Hi-Vi B3N MTM Towers and MMTMM Center

[jsalbre]

I've decided for my project that I want to build 4 MTM towers, plus an MMTMM center channel, using the Hi-Vi B3N and an as yet undecided tweeter.

Towers:
Using the online ISD at http://www.linearteam.dk/default.aspx?pageid=newdriver with the specs for the B3N from http://www.partsexpress.com/pdf/297-428z.txt (vas: 0.62 l, Qts: 0.9, Fs: 114.5 Hz) I get a required vented volume of 0.6183 cu. ft. for 2 drivers.

A tower made of .75" at 5" x 7.5" x48" gives an interior volume of 0.646 cu. ft. Am I correct in guessing that the extra volume (0.026 cu. ft.) could be successfully filled up by the drivers, crossover and bracing, or is that too much or too little?

Center:

I want to base this off of the Cynosure (http://www.partsexpress.com/projectshowcase/indexn.cfm?project=Cynosure) but using the B3N (and same un-chosen tweeter) so it will match the towers.

Using the same specs as above but for 6 drivers I get a required vented volume of 1.8555 cu. ft, while the original design plans using the Tang Band W3-926S state a required vented volume of 0.5 cu. ft. I realize these are different drivers with different specs, but that just doesn't seem right to me. A box with the original height and width (4" x 24") made of 1/2" would have to be 47.5" deep. Am I missing something?

If someone with more experience would run over my numbers for the tower and center I'd be very appreciative.

Also any tweeter suggestions would help too!

Thanks a million!

 

[jsalbre]

Slight correction: The width for the towers was supposed to read 5.5", not 5".

 

[sreten]

Hi,

Venting any driver with Qts = 0.9 is pointless. Vas of 3" drivers is
around a litre, and around 2L to 3L sealed and well stuffed each
is what is required. 2L is minimum, > 3L fairly pointless.

/sreten.

 

[jsalbre]

Hi,

Venting any driver with Qts = 0.9 is pointless. Vas of 3" drivers is
around a litre, and around 2L to 3L sealed and well stuffed each
is what is required. 2L is minimum, > 3L fairly pointless.

/sreten.

So if I understand you correctly you're saying 2-3L per driver for a sealed box, so that would be 4-6L for the 2 driver towers and 12-18L for the 6 driver center, correct?

Would venting them negatively affect the sound quality or is it just the extra required size that makes it pointless?

I'm still thinking something is wrong with my numbers, as the required size for those boxes is still turning out huge.

 

[augerpro]

That's because these programs are fairly dumb. And once Qts gets above .707 the resulting "optimum" box gets unreasonable. You have to exercise some good judgement. Read the June 12 posting here: http://zaphaudio.com/blog.html

 

[jsalbre]

That's because these programs are fairly dumb. And once Qts gets above .707 the resulting "optimum" box gets unreasonable. You have to exercise some good judgement. Read the June 12 posting here: http://zaphaudio.com/blog.html

Whew, thanks Brandon. I've been beating my head against the wall trying to figure out what I was doing wrong.

So what kind of numbers would you say I should be considering when building sealed or vented enclosures with the B3N?

 

[bjorno]

jsalbre,

FYI:
Using the given driver data and suggested dimensions in a ported box, i.e. aperiodic damped tower speaker. See pictures 1(3) to 3(3).

b

1(3)

 

[bjorno]

2(3)

 

[bjorno]

3(3)

 

[jsalbre]

Wow, thanks bjorno!

I haven't the foggiest if those are good or bad results though, would you mind translating?

 

[sreten]

Wow, thanks bjorno!

I haven't the foggiest if those are good or bad results though, would you mind translating?

Hi,

Whilst aperoidic is the theoretically the best way to do it, it really does
not matter that much when they are to be filtered by an AV amplifier.

Take a generic 3" (like the B3S), Vas = 1L, Vb = 1/2/3L, Fs = 100Hz, Qts = 0.9.

The slight bump is incorporated into the BSC of the speaker.
Going from 1L to 2L makes as much difference as going 2L to 10L.

/sreten.

edit : also see june 12th : http://www.zaphaudio.com/blog.html

 

[aud1out]

Read Zaph note. Am I understanding correctly?

Ignoring room modes/interaction -
For low Qt drivers, do programs such as Winisd provide correct response?

Is there guideline for interpreting Winisd results (ignoring room)?
What are the relative Qt ranges?
How much BS should account for with each Qt?

Very high Qt (??) - ?
High Qt (above 0.707) - account for BS. How much hump - 6db?
Medium Qt (??) - allow for some BS - ?
Low Qt (??) - Winisd is correct?

Thanks.

 

[jsalbre]

Hmm, interesting graph, thanks sreten.

I'm considering switching the whole project over to mmtmm towers with an mmtmm center, still using the B3Ns of course.

Using 4 drivers wired up series-parallel as a 2.5 way I end up with an 8 ohm load again, keeping my receiver happy.

Any opinions here?

 

[sreten]

Hi,

For 2.5 ways you need to be careful you do not overcook
the BSC for the intended placement of the speaker. You
may need to get into power tapering of the drivers, i.e.
reduce the output of the outside drivers towards the
c/o point for partial BSC rather than roll them off.

/sreten.