Connecting a 6/4 ohm subwoofer between an 8 ohm receiver and 8 ohm speaker pair

I asked this question over at audiokarma, and a member there responded that they think it should be ok but to be careful. But just for a second opinion:

I have an Advent Mini Subwoofer I -- the first one, with impedance spec of 6/4 ohms (according to the 1989 literature on this particular sub). This is a small passive sub with input/output speaker jacks, but no adjustable high/low pass filter.

If I connect this subwoofer to my 8 ohm receiver (Pioneer SX-980) and then connect my Dynaco A25's (8 ohm speakers) to this 6/4 ohm subwoofer, can either the receiver or the Dynacos be damaged?

 

This is one of those risk/reward type situations.

To answer you question directly... The SX-980 is rated to handle 4 ohm loads, however, when wired as you describe it will result in a load that drops below 4 ohms. This might be ok for the Pioneer, but then again it also might not.

The Advent is likely to provide no sonic improvement compared to using the Dynacos on their own. It will most likely result in sonic degradation. (Case in point: the Advent has an internal crossover point above 200 Hz and no level control. It's two little wee "woofers" (to put it kindly) are inferior to the two woofers in the pair of Dynacos.

So. You can risk potential damage to the Pioneer in return for no sonic reward.

I know what I'd (not) do.

Regards.

Jeff

 

Thanks. I was playing the system with this setup for about a half-an-hour yesterday, then looked up more info about the Advent Mini Sub, and saw it was 6/4 ohms instead of 8 ohms. Now I know just to leave well enough alone and run the Dynacos by themselves instead of trying to augment them. The 980 thankfully seems to be ok despite the subwoofer experiment.

On the SX-980: could it safely handle 6 ohm-rated speakers like Infinity Kappa 6.1's?

 

Yes. Given its 4 ohm rating (according the owner's manual) it will handle anything at or above that - including the Infinity. The only disclaimer to that is that while some speakers specify a "nominal" impedance rating (which is the case for the Infinity), they might sometimes have a lower minimum (at some frequencies), that could present an issue for some amps. But I don't think that's the case here (at least Infinity only gives the 6 ohm nominal rating). (The Koss CM/1030 that I use have a nominal rating of 5 ohms, and a minimum of 4 ohms - both of which have been confirmed in trade mag reviews / testing.)

Jeff

 

Not necessarily so. Some loudspeaker loads nominally are fine, but sometimes dip lower. A Pioneer SX 980 won't drive no 2 ohm load, be careful.

 

I was editing my post when you posted yours.

Fair warning.

Jeff

 

Why hasn't anyone mentioned wiring in regards to series vs parallel which do change ohm loads on amps?

From what I've understood installing DC current components in my car ohms greatly affect what an amp can take in the low end bass frequency regions. If the sub is small then its resonant frequency is going to be higher like say 80Hz vs 40Hz which isn't going to potentially damage an amp if driven hard as in loud.

But it's been a while since I read up on this and it was only for DC current in car audio. Home audio has stricter standards that involve UL certification and an electronics expert. It's one of the reasons as told to me by an electrician that wattage ratings in car audio are pretty much bogus and pointless while home audio components with AC current is not.

Just throwing stuff out there to understand the usefulness of what is being discussed here seeing I'm not an expert in electronics with both AC/DC components.

 

Because the subwoofer would never be connected in series, and there is no "DC current" component for car audio like you describe.

The enclosure has two 6.5" woofers, speaker input and output jacks, and a passive crossover. Examining the crossover, it is likely solely a high-pass filter for the main speakers, at about 350Hz, which would have been mini Advent satellites. Because of the crossover, the subwoofer impedance doesn't combine much with the main speaker impedance.

This subwoofer is not really a subwoofer, it is the woofer for the Advent satellite speakers, and its response goes well up into the mid-bass, while not reinforcing deep bass much. Advents with a 10" woofer don't need a 6.5" "subwoofer" and they don't need their output neutered by the passive crossover. It is not a good match.

 

What part of DC current are you referring to in my description? If it's in regards to series vs parallel wiring changing the load to an amp, Crutchfield told me different.

 

An amplifier in a car works the same as in your home. The speaker impedance concerns are exactly the same.

Loudspeakers are never connected in series in audiophile systems. The only time they would even work reasonably well is if you have identically matched speakers.

 

I always thought the internal wiring of home audio amps where the speakers connect on the back are already in series. It's just the way the speakers positive/negative are connected to the rear of the amp that makes it appear parallel.

My car's 250watt Alpine amp can take a 2 ohm load from parallel wiring my two 4 ohm subs. But I was told by Crutchfield that would increase harmonic distortion which I wouldn't know how to identify anyway. I still wired them in series. But I can still play them loud.

 

Inside the speaker, each driver and its crossover components are connected in parallel.



You can see the parallel nature when high frequency and low frequency have their own terminals, needing a jumper if not bi-amped:



This does not decrease the total impedance, because each driver only reproduces its frequency range.

It also might not increase harmonic distortion, because it is possible the amp has more headroom into a 2 ohm load than into an 8 ohm load. It depends on the amplifier slew rate and damping factor etc.

Take for example, the Alpine MRV-M250 MONO amplifier. Its power rating is 250W into a 2 ohm load (0.3% distortion), 150W into a 4 ohm load (0.2% distortion). If you are asking the amp to make 150 watts, then a 4 ohm speaker is at this rated distortion. However, a 2 ohm load is significantly below the maximum power and may be less distorted.

Into an 8 ohm load, this amp might only produce 75 watts before clipping.

Be mindful, if you are instead bridging a stereo amplifier into mono, that also decreases the load the amplifier sees, which may be too low to run speakers in parallel. An amplifier may be rated for 2 ohm stereo, but only rated 4 ohm when in bridged mode.

 

Very informative and interesting. Thanks.