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

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

Post by audiophyle_247 »

Such a great debate going on in another thread, I think we should bring it into its own instead of hijacking. Yes?

Why do I think ported boxes are better than sealed? Well sealed has a very important role in mobile audio, and the biggest is they take up the least amount of space, its next to impossible to make a bad one (either too small or has holes, thats about all you can do wrong), and they provide very accurate bass response. What I dont like about sealed is the poor low freq reproduction, and they pretty much rely on the cabin gain to make that low end audible. What am I talking about? Well lets take a look
Image
This is essentially a random 8" sub modeled across 3 sealed boxes, which is to show how this sub should perform in such box sizes.
The Yellow line represents a 0.4cuft sealed box, the red represents an ideal sized 1.164cuft sealed box, and the orange represents a 10cuft sealed box.
These graphs do not account for any cabin gain, which is completely different from car to car and even shifts day to day based on climate, temps, humidity, etc..... So I will ignore that for now.

Starting with the yellow (typical "tight fit" enclosure), look at that ugly boost at 100hz. This sub would have to be crossed over at 80~90hz to keep it reasonable sounding, but then look at how fast that bass drops off. At 50hz it is -9db, and at 30hz its -19db!
The Red is a little better in some spots, and worse in others. The roll off is consistant, but it is NOT flat. 90hz is -1db (1 lower than yellow, inaudible difference), is only -3db at 50hz (6db louder than yellow = twice the volume level), and then -10db at 30hz (9db louder than yellow, big difference). That red line looks a lot better than the yellow for only a difference of ~.7cuft.
Looking at the orange we see it is a little quieter up top and a little louder down low, this is more like a freeair setup than a sealed box and shows a much smoother roll off. (& why freeair setups can be very popular)



So what if we look at a ported box? Now that we understand how a sealed box should perform, lets look at the typical ported setup, assuming we have the space to even consider one.
Image
This is the same woofer as in the sealed tests, to keep things pretty close to fair. The green line represents a common prefab ported box, and similar to what many manufacturers list as a "recommended" or high output (SPL) oriented ported enclosure. This is a 1.5cuft box with a port tuned to 45hz.
The blue line represents a setup I would work toward, and most people seeking sound quality before quantity. (not a pure SQ box, more what people would refer to as a "SQL" box) It is a 2.4cuft box tuned to 35hz.
Lets compare these, starting with the (ugh) prefab box in green.
This is what often gives ported boxes such a bad name, this response gives tons of output over a very narrow band of frequencies with a sharp roll off way too early, easily becoming a "1 note wonder" box. Musically this is just bad, but if all you want is bass this is HUGE with gains easily 6+db over the sealed (to our ears that would be double the output). The low end bass falls off too early to enjoy any bass below 40hz, and even though its 30hz level is only a single db below the ideal sealed enclosure (-10db vs -9db), when compared to the overboosted mid range bass the 30hz will seem almost non-existent.
So lets look at the blue graph now, and one that I would consider a flat response.
This bass response stays true to equal volume completely down to 45hz, and then falls right off. 30hz is only -5db, that is7db louder than the SPL box without the ugly hump. 20hz drops off pretty sharply, and to keep this sub from unloading a subsonic around 25~30hz would be great, the SPL box would need a much higher subsonic probably around 35~40hz to keep it from killing itself, considering lots of music plays around 30~40hz.


Now lets compare directly the ideal sealed to the ideal ported.
Image
Look at the difference between these two, the ported is 2db louder at 70hz, 3db louder at 60hz, 5db louder at 50hz, 7db louder at 40hz, and 8db louder at 30hz! (20hz is the same level). The ported box produces bass from basically 45hz and up at the exact same level, how can anyone consider that to be a bad thing?
You could use an EQ and boost the lower signals of a sealed box to mimic this curve, however with the boosted equalization distortion can be increased, power consumption is increased, and the accuracy of the bass drops, making the sealed just as "sloppy" as a ported setup. More info on this topic here by people smarter than I.


What about the classic "dual woofers sealed vs single ported" debate? Well, for a sealed setup to make up that 8db difference at 30hz without EQ, you would need almost 8 times the output. (x2 for 3db, x4 for 6db, x8 for 9db) And what happens when you add subs/power everything gets louder, which you really dont want or even need from around 60hz & up. That also assumes that when you add another woofer (or woofers) the airspace increases too, because if you throw two subs in the same 1.16cuft ideal sealed box above it starts to look a LOT more like that yellow graph than the orange graph, which is no good either.

