Mixing 4 Ohms with 8 Ohms Speakers

 

New member
Username: Littleluk

Post Number: 1
Registered: Feb-10
Hi there,
currently I am running a 7.1 Setup with Mission 4 OHMS as stereo speakers and 8 ohms Bose speakers as surround speakers.

I have a Harman/Kardon AVR 235 reciever and everything works great, even though the Ohms are slightly different.

However, since I have a BluRay Player I'd like to buy a new amp to have HDMI.

Do I have to look for a certain feature or will the new reciever work just fine with my different Ohm speakers? I mean the Harman / Kardon worked perfectly fine for two years and I am a little concerned that a new amp won't cooperate with the different ohm speakers as the old one did.

Regards,
Luka
 

Platinum Member
Username: Nuck

Post Number: 14658
Registered: Dec-04
It used to be that H/K made some of the most honest power supplies in the mass market business (and sommore for hifi).
If it agreed that this still holds true, and if you like the H/K presentation, then why not get another, bigger one?

Maybe buy online with a 30 day trial?
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14560
Registered: May-04
.

You're missing the point of a discrete channel amplifier such as the HK and the reasoning behind mixing speakers with varying impedance.

Should you connect two speakers of varying impedance load to one channel of an amplifier you will (unless you know how to do otherwise) have a parallel load which will result in the total load on the amplifier being roughly one half of the lowest impedance of either speaker. Therefore the warning concerning mixing speakers.


You aren't using such a connection.


The 7.1 system you are using refers to discrete channels of operation both in the signal distribution from the source player and in the amplifier's assignment of channels to reproduce those channels. Each channel of the original 5.1 source (the two additional surround channels of your 7.1 are matrixed and therefore not discrete from the source) is "discrete" or separate from the other and contains information not found in another channel. To process such a source input the amplifier must utilize discrete or separate channels of amplification. In other words the HK employs seven separate channels of amplification plus the output for a powered subwoofer channel making for a 5.1 system with the capacity to matrix (process) two additional discrete surround channels to complete the "7.1" feature. As each channel sees only one speaker there is no concern about mixing impedance as there would be had you tried to connect various speakers in parallel to a single channel of amplification. Each channel of amplification is only concerned about its own load and its own survival - to an extent as there is a sympathetic situation involved in multi-channel amplifiers.


Do understand that a "four" Ohm speaker is not a consistent four Ohms across its frequency range and its total impedance curve will very likely take the load on the amplifier channel down beneath four Ohms. Most modern HT receivers do not care for such abuse and when forced to play into such a disagreeable load at high volumes they will shut down (hopefully the receiver will shut down temporarily before it shuts down permanently).


Since the lowest impedance load is represented by your front main speakers you do need to be wary of any new receiver you might consider should that receiver carry a warning concerning low impedance loads. A warning doesn't necessarily imply the receiver is incapable of driving your speakers but it means you should be cautious about such a pairing.

There is only one main power supply in the receiver to feed all those channels and, should one speaker represent a disagreeable load, all channles will cease to operate as the main power supply protects itself. As a rule it is not advised any HT receiver be subjected to low impedance loads.

Seeing a review that implies a particular receiver delivered "X" amounts of watts into a four Ohm load is not sufficient evidence the power supply of that receiver will like what occurs in real life operation rather than a simple test bench hook up.


HK has traditionally been capable of driving low impedance loads and they would be a safe consideration for your next purchase. Once again be aware how a manufacturer built their product in past years is no true indication of how they build their product now or even that all products in their line are built to similar standards. HT receivers exist in a world of gamesmanship and high power for low dollar often times wins the kitty.


As a very general rule, buy the reciever with the least amount of watts for the dollar and the receiver that weighs the most for the stated number of watts available and you should be in the safest territory possible. If funds are available to step into a higher quality product, you should consider multi-channel power amplifiers paired with a pre amp/processor. Such products typically represent better value for the dollar as they are upgradable when the processing power requires while not forcing you into a new power amplifier purchase. Consider a line such as Outlaw which has an excellent reputation for quality and durability. NAD, Rotel and Cambridge also build HT separates at "resonable" cost.


