Impedance Question

[dch]

Hello. I'm new to the forum and to higher-end audio, but trying to learn quickly. I have two Klipsch front speakers rated at 8 ohms I'm wanting to add a center speaker and some surrounds for home theater listening; however, a center speaker I just purchased but not yet hooked up is 6 ohms. Can you use different impedence speakers like that or must they all be 8 ohm? Where online can I read more on impedance?

Many thanks.

[Mr Peabody]

More important to your center is that it should match your Klipsch. You can run 6 and 8 ohms with no problem but if the center and mains aren't of the same series and brand you will not have seamless panning of sound from side to side. The 6 ohm speaker will draw a bit more current from the amp is all. You might not think the matching thing matters much if that center isn't Klipsch your difference will be very obvious.

Your fronts, left/right/center, are presenting an image. Think of it like this, would you use two different speakers for stereo? No matter the number of channels you don't want to mix speakers if you care about the sound you get.

[Mr Peabody]

I don't know of any article off the top of my head for impedance but you might try a Google search for "what is impedance" or "impedance of speakers" to see what comes up. You should definitely get links to Wikipedia and How Stuff Works. You can play with the search phrases to see if you can get closer to what you are looking for.

In speakers the impedance rating is just it's "nominal" impedance. All speakers swing from low to high impedance depending on the music program being played. More importantly and you either need to know the rep of the company or trust your sales person is if the speaker has a fairly stable impedance range. Some speakers may be prone to very low impedance swings which is tough on an amplifier. The lower the impedance goes the more current it will demand from your amp and if your amp isn't capable of delivering the current, then you have a problem.

[Kevio]

You won't hurt anything by mixing impedances as you describe. Your front speaker may have a different loudness than your L/R speakers. You should be able to tweek the center channel volume setting in your receiver for a better match. Some receivers have a "test tone" mode to help you do that.

Many people feel that you should have three identical speakers in the front. But often that's not practical due to space/mounting considerations, magnetic shielding or the fact that some speakers are only sold in pairs.

I personally don't think a mismatched center is a huge deal. In some programs, the center is involved in imaging but to a first approximation, the center is used primarily for dialog and L/R are used for music. OK with me to have different speakers for different types of program. Hook it up, balance the levels and see how you like it.

[Mr Peabody]

Sensitivity will dictate how loud a speaker will play. Klipsch is one of the most sensitive speakers on the consumer market. Though it's 8 ohms, it's highly doubtful that any other speaker will play as loud receiving the same signal. In addition, Klipsch uses horn technology and any other brand will mix like oil and water.

Bottom line, yes, you can add the 6 ohm speaker, and, no, it shouldn't hurt a thing. The rest will depend on how picky you are about your sound. I can't list every instance when your front imaging will be important but think of your side to side panning of sound like when cars go by, or when it's raining, would it bother you to have the rain sound one way from the center and another from the mains, if you will ever listen to a 5.1 concert DVD/SACD/Blu-ray, do you want the music to have a different presentation from the center than the mains. The center is the most used for dialog and center screen action but don't under estimate the importance of the other speakers for a cohesive sound and presentation, if it was just one speaker we'd all be still watching TV in mono.

[challengaaah]

Just a related question on impedance: My Technics SU-V4 Class A has switched speakers A and B or on mine, called Main and Remote. If i switch both pairs of speakers on together (and they are both rated at 8 ohms) will that reduce the load to 4 ohms that the amp sees, therefore increasing the load on it? Or has it been designed so that the amp still gets the 8 ohm load for each? A friend of mine said you shouldn't run all together as it puts too much strain on the amp, but i have never had anything blow up running them like this, even with a little extra bass boost.

Also, another question, if i may. This amp is going on 20 yrs old. I have just bought a little 8"powered subwoofer. It has 3 connection options on the back: Line (L and R RCA plugs),, Subwoofer (just one RCA plug) and speaker input terminals which are banana plugs. How do i connect it to my Amp? There is nothing on the back of the amp for a subwoofer as it is too old. If i use the Speaker terminals on the Sub, i assume the power amp section inside the sub enclosure will be bypassed, but should it be wired in parallel with the main speakers? this would certainly lower the impedance and not be good for the amp.... Thanks!

[Kevio]

If the amp is rated to drive 8 ohm loads and you have connected 8 ohm loads, you should be fine. To drive both sets of speakers simultaneously, the amplifier is obviously going to have to work harder but it is not going to blow up.

You'll want to run speaker cables to the sub and to your main speakers. The speakers inputs on the sub have high impedance so won't significantly affect the load your Technics sees - the power to drive the sub comes from the sub's internal amplifier, not the Technics.

[Mr Peabody]

It's difficult to answer your A/B question because manufacturers varied on how they wired them. Most put them in series which usually caused a less quality response because it doubled the impedance the amp saw. In addition series is safer for the amp.

If your amp has preamp outputs, hooking those to the L/R inputs on the sub would be the best way. You'll need a Y adaptor. The single leg coming from the pre out with one side back into the amp and the other to the sub.

If not, and you only have one pair of speakers, then run the sub off the "B" speaker terminal.

I sure didn't know Technics built anything Class A. If that baby did wire the A/B in parallel..... between the Class A and low impedance drawing current you'd have a small space heater there

[challengaaah]

Thanks for the advice on this- but still need to clear a few things up. i just checked the back of the amp- unfortunately no pre-amp outlets. (although the phono RCA jacks are gold plated!). So i wil have to wire the sub off the speaker outlets. However, Kevio said that doing this into the sub's speaker input (as i said, there are three choices of input connections) will use the sub's own amp, therefore will not cause a drain on the Technics. But how is this possible-? as the signal coming out of the technics "Speaker out" has already been amplified. The sub cannot de-amplify it and re-amp it, again? Surely the RCA connections are the ones with the sub's amp- using just the source signal via the amp. In this case, maybe i have to make up a splitter cable that takes a signal off the source and routes it to the sub as well as the Technics. But then i have to use splitter cables on all sources- VCR, tapedeck and CD...could get messy. Still abit confused.

