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Old 2nd April 2006, 03:15 PM   #1
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Default DCX with subwoofer

DCX2649 with subwoofer Post #1
Dear all,
This is my 1st post here. I search info abt DCX finally I got the most info here..

I got questions abt DCX2496 hope you all can help me.

I had read some posts here reco'd put a attenuator (Is that a volume control? )at DCX2496 output in order to gain back the possible dynamic loses when the analogue input of the DCX2496 is too low for its AD to operate optimaly if connection chain is:

pre-amp-->DCX-->attenuator(volume control?)-->power amp. (Correct me if I am wrong here)

I got a Active sub with volume control but without build in cross-over.

I plan to use DCX as an active cross-over for my sub. If I connect my sub as:

pre-amp-->DCX-->sub

My question is:
1. Do I stil need a attenuator/volume control since my sub got a sub volume control?
2. by adding a attenuator, do I need to vary the level of attenuator every time my mastor volume on pre-amp is vary?
3. Do you think it is better for me to get an active anolugue x-over like CX2310 or pardigm x-30 rather than DCX if I cross my sub at below 45Hz?
4. What is the actual differences between 18db/oct and 24s/oct x-over slope? If I want my sub augnment to my main speaker natural roll off bass below 45hz, which one is better for the job?

Please help me


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Old 2nd April 2006, 04:42 PM   #2
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If you run: preamp (with volume control) --
DCX ..........sub
L......amp...satellites


then you do not need a volume control after the dcx.

I would it run this way, and sacrifice a little resolution because of bit reduction. There is an argument anyway how much this bit reduction really is audible - especially as we are dealing with low volume.

I have a volume control after the DCX, dual six gang pots, this way I can attebuate all the drivers at the same time.
The way you would do it controlling your subwoofer independently from the satellites is rather cumbersome and also changes your total sound everytime you change volume - somtimes too much, sometimes too little bass. Not very practical.

If you use an attenuator/volume control after the dcx, you set the volume control at the preamp once to one setting and don't touch that dial again - sort of a level adjuster - and use the attenuator as a master volume control.

I ran my dcx at 48db/octave. When you choose steeper slopes, your driver has then only to deal with the frequencies he is designed for, and not with residues of frequencies he is uncomortable with. It also means the power of the amp driving this driver can dump all the power into this frequency band, and not waste power on frequencies you do not want to to have reproduced by this driver anyway.

Analogue xovers with steep slopes had problems with phase stability if I recall correctly. This does not seem to be a problem with digital x-overs.
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Old 2nd April 2006, 05:09 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
your active sub with it's own volume control negates the need for an extra attenuator after the DCX.
Set up the DCX for maximum unclipped input and throughput until it exits as analogue then into your sub. Adjust the sub until the bass balance is correct. and leave alone.

Now your pre-amp is your normal volume control. The disadvantage of using the pre as your volume adjuster is reduced resolution through the DCX but since most of your information is bypassing the DCX I think you will not notice the loss in performance.

There may be a couple of problems with your proposal.
1. the DCX is, arguably, poor at transmitting sub-bass signals.
2. the high output (+22dbu) 10Vrms may overload your sub input before your inbuilt attenuator, but it depends on how they have organised the circuit.

However, can I suggest a couple of alternatives.
Build an analoque 4pole low pass active filter (PCBs available as a group buy very soon).
Consider increasing your crossover one or two octaves to take some load off your existing speakers and let the sub inherit this load. 80Hz to 150Hz would help a great deal here. You now need a low pass for the sub and a high pass for the main speakers. Twice as much work/expense but possibly more satisfactory. This could be added afterwards rather than all at the beginning.

Finally, your DCX is being wasted for a single channel low pass duty. It would have 5 unused channels, but then you would never run out of memory capacity.
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Old 4th April 2006, 11:13 AM   #4
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Thank you Audio and Andrew.

The high out put of DCX is knocking my head...I think I will going to get an analogue x-over to avoid all the worries.

If I got a munually variable xover in 18db/oct slope from 35hz to 120hz. How can I know the axact x-over point instead of guessing? For example, if I want cross 43Hz, how do I know I have reach that point? If SPL meter can tell?

Thank you!
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Old 4th April 2006, 12:25 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
why 18db/oct (3pole)?
This will force you to connect one of your speaker drivers out of phase.
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Old 5th April 2006, 03:02 AM   #6
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Hi Andrew.
I currently got this :
Click the image to open in full size.

A variable lowpass from 35hz to 150hz 18db/oct slope with two mono output which only 1 output is connected to internal variable phase adjustment from 0 to 180 degree.

As picture show, the variable lowpass nob is unlabeled. So I wonder how can I know if I want to cross at 43hz?

In addition, this unit summed stereo input to a mono out. Can I mod the summed mono input to stereo input?


The spec is
http://www.paradigm.ca/Website/SiteP...Unit_Specs.htm
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