Speaking of unique surrounds, take a look at the unique surround from the fairly new company Purifi Audio.
https://purifi-audio.com/transducers/
https://purifi-audio.com/transducers/
Ask an Acoustic Engineer (me)
- Thread starter Justin Zazzi
- Start date
I know I have to hit the "upload" under where I select it (i am on an iPad)... and then that takes some patience.
Justin Zazzi
Wave Shepherd - aka Jazzi
I'm really happy you are enjoying this!
A modern convertible vehicle like a Jeep Wrangler sometimes has a sensor that detects when the roof is on or off and it can adjust the stereo's tune based on this. Roof on means more reflections and the frequencies that are reflected on those broad hard surfaces (windows) are higher frequencies. So with the roof on the higher frequencies bounce around a lot more and they tend to seem louder than they really are.
Roof off means those high frequency reflections (and midrange too) are less reflecty and so the midrange and especially the treble seems to drop off. An open-air car like a Wrangler with no roof or a dune buggy or a motorcycle will need more treble compared to an enclosed vehicle at rest, and even more in motion because of wind noise.
Roof on vs off can also have some cabin gain effects on the bass performance which might need adjusting as well, especially in something like a Wrangler if the subwoofer is in the rear cargo area and is now exposed to open-air.
Speaking of presets, I always thought it would be neat to use the sensor in the passenger seat and then switch to a 2-seat tune when a passenger is present. Then switch back to a one-seat tune when you're driving solo.
Also, remember to change out your Winter air for Summer air in your sub enclosures. I usually do mine when I get an oil change
Justin Zazzi
Wave Shepherd - aka Jazzi
You can look at the speed of sound in a material as a rough way to compare materials. A higher speed of sound means the first bending mode should appear at a higher frequency, which is better.
View attachment 11593
table borrowed from https://www.engineeringtoolbox.com/sound-speed-solids-d_713.html
The table above shows speed of sound for aluminum is about 6km/s whereas something fancy like Diamond or Beryllium is twice that at 12km/s. A low performing material might be something like cork with a speed of only 520m/s.
The speed of sound in a material is related to the elastic (Young's) modulus divided by the density. A higher modulus (stronger) and a lower density (lighter) is going to have a higher frequency for the first bending mode.
All that said, some materials have a really nasty breakup behavior and some materials have a really gentle pleasant breakup behavior. This is also driven some by the damping of the material so a larger damping is better which is another material property.
I don't think we can learn a whole lot from looking at tables and whatnot. I prefer really practical things like handling a piece of paper with my fingers and then handling a piece of thin aluminum and steel and titanium and .... so on. The sound you can hear just from handling the material with your fingers is really powerful.
THAT would be cool!
Hi jtrosky, this is an interesting question! I have these speakers and my guess on the discrepancy of why the Xmax for the GS25 and gs690 are so close is probably due to multiple factors and my understanding is as follows:
- even if those speakers are moving the same distance (4mm) and playing the same frequency, the smaller one will sound quieter as it’s not moving as much air
- To sound just as loud as the GS690, at say 300 Hz, it’s going to have to extend much farther to displace the same amount of air as the larger 6x9.
- the smaller speaker can probably get away with a smaller surround to move almost as far as the 6x9 because it is much lighter and the forces needed to move that lighter/smaller cone (and the stresses on the surround) are less than those of the 6x9. This depends on the motor (see below) and other factors I’m sure (cone material, etc)
- the motors of the two speakers also likely play a role. I can imagine two speakers that are otherwise equal but one has a better motor design that controls the cone better; this speaker may need a less beefy surround compared to one where the cone movement is less well controlled and flying all over the place.
Also interested to hear what Andy would say about this.
Sent from my iPhone using Tapatalk
I think you make some good points - some of them mirror what I noted, so that helps validate as well.
You and I both are basically essentially saying - we really don't think he (or anyone) would expect a 2.5" to play as loud as a 6x9, and we don't think he (or anyone) would expect a 2.5" to play as low as a 6x9.
