Transmission line or TQWT with 2 woofers in 2 way system ?

[jgwinner]

Martin:

Thank you very much for your response!

Lately, I get asked this question at least once or twice a week.

I'll take your suggestions and try to model it, I'd like to work the #'s before I start cutting wood.

In general (for everyone, not necc. Martin), is the MTM better than a single woofer for reasons of bass and fast response?

In other words, what offsets the complexity of having 2 woofers in a single TL? I'm assuming you get more bass and faster response due to the lighter cone than a single larger woofer (and smaller enclosure width), but is this really true?

I guess that's an MTM question not just a TL question.

 

[planet10]

In other words, what offsets the complexity of having 2 woofers in a single TL? I'm assuming you get more bass and faster response due to the lighter cone than a single larger woofer (and smaller enclosure width), but is this really true?

The lighter cone/faster response has been beat to death on the BASSList and on the LambdaList and from lurking on those posts i'd say that general concensus is that this is myth.

I like 2 bass drivers in any enclosure because i can load them push-push with the back driver providing brute force baffle-step compensation (back driver can be run all the way or rolled off above the bafflestep [avoiding some of the problems with a regular x.5 way system])

dave

 

[jgwinner]

The lighter cone/faster response has been beat to death on the BASSList and on the LambdaList and from lurking on those posts i'd say that general concensus is that this is myth.

That's really interesting as many high end speakers use this configuration.

To whit on the Thor's though, this implies that a single woofer might be easier to optimally design, and with those expensive Sea's woofers would be much lighter on the wallet also.

 

[jgwinner]

Ok, I worked the numbers through Martin's models. I used method 2) above:

Method 2 : Model a composite driver at the average location and set the T/S parameters as follows :

fd = 31Hz
Re = 3.05
Lvc .2mH
Bl = 7.2N/A
Sd=252 cm2
Vd = 74 l
Qed = .39
Qmd=2.5

L = 81 in
Driver Pos = 10.5 in (6+5 from top, but 3/4" mdf on inside)
So = 1.6Sd
Sl = .4 (Sd)

These are from the Thor article posted earlier.

I get the responses below:

I Think it looks OK, comments?

(NOTE: These images may not be here long, please refigure from Martin's Mathcad files if they do not come up! I'll edit the post and rework them if I change the params)

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An externally hosted image should be here but it was not working when we last tested it.

 

[MJK]

Hi John,

Looking at the plots, I would conclude that the area of the line was too small. The bass response is being choked off by the small area. If you have time, why not try running the simulation with increasing areas. Keep the taper teh same but try 3 or 6 times Sd of one driver.

Martin
www.quarter-wave.com

 

[planet10]

I worked the numbers through Martin's models

Thanx for those. It is good to see that my gut reaction wasn't far off. The bass extension is essentially none over a sealed box with little terminus output. Might have well stuffed it a little more, cleaned the ripple up a bit more and walk away with just the advantages of an aperiodic line.

dave

 

[jgwinner]

Interesting, I thought they looked slightly better than the default, but I'll play with it. (Not sure the default values were right either).

My wife says"Build them already!"

Note that Sd is already twice that of a single driver .. but I'll work the #'s and post something tonight.

 

[jgwinner]

Stupid Mathcad question - how do you specify square inches? I'm using 1.6 Sd (which is 2x SD of a single driver, so that's 3.2x Sd (real)) which equates out to about 80", the published area. I'd like to enter it directly, but if I enter in raised to 2 I get errors down in the calc's. I used the "Unit" window but under 'area' they have Acres

I'll rework it tonight and use x * Sd if I can't figure out in**2