So why are sealed boxes so unpopular?

[jamesj]

Market Forces

It's quite simple, in my opinion. The buying public demands more bass from smaller boxes. Reflex loading is the easy route to that end. Most loudspeaker manufacturers buy OEM drive units, and therefore most modern mid-woofers and woofers are optimised for reflex operation (low Q).

However, there is no denying that a good sealed design delivers a more natural and realistic bass performance. Once you hear and become accustomed to sealed bass, most reflex designs sound stodgy, slow and muddy. I just wish there were more high-Q drivers.

Just my $0.02.

James

 

[JWFokker]

There you are you see its all about the application.

Not once have I ever seen someone recommend a ported enclosure IF a sub is going to be used.

Ported box = a bit more bass from smaller drivers.

And what if you're using drivers that have an f3 that's too high for an ideal sub crossover and really NEED to be ported to reach below 100hz? For example, what would you use with Tang Band W3-871's that have an f3 of roughly 125hz. I wouldn't want to set a crossover that high. The sound from the sub would be way too directional.

I suppose the simple answer would be to buy better drivers, but I'd like to hear a response to this conundrum. The TBs seem quite popular and I don't know how you'd integrate a sub with them and make it sound good.

 

[Shaun]

It comes down to integration

Whatever you think of "sealed vs ported", it comes down to how the speaker integrates with the room. Really, this is all that matters. In a system where the final rolloff is steeper, group delay will always be higher. The trick is to push the peaking GD region down as low as possible (where there is "less" music), or else to make the rolloff transition as gentle as possible. Someone made the point to the effect that people (commercial or otherwise) try to squeeze the most bass out of small drivers by using a bass reflex enclosure: this is obviously a mis-application, and will always leave audio critics dissatisfied.

To get back to my first point (integration), I have come to the conclusion that, irrespective of the enclosure type, the final solution is to apply equalisation. Now this can be done (1)electronically, (2) acoustically or (3) by selecting (or designing) a speaker that integrates just right with the listening environment. The solution I propose does not promote a specific enclosure type, except the disclaimer that if you stress the driver, all bets are off. And with all LF enclosure types you will run into distortion eventually.

Now it's 4c.

 

[richie00boy]

Fact is that ported boxes 'excite' room modes far more than a sealed design.

This means that in some rooms the response from a ported cabinet can be lumpy. Whereas sealed would be far less so. Dipole bass is best of all in this regards.

This is simply not true. There is no difference in inherent excitation of room modes sealed vs. vented par se. Merely that because vented boxes often go a little deeper therefore start to hit into room gain territory thus creating a bump, then rolling off quicker than room gain thus creating a slope off, the integration can be less optimal than a sealed box and thus sound lumpy. However, this is an integration issue not really a vented box issue -- you can get a similar but maybe not so extreme situation with a high-Q sealed box that goes low.

 

[ShinOBIWAN]

This is simply not true. There is no difference in inherent excitation of room modes sealed vs. vented par se. Merely that because vented boxes often go a little deeper therefore start to hit into room gain territory thus creating a bump, then rolling off quicker than room gain thus creating a slope off, the integration can be less optimal than a sealed box and thus sound lumpy. However, this is an integration issue not really a vented box issue -- you can get a similar but maybe not so extreme situation with a high-Q sealed box that goes low.

This is from personally experience of both commercial and DIY designs in my room.

After an RTA of the response the ported box's ALWAYS had a large hump at 40-60hz. This was less so with sealed designs that actually went deeper, so the bit about extra depth exciting modes on ported is mute.

Here are most of the commercial subs I've owned:

2 x Paradigm PS1000's (Ported)
Gale cheapie (Ported)
Vibe Gamma (Ported)
Mission 78as (Ported)
2 x Servo 15's (Sealed)
2 x Ruark Log Rhythm's (Sealed)
SVS CS-Ultra (Ported)

Easily the best of these were the two servo 15's and dual Logs. Worst was the SVS CS-Ultra and it needed extensive PEQ to get a flat response.
I always use a BFD to EQ my bass to flat or a house curve.

This is in my room only and I've had 0 experience with others so what I say is possibly only true from my perspective and perhaps I should have stated that. Ported designs cause me problem in my room.

 

[ShinOBIWAN]

I should add that the two Servo15's and two Ruark Logs were stacked for less distortion at high SPL's, rather than seperated and used to smooth the room modes through distribution.

 

[quasi]

Excellence available in both concepts

For example, a friend has a pair of Duntech Sovereigns. These would be the best sounding speakers I have ever heard (IMO) and these are sealed cabinets. They are very very big though (way bigger than me). http://www.duntech.com.au/images/all.html

Another friend has a nice set of vintage IMF 50 transmission line speakers and they are excellent. Sometimes he gets sad when he listens to my bass reflex DIM's (did it myself) cause he reckon's they are very good too.

So it depends more on achieving excellence in a concept rather than the concept itself.

Cheers

 

[ShinOBIWAN]

This is simply not true. There is no difference in inherent excitation of room modes sealed vs. vented par se. Merely that because vented boxes often go a little deeper therefore start to hit into room gain territory thus creating a bump, then rolling off quicker than room gain thus creating a slope off, the integration can be less optimal than a sealed box and thus sound lumpy. However, this is an integration issue not really a vented box issue -- you can get a similar but maybe not so extreme situation with a high-Q sealed box that goes low.

Also take a look at Sigfried Linkwitz' investigations.

He has the same conclusion as me.

 

[richie00boy]

Any tips on which bit of his vast library to begin looking at?

 

[ShinOBIWAN]

Any tips on which bit of his vast library to begin looking at?

Here's the quote I was looking for:

The conventional closed or vented box design, that is used for the majority of loudspeakers on the market, contributes significantly to the room problems below 200 Hz. These designs are omni-directional radiators and they tend to excite a maximum number of room resonances, particularly when located in room corners. While this adds to the perceived bass output at certain frequencies, it can lead to a falsification of the recorded material, namely when the room resonance decays more slowly than the original sound. In general, the low frequency response of omni-directional speakers in small rooms is quite non-uniform. Attempts to treat the room with absorbers will make only marginal differences unless very many absorbers or large absorbing surfaces are used. It is best to attenuate peaks in the bass response with parametric equalization. Holes in the response cannot be filled in (Ref. 1).

By far the most uniform response in the range below 200 Hz is obtained with an open-baffle, dipole or figure-of-eight radiating source. Because of its directionality, the dipole excites far fewer room resonances than an omni-directional source. The difference in bass reproduction is startling at first, because we are so used to hearing the irregular and booming bass of the typical box speaker in acoustically small rooms. Quickly one learns to recognize the distortion of this combination and it becomes intolerable.

I haven't read this in over a year so I did mistake the findings as saying sealed was better than ported. This isn't SL's findings and he states both aren't very good in this regard. The best being dipole, as I already stated.
Of course this doesn't change my own considerable experiences from my room's point of view.

If your interested in the rest of the article, it can be found here:

http://www.linkwitzlab.com/rooms.htm

 

[richie00boy]

No problem ShinOBIWAN, your apology is accepted Thanks for the quote.

 

[simon5]

After an RTA of the response the ported box's ALWAYS had a large hump at 40-60hz. This was less so with sealed designs that actually went deeper, so the bit about extra depth exciting modes on ported is mute.

This is in my room only and I've had 0 experience with others so what I say is possibly only true from my perspective and perhaps I should have stated that. Ported designs cause me problem in my room.

Could you give your room dimensions please?
I think it might be a problem with your room, if you look at the graph I posted above, there's no large hump in FR when my ported subwoofer is in a room. If in your room, a sealed subwoofer is better, then obviously you're better to use a sealed subwoofer.

 

[ShinOBIWAN]

Could you give your room dimensions please?
I think it might be a problem with your room, if you look at the graph I posted above, there's no large hump in FR when my ported subwoofer is in a room. If in your room, a sealed subwoofer is better, then obviously you're better to use a sealed subwoofer.

14ft W x 9.5ft D x 8ft H

Roughly

 

[simon5]

I had some fun with your room to see if there was some obvious problems...

If the subwoofer is in a corner :
8' ceiling = cancellation at 35.31 Hz, boost at 70.62 Hz.
9.5' = cancellation at 30 Hz, boost at 60 Hz.
14' = cancellation at 20.18 Hz, boost at 40.36 Hz.

So to cancel ceiling, we would need to place the subwoofer where 35.31 Hz is boosted and 70.62 Hz is cancelled.

70.62 Hz is canceled when the subwoofer is at 4' from a wall.
35.31 Hz is boosted when the subwoofer is at 16' from a wall.

I think the best placement would be 3' from the 9.5' long wall, 4' from the 14' long wall.

If the subwoofer is in that place:
8' ceiling = cancellation at 35.31 Hz, boost at 70.62 Hz.
4' = cancellation at 70.62 Hz, boost at 141.25 Hz.
5.5' = cancellation at 51.36 Hz, boost at 102.73 Hz
11' = cancellation at 25.68 Hz, boost at 51.36 Hz.
3' = cancellation at 94.17 Hz, boost at 188.33 Hz.

Problem with this placement is two cancellations, one at 25 Hz and another at 35 Hz. Your room is too small to correct these cancellations.