[TJHUB]

I was wondering if any of you audio geniuses, Jim S, or Dennis M could answer a question for me?

I have a situation that causes me to want to bi-wire.  The manual does not address the the use of these 2 outputs for the purpose of bi-wiring or bi-amping.  My question does not involve the benefits of either bi-wiring or bi-amping.  I have my own findings regarding both and my special situation.

I have a Parasound 2250 2-channel amp that has 2 pairs of speaker outs labeled "A" and "B" that can be used to run 2 pairs of speakers at the same time.  The amp has switches on the front that can select "A", "B", or both at the same time.  I have the woofers wired to the "A" outputs, and the tweeters wired to the "B" outputs.   

So the question is: What is the impedance the amp will see wired this way?  Is it still going to be 4ohms, or will it be 2ohms? 

Thank you.

[Nuance]

Hopefully not 2, as you would not to send the amp that kind of load. 

Hmm...good question. 

[Kris]

The amp will still see 4 ohms. By pressing A+B you are moving the jumpers from the speakers to the amp, effectively shorting (in parallel) both "outputs".
Imaging powering 2 bulbs with one extension cord and a "T" adaptor, or using two different cords, one for each bulb. The power drawn and light output is the same in both cases.

[TJHUB]

Hopefully not 2, as you would not to send the amp that kind of load. 

Hmm...good question. 

The good news is that the amp can handle 2ohm loads, but you are supposed to set the amp to that mode. 

The amp will still see 4 ohms. By pressing A+B you are moving the jumpers from the speakers to the amp, effectively shorting (in parallel) both "outputs".
Imaging powering 2 bulbs with one extension cord and a "T" adaptor, or using two different cords, one for each bulb. The power drawn and light output is the same in both cases.

I understand what you're getting at here, but what's in my mind is more complicated.  My thought was that if I had 2 pairs of 8ohm speakers, one set on "A" and one set on "B", the amp would ultimately see a 4ohm load.  This is clear to me.  So when I bi-wire my HT2's, it is effectively like running 2 4ohm speakers.  However, the difference is that bi-wiring the HT2's is not the same as running 2 full range speakers as the woofers and tweeters do not cover the same frequency range.  Effectively the load is still 4ohms as you've stated above.

At least this is the I understand things.  What even brought this up as an issue is that a reviewer of this amp commented that the amp had these 2 pairs of speaker connections, but they are not for bi-wiring.  The manual does not address the issue at all, and all of my internet searching has turned up nothing.  I could not understand why this wouldn't work, so I did it yesterday.  Everything works great, but I just had the question regarding impedance.

[Nuance]

The good news is that the amp can handle 2ohm loads, but you are supposed to set the amp to that mode. 

I understand what you're getting at here, but what's in my mind is more complicated.  My thought was that if I had 2 pairs of 8ohm speakers, one set on "A" and one set on "B", the amp would ultimately see a 4ohm load.  This is clear to me.  So when I bi-wire my HT2's, it is effectively like running 2 4ohm speakers.  However, the difference is that bi-wiring the HT2's is not the same as running 2 full range speakers as the woofers and tweeters do not cover the same frequency range.  Effectively the load is still 4ohms as you've stated above.

At least this is the I understand things.  What even brought this up as an issue is that a reviewer of this amp commented that the amp had these 2 pairs of speaker connections, but they are not for bi-wiring.  The manual does not address the issue at all, and all of my internet searching has turned up nothing.  I could not understand why this wouldn't work, so I did it yesterday.  Everything works great, but I just had the question regarding impedance.

Well, if the amp can handle 2 ohms - nice!

In theory that all makes sense, but its odd that the manual wouldn't address this (for the amp I mean). 

Concerning the review, which one was it?  He specifically said the extra set of terminals are not for biwiring?  If so, that's odd.

[TJHUB]

The good news is that the amp can handle 2ohm loads, but you are supposed to set the amp to that mode. 

I understand what you're getting at here, but what's in my mind is more complicated.  My thought was that if I had 2 pairs of 8ohm speakers, one set on "A" and one set on "B", the amp would ultimately see a 4ohm load.  This is clear to me.  So when I bi-wire my HT2's, it is effectively like running 2 4ohm speakers.  However, the difference is that bi-wiring the HT2's is not the same as running 2 full range speakers as the woofers and tweeters do not cover the same frequency range.  Effectively the load is still 4ohms as you've stated above.

At least this is the I understand things.  What even brought this up as an issue is that a reviewer of this amp commented that the amp had these 2 pairs of speaker connections, but they are not for bi-wiring.  The manual does not address the issue at all, and all of my internet searching has turned up nothing.  I could not understand why this wouldn't work, so I did it yesterday.  Everything works great, but I just had the question regarding impedance.

Well, if the amp can handle 2 ohms - nice!

In theory that all makes sense, but its odd that the manual wouldn't address this (for the amp I mean). 

Concerning the review, which one was it?  He specifically said the extra set of terminals are not for biwiring?  If so, that's odd.

Yup, 2ohms not an issue.  Although I do think the mode you set the amp to when running 2ohms cuts it's overall output a bit to maintain low heat and stability. 

