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Old 19th June 2004, 08:01 PM   #1
kspv is offline kspv  India
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Question "Seemless" Integration?

Some subwoofers are said to "seemlessly" integrate with the main speakers, and others are not. Scientifically speaking, what causes this feeling of "seemless" integration?

I have read in Soundstage archives by Doug Backburn that the cross-over point between a subwoofer and the main-speakers should atleast be twice that of the lowest frequency the main-speakers can produce, for a "seemless" integration. But others seem to have quite a different view, totally discouraging a broad frequency overlap between the sub and the main-speakers. Who is correct? Does a higher crossover setting cause "seemless" integration, or is it something else?

On a whole, subwoofers seem to be mysterious entities. Scientific data on things like causes of "fastness" and "slowness" of subwoofers, "seemless" integration of subwoofers with the main-speakers, directionality of sound in a subwoofer and its desirability, ideal cross-over point between the sub and the main-speakers, subwoofer placement etc., is scarce.

Any wisdom on these?
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Old 19th June 2004, 08:11 PM   #2
sreten is offline sreten  United Kingdom
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checkout the REL sub site for musings on the subject, sreten.
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Old 19th June 2004, 08:37 PM   #3
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Crossover points between drivers in general will always depend on the particular drivers used. For high power ouput systems, higher-order crossovers are generally preferred - for example in PA work, the crossovers tend to be fourth-order or greater. The steep slopes minimise the out-of-band energy that all of the drivers must reproduce, and the system can therefore play louder and cleaner.

However, some say that steep slopes don't sound as good - or seamless, as you've heard. For this reason, second-order crossovers are the most popular for home audio, because of their compromise between out-of-band stresses on drivers and quality of integration.

First-order slopes have their suporters, though these shallow slopes tend to be more rare. They require specific drivers which are able to produce very wide frequency bands without trouble - something that not everyone has. Making a full speaker system with only first order slopes would probably require four drivers, though it may be possible with three. Just don't expect to be able to make a two-way with them.

Anyway, back to your question. I'm not sure what Doug Backburn means by 'seamless' - since he's probably commenting on the sound from subjective tests, the word has little definition, if any, in this case. However, good integration between two drivers is (I think) largely due to phase-linearity through the crossover region. The crossover circuit design should be such that the drivers are in phase at the crossover frequency. If they're out of phase then a cancellation will occur, giving a dip in your frequency response. If the overall (i.e. combined) measured frequency response is flat through the crossover region, it could be said the integration is seamless.

'Fast bass' is a term popular with audiophile press at the moment, but lacks any significant theory and it is thought this mysterious quality, if it even exists, is more likely due to phase-matching in the crossover region, rather than anything to do with the subwoofer itself. It's akin to the never-ending debate over how much slew-rate in an amplifier is enough. Or the cables argument. Or the crossover-steepness argument (where no one type is really 'best', and all have their following). There will probably never be a resolution to it.

Sound from a subwoofer is basically non-directional - assuming you're reproducing stuff below around 100Hz, the humar ear cannot discern the source position by its standard ITD method. So don't worry about it.

Subwoofer placement is very important - though most people don't have the luxury to put it anywhere they want - subs tend to be rather large - so they generally end up in a corner. Such placement will take advantage of corner loading (which increases the efficiency of the subwoofer due to the room boundaries reflecting the sound) but will also give maximum excitation of room resonant modes (which is a bad thing, leading to a 'boomy' sound at the resonant frequencies). Placing the sub out into the room will tend to excite less room modes, but will decrease the efficiency of the unit.
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Old 19th June 2004, 09:49 PM   #4
Ken L is offline Ken L  United States
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Default My humble and unscientific observation is that higher orders

may be desirable in a sub -

Such as 4th order, 8th order or even 52DB ( 8.5??) slopes may work better at the frequencies a sub would be crossing at.

A number of plate amps use 2nd order - but it may be difficult to get good integration

Seamless integration depends on a variety of factors - phase, behaviour of the individual drivers in their enclosure ( or horn, or baffle), driver levels, crossover slope. lobing, and other factors.

