz for tweeter.

Needless to say there will be seperate crossover for L & R channels. Also there will be some provision for fine tuning the crossover frequencies & damping to match the speakers.

Output from each range will go to a seperate amplifier module which will be connected to the speaker.

LAter on I will add amplifiers for the centre & surround channels ( no active crossovers for these.)

IS there any benefit of having seperate subwoofer for the L & R channels?

Is there anyway of extracting digital (optical or co-ax) signal from the IPod?

What do the experts think of this plan?
 

hemantwaghe

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Sep 23, 2007
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sarith

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Nov 11, 2009
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Thiruvananthapuram, Kerala
Hi All,

I had done some research & amps/speakers auditioning & came to the conslusion that i need to make the setup to suit my requirements.

My thinking is as follows:

System will be basically a 2.1 or 2.2 stereo with provision for occasional 5.1 type use.

Likely sources are DVD player(movies & music), Ipod, Laptop (for music & movies including HD) & later on a BD player.

The inputs that the unit will have are 2 optical, 2 Digital co-axial (RCA), 3 stereo inputs.
The digital signal will be decoded by a DAC chip & the Front Left & Front Right signals will be forwarded to the crossover module. The centre & surround signal will be directly forwarded to the amplifier inputs.

The crossover module will have a 4 way filter as follows:
0 - 100 Hz for subwoofer
100-800 Hz for mid bass
800-4000 Hz for midrange
above 4000 Hz for tweeter.

Needless to say there will be seperate crossover for L & R channels. Also there will be some provision for fine tuning the crossover frequencies & damping to match the speakers.

Output from each range will go to a seperate amplifier module which will be connected to the speaker.

LAter on I will add amplifiers for the centre & surround channels ( no active crossovers for these.)

IS there any benefit of having seperate subwoofer for the L & R channels?

Is there anyway of extracting digital (optical or co-ax) signal from the IPod?

What do the experts think of this plan?

2.2 is the way to go....doing it for years....I like it better
 

sridhar-v

Active Member
Joined
Sep 26, 2009
Messages
145
Points
28
Location
Pune
Hello Hemanth,

Thanks for the links.
As for budget, I am in the process of establishing the fesibility & details of what hurdles I will face.

I have an electronics expert who makes such odd amps. So once I freeze the specs I do not foresee any major problems.
 

sridhar-v

Active Member
Joined
Sep 26, 2009
Messages
145
Points
28
Location
Pune
Hello Cranky,

As far as Speakers are concerned I have considered the two options:-

First is to use standard speakers - I have shortlisted the JBL ES80 & Whaferdale Diamond 10.7.

Second option is to build my own speakers using available drivers & custom box. This currently is not looking that attractive.

I have a contact who makes special amps & speakers as per customer requirements. He has made quite a few such odd requirements and is familiar with the electronics. So the technical parts will be handled by him. We are looking into salvaging a used av unit unit for the multichannel processing & Dolby NR.

Since my original post I have had one round of discussion with this person & we have decided to use the active crossover for the 100 & 800 Hz. only. We will use the passive crossover of the speakers for the higher range frequencies. So in short I will be using a tri-amp setup.

Most of my listening will be for Music both Indian & Western. Will a low level crossover frequency of 70 Hz be appropriate?

My mains source wil be a laptop or music server. I will just make a provision for connecting the Ipod.

As for the drivers ideally I need a separate mid bass & midrange. I am looking for drivers with Glassfibre or Kevlar driver cone material. The JBL uses a Polypropylene mix but I was impressed with its tonal quality. I still have to audition the Whaferdales.

I am a mechanical engineer so I am quite blank about electronics. From whatever I managed to research on the web I came to the conclusion that midbass frequencies upto 800 hz need larger movements of the cone compared to signals of the higher freqs. So seperating out 100 to 800 hz into a speaker prevents doppler distortion of the midrange frequencies.
4000 high crossover is chosen as this seems to the average starting points of most tweeters.

