Can this be right? Passive versus Active Subs
Discussion
I need a new 5.1/7.1 surround for the TV room, but having spent a fair chunk last month on Hi-Fi budget is somewhat limited.
My current setup has a passive sub, so bare wires in to the Amp as do all the satellites. Called Sevenoaks today to explain that I know I should have an active sub, for now I'm going to keep my original speaker so needed an amp that could run a passive.
They told me no worries, get the Denon 1912 and run the sub direct from the front channels, so put a splitter on the wire from the sub and then out to both fronts. Kind of makes sense, but would it really work?
My current setup has a passive sub, so bare wires in to the Amp as do all the satellites. Called Sevenoaks today to explain that I know I should have an active sub, for now I'm going to keep my original speaker so needed an amp that could run a passive.
They told me no worries, get the Denon 1912 and run the sub direct from the front channels, so put a splitter on the wire from the sub and then out to both fronts. Kind of makes sense, but would it really work?
Are the front speaker crossovers in the speaker or in the amp.
Subs need low frequencies so you'll either need a coil or if the crossover is in the amp and it's only giving mid and top to the fronts then it wont work very well at all. Can you not just buy a mono block for the sub?
Personally I run a 2.0 with a seperate sub on passive crossovers (quad rogers b&w) obviously the full ranges have their own crossover inside each speaker as well. It sounds great and is simplicity itself
Subs need low frequencies so you'll either need a coil or if the crossover is in the amp and it's only giving mid and top to the fronts then it wont work very well at all. Can you not just buy a mono block for the sub?
Personally I run a 2.0 with a seperate sub on passive crossovers (quad rogers b&w) obviously the full ranges have their own crossover inside each speaker as well. It sounds great and is simplicity itself
I think that what they are suggesting is that if you want to use your existing passive sub then forget about the .1 content (LFE or Sub Woofer) of the Dolby Digital processing and set up the amplifier to provide full range to the front speakers. The sub can then be connected to the front speaker output and will reproduce the low frequencies. Not an ideal solution as bass notes take a lot more power to reproduce so if you are sending full range to the fronts so that they will power the bass the sound could become compromised. You are also not going to benefit from the LFE (or .1) content of anything that has it. A far better solution would be to use a powered sub connected to the amplifiers LFE line output.
hman said:
Subs need low frequencies so you'll either need a coil or if the crossover is in the amp and it's only giving mid and top to the fronts then it wont work very well at all
It will do no harm sending higher frequencies to a passive sub. Sending bass to high frequency drivers is another thing altogether!!Some passive subs have internal crossovers, some just rely on the natural HF roll off of the speaker
If you set your amplifier to 5.0, (No sub) the low frequencies should be diverted to the main channels so you're not losing much. Bridging the two fronts to power the sub was/is quite normal from what I remember. Just set the speakers to 'large' in the options menu (if possible) so they get the full range of sounds.
Sparky137 said:
It will do no harm sending higher frequencies to a passive sub. Sending bass to high frequency drivers is another thing altogether!!
Some passive subs have internal crossovers, some just rely on the natural HF roll off of the speaker
you wont damage the sub with mid and high...Some passive subs have internal crossovers, some just rely on the natural HF roll off of the speaker
but as I say it wont work very well at all
hman said:
you wont damage the sub with mid and high...
but as I say it wont work very well at all
Why not? Some of the older audiophile speakers only had crossovers on mid and high range speakers and they still outperform many of todays speakers. In many cases the design of the enclosure will attenuate high frequencies making a low pass crossover unnecessary (coupled cavity for instance). The majority of coaxial and triaxial car audio speakers only use a high pass crossover.but as I say it wont work very well at all
Sparky137 said:
The majority of coaxial and triaxial car audio speakers only use a high pass crossover.
Because they are woofers (or mids and tweets as ICE guys call them), not sub woofers .Have you looked at a modern subwoofers frequeny response- things get bad pretty quickly when you get into the midrange.
Years ago many larger speakers were used as woofers, not subwoofers, but due to their size they could give adequate bass repsonse as well.
hman said:
Because it sounds truly AWFUL for starters, which is why we have passive or active crossovers to seperate the signals nowadays.
You have missed the point and need to understand a bit more about speaker design. As said, many passive sub's don't have crossovers, they rely on frequency response of the drive unit(s)and cabinet design to attenuate the HF content. As for "which is why we have passive or active crossovers to seperate the signals nowadays". Do you think that this is new technology or something? Crossover networks have been around for nearly the same length of time as the moving coil loudspeaker itself. Active crossovers only slightly less time. The main limitation of a passive sub is that its sound cannot be electronically tailored to match the speakers it is being used with in the same way an active sub can. Yes they are a compromise but they do not sound "truly AWFUL" just because there is no crossover!. A lot of tuning can be done by room placement. Keeping them away from corners tidies the bass up considerably, placing them behind soft furnishings well attenuate the HF content even further. I have studied speaker design for many years and built a number of custom sub enclosures for clients for both home and car use (car ones are very different due to the transfer functions of the car interior), both active and passive. I pride myself that the designs I have created give subs such as those built by REL a run for their money so I hope I understand how these things work.Many purists believe that less is more when it comes down to speakers and crossovers. Go and listen to a pair of Lowthers in a folded horn enclosure driven by a six watt valve amp and you will see what I mean. Not many high tech speakers and amps can come close to their sound quality and they are a design that is very old and there is no crossover.
