Using high level connection

[novaj5]

Hi, I'm a sub newbie and planning to get a STF-2 next month or so.
I use a stereo int. amp, and will connect via the high level connection.

My question is: Would it be different if I connect both speaker and sub connecting speakers on 1 same set of outputs from my amp? I.E. Will the sub cut those frequencies under the crossover when you use high level outputs from sub to speakers?

I assume you can connect 2 separate speaker cables to 1 output and get the same sound out from the amp, am I right? (Provided that subs are self-powered and does not really effect the amps' output power)

Any comments would be appreciated.
Thanks in advance.

[amdeutsch]

Sorry, but you better research Ohm's law on google. Hooking up 2 speakers in parallel will have an effect. Especially if 1 is low and the other 1 high impedance.

[Lwang]

From what I understand you are saying, you are running two sets of wires out of your amp, one to the speaker level input of the sub, and the other to your speakers.

If that's the case, you can. But the speaker level input of the sub will not alter the overall signal going to the speaker (i.e. cut off the signal below the crossover freq). So the speaker will get the full signal originally outputted by the amp.

As far having an effect like amdeutsch said, it shouldn't have an affect, since the speaker level input of the subwoofer amp is such high impedence compared to the speaker's, its like hooking up a 2nd pair of speaker cables in addition to the one going to the speaker and just having the positive and negative connections dangling in mid-air.

[amdeutsch]

Actually it will have an effect. His question was I assume you can connect 2 separate speaker cables to 1 output and get the same sound out from the amp, am I right? and that is where my answer about Ohm's law will play. You are also limited by the design of the output and input stages with that.
Now it will depend on the definition of same sound that is applied here.

[Lwang]

I assume you can connect 2 separate speaker cables to 1 output and get the same sound out from the amp, am I right? (Provided that subs are self-powered and does not really effect the amps' output power)"

From what he seem to be saying, the 2nd speaker wire could be connected to the sub amp's speaker level input, which being a high impedence input, would pretty much have no effect on the overall impedence.

Assuming the input impedence of the subwoofer amp is 10kohm purely resistive, and the speakers are 8ohm. The effective impedence would be

1 / ((1/10k) + (1/8)) = 7.9936 ohms

Which is hardly any change to the original speaker's impedence.

[amdeutsch]

If it is purely resisitive is the assumption on your example. Most likely it will not be. As an approximation for a math study it'll do, but in the real world I have encountered otherwise.

[Lwang]

An op-amp's input impedence, which are pretty much what's used as input buffers, is in the the teraohms. To achieve an input inpedence of 47kohm that's pretty common on many amps, a 47 kohm resistor is connected from the input to ground. So that input impedence is dereived from a resistor, providing a purely resistive impedence.

[novaj5]

Hi guys,
thanks for all the helpful infos and opinions. I really appreciate them.

I'll just clarify my situation in a better example:

My Sugden A21a has only single outputs for each speakers(i.e. no bi-wiring).
I'm thinking of getting a HSU STF-2 next month.

Now, what they normally tell you to do is for you to connect your speaker cables from amp to sub first, then sub output to speakers.

I felt like it's not making real differences conceptual wise, compared to when you just connect 2 outputs from the stereo amp straight away - as long as your amp and cable connectors allows you to do that.

If this is true, then I thought connecting main speakers straight from the amp is going to be better, at least not worse, than when you connect to sub first and then connect to speakers from the sub.

What I'm thinking is: Impedence drop is going to be same both ways, so I'll just get the feed to speakers directly from the amp. Another reason is that you can connect same lengths for both speakers and the sub. (If amp-sub-speakers, speakers will have longer connection length than subs)

I know I'm talking about things which most people would think it's silly, but I want to push it as much as I can. After all, if science could justify it, why would there be all this hi-fi stuff after all? :)


And another question would precisely be: Do HSU subs cut/filter the frequencies under the crossover when they pass the signal to speakers?

Thanks again.

[Lwang]

Wiring your speakers from the sub should be no different than if you are wiring it from you amplifier.

Hsu subwoofers's speaker level output are all-pass, so it doesn't cut off any signal when your speakers are hooked to its speaker level output.

[amdeutsch]

This is what the STF-2 manual states in step 5 of the hookup: http://www.hsuresearch.com/STF_manual.pdf



Step 5: Crossover


If you are using the SUBWOOFER or LFE output on your controller, you may optionally set the CROSSOVER switch to OUT. This lets the controller handle the crossover between the subwoofer and other speakers. However, if the bass sounds boomy, it may sound better with the crossover switched IN and the CROSSOVER FREQUENCY set to 90 Hz. You may skip the rest of this step.