Now lets open up this discussion :mrgreen: (& with civility please, we dont need any negative BS here)
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by ttocs »

Never plugged any numbers into software to see what the computer told me, just used my ears. do any of those programs give #'s on port noise or accuracy? If all that was important was the numbers, then yea sure then of course go ported but if your wanting SQ the flatter graph would still be better and with the cube you can easily give a 2-3-4-5db boost to any of the freqs you want too. A couple of db's boost on a signal is not going to make it that much of a difference in signal quality but would then be close to the same output as the ported, with room to give it more.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Pillow »

... Should be an interesting discussion :)

I have pondered the same myself,and still do ponder this every time I make a box for myself or friends. I agree 100% with Audiophyle in theory with the WinISD results and is what I usually go by. The ported box will give a much flatter response curve over a larger frequency range... Now when factoring in cabin gain things get funny really quickly, but that it above my skillz to factor in when building a box. :)

Honestly on paper (er WinISD) the sealed looks terrible... But seems to work well for SQ in real life due to the cabin gain. I have never read or figured what actual frequencies get boosted in cabin gain though..? 30? 40? 50?

Also will a PG BassCube really adjust a sealed box bottom end enough to make a flat response curve in a vehicle? Lets say at 30Hz? What would the load be on the amp at that point to make those frequencies happen in a sealed box? x3 x6 x9 the power? It could get ridiculous!

In real life last week a buddy took me for a ride in his Yukon and I was impress with the tightness and accuracy of his bass... He has a cheap A/B Audiobahn amp running 4 equally cheap 12" subs (I think Pioneer or Kenwood plastic cones). His actual output cannot compare to my single 15" Brahma IMO, but his accuracy and punch was better... And that greatly saddened me :(

... Which leads to me purchasing more subs and trying sealed for the first time since the 90s! LOL stay tuned. But I am at the same point in the my mind... Sealed or SQ ported (takes up a lot of room!)?
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by bretti_kivi »

cabin gain depends on the longest length available. One story I read online (and which seemed reasonable); to simulate it, add a Linkwitz-Riley filter starting at the frequency of the cabin (i.e. the longest length you have and then use that as a half-wavelength). For me, at 3m length, this is around 57Hz.

The other point which was missed here (and is included over on a thread on the same subject at MSS) is that if you EQ the sealed, your group delay will be remarkably similar.

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

Post by bretti_kivi »

for a specific sub, the CSS SDX10; the 0dB point is at 73 Hz in a 28l sealed box. And 41Hz in a 31l ported, tuned to 28Hz.

Image

Image

I think you'll find the ported is a bit better in this application. However, the port size is a pain, that I'll agree.

- Bret
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by audiophyle_247 »

bretti_kivi wrote:cabin gain depends on the longest length available. One story I read online (and which seemed reasonable); to simulate it, add a Linkwitz-Riley filter starting at the frequency of the cabin (i.e. the longest length you have and then use that as a half-wavelength). For me, at 3m length, this is around 57Hz.

The other point which was missed here (and is included over on a thread on the same subject at MSS) is that if you EQ the sealed, your group delay will be remarkably similar.

- Bret
Sure I did, take a gander at the last paragraph of my first post, there is even a link to the MSS discussion. lol I gladly give credit where credit is due.
Something I do wonder about though, is if you were to take the ported box from above in blue and apply a high pass or subsonic to mimic the roll off of the sealed, would the group delay from the ported then match the un-EQ'd sealed since their performance would be similar. It would make sense to me, that doing so would work inversely to what happens when boosting the sealed subs output.
If I were to take the ideal ported from above, and use the EQ to cut the cabin gain back down, the group delay should decrease in those areas while bringing that freq response curve back to flat, and since It would be cutting the signal, power usage should come down too.


Cabin gain varies a lot by every car, but most are not spacious enough inside for the transfer function to center around frequencies a sealed box needs help with.
Cabin gain is also a big reason why ported boxes like the prefab one I threw up there get such a bad name because it reinforces the already peaked output range, making that tiny window of bass sooooo much louder than the rest.
If I could find a car with a resonant freq around 30~40hz I would be in heaven, as would a lot of other people Im sure. lol
Problem is, and your graph proves the theory further, that cabin gain only makes a sealed box worse because the cabin gain hits right where a sealed barely starts to roll off, and doesnt affect the curve down low where it is really needed.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Mr. Wild »

You can't decrease group delay by adding filters. Every filter or eq along the signal path adds group delay to the signal.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Eric D »

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

Post by ttocs »

I got a wallet!

Group delay - I must have missed this what is it?
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Mr. Wild »

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

Post by ttocs »

ok that is what I thought it was going to do with but do we have someone in here that can hear the differences in group delay in an A-B listening test? Seems like we are talking about some very small difference in sound to be able to hear it and bring it up in here.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Eric D »

Since it seems the majority of people think they can hear a difference in something which cannot be measured (like the difference in silver vs copper wire for example), I would guess something that CAN be measured (like group delay) has an even greater chance of being heard.

