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Old 5th July 2013, 07:44 PM   #11
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Quote:
Originally Posted by fwbutler View Post
Still cant get deep bass, in a small box from high Vas speakers.

From this 5 watts should give output in the 80db's.
Classic Hoffman's Iron Law- loud, low or small, pick two. You have already chosen small, only one choice left.

80 dB at 30 Hz is barely audible, and most pop music "bass" is in the 60 Hz range.

Given a speaker the size of what you are going to make I'd choose "loud" (which for most kids is more like at least 100 dB) over low, and like Dumptruck suggests make the Fb around 55-60 Hz, so the speaker has a chance of producing some useful musical LF output.
Sacrificing the "guts" for nearly inaudible LF will result in a couple burnt voice coils rather quickly, if your grandkids are like most kids I know.
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Last edited by weltersys; 5th July 2013 at 07:49 PM.
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Old 5th July 2013, 08:36 PM   #12
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You folks have made some very good arguments. Thanks

Maybe I am dense but if I have a flat, +/- 3 db, system at 80 db and I have to equalize the bass +20 db to get 100 db to sound correct. Why can I not just equalize it + 23 db, if the power is available?

My current system, folded horns, flat to 40 Hz, do not need equalization, (but my ears).

The kids use much less than the 12 db of bass boost on their systems, (for their ears). It would be rare to find more than 12 db of boost / cut available.

After listening to your arguments I will only invest in building one speaker for testing as a precaution

Last edited by fwbutler; 5th July 2013 at 09:05 PM.
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Old 6th July 2013, 03:37 AM   #13
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There are two things which I think are throwing you off with regards to this last post. Firstly, adjusting your signal gain by any amount of dB is not the same as getting that amount of dBSPL. In essence, you're fighting physics. You put a certain amplitude of voltage signal into a speaker and it produces 80dbSPL. To put this into perspective, a doubling of sources (that is, if you add another speaker producing 80dBSPL) will yield a theoretical 83dBSPL. This is a log scale as I'm sure you know.

Power and pressure don't behave the same because of a simple case of Ohm's law. Voltage gain works on the principle of 20dB = 10x. However, power is proportional to voltage squared, which means that 20dB increase in power means 100x more power. So, in order to increase your output by 20dB, you need to increase your input voltage by 10x which yields 100x more input power which is akin to having 100x as many sources. You can imagine therefore that if you have a single speaker, 100x more power on a single 3" speaker is going to end up a bit smoky.

My point is twofold: the dB levels that you're looking at are not the same. The bass boost is an increase in signal or a voltage gain which does not behave like power. That means that by adjusting your equalizer to get +20dB, you're not getting 20dB more SPL. You're getting a 20dB gain on your signal which unfortunately for your speaker means 100x the power. Therefore in the real world, in order to get that extra 20dBSPL that you want, you're not going to be able to rely on the EQ. You're going to simply need more speakers.
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Old 6th July 2013, 04:32 AM   #14
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It's a good thing that I will only need 3 db to make it flat. one watt for 76 db and a little over 2 watts for 80 db. I doubt they, the kids, will rarely go above that, but they do have 15 to 20 watts. Too much SPL or bass and they will exceed the "PP" point. (PP for parents patience)

This is not a home theater speaker system. Just a small low distortion extended frequency bookshelf speaker for near field audio using a C4 alignment as Thiele and Small called it. I do agree that for loud Movie soundtrack in a home theater a lot may be lacking. It will be interesting to see (hear) how they really work.

Yes P = (E^2)/R
&
db of a ratio of two powers = 10*(LOG((A/B),10))
and
Db of a ratio of Amplitude or Acoustics =20*(LOG((A/B),10))

Last edited by fwbutler; 6th July 2013 at 05:01 AM.
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Old 6th July 2013, 05:35 AM   #15
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Nobody meant to say you should be +20dB in the low bass to sound correct. It's that you don't really hear much down there until the overall level (including the low bass) is very high. Your speaker, EQ'd to flat bass, would hit xmax at around 80dB. That is not a path to the low distortion you keep mentioning.

If you take your test speaker and play a 30Hz sine wave, unless your ear is right up to it, you're probably not going to hear anything at all until you turn it up enough to get audible 60Hz (and higher harmonics) distortion. This will still sound like "bass", but it's just distortion, and is why a small speaker that has very good output at 60Hz but not much of anything below 40Hz does not need to sound wimpy (within reason).
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Old 6th July 2013, 06:52 AM   #16
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I checked my home system at the volume we normally have it at. Here is what it looks like. level checked with a db meter. Really nice clean bass. A 40 Hz note comes across loud and clear.

Have had it at 87 db but would be painful, (for me and the neighbors), for long. We use mid 70's for movies etc.

Do not understand why more than 85 db would normally be necessary even if the room was "dead" that would be accounted for in the measurements.
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Old 6th July 2013, 10:35 AM   #17
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Quote:
Originally Posted by fwbutler View Post
Do not understand why more than 85 db would normally be necessary even if the room was "dead" that would be accounted for in the measurements.
Because music is about an emotional connection, and occasionally a piece comes along that requires more than 80dB peak (at which point Xmax is reached) levels to 'get' it.
Remember that 80dB peak is usually around 70dB average.

Chris
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Old 6th July 2013, 02:21 PM   #18
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fwbutler, I think you misunderstood the point of my post. It was intended to steer you to the conclusion that simply increasing input power to a seriously power limited speaker is going to leave you with a huge amount of distortion. EQ'ing isn't a process of tuning by graph. You need to listen first, and when you listen to a 3" speaker trying to produce an authoritative 30Hz, it's going to sound awful. As people have already said, if it can produce 60Hz with good impact, then you will never care about anything below that. The brain works in mysterious ways, so those lower frequencies will not even be missed if everything else is nice and clean.
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Old 6th July 2013, 10:02 PM   #19
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i'm gonna though this in there you may not like it
its a little tiny speaker
math is all good
but you have to be practical
are you really expecting to hear it... at all?
your computer may be wrong
and if it does work cool
but i'm just saying i dought it'll work
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sometimes a 49 general electric am radio is just down right cooler than the 100+ watts of sound around
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Old 6th July 2013, 11:20 PM   #20
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Lemans, chris, dumptruck thanks, I see what you are saying. Even if it can handle the average it will distort esp on peaks as it too close to it's limits.

This will be great to evaluate as soon as I get some info on the crossover
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