If you are using the HIGH LEVEL speaker connections, you will be using the subwoofer’s crossover. Look up the lowest frequency your left and right speakers will output (the frequency they are“-3 dB” at) and set the crossover approximately to this point. Play program materials with steady, consistent bass around this frequency such as filtered pink noise or music containing bass drums, double basses, bass guitar, etc. Turn the crossover to the left until you hear the subwoofer and L/R speakers as separate sources. Slowly turn the control back to the right until the sound of all three speakers is well integrated. When using tiny front speakers that don’t have much bass, the 90 Hz setting on the control will probably yield the best results.

Your subwoofer has a sharp 24 dB/octave crossover to remove the midbass and midrange in the subwoofer. This makes your subwoofer non-directional. Unlike many other subwoofers on the market, the 24 dB/octave slope stays steep at all available frequencies, not just the high ones.

[Kelly]

...I know I'm talking about things which most people would think it's silly..


Not at all. I thought it was an easy question at first. I assumed that HSU was just tapping into the high-level inputs with high impedance amp inputs, then daisy-chaining the high-level signals back out to the speakers. If this were the case, then yes--just wire to your speakers from your amp if that's more convenient. But when I measure between the high-level inputs and outputs on my VTF-3 MK2, a capacitor charges, which surprises me. I expected a short. They're definitely not daisy-chained.

Crossover network maybe? But that would imply that lows are filtered out of the high-level inputs before being fed to the outputs, which I don't think is the case.

I think we need clarification from HSU.

[amdeutsch]

Crossover network maybe? But that would imply that lows are filtered out of the high-level inputs before being fed to the outputs, which I don't think is the case.

I think we need clarification from HSU.

Isn't that what the manual, that I section copied and linked above, implies.

[novaj5]

Thanks everyone for all the opinions :)

It's actually surprising to hear that HSU subs might actually cut the frequencies below the crossover.

I've downloaded the manual before and, after double-checking it now, recall that I did actually read that section. May be I wasn't sure if they really meant they're going to cut the frequencies. If they do, it might be a better choice to connect main speakers through subs.

I'm not sure exactly why, but I did have a strong impression that HSU subs don't fiddle with crossovers and just pass the signals straight through. I can see from other replies that it's not just me who thought they are. May be there was a different thread somewhere regarding this matter.

I wonder what'll happen with the speaker cables then. Speaker cables have their characters and I wish they don't get messed up by inserting a bridging component in between.

[Lwang]

If you are using the HIGH LEVEL speaker connections, you will be using the subwoofer’s crossover. Look up the lowest frequency your left and right speakers will output (the frequency they are“-3 dB” at) and set the crossover approximately to this point. Play program materials with steady, consistent bass around this frequency such as filtered pink noise or music containing bass drums, double basses, bass guitar, etc. Turn the crossover to the left until you hear the subwoofer and L/R speakers as separate sources. Slowly turn the control back to the right until the sound of all three speakers is well integrated. When using tiny front speakers that don’t have much bass, the 90 Hz setting on the control will probably yield the best results.


What this means is that if you want to use speaker level input, you should use the subwoofer's crossover so that it will cut the high freq from the subwoofer itself. That is why you would set the sub's crossover freq at the speaker's rolloff freq, so that it will let the main speakers operate in full range and the sub would gradually fill after they have rolled off. This is called bass augmentation and have been the 2 channel world's method of adding a sub since the very early days.

If the Hsu sub actually had an adjustable high pass crossover of any quality that would affect the main speakers itself in which it would operate in the 50-100 range, the components would be huge, with massive inductors, banks of film capacitors, and it wouldn't even be close to being accurate because it wouldn't even have a clue as to your main speakers' impedence at the crossover freq range. So avoid any subs that actually filters off the low freq from the main speaker output because you know for sure that they didn't throw in $100 of polypro capacitors in there.

[novaj5]

Hey Lwang that's right...! :D

[Kelly]

Right Lwang. I had a look at the BASH amp this afternoon, and the high level inputs are capacitively coupled to the outputs with ~900uF caps (I can't read the value on the cap because it's glued to the board. I measured it with my ohmmeter and counted seconds.) But the caps aren't part of the crossover network.

The in-coming high-level grounds are daisy-chained directly to the outputs, while the hot leads are daisy-chained through big caps. The capacitive reactance of the caps is 8 or 9 ohms @ 20hz.

Mind you, this is for the VTF-3 MKII BASH amp. I don't know if this applies to the STF-2.