Mulitple sub question

[mep]

I have a question about how to lash up a pair of subs to your preamp. As you all know, when you buy a sub it has inputs for both the right and left channels and the woofer has dual voice coils in order to handle both inputs. If you are running a siingle sub, you just run a pair or ICs from your preamp out jacks to your sub and plug them in.

My second sub is arriving today and now there are options. I can run an IC over to each sub and choose either the Right or Left input to jack into or, I can run the IC over to each sub and plug the IC into a Y-splitter so that I can plug into both the left and right inputs so I'm using both voice coils.

My question is what are people doing and is there consensus for the best way to hook up two subs? My gut tells me to use the Y-splitter.

 

[garylkoh]

I think that unless you are sure that the group delay through your power amp is exactly zero, you will get better coherence driving the speaker-level inputs on the subs by jumpers tapping off the speaker binding posts of your speakers. That way, the sub will "see" the same signal as the speakers, including whatever the speaker cables do to the signal (if any).

Subs generally have two inputs that sum, and if you are low-passing them at below 40Hz (your main speakers go pretty low) you should run jumpers from both speakers to both subs. That's the way I'd run them anyway.....

 

[mep]

Gary-Thanks for your response. I have never thought of hooking up the subs via the speaker level inputs. I kind of thought that was for people who didn't have an extra set of preamp output jacks. That would mean I would have to come up with another pair of speaker cables to go from my main speakers to the subs. And yes, I will be crossing over below 40 Hz. I will probably experiment with your recommend hook-up, but it won't be tonight. So given that I will hook them up using the line-level inputs, Y-splitter or no Y-splitter?

 

[Mark Seaton]

Hi mep,

With most any subwoofer there's no worry about group delay through the amplifier. The use of a low pass filter on the subwoofer creates an order of magnitude greater group delay.

When your subwoofer has an internal amplifier, the L/R signals are summed electrically in the amplifier, and there is no need for a dual voice coil as they used to do in some subs or car audio systems long ago. You have 2 choices...
1. If you want to run one sub per speaker channel and are placing the subwoofers near your main speakers you can just run the respective cable to each sub. If you like, you can use a short Y at the subwoofer input to drive both L/R input, but this only makes a gain difference that is the same as turning the volume up and is not required, assuming you have plenty of volume control range.
2. If you are placing the subwoofers asymmetrically or in other manner to use the subs to better smooth response through the room, you want to insure both subs are working simultaneously for the bass range and you will then want to use 2 Y splitters at the preamp output where you can then send both the L & R signal to each sub so they get the same signal.

 

[garylkoh]

What sub is it? The two inputs on a subwoofer are usually electrically summed before the crossover. I'm surprised that this one has two amplifiers and a single woofer with two voice coils. Seems to be a strange way to do it. If you are putting one sub next to the left speaker and the other next to the right speaker, I would run preamp left output to the left sub and right to the right.

When you try out the subs via the speaker level inputs, do not use a speaker cable. The input (even the speaker level) of a sub (unless it is passive) is a high-impedance input, and requires an interconnect-type interface and not a speaker-type interface.

 

[garylkoh]

Hi mep,

With most any subwoofer there's no worry about group delay through the amplifier. The use of a low pass filter on the subwoofer creates an order of magnitude greater group delay.

Mark, some tube amplifiers invert phase with 180 deg group delay. The Jadis power amps all have significant group delay. It's a problem with Genesis speakers of the old design because the bass amplifier only took line-level inputs and the mid/tweet took only speaker-level input. Customers always complained that the bass of the old Genesis speakers to be "slow" because of the lack of coherence between the bass and the midrange.

 

[mep]

Gary and Mark-I probably made a mistake when I said it has two voice coils because I assumed that to be true. The sub is the Def Tech SuperCube Reference: http://www.definitivetech.com/Products/products.aspx?path=Subwoofers&productid=SuperCube Reference

The subs will be sitting near each main speaker so I will just go with a single IC into one of the inputs. I appreciate both of your help.

My gut let me down again.

 

[mep]

Mark, some tube amplifiers invert phase with 180 deg group delay. The Jadis power amps all have significant group delay. It's a problem with Genesis speakers of the old design because the bass amplifier only took line-level inputs and the mid/tweet took only speaker-level input. Customers always complained that the bass of the old Genesis speakers to be "slow" because of the lack of coherence between the bass and the midrange.

My Defy 7 is long gone and now I'm using the Krell KSA-250.

 

[garylkoh]

My Defy 7 is long gone and now I'm using the Krell KSA-250.

I know - but speaker-level input on the sub paralleled to the main speakers will always work, whereas line-level input may sometimes fail. I don't know what's the group delay on the KSA-250.

Instead of speaker cable, you may want to try cutting the ends off a pair of cheap interconnects you have sitting around and using that as a jumper between your mains and the subs.

 

[FrantzM]

Gary

Not wanted to start a debate on mep thread .. His question were specific .. But please allow me this: I am not clear on the group delay of the Jadis being 180 deg.. I know back in the days some amplifiers , tubes in particular, did invert the polarity but that was a simple phase issue. It was also very easy to correct too: Simply inverse polarity at the speaker terminals ... I am also curious to know at what frequencies were the group delay measured ? Thanks in advance

 

[NorthStar]

If you are using the Low level inputs (RCA or XLR jacks), I read somewhere that by using both Left and Right jacks, with a "Y" adaptor, not only you are gaining some Gain (Volume), but also that you are eliminating the risk of noise contamination entering the unused input jack.

