Better for music: Sealed with Linkwitz Transform or Vented? - Page 2 - diyAudio
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Old 29th October 2011, 12:34 PM   #11
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well, a ported box has the same delay as a sealed box at double the tuning frequency (and up). So tune to 27hz and a 63hz tone would be just as fast (ms delay) as if the same sized box was sealed.

but..........
I just found this on linkwitz site.
"Not only is the frequency response extended, but the time response is also improved, as indicated by the reduced overshoot and ringing of the lower cut-off highpass filter step response." below middle of the page on linkwitz transform circuit.
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To me, your room will be storing then releasing the bass pressure (under 60hz) much slower than your subwoofer.

I sold a 6th order pair of 12" (6db boost/cut filter) ppsl to a buddy who was disgusted that this ported beat his 3 x 10" sealed qtc .707 jl audios. ppsl was deeper, punchier, cleaner, and quicker. Yes a ported seemed faster than a sealed, but the canceling of harmonic distortion and less excursion made for a much cleaner sound.

I do also know I like 30hz tuning better than 40hz listening to music then stuffing 1 of my ports.

Norman
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Old 29th October 2011, 10:12 PM   #12
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Quote:
Originally Posted by bbggg View Post
Transient response is defined by onset and decay.
Group delay defines how late the onset of sound emission is. Here vented has lots more, roughly double.
There is also the box/vent resonance decay, ie how long it takes for this component of sound emission to cease. This takes a while because air is both elastic and not too lossy. Therefore vented boxes take variable amounts of time to round up their sound emission, sometimes very long ones, depending on particulars. Closed box, LT'd or not, has none of this because there is no vent air mass to resonate.
So vented can not match closed box for time performance. At best it can hope to approach it. At worst, vented can moan, drone, huff and puff like a leaky bagpipe that's got the sniffles.
It all boils down to the nature of resonating systems. A resonance takes time to build up and time to die down. A closed box has one such resonant system. A vented box has two, and staggered ones at that, with the second one consisting entirely of air (air mass, air compliance, air friction).
"At worst, vented can moan, drone, huff and puff like a leaky bagpipe that's got the sniffles."
In fairness results this bad are somewhat rare these days. But I have heard some really bad examples in the past.

"So vented can not match closed box for time performance. At best it can hope to approach it."
Agreed, if you want a sub that can make you really jump then a closed box is the best for immediacy. That said I have heard clunky old closed box sub's bettered by newer vented systems, the best sensible sized sub's still all seem to be closed box though.

"A closed box has one such resonant system. A vented box has two, and staggered ones at that"
leaky Aperiodic systems were designs to remove or reduce the one box
hump (and allow designers to build smaller boxes) I haven't seen any Aperiodic home sub's though. I do not know if there would be any real benefits with modern EQ.

Subjectively I have always preferred closed box bass. This was a big part of the appeal of Pluto 2.1 for me.
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Old 29th October 2011, 10:38 PM   #13
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What about Mr. Cordell's EQSS? Low tuned vented enclosure with the LT applied. Replace the big port with a passive radiator if you need to. Reduced cone excursion like a vented but group delay more similar to a closed box. (I've not tried this yet myself, just something interesting.)

http://www.cordellaudio.com/loudspea...hite_Paper.pdf
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Old 30th October 2011, 12:29 AM   #14
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Thanks muchbbggg (and rob g), you've succinctly written the epitaph for "reflex" boxes.

Just occurred to me that the BR design might be thought of in historical terms as a stop-gap approach to produce some sense of extra-low bass from drivers with 35-45 Hz resonances of yesteryear. Not much reason to live with BR shortcomings (as presented previously), when you can make drivers with lower resonances and just put them in a sealed box with no high-falutin' design effort needed*.

Ben

*as far as I know, within reason almost any sealed box will give you some kind of OK bass, arithmetically optimum or not. Or slightly leaky box maybe even better too.
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Last edited by bentoronto; 30th October 2011 at 12:33 AM.
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Old 30th October 2011, 01:32 AM   #15
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Thanks for the cordell link William! very interesting. It also shows clearly one of the tradeoffs of using the linkwitz transform.. The amount of extra power required to drive the speaker (which also then implies that the drivers must be capable of handling significantly higher power).

