Fi Q judgement day (SPL #'s inside)

[tommyk90 5,000+ posts]

A laser pointer and a clamp would get you close... Clamp to match actual power levels going to the woofer, burp at your box tuning and compare with a laser sight. Heck you could simply use the laser sight to make simply make sure the DD was moving more or less and then compare scores.

I've done some comprehensive power tests with the DD versus other subs, with the DD still being out on top.

Laser pointer wouldn't be a bad idea, but it's hard to watch 2 meters (for power), and a laser pointer all at the same time during a burp.

Plus being in the car affects my score as well.

Honestly, there's just too many variables involved to say that sub A is better than sub B. Regardless of BL, xmax, FS, etc. and so forth. Numbers on a piece of paper only get you so far.

 

[JHughes 10+ year member]

Both subs don't move at the same xmax with the same force. This is what separates cheap, good excursion subs from higher power, less excursion subs. Imagine holding your hand against the cone of both subs. The higher motor strength sub will take more pressure from you to hold it back from moving outward.

I'm definitely not an expert, but physics says force = mass times acceleration. I know the mass doesn't change so it has to be the acceleration changing. I think the the stronger motor accelerates the air in the port and the vehicle, not just the cone, but at the same frequency as a weaker motor. Does this sound right? Just my observation, please tell me if I am wrong...lol //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[tommyk90 5,000+ posts]

I'm definitely not an expert, but physics says force = mass times acceleration. I know the mass doesn't change so it has to be the acceleration changing. I think the the stronger motor accelerates the air in the port and the vehicle, not just the cone, but at the same frequency as a weaker motor. Does this sound right? Just my observation, please tell me if I am wrong...lol //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Actually, the mass does change between woofers.

Different cone materials, different voice coil height, windings, winding height, etc. All that stuff adds up.

 

[sundownz Pro Seller]

Excursion does not necessarily = output in SPL enclsoures... I can get a Sundown Z15 moving so far the cone hits the spider landing (cone has dents in it from the landing)... and it does 151s.

New Nightshade v.2 prototype actually moving a little less = 156.1 dB

Same enclosure, same frequency, same vehicle... more power / more motor force with the NS v.2

Tommy is correct that motor force -- and not just raw motor force ** -- but sustained motor force over stroke can make a woofer louder at a given excursion.

** -- My Monster prototype has a BL^2/RE of 360 vs "only" 190 on the NS v.2 but is a full dB quieter as it has a far less sustained BL over stroke due to a very short coil... Monster has 42mm coil / 25mm TP and NS v.2 has 71mm coil / 40mm TP.

 

[JHughes 10+ year member]

Actually, the mass does change between woofers.
Different cone materials, different voice coil height, windings, winding height, etc. All that stuff adds up.

I get your point now. I was thinking kinda narrow-minded more along the lines of 2 different strength motors with identical soft parts, acceleration then be the only variable changing. But, that's usually not the case in the real world so I see it's mostly irrelevant. I'm just over thinking it a little I guess. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[tc300 10+ year member]

Well theres a couple reasons really.
One has to do with the enclosure size itself. By enclosure size, I mean how much room the enclosure itself takes up. If you look at newer style crx boxes they try to make the box as tiny as possible to maximize airflow around the enclosure itself. That's one aspect of a smaller box.

Also, a smaller box will change its own resonance, for better or worse nobody knows until you test it. Also, going to a smaller box will change the peak frequency, given the same port length. SPL is a funny thing really. For example, one time I tested one of my old SPL enclosures with 2 different port lengths. The boxes have external aeroports so it does not affect the airspace, however with the shorter port I lost upwards of 3 dB. The funny thing about that? My peak frequency didn't change. Like I said, SPL is tricky stuff that involves a lot of testing.

Another aspect of a smaller enclosure is the ability to pressurize it easier. And as we know, higher air pressure=higher SPL. Also, that's why you don't necessarily need to add power to get higher numbers out of a smaller box. Also, a smaller box can develop an "air spring" effect, if you will, that can help control excursion at higher power levels. That's how some people can shove 10kw into a 3" coil and have everything hold together. Of course part of that effect has to do with the port length/size as well, relative to the enclosure size.

