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Why woofers with strong motors dont do bass ( it is counterintuitive )

valerianf

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The professional woofer that have a very powerful motor do not go very low in frequency.
The reason is very simple: to be able to survive hundreds of watts the suspension needs to be more rigid.
Thus the maximum membrane excursion is limited.
 

gnarly

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That has not been my experience. Specifically, I had difficulty getting a smooth frequency response in the crossover transition between my ported bookshelf speakers and my subwoofer, much due to the group delay of the ported bookshelf speakers at the low end. Adjusting the overall time delay to the subwoofer and using PEQ (IIR) helped a bit, but it was far from ideal. I plugged the ports in the speakers, and again adjusted the subwoofer time delay and applied PEQ, and I was able to get better phase alignment between the bookshelf speakers and the subwoofer, resulting in a smoother frequency response in the crossover region.

It's just math in the end........(which does translate to listening experience).
When response is truly equal, the whole ported being different than sealed, evaporates.

The only way sealed has a real advantage with SQ, is when there is a mega boatload of sealed displacement capability, without needing low end boost, without needing a LT transform, etc. Seldom seen.

To OP, loose suspensions and weak motors work for being able to go lower in freq...but only at a significant cost to low corner, and hence overall SPL.........no free lunch.
 

richardm

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As a punk basshead kid with a bootleg copy of Perfect Box I noticed the cheapest drivers with low power handling and small magnets yielded the nicest graphs (ie. the greatest ability to irritate neighbors with dat bass). I was working with a fairly large pair of 12" woofer cabinets which I'm sure influenced my results. I was mesmerized by any driver with low Fs and high Qts.

After killing multiple drivers (typically the paper cone would detach from the rest of the motor assembly though I fried some voice coils too) I finally landed on the big magnet Pyramid Super-Pro Free Air (pawn shop superstars they were). PWFA12-US (Fs 35Hz; Qts 0.61; Vas 6.0) and I never managed to destroy them -- only smoked amps from that point forward. Those speakers were 'temporarily' placed for storage at my parents' in 1998. I finally took an interest in them 3-4 weeks ago and to my dismay the foam surrounds have disintegrated.

With full acknowledgement that Pyramid products are a joke I'm ashamed to admit I'd buy a new pair of these right now and find a use for them.
 

egellings

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It looks like woofers that have big magnets strong motors are bass limited and need bass reflex reinforcement to go reasonably down in frequency , whereas small magnet woofers do just fine in sealed cabinets on their own. Why is that and shoudnt it be the opposite ?
The strong motors can overdamp the driver, making the bass seem thin.
 

terryforsythe

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When response is truly equal, the whole ported being different than sealed, evaporates.

The only way sealed has a real advantage with SQ, is when there is a mega boatload of sealed displacement capability, without needing low end boost, without needing a LT transform, etc. Seldom seen.
In my family room I have a sealed Velodyne subwoofer, tuned down to 20 Hz. The box is relatively small given the size of the subwoofer (18"). My group delay is more in-line with the sealed plot in the graph I posted in post #19 (except a significant dip at the 55 Hz fundamental room mode - my measurement is at the listening position, about 4.5m away from the subwoofer). Below are the group delay and frequency response plots.

I also have KEF LS60 speakers in my office, which are sealed enclosure, tuned down to 20 Hz. I also have included the group delay and frequency response plot for one of those, again at the listening position. It exhibits better group delay characteristics than the ported enclosure tuned for 20 Hz (black trace) in post #19.

This week I will try to find time to close mic the sub in my family room and the KEFs to reduce the impact of the room modes to provide better comparisons. Nonetheless, I prefer the group delay characteristics of the sealed enclosures. Unfortunately, I did not keep the REW measurements for my Elac bookshelf speakers from when the ports were open. To unplug them now would take some work - internally I have adhesive backed material (No Rez) blocking the ports, and that stuff is a pain to remove.

