Ohm 4 channel amp

[mtomline]

Hi, I have a 4 channel Yamaha S701 amp and 4x B&W 655 S2 which are 8Ω (minimum 3.5Ω). I also have a Yamaha SW300 wired, so I am able to bring the low-frequency output down on the amp. My concern is running all 4 speakers at once, I would essentially running the amp too hard at around 4Ω. I have seen that if you run speakers in series then my total load would be around 16Ω which is great, but how do I do this with a 4 channel amp, I have only seen it done on a 2 channel, surely I would need to use all 4?

Any help on this would be great, as I would like to use the speakers and amp together without worry of blowing something.

Thanks
Mark

 

[everettT]

Your amp is a two channel amp with AB speaker hookups. I've you run them both at the same time you would see a 1.5ohm load at some frequencies, not advised.

 

[Verdinut]

If you want to play your 4 B & W speakers simultaneously with a stereo amp, you would have to replace your S701 with a solid amp such as the new Accuphase E-650 that can handle impedances as low as 1 ohm also for a sum of $25,000 or more. It's a Class A amp with a low power output of only 30w/ch at 8 ohms but will provide 150 watts for a 1 ohm load.

 

[mtomline]

Thanks, yeah this is my concern. Can I run them in series? As 4 of these speakers run in this way would be less for the amp than my set of 4ohm Monitor Audio Silver 8i should it not?

 

[everettT]

What is your goal? Just as some amps dont like very low impedance, same is true the other way.

 

[mtomline]

i'd just like to run all 4 at once if poss. i did have 2 sets of speakers plugged into the amp previous to getting the B&W. 1 set of floor standing 8Ω (minimum 4Ω) and 1 set of bookshelf Nominal 8Ω and i really gave it some stick without a problem (may just have been lucky). Now i have the new speakers i am more worried about it all. Is running in series an option? I could do without spending more money like $25,000 (i'd buy a whole new system with that)

 

[everettT]

You should just by speakers capable of more output. 4 stereo speakers just muddies the sound. Crown makes a 4 channel amp only, IIRC somewhere around $1300.

 

[mtomline]

Sure that makes sense, but I have found that in the large room they are In, the sound is much more even with 4 of these than my MA8i set and as they are the same speakers this helps too. I have only tested it though. Is series not an option?

 

[everettT]

You can try it but you might start to hear distortion, if so scrap that idea. A speaker selector with impedance match will work, just going divide the amps output in half.

Filling a large room with full sound takes a speaker with high SPL capabilities. Have you ever considered pro audio speakers?

 

[mtomline]

Speaker switch sounds good. The speakers are 25W - 100W into 8Ω on unclipped and the amp is 160W x 2 (max), 100W x 2 (RMS).
What do you think? Thanks for your views on this!

 

[everettT]

https://www.amazon.com/Monoprice-108231-Speaker-Selector-Control/dp/B007N43T5Y/ref=mp_s_a_1_4?ie=UTF8&qid=1535333208&sr=8-4&pi=AC_SX236_SY340_QL65&keywords=speaker+selector+with+volume+control&dpPl=1&dpID=310oEgIWT9L&ref=plSrch
Something like this.

 

[WaynePflughaupt]

A series connection will cut the amplifier power by approximately half, and that will be divided between the two speakers. For the
S701, that means each of the four speakers will see only ~25 watts each.

The speaker switch will maintain the 8-ohm load, but will similarly divide out the power. So, two speakers per channel connected through the switch means each will only get 50 watts at most. It will be less than that when you factor in the loss that comes with the switch’s resistor network.

Really, if you’re serious about doing this right you should replace the Yamaha with a pre-amp and a suitable power amp. You can get pro amps that will work with a 2-ohm load, or a 4-channel model.

Regards,
Wayne A. Pflughaupt

 

[TLS Guy]

You can not put the speakers in series. That will be like putting a resistance in series with the speakers, and their frequency response will follow the impedance curves of the speakers.

That impedance matching switch with volume control will reduce the power available to the speakers due to losses in the auto transformers. So you will gain nothing.

Your solution is more powerful/sensitive speakers, not driving two pairs. The latter never a good idea.
Lastly your B & W speakers are not 8 ohm, they are 4 ohm. Like a lot of speaker manufacturers B & W quote the impedance incorrectly to encourage sales. The rule of thumb is minimal impedance plus 10%. So just under 4 ohms for your speakers.

 

[mtomline]

ok, maybe as I use this setup for tv/film as well as cd/records would an av receiver do it? I don’t want huge speakers in this room. Running these 4 speakers is what I want to achieve, as it sounds very good. But safely. Thanks

 

[Andrein]

Ar

ok, maybe as I use this setup for tv/film as well as cd/records would an av receiver do it? I don’t want huge speakers in this room. Running these 4 speakers is what I want to achieve, as it sounds very good. But safely. Thanks

Are 2 speakers not enough for that room? You can get avr and run 4ch stereo and get higher sound levels this way.

 

[mtomline]

I don’t want to have 2 big speakers in there taking up floor space etc, these 4 B&W sound very good running at 1 time, but I need to do it safely. AVR sounds like a good route especially as they are hooked up to the tv anyway, but I have heard they won’t sound as good as an amp. or I need to get a more powerful amp as no matter how I run all 4 through this amp each speaker would only get 25w which is their minimum (maybe that is ok though?!).

 

[Kvn_Walker]

ok, maybe as I use this setup for tv/film as well as cd/records would an av receiver do it? I don’t want huge speakers in this room. Running these 4 speakers is what I want to achieve, as it sounds very good. But safely. Thanks

The worst impedance dips are usually in the bass regions, so if you're willing to cross over the sub rather high then you could most likely get by with that amp. If you can find your speakers' impedance chart online it will help a lot with tuning to reduce amplifier load.

...now I just looked up the manual for the AS701 and while it does have a subwoofer out, I don't see where it allows you to high-pass your mains. That's a weird design to me, having sub-out but always full range to the speakers. In your case a receiver with a proper subwoofer crossover will be your best bet.

 

[mtomline]

Yes I found this annoying after getting the sub. No HPF on the amp, although I think AVR mostly have this?. I have just turned the bass switch right down to release the speakers of bass which isnt ideal lol, but it must help a bit.

 

[TLS Guy]

Yes I found this annoying after getting the sub. No HPF on the amp, although I think AVR mostly have this?. I have just turned the bass switch right down to release the speakers of bass which isnt ideal lol, but it must help a bit.

It is hard to help you definitively as you have listed B & W speakers that never existed. It is not in their current range or archive list.

In general older B & W speakers have had very adverse impedance and phase curves and well above sub range at that. Usually they have very low impedance form 100 to 700 Hz or so. That is right in the power range. They are good amp busters. Their newer offerings are improving in this regard.

This is particularly a problem with the 600 range as they are intended for more modest systems, not associated with iron amps. I don't know what their new range is like, but I was never very impressed with previous offerings in the 600 range.

To help you then I need to know what speakers you actually have and whether they can be driven properly by an AVR.

I know one thing, if those speakers are bookshelf with just single 6" drivers you will not fill a large space with them unless you play them quietly.

 

[mtomline]

Hi, these are the speakers. http://m.bowers-wilkins.co.uk/speakers/home-audio/600-series/685.html

I’m busy right now, thanks for your advice!!