Help me design a mini-tower TMM DCR speaker...

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I’m looking for some advice/guidance on a future speaker project. I’ve got a pretty good idea of what I want, but I’d like some input from some of you who actually know a thing or two about speaker design, as I pretty much know nothing. In spite of that fact, I’ve come up with some ideas that I think may result in a respectable pair of speakers… let’s see if you agree.

Goals:
  • great sound
  • mini tower form factor, TMM driver arrangement
  • inexpensive
  • high WAF
  • good sensitivity (will be driven by ACA mono blocks)

The preliminary design I’ve come up with would employ two Silver Flute W14RC25-08 5-1/2” wool cone drivers per speaker with a Vifa DQ25SC16-04 1” titanium dome tweeter. The box would be a double chamber reflex as described by Claudio Negro HERE..

Now I’m going to just throw out some thoughts, ideas, and questions. Again I’m not fluent in speakerese so forgive me if my Qts offends your X-max or you’re baffled by my baffle step ;).

  • If I understand basic BR design correctly, I would simply double the volume for a single-driver enclosure for the desired F3. Then, for the DCR volumes I’d divide that total volume up 2:1 with the drivers mounted in the larger chamber. Is this correct?
  • The above applies to straight 2-way design I presume. How would the DCR volumes change when using a 2.5-way topology?
  • My understanding is that paralleling two drivers halves the impedance and increases the sensitivity by some factor. I presume that changes when going 2.5-way. Would it be preferable to use the 4-ohm version of these drivers if I were to go with 2.5-way?
  • Would modifying both of the woofers (in 2-way) or just the mid-woofer (2.5-way) with phase plugs help to improve the upper range of the woofers and permit a higher crossover point?
  • I’m planning on using 3/4” MDF. I’ve got some ideas with regards to construction, damping, etc., which will be discussed later.
  • I’m sure I’ll need some help with crossover design, but we’ll crossover that bridge when we get there.
  • I’ve ordered a Dayton IMM-6 measurement mic. It’s cheap as all get-out and certainly not pro quality, but with the AudioTools app I should be able to get some useable measurements when that time comes…

That should be enough to get the discussion rolling. I’m open to recommendations for different drivers, etc., keeping in mind that I want to keep costs down. I’m not interested in being told that I really should start with a kit, or an open baffle, or a full range, etc… I know there are a lot of great, established designs out there but I’d like to explore the feasibility of this design, as preliminary as it is. I like a challenge.

It will be a while before I’ll be able to actually work on this project due to other bigger projects, so if this discussion produces any useable info and someone else wants to be the guinea pig, be my guest!
 

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  • If I understand basic BR design correctly, I would simply double the volume for a single-driver enclosure for the desired F3. Then, for the DCR volumes I’d divide that total volume up 2:1 with the drivers mounted in the larger chamber. Is this correct?
    Yes.
  • The above applies to straight 2-way design I presume. How would the DCR volumes change when using a 2.5-way topology?
    No change. In many ways, 2.5 topology is better than simple two-in-parallel (in the TMM configuration).
  • My understanding is that paralleling two drivers halves the impedance and increases the sensitivity by some factor.
    Yes.
    I presume that changes when going 2.5-way.
    Below the crossover point (between the woofers) sensitivity increases the same as in two parallel woofers, above is the same as in one woofer alone.
    Would it be preferable to use the 4-ohm version of these drivers if I were to go with 2.5-way?
    No.
  • Would modifying both of the woofers (in 2-way) or just the mid-woofer (2.5-way) with phase plugs help to improve the upper range of the woofers and permit a higher crossover point?
    Do not modify the woofers!

DCR has no real advantage over conventional bass-reflex, especially with two 5" drivers. DCR is good (maybe) only for single 3" or 4" driver.
 
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Thanks Sonce,

One of the reasons I'm considering DCR is to minimize the negative effects of a long, skinny BR chamber. Would it be a better option to simply have two separate ported chambers? If I went with a single chamber, the inner dimensions based on Madisound's suggested box volume would be approx. 5.5" x 32" x 8".
 
It is very difficult to divide the long skinny box in two equal volumes, with two woofers mounted on the very top of the box, so go for one BR chamber. There will be a half-wave resonance along the 32" dimension, but it can be tamed with a small chamber on the top of the box (behind the tweeter) acting as Helmholtz absorber at 212 Hz. New internal height of the box should be 32" plus the height of the Helmholtz absorber. Increase slightly the width of the box, to reduce the 8" depth which in turn will reduce internal resonance, because 8" is exactly 1/4 of 32".

Another solution is to move down the bottom woofer, about at half of the box height, with an internal divider (just behind the bottom woofer) mounted at 45 degrees - the box now is divided in two equal volumes, with some additional benefit from the non-parallel internal divider.
 
frugal-phile™
Joined 2001
Paid Member
One of the reasons I'm considering DCR is to minimize the negative effects of a long, skinny BR chamber.

Why not take advantage of that? There is an ML-TL that works with 2 W14. We used a pair in a 10 L vented enclosure with FF85wKeN as mid-tweeter, they worked well in that volume althou don't get the extention they do in the ML-TL.

dave
 
frugal-phile™
Joined 2001
Paid Member
[*] My understanding is that paralleling two drivers halves the impedance and increases the sensitivity by some factor. I presume that changes when going 2.5-way. Would it be preferable to use the 4-ohm version of these drivers if I were to go with 2.5-way?

For a 2.5 way you would want to use the 8 ohm drivers and have a 4 ohm capable amp.

[*] Would modifying both of the woofers (in 2-way) or just the mid-woofer (2.5-way) with phase plugs help to improve the upper range of the woofers and permit a higher crossover point?

Probably not.

[*] I’m planning on using 3/4” MDF.

I'd recommend good quality plywood. MDFs primary asset is that it is cheap.

dave
 
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