s this setup OK? (especially for MJK and GM)

[mr_push_pull]

This is especially for Mr. MJK and Mr. GM. I have simulated this enclosure using Mr. King's sheets and the response seems pretty flat with good bass extension and little stuffing. My question is: is the setup OK, because from what I gather, with TLs the length of the enclosure must be much bigger that its width, otherwise the simulations aren't accurate.

[MJK]

I have not rerun the simulation so I am making an educated (maybe not so educated. I am actually winging it) guess about your enclosure.

The length is 30 inches. Assuming a square cross-section, at the top it is approximalety 9 inches wide and deep. At the bottom it is 9 inches wide and just over 2 inches deep. All of these are internal dimensions. So the length is over 3 times longer then any other dimension, the first couple of resonances should be along the modeled direction.

But this is a rather short enclosure and it may actually be acting more like a BR then a ML TL. I say this because of the very small amount of fiber density required to damp the waves and the lack of significant peaks and nulls in the summed response. If you modeled the enclosure as rectangular of the same volume, does the response change much?

I don't see anything wrong with what you have modeled, the MathCad TL worksheets will also model a BR accurately. Looks OK to me.

Hope that helps,

[Greg B]

I believe the used parameters are wrong. Certainly Sd is. It is listed as 221.67cm^2 in my focal catalog. Fs is 27.4, Vas 106l, Qts .30, Qms 2.9, Qes .33, Bl 9.4, Re 7.8, Le .9.

It's possible that the factory specs are wrong of course, but I've had good correlation between measured and listed specs in the past with all focals I've used.

I have a focal with very similar specs to those listed, and it works very well in a tower BR/ML-TL. My first sim attempt would be a straight pipe about 39 inches tall, with the driver at 1/3, and a port at the bottom. The Q is a little too low for a 'traditional' 2m TL IMO.

GB

[MJK]

Greg,

The Focal label is a leftover from the sample problem run in the downloaded worksheet. People don't seem to change the title, only the T/S parameters, when they run a simulation for their drivers. By not updating the title it stops others from double checking the driver's specs they are using, somebody might actually have measured T/S results for the particular driver being sim'ed.

[Greg B]

Duh, thanks Martin. I'm an idiot, as usual.

GB

[MJK]

Greg,

You are definitely not an idiot. Now the people who leave an inaccurate title so that others become confused ..............

As I keep telling my son (his younger sisters seem to know this naturally), neatness and accuracy are everything and pay attention to the details!

[GM]

>My question is: is the setup OK, because from what I gather, with TLs the length of the enclosure must be much bigger that its width, otherwise the simulations aren't accurate.
====
Looks fine to me also and should work well in a small room or if placed near a wall. If it is a larger room or they will be well away from the wall, then I recommend a straight pipe with a lower Fb. FWIW, here is my version of a T/S max flat:

L = 39.5"
zd = 14.63"
zp = 37"
So/SL = 63"^2
density = 0.2
rp = 1.25"
Lp = 4.125"

The vent looks a little small though and may 'chuff' if the driver requires much power around/at Fb. I recommend at least a 2.5" diameter vent.

Also, the BL value is off quite a bit. When I do a T/S max flat alignment it produces a dip in the response, so change it to 4.1757 to see how it affects your sim.

BTW, which driver is this, so I can label my sim?
====
>But this is a rather short enclosure and it may actually be acting more like a BR then a ML TL. I say this because of the very small amount of fiber density required to damp the waves and the lack of significant peaks and nulls in the summed response.
====
It's long enough, the 4:1 reverse taper combined with a vent really loads both the driver and vent.
====
>neatness and accuracy are everything and pay attention to the details!
====
You bet! When I was learning how to build race engines, my mentor had two golden rules: Cleanliness is next to Godliness, and God is in the details.