Family Room Group Delay

Elac R GD.jpg


Family Room SPL

Elac R SPL.jpg


Office Group Delay

KEF L GD.jpg


Office SPL

KEF L SPL.jpg
 

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R

Ramon Cota

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@Ramon Cota,
Generally speaking, only the frequency response (SPL magnitude and phase) is what determines group delay -- mathematically they are strictly related to each other -- so same low-frequency roll-off means same group delay, and same behavior in the time domain. It does *not* depend on how that frequency response was established, with EQ or not, what driver in what volume, ported or sealed, whatever.
Winisd sims seem not to agree with this statement when it comes to ported vs sealed.Ported speaker with the same frequency response will have significantly larger GD than sealed.
White line is sb34-8 ported , orange is sb34-6 sealed and purple is sb34-8 sealed.
sbcomp1.png

now look at group delay , even though ported speakers bass output is less than sealeds , the group delay is more.
sbcomp2.png

but when i apply linkwitz transform to purple line to match responses , the group delay is the same.
sb34comp6.png

sb34comp7.png


Also , using low qts woofer + linkwitz transform seems to require less wattage to reach the same spl and excursion than weaker motor sealed speaker. 115 W for sb34-8 vs 200 W for sb34-6 . Assuming digital EQ does not degrade sound this seems like the better option.
 
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Ken Tajalli

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Not quite - woofers with big magnets tend to have higher overall midband sensitivity. However, bass sensitivity is governed more by the enclosure, so the overall response characteristic is rising. So basically (aside from cost) a weaker motor in a sealed speaker is used to keep the midband sensitivity down to the the level of the bass sensitivity. A vented cabinet can bring bass sensitivity up.
Yep. That's what I knew.
+1
 

terryforsythe

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Winisd sims seem not to agree with this statement when it comes to ported vs sealed.Ported speaker with the same frequency response will have significantly larger GD than sealed.
White line is sb34-8 ported , orange is sb34-6 sealed and purple is sb34-8 sealed.
View attachment 374573
now look at group delay , even though ported speakers bass output is less than sealeds , the group delay is more.
View attachment 374574
but when i apply linkwitz transform to purple line to match responses , the group delay is the same.
View attachment 374576
View attachment 374577

Also , using high qms woofer + linkwitz transform seems to require less wattage to reach the same spl and excursion than weaker motor sealed speaker. 115 W for sb34-8 vs 200 W for sb34-6 . Assuming digital EQ does not degrade sound this seems like the better option.

Good information. Thank you for sharing!

In my experience, digital EQ at the low end doesn't degrade the sound. Also, sealed with digital EQ can serve to avoid port noise, which can be problematic on some subwoofers and on some speakers, especially speakers with ports on the front baffle.
 

Tell

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Good information. Thank you for sharing!

In my experience, digital EQ at the low end doesn't degrade the sound. Also, sealed with digital EQ can serve to avoid port noise, which can be problematic on some subwoofers and on some speakers, especially speakers with ports on the front baffle.
Yeah you get deeper bass and that's always an upgrade! But you might bring up the distortion to a more audible level, and it requires more wattage from the amp as well which could bring it closer to distortion levels.
Having that said I have a pair of small sealed 4" bookshelves at maybe 5 liters that's specced down to 70hz, but I managed to boost the low end by around 30dB to make them dig down to 30hz and it did sound quite alright, I was even a bit impressed hearing those very small things play that bass! Had them on the desk half a meter from me and could turn them up at decent levels with no apparent distortion.
Too bad I had a huge null in the room that killed way to much of the midbass so I had to resort to cross them over and let my 6" tapped horn do all the bass instead. It does it better (and louder) anyways so all good :)
 

terryforsythe

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But you might bring up the distortion to a more audible level
Not really a concern.

Here is the SPL and THD plot of one of my Elac speakers and my subwoofer - at listening position in my family room. The distortion is pretty good. The rise below 30 Hz predominantly is 2nd order. At least some of that may be due to my walls, and things on my wall, vibrating when I run frequency sweeps - those vibrations are clearly audible, especially at the low end.

Elac L THD.jpg


Here is the SPL and THD plot of my KEF LS60s - at listening position in my office. It doesn't get out of hand until below 35 Hz. Again, primarily it is 2nd order, and vibrations in the room may be contributing to it, and those vibrations are audible. But, the vibrations are not as audible as those in my family room since I measured at a lower SPL for my KEFs to correlate to the volume at which I typically listen while in the office. So, the KEFs probably have more THD below 35 Hz than my family room subwoofer, which makes sense since my family room subwoofer is moving more than twice as much air as my two KEFs combined.

