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Old 08-13-2017   #1
 
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Default Some sub considerations for the DIY

Speaker selection is an important consideration in any quality system. And one of the most important, is low frequency, and how to obtain truly impressive performance, without the common mistakes made when designing this critical section of frequencies.

There is much more to consider when selecting subwoofers, their implementation and overall balance of the system. This is where Thiele-Small parameters dictate enclosure design and sizing, and one commonly ignored. There is much more to designing this system than just buying a driver and cabinet. The mechanical and electrical Q of a driver has to be properly matched to the cabinet. And one size (diameter) doesn’t match all cabinets. And any subwoofer driver not inside an enclosure, will not produce the effect you are seeking. The trunk itself doesn’t count, as it doesn’t match the Thiele-Small parameters of the driver originally used.

Rule #1, any sub driver outside a properly matched cabinet is only half a subwoofer.

Rule #2, never disconnect the driver from the cabin of the vehicle. You cannot overlook this rule, and often attempted. Disconnected designs where you place a sub in a cabinet, and place it in the trunk, is not a desirable design in any system. Imagine taking your home audio system in your listening room, and placing the subwoofer in the garage. The only result that will produce, is a very muddy, and over emphasized port chuffing monster that doesn’t lend itself to high quality reproduction… all it creates is noise. When you place a driver outside of the cabin, you lose the intricacies of the lower frequencies needed to reproduce music accurately. The primary frequency of low A (A-0) of a piano is 27.5Hz, and its second even harmonic is 55Hz, and it’s third even harmonic is 110Hz. And that’s only one example. These subtle harmonics are lost in disconnected designs, and lower volume levels will lose all detail.

And using that same piano note as an example, it is important that the amplifier is phase accurate, especially in this arena. It’s why attention to an amplifier’s signal path is so important, and why so much attention is paid in that area. It is the foundational building block to accurately create sinusoidal waves for the drivers. This is the arena in which realism and soundstage is created, those subtle harmonics and vibrato that are created during the recording process.

Another critical area, is the damping factor of the amp you connect your subwoofer to. This is one area that is misunderstood by many, and seldom executed well. As you decrease resistance, you decrease the damping factor of your amp. It’s why you should find a solution that has only one driver per amplifier channel, and at least 4 ohm. 2 ohm designs or less, while able to create more load, and in the end, more current, (watts) however, it is not conducive to damping factor. The amp has to be able to control driver excursion, and the closer one gets to 2 or 1 ohm, the less ability that amp will be able to control it. The net result is poor performance. Also, using anything less than 10 gauge wire for subs is not recommended. An amplifier that has a damping factor of 500 at 4 ohm, will be reduced to around 100 by using only 5ft of 14 gauge, and at 2 ohm it is almost 50. Damping factors that are at least >100 is a general rule for minimum, and the higher, the better. The function of using large wire gauge (10 gauge or larger) is not for current, but the amount of voltage drop.

From Crown; "Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing." In other words, the speaker produces sound waves that are not part of the original signal. Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope. When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its suspension. So that nice, snappy kick drum turns into a boomy throb. Fortunately, a power amplifier can exert control over the loudspeaker and prevent ringing. Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor, which is load impedance divided by amplifier output impedance. High damping factor equals tight bass."

The goal is to find a subwoofer driver that matches the wattage rating of the amp, placed in a properly designed cabinet to match its Thiele-Small parameters, and connected to the cabin of the vehicle, without using the boot as the enclosure itself.

Last edited by DeltaB; 08-13-2017 at 04:56 AM..
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Old 08-13-2017   #2
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Default Re: Some sub considerations for the DIY

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...
Holy smokes, I was expecting 10 rules...
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Default Re: Some sub considerations for the DIY

Any relative info can be found on this site by doing a search. However, I suspect you will find many may disagree with the "disconnect" theory.

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Old 08-13-2017   #4
 
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Default Re: Some sub considerations for the DIY

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Originally Posted by Bayboy View Post
Any relative info can be found on this site by doing a search. However, I suspect you will find many may disagree with the "disconnect" theory.
It is what it is. I try to keep it in simplistic terms. But time and SPL alignment is lost in disconnected designs. It doesn't matter how you try to shape it. There are some basic rules in play here, no matter the opinion of others.
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Old 08-13-2017   #5
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Default Re: Some sub considerations for the DIY

I disagree with most of it. But anybody willing to research can figure that out.


