Best channels to power amp for Denon AVR

Mr Wolf

Active Member
I agree with @gibbsy , there's no issue for you with these KEF speakers. All nominally rated 8 Ohm speakers have much lower dips somewhere along their frequency curve. Also as they're quite sensitive and you listen at moderate volume levels they'll never be hard to drive for you, especially when used with a sub.

Not that the Q900s are 4 Ohm speakers but Gene at Audioholics did an article years ago which you might find useful in which he created a "ready reckoner" table as a guide to when you might have issues powering low true 4 Ohm speakers with a receiver.

Connecting 4-ohm Speakers to an 8-ohm Receiver

Basically, provided you've got at least reasonably efficient speakers and are using a mid to upper range AVR then you shouldn't ever really have any issues.
 

Dobbyisfree

Active Member
Hi @Mr Wolf with the news that my 5 channel power amp works, I am asking nicely for a new calculation. Speaker config has also changed (heights no longer permitted, speakers already sold sad face).

1. Max. listening level (to reference)
Up to -15dB.

2. Speaker sensitivity ratings and distances

FL and FR
MLP 5.5m
8 Ohms, 86 dB
Crossover 60Hz

C
MLP 5m
8 Ohms, 91 dB
Crossover 120Hz

SL and SR
MLP 2.8m
8 Ohms, 91 dB
Crossover 60Hz

SBL and SBR
MLP 1.5m
6 Ohms, 89 dB
Crossover 80Hz

3. Amplifier power per channel on 2 channel and (if known) 5 channel basis.

Rotel 5 channel power amp
100 Watts 8 Ohms 20-20,000Hz 0.03% THD
Guaranteed simultaneously into 5 channels

Rotel 2 channel power amp
70 Watts 8 Ohms 20-20,000Hz 0.06% THD
Guaranteed simultaneously into 2 channels

Thank you.
 

Mr Wolf

Active Member
No problem, what is the amplifier to channel assignment that you wish to model?

Also, I notice that your surround backs are 6-Ohm rated so it would be good if you could check the specs to see if their sensitivity rating was still taken at 2.83V (i.e. 1W into an 8-Ohm load) otherwise we won't be comparing apples with apples. If it's silent on the point then we should assume it's 1 watt into a 6-Ohm load and de-rate it accordingly for the calculations.
 

Dobbyisfree

Active Member
Yes, they are 2.83V at 1m.

And, what I'm looking for is which two channels are best to put in the two channel, if you see what I mean. Please.
 

Mr Wolf

Active Member
OK, you can re-purpose the 2CH Rotel now.

The combo that maximises dynamic headroom is AVR for L/R only and Rotel 5-channel on the rest.

The minimum amount of headroom you have on any speaker channel is 6.1dB on the L/Rs which means you should be able to crank it up to -12dB if you wanted to without issue. Would be nice to see a 90dB+ speaker on those L/R channels.

1624529913127.png
 
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Dobbyisfree

Active Member
Thank you, much appreciated. I thought it would have been better to get the amplification out of the AVR but I see your point as the power level of the AVR is optimised to the two channels.

From a convenience point of view that works better too, as daytime TV is just on stereo speakers, so will leave the (no 12v trigger) power amp off until I'm in the room!

I haven't actually bought the KEF Q150s for the fronts yet. "She" likes KEF styling, and spending up to £500 on some brand new fronts was the trade off deal against no having heights 🤣 Mostly because she said the Mission 780SEs were too ugly 🤣

I could propose an alternative with a higher efficiency to her but they would need to:
(a) Strictly not be any bigger absolute max 310H x 200W x 280D.
(b) They can have no toe in and are approx. 3.5m apart in a 5.5m wide room. Thought KEFs would have good off axis to support this.
(c) Are on a cabinet with 100mm of surface in front of them, so thought KEF driver position (i.e. no driver low down on front face) would help avoid reflections.

I'm sure you see why I thought the KEFs would fit the criteria? But yes rubbish sensitivity.

I was considering trying to wangle the Klipsch RP500M in there, slightly taller but narrower and a whopping sensitivity... but concerned how they would cope with (b) and (c).
 
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Dobbyisfree

Active Member
Sorry to tag, but @Conrad @gibbsy @DodgeTheViper you are the moderators for speakers, which I assume may mean you know a lot about them 🤣

Re: Wolfy's comments on sensitivity do you know a feasible alternative I may be able to pass off for the fronts please given my post above this one? Apparently the horn in the Klipsch may achieve equivalent dispersion but I note that the 600m (bigger model) gets some poor reviews, yet the Q150 seems to get great reviews everywhere.
 

Mr Wolf

Active Member
I think the fundamental problem you're facing is that your speaker cabinet size restriction (especially height) limits space available for woofer cone area which turn limits sensitivity/efficiency.

