Re: Value for money: a digital XO?
May I add my 2 cents here... My first system was a siingle driver TDA2005 system
When I wanted to go for a 3 way system, I started agonising about how I would get the loudspeaker to sound just right, until I could'nt bear it any longer and I just went ahead and built it, using a generic 3-way active LR circuit based on 5532s (from elektor) and unmeasured cheap drivers (Bolton) and 6 gainclones. This may be an imperfect system for the guys who've heard better, but it gave me a great deal of happiness; I got re-aquainted with all my albums. Just hearing that heartbeat on Dark Side of the Moon was worth the effort 
Not bad for a first effort (both XO and the woodworking). So maybe you should give it a try IMHO, and see if you like it.
- Ashwin
tcpip said:
May I add my 2 cents here... My first system was a siingle driver TDA2005 system
When I wanted to go for a 3 way system, I started agonising about how I would get the loudspeaker to sound just right, until I could'nt bear it any longer and I just went ahead and built it, using a generic 3-way active LR circuit based on 5532s (from elektor) and unmeasured cheap drivers (Bolton) and 6 gainclones. This may be an imperfect system for the guys who've heard better, but it gave me a great deal of happiness; I got re-aquainted with all my albums. Just hearing that heartbeat on Dark Side of the Moon was worth the effort Not bad for a first effort (both XO and the woodworking). So maybe you should give it a try IMHO, and see if you like it.- Ashwin
Another thing about active crossovers is that IMHO as long as you are ok with fairly decent cheap op-amps (NE5532, NE5534, etc) the cost of the active crossover with be much cheaper than a passive one. Of course you need the amps, but a few extra gainclones is all you need. If you seriously use really good passive crossover components, and I firmly believe that you have to, then it should still be cheaper to go active.
Once you've had active, you never go back.
Pete
Once you've had active, you never go back.
Pete
cm961 said:
Will this be true starting with a two way?
I'm right now building one (6.5" and 1" tweeter). The plan is to explore both worlds, passive :I make my own inductors with almost free high quality cooper wire, so I don't have to buy a lot of expensive coils; and active: Gainclones with Passive XO.
I think that the passive biamping is one simple way, and to change the filter, you only have to change some caps and resistors in the input of the GC. I'm working on a layout that could admit "pluging" of the filter board, so you can change fast the XO.
My only concern about the biamping is if it's going to be worth the effort in a 2way design crossing about 2-3K
Although Ive only just spotted this thread now, ill still post my thoughts.
Passive vs active
My system was passive and then I went active, even though the passive system was not perfect in anyway, and chaging to active was a means to correct this active does bring about significant gains.
With regards to power, yes you need less watts to get the same SPL over a passive system as each amp only amplifies a part of the audio spectrum. Can my active go louder then the passive?? That is debatable, I would probably say with regards to raw SPL maybe by 2 or three dB. But its how the system goes louder thats important. When the level increased with the passive, the sound changed, getting harder, more confused and basically more unpleasent. This was not I dont think the amps clipping as per say but having a harder time. When driven active, the speakers reach about the same SPL, subjectively this sounds quieter simply because there is no CRAP in the sound.
I cant remember whos signature is something like play is loud as long as its clean.! But this is true!
The active system just increases in volume until your affraid turning it up any more will blow a driver. Without altering the sound one bit, it stays silky smooth without introducing hardness to the sound or any other artifacts associated with passive systems getting louder. Acitve just gets louder, thats it.
This is probably no doubt down to the tweeter having its own amp and never being driven hard at all. I know that giving the tweeter its own amp is important, because I have done semi active with the mid/tweet using one amp and the bass using another. Simply put active sounds better just try it and you will see.
5th Element Health Warning no.1 = clean loud sound is addictive - prolonged exposure to high SPL's can damage your hearing.
This above is important because when you go acitve you will generaly play the system louder. Why? because you can. Normally people back off on level because the sound becomes fatigueing, with active this simply doesnt happen (well with my set up is doesnt, and you dont need oodles of power either 80w on the mids and tweets, 200 on the bass which is overkill) so watch out with that volume control.
