Can anyone help me understand why someone would wanted a sealed subwoofer over a ported subwoofer for home theater? - Page 2 - AVS Forum
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post #31 of 58 Old 02-24-2014, 10:07 AM
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Quote:
Originally Posted by ahmedreda View Post

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Originally Posted by Mark Seaton View Post

As the low bass gain from a small confined space becomes greater in smaller rooms this quickly helps a sealed sub catch up precisely where a ported sub has it's advantage... near the tuning frequency. .

Thanks Mark for your explanation. Regarding the above statement, would the ported sub benefit as well from the room gain down to its tuning frequency? If it does, wouldn't that mean that it will still maintain its advantage down to the tuning frequency over its sealed counterpart?

While dipole and cardioid subwoofers do interact differently, you won't find those to be very common in home theaters. Indeed, a ported subwoofer is affected by the room's gain the same as the sealed subwoofer and the net differences in output will be the same. The shape of the gain can be defined as a transfer curve or gain profile which is the result of subtracting the outdoor measurement of a subwoofer from the in room measurement. Picking a level can be arbitrary, but the result makes it easy to see how much more the room augments say 15Hz or 20Hz vs 50Hz.

Due to the nature of a ported sub's behavior, room gain below the port tuning is not very effective as the reason for the fast roll off of a ported sub is that the port and driver are progressively cancelling each others output so distortion rises quickly. Most production subwoofers electronically cut off this range making the roll off below tuning a 2-6x steeper rate than the maximum gain the room can provide. In many small rooms the combination of room gain and a very flat outdoor response of a ported sub can make for an over-emphasized response below 40Hz as a starting point which can the sound have a lot of rumble and shake, but lacking in articulation. Some/many do prefer this. I mentioned above that modern auto-EQ systems have greatly leveled the playing field, and this is that case. Audyssey, Antimode variants and similarly enabled technology/products will smooth this elevated starting point and help greatly in maximizing sound quality. That said, no room correction technology or room gain can push a ported subwoofer design (technically classified as reflex design) much below its tuning frequency. Choose wisely.
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post #32 of 58 Old 02-24-2014, 10:24 AM
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Originally Posted by ahmedreda View Post

Bill, for the longest dimension, do we use the length of the room or the diagonal (ceiling back left to floor front right)?
The longest dimension wall to wall, or floor to ceiling.
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would the ported sub benefit as well from the room gain down to its tuning frequency? If it does, wouldn't that mean that it will still maintain its advantage down to the tuning frequency over its sealed counterpart?.
A ported sub will realize the same cabin gain in a given room as a sealed sub, both above and below Fb. The difference is that a sealed sub has a nominal 12dB/octave roll off below f3, which is perfectly complementary to the theoretical 12dB/octave cabin gain (thought that is seldom actually realized, 8-10dB being more likely). A ported sub has a nominal roll off of 24dB/octave below Fb, so while it will still benefit from cabin gain that cabin gain is not enough to come even close to compensating for the speaker sensitivity loss.
Even where response in the single digits is concerned ported will have the advantage over sealed if the ported is tuned low enough, with an LLT alignment. As always the no free lunch rule applies. LLT cabs are extremely large even by ported standards.
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post #33 of 58 Old 02-24-2014, 11:05 AM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

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Originally Posted by ahmedreda View Post

Bill, for the longest dimension, do we use the length of the room or the diagonal (ceiling back left to floor front right)?
The longest dimension wall to wall, or floor to ceiling.

The theory and practical measurements coincide with the transition to a rising gain corresponding roughly to the longest dimension inside the space of the room, which will be the diagonal from lower to upper corner. Basic trigonometry gives the diagonal = (W^2 + L^2 + H^2)^0.5 (square root of the 3 numbers added up).

For the purpose you can call speed of sound ~1130 ft/sec, so the equivalent transition frequency is ~565 / diagonal (in ft). For an 18' x 24' x 8' example room (3456 cu.ft) this would be ~18Hz. The more cube/square the room dimensions, the sharper the transition corner. The more you have lossy/soft boundaries, the shallower the slope.
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post #34 of 58 Old 02-24-2014, 11:43 AM
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Quote:
Originally Posted by Mark Seaton View Post

Lots of sweeping generalizations being thrown about...