The former is simply the basics of the difference in cone size, and it's definitely something to think of how much more excursion you'd need to have a 2.5" match the displacement of even a low-Xmax 6x9.
The latter is really the reason I think the surround difference truly exists, though.
It's simply unrealistic to think a 2.5" would be expected to play as low as a 6x9... especially considering a 6x9 is pretty comparable to an 8" round. Even for a wideband, it's just not realistic.
So, given the loudness differential, it makes more sense to use more cone, less surround.
...which likely happens to also add a touch more moving mass, lowering Fs a touch, also towards the design goals of a wideband - even though it's not expected to kick out the thunder on AC/DC drum tracks.
Just to clarify - my question was just based on the fact that I just didn't understand how the GS25 speaker cone could possibly move up to 4mm with it's surround, especially since the GS690 speaker cone only moves a max of 5mm with it's MUCH "bigger" surround.
Maybe I don't understand the Xmax "spec". I am assuming that an xmax of 4mm means that the speaker cone is capable of moving out by as much as 4mm (and that the "size" of the surround is relative to the amount of movement that is "allowed" by the xmax spec). I just didn't quite understand how the GS25 speaker cone could possibly move out 4mm with it's puny surround while the GS690 speaker cone is only able to move out by 5mm with it's pretty significant surround.
Hopefully I'm explaining myself properly. The surround on the GS25 just doesn't seem "big" enough to allow 4mm of cone movement being that the surround on the GS690 only allows for 5mm of cone movement.
The surround on the GS25 is also significantly "smaller" than the surround on any of the other 3"/3.5" speakers I've seen (HAT S3SE, multiple 3" or 3.5" coaxials, etc) - all of which have xmax values less than 4mm.
Just something that I noticed and thought was strange, that's all. In reality, I can't imagine that the GS25 speaker cone would ever really need to move anywhere near 4mm in real-world usage - it barely seems to move at all, unlike bigger speakers that play lower freqs.
Maybe I don't understand the Xmax "spec". I am assuming that an xmax of 4mm means that the speaker cone is capable of moving out by as much as 4mm (and that the "size" of the surround is relative to the amount of movement that is "allowed" by the xmax spec). I just didn't quite understand how the GS25 speaker cone could possibly move out 4mm with it's puny surround while the GS690 speaker cone is only able to move out by 5mm with it's pretty significant surround.
Hopefully I'm explaining myself properly.
The surround on the GS25 just doesn't seem "big" enough to allow 4mm of cone movement being that the surround on the GS690 only allows for 5mm of cone movement.The surround on the GS25 is also significantly "smaller" than the surround on any of the other 3"/3.5" speakers I've seen (HAT S3SE, multiple 3" or 3.5" coaxials, etc) - all of which have xmax values less than 4mm.
Just something that I noticed and thought was strange, that's all. In reality, I can't imagine that the GS25 speaker cone would ever really need to move anywhere near 4mm in real-world usage - it barely seems to move at all, unlike bigger speakers that play lower freqs.
That's why I differentiated Xmax from Xmech in my response earlier.
In general (exceptions in just a second)-
- Xmax is limited by the motor. It's simply the distance the motor can move before the coil starts exiting the magnetic field.
- Xmech is limited by the suspension. That's the distance the cone unit can move before the suspension bottoms out, or something strikes hard (cone on surround landing, leads pulling, VC former on backplate).
You can put all your windings right in the magnetic field, so that when they are energized you get ALL your motor strength... but essentially then you have 0mm Xmax, since as soon as the voice coil moves in either direction, you start pushing windings out of the magnetic field. This isn't far off from how lots of SPL subs are designed though, where BL/Re (motor strength) is "the" goal.
You can spread out your windings, over a long distance, covering the whole voice coil former below the spider, if you like. Now, you have tons and tons of Xmax, but only a tiny portion of the energized windings are actually IN the magnetic field. So most of that power is wasted, and your BL/Re is very low. Lots of old-school long-throw subs use this technique.
