I have gone around and around on this subject for years with regard to live music on stage, muffler DB on vehicles like cars and boats, audio systems in show cars and now on the Trident we have pretty much analyzed all three aspects in an attempt to
A) project sound out of the boat (live acoustic reinforcement)
B) quieted the exhaust below legal levels without mufflers and
C) gained db and clarity with our premium sound system without sacrificing efficiency (power is heavy in this case) or durability (120+ degree ambient temps in amp compartment)
All science aside, I have done a lot of "seat of the pants" testing with a db meter sitting in front of me. I have re-routed exhaust through a two 90 degree turn path and dropped 4 db. No really noticeable sound loss IMO, but definitely a "smoother" sound that took some of the brisance out of the exhaust note. Still rattles windows, but dropped it from 91 db to 87. Certainly not half of the noise by any stretch. From my perspective, it was about 10% less "violent" sounding.
At level 28 on our audio system we run about 121db. You can't talk. You can't really even yell to communicate. You can however nod your head emphatically and mouth the words "Bad Ass" effectively. At 32, the gain on the subs really starts banging hard and is up on it's efficiency curve and you have a significant gain in overall volume. I would say it goes up 20%. Maybe 30%. The db goes to 127 however, defying all standard conventional analysis, which would indicate that it quadrupled in impact and SPL.
The difference between closing the doors on my truck and opening them is 4 db with all 4 12's killing it. No gain in power, just enclosure type essentially. You can't hear the difference in the car however. Certainly not twice the noise.
On stage, it is far more profound. Really good live venues will try to keep the db under 110 right in front of the sound board. Anything else is considered too loud to enjoy for a normal live event. Full bore concerts aside, most cool little joints will adhere to this unspoken rule. I could easily provide that level of sound with my two 2x12" ADA quarter stacks driven by dual Rocktron Velocity 250 power amps, but never do. Instead, I point my speakers in towards the band and use them for monitors and let the house guys mic my cabs to create the house sound. I promise you that 110 from my amps is thin and weak and quiet compared to 110 from the house. Plus, the house usually has far higher quality speakers and amps, and spreads them out all over the club usually. The more sound you project back to that board from your rig, the quieter they will turn your "good sound" down to accomplish the 110 mix. My point is simple, 110 is not 110. More speakers making 110 is a hell of a lot "louder" to the ear than fewer.
I guess what I am saying is that the only aspect of this I really don't understand is this whole doubling of sound every 3 db. I never hear it, not even close. Light tuning, in the applicable case here being removal of passive crossovers has always netted greater than 3 db gains for me when actually put to the meter, and never had a subsequent battery draw or pure volume gain as is outlined by the fuzzy math of the logarithmic curve.
If someone gets this better than I do, please jump in and explain it better... my knowledge is anectodal and experience based, not scientific.
Ummmm Pardon the Interruption:
I have been waiting patiently for the electronics dialogue to die down.
Well which one's ie... 6.5 speakers are the best---sound good----good price and durable to put in a boat???
Brand and model number would be helpful---EX. not just Focal what type of Focal.
Froggy:
I love Zapco amps the best in car or truck----- but do not know anything about their speakers for marine application. Care to comment.
KAP
I would not be afraid of these:
I run their 6X9s in the same series:
ECLIPSE SE-8365
http://www.eclipse-web.com/integrated/image/se8365.jpg
OR, they aparently have gotten into the marine industry:
ECLIPSE SM-6500
http://www.eclipse-web.com/integrate.../sm6500pic.jpg
Not really.
Really.
Yes, I have studied the heightened sensitivity of the upper midrange band on the human ear but do not profess to be an expert in this matter.
Here are some links that will help you understand the decibel scale.
Here's a little grade 12 physics you may find helpful with regard to sound pressure.
http://www.glenbrook.k12.il.us/GBSSC...nd/u11l2b.html
Here's something a little more practical. You will find the figure on the right most interesting. It clearly states that doubling the power brings an increase of 3 dB in sound intensitity level.
http://www.phys.unsw.edu.au/jw/dB.html
Extensive psycho acoustic work has been published in AES (audio engineering society) journals over the years. I'm no longer a member and haven't received the journals in a dozen years but I encourage you to go to your local engineering college and check out their journals. They're quite accessible to people, even if you don't have an advanced degree in engineering and mathematics. While the books do contain some calculus here and there, most of it is comprehensible by anyone.
