Sealed Enclosures

fantfool

Member
2007-12-24 4:24 pm
For main speakers, how much of a difference does box volume have on sealed enclusure designs? I know they are less efficient and don't quite produce the lower frequencies as ported designs, but other then that are there any other drawbacks to this type of design?
 
Sealed - Smaller, less group delay, lower order rolloff, more extreme low output, protects the driver better at very low frequencies, more tolerent of incorrect alignment.

Ported - Less cone excursion around fb > lower distortion, greater output potential, higher order rolloff.

What is more important to you is what you have to decide ;)

Personally I always build sealed enclosures, having a small room I never struggle for output and also smaller box's fit the room better.

I assume you are using them for HT given you said 'for main speakers', in which case THX recievers/processors expect the main speakers to have a 2nd order rolloff when you set them to small..
 

fantfool

Member
2007-12-24 4:24 pm
Yes for a HT application, but definately listen to music in stereo so that is important as well.

By incorrect allignment do you mean driver allignment i.e. MTM? How about being more forgiving for incorrect box volume?

Less group delay meaning quicker?

Lower order rolloff meaning more gentle rolloff on the low end?


Thanks for the response.
 
fantfool said:


By incorrect allignment do you mean driver allignment i.e. MTM? How about being more forgiving for incorrect box volume?

Less group delay meaning quicker?

Lower order rolloff meaning more gentle rolloff on the low end?


Thanks for the response.


"How about being more forgiving for incorrect box volume?"

That's what is meant by incorrect allignment.


"Less group delay meaning quicker?"

Meaning the driver stops moving quicker and also less enclosure resonance.


"Lower order rolloff meaning more gentle rolloff on the low end?"

Yes.

With ported enclosures, the driver acts as if it's in a sealed enclosure above the tuning frequency. Once the signal drops below the tuning frequency, the driver acts as if it is in free-air (no enclosure at all).
 

Hezz

Member
2002-12-22 6:52 am
Utah
fantfool said:
For main speakers, how much of a difference does box volume have on sealed enclusure designs? I know they are less efficient and don't quite produce the lower frequencies as ported designs, but other then that are there any other drawbacks to this type of design?


When it comes to natural timbre quality, sealed designed suffer the most and internal box stuffing becomes very important to get good sound to deal with all the bad reflections inside the box that are reflected back into the cone. All box speakers have this problem but sealed designs suffer the most from this. I only like the sound of critical Q sealed enclosures which generally require a larger box than a good vented system.

It really depends on what you like but closed systems have the most boxy type of sound in the mid/bass and lower midrange region. This can be dealt with but doing so messes up the bass response. If you are doing a two way that you want to sound really natural go with vented or aperiodic.
 

jnb

Member
2006-12-30 11:55 pm
Re: Re: Sealed Enclosures

Hezz said:
When it comes to natural timbre quality, sealed designed suffer the most and internal box stuffing becomes very important to get good sound to deal with all the bad reflections inside the box that are reflected back into the cone. All box speakers have this problem but sealed designs suffer the most from this.
Could you explain why you feel this is so?

fantfool said:
why are so many of the "high end" speakers ported?
For one thing, on the surface ported boxes look better on paper with their lower -3dB frequency.
 
Either way you build a box, it should has as little internal resonance as possible. Stuffing and reinforcement of the box itself are very important.

Generally speaking, close box speakers are more tolerable to volume mistakes then vented boxes speaker. Close box will give you 12db acoustical roll off of the woofer and also will protect overextension of the woofer at infra low frequencies (rarely a problem). Heating of the voice coil aren't happening as easily. Some will also say the close box will give you a better transient response and I tend to disagree with it.
Vented box speaker will give you a better bottom end extension per volume. It will be more sensitive to volume miscalculations and port miscalculations.
Driver parameters for close and vented box are different. Close box prefers a driver with higher Q. Vented boxes will perform better with lower Q driver (most of high end drivers such as Seas, Scan Speak and Eton).
In a close or vented enclosure, group delay doesn't make that much of a difference unless you've made really terrible miscalculations and misaligned drivers, but then you have other problems to deal with with.

