Ported vs Sealed, lets open this can of worms. lol

[stipud]

Generally speaking I have to trust the manufacturers specs, if published. Sometimes when doing woofer tests, DIYMA also posts their own measured T/S params.

That $99 woofer tester seems too good to be true though! I've never seen that before!

[Eric D]

Generally speaking I have to trust the manufacturers specs, if published. Sometimes when doing woofer tests, DIYMA also posts their own measured T/S params.

That $99 woofer tester seems too good to be true though! I've never seen that before!

I question the $99 cost as well.

If you look in the photo below, the white unit second from the top in the audio rack is an AudioPrecision System One, which is what Rockford used to get T-S parameters of woofers. At $50,000 it is just a wee bit more expensive than the Dayton Woofer Tester. The aluminum clamp to the right of the computer desk was used for the laser interferometer, as part of the T-S parameter testing.

[audiophyle_247]

So it seems a lot of us are on some common ground for a change.

It's amazing what a little cool head debate can iron out. I think most of the time internet bickering is just minor miscommunication & semantics with a little too much emotion.

I think maybe the modeling portion is confusing. For building designs I import entire models as 3d masses into various other programs for thermal analysis & environmental conditions.
WinISD is simply a numerical analyzer that calculates results off given variables, maybe more performance mapping vs modeling. Lol All you have to do is punch in some numbers & watch a graph, then adjust those numbers till the graphs begin to show you what you want.

You are limited to the accuracy of published T&S parameters, however the differences when modeling are most likely no consequence unless they are very far off. I think this goes back to the diminishing returns area, there are plenty of other variables you could work on easier and net better results.

That speaker tester is pretty cool, but I have my reservations on its accuracy & capability as well.

There are also a lot of parameters, but only so many need to be known to analyze various portions of the woofers performance in a box, or port velocity, or group delay, etc.... and typically the important ones are readily published by even boutique brands.

[Eric D]

I don't know what to consider as WAY off on T-S parameters, but I know many of the ones I have tested have not been very close to what the manufacturer published.

Even Rockford was notorious for this. I remember when the T-S testing for the RF Power HX2 line was done and the measurements from the lab did not end up being the measurements in the speakers documentation.

I doubt it was a typo either. Marketing probably had an idea people may actually buy one woofer over another based on certain T-S parameters, so they would change them to remain competitive. It did not make much sense to me, but those were my findings.

I don't really see why you would want to do a thermal analysis on a box as a 3D model, but I could see doing some air flow analysis on its port features. Are you using thermal analysis in some way to gain flow data? I have never done any thermal analysis on anything, but do have experience with stress analysis using modules built into SolidWorks.

[shawn k]

The test equipment that Eric is referring to in the RF lab appears to be a "Klippel machine". If it's not a true Klippel, I'm sure it's essentially the same thing. I'm not surpised that RF has such cutting edge equipment. Being a company that manufactures their own drivers (at least they used to) such precision eqipment is needed for design and developement. However, none of us here are building our own prototype drivers, and we're certainly not at the mercy of a marketing department who would have us constantly changing the parameters of a protoype in order to achieve a certain design goal. That is why RF as well as many other reputable companies need such equipment.

I have the Woofer Tester by Dayton, and it's a pretty useful tool. I have had numerous cases where a driver's TS parameters were very close to the manufacturer's published specs, which leads me to believe that the Dayton piece works. Now at the same time, I have also had several cases where the results after testing were off from the manufacturer's published specs, but I believe there are numerous reasons why. First, as Eric had mentioned, would simply be that the published specs were just simply incorrect do to poor quality control or just simply ignorance on the company's behalf. Next, and perhaps more common, would be mismatched parameters do to the age of the driver. As a driver is used and ages, the TS parameters will indefinitely change from the day it was constructed, mostly due to a shift in the compliance of the suspension. But that fact that the Woofer Tester data has been quite acurate (at least on new drivers) when comparing to the published specs of many drivers, makes me believe that it is a tool that is at least "within usable limits". No, it's not absolutely perfect, but pretty much nothing within the realm of car audio is. I personally feel it's a tool that is perhaps even more useful than the "published" specs, especially when you have a driver that either doesn't have any information, or a driver that is relatively old and perhaps has had it's TS parameters shifted.