I've been wondering myself about sealed vs vented for when I redeploy the 10" drivers in my three ways (currently vented) as dedicated subs. I will be investigating the EQSS now

Tony.
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Old 30th October 2011, 04:41 AM   #16
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Quote:
Originally Posted by bentoronto View Post
Thanks muchbbggg (and rob g), you've succinctly written the epitaph for "reflex" boxes
No, there is a positive side and that is
Quote:
Originally Posted by bbggg View Post
less harmonic distortion
because of reduced excursion demands for the same SPL. To match this, a larger driver in a sealed alignment would be needed. Depending on circumstances, a vented system may be the optimal compromise.
Conventionally produced, multimiked pop music has no phase coherence at all, because of the way it is recorded, mixed, equalized and mastered. There are a multitude of superimposed low pass filters in these procedures which render trrelevant all notions of LF time coherence in the final product. In such cases listening to vented systems will not impair things further because there's nothing left to impair.
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Old 30th October 2011, 04:48 AM   #17
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Replace the big port with a passive radiator if you need to
That's replacing air mass and air friction with passive radiator mass and suspension friction. Unlike air, those can be manipulated. Unlike air, they can also introduce distortion. Well, air can introduce distortion too sometimes -but it's fairly easy to avoid. Sometimes.
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Old 30th October 2011, 05:33 AM   #18
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That's just it though, "easy to avoid" means a large diameter port which ends up awfully long when tuned so low like this.....the reason I mentioned the PR. Or am I way off track here?
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Old 30th October 2011, 09:49 AM   #19
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Originally Posted by bbggg View Post
No, there is a positive side and that is because of reduced excursion demands for the same SPL [due to less distortion]. To match this, a larger driver in a sealed alignment would be needed. Depending on circumstances, a vented system may be the optimal compromise.
snip
True, there is less movement of the cone (and hence less distortion) in vented enclosures north of the system resonance when the vent augments the sound by feeding out system upper-resonance into the room. But I believe at box resonance and below, the situation is different.

But hard to say if distortion is harder to take in the Hz region above resonance compared to sound below resonance.

Ben
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Old 30th October 2011, 12:42 PM   #20
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Thanks to William2001,
interesting concept, I expect you would find many retail/commercial systems use a combination of low frequency equalization and porting just like this.

I find passive radiator systems sound different again to ported and closed box. PR's systems tend to be the systems that sound subjectively the slowest but great for powerful rumble in Home Cinema. I think there are excellent examples with all these systems. Annoyingly the room makes the biggest difference, by a country mile.

Mr Linkwitz makes no secret about the requirement of extra power and the need for drivers with more expensive, better quality long throw motor systems.
It is pretty obvious that there is no such thing as a free lunch.
Also I am wary of general recommendation of powerful low frequency equalization for really modest size systems going into larger spaces (driven by WAF!). Pluto pushes a small drive unit really hard to produce deep bass, I would be wary of damage from users trying to produce the deepest bass in a large room at moderately high volume.
Mr Linkwitz did not have dub bass and Massive attack on his mind when he designed Pluto, even the add on subwoofer option for that matter!

I say I have a subjective preference for sealed loading because you can look at the figures one way or another and even present the resonant reflex systems as superior, in terms of distortion, or in terms of transient response.

Choosing ported reflex systems certainly gives you more choice in terms of drive units. Also the majority of systems are ported because it is now cheap and easy to make passive speaker systems with modest cost drivers (with cheaper light weight motor systems) for obvious punchy bass, compatible with more modest power amplifiers. Since the majority of speakers are now reflex designs the majority of good designs out there are also reflex designs!

In very large speakers you can have a low distortion system that acts more like a sealed system but with a very low tuned port to extend deep bass and reduce distortion. ATC tune their speakers like this. The majority of their smaller speakers are closed box but the larger systems are ported.

Whether I am listening to Classical, Acoustic, Rock, jazz, Electronic, or whatever I tend to prefer well designed closed box speakers. Certainly the difference is greatest or most noticeable on well recorded Classical material as bbggg implies.

Linkwitz transform is a good system for getting deeper bass out of modest size systems and maintaining high quality at the same time. I have never heard an equivalent sized passive speaker produced such tight, well balanced bass with proper extension.
Usually in modest size passive systems you have to choose between too dry but well tuned bass or overt thumpy punchy bass speaker effects.
This to me is a major benefit of active speakers, at least for people who live in the real world, not the tiny minority who can fill their homes with enormous speakers and multiple sub's.
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