Speakers with twin woofers are, all things being equal, about 3dB more efficient by design than those with single woofers. Twin woofers require towers or HT focused LCR type speakers and these will all be larger than the space you have available.

If you have to go with a bookshelf speaker then you need to try and max out the driver size for the space available. The Q150 uses a 5.25" woofer - a speaker with a 6.5" woofer might not sound much larger but it would have 53% more cone area. In addition to making it more efficient, having this much more cone area is going to give it an easier time reproducing the bass frequencies asked of it due to lower excursion required. I don't have experience with KEF but I know that B&W's 6.5" bookshelves sound vastly better than their 5.25" ones and are also typically 3-4dB more efficient.

Also be aware that sensitivity ratings are not directly comparable as the SPL averages are often taken at different frequencies. If a speaker with a small woofer has a relatively high sensitivity rating then don't trust it as it's probably because it was taken at higher frequencies. In practice, the region you need the most sensitivity from your mains is in the lowest octaves they have to reproduce as they're the most demanding power-wise.
 

gibbsy

Moderator
Sorry to tag, but @Conrad @gibbsy @DodgeTheViper you are the moderators for speakers, which I assume may mean you know a lot about them 🤣
Being a moderator has nothing to do with knowledge of the particular subject. Mods ensure the smooth running of the Forum and check that no one is breaking any rules. There are members on here with far far more knowledge that I certainly have. They are the ones you should be asking for help.
 

Dobbyisfree

Active Member
Fully understood and thank you. This is why the Q900s are so efficient with the 8" drivers. In case you hadn't guessed, they won't fit in the new arrangement at the front. But perhaps back to the drawing board and find some narrower towers for the front.

And yes interesting comment on sensitivity figures quoted. The RP-500M for example, on Audioscience, shows that it peaks high but actually is nothing remarkable over most of the frequency range.

Thanks again for the guidance.

Another option is just stick to plan and actually not spend the money yet, see what the Missions sound like in that position. I love the 780SE and they are 89dB. At 45 years old, I shouldn't have the itchy pockets that I used to have!
 

Mr Wolf

Active Member
This a table of total cone area for popular sized woofers in configurations of 1-4 which gives you an idea of the relative amount of air a speaker can pump with the same movement.

1624611244491.png


Years ago I bought my current LCRs and, due to it being a fairly large room, I remember the dealer strongly advising me to go with speakers with at least twin 6.5" woofers to adequately fill the space.

I may be wrong but I suspect it's probably a much better idea to increase SPL/headroom through using more efficient speakers than amping up less efficient ones. Provided that extra efficiency hasn't been derived by using lightweight components that would compromise SQ.
 
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Dobbyisfree

Active Member
πr²

I realise you only did that because you wanted more ALT keys!

Like everything in life, there's probably a compromise made when increasing sensitivity. Donkeys years ago, as part of my studies, I had to write a Pascal computer programme that simulated a speaker with a single woofer and a bass port. I probably knew the answer then but I have had far too many real ales, lager and red wine since then.

That's what I blame it on anyway. 🤣

Back to serious, I'll have to have a look as I may find some narrow smaller (than Q900) towers with efficiency and (oh whoops) built in upfiring Atmos!
 

Dobbyisfree

Active Member
Our local:
1624613469629.png

So costs 11% more to get 44% more pizza.

Doesn't work quite as well for people who don't eat the crusts though :( Luckily I love them!
 

Dobbyisfree

Active Member
@Mr Wolf we didn't order any pizzas at the weekend. However, due to a weird path of fate (and the setup we have in a spare room), my wife asked (of course due to the aesthetics) whether our two Q200c would work set horizontally as front speakers. In the back of my mind was panic but I thought it doesn't hurt (and I'll add at this point that whenever she shows ANY interest at all in AV, I hook onto it!).

So, I temporarily setup the two Q200c where they would be in the new setup as left and right. Set them up in the x4400 just as stereo in direct mode and whacked on some tunes. These speakers are 3 way, a UniQ tweeter sat inside a midrange, with one 5" bass and another 5" radiator. They are generally reviewed as being a bit rubbish. But I really wanted to try them as the speakers are set further apart than ideal and thought maybe they might work.

I was not disappointed! Whilst I sat there in the room with the other "I was right" big smiley face, I then checked and they are 85dB sensitivity - d'oh!

Nothing that can't be planned for in the future, there's space in the AV unit for something else, connect them up to the x4400 initially then one day may look for something 2 channel maybe class D that will make them sing even more 🤣
 

Mr Wolf

Active Member
Yes, 85dB is pretty poor sensitivity. Also be aware that centre speakers used in horizontal orientation have a very narrow horizontal dispersion so not great for multi-seat set-up. They can make great mains when used vertically though.
 

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