With that in mind though, I am pretty confident I personally cannot hear the difference, but who knows maybe I could. For all I know, this could be just one of the factors as to why I think PG amps sound better than those from many other manufacturers.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by ttocs »

seems like the numbers calculated would be so small that it would be a real talent to be able to tell the difference. I mean it seems like it would be about the same as making on speaker wire 10 ft longer then the other and then being able to tell the delay from one speaker to the other?

Either way I don't think it would really effect the output here to be taken into effect especially since it has diddly to do with the box.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Eric D »

ttocs wrote:seems like the numbers calculated would be so small that it would be a real talent to be able to tell the difference. I mean it seems like it would be about the same as making on speaker wire 10 ft longer then the other and then being able to tell the delay from one speaker to the other?

Either way I don't think it would really effect the output here to be taken into effect especially since it has diddly to do with the box.
And all the numbers don't mean anything if...

-Another person rides with you
-You roll the window down
-It is a hot summer day vs a cold winter one
-Your wife leaves a blanket in the trunk
-Etc

With the cabin of the vehicle being so small, any change in the environment throws off the data significantly. Some things like rolling down a window have drastic affects on frequency response.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by holmis »

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

Post by Mr. Wild »

Now look! Group delay is just one more factor you need to consider when adjusting your system.
For example. Your subwoofer is ported and thus may have a significant amount of group delay at crossover frequency.
What to do? Add roughly the same amount of delay to the midbasses settings. Now your subwoofer and midbass will blend together better and you will have better midbass responce.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by ttocs »

so these delays you want us to throw in there is this done elctronically or through coils/caps to get everything right? Do you take that into account while you are scoping the amp to get the gains right or is that something that you can just adjust out after everything is done? Or is that done through the box design since that is what this post is about?
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Mr. Wild »

Ah sorry! I kind of take time delay adjustment for granted since it can be found in even quite affordable head units these days, If you dont have it then you just have to what you can with the crossover frequencies and slopes available.
Time delay adjustment is in effect the same as phase adjustment.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by audiophyle_247 »

ttocs wrote: do any of those programs give #'s on port noise or accuracy?
Lol, youve been talking about group delay since the beginning ttocs, ya just didnt know it.

Group delay is most definitely audible, and most definitely measurable. You have to remember that a bass note is not just s single tone but involves harmonics. A snare drum for example will have a high freq snap along with a low kick. If the sub section has a large enough delay you will hear two distinct sounds where there should only be one. Our ears and sensitivity to delay varies by frequency, but there is much debate on just how "insensitive" our hearing is in the lower registries. The biggest issue is with the harmonics of bass being out of sync, but quantifying something like this across multiple people is probably impossible, and part of why I didnt include graphs of it just yet. If anyone has heard a "sloppy" ported sub, then they know exactly what a large group delay can sound like.


However now we get to the confusing & interesting part (& why I omitted group delay graphs)
ttocs wrote: A couple of db's boost on a signal is not going to make it that much of a difference in signal quality but would then be close to the same output as the ported, with room to give it more.
My argument, and the link I provided, as well as MrWild's feedback, is that applying EQ to match the ported makes the sealed sound exactly like the ported, because the group delay of the sealed box will suffer just as much. If boosting the bass of the sealed makes no audible difference in accuracy to you, then you would not hear the difference in accuracy by using a ported box instead, because they would be the same. (Not directing this at ttocs, he said it but this applies to everyone who thinks along these lines.)

Essentially you could have a ported box and sealed box have the exact same freq response curve and output, but the "accuracy" of the sealed will be identical to the ported, it will require significantly more power to get the sealed to match the ported, and the sealed sub will be getting pushed far harder than the ported sub would be for identical output. The only sacrifice made by going ported is the enclosure volume required, and conveying that was my intent on starting this thread. This of course assumes you are comparing boxes of similar goals, a good sealed design to a SQ oriented ported design, because making a good sealed box sound like a SPL oriented ported box will make the sealed sound just as less-musical as the SPL box, but of course require even higher power levels to reach the much higher freq peaks.


Mr Wild,
Time alignment is done across a speaker's (or channel's) entire frequency spectrum it does not target specific frequencies, so I dont think you can do such a thing to match a midbass to a sub's delay. This also neglects the issue of harmonics of the bass, where a long group delay across both mids & sub would make a snare drum sound even worse. The only way to fix is keep group delay within a range our ears are not sensitive enough to catch, which I have not found any concrete numbers on. I am no pro here, but what I gather is the group delay is not a product of signal manipulation but instead a mechanical byproduct. Ie the ported relying on matching alignment with the backwave to gain in signal amplitude, and the sealed sub physically fighting harder against the enclsoure's air spring when trying to reach higher excursion levels than normal where signal boosting has taken place.