I also had a look at the frequency responce grapha of some HIVI & Peerless drivers which sort of reinforced my conclusions.
 

sridhar-v

Active Member
Joined
Sep 26, 2009
Messages
145
Points
28
Location
Pune
Hello Cranky,

have found this link for a 5.1 decoder:

h__p://www.alibaba.com/product-free/11637437/AC3_DTS_Decoder_for_True_5_1_Channel_Multi_Connector.html

ur comments please.
 

sridhar-v

Active Member
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Sep 26, 2009
Messages
145
Points
28
Location
Pune
Hello Sarith,

When u say 2.2 are u using seperate subwoofers for L & R channels?

What is ur set-up like & at what frequencies do u crossover the various drivers.?

Have u got any measurements on how low tabla (especially the large one) frequencies go?
 

suri

New Member
Joined
Mar 15, 2009
Messages
2,259
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Location
kannur
Hello Cranky,

As far as Speakers are concerned I have considered the two options:-

First is to use standard speakers - I have shortlisted the JBL ES80 & Whaferdale Diamond 10.7.

Second option is to build my own speakers using available drivers & custom box. This currently is not looking that attractive.

I have a contact who makes special amps & speakers as per customer requirements. He has made quite a few such odd requirements and is familiar with the electronics. So the technical parts will be handled by him. We are looking into salvaging a used av unit unit for the multichannel processing & Dolby NR.

Since my original post I have had one round of discussion with this person & we have decided to use the active crossover for the 100 & 800 Hz. only. We will use the passive crossover of the speakers for the higher range frequencies. So in short I will be using a tri-amp setup.

Most of my listening will be for Music both Indian & Western. Will a low level crossover frequency of 70 Hz be appropriate?

My mains source wil be a laptop or music server. I will just make a provision for connecting the Ipod.

As for the drivers ideally I need a separate mid bass & midrange. I am looking for drivers with Glassfibre or Kevlar driver cone material. The JBL uses a Polypropylene mix but I was impressed with its tonal quality. I still have to audition the Whaferdales.

I am a mechanical engineer so I am quite blank about electronics. From whatever I managed to research on the web I came to the conclusion that midbass frequencies upto 800 hz need larger movements of the cone compared to signals of the higher freqs. So seperating out 100 to 800 hz into a speaker prevents doppler distortion of the midrange frequencies.
4000 high crossover is chosen as this seems to the average starting points of most tweeters.

I also had a look at the frequency responce grapha of some HIVI & Peerless drivers which sort of reinforced my conclusions.


hi sridhar_v,

loudspeaker design is a black art and most forays into this result in sub-optimal results.

one comment i must needs make - the best results are had with the best tweeters - and these tweeters can work from 1500 Hz and up. - really, the foundation (and integration of other transducers) of the loudspeaker rests on the quality (and range) of the high frequency transducer.

Two-ways are the best compromise - for other options visit -

Linkwitz Lab - Loudspeaker Design

well, IMO:)
 

kaushik

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Mar 3, 2008
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sridhar-v ,

There are ways to do things in a smarter way ...

leave the dolby part to a AVR..

fine tuning good audio active circuits is not easy
but u can build one , fine tuning to reach mid level optimal performance should be possible.


I think you need to have the speaker curves if using a ready made set of speakers.

there are 2 hurdles
1) if DIY : Drivers need to be imported (waste of money in shipping)

2) measurements of the speaker response ... need to make a setup ..with good microphone

From my experience i have found that many things are theoritically impossible to get to work properly by individuals , but are possible ,just it takes time.
 

sridhar-v

Active Member
Joined
Sep 26, 2009
Messages
145
Points
28
Location
Pune
Hello Suri,

The reason I am trying to go for an active crossover setup is because I have found that most passive crossovers leak, especially for the lows. Also by having seperate amps I will be able to adjust the amplification for each freq range.

Also I have found that using amps & speakers at 25-30% of rated capacity seems to give the best sound quality.