And independently, your suspension and basket (and to some degree the length of the VC former) comprise Xmech, which define how far the whole assembly can actually physically move.
Usually, your Xmax is reached before your Xmech, which usually keeps people out of trouble - no hard parts hitting.
But there have been exceptions. I think it was the original RE XXX that had such a long-throw XBL^2 motor, but used an off-the-shelf basket and spider, such that the Xmax and Xmech were either nearly the same, or maybe even the Xmech was less than the Xmax. At any rate - if I'm thinking of the wrong sub, it's happened... so it's still possible, but unlikely to be something you run into.
...and my main point is "the alignment will be determined by the intended usage", which brings me back to my theory:
The 6x9 is much more similar to a bass driver than a midrange. So it needs excursion capability. A user will expect it to play right down to their subwoofer - or even to BE a subwoofer. So it makes sense to ensure the Xmech is significantly longer than the Xmax... whatever the Xmax target might be.
A 2.5" speaker is going to be expected primarily to be used as a midrange - maybe even as a tweeter. The whole "wideband" application is a bonus, and realistically can still only play so low. And your available hard parts don't have much excursion room... plus you might be designing a speaker to fit into a small sail panel, so can't be too deep, etc...
So if that 2.5" has an Xmech that's nearly the same as the Xmax, that's fine... it's not expected to play that low. The Xmax in this case might simply be here for linearity - because the BL curve for any given speaker will be flatter when played at the center of it's motor excursion, and that reduces intermodulation distortion (intermodulation literally means "fluctuations when moving", and the distortions could be caused either by motor strength changing across the excursion range, or the suspension compliance changing across the excursion range), which also makes sense for a midrange since it's the most audible type of distortion, and we most easily perceive audible distortion in the midrange realm.
So it's not the Xmax that's different between these two drivers, it's Xmech - and I truly believe that's by design because of how they will/can be used:
Having a similar Xmax makes sense for two different reasons (raw excursion for bass vs flat BL for midrange), and having different Xmech makes sense for the same reasons.
Just to clarify - my question was just based on the fact that I just didn't understand how the GS25 speaker cone could possibly move up to 4mm with it's surround, especially since the GS690 speaker cone only moves a max of 5mm with it's MUCH "bigger" surround.
Maybe I don't understand the Xmax "spec". I am assuming that an xmax of 4mm means that the speaker cone is capable of moving out by as much as 4mm (and that the "size" of the surround is relative to the amount of movement that is "allowed" by the xmax spec). I just didn't quite understand how the GS25 speaker cone could possibly move out 4mm with it's puny surround while the GS690 speaker cone is only able to move out by 5mm with it's pretty significant surround.
Hopefully I'm explaining myself properly.
The surround on the GS25 is also significantly "smaller" than the surround on any of the other 3"/3.5" speakers I've seen (HAT S3SE, multiple 3" or 3.5" coaxials, etc) - all of which have xmax values less than 4mm.
Just something that I noticed and thought was strange, that's all. In reality, I can't imagine that the GS25 speaker cone would ever really need to move anywhere near 4mm in real-world usage - it barely seems to move at all, unlike bigger speakers that play lower freqs.
Just to clarify - my question was just based on the fact that I just didn't understand how the GS25 speaker cone could possibly move up to 4mm with it's surround, especially since the GS690 speaker cone only moves a max of 5mm with it's MUCH "bigger" surround.
Maybe I don't understand the Xmax "spec". I am assuming that an xmax of 4mm means that the speaker cone is capable of moving out by as much as 4mm (and that the "size" of the surround is relative to the amount of movement that is "allowed" by the xmax spec). I just didn't quite understand how the GS25 speaker cone could possibly move out 4mm with it's puny surround while the GS690 speaker cone is only able to move out by 5mm with it's pretty significant surround.
Hopefully I'm explaining myself properly.
