3db loss / "Y" IC

treitz3

I have heard from three different sources now that installing a "Y" interconnect yields a 3db loss. I don't have any test equipment to verify that this is true or not, but it has been on my mind since last November.

Now this is posted in the subwoofer section and I would like to throw out there that it may not be true with lower frequencies, or it may be. At this point I don't know. Point being , if there is such a loss in db......where in the frequency range would the db loss occur?

True? No?

Dennis Gardner

There is a 3 db loss in signal, due to the drop in the split voltage. This doesn't mean that the sub will produce 3db less in volume since most subs reach their peak clean volume before reaching the limit of travel of the volume knob. It will simply reach that clean peak a little higher on the knob's travel.

engtaz

Please provide info to the statement. I am not doubting it but would like article showing this and not someones opinion or theory.

Thanks

Dennis Gardner

Are you referring to my post?

engtaz

I type slower then you check the times

treitz3

engtaz, If I am reading this correctly, I take it that you were ressponding to me? Unfortunately, I have no article or proof beyond a shadow of a doubt that there is a 3db loss. It is just what I have been told from some folks in the industry, including one who works at a mid/high end shop. I, myself do not know, but I would like to know the answer because it affects my system.

I can tell you this, though. Now I have heard it from 4 people.

MikeC78

There is not a 3db loss there is actually a 3db gain.

With a "Y" splitter installed, your sub will sum the two inputs and send a 3 dB higher level signal to the sub amp. You can do *exactly* the same thing by turning up the output level of your reciever by 3 dB. If you already have adequate input signal, you won't do yourself any good by adding a Y-splitter.

treitz3

Wrong application for me, Mike. But thanks for your input.

Allow me to clarify. When going from the amplifier "Y"ing out to two subs, using LFE (for example), or going from the internal crossover within the sub "Y"ing out to two amplifiers......is there or is there not a db change at the end result? I.E speak's. I don't know......

Dennis Gardner

Mike is correct. There is a gain in a sub that sums its inputs. Sorry for my backward thinking. I was confusing splitting of the input with a voltage drop.

I do stand by the rest of my statement though...Increasing or decreasing voltages at the inputs doesn't really make an amp put out more or less power unless the volume section doesn't have enough gain to reflect the change.

WilliamM2

So is there a loss or not? I plan on using a y connector to bi-amp my center channel. I had always thought there was no loss.

mantis

Using any kind of Splitter will yield loss. Go to Radio Shack and look at a 2 way cable splitter. Most of them yield a 3db loss. It is safe to assume that a 2 way splitter of line level voltage will have very close results.
With that being said you can make sure you have your sub level correct with a Sound Pressure DB level meter. This will compensate for the signal loss. You simply set yoour level to 75db at reference level which you also match all speakers in the system.

Why use a Y splitter on a Sub?? there is no reason at all. Unless your trying to run more then one sub off the same output, there is no need for it. A sub is a mono input speaker. Single input on left, right , lfe in will all have the same result.

Years ago it was provided a Y splitter to send signal to both left and right inputs of a subwoofer. To this day I don't see any reason to do so. I always removed the Y splitters from the sub boxes and ran a single feed to a input of the woofer.

Dan

WilliamM2

In my case, I want to use it on my center to bi-amp. The reason I thought there was no loss, is because the resitance is also halved, like parralelling two speakers, they will go from 8 to 4 ohms In theory, this would double the output of the amp.

If using a splitter will cause a 3db loss, but bi-amping causes a 3db gain (doubling of power), what is the point of bi-amping?

treitz3

Mantis, I will answer your question soon and expose to all what I would eventually like to accomplish and how I have arrived at what kind of setup I've got and why I would like to do what I am doing. My rig is kind of unique.

Give me a couple of days, please as I am dealing with salvaging gear on my rig as we speak. Mother Nature sent me a message via a lightening bolt. Not good.

