Amplifiers and Speakers. Power and dB SPL explained simply

G’day fello audio enthusiasists : )

Yes I am back again with a smile : )

In searching to convince myself that I needed a larger amplifier or more efficient speakers. I found this article. Please have a read and enjoy. I fit into the first category at age 57. I think I listen to peaks at 88 dB SPL with 84 dB speakers connected to a Nait XS 2 amplifier, 70 watts into 8 ohms and 100 watts into 4 ohms.

I feel a lot more comfortable with my amplifier and speakers now, which have been niggling me for years.

For those that do not already know. My speakers are a pair of Celestion SL6Si 84 dBSPL, 8 ohms, 120 watts.

Warm regards,

Paul…Oops,Galah or was it Drongo :wink:

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I’m not sure that an article reliant solely on maths really helps. All it does is take specified sensitivity and calculate the watts needed to give a set number of dBs. It tells us nothing, or very little, about how a speaker and amplifier will perform in the real world. The SL6 variants are generally described as dull, undynamic and hard to drive by those being kind, and the worst speaker I have ever heard by those being less kind.

I’d forget the maths and try some alternative speakers to go with your Nait XS. If none are better, you have your answer.

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I’d quite like to change my speakers soon. Perhaps this guy will develop a handy app, so that you can enter your age, and power amp specs, and it will tell you what speakers you need.

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G’day HH, Thank you for your reply.

I really like my SL6Si speakers. Though they are a little too soft on bass, yet I can still tap to the bass line (I used to play bass at my local church). As I mentioned in another post which I was possibly a little too severe on saying a love/hate relationship I have with them. It is more love and I wish they could do a little more. Like obtaining the last drop of a nice whiskey out of a bottle and it is the last bottle for the year.

The article I found interesting for the basics as it is stated “For Dummies”. I feel happier now with my speakers and do not have the upgrade bug for a SN3 or similar.

Yes I will change the speakers…one day. Though not today.

I thought the idea of being 57 years old and sitting two metres, maybe three from the toed in speakers aligned with my home situation.

It took the pressure off myself to purchase a larger amplifier or more efficient speakers for the moment. I do not have loads of cash as my budget approach to a nice home hifi system for our retirement. Piece by piece.

As I am on topic for a possible new pair of speakers. As speakers outside Australia might not be available in Australia. Would anybody have a dollar guide to go by please?

I spent $4,000 AUD on my Nait XS 2 and $1,800 AUD on the Flatcap XS. Please note not at the same time. There was a possible two year gap between purchases and it was an impulse purchase with regards to the Flatcap as my local HIFI shop was doing a run out sale. They are 150 kms away.

What I mean, as I spent, the above dollars on the components already mentioned and $4,200 on CD 5 XS. There is the possibility of over capitalising. Should spend $4k AUD on speakers, or $8k AUD or more? Trying to compare apples with apples, country to country. If you google my hifi store it is called Audio Trends in Melbourne Australia. They have a list of speakers there for sale.

Over to your thoughts.

Warm regards,


In this scenario, I would be tempted to spend 8k+ of your monies on a decent and coherent cable set. 5k+ on a quality rack support.
If your happy with what you have and want to get out that little bit more.

G’day TJ,

The cable from the CD 5 XS to the Nait XS 2 is a grey superline. Speaker cables are 5 metres each of Naim speaker cables.

Yes the mounting is inadequate. It is an IKEA TV Flatpack TV stand that holds up a 50" Pioneer Plasma and 4 x 2 pigeon holes for the Naim Audio Equipment.

I do not own Power Lines, though have a noise limiting power board and 3 time Isotek EVO3 Sequel Power Cable (2 Metre C13) power IEC power leads for each component.

That is as far as my last purchase stretched.

I am considering a turntable. Though maybe the money would be better spent one the speakers. Looks like it is time for a sound trial.

Thank you for your post.

Warm regards,


If you really listen with only 88dB peaks, sitting 2m from each of a pair of 84dB @1m speakers, that corresponds nominally to just 5W peak, so the power handling capacity of the speakers and the power capability of the amp, being much higher, are of absolutely no concern. That being the case, Assuming you have quoted the loudest you listen, all you need to worry about is whether it sounds good to your ears. If it doesn’t, The question may be whether the amp has enough control over the speakers, but I suspect it is more likely to be the character and ability of those speakers than the amp.

Different if you are listening at 88dB average with music having a fairly wide dynamic range with peaks of, say, 105dB, which requires 250W. If the Nait has similar peak capability as the NAP200, also 70W RMS but peak capability quoted as 300VA, then it won’t be driven into clipping and the limiting factor would be whether the speakers can take it without distortion, or damage. But a peak just 1dB louder at 106dB (316W) would very likely cause the amp to clip. Whilst that is unlikely to damage the speaker, and but very occasional and brief clipping can destroy speakers even where their nominal power handling is greater.

How did you assess that you are listening at 88dB peak?

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Dear I.B.,

Thank you for your post. It is very much appreciated.