Here is the review: 

http://www.hometheaterhifi.com/amplifiers-products-menu-column1-40/362-a-secrets-preamplifier-and-power-amplifier-review.html

The review specifically states: "Dual binding posts are provided, but not for bi-wiring."

Seems to work fine for me. 

[Nuance]

Well, if it works, it works. 

Yeah, I was going to say that you'd have less overall output if you switched to 2 ohms, but you don't listen loud anyway, Miss Daisy.     haha!

[TJHUB]

Well, if it works, it works. 

Yeah, I was going to say that you'd have less overall output if you switched to 2 ohms, but you don't listen loud anyway, Miss Daisy.     haha!

Miss Daisy?  Thanks bud...

I may not listen all that loud, but at least I'll still have great hearing when I'm older.  Or wait, I am already "older".   

[oneinthepipe]

Well, if it works, it works. 

Yeah, I was going to say that you'd have less overall output if you switched to 2 ohms, but you don't listen loud anyway, Miss Daisy.     haha!

Miss Daisy?  Thanks bud...

I may not listen all that loud, but at least I'll still have great hearing when I'm older.  Or wait, I am already "older".   

Nah, you guys are young.  You don't cross over to the "other side," i.e., eligible for AARP membership, until you reach age 50. 

 

[TJHUB]

Well, if it works, it works. 

Yeah, I was going to say that you'd have less overall output if you switched to 2 ohms, but you don't listen loud anyway, Miss Daisy.     haha!

Miss Daisy?  Thanks bud...

I may not listen all that loud, but at least I'll still have great hearing when I'm older.  Or wait, I am already "older".   

Nah, you guys are young.  You don't cross over to the "other side," i.e., eligible for AARP membership, until you reach age 50. 

 

Thanks.  Now I feel better about myself. 

Now, so as we don't make the original poster angry for derailing his thread, anyone know the real answer to the question?

[Jeff B.]

Hopefully not 2, as you would not to send the amp that kind of load. 

Hmm...good question. 

The good news is that the amp can handle 2ohm loads, but you are supposed to set the amp to that mode. 

The amp will still see 4 ohms. By pressing A+B you are moving the jumpers from the speakers to the amp, effectively shorting (in parallel) both "outputs".
Imaging powering 2 bulbs with one extension cord and a "T" adaptor, or using two different cords, one for each bulb. The power drawn and light output is the same in both cases.

I understand what you're getting at here, but what's in my mind is more complicated.  My thought was that if I had 2 pairs of 8ohm speakers, one set on "A" and one set on "B", the amp would ultimately see a 4ohm load.  This is clear to me.  So when I bi-wire my HT2's, it is effectively like running 2 4ohm speakers.  However, the difference is that bi-wiring the HT2's is not the same as running 2 full range speakers as the woofers and tweeters do not cover the same frequency range.  Effectively the load is still 4ohms as you've stated above.

At least this is the I understand things.  What even brought this up as an issue is that a reviewer of this amp commented that the amp had these 2 pairs of speaker connections, but they are not for bi-wiring.  The manual does not address the issue at all, and all of my internet searching has turned up nothing.  I could not understand why this wouldn't work, so I did it yesterday.  Everything works great, but I just had the question regarding impedance.

You have nothing to worry about, and you essentially have it correct already.

First, consider that a speaker with 4 ohm woofers and a 4 ohm tweeter are connected in parallel internally via a crossover. Their combined impedance is still a nominal 4 ohms and not 2 ohms because the woofer's low pass crossover has a rising impedance out of band and the tweeter's highpass crossover has the same as the frequency goes lower. As a result when these are placed in parallel the combined impedance sums to a complex load that is essentially that of each section by itself in its frequency range.

Now, if you split these and provide bi-wiring terminals they will still be connected in the same parallel connection somewhere - in this case back at the amp where the wires come together. In your case, when you turn on Speakers A+B your amp connects both of these two inputs in parallel, so it is no different than if you simply connected both wires to the same set of terminals, and the combined impedance is no different than if you bridged the terminals on the back of the speaker and connected them with one run of speaker wire.

So, in the end, the impedance is no different in any of these cases, and that's because the lowpass and highpass crossover keep the two driver sections from overlapping electrically due to their rising impedances. If they were two fullrange speakers then the combined impedance would be 2 ohms, but that's not the case here. If will add; you don't gain anyting by using Speakers A & B though, as opposed to simply connecting both runs to same Speakers A connector - unless you just don't have room to connect all that wire to one set of terminals.

Jeff Bagby

[Nuance]

Great post, Jeff. 

So there you go, Terry; it's still a 4 ohm load, so don't move the switch.  You've got nothing to worry about...except maybe me sneaking into your house when you're on vacation and steeling your front end electronics and HT2 TL's. 

Nah, you guys are young.  You don't cross over to the "other side," i.e., eligible for AARP membership, until you reach age 50.

 

LOL! 

[TJHUB]

You have nothing to worry about, and you essentially have it correct already.