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Old 08-13-2017   #6
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Default Re: Some sub considerations for the DIY

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Originally Posted by DeltaB View Post
It is what it is. I try to keep it in simplistic terms. But time and SPL alignment is lost in disconnected designs. It doesn't matter how you try to shape it. There are some basic rules in play here, no matter the opinion of others.
Any specific reason you're trying to "keep it in simplistic terms"?

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Old 08-13-2017   #7
 
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Default Re: Some sub considerations for the DIY

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Originally Posted by Bayboy View Post
Any specific reason you're trying to "keep it in simplistic terms"?
It's a public forum.

I will say this though, I'm keenly aware there are lots of various opinions when it comes to audio. It's kind of like the quote from Crown Audio Engineering that I quoted above, who is one of the most respected professional audio companies out there, and certainly know loudspeaker, and it's interaction with various designs. And invariably someone who will come up and have a differing opinion. That's okay with me.
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Old 08-13-2017   #8
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Default Re: Some sub considerations for the DIY

Your quote from Crown Audio Engineering didn't support anything you said. I agree with some aspects, like understanding T/s.

But... Rule #1: you build a cabinet based on performance expectations. I agree.

Rule #2: what does disconnected from the cabin mean? A sub in the trunk can do very well. Your example of a disconnected cabin design doesn't make sense. If it was as critical as you say then we'd all have hatchbacks and SUVs on this forum.

Dampening factor... Read about that on this forum and it's generally considered an issue for theorists. You cover that by stating how misunderstood and uneducated most are... But don't provide any evidence or argument otherwise.

Your op doesn't provide a good foundation for argument. It seems inflammatory more than anything


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Default Re: Some sub considerations for the DIY

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Originally Posted by DeltaB View Post
It's a public forum.

I will say this though, I'm keenly aware there are lots of various opinions when it comes to audio. It's kind of like the quote from Crown Audio Engineering that I quoted above, who is one of the most respected professional audio companies out there, and certainly know loudspeaker, and it's interaction with various designs. And invariably someone who will come up and have a differing opinion. That's okay with me.

I still don't understand your point in that. Public forum, yes. But are you hinting at the forum is full of people that can't comprehend the level you claim?

As far as opinions. Not sure what that has to do with factual aspects. By factual, I mean actual proof from measurements. There's plenty of technical write ups on here to show that most here are not beyond reason when relative proof is provided. But I digress... I've got a dual opposed manifold to finish up and would like to hear the results before this day is over with.

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Default Re: Some sub considerations for the DIY

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Originally Posted by Bayboy View Post
I still don't understand your point in that. Public forum, yes. But are you hinting at the forum is full of people that can't comprehend the level you claim?
I'm not eluding to anything. "If you can't explain it simply, you don't understand it well enough." - Albert Einstein

Quote:
As far as opinions. Not sure what that has to do with factual aspects. By factual, I mean actual proof from measurements. There's plenty of technical write ups on here to show that most here are not beyond reason when relative proof is provided. But I digress... I've got a dual opposed manifold to finish up and would like to hear the results before this day is over with.
Measurements are great, that I agree. But it doesn't replace ears. Two simple rules above were, you need a cabinet that meets speaker Q, and, you can't disconnect the driver from the cabin. The rest is info you should know.
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Old 08-13-2017   #11
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Default Re: Some sub considerations for the DIY

DeltaB, if you're attempting to contribute a How-to-article then the burden of proof lies on you. Otherwise, you didn't contribute anything but an opinion. You can't justify the how-to with "if you understood, then I wouldn't have to explain..."

My teachers never taught anything that way.


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Old 08-13-2017   #12
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Default Re: Some sub considerations for the DIY

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Originally Posted by I800C0LLECT View Post
DeltaB, if you're attempting to contribute a How-to-article then the burden of proof lies on you. Otherwise, you didn't contribute anything but an opinion. You can't justify the how-to with "if you understood, then I wouldn't have to explain..."

My teachers never taught anything that way.
Hence my reference in post #2.

I just need to figure out how to link to the picture of Charlton Heston carrying those tablets.

,<edit>
Thy Sub shall be done thusly...

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Old 08-13-2017   #13
 
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Default Re: Some sub considerations for the DIY

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Hence my reference in post #2.