By the way, Mr Peabody, these Class A DC amps from Technics (or Super Class A as they call them) were very popular (SU- V2, V4, V6 and SU-V8) and i often still see wanted ads in the classified for techo's wanting these amps. It has MM and MC switched provision, High Filter (7khz) and Subsonic filters (30hz) and a beautiful level meter with switched ranging. It is only rated at 65w per channel but anything much over 2 on the Volume starts getting very loud. I usually run both Main and remote together to supplement the Infinity's poor bass. I think they are wired in parallel as there is no discernable difference in music quality when using both compared to one.

thanks!

[Kevio]

But how is this possible-? as the signal coming out of the technics "Speaker out" has already been amplified. The sub cannot de-amplify it and re-amp it, again?

That's exactly what happens. The sub takes the voltage from the speaker connections but takes negligible current and thus negligible power. The electronics in the subwoofer amplifies the voltage and delivers both voltage and current to the subwoofer speaker.

If you really want, you can hook the sub up with an RCA cable to the tape out of the amplifier and that will sort of work. Problem there is that the level at the tape out does not change when you adjust the volume. To change listening level, you'll need to adjust volume at the amplifier and reach around and adjust on the subwoofer too.

[Mr Peabody]

If no preamp out you will definitely want to use the speaker level hook up. As Kevio said source direct to sub will have no way to control the sub's volume and a mess of cables. Going to the speaker levels the sub will step the amp's signal down from it's high level state and the sub's amp will see the converted signal. it works, not optimum, but it works, or else they wouldn't be there, right?

Which Infinity speakers do you have? Most Infinitys have a good bass response. Are you careful to connect (+) red on the amp to (+) red on the speaker and vice versa black (-)? Phase is very important, especially to bass response. If that Technics is what it's supposed to be and those Infinity are vintage you should be having good bass and if floor standers, shouldn't really need a sub at all. I'd also recommend experimenting with one set at a time.

[challengaaah]

HI Guys- firstly, i appologise to DCH, the initial thread starter, for stealing his impedance post! And thanks for clearing up that about the sub connections. I had NO IDEA the sub could do that with inputs and voltages. The RCA idea with the messy volume settings would be a pain, i'll use the speaker connections. Mr Peabody, my Infinity's are SM-112. SM standing for Studio Monitor. They are second generation Infinity -First generation being the expensive, low production models most noted for the semi transparent drivers and Emit ribbon tweeters. Apparently then, the small dedicated company was bought out by ??? and turned into a much bigger production concern - with profits being a greater concern (how often have we heard this sad story?). The speakers, like mine, were still competant but now made to a budget and quality had suffered. Cabinets were still solid, but had a plastic veneer, cheaper dome and Polycell tweeter and poly coated cones. Mine did not even have any internal damping at all! I have read many reviews of them- they all say the same thing: Bass is nice but very lacking, midrange overly bright (not able to be attentuated on mine) and often intrusive, although no complaints about the top end. I have just put these speakers in to get the bass drivers refoamed. I asked him to put an L pad (attentuator) on the mid for me and he is adding extra damping to the damping i placed in there as a young fellow. He said damping usually helps the bass. I am also considering that the amp might not be the best choice for these speakers. This amp is also considered "bright". Something else to look at as well. But in the meantime i will try the sub at a low level- as a subtle tonal supplement only - and see how it all goes.

By the way- i checked the phasing so many times i think i wore out the stripes on the speaker wires just by looking at them so often!!

Thanks again for advice.

[Mr Peabody]

That explains it. The Studio Monitors were hot sellers because of their high sensitivity which could have made them a good match for your amp if they didn't sound the way they do. They were made as disco/rock & roll speakers, NOT AT ALL TYPICAL OF OTHER INFINITY series. It's a shame you just sunk money into them, I would have recommended a RS series, I was always partial to the black coned woofers (IMG) injected molded graphite. May not play as loud but you get some deep quality bass. Or, if you can find something in the Kappa series. Really all of those are pretty old though and Infinity don't keep any replacement parts for long. You'd be better off doing what you are doing, adding a sub, or, buying something new that has good synergy with the amp if you plan to keep it for a while.

[challengaaah]

Oh yes, you are very right there. These are very sensitive (100db/W/1m). I would just love some RS series Infinitys but they are just not around anymore. I spent $200 on these speakers (about US$140) and that was for him to redo the speaker suspension with original Infinity parts, put in the midrange attenuators (which i supplied from some old Jensen speakers), glue up the edge of a cabinet that had come loose, and put in some extra damping. That price included pickup and dropoff at my house. Not bad really! And i got the speakers new in Singapore for $400, a bit less than 30% of their new price in Australia which was about $1500 in 1990.

So all told, i'm still in front. But here are some interesting stories: We have Kerbside Collections here in Australia- maybe you do as well over there. The local council picks up your old junk, twice a year. People often throw out some amazing stuff. I got a set of Jensens, my friend picked up some Celestion Ditton 44's someone had thrown out (only one driver needed suspension) which are a very sought after speaker and just today i heard a story where a fellow had wanted some certain model of speaker for many many years but could never afford them. They sold for $3000 in 1976- a huge sum then- equivalent of a cheap new car today- around $25,000. Well, this fellow went out from his house and about 200 meters away- there was the exact set of speakers he had dreamt about waiting to be picked up! They were the top of the range Gale's made in England. Amazing.

[Mr Peabody]

Boy wouldn't that make your day.