KEF L THD.jpg
 
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KSTR

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Now I'm confused ;-)
First you say
Winisd sims seem not to agree with this statement when it comes to ported vs sealed
and then later in your post you prove exactly that once you match the frequency responses the group delays are getting matched as well... which is just what I think I said, right?
Anyway, no worries of course ;-)
 

terryforsythe

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Now I'm confused ;-)
First you say

and then later in your post you prove exactly that once you match the frequency responses the group delays are getting matched as well... which is just what I think I said, right?
Anyway, no worries of course ;-)
You might want to go back and review the group delay traces.

Hint:
White line is sb34-8 ported , orange is sb34-6 sealed and purple is sb34-8 sealed.
 
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Scgorg

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I think what KSTR has written is both clear and correct.
If you match the frequency response, the slope of the phase (and hence the group delay) will be the same. In the first examples the frequency responses are not matched, and so their phase responses/group delay are different. The rate of phase change is higher for the ported enclosure (due to its sharper rolloff).

The frequency responses are then matched, and the group delay for the various configurations are now the same, just like KSTR wrote. He never claimed that an unmodified ported and sealed loudspeaker would have the same group delay. Perhaps the source of confusion is the wording of "same low-frequency roll-off"? This does not mean "same f3/f6/f10" or whatever other frequency. It means the exact same frequency response shape.
 

Holmz

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@Ramon Cota,
Generally speaking, only the frequency response (SPL magnitude and phase) is what determines group delay -- mathematically they are strictly related to each other -- so same low-frequency roll-off means same group delay, and same behavior in the time domain. It does *not* depend on how that frequency response was established, with EQ or not, what driver in what volume, ported or sealed, whatever.

When using the same driver and modelling it with s/w, the sealed, ported and bandpass all showed wildly different group delay curves.
A first order ‘box’ was not modelled, but would probably be the lowest group delay.
 

KSTR

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When using the same driver and modelling it with s/w, the sealed, ported and bandpass all showed wildly different group delay curves.
Yes, sure.
But once the frequency responses are equalized to the same target then group delay also is the same, as it must be. Working principle of the woofer does not matter after EQ, which is the whole point.

Perhaps the source of confusion is the wording of "same low-frequency roll-off"? This does not mean "same f3/f6/f10" or whatever other frequency. It means the exact same frequency response shape.
Exactly. Actually, the response match over the whole bandwidth matters but the low-frequency roll-off is the most important part.
 
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Ramon Cota

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Yes, sure.
But once the frequency responses are equalized to the same target then group delay also is the same, as it must be. Working principle of the woofer does not matter after EQ, which is the whole point.


Exactly. Actually, the response match over the whole bandwidth matters but the low-frequency roll-off is the most important part.
How would you EQ a drivers rolloff in ported enclosure to match that of a sealed and reduce group delay ?
 

Holmz

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Yes, sure.
But once the frequency responses are equalized to the same target then group delay also is the same, as it must be. Working principle of the woofer does not matter after EQ, which is the whole point.
...

Is that with IIR PEQs?
or FIR EQs?
 

KSTR

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How would you EQ a drivers rolloff in ported enclosure to match that of a sealed and reduce group delay ?
Obviously, that doesn't make too much sense because of the massive boost at subsonic frequencies (and theoretically infinite boost at DC), where we rather want to reduce signal with a subsonic protection highpass.

The only practical way to reduce group delay for a ported box (EDIT: with the same corner frequency**) is FIR phase unwrapper which rolls back the phase to that of a sealed woofer (or to zero, in the extreme case) but leaves the magnitude alone.
However, the result is not minimum phase anymore and has some pre-ringing (not actually a ringing, but still a signal that emerges before the main signal and that sometimes is audible. No free lunch).

**) When the ported speaker goes lower, you have some room for a partial correction and that is what I did in the mentioned project in post #20
 
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