When I put my TL inside my enclosure, I can hit upwards of 170 dB. If was to put my 10" in 4 cubes, that number would most likely drop dramatically.

Also, don't think that excursion is the only aspect to high SPL numbers. I can move a CVR (or any other cheaper sub with decent xmax) peak-to-peak and put the DD in the same setup with less power, moving 1/4 as far, and odds are the DD is going to be louder.

Why? Because of motor FORCE. Think of it like this. You can punch a wall gently 1 time every second, or you can punch as hard as you can 1 time every second. In essence the "sine wave" you create by moving your arm back and forth will be the same length and height, but the force behind the 2nd one is much greater.

More force=more SPL.

Going off your statements, one would think that a larger box will always be louder, which we know isn't the case.

GOD HAS SPOKEN.........

 

[JHughes 10+ year member]

Also, don't think that excursion is the only aspect to high SPL numbers. I can move a CVR (or any other cheaper sub with decent xmax) peak-to-peak and put the DD in the same setup with less power, moving 1/4 as far, and odds are the DD is going to be louder.

Why? Because of motor FORCE. Think of it like this. You can punch a wall gently 1 time every second, or you can punch as hard as you can 1 time every second. In essence the "sine wave" you create by moving your arm back and forth will be the same length and height, but the force behind the 2nd one is much greater.

More force=more SPL.

Excursion does not necessarily = output in SPL enclsoures... I can get a Sundown Z15 moving so far the cone hits the spider landing (cone has dents in it from the landing)... and it does 151s.
New Nightshade v.2 prototype actually moving a little less = 156.1 dB

Same enclosure, same frequency, same vehicle... more power / more motor force with the NS v.2

Tommy is correct that motor force -- and not just raw motor force ** -- but sustained motor force over stroke can make a woofer louder at a given excursion.

** -- My Monster prototype has a BL^2/RE of 360 vs "only" 190 on the NS v.2 but is a full dB quieter as it has a far less sustained BL over stroke due to a very short coil... Monster has 42mm coil / 25mm TP and NS v.2 has 71mm coil / 40mm TP.

One question related to all this and mostly the part in bold:

Is this an effect of the stronger motor being able to move (accelerate) the air in the port more efficiently and evenly with the cone thus actually increasing displacement with less excursion and creating more SPL?

 

[2003F150 10+ year member]

Excursion does not necessarily = output in SPL enclsoures... I can get a Sundown Z15 moving so far the cone hits the spider landing (cone has dents in it from the landing)... and it does 151s.
New Nightshade v.2 prototype actually moving a little less = 156.1 dB

Same enclosure, same frequency, same vehicle... more power / more motor force with the NS v.2

Tommy is correct that motor force -- and not just raw motor force ** -- but sustained motor force over stroke can make a woofer louder at a given excursion.

** -- My Monster prototype has a BL^2/RE of 360 vs "only" 190 on the NS v.2 but is a full dB quieter as it has a far less sustained BL over stroke due to a very short coil... Monster has 42mm coil / 25mm TP and NS v.2 has 71mm coil / 40mm TP.

The more coil in the gap the better and yes dd uses the lightest/strongest materials they can find to keep the mass down thus making them a "faster" woofer

 

[sundownz Pro Seller]

Lower mass doesn't make the woofer faster... although lower mass can increase SPL. In my particular application roughly 0.1 dB per 10 grams all other factors remaining equal.

Woofer "speed" paper :

http://stereointegrity.com/docs/WooferSpeed.pdf

"Guess what - we just answered the original question! It turns out that transient response of a woofer is not a function of the moving mass, as is commonly espoused (one of the most infamous audio myths). In actuality, it is based upon the inductance of the driver. And the greater the inductance, the slower the driver - the lower the transient response."

 

[hrtbrk1 5,000+ posts]

wow i've learned so much! keep up the knowledge flow

 

[T3mpest 10+ year member]

Lower mass doesn't make the woofer faster... although lower mass can increase SPL. In my particular application roughly 0.1 dB per 10 grams all other factors remaining equal.
Woofer "speed" paper :

http://stereointegrity.com/docs/WooferSpeed.pdf

"Guess what - we just answered the original question! It turns out that transient response of a woofer is not a function of the moving mass, as is commonly espoused (one of the most infamous audio myths). In actuality, it is based upon the inductance of the driver. And the greater the inductance, the slower the driver - the lower the transient response."