Cheers, Rivercrazy.
I guess what I am saying is that the only aspect of this I really don't understand is this whole doubling of sound every 3 db. I never hear it, not even close.
[snip]
If someone gets this better than I do, please jump in and explain it better... my knowledge is anectodal and experience based, not scientific.
Froggy, your ears have an automatic 'gain', of sorts. That is to say, you can go to a concert and have your hair blown back by the sound pressure levels and you can also hear a pin drop..... with the same set of ears.
If someone were to drop a pin next to you at a concert, I would suggest it's unlikely you would hear it. That's because your ears have 'gained down'.
This has the effect of making sound perception non-linear. Sound perception is roughly logarithmic.
A 3 dB increase in sound pressure level is indeed twice the sound pressure. There is twice the sound energy in the air and it will be applying twice the energy to your ears. As you mentioned, a 6 dB increase is a doubling of the doubling (2 x 3 dB increases), or a quadrupling. This is real. It is not how our ears perceive it, however. Our ears reduce sensitivity with volume, causing a doubling of sound pressure to sound only slightly louder.
... so.... you can hear really loud... and you can hear really quiet... but you can't hear them both at the same time. This automatic sensitivity feature of human hearing has the effect of causing us to perceive an artificially high dynamic range in hearing ability that we really don't have. We just have the ability to adjust our hearing sensors.
The rule of thumb is that a 10x increase in sound pressure (10 dB) will sound approximately like a doubling in perceived loudness.
As Rivercrazy pointed out, our sensitivity varies somewhat with frequency but the general rule holds.
Froggy, your ears have an automatic 'gain', of sorts. That is to say, you can go to a concert and have your hair blown back by the sound pressure levels and you can also hear a pin drop..... with the same set of ears.
If someone were to drop a pin next to you at a concert, I would suggest it's unlikely you would hear it. That's because your ears have 'gained down'.
This has the effect of making sound perception non-linear. Sound perception is roughly logarithmic.
A 3 dB increase in sound pressure level is indeed twice the sound pressure. There is twice the sound energy in the air and it will be applying twice the energy to your ears. As you mentioned, a 6 dB increase is a doubling of the doubling (2 x 3 dB increases), or a quadrupling. This is real. It is not how our ears perceive it, however. Our ears reduce sensitivity with volume, causing a doubling of sound pressure to sound only slightly louder.
... so.... you can hear really loud... and you can hear really quiet... but you can't hear them both at the same time. This automatic sensitivity feature of human hearing has the effect of causing us to perceive an artificially high dynamic range in hearing ability that we really don't have. We just have the ability to adjust our hearing sensors.
The rule of thumb is that a 10x increase in sound pressure (10 dB) will sound approximately like a doubling in perceived loudness.
As Rivercrazy pointed out, our sensitivity varies somewhat with frequency but the general rule holds.
I had always thought that 3db was double the sound. So by porting I though would gain you 3db at a certain frequency over not porting, basically it's doubling the sound or output of the woofer. If you have one 4 ohm mid and switch to two 8 ohm mids in parallel you gain 3db or double the sound. I had never heard that your ear is reacts or can become sensitive to a certain enviroment but it makes sense. The sound of the pin drop is still there, you've just managed to block it out because of the loud noise.
I dropped a roll of quarters in a casino one night and the change lady, with her back to me turned around and said you just dopped your quarters. I said how did you know????? She said she heard it hit the floor, she had become accustomed to the noise in the casino, but all I heard was slot machine noise.
I had always thought that 3db was double the sound.
If you're talking about sound pressure, it is double.
We won't perceive it as double but 3 dB gain in sound pressure is double, by definition.
So by porting I though would gain you 3db at a certain frequency over not porting, basically it's doubling the sound or output of the woofer.
I've had bass reflex enclosures described to me as implementing a hole to allow the rear wave to come out the front of the enclosure, effectively doubling the amplitude. Perhaps you've heard the same. This is not correct.
A ported enclosure does not work on that principle at all. Ports are typically designed to amplify bass by 12~15 dB in a fairly narrow band, typically well under an octive. Also, the port can be in phase with the cone (but doesn't have to be). That is to say, both emit high and low pressure at the same time.
