# 8Ohm and 4Ohm on a single amp?



## Spadez (Oct 14, 2009)

Hi,

I have been told that its possible to put two front 4Ohm speakers on Onkyo 607 amplifier, with two side 8 Ohm speakers as well.

However, I would like confirmation of this, since my amp seems to have a universal Ohm setting for all the speakers, and if I set it on the 6-8Ohm setting, im not sure my 4Ohm speakers would work.


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## Jungle Jack (Jul 28, 2009)

Hello,
I would leave it in the 6-8 ohm setting unless you are having shutdowns. When you set it to 4 ohms, the current and power on the Onkyo is greatly reduced. 

You should be fine as described. Again, only if the Onkyo shuts down should you consider the 4 ohm setting.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

Thank you for the reply. The trouble is, im about to embark on an order of products for a 4Ohm diy project (Zaph 3.5). How likely is it that my amp will shut down when I run these 4ohm speakers with my 8ohm speakers? Im a bit buggered if it does shut down because I wouldnt be able to afford another amp or anything.


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## Jungle Jack (Jul 28, 2009)

Hello,
It is almost impossible for me to answer that question. Your room size and volume level will play a part.
All I can say is you get the most power out of the 6-8 ohm setting. Unfortunately, the 607 does not have preamp outputs. It should be fine, but I would gradually raise the volume and see how it performs.

Units like the 607 are usually not mated with 4 ohm Speakers as it is an entry level model. Most speakers that are used with entry level AVR's are 8 ohm and efficient. This makes them easy to drive.

I would just try it as proposed. It should be fine. Hopefully, the speaker does not go below 4 ohms.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

Hi,

The 607 does have preamp outputs, but they are being used for my subwoofer currently.

This is a link to the power handling of the speaker im looking at:









It looks like it goes lower than 4Ohms on the diagram.


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## CasePro (Dec 23, 2009)

If you are running a subwoofer and crossing the front main speakers over at say 80 Hz or higher, which you would probably want to do anyway, you should be just fine running the 4 ohm speakers. Your amp might struggle with them if you were running them full range, but if you are crossing them over you need to look at the chart from the crossover point up, since this is what your amplifier "sees".


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## Spadez (Oct 14, 2009)

Ok. I might need someone to explain to me why there are multiple Exc lines. I cant really judge what Ohms im looking at running because there are 8 visible Exc lines on that graph.

I actually got my amp on a bit of a discount. It was £225. I think I could probably sell it for what I got it for on ebay so should I do that and get a better amp?

Finally, are there no good 8Ohm speaker kit designs out there? I havent seen any, are they not as good as 4Ohm?


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## Jungle Jack (Jul 28, 2009)

Hello,
The only preamp output on the 607 is the Subwoofer output which all AVR's have. The 607 does not have
preamp outputs for all channels which would allow adding an amplifier. The 707 and above do.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

. Ok, i might have been better off going for those them.

Would you mind having a look at this page, and telling me if this speaker would work on my amp? Its woofers are 8Ohm nominal and the tweeter is 6 ohm so I might be alright?

http://www.zaphaudio.com/Waveguidetmm.html


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## Spadez (Oct 14, 2009)

Ive been looking into this, but it seems its more of a 4 Ohm nominal.

Doh! 

I know that this isnt very "eco", but couldnt I just mount a fan inside my amp and have it cooled better, to better my chances of my amp being able to cope?


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## Spadez (Oct 14, 2009)

These might be more up my alley though:

http://www.audioheuristics.org/projects_gallery/ER18DXT/ER18DXT.htm


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## Spadez (Oct 14, 2009)

Whoops.


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## Jungle Jack (Jul 28, 2009)

Hello,
For AVR's in its price range, the TX-SR607 is quite powerful. The kit which you linked to looks like it would be a good match with your 607.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

Hi,

Which kit are you refering to, the wave guide or the ER18DXT?

Thanks


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## CasePro (Dec 23, 2009)

Spadez said:


> Hi,
> 
> The 607 does have preamp outputs, but they are being used for my subwoofer currently.
> 
> ...


The green line is the impedance curve. The flatter curve is frequency response at different spl levels, and the other red curves are excursion at those same spl levels. 

