Combining two W4-1320SIF in TL??

Anderskson

Member
2019-11-19 10:44 am
Hey guys! New to the forum and kind of new to building speakers as well. I was planning on building my first TL using a W4-1320SIF as driver.

Speaking in general terms, is there any rules/dos-and-dont´s regarding using two full range drivers in the same enclosure? Is it possible and what would the benefits/disadvantages be? Does the line need to be longer or shorter with two drivers?

Hope you can help me out :)

Thanks, A
 

zman01

Member
Paid Member
2011-02-04 11:35 am
Dhaka
Anderskson,

Some quick comments:

- For same tuning frequency for a TL/MLTL type cabinet, with 2 drivers the line length will remain same, but cabinet volume needs to be 2X. So cabinet needs to be deeper and/or wider. For bass reflex box with same tuning, 2 drivers will need 2x cabinet volume vs single driver.

- For 2 drivers, you will have more cone area, so theoretically that should increase your low frequency output; however with 2 wide-band (aka full range) drivers, there might be some comb filtering issues (loss of higher frequencies), specially if you are listening from closer distances.
 
I have used this trick with 3 inch drivers to compensate for the small size and it worked very well, I haven't tried it with two 4 inchers but the key it to put them as close as possible to each other. Another option not mentioned in the posts above is a dipole or a bipole - I don't remember which is the correct term since I am not particularly interested in these, but basically you have two drivers sitting in the same enclosure one behind another, one firing in the opposite direction (in phase or out of phase - don't know) and another configuration is the second one firing towards the ceiling (search for Castle Microtower).
By the way if norman bates says it didn't work that does not mean you should shy away from trying anyway - some thick cardboard, it should be done in about an hour and you can check how it sounds.
The advantages are these: extra sensitivity - plus 3 db (but you will have 1/2 or 2x impedance), so less energy consumption (less heat at the voicecoil) for same SPL, half the distortion, more dynamic sound/effortless sound effect, better behaviour in the low frequencies (not deeper, just better defined), higher max SPL. Your drivers will have to do half the effort for same SPL, this is were the advantages come from.
 
I have build several bipolar speakers with small full range drivers (in my case 4 or 4.5 inch drivers). The drivers are connected in-phase. You can search this forum for examples of my past work. The drivers have been placed on the front and rear baffle of the enclosure either back-to-back or in offset positions.

The drivers radiate in-phase for a bipole and create a broad polar radiation pattern. The sound energy essentially radiates into 360 degrees over the frequency band. Thus you have full energy within the room so reflections from the front and back walls could be of concern to listeners. Locating the speaker away from the walls by 3 feet or more would enable the listeners to hear the sound without reverb thanks to your ear/brain hearing only the first arrival sound. If you enjoy reverb, then you can space the speakers to achieve your preference.

Bipole speakers typically don't need baffle step compensation as you have sound radiating into full space all the time. Thus you can have near omni-directional sound within your room.

One shortcoming of a bipolar speaker is that the sound wraps around the enclosure so when the front to back distance reaches 180 degrees phase difference, then a cancellation can occur. My experience is that you might have a narrow 4-5 dB dip in the frequency response which may be audible. You can reduce or eliminate this dip via various methods.

The Castle Microtower is a form of a bipolar speaker which uses the distance from the top driver to the ceiling to mitigate reflected sounds.
 
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Anderskson

Member
2019-11-19 10:44 am
That’s great, thanks for all the input! I was looking at a simple baffle step calculator. One of the values to enter was amount of attenuation required. How do I get that Db value?

A 1.5 way speaker sounds like a good start. Do i put the speakers in series then? With the inductor between the two speakers? I feel like a noob..

Have a nice weekend guys!
 
I'd run the 2 drivers in parallel, but put an inductor in series with one of them.

Baffle shape size and wall distance are factors for what value.
Hopefully the impedance curve is relatively flat............

Bipolar.

Seeing the 400hz dip in stereophile's review of clairaudient 2+2 model (2 x 3" firing forward and 2 x 3" firing backward), see figure 3, and maybe the extra thump in the step response (figure 8), I'm not so sure it'd be for me.

Audience ClairAudient 2+2 loudspeaker Measurements | Stereophile.com
 
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