Evaluating Subwoofers

[audioholic 5,000+ posts]

Audioholic I only use sealed enclosures. I know vented enclosures is all about the frequency response and tuning. But in a sealed enclosure xmax and power handling is everything.

I thought you said xmax and cone area was everything. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

In a sealed setup, yes excursion and cone area directly affect the spl created. But hoffman's iron law tells us efficiency is still important for enclosure size, and power handling is important because if you cant reach full excursion in the proper sized box without popping the coil then xmax doesn't really mean much. Fs also affects frequency response quite a bit in sealed systems, if we want to branch out from the vague topic of simple air displacement potential.

The more you learn about speaker specs, the wider your vision of the importance of all the specs becomes.

 

[hispls 5,000+ posts]

BL over displacement is important - that is only shown as a curveCompliance over displacement is also important - show an a curve

inductance can be important - this can also be shown as a curve but its a high order derivative so its non linear effects do not directly affect the system as greatly as say compliance or BL which are direct forces on the system.

Other motor distortions such as flux modulation or unwanted eddy currents- non-conductive formers, shorting rings, motor saturation etc can deal with these

sensitivity is a big one let me repeat: BIG ONE, but you also need to consider sensitivity over the displacement which is basically xmax (give or take)

BL gives you sensitivity and resistance (or the DC resistance ace of the voice coil ) will reduce your sensitivity which is why the formula is BL^2/Re for pure motor force factor spec'ed in Newtons squared per Joule per Second, or watt. Combine that with the moving mass and cone area and you define raw SPL.

RMS is not a woofer spec its an amp spec. LOTS of brands will hype up "cooling" or high RMS - i have yet to see any conclusive results of any of it. If it helps its only going to help for very long term thermal abilities. Any and all woofers will takes tons of power short term. Which is why some brands spec SPL woofers at say 20,000 watts which for a 1 second burp is actually not impressive from a thermal standpoint, especially at a high frequency where the mechanical displacement limits wont be reached. The issues with say 20,000 watts (for example) is that the accelerations are very extreme but we don't see thermal break down over a short period of time, but you'll often see mechanical break down from high force - broken cones are very common.

The last specs are the hidden specs - durability, longevity. etc - is it generally going to last for the time i expect it to last? One major one for example is foam vs rubber surround. Foam may give you say ~1.5dB Extra SPL but it not UV or water proof and can wear away over the years. Point is here they are always trade offs to consider.

I also believe "SQL" simply stands for sound quality + loud? where SQ is stickily "Sound quality" and "SPL" is for spl woofers.

I actually think those terms are rather idiotic and misleading. In fact a good woofer can indeed be loud and sound very good. Many of this things that make a woofer sound bad also make it less loud.

^^^^^^^

Should be stickied

 

[sundownz Pro Seller]

I agree with Kyle pretty well here... I design SPL woofers based primarily on BL^2/RE and MMS... both of these I have observed direct correlations to SPL in my testing over the years (box remained the same... change woofers).

Same goes for shorting rings and alternative former materials -- doing alot with that now //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I have done tons and tons of head to head testing of different things in my Jeep... really helps develop a good SPL woofer to actively test them and see how they stack up in the lanes, IMO.

 

[ahole-ic]

Since we've already had one guy make an ass of himself, let me make one of myself. Jacob you're talking about playing with former materials. I have often wondered why a thermally conductive acrylic/ceramic couldn't be used. They are used all the time in Heatsink Epoxy. They harden to be rigid, light, and dissipate heat much better than regular old plastic. They are also electrical insulators. For this reason I wonder why formers couldn't be made of this, the shellac or glue sanded off of the inside and outside of the voice coil. This provides an unimpeded contact joint with the VC and former and then the former would act as a sort of heat spreader. Then it could attach to the dustcap. the dustcap could be some lightweight heatsink. (I think this is a good idea because since you have all of this increased thermal ability, you could adjust the FS by different dustcap heatsink weighting) If you really wanted to get fancy, you could incorporate heat pipes as seen in CPU coolers. They are ducts that contain a liquid that vaporizes at very low temperatures. It goes up and is cooled by the heatsink and returns in liquid form again to cool the component.

I realize this would be ridiculously expensive, BUT with people such as yourself persuing NEO motors, people purchasing carbon fiber cones and caps, I think SOME of this could be justified.... at least for a small portion of the market. If you use this, I would at least like the former to be named after me. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I agree with Kyle pretty well here... I design SPL woofers based primarily on BL^2/RE and MMS... both of these I have observed direct correlations to SPL in my testing over the years (box remained the same... change woofers).
Same goes for shorting rings and alternative former materials -- doing alot with that now //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I have done tons and tons of head to head testing of different things in my Jeep... really helps develop a good SPL woofer to actively test them and see how they stack up in the lanes, IMO.

