Please help me understand speaker impedance

[TLS Guy]

Are the drivers on the Ushers high excursion? Does high excursion factor in with impedance dips? It would seem they would be somehow related? Sorry, I just never addressed this before.

So long as the Ushers don't go much lower than their average impedance rating the RX-V661 should do fine for all but the largest of rooms. Of course speakers that size aren't intended to fill large rooms with sound anyway.

In the event that the receiver is running out of steam, which I doubt it would ever become a problem, you could always add some amplification.

The impedance dips are not related to excursion. However a speaker driver's impedance rises with frequency and the lower impedance ranges are where the power is.

The problem is worse than that. Small speakers especially loose coupling to the air below 500 to 600 Hz. Good speaker designers have a whole bag of tricks up their sleeve ameliorating this. However they ALL involve dropping the impedance and drawing more current from the amp.

Now the crossovers on those Ushers are designed by Joe D'Appolito. Like I do, he hates speakers that do not attempt correction of this problem. Through numerous articles in Speaker Builder and Audio X-press over the years he has been very generous and opened his bags of tricks.

I would bet that those speakers are probably quite a difficult amp drive, just based on the designer. In fact I suspect it is one of the reasons the OP liked them so much. I bet the mains also drop impedance more than the spec sheet lets on.

I believe that there is a direct correlation with the proper sound balance of a speaker and impedance drop below 400 Hz, in narrow fronted speakers. The smaller the speaker the more this is true.

As I designer I feel these current limited receivers are a boat anchor to improved loudspeaker performance. As far as I'm concerned they can't be gone from the planet too quickly.

As I have said before the best solution will be a move to powered speakers, were these kind of problems can be corrected before the amp/loudspeaker interface. The loudspeaker/amp interface is a bad place to address these issues.

 

[PENG]

The impedance dips are not related to excursion. However a speaker driver's impedance rises with frequency and the lower impedance ranges are where the power is.

The problem is worse than that. Small speakers especially loose coupling to the air below 500 to 600 Hz. Good speaker designers have a whole bag of tricks up their sleeve ameliorating this. However they ALL involve dropping the impedance and drawing more current from the amp.

Now the crossovers on those Ushers are designed by Joe D'Appolito. Like I do, he hates speakers that do not attempt correction of this problem. Through numerous articles in Speaker Builder and Audio X-press over the years he has been very generous and opened his bags of tricks.

I would bet that those speakers are probably quite a difficult amp drive, just based on the designer. In fact I suspect it is one of the reasons the OP liked them so much. I bet the mains also drop impedance more than the spec sheet lets on.

I believe that there is a direct correlation with the proper sound balance of a speaker and impedance drop below 400 Hz, in narrow fronted speakers. The smaller the speaker the more this is true.

As I designer I feel these current limited receivers are a boat anchor to improved loudspeaker performance. As far as I'm concerned they can't be gone from the planet too quickly.

As I have said before the best solution will be a move to powered speakers, were these kind of problems can be corrected before the amp/loudspeaker interface. The loudspeaker/amp interface is a bad place to address these issues.

In general I don't disagree with what you are saying about the problem with "current limited" receivers. The same would apply to current limited separate power amplifiers, just to different extents depending on the specific products.

That being said, we should not automatically assume a receiver cannot do a sub $1K L/C/R speaker system justice. Specs are good and allows us to predict the outcome if they are complete, but invariabley specs are not complete. I know the current draw by my 4 ohm minimum speakers that have multiple drivers would not exceed 10A peak (very short duration, I had the right meter to capture it) when reproducing bass drum and timpani peaks until the SPL in my 20X12 room exceeds 100 dB (give or take a couple as I am going by memory now). With any other kind of music such as jazz stuff, the current was much lower than one would expect. The readings were so know I am not going to bother mentioning it. I did this with my 3805, 4BSST , and the Adcom 555. They all produced the same readings and there was no audible distortion in each case. After conducting enough tests myself I stopped doubting my 3805. I left the 555 for the front speakers such because I have no other use for it.

I also disagree with your claim that a speaker such as the S-525 that has two woofers in it would yield half the rated impedance. I sure hope manufacturers are not so dishonest. Of course the equivalent impedance of two identical 6 ohm loads is 3 ohms but unless you have seen the circuit diagram you do not know how the two drivers are wired together. What I assume you know is, the effect of the crossover network on the overall impedance.

 

[PENG]

Thanks again everyone, I think I understand better – I may not be able to get the full potential out of the 4 ohm center but it might not matter because it depends on my space and how loud I play my music. There are a few “ifs” I’ll need to think about. I just wish it were easier to judge speakers before I buy. The dealer offered to have me bring my receiver, so I’m pretty sure he’ll break open the center box to test it there and reassure me.

Mazer, I haven’t heard the CM series, they look great, but they’re just a bit more than I’d like to pay. I’d like to keep it under/around $1k for L/R/C speakers.

If you like the sound of those speakers, go for it. I suggest you play the system a little louder than what you normally do with the S-520 only, and measure the temperature on top of the 661 after an hour or so. Then turn everything off, let it cools to room temperature and repeat the test with one of the S-520 replaced with the S-525. If this time the temperature is significantly higher, go buy an Outlaw monoblock 200W amplifier. The nice thing about the 661 is that it has preouts.

 

[zippy753]

To follow up; I brought home the S-520 & S-525 today, hooked them up (with a pair of Nanosats in the back), and just finished watching a movie without issue. My receiver handles the 4 ohm center speaker just fine and didn’t get too hot after a 2 hour action movie played louder normal….and it was plenty loud.

In the end, I guess I underestimated the sonics of my space because these little things shake my walls even without a sub - I don’t need much volume to get a satisfying effect. I like the Usher speakers very much and would highly recommend them.

As a side note, the S-525 is huge, it’s almost exactly two S-520s stacked end to end.

Thanks all for the advice.