# connect to DSP 1124P



## neophyte

i want to buy and use dsp 1124p like parametric eq for my velodyne spl1000, can i connect it from another subwoofer and its speaker level output? is it correct and good idea?


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## brucek

> can i connect it from another subwoofer and its speaker level output? is it correct and good idea?


Nope. The BFD accepts line level inputs normally fed from a receiver or processors subwoofer/LFE ouput.

brucek


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## neophyte

and if i use some resistor to decrease level of output signal from subwoofer? because i dont have receiver with pre out but 2.1 pc repro


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## neophyte

any ideas?:sad:


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## brucek

> any ideas?


Yes, it is possible to create a small circuit to accomplish what you're trying to do, but it usually takes some trial and error testing, combined with the abililty to solder and the specs of the subwoofer amplifier with regard to whether it is a bridged output and its power rating.

Your best bet would be to use a set of 5.1 speakers, thus enabling the sub out jack in that mode. Then you can tap the line-level output to feed the BFD and Vel.

If you simply used your 2.1 set of speakers as mains left/right and then added a powered center channel speaker, you could enable 5.1 mode to make the center/sub line out active.

brucek


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## neophyte

yes, but if i connect center+sw to my 2.1 speakers i will not have volume control together for all channels..

so, i try to use some resistor, but i dont know how much ohms..


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## brucek

> yes, but if i connect center+sw to my 2.1 speakers i will not have volume control together for all channels


You don't connect them to the 2.1 speakers, you connect them to the soundcard.

If you enable 5.1 sound in your Audigy 4 software, then all 5.1 line level jacks will be enabled and controlled by the main volume control.

I believe your present hookup would be like this? All you will be doing is adding a center channel speaker and your BFD sub to the red jack shown.









If you enable 5.1 sound the center / subwoofer jack as shown below will be enabled.











Use a cable that breaks out the red 1/8" stereo jack and one channel will be sent to the new powered center channel speaker and the other to the BFD.










you of course could add the rear channel speakers also, but not really necessary unless you're using it for movies.

Does this make sense?

brucek


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## neophyte

yes it wil be controlled by the main volume control, but on the sound card, not on my 2.1 speakers


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## brucek

> yes it wil be controlled by the main volume control, but on the sound card, not on my 2.1 speakers


By that you mean the volume adjustment on the speaker set themselves and not from the Windows volume control? Why is that a problem.....is it a convenience / location thing?

brucek


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## neophyte

no.its not, but then i have to have my speakers on full output and there will be a lot of noise in the low listening levels..


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## brucek

> then i have to have my speakers on full output and there will be a lot of noise in the low listening levels


Yeah, OK, this is one of the problems with some powered PC speaker systems. The amplifiers have extremely high S/N ratios.

So are you determined to feed a BFD from your sub speaker?

brucek


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## neophyte

yes iam thx


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## brucek

I hesitate to go down the road of telling you how to hook your BFD to a speaker since it is fraught with problems - the least of which is shorting out your speaker amplifier.

But either way, it's not that difficult.

There are a couple pieces of information that we need to know.

1. Is the Negative (-) terminal on the subwoofer speaker wire at ground potential?
This is essential since some amplifiers rely on a bridging technique to boost the power. I don't have a schematic of your speaker system with amplifier, so I can't determine this without you measuring it.
With the power off you need to measure with a multimeter on the lowest scale between the Negative (-) subwoofer speaker wire terminal (at the speaker) and ground of the amplifier. Be sure there is a short indicated.

2. What is the rated power (watts) of the subwoofer amplifier? This is necessary to roughly calculate the attenuation required to bring the signal to a line level that the BFD is familiar with.

3. What is the impedance of the subwoofer driver in ohms. (i.e. 8 ohms or 4 ohms)

3. Can you solder? If not, better forget it. 

brucek


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## neophyte

1. i dont have multimeter, but i will try to get some..
2. speakers are logitech z2300 thx, its written 2*40+120W:scared: 
3. 4ohm


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## brucek

OK good, just make sure about the ground on the negative terminal of the sub speaker......


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## neophyte

1. no its not. (ground of the amplifier-i took metal cooler on the back of the sub-is it right?)
2. 120W RMS 8ohm, 10percent THD
3. 8ohm


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## brucek

> no its not. (ground of the amplifier-i took metal cooler on the back of the sub-is it right?)


Don't really understand, but you must measure from the subwoofers negative speaker terminal to the amplifiers DC ground.



> 120W RMS 8ohm


Where did you find that the subwoofer driver was 8 ohms? Is it written on the driver?

brucek


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## neophyte

8ohm-its in the manual

i dont know where is the amplifiers DC ground. must i demount subwoofer?


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## brucek

Sorry, I don't know the physical layout of your sub. You would need to have access to the sub driver itself to get to its terminals and you also require an amplifier ground. Certainly the shield pin of any line level connector plug connects to ground. 

brucek


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## neophyte

ok i will try it

now, please write me what are the next steps, when the minus of the speker is grounded and when it is not. thx


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## brucek

> ok i will try it


Good. When you're able to establish that the negative lead of the subwoofer driver is at ground potential we'll carry on. There's no use otherwise, it's a showstopper.

brucek


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## neophyte

its grounded. what is the next step?


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## brucek

> its grounded. what is the next step?


OK, as long as the negative terminal of the speaker wire on the subwoofer driver is at ground, a simple resistor attenuation modification won't short out your amplifier when connected to the BFD.

Since the power specified is 120 watts RMS into 8 ohms, then we can assume by rough approximation that the maximum RMS voltage at the sub speaker terminals is about 31volts. (e=sqrt of resistance times power).

The BFD has a maximum input level when using the -10dBV switch setting of +2dBV which calculates to about 1.26vRMS. This is the level we need to attenuate to when the speaker is at its theoretical maximum output.

So, if we want to voltage divide the subs maximum speaker voltage of 31 volts we need to drop by a factor of about 24.6 = 27.8dB. 
So the speaker level needs a voltage divider (with appropriate input and output impedances) to produce a line level of 1.26vRMS. For this we can use the resistors shown in the diagram below. The 15K is close enough to the calculated 14.8Kohm when using 600 ohms as the output impedance. There's no power dropped across the resistors so 1/4 watts will do (but bigger if you find them easier to physically work with).

This has an acceptable output impedance of ~600 ohms and an appropriate 28dB attenuation. If you find the line level to the BFD too low, then you can increase the voltage output of the divider by increasing the value of the 600 ohms. I wouldn't go above 1K though.

Once you've connected the resistors to the speaker (making sure of the positive and negative speaker terminals), then connect shielded cable (with the cables pin going to the junction of the 15K and 600 ohm resistors and the shield connecting to the negative of the speaker terminal) and then terminate in an RCA connector (just cut the end off an old RCA interconnect and use that as the cable and connector). 

Plug the connector into a phono to mono 1/4" jack plug adaptors as shown below and then into the 1/4" input of the BFD.

If you short your amplifier out, you can't say I didn't give ample warning. 



















brucek


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## neophyte

ok thanx a lot

1 thing remains: is it possible to use all 24 filters of bfd for equalizing sub? and how to connect it?


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## brucek

Yes you can use 24 filters. Feed one output to the other input. There should never be an occasion when you require more than 12 filters though.

See this Guide

brucek


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