I just need to figure out how to link to the picture of Charlton Heston carrying those tablets.
+ YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 08-13-2017   #14
 
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Default Re: Some sub considerations for the DIY

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Originally Posted by I800C0LLECT View Post
DeltaB, if you're attempting to contribute a How-to-article then the burden of proof lies on you. Otherwise, you didn't contribute anything but an opinion. You can't justify the how-to with "if you understood, then I wouldn't have to explain..."

My teachers never taught anything that way.
I'm not into your contention. You don't pay me enough to be your instructor. If there is one thing the matriculation process should have taught you, and in turn the most important thing any teacher can teach you, is how to do research, filter that research, and apply the things learned from that research. Obviously, philosophy of education wasn't your major.

It does appear though, you don't like what is being said. And that's your "opinion." Have a great day.
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Old 08-14-2017   #15
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Default Re: Some sub considerations for the DIY

In the spirit of helping, it "sounds" like a 4-ohm sub is recommended over a 2-ohm.
I have 300W at 4-ohms and 500W at 2-ohms.
For a SQ setup should I run a 8" or 10" sub at 4-ohm?
Can a difference be heard?
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Default Re: Some sub considerations for the DIY

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Originally Posted by Holmz View Post
In the spirit of helping, it "sounds" like a 4-ohm sub is recommended over a 2-ohm.
I have 300W at 4-ohms and 500W at 2-ohms.
For a SQ setup should I run a 8" or 10" sub at 4-ohm?
Can a difference be heard?
Ohms dont matter at all other than power. There is zero audible different other than loudness
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Old 08-14-2017   #17
 
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Default Re: Some sub considerations for the DIY

Quote:
Originally Posted by Holmz View Post
In the spirit of helping, it "sounds" like a 4-ohm sub is recommended over a 2-ohm.
I have 300W at 4-ohms and 500W at 2-ohms.
For a SQ setup should I run a 8" or 10" sub at 4-ohm?
Can a difference be heard?
The first thing to recognize, is that SQ is not a function of power, but one of control. When I was at Altec-Lansing before Mark IV Industries sold the brand to Chinese in the late 90's, many hours were spent in the anechoic chamber looking at just this very issue. Amplifier design, and it's output impedance varies widely on it's class, it's engineering design, and the devices in the output stage itself. But in general, you will find control becomes aggressively out of control with driver combinations getting as low as 2 ohm or less, especially at higher SPL, which lends nothing to SQ. The larger the mass, (the larger the driver) the harder it becomes to control at high excursion. To answer your question, "can it be heard?" Yes. And an anechoic chamber proves it time and again when you compare the input signal against the output of the driver/cabinet. General rule of thumb, the higher the damping factor, the less overshoot will be seen. SQ is found in control of the driver, so that it reproduces faithfully the input.

Courtesy of Crown;

http://www.acorn-designs.com/articles/133472.pdf
Please pay attention to pages 14 & 15. And as I stated before the desired DF of >100, Crown recommends upwards of 500.

Courtesy of EAW;

Amplifier damping factor (DF) is defined as “the ratio of the load impedance (loudspeaker plus wire resistance) to the amplifier internal output impedance.” This basically indicates the amplifier’s ability to control overshoot of the loudspeaker, i.e., to stop the cone from moving. It is most evident at frequencies below 150 Hz or so where the size and weight of the cones become significant. A system where the damping factor of the entire loudspeaker/wire/amplifier circuit is very low will exhibit poor definition in the low frequency range. Low frequency transients such as kick drum hits will sound “muddy” instead of that crisp “punch” we would ideally want from the system.

The formula for calculating damping factor is



Where:

Z L = The impedance of the loudspeaker(s)

Z AMP = The output impedance of the amplifier

R W = The resistance of the wire times 2 for the total loop resistance.

Very few amplifier spec sheets state the output impedance, but you can generally call the manufacturer for this spec or you can calculate it by dividing the minimum rated load impedance by the damping factor rating. For example, if we are using amplifier with a damping factor rating of 400 and it requires a minimum load of 2 Ohms, then its output impedance would be calculated as being 0.005 Ohms.

