Dayton RS Series - TL & MLTQW Designs

[Marzen]

I wanted to throw this up due to some interest in rev'ing the orig Modula or Nat P into a transmission line or mass loaded tapered cabinet. I updated my site just now with some prelimary info. I'll put up more later, but I just spent an hour doing what any 12 year old could do in 10 minutes.
Ward's speaker page
Cheers,
Ward

[ThomasW]

Congratulations that link loads ...... :T

All the best web designers are 13yrs old and using a Mac, so don't feel too bad.... :wink:

[cjd]

Congratulations that link loads ...... :T

All the best web designers are 13yrs old and using a Mac, so don't feel too bad.... :wink:

Hey!

Er... oh yeah, I don't get paid to do web design these days.

Linux, and I ent 13, though I have a rew more days than that to an age that sounds awfully similar...

C

[jdybnis]

Marzen,

I ran a ported 75 liter enclosure with 2 parallel RS180's through Unibox. That is the same internal volume as the TL. The box is tuned to 29Hz. I do this to have a baseline for comparison. Unibox doesn't include quarter wave resonance so the upper response is always going to be unrealistically smooth compared to MJK's worksheets.

[jdybnis]

Here is a comparison of the MathCAD model and the Unibox model of an MLTL enclosure for the Modula MT.

The first image shows the Unibox volume for a 63 liter enclosure. That is the internal volume of the box I want to build. I use Unibox to come up with a starting point for the tuning frequency/port size. The 2" port is 4" long. The tuning frequency is 24Hz. Unibox, in addition to calculating the port length for a given frequency tells you some other stuff the MathCAD sheets won't. In this case you can see that the driver reaches xmax at about 94dB when playing below 40Hz. Even though the box extends down to 24Hz, the 7" driver can't move enough air to knock your socks off. That's OK though, thunderous bass isn't one of the design goals for this design. The low tuning does serve a purpose. It protects the driver from unloading at low frequencies. Otherwise the speaker would choke, even at moderate volumes when it tries to reproduce anything with sub 30Hz content.



The second picture is the MathCAD model with the port at a position that minimizes bumps in the FR. The port here is 18.5" from the bottom of the enclosure (internally). You can see it matches the Unibox plot pretty closely.



The final picture shows the port at the bottom of the enclosure (internally). This demonstrates how if the port is placed at an arbitrary place the quarter-wave resonances will cause midrange junk to come out of the port. See the anomally between 150Hz and 250Hz. MJK's MathCAD worksheets are useful for finding an optimal port placement.



I have not built this enclosure yet. When I do I will verify the model. I will look at the measured impedance and see if it contains the extra bumps predicted by the MathCAD model but not Unibox.

[Marzen]

Hey Josh, is your terminus on the front or rear baffle?
For comparison with Martin's pgm; looking over Augspurger's extended TL alignment tables I come up with the following quick calculations for a pair of drivers, assuming I factor these correctly:
RS180S-8: Qts = .38 Fs = 38hz Vas = 48.7L net
-----------------Offset Driver Tables---------------------
___Qts_____F3/Fs_____F3/Fp_____Fs/Fp_____Vas/Vp
___0.41____1.30______1.20_______0.94______0.60
---------------------------------------------------------
Calculating the above listed ratios as:
F3/Fs: 1.3 x 38hz = 49.4hz
F3/Fp: 49.4hz / 1.2 = 41hz
Fs/Fp: (alternate formula for Fp, similar to F3/Fp used above)
Vas/Vp: 48.7L / .60 = 81.16L (2.86 cu/ft)
Line length ~80in, ~.5lbs/cuft AccustaStuff
Line taper 4:1
Ward

[EdL]

I've done some sim's for the Modula in a MLQW case. 4 slightly different versions are included on the attachment. Note the effect of small changes in stuffing density and port length.

This raises a question I have about my efforts: Should I relax my attempts to maintain a "flat" speaker response? I am concerned about the contribution of room lift. So, I think the gradual roll-off shown by jdybnis' work is closer to what I should be looking for. Whadaya think?

[ThomasW]

Ignore the null that's purely a function of the mic position. This plot gives a pretty clear example of room gain in the average room.

If one has a big open floorplan room with the speakers well away from the walls, things will be a bit different.

[jdybnis]

Marzen,

I don't know yet what side I'm going to put the terminus on. I'll build first and then measure. I have a backup side panel for one of the speakers. I'm going to stick the port there first and measure the noise. If it is low enough I'll cut a hole in the front baffle, otherwise I'll put the port in the back.

[Marzen]

This raises a question I have about my efforts: Should I relax my attempts to maintain a "flat" speaker response? I am concerned about the contribution of room lift. So, I think the gradual roll-off shown by jdybnis' work is closer to what I should be looking for. Whadaya think?

Ed,
I built Paul K's model you sent me. It didn't work out too well for my usage. I'm in need of a wall hugger, although even 4ft out it sounded pretty full compared to the 50L ported cab. The 50L ported cab blended almost seamlessly with my sub which was setup with my Modula's in the 1 cu/ft ported cab. I think the B3 or QB3 alignment lends itself to a smoother transition between the two. I wouldn't mind giving it another go if a B3/front terminus design should pop up.
Ward

[jdybnis]

What you might need for a wallhugger is a crossover without baffle step compesation.

[Marzen]

What you might need for a wallhugger is a crossover without baffle step compesation.

I'm not completely sure that would work in my favor. Even in 2 pi space I have a large wall area to contend with, and I sit about 16 feet away.
I've already changed the xo in one spkr for a little more rise in the midrange. I 'think' I like it so far; what with ever so slightly forward mids now.
I can always taper off the low end with some eq if needed, or compromise bsc at around +3db for a flush to wall use. I need to take a vacation day so I can fiddle around more with Room EQ Wizard & SoundEasy without the family around. Making comparisons is like a visit to the optometrist -
'...which is better, this...or 'this'? :banghead: