Hello
I have a REALLY bad center in my surround setup that i have never had the "time" to replace. So now im going to build a new one, im not a very good diy but as it cant really get any worse im giving it a shot anyway
I have 4 of these The Madisound Speaker Store
My first thought is to put them in a 15 liter box with 2 ports 39mm diameter and 102mm lenght, at least thats what WinISD is suggesting
Strassacker: Speaker Building, Components
The TR44 is 39-44, im guessing i can put in 39mm in WinISD ?
The local wood shop have 10 – 12 – 16 – 19 mm MDF, wich one would you prefer ?
What would you use as damping ? im thinking this could be an option: LYDDÆMPNINGSPAP AS. 4. - køb på nettet og få leveret til døren
Anything else I should know before starting the project ?
I have a REALLY bad center in my surround setup that i have never had the "time" to replace. So now im going to build a new one, im not a very good diy but as it cant really get any worse im giving it a shot anyway
I have 4 of these The Madisound Speaker Store
My first thought is to put them in a 15 liter box with 2 ports 39mm diameter and 102mm lenght, at least thats what WinISD is suggesting
Strassacker: Speaker Building, Components
The TR44 is 39-44, im guessing i can put in 39mm in WinISD ?
The local wood shop have 10 – 12 – 16 – 19 mm MDF, wich one would you prefer ?
What would you use as damping ? im thinking this could be an option: LYDDÆMPNINGSPAP AS. 4. - køb på nettet og få leveret til døren
Anything else I should know before starting the project ?
Four fullrange drivers in a row is going to produce comb-effect in the horizontal plane.
With 15 liter box group delay is too big. Use 10 liter box with two TR44 tubes.
19 mm MDF is fine.
For damping use cheap polyester material about 1 inch thick, it come in big rolls like this
HOBBS POLY 6 oz. 96" Batting 25y
but you need only small amount to cover all internal panels of the loudspeaker box, except the front one. Use staples or glue to fix it to the panels.
With 15 liter box group delay is too big. Use 10 liter box with two TR44 tubes.
19 mm MDF is fine.
For damping use cheap polyester material about 1 inch thick, it come in big rolls like this
HOBBS POLY 6 oz. 96" Batting 25y
but you need only small amount to cover all internal panels of the loudspeaker box, except the front one. Use staples or glue to fix it to the panels.
See pages 6 and 7 for comb-filter effect:
http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/01/line-array-paper.pdf
Pictures are for 16 loudspeakers mounted in a vertical column, but the same is for a horizontal and it is similar for 4 loudspekers.
Peak group delay of 15ms is big too, but it is better than 17ms. Another benefit is less material for the box and less bulk, the 10 litre bass-reflex box is only 2/3 of the 15 litre box. The sealed box has the lowest group delay and the best sound.
http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/01/line-array-paper.pdf
Pictures are for 16 loudspeakers mounted in a vertical column, but the same is for a horizontal and it is similar for 4 loudspekers.
Peak group delay of 15ms is big too, but it is better than 17ms. Another benefit is less material for the box and less bulk, the 10 litre bass-reflex box is only 2/3 of the 15 litre box. The sealed box has the lowest group delay and the best sound.
hmm okay i think i understand comb effect a bit more now, but that should be a problem with almost all speakers have more than 1 speaker covering the same frequencies ?
In a 10 liter cabinet the 2 ports should be 17 cm, thats a lot in a 10 liter cabinet where you want 4 speakers in a line. I will take a look at it though.
I did consider sealed it just need a 49 liter box to get a QTC of 0,7 and i do like the extra OOMPH in a ported cabinet. Not saying it has to be ported though
Im open to any suggestion and very thnakful for your responses
In a 10 liter cabinet the 2 ports should be 17 cm, thats a lot in a 10 liter cabinet where you want 4 speakers in a line. I will take a look at it though.
I did consider sealed it just need a 49 liter box to get a QTC of 0,7 and i do like the extra OOMPH in a ported cabinet. Not saying it has to be ported though
Im open to any suggestion and very thnakful for your responses
Get one more driver and wire them up as a Bessel array to deal with the comb filtering same as is sometimes done for consumer soundbars. The downside is that the array will only be as efficient as a single driver: https://www.google.com/search?q=bes...e.com%2Fsd%2Fpaulkemble%2Fsoundf.html;336;287
GM
GM
Then you're 'caught between a rock and a hard place' since the CC is the dialog channel and any comb filtering will 'smear' them enough to hear it at least through our most acute hearing BW centered at ~2 kHz.
The only option AFAIK that will work IME, though only might be acceptable to you since we all hear the same, yet not so much, is to do what the pioneers of audio/cinema sound did due to the extreme collapsing directivity of the ultra-wide BW horns required to play loud enough in large spaces, i.e. put speakers above, below the screen in a 'cross-fire' layout [left channel aimed at the right 'sweet spot' and vice versa] with each top/bottom pair focused to sum at the LP.
The downside is you'll only get the extra driver efficiency as they will obviously be too far apart to couple acoustically for all but the lowest frequencies around the XO point unless you have a small screen.
GM
The only option AFAIK that will work IME, though only might be acceptable to you since we all hear the same, yet not so much, is to do what the pioneers of audio/cinema sound did due to the extreme collapsing directivity of the ultra-wide BW horns required to play loud enough in large spaces, i.e. put speakers above, below the screen in a 'cross-fire' layout [left channel aimed at the right 'sweet spot' and vice versa] with each top/bottom pair focused to sum at the LP.
The downside is you'll only get the extra driver efficiency as they will obviously be too far apart to couple acoustically for all but the lowest frequencies around the XO point unless you have a small screen.
GM
Yes, comb-filter effect is big problem with all (center) loudspeakers with 2 or more same loudspeakers (mounted on the flat front baffle) covering the same frequency range.hmm okay i think i understand comb effect a bit more now, but that should be a problem with almost all speakers have more than 1 speaker covering the same frequencies ?
In a 10 liter cabinet the 2 ports should be 17 cm, thats a lot in a 10 liter cabinet where you want 4 speakers in a line. I will take a look at it though.
I did consider sealed it just need a 49 liter box to get a QTC of 0,7 and i do like the extra OOMPH in a ported cabinet. Not saying it has to be ported though
If you are the only listener in the room, build box with the curved (arc) front baffle, arrange 4 loudspeakers tightly together on the arc. There is no comb-filtering effect if the arc has radius equal to the distance from you to the center loudspeaker.
In a 10 liter box with the same ports resonant frequency of the vented box will be a little bit higher, no problem with that, bonus is 1-2 dB more output from 70 to 200 Hz.
10 liter sealed box has Qtc less than 0.8, which is excellent also.
I am going to say this once and then go away. All of the above problems can be audible and the reason that I use a phantom center. No problems with SPL disparities. No comb filtering. No problem with finding space for an adequate sized speaker or settling for a too small speaker. Works for me out to ~30* off center. Beyond that I neither know or care. (Mains are currently A10.3's.
Bob
Bob
okay but almost all center channels i know of have 2 mids, i guess i have to go into the thinking box again
okay but almost all center channels i know of have 2 mids, i guess i have to go into the thinking box again
That is done for reasons that have nothing to do with sound quality - aesthetics and symmetry.
There are only a few ways that arrangement works, one is to cross over really low, and the other is to use a coaxial in the center like KEF do.
I use one of those speakers you have for a center channel in a ultra-nearfield gaming system and it goes plenty loud. If you cross it high enough, a single driver will go loud enough for moderate levels in center channel duty - you have to increase the center channel level in your receiver. Three of them wired in a power tapering array will still have low sensitivity, but excellent power handling. These are tough little suckers.
good point
theoreticly this should be even worse cause the mids will be farther apart ? at least thats my thought
Any two speakers producing the same frequency will suffer from comb filtering, simply placing them further apart does not lessen or enhance the problem, it just changes the frequencies and radiation pattern where this happens.
We encounter this all the time in stereo also, which is why the sound changes a bit when we move our head from left to right. It is made worse in multichannel systems hence it is up to the engineers to ensure that the sound does not suffer from combing. the only sound that stays fixed in space is the center, because that is how movies are made, with the actors in the center and the dialogue originating there. It is rare for the center to carry much more than speech, most of the powerful effects are purposely mixed to L/R to avoid loading the center.
In real life, this is not as important as it might seem unless you keep shifting your position or have audience beyond the speaker's horizontal dispersion arc. If the speaker manages a reasonable axial response, a small audience should be easily covered and intelligibility of dialogue should not be a problem. The issue with phantom center is that the response changes quite dramatically with horizontal angle, far more so than a conventional center unless the mains are really special. Thus some viewers at the edge of the stereo field will have problems. For a single listener, it doesn't matter whichever way you go.
We encounter this all the time in stereo also, which is why the sound changes a bit when we move our head from left to right. It is made worse in multichannel systems hence it is up to the engineers to ensure that the sound does not suffer from combing. the only sound that stays fixed in space is the center, because that is how movies are made, with the actors in the center and the dialogue originating there. It is rare for the center to carry much more than speech, most of the powerful effects are purposely mixed to L/R to avoid loading the center.
In real life, this is not as important as it might seem unless you keep shifting your position or have audience beyond the speaker's horizontal dispersion arc. If the speaker manages a reasonable axial response, a small audience should be easily covered and intelligibility of dialogue should not be a problem. The issue with phantom center is that the response changes quite dramatically with horizontal angle, far more so than a conventional center unless the mains are really special. Thus some viewers at the edge of the stereo field will have problems. For a single listener, it doesn't matter whichever way you go.
While I agree with Bob that a phantom CC can 'solve' the design/integration problems of a discrete CC [I use one], it's nothing but a mass quantity of euphonic comb filtering [i.e. stereo] and doesn't perform as well overall as a properly designed/implemented HT L_C_R mains system for movies, etc. mixed for them [excluding mono and stereo soundtracks].
Consequently, I prefer to offer up the various solutions to folks who ask about CC system design, but the reality is that most will not tolerate turning their living/family/bed room into a dedicated HT or even just going the 'extra mile' to do what it takes to make a proper CC to meet the needs of their particular app, so for the vast majority of them a phantom CC is really the only viable choice.
There have been so many threads on this topic that 'boil down' to this that maybe we ought to just have a 'sticky' thread telling folks this and be done with it.
GM
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