The surround on the GS25 is also significantly "smaller" than the surround on any of the other 3"/3.5" speakers I've seen (HAT S3SE, multiple 3" or 3.5" coaxials, etc) - all of which have xmax values less than 4mm.
Just something that I noticed and thought was strange, that's all. In reality, I can't imagine that the GS25 speaker cone would ever really need to move anywhere near 4mm in real-world usage - it barely seems to move at all, unlike bigger speakers that play lower freqs.
Yes, I agree. It’s surprising!
My understanding is that xmax is the maximum linear excursion which is not the maximum length it can travel but the limit for which it can travel linearly.
I agree, it’s a small surround. And also agree it barely seems to move. I think this is more because it’s not being asked to play low frequencies very loudly.
I thought this was cool from Andy explaining frequency response graphs and how they relate to cone movement:
What I think is neat, and correct me if I’m wrong, is that within region one is where xmax is defined - or at least I think it would, as within this region the cone is moving linearly. In this region, where the lower frequencies are, is where you may approach xmax and where the speaker is designed to stay within xmax (the speakers “sweet spot” if you will). Above this region, you are NOT exceeding xmax but rather the cone is being asked to move much quicker (back and forth) and for the given properties of that cone, motor, etc. the cone starts flexing under that stress and “cone breakup” starts to occur.
You could, however, force the cone breakup to occur much earlier than designed (say in region 1) by sending too much power to it for example.
Just some neat stuff that as always, Andy describes very well. I thought it was interesting to think about in the context of Xmax.
Sent from my iPhone using Tapatalk
I don't really want to jump into Justin's thread, but mauian is correct on Xmax. It is not simply the excursion of the motor. Many manufacturers simply use the overhang method for calculating Xmax (Hc-Hg/2) and call it a day. Some use modified versions of the formula ((Hc-Hg/2)+(Hg/3)) to make their drivers look better, but at least they are open about how they calculate their figure.
Arguably, the best methodology to determine Xmax (actual linear excursion) is to test/measure the driver with something like a Klippel. Now, the Klippel simply gives you the data and relies on appropriate testing procedures. It is up to the manufacturer (or tester) to determine which data they will use and how they will use it. But the Klippel does allow for measuring non-linearities based on Kms (suspension stiffness), Bl (force factor), Le (Inductance). I won't attempt a deep dive in to how each of the types of nonlinearities might factor in for different driver types. Just know that testing like that done with the Klippel provides a far more accurate representation of Xmax than the overhang (or other calculated) method.
And in car audio, chances are you will have no idea HOW a manufacturer determined the Xmax (if provided) for their drivers. There are a few that provide that information, but they are certainly the exception, not the rule. There have also been several instances where manufacturers who were "caught" with exaggerated Xmax figures when independent Klippel testing was performed.
Arguably, the best methodology to determine Xmax (actual linear excursion) is to test/measure the driver with something like a Klippel. Now, the Klippel simply gives you the data and relies on appropriate testing procedures. It is up to the manufacturer (or tester) to determine which data they will use and how they will use it. But the Klippel does allow for measuring non-linearities based on Kms (suspension stiffness), Bl (force factor), Le (Inductance). I won't attempt a deep dive in to how each of the types of nonlinearities might factor in for different driver types. Just know that testing like that done with the Klippel provides a far more accurate representation of Xmax than the overhang (or other calculated) method.
And in car audio, chances are you will have no idea HOW a manufacturer determined the Xmax (if provided) for their drivers. There are a few that provide that information, but they are certainly the exception, not the rule. There have also been several instances where manufacturers who were "caught" with exaggerated Xmax figures when independent Klippel testing was performed.
cueball981
Noob
I would as well - and I'd also advocate Bnlcmbcar to do some searching some of the DIY audio forums that have home theater sections.
From the diagrams that you posted, I'd be concerned as you are (especially in a car) that you'd narrow the image, because you are pulling some of the L and R content into the center - which, most troublingly - brings some of the L content to your R side, if you are in the driver's seat. Conversely, for a passenger, brings some of the R content to the L of them. Eek.