Open Vs. Vented.
Hard to say. Either way you could get very good results. My personal preference is Vented design. I like to get 45Hz out of a relatively small bookshelve speaker. With computer software and measuring equipment it's becoming easier and easier to design a fantastic speaker.
Why most high end manufacturers use vented schematics?
I think because it allows them to use lower Q drivers and produce more bottom end per box liter.
Commercial manufacturers need to build as good of a speaker as possible and at the same time as small as possible. Imagine that you as a speaker maker just created a fantastic close box design that takes half the room. Unless your customer is half crazed single guy, who the hell is going to buy it?
If you are building a HT set up, I would build 2 main speakers ported (I like MTM) to get a good base extension without use of a subwoofer (not to say a sub is a bad idea), use close horizontal MTM for center channel and vented or close boxes for rear channels. Wait, I already have that and it sound fantastic!
 

Brett

Member
2002-01-07 6:02 pm
Re: Re: Sealed Enclosures

Hezz said:
When it comes to natural timbre quality, sealed designed suffer the most and internal box stuffing becomes very important to get good sound to deal with all the bad reflections inside the box that are reflected back into the cone. All box speakers have this problem but sealed designs suffer the most from this. I only like the sound of critical Q sealed enclosures which generally require a larger box than a good vented system.

It really depends on what you like but closed systems have the most boxy type of sound in the mid/bass and lower midrange region. This can be dealt with but doing so messes up the bass response. If you are doing a two way that you want to sound really natural go with vented or aperiodic.
I actually think you have that backwards. For a given cab volume, shape and driver, the internal reflections in the midbass and up (above area of helmholtz resonance in a ported box) the ported will be MORE likely to have issues. Simple fact is most ported enclosure have some (miminal) damping around the wall or none at all, which does nothing to minimise internal reflections coming back out through the cone. However, most sealed boxes do have some stuffing/damping and are therefore far more likely to have some control over these internal reflections. Sealed boxes also lack MF coming back out through the port which can be audible in some designs.
 

fantfool

Member
2007-12-24 4:24 pm
Re: Re: Re: Sealed Enclosures

Brett said:
I actually think you have that backwards. For a given cab volume, shape and driver, the internal reflections in the midbass and up (above area of helmholtz resonance in a ported box) the ported will be MORE likely to have issues. Simple fact is most ported enclosure have some (miminal) damping around the wall or none at all, which does nothing to minimise internal reflections coming back out through the cone. However, most sealed boxes do have some stuffing/damping and are therefore far more likely to have some control over these internal reflections. Sealed boxes also lack MF coming back out through the port which can be audible in some designs.


OK so then if you stuff a ported box design with poly or something and have interior wall treatments i.e. thick carpeting/padding, is this the best of both worlds?
 

Hezz

Member
2002-12-22 6:52 am
Utah
Re: Re: Re: Re: Sealed Enclosures

jnb said:

Could you explain why you feel this is so?

I will try to explain why this is so based on my own personal theories but for the most part it is listening to many good sounding speakers. I know there are good examples of closed boxed speakers but of all the ones that I have listened to I have never heard any I liked a great deal except a couple of critical Q designs which were rather large compared to the driver surface area.

My theory is this. It is basically similar to Lynn Olsens on why boxed speakers have a tendency to sound boxy. First, this applies to all boxes. Standing waves, internal reflections and pressure stratification inside the box at generally the worst possible frequencies.

Now when talking about sound quality two things must be separated out. Timbre quality and frequency smoothness and extension. All these kinds of speaker loadings have different strengths and weaknesses in reguard to these things. Now on paper a sealed design would seem to have several things going for it except for deeper bass response. But in addition to the standing waves and internal reflections, internal non linear air compression causes time smear because the air spring is not the right strength in most speaker designs. And this is for two reasons mainly related to marketing. Exaggerated bass is needed to make the speaker stand out and small size is needed for wife acceptance factor or real space constraints. Yet only in a critical Q designs is the air spring of the correct strength so that the driver is properly tuned for accurate reproduction. And the kind of drivers that can go quite low in the bass department in this kind of enclosure, require a rather large enclosure.