XJRGUY

WilliamM2 wrote: »

In my case, I want to use it on my center to bi-amp. The reason I thought there was no loss, is because the resitance is also halved, like parralelling two speakers, they will go from 8 to 4 ohms In theory, this would double the output of the amp.

If using a splitter will cause a 3db loss, but bi-amping causes a 3db gain (doubling of power), what is the point of bi-amping?

I have an RTI12 front end and the center RTI12 I biamp.

I am doing the exact same thing you want to do.

I'm using a Monster splitter that cost me $15.00 at Fry's and I am using two separate amps to bi-amp.

There has been no noticeable loss in level by using the Monster Y splitter off my STR-DA777ES to bi-amp the center channel.

XJRGUY

treitz3

OK, Mother nature didn't mess with the rig too god awful bad. Only lost an amp from preliminary testing. Thank god for good surge protection!

So mantis, to answer your question about why I would use a “Y” splitter on a sub. I have collectively learned that the best way to utilize a sub is to use line level –vs- speaker level inputs. That said; let me introduce you to what I call “Crackbaby”. She is a dual amped, dual speakered stereo system, with sub. To keep it simple for now, I’ll just list part of the basic wiring of the rig. From the source…….

SIZE="1"][B][COLOR="black"][COLOR="black"]Choose from the Rega Apollo, Denon DVD2910 SACD / Universal player, TT, satellite, or a Panasonic DMR-ES35V VCR/DVD combo[/COLOR][/COLOR][/B][/SIZE to a Carver CT-7 pre to The Polk PSW1000’s line level input. Here's where it gets interesting...I took the outputs off the sub (line out) after the crossover and installed a "Y" interconnect on both the right and left channels

Route 1 of the "Y" interconnect.....straight to Carver M-500t straight wired to a pair of Focal 807v’s [bookshelves]. The Focal's only have one binding post, so I am utilizing the full spectrum of this set of speakers

Route 2 of the "Y" interconnect....straight to a Carver M1.5t straight wired to just the lower binding post only, basically utilizing the full potential of a set of Polk RTi10’s, but bypassing altogether the tweeter. To my delight, all of the "speakers" within the RTi10's were still operational, just not the tweeter [sorry, just not a big fan of that particular tweeter for 2 channel music].

Having said that, to answer your question, the reason I have set up my rig the way it is configured is because of the fact that I have owned many different speakers throughout my life and the one thing that I have collectively gained in speaker knowledge is that no speaker is the "best". Each set of speakers have their own advantages and disadvantages, unfortunately. Knowing this and at the time wanting to improve the damping factor, I opted for something unconventional. I came up with crackbaby, which is my rig.

So, to sum up, I basically took the best attributes from both speakers and utilized them into one system. Basically, I have a Polk RTi10 speaker with the tweeter being replaced with the full sound of the Focals

Hence the reason for a “Y” IC coming from the sub and the reason for the inquiry

PolkThug

MikeC78 wrote: »

There is not a 3db loss there is actually a 3db gain.

Agree 100%. I have tested this myself, theres is gain in SPL.

ben62670

When you have an amp it has an input impedance (like speakers). So if your sub amps have a 50k input impedance the total impedance drops to 25k (y adapter = parallel). So your op amps will put out theoretically double the power. Every time you double the power you get a 3db boost. Now if your sub amps were 10k input(highly unlikely), and you y'ed them you would have a 5k load on the op amps. When you do this the high frequencies roll off first, and it makes the op amp work too hard.
Long story short y=3db boost;)

treitz3

For that particular application. For mine I am splitting the signal in two after utilizing the crossover on the sub. This signal goes to two separate amplifiers and from what has been discussed so far, I will yield a 3db loss in each path.

treitz3

I am discussing what would happen from the line level output of the PSW1000 going to two separate amplifiers.

PolkThug

When you go from a source to a sub amp, sub amps will sum the L and R inputs and can actually result in up to a +6db gain. And, no, this does not answer treitz3's question.

ben62670

treitz3 wrote: »

I am discussing what would happen from the line level output of the PSW1000 going to two separate amplifiers.