I am going from memory and will do another test tomorrow morning when my wife is awake. When I took the measurement from memory it was an APP on my iPhone 5SE. I was surprised myself as I thought previously in another post that the level was higher. Though I do not think so. Possibly it was 88 dBSPL nominal and with a possible headroom???

70 watts RMS equals 99 wats peak. Please correct me as you have stated a peak capacity of 300VA which would determine a RMS level of 212 watts. I would love if my amplifier is capable of such peak power.

Then the NAIT XS 2 is quoted at 70W RMS into 8 ohms and 100 watts into 4 ohms. If 100 watts into 4 ohms is nominal. Then this would allow a peak power of 141 watts into 4 ohms. Is this reasoning correct. I am very happy to be corrected. Please do so.

I again am relying on memory and I thought the max output of the amp to power the speakers was around 102dB. This again is going from memory. I did once post a link to a spreadsheet which allowed 14dB headroom for rock and 20 dB for classical. I am not sure how much headroom is built into the NAIM amplifiers. Though Paul from PSAudio said a rule of thumb for good amplifiers is 23dB. I do not know if my NAIT XS 2 is capable of this.

Lost in thought at the moment and off to bed shortly. I will do some experiments tomorrow. I set the NAIT XS 2’s volume at 9 o’clock. I this is any guide.

Kind regards,


You are looking at the mathematics of a sine wave, however that does not apply to the maximum continuous (rms) power an amp can supply and the instantaneous peak current it can supply as on a music transient… The relationship between these is nothing to do with mathematics, rather it is the limitations set by acceptable distortion, onset of signal clipping and power capability of output transistors before they cook themselves or behaviour of circuitry designed to prevent that happening). Most commonly amps are rated as having a peak capability before clipping of about double their rated continuous RMS output capability. Naim, through their design process, claim they achieve a much higher ratio, around 5x (e.g. NAP 200 = 70W rms continuous, 300 VA peak, NAP 300 = 90/500).

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Hi Paul,

I’m feeling slightly guilty here because I (perhaps more than anyone) advocated the XS series amp, in your earlier amplifier and CD player threads on the old forum.

I have found that my XS series amps work superbly with Naim Allaes. They were recommended to me by a forum friend and I am very glad and thankful of his advice, which I took. When they were current they were expensive and were never recommended by Naim with less than a CDX2 and SN. But used Allaes are available at good prices now in the UK. If a pair ever come up in Melbourne I would snap them up.

I think they are 89dB sensitivity and a 6 Ohm load, if it helps.

With a CD playing, 9 o’clock on the volume is painfully loud in my 15m2 room.


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Dear I.B. and Christopher_M,

It is mid morning here in Australia and as promised I have completed an audio test from my listening position which is 2.4 metres from each speaker at the centre of the sweet spot.

Average listening level is 74 dB with a peak of 80 dB. So it looks like I was way off in my quotes last night. The volume pot was more likely at around 8 o’clock to 8:30 position. Not 9 O’clock as I mentioned last night.

Thank you I.B., it was late last night and you are quite correct and picked up my errors. I was in electrician mode and not in audio mode. I do recall peak power from an amplifier can be up to four times the rated rms power. In the case of Naim I will take your word for it being five times.

Christopher, please do not feel guilty. (Feeling nervous here) With these details I feel more than comfortable with my NAIM amplifier. If my nominal listening level is 74 dB SPL, 23 dB head room places that at 97 dB SPL and if I remember correctly ( have done this before with errors) I think the max my system can produce is 102 dBSPL. Though I.B. may correct me here. If the NAIM can supply four times the peak level that may put the peak at 108 dB SPL.

I do have a couple of spreadsheets that I have picked up on my internet travels and would love to share them.

Warm regards,

Paul. Off to check my spread sheets.

P.S. Please be gentle I.B. :grinning:

I hope I wasn’t other than!

Pair of speakers 84 dB/W @ 1m. = 87dB Im in front of both (assuming identical signal to both, and sound in-phase at the listening point, and ignoring any room reflections).
2.4 m away = -7.6 dB = 79.4 dB for 1W.

Rated 70W rms power output continuous into the nominal 8 ohm load of your speakers = + 18.5 dB, so you can sustain a continuous level of 98 dB at 2.4m. Provided that peaks don’t go (or try to go) above the limit you would probably be able to sustain that as a continuous average listening level, though that also depends on other factors such as ambient temperature and airflow around the amp for cooling. (And absolutely not for the good of your ears!)

Naim don’t state a peak power figure for the XS2 in the online specification, and I certainly don’t know it. However, their separate power amp with the same 70W rm continuous rating, the NAP 200, has a published peak power capability of 300VA, and it seems a reasonable assumption that the XS2 might achieve similar. 300VA, taking that effectively to be 300W, = +24.8 dB relative to 1W, so your instantaneous peaks could reach 104 dB at 2.4m before clipping. (Less if the Nait XS2 has lesser peak capability than the NAP 200.)