Now the reason I think that a vented enclosure sounds better other than subjective preference is because I think that the port is not always energized with a resonating air column. Only at those times when there is a signal which excites it. So depending on music material, the box may be behaving somewhat more like an infinite baffle or aperiodic part of the time. With some music material which does not constantly excite the port it could be a great deal of the time. So the vented box has a little more relaxed feel to the sound which I feel is a little more natural.


Brett said:
I actually think you have that backwards. For a given cab volume, shape and driver, the internal reflections in the midbass and up (above area of helmholtz resonance in a ported box) the ported will be MORE likely to have issues. Simple fact is most ported enclosure have some (miminal) damping around the wall or none at all, which does nothing to minimise internal reflections coming back out through the cone. However, most sealed boxes do have some stuffing/damping and are therefore far more likely to have some control over these internal reflections. Sealed boxes also lack MF coming back out through the port which can be audible in some designs.

Ok, I can accept that heavy port noises might modulate upper midrange energies in the box. But the fact is that the most important frequencies for reproduction are not in that range. But in the upper bass and lower midrange. And while I agree with your logic for some reason in my experience the empirical observations don't match up. The reduced cone motion near the port frequency may allow the driver to reproduce motion that is a little higher in frequency at a somewhat lower distortion level. There is less doppler distortion on the cone I may presume. Also, I believe that the most important frequencies that must be gotten right for good sound are between about 80Hz and 1500Hz. If anything is compromized in this range it doesn't matter how good any other parts of the reproduction are. You will never have natural sounding speakers.




fantfool said:



OK so then if you stuff a ported box design with poly or something and have interior wall treatments i.e. thick carpeting/padding, is this the best of both worlds?

Yes and no. The best would be to have a three way system where the midrange and the majority of the midband is in some kind of less resonant enclosure like an aperiodic or transmission line or open-back that is sealed off from the woofer enclosure. However, if you have only a two-way I would say you are correct. You can line all the walls with sound absorbing and damping material and stuff perhaps 50% of the box with fiberfill but with a vented box it works best if there is an unobstructed path for air movement between the port and the driver. You just have to get the best balance for the cabinet that you have made.
 
Re: Re: Re: Re: Sealed Enclosures

fantfool said:
OK so then if you stuff a ported box design with poly or something and have interior wall treatments i.e. thick carpeting/padding, is this the best of both worlds?

Some would say yes. Do this properly and you have an aperiodic box.

In the end which box is better depends on the driver, the room, the amp...

BR are common in the commercial field because they are an easy sell.

dave
 
Based on initial question, I don't think Fantfool is at the level there he can measure actual room response and alter frequency response of the speaker to match. Let's just say we could shoot for a speaker with maximally flat frequency response at this point. My understanding from the post is that he has a small to medium size room so a high quality bookshelves would be quite sufficient.

Don't think the amp should be a consideration for a choice of a driver. After all amp (with enough power) will make little or no difference in the outcome. It's the Record-Speaker-Room deal. Besides if Fantfool is using this non-existing yet speakers for home theater, it would probably be safe to assume that a multi channel receiver will provide juice.

Anyways, ported or closed depends more on his preferences and I think we covered the basics to the extend. We could also bunch up and come up with design based on his desired drivers and preferences. I could do Bass box pro and J-peg the file. Perhaps it could be a joint kick *** design.

And I second Hezz on critical Q design teory. I have simular observations.

Regards, Roman.
 

fantfool

Member
2007-12-24 4:24 pm
R-Carpenter said:
Based on initial question, I don't think Fantfool is at the level there he can measure actual room response and alter frequency response of the speaker to match. Let's just say we could shoot for a speaker with maximally flat frequency response at this point. My understanding from the post is that he has a small to medium size room so a high quality bookshelves would be quite sufficient.

Don't think the amp should be a consideration for a choice of a driver. After all amp (with enough power) will make little or no difference in the outcome. It's the Record-Speaker-Room deal. Besides if Fantfool is using this non-existing yet speakers for home theater, it would probably be safe to assume that a multi channel receiver will provide juice.

Anyways, ported or closed depends more on his preferences and I think we covered the basics to the extend. We could also bunch up and come up with design based on his desired drivers and preferences. I could do Bass box pro and J-peg the file. Perhaps it could be a joint kick *** design.