To quickly address the room gain question: As the low bass gain from a small confined space becomes greater in smaller rooms this quickly helps a sealed sub catch up precisely where a ported sub has it's advantage... near the tuning frequency. Modern auto-EQ systems have helped greatly to even the playing field, where the typically delivered response shape of commercial ported subs tend to be less complimentary to the gain observed in small rooms, where a well designed sealed subwoofer can easily compliment a small room very well.

Something to consider here... If you have a complimentary gain with a sealed subwoofer in a small room (specifically with designs that do not electronically cut the shallow roll off), you can see extension into the 8-14Hz range. With a ported subwoofer, adding more subwoofers means you only get louder at the same frequency range near and above the tuning frequency. With a sealed subwoofer delivering deep, in-room extension, adding more subwoofers from the start or in the future will increase the headroom at those lowest frequencies and make them more and more useful and noticeable. The only VLF limit to a sealed subwoofer is how loud it can get in room. With a ported sub the port tuning sets the hard limit.

Size vs. possible low frequency extension is another huge differentiator. No matter the power or driver available, moving lots of air down below 20Hz with a ported box requires a significant size/area port, and a significant size box to tune it low in. A very compact ported box tuned to 16Hz isn't happening without serious compromises in output capabilities.
Good show Mark. All "generalizations aside", I would add that it is possible to have a shallower roll off than 12dB/octave and I think that what LLT strives for in extension, comes at the expense of efficiency higher up the FR and elevated distortion from about 20 - 30Hz. We see this in Ricci's test of the FV15HP. It is possible to utilize high Sd in a small footprint even if Xmax is somewhat reduced. I personally believe that there needs to be less emphasis on crazy Xmax and more emphasis on designing better all-around high Sd drivers [21" especially] that can work in smallish cabinets. Only pro-sound drivers allow you to realize this currently, with high BL/low qts.

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post #35 of 58 Old 02-24-2014, 01:06 PM
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Originally Posted by shadyJ View Post

Everything else being equal, a sealed sub is smaller and lighter. It's also a simpler design to build than a ported, for those who go with DIY. Ported subs tend to have longer decay times and more group delay, so sealed can have a tighter sound. For those who listen to music, many of these ported subs offer no advantage since many of them are tuned to 20 Hz. Porting doesn't offer much mid or upper bass advantage to subs tuned that deeply, and since music doesn't dip below 40 Hz very often, porting just doesn't help in those circumstances. Also, as was mentioned above, sealed offers better protection for the driver, everything else being equal. Those are a few advantages that sealed have over ported. Another advantage of sealed is for those who chase after super deep bass, the lower teens and even single digit frequencies. Ported rolloff is usually pretty sharp, and doesn't cough up much output below its tuning point. Everything else being equal, a sealed sub will offer more output below a ported sub's tuning point. This diagram explains the difference, sealed being the blue line:



To get any real output at those deep frequencies, you need a bunch of very serious sealed subs, but at least it is achievable with sealed, whereas it can not be done at all with ported.

One word: equalizer. The difference in response between ported and sealed boxes is the influence of the box which is can be thought of as being an equalizer or if you will, an unequalizer. Take a hair of the dog that bit you! ;-)

Another viewpoint:

Here's the response of a subwoofer taken 1" from the apex of its driver:

(http://www.hifizine.com/2011/06/bass-integration-guide-part-1/)



All response seems to be below the measurement threshold by 150 msec

Here is the in-room response of that sub in a system at a listening location:



At 18 and 47 Hz more or less, the response is still going strong after 300 mSec.

Clearly the room has primary responsibility for perceptions like ""tightness" or "speed".
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post #36 of 58 Old 02-24-2014, 05:44 PM
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 I bet the SB Ultra 13 would be plenty in the typical UK sized living room too.
 

Would that be in England, Northern Ireland, Scotland or Wales?

