AV receiver technical questions

[dayneger]

I'm pondering finally moving into HT and could use help with a couple of questions!

First, can the output levels be adjusted to level out speakers of different efficiencies? My front LR are approximately 87db and the rest likely 84db.

Second, can receivers of the lower ranks handle 4 ohm loads? Since my HT needs are very modest I'm considering the Denon 1404, which gives its power ratings at 6 ohms. My speakers drop down to about 3.6 ohms, though. Any idea if this'll work out? I'm planning on using an active sub, so the receiver shouldn't be under serious strain.

Third, what happens to the bass for the center and surrounds if they're set to small and the front speakers set to large?

Thanks in advance for the help!

:-) Dayne

[Sonnie Parker]

Welcome to the forum Dayne! Glad to have you on board.


Sounds like exciting times are ahead for you. HT is so much fun and so is the shopping for it. I get excited with every piece of equipment.

I believe most receivers of respectable quality should allow speaker level adjustments. Some will even offer individual delay settings for each speaker. You might download the manual and read up on it before making your decision.

Speakers will vary resistance (impedance) across the frequency range with some dropping down to 2 ohms or maybe even lower. The ratings you see are nominal. If 3.6 is the low end then I wouldn't think you'd have too much to worry about. Someone else might be able to get more technical for you on this.






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[dayneger]

Hi Sonnie,

Thanks for the post! It would be great if I can get away with 3.6 ohms, since something genuinely stable like an NAD T742 is more than twice what I need.

I like your "Lower Alabama" reference. My sister now lives in the Sampson area. Does that also qualify?

Hopefully someone can chip in on the other questions!

:-) Dayne

[ThomasW]

Speakers with a nominal impedance of 3.6 ohms should not be used with receivers rated for 6 ohm speakers.

When the center and rear speakers are set to small and the mains are set to large, the LFE is sent to the front speakers




theAudioWorx
Klone-Audio

[Andrew Pratt]

I agree with thomas those speakers shouldn't be used with a budget receiver since they'll cause the amps to over heat and likely go into protection mode. While Denon generally makes a fine receiver I know first hand that their bottom to middle teir receivers don't like low ohm loads. I used to have the denon 3300 paired up with magnepan speakers which are a constant 4 ohm load and while it was ok with two maggies when I added the other 3 it wasn't able to keep up with the current demands.

With that in mind most budget receivers aren't going to be happy with that load. Quality units like the Rotel 1055 or some NAD receivers would likely handle it ok but those aren't in the same price bracket as the Denon you made mention of above.

For ballencing yes you'll be able to adjust each speaker's output individually to compensate for different distances, amp power and efficiencies

[Sonnie Parker]

Dayne, I believe Sampson will qualify as being in L. A. That's acually about 25 miles south of us.

What speakers are you referring to and what is the nominal rating?

I have an el cheapo Denon PMA-715R (65wpc) that shows a 4 ohm load in the specs. I use it to power a pair of B&W 600i's and a pair of Klipsch SA-3's. We hammer it fairly hard and for long hours for the outdoor horseshoe tourneys with no problems. I'm not sure if that would equal home theater though. I know it probably wouldn't be enough power.

Is this the only receiver you've looked at in your price range?






SONNIE

Cedar Creek Cinema

DVD Collection

BFD Comprehensive Setup Guide

[dayneger]

Thanks for the responses.

My speakers are a kit from the infamous Peter of AV Reality in Denmark. They're a 2-way monitor based on the Vifa XT ring radiator tweeter and the Scan Speak 7" Super Revelator mid-bass driver. They're a nominal 4 ohms, and dip to about 3.6 ohms in the 60 Hz area if I recall correctly.

I'm planning on high-passing them in the 100 Hz area and use small twin subs. At this point they're always above 4 ohms gently rising to about 8 at 20khz.

I'm very open to other receivers, so suggest away! I've simply read good things about this Denon. I have a combined 2-channel and HT setup planned, so it would also be possible to use LR preouts, provided any of the inexpensive units still have them.

Take care,

:-) Dayne

[Andrew Pratt]

They're a 2-way monitor based on the Vifa XT ring radiator tweeter and the Scan Speak 7" Super Revelator mid-bass driver

Very nice:T I"m using the same tweeter in my M8a speakers

My suggestion would be to go for either a higher priced receiver like the Rotel 1055 or go for a lower priced receiver that has pre outs and use it as a pre amp to a budget power amp. I don't know what's available on the used market in your area but I'd look for a used 5 channel amp and add a new cheap receiver to do the processing. This will likely cost quite a bit more though then what the denon 1404 cos.s... but music is important and those speakers do demanding and deserve quality power.