What about going from the LFE output to a stereo amp input (you could use a splitter to get 2 phono connectors so both channels working) then you could connect one or even two passive subs to that amp and it would be amping the correct LFE signal and you have an extra volume control to tweak the levels aswell.
^^^^
What he said.
I am running 3 passive subs from a dedicated amp. (2 LFE channels) The LFE channel from the pre amp runs to a Behringer amp (which is dedicated for the subs) and this then powers the subwoofers. The subs are then integrated into the system using the onboard Audyssey equalisation which balances the sound.
This way you could keep your passive sub if you are so inclined and allow the receiver to power the mid and high range which is a lot less demanding on the system
ETA This is the one I am running but there are models with a bit less power if required.
http://www.behringer.com/EN/Products/EP4000.aspx
This one quite happily runs 2 15 inch subs and 1 18 inch.
Just need to watch out for fan noise although it can be modified to run quieter. Loads of info on doing it on web
What he said.
I am running 3 passive subs from a dedicated amp. (2 LFE channels) The LFE channel from the pre amp runs to a Behringer amp (which is dedicated for the subs) and this then powers the subwoofers. The subs are then integrated into the system using the onboard Audyssey equalisation which balances the sound.
This way you could keep your passive sub if you are so inclined and allow the receiver to power the mid and high range which is a lot less demanding on the system
ETA This is the one I am running but there are models with a bit less power if required.
http://www.behringer.com/EN/Products/EP4000.aspx
This one quite happily runs 2 15 inch subs and 1 18 inch.
Just need to watch out for fan noise although it can be modified to run quieter. Loads of info on doing it on web
Edited by rex on Monday 14th May 23:16
Forgive me if I've missed it somewhere in this thread, but what connections are on the passive sub? If there is only one pair of connections, then joining both your front speaker outputs to a single pair of connectors on the sub will short the left and right signals together. While it may not damage the amp, you will at least end up losing the stereo effect from the front left and right. If there is a speaker in and outputs for the left and right then this means you can do what Sevenoaks suggest as there would be a crossover built in.
If you have to do this without a crossover, I would suggest that you use the centre speaker connection, with it set to 'large' in the setup menu, as most bass tends to be directed towards the centre of the stereo pair. This may still cause issues if you can't select 'small' for your left and right speakers as you will lose some bass that they won't be able to produce. As a stop gap it would do for the time being, hopefully there is some kind of a crossover in the sub, though the centre will still be fed with the sub bass as well which means you need to be sensible with the levels you use it at or risk overdriving the centre.
If you have to do this without a crossover, I would suggest that you use the centre speaker connection, with it set to 'large' in the setup menu, as most bass tends to be directed towards the centre of the stereo pair. This may still cause issues if you can't select 'small' for your left and right speakers as you will lose some bass that they won't be able to produce. As a stop gap it would do for the time being, hopefully there is some kind of a crossover in the sub, though the centre will still be fed with the sub bass as well which means you need to be sensible with the levels you use it at or risk overdriving the centre.
Yes so it is a bit confusing.
The (passive) sub only has 1 wire (well 2 wires joined, one plain and one with a tracer) out of it, so the plain one goes to the black clip in the back and the one with the tracer goes to the red clip in the back (might be other way round it's been so long since I looked).
What the guys at Sevenoaks are saying is. Split the plain wire to each left and right plug on the back of the amp and split the tracer wire to the other plug on the back of the amp, Bob's your Uncle. Now I've no reason to doubt them, but it just doesn't seem right to me.
Running it to the centre seems to make much more sense
The (passive) sub only has 1 wire (well 2 wires joined, one plain and one with a tracer) out of it, so the plain one goes to the black clip in the back and the one with the tracer goes to the red clip in the back (might be other way round it's been so long since I looked).
What the guys at Sevenoaks are saying is. Split the plain wire to each left and right plug on the back of the amp and split the tracer wire to the other plug on the back of the amp, Bob's your Uncle. Now I've no reason to doubt them, but it just doesn't seem right to me.
Running it to the centre seems to make much more sense
If you wire it as they suggest you will be joining the left and right amplifier channels together which will probably result in a big bang!! I assumed that your sub either had a dual voice coil or a pair of speakers in one box thus giving two channels of operation. Wiring it to the centre channel normally won't work as the centre is a dialog channel and has the bass that is fed to it limited. It may be possible to configure it as a full range channel which would allow the sub to work if there is bass content present with the dialog - not normally the case though. As it is you will only be able to use your sub on one of the left or right speaker outputs to get any bass signal to it - not ideal. I think the best thing that you can do is not use the passive sub and wait until you can get an active sub. Often they can be bought on ebay for very little money.
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