Passive vs active
My system was passive and then I went active, even though the passive system was not perfect in anyway, and chaging to active was a means to correct this active does bring about significant gains.
With regards to power, yes you need less watts to get the same SPL over a passive system as each amp only amplifies a part of the audio spectrum. Can my active go louder then the passive?? That is debatable, I would probably say with regards to raw SPL maybe by 2 or three dB. But its how the system goes louder thats important. When the level increased with the passive, the sound changed, getting harder, more confused and basically more unpleasent. This was not I dont think the amps clipping as per say but having a harder time. When driven active, the speakers reach about the same SPL, subjectively this sounds quieter simply because there is no CRAP in the sound.
I cant remember whos signature is something like play is loud as long as its clean.! But this is true!
The active system just increases in volume until your affraid turning it up any more will blow a driver. Without altering the sound one bit, it stays silky smooth without introducing hardness to the sound or any other artifacts associated with passive systems getting louder. Acitve just gets louder, thats it.
This is probably no doubt down to the tweeter having its own amp and never being driven hard at all. I know that giving the tweeter its own amp is important, because I have done semi active with the mid/tweet using one amp and the bass using another. Simply put active sounds better just try it and you will see.
5th Element Health Warning no.1 = clean loud sound is addictive - prolonged exposure to high SPL's can damage your hearing.
This above is important because when you go acitve you will generaly play the system louder. Why? because you can. Normally people back off on level because the sound becomes fatigueing, with active this simply doesnt happen (well with my set up is doesnt, and you dont need oodles of power either 80w on the mids and tweets, 200 on the bass which is overkill) so watch out with that volume control.
That's not half the story. There are big limitations on how accurate you can make a passive crossover, especially when you consider that at 1kHz the impedance may easily vary between 8-ohms at some funny angle, and around 10-ohms at some other funny angle, all within seconds. Why? Because as you turn up the volume, the other 99% of the power simply heats up the voice coils and their resistance goes up. The resistance goes up, the inductance stays the same, and hence: the impedance changes dynamically and all of the Zobel compensation circuits, L-pads, low-pass filters, high-pass filters, band-pass filters, notch-filters, mechanical time-alignment, and what-have-you? go wildly out of tune.5th element said:
I'm sure that some loudspeaker companies try to compensate for all the various effects of hot voice coils, but then what? The speaker then sounds worse at low volume, better at some medium volume, and worse again at high volume. The effects of the passive crossover "detuning" are cumulative, meaning that a precisely tuned and complicated crossover will only sound ok in a narrow voice-coil temperature range, before going out of tune.
In other cases, people swear by the good sound of big speakers with simple crossovers that are designed for very high power. If a loudspeaker has multiple drivers that are each rated for 150W, then obviously your ears will take a hammering before the heating effects are too noticeable. Combine a powerful loudspeaker with a crossover that's been optimized for operation at high voice-coil temperatures, and you get cringe-worthy reviewers' descriptions like: "these loudspeakers need a powerful amplifier to sound their best...", and other such stuff.
Bearing that in mind, it's not so much that active crossovers make speakers sound any better, they just don't have many of the extra problems that are unique to passive crossovers.
CM
can i invade this thread and ask a quick newbie Q
- if i
Do this,is this basicaly all i need to to know,to use an active filtered system on some Vifa 5" + 1" tweeter,( i forget the # numbers,they all seem so similar)
edit- i think its
D26TG05-06 1" textile dome
P13WH00-08 5" poly cone
can i expect ok resulst? i can get RTA and mic....
Does anyone have a walkthrough?
im not looking for monitor quality-just an improvement.
Thanks much appreciated!
Mike.e
- if i
Do this,is this basicaly all i need to to know,to use an active filtered system on some Vifa 5" + 1" tweeter,( i forget the # numbers,they all seem so similar)
edit- i think its
D26TG05-06 1" textile dome
P13WH00-08 5" poly cone
can i expect ok resulst? i can get RTA and mic....