What the chart shows is that the speaker will be excursion limited below about 80 Hz at the higher volume levels. It also shows impedance peaks at two points. These are both insignificant if you run a subwoofer and run a high pass xover for these speakers.


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## Spadez (Oct 14, 2009)

Ah, I totally misunderstood the graph. So really these are 8 ohm nomincal speakers, because it doesn't seem to drop to 4ohm at all. Are you also saying that the peaks in impedance is a problem for my amp as well? Would the peak at 80hz also cause my amp to possibly shutoff?
_Posted via Mobile Device_


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## lcaillo (May 2, 2006)

Peaks in impedance will not cause your amp to shut down.


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## Spadez (Oct 14, 2009)

Ok. Obviously im getting some of this stuff wrong because I dont fully understand it. Can someone please answer these questions and then I think I will understand it properly.

1. If I put my amp on 6-8Ohm mode, what will be the result if my 8ohm nomial speaker goes down to say, 4Ohm during load.

2. What will the result be of a peak in Ohms, much like the one in the diagram above. Will my speaker be able to cope with it short term, or will it cause the volume to fluctuate?


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## CasePro (Dec 23, 2009)

Zaph's comment about the 3.5 on his build page:

"This is a solid 4 ohm nominal design, so be careful with wimpy low end receivers. Impedance drops to 3.2 ohms in the midbass, which is typical for a 4 ohm nominal design. I did seem to power it fine with an inexpensive Panasonic digital HT receiver, and of course my 120w/chan NAD powered it as loud as I could stand. "

Although the Receiver that you have is at the low end of Onkyo's line, I would not consider it a wimpy entry level receiver that Zaph warned about using. 

What the lower impedance means is that the receiver is going to have to work a little harder and dump more current to drive the speakers. If it is your plan to play very dynamic music at extremely loud levels for long periods of time, then maybe you might run into issues. 

However, if you are just going to listen to movies quite a bit, that is a completely different story. When I watch a movie it is typical that I have the volume set at about -15 or -20db. I won't bother doing the math, but average power output at that level is maybe 5 watts!

If you have a subwoofer and you plan to high pass your main speakers, you will be absolutely fine, I promise!


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## Jungle Jack (Jul 28, 2009)

Hello,
The 4 ohm setting is there on your Onkyo as a safety feature. By using it, you will get greatly reduced output power. You can use 4 ohm Speakers with the 607 in the 6-8 ohm setting. There is the possibility that it might shutdown at high volumes. This too is a safety feature and will not damage your AVR.

I am a little bit concerned about using the 607 with 4 ohm Speakers. While more powerful than other entry level AVR's, it is still an entry level AVR and does not have the power supply and capacitance of the higher level models. The only way to know is to try it. Worst case, you will have to keep the volume levels lowered.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

Trouble is, I am going to be listening to them loud, it is going to be for modern music, and they are likely to be on a lot of the day. I am crossing them over at 80 Hz though.

I posted this message on another forum, but i would also like to get your take on this too. I keep getting told by people that a 2.5 system undoubtedly going to be 4Ohm so I need a new amp if I want that.

However, Ive just checked my dads B&W speakers which are TMM configuration, with a great performance, and they are 8Ohm.

Why is it all the DIY 2.5 at 4Ohm but commercial speakers can keep them at 8Ohm?


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## Jungle Jack (Jul 28, 2009)

Hello,
Just to give you an idea of the current limitation when set to 4 ohms, look at the results from the bench test of the TX-SR806:http://www.hometheaterhifi.com/receivers/469-a-secrets-receiver-review.html?start=5

As it shows, when placed in 4 ohms, power is greatly reduced.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

Wow. Thats terrible. Is that the same story with the 807 and 907 onkyo?


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## lcaillo (May 2, 2006)

Not terrible, just the limitation of smaller power supplies that you find in receivers. The Onlyos are not particularly different, in general, than other brands in this regard. More beef is why you buy a separate amp.


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## CasePro (Dec 23, 2009)

I would take those measurements with a grain of salt. They are made with the receiver driving a dummy load at full rated power. They are not real world conditions, but they are telling about what the 4 ohm switch actually does. It limits current to prevent overheating. 