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post #37 of 58 Old 02-25-2014, 11:20 AM
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Sound & Vision happened to have an article about this issue of sealed vs. ported just recently. Apologize if it's already been posted:

http://www.soundandvision.com/content/subwoofers-guts-and-glory
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post #38 of 58 Old 02-25-2014, 12:40 PM
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I can tell you why I went with a sealed subwoofer. The reason is that I'm a beginner at building subs and a big advantage of sealed subs for builders is that they don't require tuning like ported subs. In other words, the enclosure measurements aren't critical. I got a great sounding product on the first try. Those of us with sealed subs seem to be in the minority, however. Most people prefer the efficiency and extension of the ported subs.
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post #39 of 58 Old 02-25-2014, 01:05 PM
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When I had a dedicated room, sealed subs leveled the playing field against vented alignments I also had. On a one to one basis, sealed IMO will have a lot of ground to make up over a ported box using the same driver. Myself, I've never used one sub so I currently have 8) sealed 18s in an open living room and still get loads of bass that you feel at the deepest frequencies.
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post #40 of 58 Old 02-25-2014, 01:15 PM
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That said, I'm still looking to experiment with some vented alignments to hear/feel potential differences in the bass presentation.
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post #41 of 58 Old 02-25-2014, 03:12 PM
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Originally Posted by gpmbc View Post

When I had a dedicated room, sealed subs leveled the playing field against vented alignments I also had. On a one to one basis, sealed IMO will have a lot of ground to make up over a ported box using the same driver. Myself, I've never used one sub so I currently have 8) sealed 18s in an open living room and still get loads of bass that you feel at the deepest frequencies.
I will be very happy having your kind of bass now, Greg smile.gif
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post #42 of 58 Old 02-25-2014, 03:47 PM
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Originally Posted by Mike Butny View Post

If you want High Fidelity sound stick with a sealed sub, usually 12inch. IMO, sealed subs hit harder and tighter.

All of this is wrong. Sealed subs don't hit harder and are not tighter. The system design of the sub woofer effects the subs ability to play accurately. Further drive size has no influence on accurately in the sub woofer range. The ability of the driver to play accurately is as I a said a function of the system design and the quality and design of the driver. For example bad designs choices such as, too little amp power, too small or too large of an enclosure, a motor design that is not right sized for the driver, or even a high pass filter executed poorly can effect how "tight a system sounds. We also have to remember room modes also play a role.

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post #43 of 58 Old 02-25-2014, 03:51 PM
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Also just a point to anyone who wants the nice natural roll off a sealed sub woofer. You should know that some companies place high pass filters that filter out content below a certain frequency. What that means is you won't get the extended response. For example The JL audio sub woofers have a steep high pass filter to prevent over excursion downlow. On the other hand designs like the Seaton Submersive, The PSA Triax and XS30, the Funk audio 18.0 and others don't. If you going to buy sealed make sure the manufacturing your buying from isn't using a high pass filter.

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post #44 of 58 Old 02-25-2014, 04:01 PM
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Originally Posted by oneeyeblind View Post

All of this is wrong. Sealed subs don't hit harder and are not tighter. The system design of the sub woofer effects the subs ability to play accurately. Further drive size has no influence on accurately in the sub woofer range. The ability of the driver to play accurately is as I a said a function of the system design and the quality and design of the driver. For example bad designs choices such as, too little amp power, too small or too large of an enclosure, a motor design that is not right sized for the driver, or even a high pass filter executed poorly can effect how "tight a system sounds. We also have to remember room modes also play a role.

I was waiting for someone to comment on that misnomer. smile.gif

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post #45 of 58 Old 02-25-2014, 06:56 PM
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Originally Posted by Bill Fitzmaurice View Post

Where subs are concerned group delay is moot; if you were to hear it the speaker would be so flawed that it would be unusable. As for 'tightness' and 'speed', those terms don't have any real meaning with respect to subs, and are typically used by those who don't know what technical term does apply to whatever it is that they're trying to describe. As for the slower roll off of sealed, much is made of that, but again, it's only apparent in its effect well below 20Hz, making it a moot point as well in the vast majority of cases. If you're trying to reach the single digits then sealed or IB is the way to do it, but the number of speakers and the amplifier power required to realize it at worthwhile levels is far beyond what the average budget would allow, let alone WAF.

You write so much like Tom Nousaine. A compliment.

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post #46 of 58 Old 02-26-2014, 06:47 PM
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Every time this subject comes up over the years, someone posts a computer model of a driver in a ported box vs the same driver in a sealed box. There's little to be gained in an exercise that chooses a driver at random to examine the differences of that driver in ported vs sealed alignments. Take, for example, the driver used to model the posted comparison and put it in a horn to show the limitations of the horn alignment and someone will immediately jump in to tell you the driver isn't suited to a horn and the box, horn length, flair, amp wattage, etc. are all wrong for the example.