Seamless integration - is not the same as the Holy Grail - but it is sure kin to it - it is quite difficult to achieve - but it is doable _grin_


Quote:
Originally posted by kspv
cross-over point between a subwoofer and the main-speakers should atleast be twice that of the lowest frequency the main-speakers can produce
perhaps you or he mean lowest frequecy that it is "flat" to" or "flat within 3 DB" or some additional qualifier -_grin_

Even so - even if that was fully stated - there would be a bit more to it than that -

I think I read Doug Blackburns article on sub integration several times and believe it is probably one of the better tomes - if it is the one I'm thinking of it is an excellent read and guidance - however, I wouldn't consider it to be the sole source on the subject _big grin_ I do believe it is an excellent starting place and I learned a lot from it.

As to "fast bass" I'm in agreement with Wingfeather that this is simply a popular term -

A better and more descriptive term might be "fast transients" or "excellent transient speed" . In certain circles use of the term "fast bass" is likely to start intense discussions _big grin_

Nothing mysterious here that more surfing, reading and questioning won't clear up._smile_

Regards

Ken L
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Old 20th June 2004, 01:24 AM   #5
Bose(o) is offline Bose(o)  Canada
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I think of seamless integration as, not adding volume necessarily to what is already being reproduced from your speakers carrying the task of higher frequencies, but simply adding that extra octave or two below such speakers. In other words, lowering your cutoff frequency of the system as a whole.

Localization also adds itself to the integration of a subwoofer. If you can easily say that a subwoofer is playing, it's too loud (usually) or, it's placement within the room is degrading sound quality. For example, a subwoofer in behind you and off to the left will rarely integrate well unless matched with another sub and turned down a lot whereas you can make more use of your sub if it were in front of you. Since, many concerts I attend, the musicians (source) have always played in front of me then shouldn't your (source) subwoofer also play in front of you?

In addition to subwoofers being non-directional...they can be very directional. For example, you can hear whether it is louder left to right or front to back. So, if the subwoofer is closer to your ears than your speakers and on your left then the chances of directionality (localisation of the subwoofer) are greater. Then there is the time when the subwoofer is the only transducer that is able to produce a sound at a playable level in comparison to the other speakers in the system. In localisation I'm refering to a person being able to identify the general location of the subwoofer.

If at any time you can say, the subwoofer is over there and you are not pointing anywhere forward, you should continue the placement exercise of your subwoofer.
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Old 20th June 2004, 04:20 AM   #6
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Default The term is *"seamless"*, not*"seemless"*

Seamless integration is simply integration between 2 units without seans showing or any change of character or shift of "tone" to call attention to the fact that reproduction has shifted from one reproducer to another. In the case of subs, this is aided by ensuring that the sub is unable to be spacially located for **ANY** reason! If, under any circumstances you can locate and point to the location of the sub ,one or more (or all of the following) Are the culprits.
1) wrong Xo frequency for the sub. This MUST be determined by the highest freq the sub can NOT be located by, in YOUR room. The XO point must be kept at or below this freq. Generally 100 HZ or slightly below works, but NOT ALWAYS!
2) wrong match between units . If you have a ported main then ITS sonic characteristics are USUALLY best matched with a ported sub so the tone and character dont suddenly shift, calling attention to it. Sealed with sealed , etc. Again experiment.
3)steep enough XO that undue STRESS does NOT occur at XO, on BOTH drivers in the XO freq. area.
4) OK, only now can we talk about matching volume! The sub should(for music) fill in the bottom adequately, not become the focal point of the system. THIS is TOTALLY taste dependant.
5) Sometimes using all the above, a sub can STILL be located. Why ?
Is it rattling, Chuffing, wheezing,whistleing, or are the hard feet dancing on a hard floor making noise, is it too loud? In other words , search for noises that are occuring ABOVE the XO point, that can cause you to locate where the sub is!! I have expierienced all of these !

GREAT! now that it is*IMPOSIBLE* to locate the sub you can put it ANYWHERE IT SOUNDS BEST! And out in the room does seem to excite room modes less.
Use room treatment AND PLACEMENT of the speakers to further smooth responce.
Case in Point. Every new person I demo my system to asks "where are the Speakers?" this in spite of the fact that the 2 -12"Subs , 15"X24"X12", are on either side of the listening chair, 42 INCHES to each side!! They can see them but they think they arent playing cause they cant hear where the sound is coming from! It seems to come out of the front wall. The sealed subs are time aligned with the sealed sats as they are ALSO 42 inches away on about 40 deg either side in front. Its set up near field! NONE of the speakers can be located as they all dissapear! This is aided by the room treatment. The entire front wall is covered by Berber carpet 6'highX 18' long, set out from the wall 3 " on firing strips, forming a bass trap of 25 Cu. FT! There is an open window behind the carpet to act as a drain to prevent standing waves . And i only loose 3 inches from the depth of the room ! The carpet clears the floor by 3"as well. the sound is smooth as silk from bottom to top, and the subs are down 4DB @ 20HZ! The image is "to die for".
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Old 20th June 2004, 06:06 PM   #7
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Default adendum

A phase adjustment for the subs sometimes helps,but "in phase: is best in my room/setup. I use 2 subs (highly recomended) and @ the XO point I use,100HZ, they act as a line source im sitting in the middle of As im 5' from the front wall (at my desk), and 7' from the back wall, 8' (or 19' counting kitchen) from 1 side wall and 10 ' from the other, and 42" (near field) from both the subs and sats, room reflections are simply near inaudibility allowing the ambiance of the recording venu to shine. This setup is very much "you are there", as opposed to "they are here". The room is irregular, an advantage. The room is 18' long , a 4' high counter, then another 11' (kitchen) X 12' deep, with 8 1/2' ceilings. My XO is a PLLXO @ 12 DB/ octive and the sys. is of course, bi amped. I consider bi amping to be MANDATORY for good integration, as it is so flexible, and solves so many probs. Matching the Efficiency of the subs / sats , among other things ,is simply a matter of turning a knob. The switch in radiation from sats to subs is undetectable. The Image replaces the front wall
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Old 4th July 2004, 08:06 AM   #8
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Default Subwoofer XO localization and "fast bass"

Subwoofers are usually very easy to intregate in my opinion. Because most subwoofers have a seperate amplifier and are not merely passive subs an active crossover is typical. This will avoid the phase problems as far as i know. XO frequency needs to be below 100hz for sure. I personally think it is better to have mains that have flat response at least to 50hz and crossing over the sub lower. If equalization is easy to come by flat response can be achieved easily even with the sub/mains overlapping. It seems to me that when the subs and mains overlap it gives a higher localization of the bass from your main speakers where it really ought to be. Lower frequencys cannot be truely localized anyhow due to the physics of a low frequency wave. Higher frequencys can be localized using aural intensity differences and i would presume phase shifts between ears. bass waves wrap right around your head as if it werent even there causing no difference in intensity difference between ears, and due to the extremely long wavelengths no noticable phase difference. as the frequency gets higher it comes to a point where it is easily localized. I think a thread about sound localization is in hand. Im going to start one. as for "fast bass" it could mean anything. its a stupid term if you ask me. the speed of sound dont change depending on your woofers, so one woofer wont have faster bass than another. faster transients i guess? whoever made it up coulda just said good transient response and we'd know exactly what it meant
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Old 5th July 2004, 12:49 AM   #9
Bose(o) is offline Bose(o)  Canada
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Low frequencies can not be easily localised because of psychoacoustics, the perceiverence of sound. Room modes, nulls, etc. occur because of the physics part.

Subwoofers CAN be localised....for sure. Since, your subwoofer doesn't necessarily produce just low frequencies or, at least the non-localisable frequencies. There are harmonics and resonances that usually accompany the sound. This may come from mechanical distortion, air leakage (seapage), amplifier distortion and many more.
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Old 5th July 2004, 01:53 AM   #10
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Default Re: The term is *"seamless"*, not*"seemless"*

Quote:
Originally posted by kspv
Some subwoofers are said to "seemlessly" integrate
Quote:
Originally posted by THOR
Seamless integration
Sometimes what we think of as an incorrect spelling might not be.

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