For example…

So let’s look at several examples and figure out what we can control in the design of our system to achieve the best results. Say we have two 8 ohm subwoofers connected to an amplifier with a damping factor of 400 with 100’ of 12 ga. wire with a resistance of 0.00159 Ohms/ft times 100’ gives us a total resistance of 0.159 Ohms. Plugging the numbers into our formula, we get:



In this case, our system damping factor is just 12. Most experts agree that a reasonable minimum target DF for a live sound reinforcement system would be 20, so we need to consider changing something to get this up.

The critical element in this definition is the “loudspeaker plus wire resistance” part. In this case, the resistance in 100’ of 12 ga. wire with a 4 Ohm load results in around 0.7 dB of loss, much greater than the maximum target of 0.4 dB of loss, so let’s try bigger wire. 10 ga. wire has a resistance of .000999 Ohms/ft times 100’ equals .0999 Ohms and will get us to the 0.4 dB target. What will it do for DF?



Ok, now we’re pretty close to the 20 we were looking for. Notice that the loudspeaker impedance can also give us a big change. The higher the circuit impedance, the less loss we have due to wire resistance. What if we change our wiring so we have one 8 Ohm loudspeaker connected instead of two? Going back to our 12 ga. wire, we calculate:



Even better! In fact, if you run the numbers a few times, you will see that in a system with some significant length of wire, we will find that damping factor will generally be 20 or higher as long as our total wire loss is 0.4 dB or less.

What if we have a self-powered subwoofer? In this case, our loudspeaker wire is probably around 14 ga. and since the amplifier is in the loudspeaker enclosure, it is probably less than a couple feet long. Assuming the manufacturer is connecting two 8 ohm loudspeakers to the amplifier, and 14 ga. wire has a resistance of .00256 Ohms/ft times 2’ equals 0.00506 Ohms of resistance, and our amplifier has a damping factor spec of 400, what do we get?



Wow! Now that’s a significant difference! Kind of supports the idea of using self-powered subwoofers, or at least putting the subwoofer amps as close as possible to the subs.

Amplifier DF Ratings

So we’ve looked at the differences in the size and length of our wire and the differences in hanging one loudspeaker on the line vs. two to change the impedance of the line. What if we choose an amplifier with a higher damping factor spec., say 3000? That’s a big difference, so we should see a much higher damping factor in our circuit, right? Assuming this amplifier can drive a minimum 2 Ohm load, we find the output impedance would be 0.001 Ohms. Plugging the numbers into our single loudspeaker with 12 ga. wire system, we get:



Hmmmm, not such a big deal. That higher amplifier damping factor only improved our system damping factor by 0.31 over the amplifier with a DF spec of only 400.

What if we use the amplifier with the 3000 DF spec in our self-powered sub with 2’ of 14 ga. wire?



Remember our calculation using the 400 DF amplifier was 264.55, so now we start to see when the amplifier spec becomes significant. Essentially, in sound reinforcement systems where we have some significant length of wire between the amplifier and the loudspeaker, the amplifier DF spec has little affect on the performance of the system.

In Summary…

So what have we learned? In live sound reinforcement systems, damping factor is really driven by the length and size of our wire and the impedance of the loudspeakers we connect at the other end. Since damping factor mostly affects low frequency, we should endeavor to keep our subwoofer loudspeaker lines as short as possible and/or use larger gauge wire. We should keep the impedance of the connected load as high as possible by connecting only one transducer per wire instead of two.

So is more amplifier damping factor better? As one of my colleagues recently said, “Sure! If the loudspeaker terminals are welded to the amplifier output terminals!” Well, maybe he overstated it a little bit, but yes, as long as the loudspeaker wire is really short, then by all means!

Last edited by DeltaB; 08-14-2017 at 05:44 PM..
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Old 08-14-2017   #18
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Default Re: Some sub considerations for the DIY

I'm not sold on damping issues. I think it's a crusade for perfection through theory

http://www.audioholics.com/audio-amp...ystem-response


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Old 08-15-2017   #19
 
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Default Re: Some sub considerations for the DIY

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Originally Posted by I800C0LLECT View Post
I'm not sold on damping issues. I think it's a crusade for perfection through theory

Damping Factor: Effects On System Response | Audioholics
Transistor amps didn't exist until the 60's, so research from 1934 when Fritz did his work "Radiotron Designer's Handbook" when tubes reigned supreme, transformer based output reacts quite differently to load.