I went to Josh Ricci's excellent treasure trove of measurement data and picked one of the top available ID ported subs vs one of the top sealed DIY drivers to get a better picture of the differences.

I selected the UXL-18 driver in a sealed box vs the Rythmik 15" ported sub in 20 Hz tune. They're both in about the same sized box and both very good subs, one ID and the other DIY. Both cost about the same, including time and materials in the case of the sealed DIY sub.



First, the notion that room gain begins at a frequency whose wavelength is equal to 2X the rooms longest dimension is a perpetuated myth based on no evidence I could ever find from actual data. Over the years, I've gathered data from dozens of members' in-room measurements and matched those results against the known outdoor measurements of the subs they used and derived their room gain profiles from that gathered data.

In the top graph, you'll see the room gain profiles of 7 well-known members. The rooms of the noted members vary in size from 2,000 cubes to over 6,000 cubes. Some of the rooms are closed off and some are wide open to the rest of the house. Some have one or more doors and some posted measurements were taken with those doors opened vs closed, etc. Yet, we clearly see a room gain profile spread that is far removed from the longest dimension X2 theory. In fact, they are +/- 2dB similar.

Room gain begins in the 30-40 Hz decade and rises an average of +7dB/octave below that point. There are resonances and room boundary transmission loss differences that can alter that result in narrow bands below 30 Hz, but the evidence as to where room gain begins and how it proceeds is clear, and the gain continues until the electronics signal chain roll off becomes dominant at the extreme low end.

Taking the outdoor measured basic responses of the 2 subs in my example and applying the average room gain profile to both shows the basic projected in-room response difference. I then added a +6dB L/T boost to the sealed sub and used EQ to flatten the ported subs humped response at tune (which results from any sub whose native response is flat to below 30 Hz, where room gain will bump it above flat accordingly). I also showed the altered in-room response before and after the typical signal chain-induced roll off in the case of the sealed sub. The ported sub, of course, rolls off above the signal chain roll off, so no such effect there to show.

Since it's not recommended for the health of any ported alignment to boost the low end below tune, the difference in-room becomes quite dramatic (shaded area).

The only way to get more extension from a ported sub is to dramatically increase the size of the enclosure and port, both of which will grow exponentially as tune point decreases, the practical limit of which is slightly above 10 Hz in a very, very large box with a huge diameter port. SVS, Hsu and Rythmik offer lower tunes by blocking ports, but an undersized port will compress very early and with the associated chuffing noises. This will result in a drastic difference in their basic responses vs the response when pushed to their higher frequency playback capabilities.

The bottom graph is my own sealed subs native, L/T'd and in-room measured responses with a quick guide to creating your own room gain profile, for anyone who's interested.

The basic advantages of sealed are:

1) Much smaller package allows for much higher number of multiples of subs and placement options. Multiples of sub are required for a smoother in-room response and if there is any hope to reach clean playback at reference levels.
2) A 2nd order roll off that can be controlled through mechanical means side-stepping the need for electronic driver protection methods which alter the roll off order.
3) Signal shaping adaptability for flat in-room extension to the bottom of the signal chain.

That's it in a nutshell. If you want to fit enough firepower for full content playback at reference levels, sealed is the only option aside from Thigpen's Rotary Woofer. Ported (and PR'd, horn, transmission line, bandpass... any resonant system) simply will not get the job done.

All subjective descriptions of differences in subwoofer SQ are the result of distortions in the form of excessive (audible) harmonics, non-flat response, house curves, bumped SW trim and early roll off vs flat-to-single digit response.
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post #47 of 58 Old 02-26-2014, 08:19 PM
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Just a heads up Bossobass is a sealed sub evangelist and has almost always knocked ported subs. Take his posts with a grain of salt. He also did / dose sell custom subs that where sealed and has a vested interest in that style of sub.

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post #48 of 58 Old 02-26-2014, 08:28 PM
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Another way to look at the sealed vs ported from my perspective is, if you can put extremely high quality DIY sealed subs together, and put lots of them in your room, with gobs of power, you can get superb low frequency extension for movies.  If you have $600-$1k to spend on one premade sub, you are not going to get strong performance for movies with a sealed sub unless you get plenty of room gain, and a ported sub will have much higher output under 30 Hz.


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post #49 of 58 Old 02-26-2014, 09:09 PM
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Quote:
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Just a heads up Bossobass is a sealed sub evangelist and has almost always knocked ported subs. Take his posts with a grain of salt. He also did / dose sell custom subs that where sealed and has a vested interest in that style of sub.
It is not a knock. The limitations of a vented alignment are clearly illustrated. Bosso simply has a preference for as much of the signal as can be delivered. Sealed is the best way to do it, and without the silly limiters and highpass filters put on many commercial offerings.

You have to admit that vented cannot get as low. Stupendous output? Yes, but that will be an advantage only realized when one is financially constrained. Is the material below 10Hz relevant? You will have to consult the master bass list on this site, but the collection is pretty cogent on matters below that threshold. Some will choose to dismiss such matters, and it will likely include those who don't have the capability. This is admittedly rather caustic but if the shoe fits, wear the wig too...tongue.gif
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post #50 of 58 Old 02-26-2014, 09:50 PM
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Quote:
Originally Posted by oneeyeblind View Post

Just a heads up Bossobass is a sealed sub evangelist and has almost always knocked ported subs. Take his posts with a grain of salt. He also did / dose sell custom subs that where sealed and has a vested interest in that style of sub.
I'm sure Bossobass can defend himself if he chooses to, however...

To my knowledge @bossobass has not himself made that public knowledge on AVS. I believe he probably deliberately avoids mentioning it, unless responding to a direct question. Also, in the year that I've been following Bossobass' posts, he has never made any promotional linkage between the content/topic of a post and product(s) he sells. In addition, there's no mention of it in his avatar, signature or member profile.

.
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post #51 of 58 Old 02-27-2014, 08:38 AM
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What anyone prefers or sells has nothing to do with the question asked in the OP nor the answer I gave.

Again, my post contains 2 main points:

The theory that room gain begins at the frequency whose wavelength is 1/2 the rooms longest dimension is not true in any case I've examined. This goes to the general myth that a sealed sub is better in a small room and a ported sub is better in a large room. This is important information when searching for the right system for your listening entertainment. Some members change systems like most of us change socks, but the majority tend to prefer to nail it out of the gate and move on.

The 2nd point sums the difference between resonant systems and sealed as it pertains to movie soundtrack reproduction... "...for Home Theater".

As always, I back what I say with data and present it in picture form. It takes lots of my time to process the data from many sources, scale it in a normalized fashion and present it to whomever may be interested, FWIW.

I appreciate the support but there's nothing to defend in my post. I already know the information, I've never tried to sell anything to anyone on this or any other forum and have never jacked a thread about ported subs to "knock" the ported alignment. All resonant systems have a price to pay for added efficiency across a small slice of the SW bandwidth.

The poster who decided to add nothing to the thread is the main reason there is less and less science in AVScience forums.
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post #52 of 58 Old 02-27-2014, 08:50 AM
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Thanks very much for the technical content.

I am curious about the 7 dB/octave figure for room gain as that is a very odd value. Any idea where that comes from? Is that purely empirical for the average room?

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post #53 of 58 Old 02-27-2014, 09:17 AM
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The poster who decided to add nothing to the thread is the main reason there is less and less science in AVScience forums.


+1

Dave, when I first set out to rally the troops in convincing David and Allen to create a separate forum for the DIY group, it was because I saw a lot of individuals who had a thirst for knowledge and members who possessed that knowledge was willing to share it, even if sometimes it was more subjective than objective. If it weren't for you and a slew of other vets on this site, we wouldn't be where we are today (Fact). My hat goes off to members such as yourself and others, and I'm grateful (and teary eyed) that there's such a place like AVS to come to. As you can see I rarely post, as my duties with AVS were different and unfortunately didn't have the time to do so.cool.gif

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post #54 of 58 Old 02-27-2014, 10:01 AM
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Originally Posted by DonH50 View Post

Thanks very much for the technical content.

I am curious about the 7 dB/octave figure for room gain as that is a very odd value. Any idea where that comes from? Is that purely empirical for the average room?

The theoretical number of +12/octave has been mentioned many times over the years. I have tended toward actual data vs theory as a rule over the years. 7dB/octave is the average of around 30 rooms I've nicked the posted data from over the years.

