4-8 ohms Speakers

amplifiers, receivers and loudspeakers
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forbiddenmolec
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4-8 ohms Speakers

Post by forbiddenmolec » 13 Aug 2019 17:15

Helllo.

I have receiver 100 W 8ohms onkyo trx646

and i want this speakers which is 4-8 ohms impedance :
https://www.amazon.co.uk/Magnat-Monitor ... B00TKIVGYW

is it good for? or it will be my receiver burn ?

forbiddenmolec
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Re: 4-8 ohms Speakers

Post by forbiddenmolec » 13 Aug 2019 18:56

UP

JoeE SP9
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Re: 4-8 ohms Speakers

Post by JoeE SP9 » 13 Aug 2019 19:25

The load a speaker places on an amplifier will vary depending on the frequency it's reproducing. An 8 Ohm rated speaker may drop to below 4 Ohms at certain frequencies.

I suspect that your receiver is rated for 100WPC at 8 Ohms. This does not mean you can't use a speaker with an impedance other than 8 Ohms. Check the manual for your receiver and read the power specs. It's likely it has a power rating for both 4 and 8 Ohm speakers.

Note the excerpt below from the manual. Notice that it has separate power ratings for 3, 4 and 8 Ohms. This is a clear indication that it can drive 4 Ohm speakers.

IEC60268-Short-term maximum output power
240 W (3 Ω, Front)
210 W (4 Ω, Front)
120 W (8 Ω, Front)
THD+N (Total Harmonic Distortion+Noise)

FWIW: Amplifiers are not restricted to driving only one Ohm rating for loudspeakers. In essence there is no such thing as an 8 Ohm receiver or amplifier. A PDF of the manual is available on the Onkyo website.

forbiddenmolec
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Re: 4-8 ohms Speakers

Post by forbiddenmolec » 13 Aug 2019 20:19

it says connect only 8-16 ohm speakers. for 4 ohm configure in setup to 4 ohm impedance. so in this mode the receiver will not damage with those speakers?

hobie1dog
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Re: 4-8 ohms Speakers

Post by hobie1dog » 13 Aug 2019 20:33

The TX series of Onkyo receivers will drive those speakers as you can go into the menu and select 4 or 8 ohm speakers.

What Joe said... =D>

josephazannieri
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Re: 4-8 ohms Speakers

Post by josephazannieri » 13 Aug 2019 21:06

Yo forbiddenmolec:

I do not think that you will get into trouble with your speakers that have an impedance rating of 4-8 ohms. The best I can figure is that your instruction manual is giving instructions for the situation where you have more than one set of speakers paralleled onto one channel. If you parallel 2 sets of 4 ohm speakers on one channel you will get an effective impedance rating of 2 ohms. This is far enough below your 3 ohm short term maximum power rating so that you run the risk of overheating the output boards and either driving the amp into protection so it shuts itself off, or damaging the output boards. These recent receivers use high power integrated circuit boards which are mounted on big heat sinks, and the chassis are very cramped, so you need to make sure that there is room around the receiver to permit airflow into the heat sinks so the receiver will not overheat. So long as you only have one set of speakers rated 4-8 ohms on each speaker output you should be OK.

JoeE SP9's statement is correct. In general, a speaker's impedance rating is taken at the lowest point on the speaker's impedance curve. A speaker rated at 8 ohms will usually have an impedance peak of between 20 and 30 ohms at its low frequency resonant point, which will be in the 40-60 Hz area for the speakers you want to use, based on their low frequency limit of about 40 Hz. The speaker impedance will go down until it reaches a low point, between 4 and 8 ohms, which will occur somewhere around 400 Hz, and then start to rise again.

So long as you do not attach more that one set of these 4-8 ohm speakers to each set of speaker terminal, your speakers will not overload your amp. If you are going to connect more than 1 set of speakers to each speaker terminal, you can determine the impedance of the whole system by resorting to this formula, where Z is the rated impedance of the speaker. 1/Za + 1/Zb = 1/Ztotal. With 2 speakers of 4 ohms each 1/4 + 1/4 = 2/4, or 1/2, which means that two 4 ohm speakers give a total impedance of 2 ohms, which is too low. Another example: where you have one 8 ohm speaker and one 16 ohm speaker, 1/8 + 1/16 = 3/16 =1/5.3. With this configuration, you get a total impedance of 5.3 ohms, which will work with your amplifier. Two 8 ohm speakers will work out like this: 1/8 + 1/8 = 2/8 =1/4. the impedance of two 8 ohm speakers in parallel will be 4 ohms.

You also have the option of hooking the speakers up in series. The formula here is Za + Zb + Ztotal. By using series and parallel wiring, you can hook up any combination of speakers and not overload your amplifiers.

And good luck from the old speaker shunter,

Joe Z.

forbiddenmolec
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Re: 4-8 ohms Speakers

Post by forbiddenmolec » 14 Aug 2019 09:13

nice tips
thanks J

josephazannieri
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Re: 4-8 ohms Speakers

Post by josephazannieri » 14 Aug 2019 15:40

Yo forbiddenmolec:

Mistake in my last post. Correct formula for speakers wired in series is: Za + Zb = Ztotal. You add the impedances for speakers in series.

Good luck from the mistaken old guy,

Joe Z.

lenjack
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Re: 4-8 ohms Speakers

Post by lenjack » 14 Aug 2019 17:39

Should not be a problem.

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