Sealed Enclosures

[fantfool]

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?

[FullThrottleRic]

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]

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.

[chops]

Originally posted by fantfool


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).

[fantfool]

It would seem that sealed enclosures have more plusses then ported, if that is the case why are so many of the "high end" speakers ported?

Thanks for the information.

[Hezz]

Originally posted by fantfool
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]

Originally posted by Hezz
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?

Originally posted by fantfool
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.

[R-Carpenter]

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]

Originally posted by Hezz
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]

Originally posted by Brett
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?