In my own HT system I have used the same HK power amplifier for the past fifteen or so years while the pre amp/processor has been changed out several times over that same time period. Separates cost a bit more up front but typically save you money in the long run. As is, you are about to ditch a two year old receiver. Had you purchased separates in the first place, you wouldn't need to scrap the entire system for the sake of a single HDMI connector. Check out the lines I mentioned, since they are not found in your typical big box store like Best Buy they will require you also search out a better quality of dealer as well.

If your current HK receiver has provisions to connect another processor to the main amplifier (pre amp outputs and power [main] amplifier inputs) of the receiver, you could conceivably start with just a new processor. Use your HK reciever as a multi-channel power amplifier for the time being and have the flexibility to upgrade the single portion of the system that is in constant need of change - the inputs and processor.


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Platinum Member
Username: Nuck

Post Number: 14660
Registered: Dec-04
The AVR235 does indeed have pre in/out.

The unit lists at 33 lbs and 50W X 5. The 6th and 7th are matrixed or passed as mono from the 3rd ad 4th.

I would keep this receiver and invest in a prepro for now. It is proven.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14562
Registered: May-04
.

Gee, Nuck, why didn't I think of that?






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New member
Username: Littleluk

Post Number: 2
Registered: Feb-10
Hello Jan, Hello Nuck,
thank you very much for this detailed explanation, it was very helpful and informative.

The Harman / Kardon features a Pre-Amp, this is right. Just that I understand it correctly - Would I simply buy another processor with the features that I want (Multiple HDMI connectors, DTS-HD, Dolby True HD) and attach it to my Harman / Kardon? I'm an absolute novice on that area, so could you recommend me such a product?

It's not that I am disappointed with the sound quality or that the maximum volume is too low, I really like the receiver. I'd just love to have all my HDMI devices bundled in one single unit and enjoy DTS-HD and Dolby True HD sound - This is the main reason why I am planning to change my HT system.

I was given the Mission 782 speakers two years ago and I love how they sound. I ditched my Bose Acoustimass System for them and am now using the Bose satellites as surround speakers and the Bose Bass Module as the subwoofer for the whole system.

By the way, I wouldn't be going to BestBuy anyway since I'm from Germany.

Best regards from Nuremberg,
Luka
 

Platinum Member
Username: Nuck

Post Number: 14663
Registered: Dec-04
Luks, aren't there some other brand available to you there?
Like Braun ...and more?
 

New member
Username: Littleluk

Post Number: 3
Registered: Feb-10
Braun ... Don't they produce shavers?
 

Platinum Member
Username: Nuck

Post Number: 14668
Registered: Dec-04
Thats BIC
 

Gold Member
Username: Dmitchell

Ottawa, Ontario Canada

Post Number: 3707
Registered: Feb-07
BIC makes speakers too. Probably not good ones.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 14564
Registered: May-04
.

"The Harman / Kardon features a Pre-Amp, this is right. Just that I understand it correctly - Would I simply buy another processor with the features that I want (Multiple HDMI connectors, DTS-HD, Dolby True HD) and attach it to my Harman / Kardon? I'm an absolute novice on that area, so could you recommend me such a product?"



Take your owner's manual to the store when you go shopping. They can look at the description of the back panel of the receiver and advise you regarding the best way to proceed. But, yes, I would think a new processor would be in your future. A good processor should cost about the same as a new, higher quality HT receiver. Possibly not, HT receivers are relatively cheap to build nowdays and you can get HDMI on just about anything.

Consider your total cost down the road and I think you'll find a new processor makes more sense than continually upgrading your entire receiver. As with HT receivers, the fewer the features and the less time the salesperson spends explaining all the geegaws on the remote, the better the chance you have a good sounding product rather than just another flashy pole dancer. In other words, simple is better, buy what you need and you'll probably be spending on sound quality and not on buttons and knobs. Remember, most mass market disposable HT receivers are sold on how many features are on the remote and how many connectors and lights are on the front and back panel. Most high quality audio gear sells on how it sounds and how long it will be serviceable to you.


I understand Germany has some very serious audiophiles and numerous shops that cater to them. Find a good shop and ignore the big box equivalents to the box pushers that we have far too many of over here. Take your time and discuss a long range plan for advancing your system beyond donated speakers and Bose-not-really-subwoofers.


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New member
Username: Timmayor

Post Number: 1
Registered: Jul-10
I have a similar question: I am incrementally updating a 10 year old AV system. I recently added a new HDTV and now am looking to purchase Mirage OMD-15 floor standing speakers. The OMD-15s advertise a nominal impedance of 6 ohms.

Initially I would like to run the new speakers in place of two of my (8 ohm rated) Infinity HTS10 satellites and retain the other three as the center and (left & right) rear channels. I use these with an active Polk Audio PSW10 subwoofer. My current receiver is an old Sony STR V333ES receiver (rated at 90 RMS in the 5.1 mode, 110 RMS in 8 ohm and 100 RMS in 4 ohm Stereo mode). The Sony manual states it is capable of driving either a 4 or 8 ohm load and makes the following statement:

"To enjoy multi channel surround, connect front, center, and rear speakers with a nominal impedance of 8 ohms or higher, and set the speaker IMPEDANCE SELECTOR to 8fC.
You may connect a pair of speakers with a nominal impedance between 4 and 8 ohms to all of the speaker terminals. However, even if one speaker within this range is connected, set the IMPEDANCE SELECTOR to 4fC.
Notes: Be sure to connect front speakers with a nominal impedance of 8 ohms or higher if you want to select both sets (A+B) of front speakers (see page 28). In this case, set the IMPEDANCE SELECTOR to 4ohm. Do not set the SPEAKER selector to A+B if you connect speakers with a nominal impedance of 4 to 8 ohms to either FRONT A or B jacks.

That statement doesnt help me too much. My question is do you think I will cause any problems with my receiver mixing the 6 ohm nominal resistance of the two OMD-15s with the 8 ohm resistance of the three Infinity HTS10s?

Thank you,
Tim
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 15066
Registered: May-04
.

Impedance seems to be the issue of the month. Check out the other posts in this section and the "speaker" section of the forum which are asking similar questions regarding impedance and amplifiers.




"Power" is a terribly misunderstood term. "Watts" are a function of voltage and amperage (current) working into a load (Ohms). More (or fewer, for that matter) "watts" is a function of changing the math by way of changing the amount of voltage or amperage or by changing the load value in the traditional Ohm's Law equation. Normally, you would think, if you understand Ohm's Law; http://www.ndt-ed.org/EducationResources/HighSchool/Electricity/ohmslaw.htm, that when impedance (load) drops the "watts" should increase. If voltage remains stable (which it will in a consumer amplifier ), higher current flows into a lower load impedance which results in higher overall "watts". Indeed this is the normal course of events for a modern amplifier working into a strict "resistive" load. One issue for consumers would be no common consumer oriented speakers will be a strict 8, 6 or 4 Ohm resistive load as you would find on a test bench represented by a large load resistor. All speakers have an "impedance" which combines the elements of resistance, capacitance and inductance. In addition (virtually) all speakers are motors which generate their own voltage and current back into the amplifier. This makes the "load" shown to the amplifier far more complicated than any one spec will indicate.

The Sony specs you've provided indicate the receiver will produce less power into a four Ohm load than into the higher, more stable eight Ohm load. This is counter-intuitive and indicates the Sony cannot produce sufficient current when loaded down to a four Ohm impedance. In part this is a function of the 8/6 Ohm switch you are advised to change when driving lower impedance speakers from the Sony receiver. This switch limits current to the speakers - which is exactly the opposite of what the speakers require - in an attempt to minimize heat and stress on the circuits. All together this tells you Sony has provided a crap amplifier and wants you, the end user, to live with their decision by limiting the quality of sound you desire.


In the end, what will do the Sony in is not the mixing of load values on individual channels but the overall lack of quality in the product.

Hope that helps.



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Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 15067
Registered: May-04
.

http://www.ecoustics.com/electronics/forum/home-audio/643519.html
 

New member
Username: Timmayor

Post Number: 2
Registered: Jul-10
Thanks Jan; very useful information in responses to Luka (HK) and Mike (Pioneer) and in speaker threads. It sounds like a new receiver and speakers may be in the cards. Receiver or amp/pre-amp is still a mystery but now considering Paradigm Monitor 7s for front rt. & lf. It's been more straight forward with my Teac AG-6500 and HK bookshelf speakers. Upgrades don't happen frequently for me so I appreciated your detailed input.
 

Platinum Member
Username: Nuck

Post Number: 15269
Registered: Dec-04
8 ohm speakers are usually recommended here for any receiver.
After checking with people who actually know to find out the minimum impedance dip/frequency and according phase shift.

Go light on a receiver.
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