 

[cam5860 10+ year member]

A driver with a higher maximum power rating cannot necessarily be driven to louder levels than a lower-rated one, since sensitivity and power handling are largely independent properties. In the examples that follow, assume (for simplicity) that the drivers being compared have the same electrical impedance; are operated at the same frequency within both driver's respective pass bands; and that power compression and distortion are low. For the first example, a speaker 3 dB more sensitive than another will produce double the sound pressure level (or be 3 dB louder) for the same power input; thus, a 100 W driver ("A") rated at 92 dB for 1 W @ 1 m sensitivity will put out twice as much acoustic power as a 200 W driver ("B") rated at 89 dB for 1 W @ 1 m when both are driven with 100 W of input power. In this particular example, when driven at 100 W, speaker A will produce the same SPL, or loudness, that speaker B would produce with 200 W input. Thus, a 3 dB increase in sensitivity of the speaker means that it will need half the amplifier power to achieve a given SPL. This translates into a smaller, less complex power amplifier—and often, to reduced overall system cost.

 

[sundownz Pro Seller]

Not necessarily true... if subwoofer A is 96 dB sensitive but has an F3 of ~67 hz... and subwoofer B is 90 dB sensistive and has an F3 of ~43 Hz... which has more output at 100 watts at 40 Hz ? The second woofer will have ~4 dB MORE output at 40 Hz with a 6 dB lower sensitivity due to more low-end extension. Just a rough example... but you get the picture.

Moral of the story -- high sensitivity subs tend to have less low-end extension, especially sealed. As audioholic stated... sensitivity is typically measured well outside of the pass band of subwoofers.

 

[cam5860 10+ year member]

Honestly I look for high sensitivity systems if someone is on a budget. It allows you to use less power and still have a loud system. JBL is known for there high sensitivity levels in there speakers which make them a great choice for a budget system. I put a azz of JBL GTO subs in budget systems because they have high sensitivity levels and good output levels for there price range.

 

[ahole-ic]

Honestly I look for high sensitivity systems if someone is on a budget. It allows you to use less power and still have a loud system. JBL is known for there high sensitivity levels in there speakers which make them a great choice for a budget system. I put a azz of JBL GTO subs in budget systems because they have high sensitivity levels and good output levels for there price range.

You're not paying attention. Efficiency is rated at 1000hz. Subwoofers don't play over 100hz. Efficiency as currently rated is irrelevant at sub bass frequencies.

 

[Kastlez_ 10+ year member]

You're not paying attention. Efficiency is rated at 1000hz. Subwoofers don't play over 100hz. Efficiency as currently rated is irrelevant at sub bass frequencies.

X2, was stated before.

 

[Blasphemy 10+ year member]

Some good info ITT.

 

[cam5860 10+ year member]

Sundownz you have a good point. There are so many variables that play a role in a loud speaker. You have to also factor in the F3 spec.

 

[soldiermedic 10+ year member]

Not necessarily true... if subwoofer A is 96 dB sensitive but has an F3 of ~67 hz... and subwoofer B is 90 dB sensistive and has an F3 of ~43 Hz... which has more output at 100 watts at 40 Hz ? The second woofer will have ~4 dB MORE output at 40 Hz with a 6 dB lower sensitivity due to more low-end extension. Just a rough example... but you get the picture.
Moral of the story -- high sensitivity subs tend to have less low-end extension, especially sealed. As audioholic stated... sensitivity is typically measured well outside of the pass band of subwoofers.

So if I am using a sealed enclosure, which spec should I focus on since I am not looking for a loud sound, but a clear one?

 

[audioholic 5,000+ posts]

You're not paying attention. Efficiency is rated at 1000hz. Subwoofers don't play over 100hz. Efficiency as currently rated is irrelevant at sub bass frequencies.

Not to mention, he's completely ignoring hoffman's iron law which states that 3db more efficient sub is either going to have worse LFE than the less efficient driver, or its going to require a significantly larger enclosure. Higher efficiency is not the end-all be-all positive improvement a lot of people think it is in a subwoofer.

 

[JimJ 5,000+ posts]

Given the choice, I'd rather deal with a much larger enclosure than make the tradeoffs for smaller size //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

But then again, I have six foot tall enclosures for 6.5" drivers...//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[IMOVeCHICKENS! 10+ year member]

You're not paying attention. Efficiency is rated at 1000hz. Subwoofers don't play over 100hz. Efficiency as currently rated is irrelevant at sub bass frequencies.

as ive read thru the thread ive noticed he doesnt pay attention at all...