Sound level increase...

[ziggy1971]

I have a question that's been bothering me.

Case scenario:
Assuming that all the specs of 2 different speakers are nearly identical:
Impedance: 8 Ohms
Power Handling (RMS): 100 Watts
Sensitivity: 89dB
Frequency Response: 34Hz-225Hz (8"); 32Hz-225Hz (12")

And, taking into accout the obvious fact that speaker enclosure size and ports will be different between the 2 speakers.

Both speakers have the same 89dB 1W/1m) and the same RMS power handling.

If I fed each speaker the rated wattage (100 watts), would both of them produce the same SPL?
Something tells me that there would be a significant difference due to the fact that the 12" speaker is about 2.25x larger in area.
An 8" speaker has about 50.27 square inches, while a 12" speaker has about 113.1 square inches.

Correct me if I'm wrong, but to me it would seem that the larger speaker would produce somewhere around 6dB (twice as loud) more (I don't have the math, and my assumption is solely based on the fact that the 12" speaker is more than two times the size of the 8"

Can anyone clarify this for me?

I read many articles about audio, but for some reason, I still have this question.
Even this article http://www.globalrph.com/master_speaker.htm doesn't explain it.

Anyone?

[turk690]

Something tells me that there would be a significant difference due to the fact that the 12" speaker is about 2.25x larger in area. An 8" speaker has about 50.27 square inches, while a 12" speaker has about 113.1 square inches.

True, but cone area isn't the only factor in consideration. The other significant factor is excursion. The smaller speaker's cone can be made to swing a wider distance than the bigger one so that both can move the same amount of air, and therefore produce the same SPL at a frequency well above their -3dB points, like, say, 100Hz.

[ziggy1971]

Using the same power source (100 Watts), the excursion will be different between the two drivers for many reasons. I've never measured it, but an 8" driver probably moves twice as far as a 12" driver (has to work twice as hard to produce the same results). That's just hypothetical, I know, because different speakers are built differently. For instance, a 12" driver would probably have a stiffer spider (possibly even more than 1 spider) than an 8" speaker, this changed Thiele/Small parameters.

However, in this scenario, same power applied, same Sensitivity of each speaker as the same distance and everything else considered, I think the larger speaker would still produce ~2x the SPL, right? Or am I wrong?

I knew I should've done this testing when I had the speakers available.

[netmask56]

Frequency Response: 34Hz-225Hz (8"); 32Hz-225Hz (12") Going by the frequency response stated the upper frequency (225Hz) is near middle C (261.62Hz) they are Woofers. What is the overall response including the midrange and tweeters as their power handling capacity is an issue and especially 'perceived' loudness.

[ziggy1971]

225Hz is the far upper frequency of the drivers, cutoff frequency is 120Hz with 24dB/octave rolloff.
Both are ported/vented enclosures (tuned to slightly different frequencies, don't recall right now, but in the mid-40's range).
Both also have damping material to minimize resonance (among other things).
Material used is 3/4" medium density fiberboard along with appropriate bracing also to minimize vibration, resonance, etc.

All I'm trying to do is determine whether or not there is any significant SPL difference between the two.

SPL is SPL, perceived or not; the meter will still measure the SPL.

I didn't think it would be this complicated.

[netmask56]

In theory the larger speaker should be able to produce higher levels with lower distortion than the 8" BUT there are so many possible variable factors to do a "paper" analysis. One paper I read, I think in the AES Journal analysed the resonance of the volume of air contained within the cone area affecting the results. I suspect only a practical real life test would yield any worthwhile answers.

[Hoser Rob]

As mentioned, there are so many other factors.

But IMHO the biggest one is that the sensitivity ratings are often way out of whack. OK, they frakkin' lie. 2 different speakers that have the same dB/1W rating may be actually 6dB off in reality. Maybe more.

Smaller bass drivers will also crap out at higher volumes, as mentioned. This means the overall volume may not be that different in comparison but the bass will drop off. It's called spectrum shift and with small speakers with 5" drivers it's quite noticeable and starts below 150Hz or more.

The speaker impedance matters too, but not in the way you might think. A 4 ohm speaker almost always does not give you double the power of an 8 ohm one. Almost no amplifiers actually give you double the 8 ohm wattage at 4 ohms. The ones that do are very, very expensive. A mediocre amp will probably start to crap out with a 4 ohm speaker. In fact it may be less loud at high volumes than an 8 ohm one for that reason.

All else being equal, which they rarely are, the speaker with the more powerful woofer will only give you more volume when a sufficiently high voltage bass signal is present.

One more thing. Those frequency response specs are even more useless than the sensitivity specs. Those have no +/- dB qualifications. They're also always at very quiet levels ... background at best. Crank them up and you'll get spectrum shift.

[Cornucopia]

Also, they are really only "equal" in a single-state averaged setting. Sensitivity is usually only measured at a single freq. (such as 1kHz), SPL is very averaged both in time and in freq. spectrum. Similarly, Impedance & Damping is freq. dependent. So even with 2 speakers whose figures match, the real-world performance could vary wildly.

Yes, it is this complicated. More.

Scott

[ziggy1971]

I agree with many of the statements regarding "manufacturer specs on products"; sometimes it's simply unbelievbale that they are allowed to do that.
I also know that there are a LOT of factors that could affect the outcome.

With the explanation I've given I guess I assumed people would automatically assume the rest of the speakers parameters in question would be very similar (if not identical) and simply give a answer based on that; the difference in size, everything else being equal. I know that you could introduce many different factors like the different products used in manufacturing (voice coils, spiders, type of magnet, actual cone size/construction, even the quality of wire used for the voice coil). But I'm talking about two identical speakers, except 1 is an 8" and the other is a 12", nothing more, nothing less.

Let's put it another way.
If someone offered you a choice between the two speakers (all things being equal, except 1 is an 8" and the other is 12") which one would you pick?
I'm fairly certain that most people would choose the larger one, but the reason for choosing that one over the smaller one must be more than, how did Rose on Titanic put it "Do you know of Dr. Freud? His ideas with male preoccupation with size might be of particular interest to you..."

Another note, ever notice that SPL competitions in car audio rarely, if ever, use 8" subs? Most use larger drivers and I'm guessing that people use them for reasons other than the fact they are bigger. The fact they are bigger must also equate to some performance gains over smaller drivers.

Sound is created by moving air. Both speakers having identical parameters and produce the same 89 dB SPL 1W/m should be moving the same amount of air to get that result. Now applying 100 watts to each speaker (one at a time for testing), shouldn't there be a difference in the amount of air being moved (i.e. different cone size)? Therefore, you should yield different results, right?

[ziggy1971]

Here are some links:
http://www.audioholics.com/loudspeaker-design/loudspeaker-sensitivity
http://thehub.musiciansfriend.com/tech-tips/tech-tip-wattage-speaker-efficiency-amplifier-loudness

[Cornucopia]

The difference, IMO, has to do with evenness & efficiency. In general (and that's already too much of a stretch), the 12" cone will have more extended low end and thus be more efficient as a woofer/subwoofer than the 8", both can be even with their freq. response, but the 12" would probably need less acoustical/electrical "tuning" (mods) to get it that way (none are perfect, so ALL will need some adjustment). But the 12" would have more difficulty in the higher end than the 8" - simple physics.

Again, the only way you can equate these 2 speakers is if you did something like input a steady-state (tone?) generator and measured for just one particular loudness level & one particular frequency. How they actually react to real-world spectrum of frequencies & dynamics will never line up exactly (probably not even with same speaker model & cone size & material). Those SPL & sensitivity #s should just be considered starting benchmarks, prior to actual listening tests to determine which work best. And the next part is...work best FOR YOUR SYSTEM (your ears, your electronics, your listening environment, your listening material).

Most of those competitions you mention DO suffer from Freudian/Macho overcompensation, not as a quest for improved sound level and/or quality.

Scott

[John_Ro]

The choice of the speaker depends on where you want to use them for, in the meaning of the environment. In an normal living room i would not use a 12" speaker. Mostly such big speakers are used to let the waves carry further, like with hall amplification. There are cheeples who place such speakers in their car....mostly people who do not appreciate their biological hearing devices.

[jimmer]

The sensitivity, in this case 89dB, means that the output measured 1 meter from the speaker, will measure 89 dB, measured by a microphone when the speaker is "feeded" with 1 Watt power, so the sound level, in dB should be the same for the two speakers, given that the two speakers data and measuments are correct.

But, you wil propably find that the speaker with the largest woofer sounds louder, because loud music from a speaker with a large area, not only is heard by your ears, but also felt by the human body.


Loudspeakers, sound pressure and levels in dB are hard to understand, so you should use Google, if you are curious og just want more knowledge about the subject.


http://www.colomar.com/Shavano/spl.html

[hello_hello]

Smaller bass drivers will also crap out at higher volumes, as mentioned. This means the overall volume may not be that different in comparison but the bass will drop off. It's called spectrum shift and with small speakers with 5" drivers it's quite noticeable and starts below 150Hz or more.

I'd be keen to learn what spectrum shift has to do with it. Not that I've really heard the term used much in relation to audio, but I'd imagine spectrum shift would be a way of describing the Doppler effect, ie where the sound of a siren increases in pitch as it gets closer, then decreases as it gets further way. The same would apply to a speaker reproducing multiple frequencies. The cone moves in and out to reproduce a low frequency while at the same time moving in and out much faster to reproduce a higher frequency. The higher frequency effectively "rides" on the lower one and would therefore in theory be subject to the Doppler effect, or spectrum shift, but I'm not sure how spectrum shift relates to a speaker's ability to reproduce low frequencies.

Speakers have to move air, so all else being equal a 12" inch cone should move more air than a 8" inch cone. If smaller speakers crap out at higher volumes it'd be because they're less efficient at producing low frequencies or because they simply can't handle the power required. Reproducing low frequencies takes a lot more power and air movement to result in a "flat response" compared to high frequencies. The larger the cone though, the less accurately it'd be able to reproduce high frequencies (all else being equal). Smaller bass speakers might produce a "tighter" bass sound but not be as efficient at the really low "sub" frequencies.

And, taking into account the obvious fact that speaker enclosure size and ports will be different between the 2 speakers.

Sub speaker enclosures are obviously a big part of how efficiently the speaker can reproduce certain frequencies. You could describe the setup as being "tuned" to boost or enhance certain frequencies and the porting allows the speaker to reproduce frequencies it might otherwise not be able to reproduce in a closed cabinet. Enclosure size and porting would make a big difference even if the same speakers were used.

A 89dB 1W/1m rating might be equal for both speakers at the same frequency, but it doesn't mean it applies to all frequencies. The frequency response is never flat, so if one speaker is more efficient at the measured frequency the rating can be misleading. The frequency response should at least be qualified in respect to how flat it is (plus or minus "x" dB etc).

There's some info here you might want to read.
http://forum.blu-ray.com/showthread.php?t=71469
http://en.wikipedia.org/wiki/Bass_reflex
http://en.wikipedia.org/wiki/Woofer