I normally use Denon, but cust service says don't do it. I have a customer that has 7 bookshelf speakers that are 4 ohm, each has dual 5" & tweeter. Customers little JVC rxd402b is only rated to 6 ohms & unit shuts down after just a few minutes. I did not spec job. Maybe the 5" drivers are 8 ohm & wired in parallel & I could just disconnect one of the mids. Any thoughts, solutions. Erik

Run away?

Seriously, though...impedence-matching speaker selector switchbox is about the only thing I can think of here.

Anybody? Anybody? Bueller? Bueller?

Fred Forlano
Higher Defintion

Run from the tape out into a high quality amp like

[Link: wholehouseaudiocontrol.com]

or

[Link: wholehouseaudiocontrol.com]

I have a B Stock Sonance 12 channel if needed

This is just plain weird.


At what sort of volume level? Any amp, no matter what its power rating, will work with four ohm speakers. The difference is that a four ohm speaker will try to pull twice the current that an eight ohm speaker will at any given volume control setting. If you turn the volume down, it should always work. The amp would have to be way underpowered for four ohm speakers to trip circuit protection at medium listening levels. At movie theater volume, sure, the amp could go into protection; that would be the sure sign to the customer that his speakers need to be replaced with eight ohm models or his amp needs to be seriously upgraded.

For instance, if an amp is rated 100 watts at eight ohms, it might -- and I mean might because there are a lot of variables here -- put out fifty into four ohms without going into protection. And that fifty might be just as loud as the 100 into eight ohms; that depends on the efficiency. Or not. But the point is, you can't turn the knob up as far on that amp. If you had a 200 watt amp, you might get 100 out of it. You have embarked on an art project here, which is what I call any bit of a project where the customer wants something that is impossible to estimate because the time to do it cannot be estimated and what it will take to do it is unknown. But they want it anyway.


No, you can't do that. The crossover needs a four ohm load. If there are two 8 ohm units in parallel and you disconnnect one, its low frequency cutoff will shift up an octave. The audio output from that mid will be less than you had from both mids, so the tweeter will sound too loud. This is a totally unpredictable idea. If it has occurred to you to mess with the sound coming out of the speakers, it should have occurred to you to tell him that he is out of luck using these speakers (unless you seriously upgrade the power amp), so let's look at eight ohm speakers!

Problem with that is the tape out is before the surround processor, so it would be two channel information....

I didn't even realize this was for a theater application. I would suggest verifying all speakers are 100% functional. Blown tweeters, crossovers, etc. Is there any stray wires shorting out? Will it run ok with only the 3 fronts connected? At what volume does the unit shut down? What brand speakers are we dealing with? More info might help

Choice A) Buy a decent reciever. Anything under $1,000 probably won't cut it. B&K certainly will. I would bet that a Yamaha RXV1600 or 2600 would too.

Choice B) Buy a quality 7 channel amp w/preamp. This will definately work

I use upper end Denons on Triad all the time, and ALL Triads are 4 ohm...

If this is an AVR-3805 or higher, I wouldn't sweat it.

BTW, what speakers is he using??

Since I am sitting here at my computer anyway, I went to the Denon site...

ALL models from the AVR-1506 and up are checked yes under "low impedance drive capability".

Maybe the customer service rep you spoke with is in CYA mode since you said that the JVC shut down, but the Denons have never had a problem for me with low impedance speakers in the past 4 or 5 generations.

Better amps like Denon, Yamaha, Onkyo, Integra, etc in the middle zone of things are routinely designed as high current amps and able to handle a 4 ohm load. This is as opposed to Sony, Technics, Kenwood, and the like, which barely accomplish rated output and low impedance is not advisable for them.

I echo Ernie that only at theater levels should shutoff be an issue.

You could spec an upper mid Denon that you are familiar with, but advise the customer that you will put it in on trial basis and have your backup 7 channel amp priced and committed to. My guess is you are going to be fine.

Add to the equation the fact that you can set the speakers to "small" in the setup menu, and route less bass ("high current") to them. This will let the amp rest a little easier.