...Instead of using only one jack (usually the Left one).

And same in a multiple sub configuration.

Comments?

* If I may add: Using the High level inputs (speaker terminals), is there a chance of impedance mismatch between the mains and sub?

 

[garylkoh]

Gary

Not wanted to start a debate on mep thread .. His question were specific .. But please allow me this: I am not clear on the group delay of the Jadis being 180 deg.. I know back in the days some amplifiers , tubes in particular, did invert the polarity but that was a simple phase issue. It was also very easy to correct too: Simply inverse polarity at the speaker terminals ... I am also curious to know at what frequencies were the group delay measured ? Thanks in advance

Group delay is the time delay of the entire signal. So, it should not be frequency-related. The Jadis is not 180 deg - but it is quite significant. If it's exactly 180 deg, then it is very easy to correct. However, if it is more or less than exactly 0 or 180 deg, then the integration between the low-pass of the sub and the high-pass of the midrange becomes a problem.

You might be thinking about phase delay because all crossovers have phase shift at the crossover points.

 

[garylkoh]

* If I may add: Using the High level inputs (speaker terminals), is there a chance of impedance mismatch between the mains and sub?

Unless the sub has very low input impedance, no. Since the high-level inputs have to be attenuated and then fed into the active crossover/preamp of the sub, the input impedance is often even higher than the RCA/XLR inputs.

 

[Steve williams]

Gary

Not wanted to start a debate on mep thread .. His question were specific .. But please allow me this: I am not clear on the group delay of the Jadis being 180 deg.. I know back in the days some amplifiers , tubes in particular, did invert the polarity but that was a simple phase issue. It was also very easy to correct too: Simply inverse polarity at the speaker terminals ... I am also curious to know at what frequencies were the group delay measured ? Thanks in advance

my preamp is an inverting preamp and as a result I switch the polarity of the speaker cables at the amp side of things

 

[mep]

Sub just arrived via Estes which I have never heard of before. The guy comes in a tractor trailer and I had to help him lift it out of the truck and carry it to the door. It is in my room and hooked up via the IC and music is playing via the music server to start breaking it in. Speaking of breaking, when I unpacked the sub I noticed the top plate was sliding around. I pulled it off and had a look-see and 3 out of the 4 buttons that hold the top on were broken off. Good thing that little things like that don't drive me crazy.

 

[NorthStar]

I know few people that wouldn't tolerate small things like that broken off...
Not me though; if I can fix it and it's working properly. :b

 

[FrantzM]

Group delay is the time delay of the entire signal. So, it should not be frequency-related. The Jadis is not 180 deg - but it is quite significant. If it's exactly 180 deg, then it is very easy to correct. However, if it is more or less than exactly 0 or 180 deg, then the integration between the low-pass of the sub and the high-pass of the midrange becomes a problem.

You might be thinking about phase delay because all crossovers have phase shift at the crossover points.

Not sure I agree with you according to what I think I know.. Group Delay is frequency dependent ... Its very definition introduces the frequency as the variable .. . References will be provided if needs be.

Aplogies to mep ... HWe can always move this to a different thread or PM ...

So how does it sund so far ? Have you tried the geddes positionning? I know from reading your posts that you flank the mains with the additional subs ... I will definitely work since you have now more headroom in the bass, you may have had likely reduced all the subs output thereby lowering their distortions ... Youcare also moving more air which add to the palpability of the system ...

 

[garylkoh]

Not sure I agree with you according to what I think I know.. Group Delay is frequency dependent ... Its very definition introduces the frequency as the variable .. . References will be provided if needs be.

Aplogies to mep ... HWe can always move this to a different thread or PM ...

So how does it sund so far ? Have you tried the geddes positionning? I know from reading your posts that you flank the mains with the additional subs ... I will definitely work since you have now more headroom in the bass, you may have had likely reduced all the subs output thereby lowering their distortions ... Youcare also moving more air which add to the palpability of the system ...

You are right: http://en.wikipedia.org/wiki/Group_delay_and_phase_delay

I was assuming that a good amplifier should be linear phase with respect to group delay. If an amplifier is not linear phase, then all bets are off!

 

[Robh3606]

Mulitple sub question
I have a question about how to lash up a pair of subs to your preamp. As you all know, when you buy a sub it has inputs for both the right and left channels and the woofer has dual voice coils in order to handle both inputs. If you are running a siingle sub, you just run a pair or ICs from your preamp out jacks to your sub and plug them in.

My second sub is arriving today and now there are options. I can run an IC over to each sub and choose either the Right or Left input to jack into or, I can run the IC over to each sub and plug the IC into a Y-splitter so that I can plug into both the left and right inputs so I'm using both voice coils.

My question is what are people doing and is there consensus for the best way to hook up two subs? My gut tells me to use the Y-splitter.

Hello mep

I use a Y spliter to run my pair of LFE subs and it works just fine. Powered subs sum the L+R to mono so it doesn't matter if you don't have a jack open. You could always cap them if you are worried about noise.

Rob

 

[NorthStar]

Are Digital Class D amplifiers linear?

And why consciencious people don't use them in their subwoofers, or their separate amplifiers for that matter?