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Ask Me Anything About Audio System Design
11-14-2010, 11:27 AM
#11
Comparing two subwoofer setups...
One sub is a 12", 89.5 dB sensitive, in a ported box. The other setup is two 12", 86.5 dB sensitive each, in a sealed box. Both are on the same power, the ported box is tuned to 30 HZ, and the sealed subs roll off at 30 HZ at -8 dB/octave (30-20 HZ). If the sealed 12" are 86.5 dB + 3 dB (double cone area), is the ported box generally at +3 dB over the sealed or does doubling the cone area serve another purpose (above the tuning freq. & roll off) other than a +3 dB gain in sensitivity?
For sealed subs that have a low QTC (.5), how much top end is lost, and is it a near-exact roll off (like -8 dB/octave) for all sealed boxes?
One sub is a 12", 89.5 dB sensitive, in a ported box. The other setup is two 12", 86.5 dB sensitive each, in a sealed box. Both are on the same power, the ported box is tuned to 30 HZ, and the sealed subs roll off at 30 HZ at -8 dB/octave (30-20 HZ). If the sealed 12" are 86.5 dB + 3 dB (double cone area), is the ported box generally at +3 dB over the sealed or does doubling the cone area serve another purpose (above the tuning freq. & roll off) other than a +3 dB gain in sensitivity?
For sealed subs that have a low QTC (.5), how much top end is lost, and is it a near-exact roll off (like -8 dB/octave) for all sealed boxes?
11-14-2010, 11:24 PM
#12
50 Watt CAFz'r
Thread Starter
Join Date: Nov 2010
Posts: 230
Here's one. I have 2 batteries in van. One in front, one in back. The vehicle has "Big 3" completed in 1/0. I have 2 runs of 1/0 connecting the batts grounds together + one 1/0 from rear batt to body ground. 1-2/0, + 1-1/0 connecting the pos batt terminals together. Then I have 2 1/0 runs of pos/neg connected to rear batt for sub amp (Atomic 7K) and one run of 4ga pos/neg for the highs amp (RF Power 800.4).
Question is... why is it that when I clamp the power in on amp, sometimes shows a (-) amperage. Also if I clamp other lines, some read (+), others read (-) amperage. The two positive lines should have similar amperage draw correct? Why would one be (+) and the other show (-) readings?? Then if I wait a lil and test again there might be no (-) draw showing, or one of the other lines will show (-), and the other one will show (+). Hell, last time I checked both the positive lines were clamping (-) amperage??
Totally confused...
Question is... why is it that when I clamp the power in on amp, sometimes shows a (-) amperage. Also if I clamp other lines, some read (+), others read (-) amperage. The two positive lines should have similar amperage draw correct? Why would one be (+) and the other show (-) readings?? Then if I wait a lil and test again there might be no (-) draw showing, or one of the other lines will show (-), and the other one will show (+). Hell, last time I checked both the positive lines were clamping (-) amperage??
Totally confused...
Fear not!
You're using your amp clamp incorrectly...
The clamps has a hall effect sensor in it that measures electrical fields - your clamp like a DMM has a positive and negative electrode - so next time you measure a + cable and you get a - Voltage on your display, open the clamp and turn your meter 180 degrees and re-clamp the wire - you will now get a + voltage...
Now for the varying Voltages and Zero scores - if you measure more than one cable at a line (inside the clamp or beside the cable or simply to close another cable) the scores can and will either divide, average, or cancel.
Once you’re on the right track, you may still discover that you get difference current scores down each branch - which is often correct because each branch may in fact be passing a different amount of current...
Keep me posted and I will work with you through to the next level –once you sort out how to use the meter correctly...
11-14-2010, 11:37 PM
#13
50 Watt CAFz'r
Thread Starter
Join Date: Nov 2010
Posts: 230
Comparing two subwoofer setups...
One sub is a 12", 89.5 dB sensitive, in a ported box. The other setup is two 12", 86.5 dB sensitive each, in a sealed box. Both are on the same power, the ported box is tuned to 30 HZ, and the sealed subs roll off at 30 HZ at -8 dB/octave (30-20 HZ). If the sealed 12" are 86.5 dB + 3 dB (double cone area), is the ported box generally at +3 dB over the sealed or does doubling the cone area serve another purpose (above the tuning freq. & roll off) other than a +3 dB gain in sensitivity?
For sealed subs that have a low QTC (.5), how much top end is lost, and is it a near-exact roll off (like -8 dB/octave) for all sealed boxes?
One sub is a 12", 89.5 dB sensitive, in a ported box. The other setup is two 12", 86.5 dB sensitive each, in a sealed box. Both are on the same power, the ported box is tuned to 30 HZ, and the sealed subs roll off at 30 HZ at -8 dB/octave (30-20 HZ). If the sealed 12" are 86.5 dB + 3 dB (double cone area), is the ported box generally at +3 dB over the sealed or does doubling the cone area serve another purpose (above the tuning freq. & roll off) other than a +3 dB gain in sensitivity?