What I'd like to see in a center channel for a car, would be "(L+R)-(L-R)". That way, it's only bringing the content from both speakers to the center, and even if there's a little content that's on both channels but simply louder on one than the other, it still mitigates that by attenuating that sound at the center channel. I'd believe that would at least help keep the stage width - hopefully as wide as with just a stereo pair.
But I think really, in a car, the KISS rule applies... there's already glass, and absorbant upholstery, and plastic, all pointing different directions - you could have ONE speaker in a car and end up with a nightmare of multiple pathlength distances, direct and reflected (with each of those having a 180 degree shift - plus pathlength difference offset!) creating anything but a flat response as it arrives at your ears.
So I subscribe to the "the fewer speakers the better" theory for car audio. There's exceptions - for example, three way components where you actually aim the mid and tweeter - can provide better imaging. But my default recommendation is simplicity over complexity, for those pathlength reasons.
I'm really interested in this myself, but in no way for creating a center channel (IMO, there's already enough direct and reflected pathlength sounds wreaking havoc on image-killing phase interactions as they all ultimately arrive at the listening position)...
I want to make a "L-(L+R)" channel and a "R-(L+R)" channel to add some rear fill (something I otherwise also don't believe in, for those same image-killing phase interaction reasons) plus some additional delay, so I'm going to be researching this soon myself. My DSP will only help with delay and passband. I'd be interested if you find any good threads.
I have to agree with your simplicity statement. The best sounding systems I've had are the ones where I've only used a 2-way front stage with 1 sub. I'm currently running 3.5" coaxial in the upper corners of the dash, which I call a pseudo 3-way, and my staging and center imaging are fantastic!
cueball981
Noob
I'm one of those who is using just my truck's stock electrical without any issues. No "big 3", no upgraded alternator (truck comes with 220amp stock), and no capacitors...just one big 1/0 gauge power wire off the battery and a very solid short (<6 inches) ground at the amp ramp. I'm running 2 Alpine PDX-V9s and a PXE-850S DSP without any problems whatsoever. I'll be honest, I agree with JZazzi...it's better to install your equipment first, then see if anything needs upgrading. You may end up being surprised that there's nothing more you need to upgrade. Now you have money to invest in other areas of your system like sound damping!
Justin Zazzi
Wave Shepherd - aka Jazzi
/r/maybemaybemaybe
I'd like to educate myself more on the idea of absorption and materials and how they're rated. Perhaps how acoustic absorption works in a car.
I was reading about the Magic Bus awhile back and while he is.. eccentric..he was talking about having the acoustic energy or decay in a room be equal across the spectrum. I don't recall exactly what it was.
Im looking for reading material that doesn't take a degree to understand. Really anything on absorption that anyone here would recommend.
I was reading about the Magic Bus awhile back and while he is.. eccentric..he was talking about having the acoustic energy or decay in a room be equal across the spectrum. I don't recall exactly what it was.
Im looking for reading material that doesn't take a degree to understand. Really anything on absorption that anyone here would recommend.
At first glance, I was thinking you meant "box stuffing" before my brain kicked in - and since my brain is wired for car audio rather than real life, before I realized what you really meant, I said "Yes, box stuffing IS sort of like what @ckirocz28 is talking about!"
It's funny you raise this topic though, here.
In my house, I'm currently looking for sound absorbing materials, simply because I have a finished basement with a drop ceiling, and the cold air return goes over the middle of the space down there... so any sound, TV, stereo, video games, anything - only has a thin sheet metal cold air return preventing the sound from being piped up to the first floor via the cold air return. So in my case, I'm looking for a material that will BLOCK sound. And in the home space, there are sound-absorbing boards, sound-absorbing acoustic foam (like anechoic chambers or recording studios), and I've recently been told by a professional commercial-space drywall buddy of mine to look into mineral wool - sold pretty cheaply in the insulation aisles of home centers.
Those materials are designed to absorb sound, so it doesn't pass through them.