That I know, but that's not quite where we are going this time. We are trying to figure out displacements role in SPL when playing near tuning. As far as I can tell, it's still the deciding factor. We fix the frequency response, 50hz means a driver MUST move 50x back and forth per second. Lower inductance allows it to move "faster" and play a higher frequency. However, we are concerned about staying at the same frequency. As far as I can tell, displacement near tuning would be the key factor to higher output. Higher velocity on the cone since more displacement leads to more displacement/time, since time and the number of strokes is fixed.

Think of it this way, each speaker goes back and forth 75 times per second. Woofer a moves .25mm each way so .5 each cycle. That's a distnace of 37.5mm/second. If woofer be can move .5mm each way or 2x as far mm each cycle over the same time interval we have a woofer moving 74mm/second. I can't see how a woofer could "move less" and somehow be loweder. To displace air the woofer has to move. Since frequency is fixed the only way it can "have more force" is to simply move faster and further each stroke while still occilating at the frequency specified.

 

[sundownz Pro Seller]

That I know, but that's not quite where we are going this time. We are trying to figure out displacements role in SPL when playing near tuning. As far as I can tell, it's still the deciding factor. We fix the frequency response, 50hz means a driver MUST move 50x back and forth per second. Lower inductance allows it to move "faster" and play a higher frequency. However, we are concerned about staying at the same frequency. As far as I can tell, displacement near tuning would be the key factor to higher output. Higher velocity on the cone since more displacement leads to more displacement/time, since time and the number of strokes is fixed.

This is not the case as you can see in my example... I've been using the same box for a few years in the same vehicle at the same frequency. At a given displacement I have seen a difference of 6 dB in among various woofers.

Lowest score is 150.1 with one SA-15 and highest is 156.1 with one Nightshade v.2 15 all at a nearly identical excursion (within a few mm - obviously I don't have a measurement system in my Jeep but the mechanical limits of all the drivers are about the same)... using displacement theory the Nightshade v.2 would need to move four times more to generate that extra 6 dB //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I drive all woofers in this box to maximum displacement... until it quits getting louder and/or cones hit the spider landing.

 

[sundownz Pro Seller]

I should add... PORT displacement increases with the louder drivers but CONE displacement does not. In other words... the port is moving more air even though the cone is not moving any farther.

 

[T3mpest 10+ year member]

I should add... PORT displacement increases with the louder drivers but CONE displacement does not. In other words... the port is moving more air even though the cone is not moving any farther.

where is the port getting the added excitation from? The port only moves because of the cone imparting energy to it. If it can only impart energy 40x/second how do you get increased energy to it without increasing displacement? You can't "push" against it more times as frequency is fixed. To push against it harder or with more force would allow the cone to move further on each trip. I suppose it could move quicker and they could both run into mechanical limits at the same distance? In that case though the louder speaker is far from optimized as it probably could have moved further each stroke had it not hit a wall, so to speak.

 

[sundownz Pro Seller]

where is the port getting the added excitation from? The port only moves because of the cone imparting energy to it. If it can only impart energy 40x/second how do you get increased energy to it without increasing displacement? You can't "push" against it more times as frequency is fixed. I suppose it could move quicker getting there and they could both run into mechanical limits at the same distance? In that case though the louder speaker is far from optimized as it probably could have moved further each stroke had it not hit a wall, so to speak.

I have a book that breaks it all down at the house... let me try to paraphrase from memory (haven't looked at it in a few years). The pressure of a woofer is highest at the zero point of displacement -- in other words -- pressure and displacement are 90 degrees out of phase. The sub is putting the highest pressure on the port at the 0 position -- also where motor force is the highest.

If you like I can try to remember to bring that book in and scan it for you... to make sure I paraphrased correctly //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

My real world tests show it is true -- I didn't get 6dB from nowhere //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif