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-   -   Active 3 Way vs Active 2.1: Too many alignments and too may questions. (http://www.diyaudio.com/forums/multi-way/55916-active-3-way-vs-active-2-1-too-many-alignments-too-may-questions.html)

goldyrathore 22nd April 2005 12:52 PM

Active 3 Way vs Active 2.1: Too many alignments and too may questions.
 
Hi,

I am about to build an active speaker system primarily for music. I like detailed highs, slightly relaxed mids and tight bass (with slight punch) and good extension.

My room is untreated; size is about 250 cubic feet.
Placement: Left speaker will be close to one corner of room. Right will be about 3 ft away from the other corner close to the wall.

The have purchased the following drivers for this project:

Tweeter: Vifa D25 aluminium dome.
Midrange: 5.25” midbass (fs=57Hz, Qts =0.48, Vas = 20 lts, Xmax = 2 mm, Power = 30W RMS)
Subwoofer: Two 12” subs (fs=27Hz, Qts = 0.48, Vas = 155 lts, one way Xmax = 6mm, Power = 100W RMS).

I am in a dilemma with the alignment for the sub drivers. The following are the combinations I have in mind

1) Fullrange floorstanders: TM (sealed) on the front. Side firing sealed sub. Separate enclosure for the sub inside the floorstander. Maybe thin layer(3mm-4mm) of sand ’ween the boxes to isolate them. Too sad, I only have about 28-32 ltrs for the sub. Can I use LR correction since I have 2 subs? What are the other advantages of stereo subs? Can I get the distortion cancelling effect by mounting one of the subs the opposite way? (Electrically out of phase but acoustically in phase, Of course).
The subs in this case will be far apart but they will be equidistant from the listening position. Will distortion cancellation work in this case?

2) Stereo bookshelf/satellites (sealed) with single sub.
a) Two sub drivers mounted opposite way in the same sealed enclosure(Compound: Push-Pull). The advantages are reduced distortion due to push-pull configuration. Vas will double in this case so can I use a combination of stuffing, LR correction and a variovent to get the box size within the bounds of sanity?
b) Two sub drivers in isobaric sealed configuration. The advantages are reduced distortion due to isobaric configuration. Vas is halved but the downside is that the drivers donot have enough xmax so clean SPL will be an issue.
c) Two drivers in isobaric vented. The advantages are reduced distortion due to isobaric configuration. Vas is halved, so I can tune lower and extension will be greater but I have no idea how low should I tune considering the room gain.

I have no idea as to how different alignments will sound.
Can we have a discussion to help me arrive at a good trade-off and choose the right alignment?

Thanks in advance,
Goldy

AndrewT 22nd April 2005 02:42 PM

Hi,
what is the difference between isobaric and compound push pull?
The main advantages in separating the sub from the satelite is vibration (intermodulation) isolation and ability to locate each part in nearer ideal location.
Mid & high away from early reflection i.e. out in the room and frequency absorbers at the obvious reflector positions (carpet on the floor etc)
Bass will always reflect unless the absorbers are very thick and most of the room surfaces are also well within a quarter wavelength. So instead use the reflection to best advantage; stick the enclosure up against the wall and make it look like a table! You are now driving only a quarter space & get increased efficiency out of your smallish xmax. You can put it in the corner (1/8 space) but many say this sounds too exaggerated driving room modes too well. It also puts it too far away from the listening position complicating the xover phases.


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