The same thing would happen as I posted earlier if the crossover in the subs line out is active. If it is passive then you are going to drop the crossover frequency considerable. Say if the subs out is 80hz it will drop to about 50hz. I doubt that it is passive though.

John K.

T3, that's a rather interesting combination of connections that you have there. The point about Y-connections in general has been discussed here before, e.g. last year in this thread . Although you've made clear that your application doesn't relate to the sub amp, the same principle of the voltages being equal on each branch of the Y, as explained in the first link given last year, also applies to your use, and doesn't result in a 3dB voltage reduction(and even if it did, your CT-7 has plenty of voltage output capacity and would just need a slightly higher volume control setting).

The next point is that although your PSW1000 doesn't have a full crossover as such(the control on the back simply varies the low-pass filter on the sub), there is a separate high-pass filter on the outputs to the external amplifiers, nominally fixed at 80Hz. The effect of this is to roll off the response to both your 807vs and RTi10s at a frequency which can't be calculated with precision without knowing the exact impedances of each of the amplifiers at the frequency in question(resulting in a certain combined net impedance), which are being driven in parallel. So, no voltage loss concern, but be aware of a high-pass rolloff in the signal that's being sent to your separate amplifiers.

Dr. Spec

Using a Y splitter on the subwoofer will yield a 3 dB increase in sound pressure.

The voltage remains the same, it is not doubled. The input wattage is what’s doubled. This causes the 3dB increase in output. If you measure the voltage across one of the Y-adapter’s branches it will equal the output of the other. If you remove the Y-adapter and measure the voltage through the single RCA you will see the same voltage as the two branches.

The circuit sees the same voltage level regardless if you use one or two inputs. The input load is halved allowing more current to flow through the circuit and this is where you see your 3dB of gain.

For example (using an arbitrary impedance):

Single input at 1V (this is the output level sent from the receiver), across a 2 Ohm resistor.

Power = V^2/R

Power = 1^2V/2

Power = 0.5W

Two inputs at 1V (this is the output level sent from the receiver), across two 2 Ohm resistors in parallel.

Power = V^2/R

Power = 1^2V/1

Power = 1W

Power difference (dB) = 10*(log(P1/P2))

Voltage difference (dB) = 20*(log(V1/V2))

Power difference = 10*(log(1/0.5)

Power difference = 3dB

John is correct - many line level outputs on subwoofers have a high pass filter (usually 12 dB/octave) at 80 Hz. That is why subwoofers should never be daisy-chained unless the high pass can be defeated.

McCelery

Isn't the resistance being halved offset by the fact that the current is also split in half across the two pathways? Otherwise, aren't you essentially creating energy with this argument? By this method, you could conceivably make a sub with 4 inputs and fashion a quad splitter and get a 6db increase. Which I believe is probably nonsense. Isn't the NSD-PB10's single input an argument for the fact that you don't get an increase from splitting the input signal?

I swear I'm not trying to be a nuisance!! Just getting clarification, as this has really been bugging me lately and I can't remember my circuits class from college well enough. Your examples above seem compelling but I'm having mental blocks. And, of course, I don't work for a great subwoofer company, either, so my credentials are a bit lacking

PolkThug

McCelery wrote: »

Isn't the resistance being halved offset by the fact that the current is also split in half across the two pathways? Otherwise, aren't you essentially creating energy with this argument? By this method, you could conceivably make a sub with 4 inputs and fashion a quad splitter and get a 6db increase. Which I believe is probably nonsense. Isn't the NSD-PB10's single input an argument for the fact that you don't get an increase from splitting the input signal?

I swear I'm not trying to be a nuisance!! Just getting clarification, as this has really been bugging me lately and I can't remember my circuits class from college well enough. Your examples above seem compelling but I'm having mental blocks. And, of course, I don't work for a great subwoofer company, either, so my credentials are a bit lacking

Dr. Spec has forgotten more about subs than you will ever know. Bow down newb!