[ThomasW]

My speakers are a kit from the infamous Peter of AV Reality in Denmark

'Infamous' is correct ........

I don't pay much attention to receivers but given the 3.6 ohm load you don't want skimp. Make sure whatever you buy is rated for 4 ohms not 6 ohms. Look at some of the offerings from Onkyo, they make nice gear and show power ratings down to 3 ohms




theAudioWorx
Klone-Audio

[brucek]

First, can the output levels be adjusted to level out speakers of different efficiencies? My front LR are approximately 87db and the rest likely 84db.

Yes.

My speakers drop down to about 3.6 ohms, though. Any idea if this'll work out?

The lower the impedance of the speaker you use, the more current they will draw from the amplifier, and the more heat will be generated.
Certainly the specified impedance load for a set of speakers is average over the audio range. This impedance changes greatly depending on frequency (as you've noted already). The result of using a load that is lower than allowed for an amplifier will be in the form of heat and a thermal shutdown if taken too far.
A test of the lower load, while monitoring the amplifiers heat sinks temperature, would tell you pretty quick whether that load is OK or not. You'll know, long before you do any harm to your amplifier, if it will tolerate a "specific" set of speakers.
Be sure that if a receiver specs a lower impedance handling capability, that it's as a result of a better power supply, heat sinks etc and not as a result of a switchable rail. Some amplifiers, that can't tolerate low impedance loads, have the selectable switch on them that allow lower impedance speakers to be used. In reality, this switch simply alters the amount of power supply (rail) voltage available to ensure your amplifiers transistor output stage doesn't overheat when using lower impedance speakers. It's a simple matter that by lowering the output voltage available across the speakers, a lower the amount of power is dissipated. It's a wiser choice to purchase an amp that comes by its low impedance handling capability through better design and properly sized components.

Third, what happens to the bass for the center and surrounds if they're set to small and the front speakers set to large?

If any or all the speakers are set to small, the low frequencies below the crossover setting (i.e. 80Hz) will be mixed and directed to the subwoofer output. So, if your fronts are set to large and the surrounds and center are set to small, a full range signal will be sent to the fronts and a bandpassed signal will be sent to the surrounds and center, with low frequencies from the surrounds and center (below the crossover frequencies) mixed together and sent to the sub.
Generally (depending on the receiver), if you have sub set to yes, the LFE will continue to pass to the sub whether you have your mains set to large or small. If you have sub set to none, then LFE will pass to the mains if set to large.

I'm planning on high-passing them in the 100 Hz area and use small twin subs.

I would recommend a single large sub over two small subs. Two subs are difficult to set up and you'll likely get better bottom end with a single large sub.

For my two cents, I vote for the inexpensive receiver and add a decent external two channel power amp to start. Look at Rotel.

brucek

[dayneger]

Thanks for the helpful tips!

Andrew, your setup looks pretty nice. Those subs are huge! Would probably blow the doors off of my apartment. Well actually not, the Swiss have a habit of building to a 300 year standard. 8O I'm not kidding!

If thermal overload tends to be the problem, could I stick a very quiet fan near the heat sink to keep the system cool? Or would that simply cause the PS to fry?

Getting a used/inexpensive receiver to use more or less as a pre-processor would be an option, but I can't seem to find one with DPLII etc the has preouts.

What I REALLY don't get is why I can't find a regular preprocessor for reasonable cash--it just doesn't seem normal that it's cheaper to buy an entire receiver with 5-6 channels of amplification that just the front end. Must not be a big market. Well, if anyone has suggestions about inexpensive preprocessors or receivers with 4-5 preouts, I'm all ears!

Brucek, others have written that twin subs can help even out the bass since with 2 separate locations you activate more nodes in the room. It's also supposed to add a greater sense of depth, at least for 2-channel applications (the majority of my listening). Sounds worth a shot, anyway!

:-) Dayne

[brucek]

If thermal overload tends to be the problem, could I stick a very quiet fan near the heat sink to keep the system cool?

That's a band-aid - not a good idea.

others have written that twin subs can help even out the bass since with 2 separate locations you activate more nodes in the room.

I'm afraid that with one sub it is difficult enough to control cancellation problems with the mains around the crossover region and to tame room interactions. Adding a second sub is very difficult to set up because of phasing cancellations created from the first sub. Don't try it - you'll be disappointed. The only way to control two subs is to co-locate them - why bother - get a larger single.

Use a single sub, locate it in a corner to maximize room coupling and you'll excite all the resonances in the room and you may even get away without any equalization...

brucek