Does anyone have a walkthrough?
im not looking for monitor quality-just an improvement.
Thanks much appreciated!
Mike.e
Welcome back, Gurudev. Will you please give your considered opinion and expert comments on the "Simple discrete unity gain buffer" which you started, after a fashion, and which has been waiting with bowed head for your comments?angshudas said:
Specially, some comments about distortion, PCB layout, decoupling caps for discrete circuits like this one, etc, will be most delightful.Tarun
Based on encouraging remarks from you and Ashwin, and building on Guru Angshu's divine guidance, I'm now halfway towards building a two-way with active analog xo. The driver choice and the xo frequency is Angshu's, and he's pleased with the results. (Which means I don't have to think any further, I can just do the donkey work.)Raka said:
The drivers we're using/have used are the Peerless India 60W tweeter and the Bolton 16SJW22 polycone midbass driver which the manufacturer calls a "sub-woofer" because it has a longish Xmax (6mm on either side, I think). There's also the 16IM22 or something, which is the same driver with a shorter air gap.
Angshu has crossed these two drivers over at 2.5K for his system, active LR4. I'm doing the same. He's also done the hard work of measuring the response characteristics of the drivers, and the T/S parameters too. (Bolton supplies nothing.) I know that with such manufacturers, each piece is different, and I should be measuring my units myself. But I've never done it, and I'm too lazy to do it at this moment.... I'm just assuming that Angshu's data will apply to mine. With this data, the midbass driver, in a sealed 20L enclosure, gives me an fc between 50 and 60Hz and a Qtc of 1.05 or so. I'll go with that, and apply a Linkwitz transform. I'll try to get to about 30-35Hz and a Qtc of 0.8 or so, if I can. This is the part where I'm expecting to do a lot of listening and tuning, partly because the calculated T/S parameters will not match the drivers.
The obvious limitation of this approach and this driver is getting high SPLs at low frequencies... you run out of excursion. Either you get a different driver, or you use more drivers. Driver choices are non-existent in India, practically, so I'm getting more of them. (They're inexpensive, at about USD 10.00 each.) I've decided to try a 40L enclosure with two drivers (maybe I'll do an MTM) and an 80L floorstander with four drivers, in TWWWW layout. I may not do anything about time alignment of the tweeter to the woofers, or do a stepped baffle, or get Angshu's time alignment circuit and put it in. Let's see; laziness will decide.
Currently, I'm in the process of procuring the midbass units straight from the manufacturer, again with Angshu's help. We live in a country where even dealers don't bother to replenish stocks, and tell you that they'll take 30 days+ to get you a set of drivers even after you agree to 100% advance payment and give a special order, and (I just discovered this) when the dealer commission is a 50% markup on the ex-factory price. So, with Angshu's help, I'm getting them directly from Bolton in Haryana.
Once I get the drivers, I'll start putting the pieces together. Currently I have a couple of Rod Elliott LR4 PCBs; I'll use one of those. For amplification, I'll use a LM3886 or LM3875 (non-inv) for the tweeter. For the midbass drivers, I'll either use one LM3886 for each midbass driver, or hook up four of them series-parallel and drive them through a discrete SS amp. For discrete amps, I will either use the Randy Slone ultra-low-distortion BJT design (a derivative of Self's blameless, I'm told) or his Opti-MOS design. The Opti-MOS will be the right power rating for four of these drivers, though the BJT blameless will probably be adequate for the two-driver approach. With sealed box and Linkwitz Transform, I guess I'll need some spare power to drive them.
For the box, I'm making it out of 25mm MDF. Front and rear baffles will be double-sheet, and side baffles will have 12mm glass sheets stuck on from the inside with Araldite. Hoping to do 2" radius rounded for both front vertical edges.
Pray for me. I need it.
And needless to say, comments invited.Tarun
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