First MTM/MMT build -sanity check

[mondogenerator]

Hi,

For ages now I have been using some repurposed upcycled boxes to house my TV/Movie speakers.

They use Fountek FW100B 4" midwoofers

https://www.google.com/url?sa=t&sou...FjAAegQIAhAB&usg=AOvVaw1ZutxADGVERa9BcsRLQaus

I have 2 pairs of these woofers, and so I am planning to build either MTM or MMT(2.5way) with them.

In MTM, the C to C distance between the two woofers will be about 8 inches.

So I'd guess, (13500/8)/4 = about 400Hz.

I guess I need to low pass lower than this?

I'm planning on using Tangband W3 1285SG as midtweeter, which *should* be OK with a 400Hz high pass.

I am intending, in the beginning at least, to use as low order passive XO as I can, probably 2nd order, though I'd prefer to keep it simple, as possible, without huge compromise.

It seems with a 400Hz XO, I may just be able to get everything within 1/4 wavelength

In TMM, the 2nd woofer would be used as 0.5 way, providing BSC support.

I feel this may be more complex than it seems as the low XO at 400Hz will be below BSC frequency, which I guess estimate at 800Hz - will the effort be worth it?

Any glaring errors in my thinking?

 

[markbakk]

Err, that TangBand at 400Hz only does only about 89dB SPL at 1m before exceeding the maximum linear cone movement (Xmax). The Founteks together reach about 95dB at 100Hz in their linear range. I'd cross the TB a bit higher, at 600Hz it does about 95dB before reaching Xmax.The power distribution is also better. And apply a reflex enclosure on those Founteks, so they will do something under 100Hz.

 

[Lojzek]

Wide range unit compromises the HF part of the band, so in the same way you would design a filter for it, you could do the same for a real tweeter unit, easier and less expensive of a job too. Either an MTM with a small flange driver like Monacor DT28N (cpc farnell 20 gbp) or perhaps a TMM with a Morel cat 298 (falcon acoustics 43 gbp). It could become a permanent solution and a very nice performing mini loudspeaker.

 

[mondogenerator]

Thanks for your comments!

This is an attempt to use drivers I have acquired over the years, and using the Tangband W3 was just a way to "use" them!

I also have W2 800SL, which is more tweeter like, and smaller 2 inch, so would reduce C to C spacing a little.

However, talking of drivers I havent used up, I have a pair of Audax TW025F1, which are small diameter mounting, maybe slightly less than 3 inches.

With the high Q of the Fountek FW100B, I certainly could vent the design, but I am very tempted to just build a closed box. 3.5 litres per driver gives a Qb of around 0.8 and F-3dB of about 98Hz, which should match a sub well, if I get one!

 

[mondogenerator]

Err, that TangBand at 400Hz only does only about 89dB SPL at 1m before exceeding the maximum linear cone movement (Xmax). The Founteks together reach about 95dB at 100Hz in their linear range. I'd cross the TB a bit higher, at 600Hz it does about 95dB before reaching Xmax.The power distribution is also better. And apply a reflex enclosure on those Founteks, so they will do something under 100Hz.

You're correct of course, the Xmax is a tiny 0.7mm, but Xmech is considerable, probably 4mm peak.

SPL is more my concern there than exceeding 0.7mm, I guess they'll will go back on the shelf haha

 

[Lojzek]

Splendid, you can experiment a bit and I am certain you will achieve your goal this way or the other.