And I second Hezz on critical Q design teory. I have simular observations.

Regards, Roman.

About a year ago I built set of mains and center using the same drivers. 2 of the Zetag Hi G1 woofers and 1 focal TC90 tweeter in each box. The mains were built in a ported box design based on the information the person who sold me the drivers had on those 6 1/2" woofers. I used that iformation to design the boxes including the port area. The center I built sealed design MTM using the same drivers. The problem I think I'm having is that the information given to me, which I based my designs from may have been incorrect which would make my boxes and port calculations incorrect for those drivers, hence I'm not getting the sound quality I was expecting. That is why I was asking about the sealed enclusure being more forgiving as far as enclusure design relating to speaker specs. Someone earlier mentioned they had the same speaker set design of ported for mains and sealed for center and they were happy with it. I am trying to figure out the best way to address my main cabinets, since I still don't have the T/S specs on those drivers, without blowing up the whole thing and starting over. Modifications would be fine, especially internal modifications to the mains I can do i.e. more or less damping, de-creasing the internal volume, even changing the port area. But i guess the problem still goes back to not having the T/S specs to go by.
 

vasyachkin

Disabled Account
2007-12-31 1:16 am
advantages of vented box

why if sealed box is the best does virtually every speaker use ported design is a good question to ask.

it seems like the answer is mostly economics, but not limited to just that. in the same enclosure the port can move more air than the driver while costing pennies.

port allows you to use a smaller driver to get the same amount of bass which can have the following advantages over sealed box:

1 - lower cost
2 - higher efficiency
3 - better high end extension

#1 is obvious. smaller driver costs less.

#2 there are two reasons for. one is that you can use a lower Q driver which almost same as saying a higher efficiency driver. another reason is that you need less Xmax when the port is helping you so larger portion of voice coil is in the gap and efficiency is improved.

#3 also has to do with less Xmax. shorter voice coil is lighter and has less inductance so response of the driver is improved at the top end.

depending on how cheap you are (commercial manufacturers are super cheap) you may think of the port as a separate driver covering a separate frequency range turning your 2-way into a 3-way at virtually zero cost. i guess this is why they almost always use a port.

as far as internal damping i believe most speakers dont use enough of it whether ported or sealed. with ported boxes though too much damping may not make as much sense as with sealed ones. because as you keep damping a ported box more and more its efficiency will start to approach that of a sealed box while you're still going to be stuck with the additional group delay.

i believe that the optimum damping strategy for ported box is to line the sides with about 1" to 2" of acoustical foam and leave the rest of the box volume alone. for a sealed box i would use the foam on the sides but also fill the rest of the volume with something like wool or acousta-stuff.
 
Hello,

I made a lot of DIY project and the first time I tried a closed design it was a serious revelation for me. No more boominess of the bass frequencies, tight control of the cone, less fuziness in the lower midrange too, and even less boxy sound than ported enclosure even if not everyone thinks alike. I aim for a Q of 0.8 to 0.9 and it's really optimal most of the time. The adjustments are way easier than a ported design and the stuffing is easy too. I can't think of any drawback compared to ported design. Even if you get only a -3db point at 70Hz anechoic I can garanty you won't miss the bass because of the room natural bass boost and the softer rolloff of the bass. The only drawback I see is that you need a high quality driver with healthy Xmax but I only use Scanspeak anyway so it's not a problem for me. I even made a very simple closed sub with a 10inches Scan speak and the -3db is "only" 40Hz without any boost and I'm totally satisfied about it. With closed design, to my taste, you loose quantity of bass but you gain a lot of quality. The only way is to try it yourself and with a good speaker. I'm happy the new SEAS line is having wider Xmax than before, they can make good candidates for closed box at a good price now.
 

fantfool

Member
2007-12-24 4:24 pm
phase_accurate said:
It I were you I would measure the TSPs and then you will see if there is a need to redesign/tweak/optimise your current boxes.

Even though there are TSP sets that allow for both kind of boxes (or sometimes even the same box size for both types) - I wouldn't mix both within one set-up.

Regards

Charles


Is there a way to determine the T/S specs on a driver yourself? That would be the ideal thing for me to do.