[audiophyle_247]

I don't really see why you would want to do a thermal analysis on a box as a 3D model, but I could see doing some air flow analysis on its port features. Are you using thermal analysis in some way to gain flow data? I have never done any thermal analysis on anything, but do have experience with stress analysis using modules built into SolidWorks.

Lol, I said a building not a box. I have to quite literally build an entire structure from the ground up and have an almost complete building in order to test thermal characteristics, air flow, insulation values, solar gain, & sizing of HVAC & structural systems.

Enclosures require none of that.


As for the difference in specs, you can alter the T&S parameters of the driver while its being graphed. Shift some of the readings up & down & see what it does to the performance, the differences Ive seen are not terribly big but I dont actively pursue that info so I cant say for sure just how much variation there is among manufacturers.
Although there is a thread on DIYMA about Polk's new MM subs having inflated xmax values.

[Eric D]

Rockford also had a Klippel, but that was setup in different lab. Other than unboxing it and getting the software installed and working on a PC, I did not really get to play with it much.

The AP System One did pretty much what the Klippel does, just not in the convenient package deal Klippel offered.

I do remember running some BL curves on the (new at that time) Rockford Punch HX2 18. This 18 was based on the Power HX2 motor, with the Punch HX2 look. What was really fascinating to me is we found the BL curve to be shifted, which was a clear indicator the voice coil was not centered in the gap. We determined that the significant weight of the 18in woofer's cone and suspension caused it to sag when in the box and sitting on a shelf. With this in mind we started offsetting the coil height in production, such that when a woofer sat for about a month or two the coil would move into alignment. Once a customer used the woofer in a vertical position, the sag would be for the most part permanently set, so there was no issue. One potential problem though would be anyone mounting the woofer facing down (for example to show off the motor). I assume over time the coil would become significantly out of alignment.

Also of note, the JL 12W7 did not have an aligned BL curve either. We were not sure this was from cone weight, or part of the design, or just poor quality. JL seemed to be great quality, so we did not put much weight on the poor quality theory.

[shawn k]

I do remember running some BL curves on the (new at that time) Rockford Punch HX2 18. This 18 was based on the Power HX2 motor, with the Punch HX2 look. What was really fascinating to me is we found the BL curve to be shifted, which was a clear indicator the voice coil was not centered in the gap. We determined that the significant weight of the 18in woofer's cone and suspension caused it to sag when in the box and sitting on a shelf. With this in mind we started offsetting the coil height in production, such that when a woofer sat for about a month or two the coil would move into alignment. Once a customer used the woofer in a vertical position, the sag would be for the most part permanently set, so there was no issue. One potential problem though would be anyone mounting the woofer facing down (for example to show off the motor). I assume over time the coil would become significantly out of alignment.

Wow! That's crazy! I know exactly which driver you're talking about. I wonder why they chose to rectify the problem in that manor. Perhaps it was just too costly to swap parts and or rework the suspension. I suppose, as you stated, that the sub would indeed be fine in a vertical state, but it really sounds like the suspension was inadequate for that particular cone & cap mass. Even with the offset in the VC, it seem like any horizontal positioning for that driver (either normal or inverse) would cause some serious issues over time.

I now that they had two generations for that driver, I wonder if they made any revisions to the suspension between the two.

[Eric D]

The second generation one is the one I know of with this issue. It had a Power HX2 motor, spider, and coil, with a new cone, and the same Punch style cast frame.

The Power HX2 suspension was already very stiff out of the box. Making it any stiffer would have had negative results in other areas.

Keep in mind there is a practical reason why 48in woofers are not common. Moving heavy parts that are supposed to in theory be perfectly rigid (with no mass) becomes a nightmare.

[shawn k]

The Power HX2 suspension was already very stiff out of the box. Making it any stiffer would have had negative results in other areas.

Very stiff, but still not stiff enough if you cannont prevent severe sag after only a month or so of storage.

IMO, rasing the compliance (stiffer suspension via multiple spiders and/or swapping the big rubber surround to high roll foam) would make more sense than to have a driver that suffers from sag

Keep in mind there is a practical reason why 48in woofers are not common. Moving heavy parts that are supposed to in theory be perfectly rigid (with no mass) becomes a nightmare.

Quite understandable, but there are still plenty of 18" drivers from other manufacturers that don't suffer from this problem. IMO it's really just a poor design that could have been rectified. However, it was probably too costly in the long run.

[Pillow]

WOW, this thread went from slow start to crazy!