Sid was the first, that I can remember to post about the db difference by merely switching the inputs. I was able to duplicate the results as well.

Dr. Spec

McCelery wrote: »

Isn't the resistance being halved offset by the fact that the current is also split in half across the two pathways? Otherwise, aren't you essentially creating energy with this argument? By this method, you could conceivably make a sub with 4 inputs and fashion a quad splitter and get a 6db increase. Which I believe is probably nonsense. Isn't the NSD-PB10's single input an argument for the fact that you don't get an increase from splitting the input signal?

I swear I'm not trying to be a nuisance!! Just getting clarification, as this has really been bugging me lately and I can't remember my circuits class from college well enough. Your examples above seem compelling but I'm having mental blocks. And, of course, I don't work for a great subwoofer company, either, so my credentials are a bit lacking

Be nice PolkThug.

The whole point is the current is not being split in half. The lower resistance draws more current from the op-amp (pre-out) at the same voltage, so the power level doubles and the SPL increase by 3 dB.

Obviously a Y splitter cannot add amplifier power or subwoofer performance - it just draws more juice from the op-amp at the same subwoofer channel level. It's easy enough to confirm if you have a Y splitter and an SPL meter.

IMO, the only remotely legitimate use for a Y splitter on a single subwoofer is to help keep the auto-on-circuit from cycling on/off at low playback volumes.

And even then, the same exact thing can be accomplished simply by bumping the AVR sub channel level a few dB and recalibrating by lowering the gain at the subwoofer amp the same amount.

The only thing I use a Y splitter for is dual subs - and for that application, they work just grand.

McCelery

Hehe, I knew I was walking directly into the firing line, BUT IT WAS WORTH IT!! Thanks for the clarification. I know threads like this come and go and I've read all the other ones. But lots of the reasons out there are just plain wrong in light of basic circuit knowledge ("the voltages are summed!") so I was a bit confused.

So, uh, what's the Polk Club discount for an SVS?

Dr. Spec

McCelery wrote: »

Hehe, I knew I was walking directly into the firing line, BUT IT WAS WORTH IT!! Thanks for the clarification. I know threads like this come and go and I've read all the other ones. But lots of the reasons out there are just plain wrong in light of basic circuit knowledge ("the voltages are summed!") so I was a bit confused.

So, uh, what's the Polk Club discount for an SVS?

No probs. It's a sliding scale - newbs actually pay more than MSRP and Russman gets his subs for free.

treitz3

Is there a way to bypass the filters leading to the amplifiers using the line out? I would like the sub to perform the same exact job as it is, but I would like the amps to send the full spectrum of frequencies to both sets of speakers.

Another question. When a db loss/gain occurs, does it occur equally across the entire spectrum or does it affect certain parameters of the frequency range? Would this change in db levels be the same in both scenarios described and discussed in this thread? [One being before the sub's amp and one being after the subs amp.]

Thank you all for input so far and thank you in advance for any further input.

Dr. Spec

treitz3 wrote: »

Is there a way to bypass the filters leading to the amplifiers using the line out? I would like the sub to perform the same exact job as it is, but I would like the amps to send the full spectrum of frequencies to both sets of speakers.

Another question. When a db loss/gain occurs, does it occur equally across the entire spectrum or does it affect certain parameters of the frequency range? Would this change in db levels be the same in both scenarios described and discussed in this thread? [One being before the sub's amp and one being after the subs amp.]

Thank you all for input so far and thank you in advance for any further input.

If there is a high pass filter on the line level outputs, it cannot be defeated unless there is an external defeat switch.

Any unfiltered gains or losses affect the entire pass band equally.

treitz3

Dr. Spec wrote: »

If there is a high pass filter on the line level outputs, it cannot be defeated unless there is an external defeat switch.

Damn. Damn. Damn......................Damn! Sure?

Dr. Spec wrote: »

Any unfiltered gains or losses affect the entire pass band equally.

Thanks!