(box stuffing does that also - but now makes me wonder why we use polyfill rather than mineral wool, since I believe mineral wool has better properties)
On the other hand, if my cold air return was buzzing and vibrating every time my furnace kicked on, that would be annoying sound caused by the panels themselves. Same if my basement stereo system caused panels to buzz every time certain songs were played loud. in that case, I'd be looking for damping materials - like Dynamat or Second Skin (or whatever the kids use these days) to stop the panels from vibrating. You'll notice if you close a cheap car's door, it makes a higher pitched "empty can" sound than the dull "thud" of closing a luxury car door. That's mainly the effect of damping materials lowering the resonance of the doors. If I apply that material to those panels that vibrate - I'll (hopefully!) stop them from vibrating and resonating.
And a third type of acoustic absorption might actually be what you are talking about... In a car we've got a terrible combination of hard, reflective glass and plastic surfaces - and plush, soft, foam-filled seats. The glass causes some reflections, and the seats cause some of the sound to be absorbed. Both, in combination wreak havoc on our actual frequency response at our seating position. I hope you aren't asking for a simple (or even complex) way to predict these effects in any accurate way? :whistle:
I think like Holmz said - a bandpass box would get you close, although it's more the speaker between two boxes.
What you are asking is "what would the effect be, if you built a big sealed box with a little vented box just sitting inside it - no speaker attached to the vented box, just a box with a port in it" right?
Let's think through it to see if we can get close-
I'd believe sure enough the sub in the sealed box would cause pressure fluctuations in the sealed box... which would in turn act on the air in the vent, which would move in resonance with whatever frequency it was tuned to given that box... and that would follow the same rules as vented boxes, as far as the vent resonating in phase or out of phase with the cone...
That WOULD have the excursion limiting effects on cone motion (I believe) above the tuning frequency, since the port air motion in this case would purely be adding to or decreasing the effective pressure in the enclosure - same as a vented box, but not [significantly, anyway] contributing to the sound outside the box, since the vented box is trapped inside the sealed box.
Also similar to a vented box, I would think that below the vent tuning frequency, the vent-effect collapses, and now you'd re-capture the air inside the vented box, for use by the sealed box.
Same goes if you used a passive radiator, if my thinking above is all correct.
So let's assume we stuck a 1 cu.ft. empty box with a vent (or passive radiator) in it tuned to 40hz (but no sub or sub hole) inside of a sealed box that was large enough to give us a 2 cu.ft. sealed volume even with that vented box inside it...
if the air inside box one is Vb1 and the air inside box two is Vb2, I'd predict (but I don't know for a fact):
- Below 35-40hz, the sub would behave as if it were in a 3 cu.ft. box. So if you modeled up a 3 cu.ft. box, and looked at 40hz and down - that's what you'd get.
- Right near 40hz, the sub and vent are as close to in-resonance as it gets - which would in this case cause the vent to add pressure inside the sealed box causing a sharp reduction in excursion, causing a dip in frequency response.
- Above 40hz, the sub and vent go progressively out-of-phase, so that destructive interference would fade away, until you get to whatever frequency the vent wouldn't have any impact any more... above that frequency, we're behaving like we're in a 2 cu.ft. sealed box... which at those upper frequencies is going to be pretty close to the 3 cu.ft. response anyway.
So - overall, I think if you modeled your sub in a 3 cu.ft. box and imagined a decent dip in the frequency response around 40hz (I'm guessing about 6dB), and then rising back up to the -0dB level again progressively by about an octave higher (1 octave is also a guess) as you move further up the frequency spectrum.
But that's just me trying to think through it - I can't say I know that is what would happen. I don't believe there's any software that models this, to know for sure.
Do you have a need for a sealed box with a dip in the response? I could only see this as being really beneficial for subs stuffed in sealed boxes that are too small and have peaky responses to iron out - but in those cases of course you don't have room to stuff a vented box inside, or you'd have enough air space to begin with.