We may be completely ignoring the fact that rated impedance is a NOMINAL rating, not a fixed rating. Certain speakers have peaks and dips where certain amps cannot handle it...amp goes nuts...customer follows. Cheaper speakers may be more forgiving with less radical peaks and dips. Higher end speakers, with more complex crossovers and sometimes less efficient drivers, may have dips that challenge the midrange quality amp and require a powerhouse separate amp.

I've dealt with it for many years in our "former" repair department, so it's nothing new. I think the customer service guy was reading a script with zero understanding.

Pick a Rotel, any Rotel. They make a five channel amplified/7 channel processing receiver, and a seven channel receiver ($1299, $2199 respectively). Better sounding than any Denon, Marantz, etc. and a five year warranty.

Just my suggestion.

Yeah Rotel or Harman/Kardon. They produce high current amps, that will deliver their power into low ohm without straining.
Both Rotel and Harman are very rare among amps/av receivers in that they actually specify their high current ratings! That is why Harman/Kardon products always put out more actual power then they quote on paper, and its continuous to all channels, and they will do it all day long into any load. Rotel seem the same from what I have seen.
Some Denon, Onkyo, Yamaha, Marantz and others have aggressive power protection systems that will kickin if the amp is asked to drive low ohm for too long, so might be worth bearing that in mind. Never had that problem on Harman or Rotel.
Goodluck.

Whoah! Thanks for the education in what some of you believe about how to approach this problem. I come from 20 some years of car audio background & am very familiar with calculating loads on amplifiers & also know from that & home a/v experience that some manufacturers will definately perform well past stated specifications, hence my original question about manufacturers. Tom, the 1st guy at JVC said I "could run upto 6 ohms no problem, so 4 should be no problem"! I then asked for level II tech support hoping to talk to someone who at least understood what I was asking. Denon's tech line also said not to run their a/v recievers below 6 ohms. Not quite sure I understand Fred Forlano's suggestion in that an impedance matching speaker switching box would only maintain that same 4 ohm load. Maybe you thought I was referring to multiroom? Anyway, The guys reciever is a lo-fi "digital" 7 ch surround reciever & I did suggest to him before we did the install that I was not sure that he would be happy with the little unit he had, but we could try it. Just did not even think to check if the speakers we're 8 or 4 ohm. All equipment is new. When I 1st powered it up I could tell it was WAY underpowered. Unit played fine for a day & then shut off. Turn it on & it shuts down right away. I checked all speakers through the wires & they all read 3.7 to 3.8 ohms resistance, no dead shorts & of course that is just a static reading, not dynamic. The speakers we're actually built by Posh for Boxlight Corp. & rebadged as Studio Experience. Seem to be pretty decent quality & are rated to 250 watt continous max. The room is pretty large & it is certainly possible that he cranked it way past what he should have & maybe put the thing into permanent protection mode. Sorry if my original post sounded goofy! When I originally asked the question about disconnecting 1 driver to achieve an 8 ohm load it did not feel right to me. I was in a hurry to get out the door this morning & was sort typing what I was pondering & forgot about the crossover points changing as the load changes. Been a while since I built a crossover. Any body remember the "Rockford way" from Rockford fosgate training in Tempe, AZ way back in the 80'S? Thanks for all the participation! Erik

Git 'er done w/ an Audio Control Meastro pre- amp

[Link: hometheateraudiocontrol.com]

and their theater amp.

[Link: hometheateraudiocontrol.com]

And their a big car audio name too !

Ernie,
Most amps I have seen are rated higher power at lower impedence. The Denon 3805 for example is rated at 120 watts at 8 ohms but 160 watts at 6 ohms.

Weird thing is the dynamic power is 140 at 8 ohms, 180 at 4 ohms, 240 at 2 ohms but the amp is rated only for 6 - 16 ohms.

I still have my RTTI binder from the Punch/Power era when the Punch 150 was the big seller and the Power 1000 was King.

I was more of a PPI/JL guy... My old store was JL dealer #6 or #9, and we were the first outside of FL.