As I indicated in my first post, the sound level capability of the amp and speakers seems to be well above your normal listening requirements (unless you sometimes want to play much louder than you indicated) - but that is only talking about achievable sound levels, which has no bearing on whether the Nait is capable of exerting adequate ‘grip’ on the SL6 to get the best out of them, which it may it may not. It also has no bearing on how the SL6 will behave or sound when played at these or lower levels. It seems you have doubts about something, and I wonder if the speaker may be a limiting factor, rather than the amp.

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Your revised average listening level of 74 dB corresponds to 0.29W average power output, while peaks of 80 dB are only just over 1W.

The phone app may of course not be accurate - which one did you use? What weighting was it applying? (normal for this sort of purpose is A-weighting). What response time for peaks? (You want tge fastest, some call impulse.)

A couple of years ago I compared several free apps on my my iPhone (5 IIRC) and found significant difference between readings on two, up to 6dB difference on average readings, I don’t recall peaks IIRC one didn’t use and didn’t have option for A-weighting, I don’t think a reason for difference was obvious for the another. 3 were consistent, generally 1dB or less different, and gave results consistent with my expectation for some things, so I reasoned they were the most likely to be tolerably correct, and settled on two of those for use (Decibel X and dB Volume) choosing whichever best suits what I’m measuring, though still not calibrated so I don’t know how accurate.

Aside from absolute accuracy, I don’t know if phone apps respond fast enough to grab true instantaneous peaks, so it is possible very sharp peaks could be higher level than indicated.


maybe you might like to see the video by John Darko ( Dont buy speakers ) on another thread on the same forum.

It might be helpful for you


This is the single most important sentence in this entire thread.

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G’Day I.B.,

The phone App I use is Decibel X. I played the complete Dire Straits Album Brother’s in Arms from track one to track nine. There were parts down to 40dBSPL though the were not so rare though not so long in time. These passages quickly rose to around 65 to 70 dBSPL with average over the whole album being 72.9 dBSPL and the Max being 83.5 dBSPL. I will let you do the math as I am too tired and my wife and I are preparing to head off to Queensland some 2,000 kilometres away to see my mum, whom appears to be in her last days.

If you take some of the passages in some songs as 40dBSPL to a Peak of 83.5 dBSPL. That is a dynamic range 43 dB. Still with some 20 dB left for higher transients. I think I am safe with my setup and may possibly look at a Sub-Woofer since the Nait XS 2 has the facility for such. Though which one? For any replies please go to Audio Trends in Australia to pick one as that will be where I will be doing my shopping.

Just a quick thought, if my MAX dBSPL is 83.5 dBSPL? That is pretty close to one watt as one can get. Actually it is a little less. Then one has to take in the distance from the speakers at about 2.4 metres. Nope too complicated at the moment. I will leave it to I.B. to figure out or I will do it on my return from Queensland. If I generalise? There is a 3dB loss per metre away from the speaker. Though since there are two speakers there is a 3 dB gain. So the first metre nulls out, with a final loss of 3dB for the last metre. So possibly the speakers are outputting somewhere between 86 to 89 dBSPL. Which leaves from memory a headroom of an extra 12 dB. Though this does not allow for the 4x peak power capacity. Which I am little reluctant to say gives another 12 dB in headroom. 12db + 12 db = 24 db in headroom. Ample I think for my situation. Though a SN2 or SN3 would be a nice addition.

I think I can feel safe enough with 80’s rock. Now to try some Bach and Wagner :smiley:

No, 6dB.

If you refer to my last post, 80 dB peak corresponds to about 1W. If 84 as your most recent reading, that’s 2.5W. As my second to last post calculated, on paper your amp with those speakers can play at up to 98 dB average at your listening position continuously, and can probably be happy with peaks up to 102. If you are wanting to learn more about sound levels and their measurements that is another matter, but you clearly have bags of leeway, even if your phone is reading several dB low. You clearly have absolutely nothing to worry about in terms of safety, overload or whatever, And appear to be worrying about nothing!

I note you keep using the term headroom apparently in relation to that leeway to play louder: headroom is More commonly used, I believe, to mean the difference between the average level and the absolute highest maximum music peak that anything you play might have while listening at that average level.

If you want to know if that amp is driving your speakers optimally, that is something you cannot tell from specifications or dB measurement measurements: if it sounds good it’s probably is. With small speakers like that low bass will be missing and a sub to me would be essential: but I have no experience with subs so can’t recommend other than saying make sure it is one designed for music rather than primarily intended for home cinema.

Incidentally with that app if you go to settings you can check that it is set for A weighting and fastest response: it does have various settings and they can cause it to read differently.

Meanwhile I am sorry to hear about your mother. Go spend some time with her make the best of it: that is infinitely more important than any of the above as I am sure I don’t need to say. If what you said is the case then I hope she has has good a time of it as she can and he’s not in pain. It will be a tough time for you: that it is the natural order of things and however you feel once she has gone then I can tell you from experience you to get over it, though of course you never forget.

Best wishes to her and yourself, and any other family. IB.

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