For sealed subs that have a low QTC (.5), how much top end is lost, and is it a near-exact roll off (like -8 dB/octave) for all sealed boxes?
I'd love to get you on the right path to figuring these things out..
So let’s start by education you in some basic requirements for learning
1. you must have access to and use accurate data - computer software modeling doesn't meet this requirement.
2. you must assume anything you must objective measure everything.
3. when comparing data, all the variables must be identical other than a small group of highly predictable of objectively measurable variances.
In your comparison you lack the aforementioned and that's why you're confused...
I am going to recommend that you purchase and read the 1st & 3rd additional of Vance Dickenson 'Loudspeaker Design Cookbook' - once you have digested those to publications you will be close to having the answers you seek; however, you will be significantly versed in the language of loud speaker design and specifications and I will be able to guide you the balance of the way in...
We all started somewhere, and step one was to learn the language...
11-14-2010, 11:44 PM
#14
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Join Date: Nov 2010
Posts: 230
Planning dual audison lrx 5.1 build with a DEX-P99RS with focal k3p, with dual 6 1/4 midbass. Unsure of sub, maybe JL 13W-7 (obviously ported tuned low). 4 way active. 50 watts mid and tweet, 160 dual mid bass, 1100ish per coil on the JL. Chevy colorado, regular cab. Think I can squeeze 3 cubic feet, for box fibreglass. How many runs of 0/1 gauge? Already own all equipment. All responses welcome. (Yeah I'm a lurker) TIA.
225 amps continuos - peak of 450 amps @ 13.3 Volts
Equals = 2 pulls front to back!
11-14-2010, 11:56 PM
#15
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Posts: 230
so I've got 4 12''s in a box on a 3k watt amp. I'm planning on adding two batteries and replacing my starting battery to give me 3 in total. wiring will all be changed from 2 guage to 0 in the near future. I need to hit above 150. if possible enough to bass race a 49.9. its gonna be for daily driving, so I need the loudest box possible.
or
I have an issue with a turn off thump. thats not the thing that bothers me though. it seems I have a hum from the subs, but its not constant. I only hear it at lower volumes but that might be because its drowned out by music. and it doesn't stay for long, it just comes and goes as it pleases. I've tried a ground loop isolator, but that seemed to reduce the loudness of lower bass notes and increase the loudness of higher bass notes. I've also tried grounding the rcas but that didn't help. I've been told there is a fuse in my deck that may have popped, causing the problem. I need to know what it is.
or
I have an issue with a turn off thump. thats not the thing that bothers me though. it seems I have a hum from the subs, but its not constant. I only hear it at lower volumes but that might be because its drowned out by music. and it doesn't stay for long, it just comes and goes as it pleases. I've tried a ground loop isolator, but that seemed to reduce the loudness of lower bass notes and increase the loudness of higher bass notes. I've also tried grounding the rcas but that didn't help. I've been told there is a fuse in my deck that may have popped, causing the problem. I need to know what it is.
But let me share an awesome truth with you - the loudest type of box in the world is a Tapped Horn...
Check out Danley Sound Laps and Google Tom Danley...
They build the loudest pro audio bass systems in the world and to my knowledge - no one has put one in a car...
Nothing louder... think bold, think big, think loud and build Tapped Horn... and BE all THREE!
As for your noise - very tuff / impossible to solve without being there, I really need to hear the noise myself - sorry otherwise i would be guessing...
Question though - did the ground loop isolator resolve the sound? If so, it is tell us something that i can work with...
Let me know
11-15-2010, 12:07 AM
#16
50 Watt CAFz'r
Thread Starter
Join Date: Nov 2010
Posts: 230
Fair question: If you will allow me to, I will keep my name out the forums; however, I will share that many people in this forum know of me either through direct contact at train seminars/programs, magazines or TV. I am a 25 year vet in all industries relating to pro audio consumer audio and commercial audio...
I run my own engineering consulting company and have a significant list of major manufacturers and retailers as customers...
Did this help improve my credibility in your mind?
Dogbaker isn’t an anagram of my name but is directly related to my name...
Last edited by dogbaker; 11-15-2010 at 12:12 AM.
11-15-2010, 12:32 AM
#17
50 Watt CAFz'r
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Join Date: Nov 2010
Posts: 230
In basic non-technical terms: single bit DAC's have been proven unable to reproduce Hi-Fi, which is to say a truly transparent, 3-dimentional sound field (along with other desire hi-fi qualities)and therefore has be sent down to the low-fi market places...
Multi-bit DAC's (are numerous) had and is still proving to possess a greater likely hood to deliver on the aforementioned qualities...
In an SQ system, I would only consider a Multi-bit DA topology etc... But there is some entry-level multi-bit DAC's that product more error then higher quality single bit designs...
In terms of car audio head units - go for multi-bit and audition them...
11-15-2010, 12:42 AM
#19
50 Watt CAFz'r
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Join Date: Nov 2010
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No - No - Right Thread - your woofers are too small! Just Kidding!