The differences in gain per octave are the result of varying transmission losses through boundaries.

I've always hoped someone with data crunching spreadsheet skills would address the subject further by creating a metric for boundary transmission losses for HT, since there are not that many variations in boundary construction. The numbers for that are harder to come by <100 Hz, so there would be some effort involved to tackle that. But, it would allow the average enthusiast to take the theoretical number and apply a multiplier according to the construction method of his specific boundaries and approximate his room gain rate.

Bottom line is that guys like MKTheater get a bit more because his walls and floor are masonry and guys like me get a bit less because my walls and floor are wood frame covered with plywood and or sheetrock.

If you know your room gain profile and approximate boundary transmission losses you then know what native FR curve best suits your room and how many subs will be required to satisfy your preferred listening levels.

A good case study is that of member notnyt's story. He began with big horns. He moved to a larger and higher powered sealed system and gained around 2 octaves of in-room extension. He has recently moved to a 15 Hz tuned ported version of his sealed system. In that move he gave up an octave of extension and a lot more space for the much larger ported enclosures. He augmented the extension loss with Crowson shakers and he gained 6-10dB of output at tune. I refer to those sorts of examples because Rob is an engineer with a very high level of skill, he has carefully documented all 3 systems in the same room, which includes accurate measurements and his subjective comments are coherent enough for a dense guy like me to make sense of.

You can check it and similarly great systems docs out in the DIY forum.
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post #55 of 58 Old 02-27-2014, 10:03 AM
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Originally Posted by V.X.Donique View Post

+1

Dave, when I first set out to rally the troops in convincing David and Allen to create a separate forum for the DIY group, it was because I saw a lot of individuals who had a thirst for knowledge and members who possessed that knowledge was willing to share it, even if sometimes it was more subjective than objective. If it weren't for you and a slew of other vets on this site, we wouldn't be where we are today (Fact). My hat goes off to members such as yourself and others, and I'm grateful (and teary eyed) that there's such a place like AVS to come to. As you can see I rarely post, as my duties with AVS were different and unfortunately didn't have the time to do so.cool.gif

I remember and am eternally grateful. Separating the 2 groups has had its down side but the upside has been priceless to accumulated knowledge and the ultimate success of both forums.
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post #56 of 58 Old 02-27-2014, 10:28 AM
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I remember and am eternally grateful. Separating the 2 groups has had its down side but the upside has been priceless to accumulated knowledge and the ultimate success of both forums.
Always good, documented info Dave and it is always appreciated. I have always thought of the DIY as the deep and SBT as the shallows as it were. That is not meant to be condescending but sometimes one can feel like a fish out of water away from the former. It does seem that the more one learns, the more one encounters observations that contradict held theory or generalizations. I'm an outside the box type of bloke, so "usually" I will welcome challenging ideas, even if I do resist them initially. I also have a weird proclivity to choose the path of MOST resistance. As such, nothing I ever do is done the usual way. That extends to many things beyond subwoofers I'm afraid. Between you Dave, Mark Seaton, and even the notorious Steve Callas, I have learned much over the last nine years and hope to grasp even more in the future.wink.gif

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post #57 of 58 Old 02-27-2014, 11:55 AM
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Quote:
Originally Posted by bossobass View Post

Quote:
Originally Posted by DonH50 View Post

Thanks very much for the technical content.

I am curious about the 7 dB/octave figure for room gain as that is a very odd value. Any idea where that comes from? Is that purely empirical for the average room?

The theoretical number of +12/octave has been mentioned many times over the years. I have tended toward actual data vs theory as a rule over the years. 7dB/octave is the average of around 30 rooms I've nicked the posted data from over the years.

The differences in gain per octave are the result of varying transmission losses through boundaries.
< elided >

You can check it and similarly great systems docs out in the DIY forum.

Thanks! I have seen 6 - 12 dB/oct and often used 6 dB/oct as a rule of thumb for "real" rooms but have not been involved with that side of the business for decades. My vague memory was 12 dB for perfectly reflecting and 0 dB for perfectly absorbing.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #58 of 58 Old 02-28-2014, 09:10 AM
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There's some different examples of transfer functions here too.

http://www.nousaine.com/pdfs/Monster%20Bass.pdf

Tom V.
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