If the port is in phase with the cone, it should be positioned on the front of the enclosure. If the port is 180* out of phase with the cone, it should be positioned on the rear of the enclosure.
A port could easily be designed to amplify much more than 15 dB on a narrow part of the specturm but it would cause a chauffing sound. I've heard production enclosures make this noise at high volumes. The problem is air in the port going supersonic. That will give you an idea how much energy can be harnessed with a bass reflex design.
A port is a somewhat seperate chamber of air that is designed to resonate at a given frequency. Sound pressure in the box causes the port to resonate. The amplitude of the resonation goes up sharply as the sound pressure off the back of the driver approaches the resonant frequency of the port.
While some direct emissions from the rear of a driver will leak out of a port, a good design will minimize this. Basically, the sound pressure from the back of a driver causes air in the port to resonate which causes sound pressure to emit from the front of the port.
I've had bass reflex enclosures described to me as implementing a hole to allow the rear wave to come out the front of the enclosure, effectively doubling the amplitude. Perhaps you've heard the same. This is not correct.
A ported enclosure does not work on that principle at all. Ports are typically designed to amplify bass by 12~15 dB in a fairly narrow band, typically well under an octive. Also, the port can be in phase with the cone (but doesn't have to be). That is to say, both emit high and low pressure at the same time.
If the port is in phase with the cone, it should be positioned on the front of the enclosure. If the port is 180* out of phase with the cone, it should be positioned on the rear of the enclosure.
A port could easily be designed to amplify much more than 15 dB on a narrow part of the spectrum but it would cause a chauffing sound. I've heard production enclosures make this noise at high volumes. The problem is air in the port going supersonic. That will give you an idea how much energy can be harnessed with a bass reflex design.
A port is a somewhat separate chamber of air that is designed to resonate at a given frequency. Sound pressure in the box causes the port to resonate. The amplitude of the resonation goes up sharply as the sound pressure off the back of the driver approaches the resonant frequency of the port.
While some direct emissions from the rear of a driver will leak out of a port, a good design will minimize this. Basically, the sound pressure from the back of a driver causes air in the port to resonate which causes sound pressure to emit from the front of the port.
Complicated stuff..........
I understood a ported enclosure with the port in front of the driver to be a bandpass box. Those I have heard can increase the output of the driver by as much as 15db in a narrow frequency range. I personally don't know how figure or build one correctly and haven't attempted to. Since I have an Onkyo home stereo with a sub box, that has only a small port in the front of it, I would assume that it's a bandpass box. From what I understand they are not very forgiving if any of the factors, rear enclosure, front enclosure or port volume aren't all precise.
The way I understood a ported box (or a box with the port in behind the driver) to work, is that the rear wave exits the enclosure, being delayed properly by the volume of the port, in phase with the wave created by the driver, therefore doubling the output of the driver. In a perfect world you would have double the energy, in phase and double the sound.
Do I have this wrong? Or are they just generalizations and not necessarily truths?
Complicated stuff..........
I understood a ported enclosure with the port in front of the driver to be a bandpass box.
Sounds right.
Here is some reference that will explain enclosure styles much better than I could ever dream of doing in text.
Enclosure types (http://www.electronixwarehouse.com/e...sures/main.htm)
The way I understood a ported box (or a box with the port in behind the driver) to work, is that the rear wave exits the enclosure, being delayed properly by the volume of the port, in phase with the wave created by the driver, therefore doubling the output of the driver. In a perfect world you would have double the energy, in phase and double the sound.
It sounds like you're pretty much on this but a port can provide far more than 3 dB of gain. Typically, ports are designed to provide 12 dB of gain. Even at 12 dB, care needs to be taken to insure air in the port does not go supersonic.
A port is a column of air that is induced to resonate by the energy that comes off the back of the driver and is contained in the enclosure. Basically, you have one energy source creating another, which creates another.
Well, look who must be living in a Holiday Inn Express these days!
That explains clearly why the science never jived with my perception.
I will say this, if I leave the stereo on at 32, power down, go away and then come back later and just hit the power button... I am in disbelief that I listen to music that loud. Yet, on the sandbar all I can think of is how to get even more sound out of it.
As you say, the tolerance is built progressively.
A lot makes sense now. Thanks for taking the time to explain it.
Wes
Posting Permissions
Reply With Quote