The Zaph 3.5 are about 88 db efficiency IIRC. That would mean that, with about 64 watts you get 106 db at one meter. That is pretty stinking loud. 

You did say that you plan on playing modern music and playing it pretty loud. I still say that high passing the full range speakers takes much of the load off of the amplifier and you would be OK, but what I consider to be loud and what you might consider loud could be two different things. If that is the case and you want to make it easy on your receiver, maybe you might take a look at this zaph design:

http://www.madisound.com/catalog/product_info.php?products_id=8691

higher impedance and much more efficient. They would require half as much power to drive than the other kit you are considering.


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## Spadez (Oct 14, 2009)

Thank you both for the reply. Im quite happy to see CasePros reply, I was kind of assuming if I wanted some serious output I would need to sell the brand new amp I just brought.

I wasnt sure about "high passing" the full range speakers, because I wanted them to mesh nicely with the sub. However, if I have this correctly, you cant tell where the sound is coming from below 80Hz so I guess it doesnt matter too much.

This isnt crazy loud, but I would like to think I could get between 100-110DB. I'm intrigued by the kit you posted, as a finished speaker its quite expensive, but I think I might be able to DIY it for around $600? How does this kit compare with the other ones I was looking at in terms of DB output and quality of sound?

Also, you say its much more efficient, is this highly likely that I could get away with keeping my Onkyo for this setup? 

Ill read up on it now though with a nice cuppa


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## Jungle Jack (Jul 28, 2009)

Hello,
The 4 ohm setting is similar in all Onkyo's. Again this is current limiting to keep the amps from overloading. The upper range Onkyo's have no problems driving 4 ohm loads. Just do not set it to 4 ohms.
Cheers,
JJ


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## Spadez (Oct 14, 2009)

What actually makes this design more efficient? Since I already have a subwoofer im not sure I would need to go to Zaph design with an addition 2 12" drivers, ive already got 3!


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## CasePro (Dec 23, 2009)

The speaker is more efficient because of the drivers that are used. When you see a speaker rated at 88 db 1W/1M, that means that a microphone placed one meter away on axis will measure 88db with one watt applied to the speaker. Each 3 db increase in output requires double the amount of power (theoretically). So the 88 db speaker will play 91 with 2 watts, 94 with 4 watts, 97 with 8 watts, 100 with 16 watts, 103 with 32 watts, 106 with 64 watts, 109 with 128 watts. 

So for example if another speaker is 94 db efficient, then that means it is 6 db louder with the same amount of wattage applied. So this speaker would play the same volume as the 88 db speaker with 1/4 of the power applied. It plays 109 db with 32 watts applied compare to the other speaker that needs 128 watts to play that same volume level.

The chart that you showed earlier shows how you can't just keep applying more and more power to get louder. Eventually you run into the excursion limits or the thermal limits of the driver and you get distortion.

Zaph's 3.5 design is optimized for the flattest, most accurate possible sound. I wouldn't say that it is inefficient. It is average with regards to efficiency. The tradeoff in the design is that it is a lower impedance design a little more difficult to drive for the amplifier. 

The big tower that I linked to is $1000 just for the parts and you still have to build the enclosures, so it is quite a big more expensive than the 3.5.

If you want accurate sound on a budget around $500, the Dayton UA701 kit is outstanding and it is an easy 8 ohm load. The usher mid that is used has very low distortion and excellent low end response. Zaph calls it "class leading" with regards to harmonic distortion and it is half the price of some of the mids that it is compared to.

The Dayton kit will be very easy to assemble. The crossovers on the 3.5 kit are fairly complicated and would be a challenging first build.

I think the Dayton 701 kit is a much safer bet for you. They are a tried and true design.


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## Jungle Jack (Jul 28, 2009)

Hello,
I really think with the 607 and your indicated desire to playback at high volumes, that an efficient 8 ohm Speaker should be the order of business. Without the ability to add an external amplifier, you cannot add a more power. It is really the only thing I am not crazy about with the 607. However, with the exception of H/K, almost all entry level AVR's lack preamp outputs. Ironic, the AVR's that could most benefit from an outboard amplifier are usually the ones without preamp outputs.
Cheers,
JJ


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