I have setup a 2 way speaker, with outboard crossovers, in my santro car. After some tinkering I have managed to get its sound quality up to very good levels."" all the purists are going to flame me for me next few words" - I actually found this Rs 4550 speaker setup better than & B&O 2 way bookshelf I auditioned recently.

see http://www.hifivision.com/car-audio/1406-urgent-help-car-audio-please-sos-2.html for some images
 

sridhar-v

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Sep 26, 2009
Messages
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Location
Pune
Hello Cranky,

Many thanks for the feed back. Ur comments set me thinking & I did some research on the range of frequencies of Indian Music (both voice & instruments).

I agree with you re the crossover frequencies. So now I am planning for first crossover around 70 Hz, second at around 350 Hz & high at 4000 Hz.

I will now start looking around for speakers that fit these requirements.

What I find amazing is that the 2 speakers I had shortlisted have set their crossovers @ 800 Hz. Seems like they were designed by a committee chaired by the cost cutting accountant.
 

sridhar-v

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Sep 26, 2009
Messages
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Points
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Location
Pune
Finally I have managed to clear my thoughts on the specs. I will be using a Behringer CX3400 available from Audio Plus India. (www.audioplus-india.com). As the crossover frequencies are adjustable i can play around & work out the best combination I need.

I am looking for a 3 way speaker with 8" bass, 2*5.25" for midrange & 1" tweeter. Do not need crossovers. So I may land up buying a standard floor stander & ripping out the passive crossovers. Any suggestions?

Now I have to search for a good cost effective 6 channel amplifier. I need 2*50 + 2*35 & 2*10 watts rms capacity. Any leads?

Thanks
 
Last edited:

sachi

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Aug 4, 2006
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Portland, Oregon
what are the hurdles towards good SQ while using active Xo. I have a set of tower speakers with totally crap xo , want to replace the xo than to mod it, someday .

You know, now that I did build a 3 wa active speaker , I would have done so many things differently if I were to do it again..

1> The main source of the quality of a speaker system, active or passive is still the enclosure or not (if you go open baffle, got to listen to the Emerald Physics CS series to appreciate what can be achieved).

2> The quality of the crossover without a doubt matters as well. It is generally preferred to have 4th and higher order crossovers when you go active. Mainly cause you can since the restrictions that are in place in a passive crossover situation is not present.

3> Amplification..this matters a lot when it comes to active speakers, more so than passive ones. For the woofer especially the damping factor of the amplifier actually matters for active configurations. A chip amplifier just won't cut it here. I'd say a nice Class AB solid State ought to do the job here. I'd go for a pair of tube hybrid amps for the mids and tweeters.

There is some opinion that a passive first order crossover between the mids and the tweeters might be better technically, (if the drivers are chosen well ) giving a more natural, musical sound. I haven't experienced this myself, but I remember reading this when I was going about designing my own speakers.
 

kaushik

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sachi,

I m sad that getting quality drivers and many of the components is not possible for me at this point of time due to cost ..

however i will initiate a basic one after my DAC is done.


EDIT: Thank you for the detailed information,this will help all of us ..
 
Last edited:

sridhar-v

Active Member
Joined
Sep 26, 2009
Messages
145
Points
28
Location
Pune
I am going thru this proj based mostly on my hearing test 7 some rudimentary knowledge of electronics. I have found that most speakers have compromised passive crossovers that leak on both sides of the crossover frequency. Mostly 1st order designs with suboptimal sizing.

So I decided to go in for active crossover setup. The Behringer is a 4th order Linkwey-Ritz with 24Db/octave for all 3 x-over points.

Sachi's point regarding class AB amp for woofer is important. Will keep in mind.

Regarding speakers - if I do not get anything suitable I am planning to use Pioneer Car Components (1520C for tweeter & bass/mid range) & a 8-10 inch subwoofer for the low frequencies. Will chuck out their crossovers. My hunch is that as these are very stiff drivers & are designed for a harsh environment of car cabin they will not be affected significantly by shortcomings in the cabinet sizing & design.

My friend who will be looking into the toatal electronics cannot digest this as he has Paper Cone drivers drilled into his head from his engineering days. But, based on my experience with components in my Santro I have decided to take a risk.
 
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