This evening I'll post a graph of group delay comparing the ideal sealed, ideal ported, and SPL ported so everyone can see the difference in accuracy, and how different it is at each freq.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by capitolj80 »

Eric D wrote:
ttocs wrote:seems like the numbers calculated would be so small that it would be a real talent to be able to tell the difference. I mean it seems like it would be about the same as making on speaker wire 10 ft longer then the other and then being able to tell the delay from one speaker to the other?

Either way I don't think it would really effect the output here to be taken into effect especially since it has diddly to do with the box.
And all the numbers don't mean anything if...

-Another person rides with you
-You roll the window down
-It is a hot summer day vs a cold winter one
-Your wife leaves a blanket in the trunk
-Etc

With the cabin of the vehicle being so small, any change in the environment throws off the data significantly. Some things like rolling down a window have drastic affects on frequency response.
Mine have always sounded louder and cleaner with a window down or a door open.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Eric D »

capitolj80 wrote:
Eric D wrote:
ttocs wrote:seems like the numbers calculated would be so small that it would be a real talent to be able to tell the difference. I mean it seems like it would be about the same as making on speaker wire 10 ft longer then the other and then being able to tell the delay from one speaker to the other?

Either way I don't think it would really effect the output here to be taken into effect especially since it has diddly to do with the box.
And all the numbers don't mean anything if...

-Another person rides with you
-You roll the window down
-It is a hot summer day vs a cold winter one
-Your wife leaves a blanket in the trunk
-Etc

With the cabin of the vehicle being so small, any change in the environment throws off the data significantly. Some things like rolling down a window have drastic affects on frequency response.
Mine have always sounded louder and cleaner with a window down or a door open.
Mine too. I like sunroofs for this reason.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Pillow »

... Since we are trying to determine the ultimate SQ...L system, let me introduce the topic of the Passive Radiator box. Apparently the PR box can achieve the same bump in low end that the ported can while retaining the SQ of the sealed box due to the lack of port "chuff" and dampening of the PR to prevent over excursion.

I am actually amazed more people in SQ car audio are not running these PR boxes..? Cost? Lack of information on design/tuning? It seems very popular for Home Theatre use.

Anyone have experience good or bad with a PR box? Also you will still have the cabin gain issue just like in a ported or sealed box.

Here is a good read IMO:
http://www.diycable.com/main/pdf/Shiva-PR.pdf

Please discuss :)
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Eric D »

I have had great luck with passive radiators and I firmly believe in the benefits of their use.
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by Killerwatt »

I'm gona chip in with my thinking.
The reason that sealed boxes work rather well for sq applications is that the rolloff roughly matches cabin gain for a car. This leaves you with a roughly flat frequency response and low group delay.

Now just in terms of freq response most ported boxes would leave you with a hump somewhere in the bass range. After being combined with cabin gain that is. So that box with a flat response would not sound too good in a car. Now with some eq you can get rid of that hump and get a similar freq response to a sealed box. But because of the eq cut you now place much less stress on your electricals.

Now on to group delay. How much is actually audiable? General consensus is half a wavelength. Now for 30hz this is (1/30)*1000/2 or approximately 16ms. For 20 hz its 25ms and 50hz is 10ms. So a ported box with a delay lower than this shoul in theory sound as good as a sealed on. Most of the shelf boxes exceed this delay by quiet a lot.

So to sum it up, to get a ported box to work for sq you need to work the volume and tuning to keep group delay as low as possible or below the half wavelength cycle. Then use a bit of eq to bring the freq response back to flat.

Well that's my story...
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Re: Ported vs Sealed, lets open this can of worms. lol

Post by audiophyle_247 »

Killerwatt wrote:I'm gona chip in with my thinking.
The reason that sealed boxes work rather well for sq applications is that the rolloff roughly matches cabin gain for a car. This leaves you with a roughly flat frequency response and low group delay.

Now just in terms of freq response most ported boxes would leave you with a hump somewhere in the bass range. After being combined with cabin gain that is. So that box with a flat response would not sound too good in a car. Now with some eq you can get rid of that hump and get a similar freq response to a sealed box. But because of the eq cut you now place much less stress on your electricals.
I do believe the graphs above prove this concept wrong, cabin gain does not smooth response. Cabin gain acts like a port by reinforcing freq around the vehicle cabin's resonance. You need a huge suv or bus to get a resonance under 35~40hz (if even possible), where a sealed box really starts to fall off. The only "sq" factor I see working for a sealed enclosure is low group delay at the cost of weak low end. I'm working on an F150 4dr that I put 6 8" type R's in and it's painfully loud at 50-60hz but almost nonexistent below 35hz, even with the windows down (which lowers cabin resonance freq). Going with a ported box this time, keeping all 6 subs, and only loosing legroom for a 5th passenger. Lol

Your numbers on acceptable group delay seem to make sense for freq, and I want to dig deeper into that. Any links you can provide for good reading?
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