11-15-2010, 12:51 AM
#20
50 Watt CAFz'r
Thread Starter
Join Date: Nov 2010
Posts: 230
Quote:
Originally Posted by BradSk88
I suppose my mistake was trying to 'sell' cable improvements, rather than just pointing out that there are factors that make cable A better than cable B.
Sorry.
I'm also gonna retract the thing I said about pre-worn. I had a chat with some of the professors in my EE dept at university and they all agreed that while burn-in is a real thing, it only applies to dc current, because audio is AC it is random and burn-in wouldn't have any benefit.
__________________________________________________ __
Hi Brad
No need for you to change your position!
Headunits and Amps output a lot of DC at times (when their power supplies clip) that’s why most VC's end up black or burnt etc... AC rarely (in properly designed and calibrated systems) does the same!
Speakers have both an electrical side and mechanical side... and they are to large extent inversely related to each other. On the electrical side we measure loss (QES) and weight them against the mechanical losses (QMS) to derive a system Qts or in a box Qtc...
It has been well documented that a speaker’s suspension is in a constant state of decay (slow death or change). The suspensions loss comes predominately from the surround and spider and their innate mechanical resistances and their bias (Kms & Cms) north or south position (bias +/-) of the cone itself etc...
As a driver moves in and out, the spider and the surround ages and loosens up - and the bias often shifts as well. In fact, gravity has a major effect on cone bias - that's why all speakers should be mounted in perpendicular (to the earth) only. It is common to see large subs that have been installed in parallel with the road (earth) that have completely sagged downward (- bias) - when this occurs all bets are off, as the drive is grossly damaged or outside of its original spec...
These shifts effect Qms Scores will direct affect Qtc scores and in fact, as the driver is used its magnet motor is also in a state of decay - the magnet becomes weaker (Bl), the suspension becomes looser and the coil winding (copper) becomes more resistive and on and on this cycle goes until one day the system requires a complete recalibration or even product replacement...
3-5 years is the max a quality car system can retain its original sonic qualities... Speakers being the weakest and quickest to shift in performance, because of a constant varying in mechanical and electrical resistances - and resistance controls all elements of transfer function...
So does break in matter for basic car audio installs - not really - the driver is in a constant state of change any way, so why use up some of its life on a test bench, rather than in your car. There is only one benefit - the speaker is less likely to fail during initial system turn on, calibration and SPL testing - 18-24 hours helps in this regard... As a designer, I often order a batch of drivers break them, if you will, in overnight and measure their T/S and average my findings and use the average scores within my design considerations...
I hope that didn't hurt too much! I can send you graphed measurements which prove these statements...
Originally Posted by BradSk88
I suppose my mistake was trying to 'sell' cable improvements, rather than just pointing out that there are factors that make cable A better than cable B.
Sorry.
I'm also gonna retract the thing I said about pre-worn. I had a chat with some of the professors in my EE dept at university and they all agreed that while burn-in is a real thing, it only applies to dc current, because audio is AC it is random and burn-in wouldn't have any benefit.
__________________________________________________ __
Hi Brad
No need for you to change your position!
Headunits and Amps output a lot of DC at times (when their power supplies clip) that’s why most VC's end up black or burnt etc... AC rarely (in properly designed and calibrated systems) does the same!
Speakers have both an electrical side and mechanical side... and they are to large extent inversely related to each other. On the electrical side we measure loss (QES) and weight them against the mechanical losses (QMS) to derive a system Qts or in a box Qtc...
It has been well documented that a speaker’s suspension is in a constant state of decay (slow death or change). The suspensions loss comes predominately from the surround and spider and their innate mechanical resistances and their bias (Kms & Cms) north or south position (bias +/-) of the cone itself etc...
As a driver moves in and out, the spider and the surround ages and loosens up - and the bias often shifts as well. In fact, gravity has a major effect on cone bias - that's why all speakers should be mounted in perpendicular (to the earth) only. It is common to see large subs that have been installed in parallel with the road (earth) that have completely sagged downward (- bias) - when this occurs all bets are off, as the drive is grossly damaged or outside of its original spec...
These shifts effect Qms Scores will direct affect Qtc scores and in fact, as the driver is used its magnet motor is also in a state of decay - the magnet becomes weaker (Bl), the suspension becomes looser and the coil winding (copper) becomes more resistive and on and on this cycle goes until one day the system requires a complete recalibration or even product replacement...
3-5 years is the max a quality car system can retain its original sonic qualities... Speakers being the weakest and quickest to shift in performance, because of a constant varying in mechanical and electrical resistances - and resistance controls all elements of transfer function...
So does break in matter for basic car audio installs - not really - the driver is in a constant state of change any way, so why use up some of its life on a test bench, rather than in your car. There is only one benefit - the speaker is less likely to fail during initial system turn on, calibration and SPL testing - 18-24 hours helps in this regard... As a designer, I often order a batch of drivers break them, if you will, in overnight and measure their T/S and average my findings and use the average scores within my design considerations...
I hope that didn't hurt too much! I can send you graphed measurements which prove these statements...