First, consider that a speaker with 4 ohm woofers and a 4 ohm tweeter are connected in parallel internally via a crossover. Their combined impedance is still a nominal 4 ohms and not 2 ohms because the woofer's low pass crossover has a rising impedance out of band and the tweeter's highpass crossover has the same as the frequency goes lower. As a result when these are placed in parallel the combined impedance sums to a complex load that is essentially that of each section by itself in its frequency range.

Now, if you split these and provide bi-wiring terminals they will still be connected in the same parallel connection somewhere - in this case back at the amp where the wires come together. In your case, when you turn on Speakers A+B your amp connects both of these two inputs in parallel, so it is no different than if you simply connected both wires to the same set of terminals, and the combined impedance is no different than if you bridged the terminals on the back of the speaker and connected them with one run of speaker wire.

So, in the end, the impedance is no different in any of these cases, and that's because the lowpass and highpass crossover keep the two driver sections from overlapping electrically due to their rising impedances. If they were two fullrange speakers then the combined impedance would be 2 ohms, but that's not the case here. If will add; you don't gain anyting by using Speakers A & B though, as opposed to simply connecting both runs to same Speakers A connector - unless you just don't have room to connect all that wire to one set of terminals.

Jeff Bagby

Thanks Jeff.  I really appreciate the explanation.  I thought that was how it worked, but I wanted to be certain.  Everything I have is new and I didn't want to cause any damage.

Great post, Jeff. 

So there you go, Terry; it's still a 4 ohm load, so don't move the switch.  You've got nothing to worry about...except maybe me sneaking into your house when you're on vacation and steeling your front end electronics and HT2 TL's. 

I'm not worried.  The house is being watched and they have your picture. 

[Kris]

Well, Jeff is more fluid spoken than me, so i understand you have to thank him, even tho that's exactly what i tried to explain in my post. I guess i need some time to gain the respect that i deserve. 

[oneinthepipe]

Well, Jeff is more fluid spoken than me, so i understand you have to thank him, even tho that's exactly what i tried to explain in my post. I guess i need some time to gain the respect that i deserve. 

Kris:

Jeff was just backing you up.  Since he is new to Audio Circle, we need to make him feel welcome. 

You are already an established member, so you just get the regular treatment.

[DMurphy]

Hi  I asked Jeff to post because he's the real deal electrical engineer.  Plus the designer of the great open-back Salk Speaker.  (Did we ever come up with a name for that thing?)  When you're dealing with active circuitry, it's best to make really sure whatever you're planning on doing doesn't blow up the living room.   In this case, you guys already nailed it.  But better safe than................sizzle.

[Nuance]

I'm not worried.  The house is being watched and they have your picture. 

  Just messin' with you bro.  I would never take away your newfound pride and joy.  Now you have to help me complete my system so we can both be in sonic heaven. 

Also, I think just for fun I should bring my ST RT's up by ya.  I can actually hear them in a good room for once.   aa

[TJHUB]

Well, Jeff is more fluid spoken than me, so i understand you have to thank him, even tho that's exactly what i tried to explain in my post. I guess i need some time to gain the respect that i deserve. 

Sorry Kris, I meant no disrespect to you.  I guess I skipped over your post as it was too simply stated.  Jeff's post spelled out the issue well.  I too thought the impedance would remain 4ohms, but it was Jeff's post that best explained why. 

[TJHUB]

I'm not worried.  The house is being watched and they have your picture. 

  Just messin' with you bro.  I would never take away your newfound pride and joy.  Now you have to help me complete my system so we can both be in sonic heaven. 

Also, I think just for fun I should bring my ST RT's up by ya.  I can actually hear them in a good room for once.   aa

So...  I see curiosity has bitten you.   If you must know what you need to know, you are welcome to pick a date and I'll try to make it work for you.  Just know that Saturdays before 1 p.m. for me is out as it's now soccer season and I'm coaching my son's team. 

[Jeff B.]

Hi  I asked Jeff to post because he's the real deal electrical engineer.  Plus the designer of the great open-back Salk Speaker.  (Did we ever come up with a name for that thing?)  When you're dealing with active circuitry, it's best to make really sure whatever you're planning on doing doesn't blow up the living room.   In this case, you guys already nailed it.  But better safe than................sizzle.

Thanks Dennis, but I should probably clarify something - I am not an electrical engineer. In fact, I have never even had a class in electrical engineering. Now, that doesn't mean that I don't know anything  , just not a lot of anything 

In a nutshell - I have two degrees: one in Mathematics, and one in Biology. I taught college Physiology for short time a long time ago. Then I got a job as a Statistical Engineer in the automotive industry. This was just supposed to last until I went back to school, but it evolved into a job as a lead Product Quality Engineer over Automatic transmissions, which is a Mechanical Engineering position. No, I don't have any formal training there either  , but I have been doing it for the last twenty-four years now and have reached the top spot in my field where I work, so I guess I am one anyway  At any rate, speaker building is just a hobby, but one I took a special interest in and tried to learn as much as I could, which enbled me to create the software that I have done. I have been a scientist and an engineer for my entire adult life, and speaker building is just an extension of that type of thinking. Anyone who wants to learn can set their sights on something and learn it, and if an idiot like me can do it, anyone can.
Jeff B.