I switch my gear... Although not an apples to apples comparison... Old: Brahma 15" in a 3 cu ft ported box. New: Ascendant Audio Avalanche 2- 15" in a sealed box at a Q of .74 about 4.5 cu ft with a little polyfil added and birch plywood box. Same MMATS Pro 1400.2 amp.

The sealed is "tight" and I agree with Eric on that! The music is definitely more SQ oriented. The bass impact on a kick drum is wonderful. BUT there is a noticeable drop in low end brutality from the ported. Make no mistake the SQ of sealed is well worth the effort!

Just from an SPL standpoint the single Brahma 15 would rape the dual 15 Avas sealed.

From a SQ standpoint the dual Avas rape the Brahma. Just at a much lower output level. But the sealed IMO is also missing the deep lows.

Tested with my ears using the Focal demo discs (available for download on DIYMA).

... I still want to try a PR setup. I think that would offer the best of both worlds for SQ and SQL. But I am out of play money at the moment and need to focus on the restoration of my 1948 Spartan Mansion trailer... So the PR project might be on hold for a while.

[Eric D]

The Power HX2 suspension was already very stiff out of the box. Making it any stiffer would have had negative results in other areas.

Very stiff, but still not stiff enough if you cannont prevent severe sag after only a month or so of storage.

IMO, rasing the compliance (stiffer suspension via multiple spiders and/or swapping the big rubber surround to high roll foam) would make more sense than to have a driver that suffers from sag

Keep in mind there is a practical reason why 48in woofers are not common. Moving heavy parts that are supposed to in theory be perfectly rigid (with no mass) becomes a nightmare.

Quite understandable, but there are still plenty of 18" drivers from other manufacturers that don't suffer from this problem. IMO it's really just a poor design that could have been rectified. However, it was probably too costly in the long run.

I don't remember how far the shift was, but it was not 10mm or anything like that. At around 2mm it would have been more than the smaller subs produced, but not too far outside the bounds of the manufacturing tolerances themselves. I think what really flagged the issue was all the woofers were shifted in the same direction by a similar amount, whereas the other drivers produced fluctuated above and below nominal.

But, look at the bigger picture. Rockford has never been known to be an SQ oriented company, or to be the highest quality either. If you want loud, than RF was high on the list of choices, but outside of that, there are so many better options out there.

The only thing SQ oriented Rockford Corporation (not Rockford Fosgate) has developed speaker wise, has been the Hafler TRM series of nearfield monitors.

[shawn k]

Rockford has never been known to be an SQ oriented company

I'm an RF fan, and I will agree with that.

[Mackenzie]

The Power HX2 suspension was already very stiff out of the box. Making it any stiffer would have had negative results in other areas.

Very stiff, but still not stiff enough if you cannont prevent severe sag after only a month or so of storage.

IMO, rasing the compliance (stiffer suspension via multiple spiders and/or swapping the big rubber surround to high roll foam) would make more sense than to have a driver that suffers from sag

Keep in mind there is a practical reason why 48in woofers are not common. Moving heavy parts that are supposed to in theory be perfectly rigid (with no mass) becomes a nightmare.

Quite understandable, but there are still plenty of 18" drivers from other manufacturers that don't suffer from this problem. IMO it's really just a poor design that could have been rectified. However, it was probably too costly in the long run.

I don't remember how far the shift was, but it was not 10mm or anything like that. At around 2mm it would have been more than the smaller subs produced, but not too far outside the bounds of the manufacturing tolerances themselves. I think what really flagged the issue was all the woofers were shifted in the same direction by a similar amount, whereas the other drivers produced fluctuated above and below nominal.

But, look at the bigger picture. Rockford has never been known to be an SQ oriented company, or to be the highest quality either. If you want loud, than RF was high on the list of choices, but outside of that, there are so many better options out there.

The only thing SQ oriented Rockford Corporation (not Rockford Fosgate) has developed speaker wise, has been the Hafler TRM series of nearfield monitors.

What about the mb quart models? I have an old mb quart 15 laying around somewhere.

[Eric D]

I suppose some credit can be given to the Quart stuff, but Rockford Corporation only owned Quart for a few years, and in the beginning of that time, most development stayed with Quart in Germany. Later some development shifted to the U.S., then I think it might have all went to China.

The MB Quart Reference and Premium subs from around 2002 or so were designed and manufactured at the Rockford loudspeaker facility, and I do agree they are some of the better SQ subs ever produced by anyone.