Last edited by DeltaB; 08-15-2017 at 04:12 AM..
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Old 08-15-2017   #20
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Default Re: Some sub considerations for the DIY

OK, I'l bite.

How does the amp control cone motion and how does damping factor play a role? If we're so worried about cone control, why isn't inductance included in the above calculations? Given the answers to these, what is the approximate contribution that amplifier damping has on cone control compared to mechanical/electromechanical deficiencies of the sub and enclosure?

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Old 08-15-2017   #21
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Default Re: Some sub considerations for the DIY

I suppose that the other way to consider it is that 500W is about 600w, which is 3dB high SPL than 300W, so I give up 3dB of SPL.

A subwoofer with an SPL of 82dB/w + 24-dB (300w) yields an SPL of 106dB.
(Maybe that is not dBA.)

So the question remains, is that enough SPL for general use without it being designed as a thumpfest?
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Old 08-15-2017   #22
 
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Default Re: Some sub considerations for the DIY

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Originally Posted by SPLEclipse View Post
OK, I'l bite.

How does the amp control cone motion and how does damping factor play a role? If we're so worried about cone control, why isn't inductance included in the above calculations? Given the answers to these, what is the approximate contribution that amplifier damping has on cone control compared to mechanical/electromechanical deficiencies of the sub and enclosure?
The voice coil resistance is a key factor in limiting the amount of damping that can be achieved electrically, because its value is larger (say between 4 and 8Ω typically) than any other resistance in the output circuitry of an amplifier that does not use an output transformer (nearly every solid-state amplifier on the mass market). I said this before but bears repeating;

From Crown; "Loudspeakers have a mind of their own. You send them a signal and they add their own twist to it. They keep on vibrating after the signal has stopped, due to inertia. That's called "ringing" or "time smearing." In other words, the speaker produces sound waves that are not part of the original signal. Suppose the incoming signal is a "tight" kick drum with a short attack and decay in its signal envelope. When the kick-drum signal stops, the speaker continues to vibrate. The cone bounces back and forth in its suspension. So that nice, snappy kick drum turns into a boomy throb. Fortunately, a power amplifier can exert control over the loudspeaker and prevent ringing. Damping is the ability of a power amplifier to control loudspeaker motion. It's measured in Damping Factor, which is load impedance divided by amplifier output impedance. High damping factor equals tight bass."

A loudspeaker's flyback current is not only dissipated through the amplifier output circuit, but also through the internal resistance of the loudspeaker itself. Therefore the choice of different loudspeakers will lead to different damping factors when coupled with the same amplifier. (this is why selection of driver/cabinet/amp selection is important in SQ)

The driver's motor itself is an inductor. And it resides in a magnetic field, which also makes it a generator.

Mechanical Q (driver loading) is accomplished by the cabinet. Damping factor will not help you much in deficiencies of a poorly matched driver/cabinet.

Last edited by DeltaB; 08-15-2017 at 05:54 AM..
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Old 08-15-2017   #23
 
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Default Re: Some sub considerations for the DIY

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Originally Posted by Holmz View Post
I suppose that the other way to consider it is that 500W is about 600w, which is 3dB high SPL than 300W, so I give up 3dB of SPL.

A subwoofer with an SPL of 82dB/w + 24-dB (300w) yields an SPL of 106dB.
(Maybe that is not dBA.)

So the question remains, is that enough SPL for general use without it being designed as a thumpfest?
A 3dB increase in power does not equate to a doubling of SPL. Sorry.
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Old 08-15-2017   #24
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Default Re: Some sub considerations for the DIY

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Transistor amps didn't exist until the 60's, so research from 1934 when Fritz did his work "Radiotron Designer's Handbook" when tubes reigned supreme, transformer based output reacts quite differently to load.
What does that have to do with that article? That book wasn't referenced.

In your above response, he didn't even mention "doubling SPL" but you negated his question with that.



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Old 08-15-2017   #25
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Default Re: Some sub considerations for the DIY

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Originally Posted by DeltaB View Post
A 3dB increase in power does not equate to a doubling of SPL. Sorry.
How does it work then?
The speakers have numbers associated with them in terms of dB/watt.
So I assume I push an RMS watt in, and I should get the exact SPL dB/watt that they are rated at.

So if I have the amp cranked up to 3 dBW, then what does that equate to in a SPL dB(s) change compared to when it was at 0-dBW?
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