GM

[mr_push_pull]

Originally posted by Greg B
I believe the used parameters are wrong. Certainly Sd is. It is listed as 221.67cm^2 in my focal catalog. Fs is 27.4, Vas 106l, Qts .30, Qms 2.9, Qes .33, Bl 9.4, Re 7.8, Le .9.GB

This is all my fault, I discovered after returning home (I post from work), that I forgot to change the name of the driver. It is a Visaton W 170 S / 4 Ohm. Sorry for leading the thread in that direction, I am the idiot. And, those are the factory specs, not the meausred ones (I don't owm that driver now), so this is more of an estimation.

Originally posted by GM Looks fine to me also and should work well in a small room or if placed near a wall. If it is a larger room or they will be well away from the wall, then I recommend a straight pipe with a lower Fb. FWIW, here is my version of a T/S max flat:

L = 39.5"
zd = 14.63"
zp = 37"
So/SL = 63"^2
density = 0.2
rp = 1.25"
Lp = 4.125"

The vent looks a little small though and may 'chuff' if the driver requires much power around/at Fb. I recommend at least a 2.5" diameter vent.

Also, the BL value is off quite a bit. When I do a T/S max flat alignment it produces a dip in the response, so change it to 4.1757 to see how it affects your sim.

[/B]

Thanks for taking the time to answer my question. I will try your suggestions, they will probably lead to better results.

Originally posted by GM BTW, which driver is this, so I can label my sim? [/B]

I already answered this...

Originally posted by GM It's long enough, the 4:1 reverse taper combined with a vent really loads both the driver and vent. [/B]

But, aren't the principles used for the both sheets the same? I asked my question about the length because someone told me that the sheets assume the length of the enclosure is much bigger than its width, because otherwise the transversal waves become comparable in strength with the longitudinal ones, and the sheets only account for the longitudinal ones. Actually, the guy who told me that learned it from a failure with a square box, and Mr. King told him that the source of the problem is the shape of the box. I have to admit I'm pretty confused on this one...

Originally posted by MJK >neatness and accuracy are everything and pay attention to the details![/B]

OK, I deserve that. To be frank, I thought that my mistake may lead to confusion, and I appologize again. That's the effect of saturation, I have spent to many hours looking at MathCAD

[mr_push_pull]

What if one completely ignores all the graphs except the SPL response? More exactly, what is the worst case when obtaining a perfectly flat and extended SPL response and ignoring all the others? And how audible is the difference?

[MJK]

Actually, the guy who told me that learned it from a failure with a square box, and Mr. King told him that the source of the problem is the shape of the box. I have to admit I'm pretty confused on this one...

The worksheets were written assuming that one dimension was so long that it dominated the low frequency resposne enough to ignore the other two dimensions. Between 10 Hz and 100 Hz this is easily accomplished and the T/S modeling is accurate.

But then I plotted the responses out to 1000 Hz so that the harmonics of the fundamental could be seen and placement of the driver to suppress the harmonics could be studied. At some point above 100 Hz the model startes to become less accurate for a number of reasons one being standing waves in the remaining two dimensions of the enclosure. Hopefully stuffing will attenuate these out of plane waves and the plotted results will be reasonable.

As an estimate of the limits over which the worksheet is accurate you might consider the following calculations.

1) The worksheet will determine the tuning frequency in the direction modelled and it is easily seen in the acoustic impedance plot when no stuffing is present as the first large peak.

2) The first driver to back wall standing wave's frequency can be estimated by the following calculation

f = c / (4 x d) where d is the depth of the air in the cabinet

3) The first side to side standing wave'e frequency can be estimated by the following calculation

f = c / (2 x w) where w is the width of the air in the cabinet

These are rough estimates of the out of plane resonant frequencies. The calculations assume a rectangular enclosure. If the difference between the transmission line tuning frequency and the out of plane frequencies is large, then the model is valid for the frequency range below the lower out of plane frequency. For a more exact estimate of the out of plane frequencies for any geometry I would recommend a FE solution, I personally use ANSYS to verify the applicability of my MathCad worksheets to a particular geometry. If the frequencies are all reasonably close, like in a square box, I would be careful using the results and would expect some surprises in the finished design.

How far apart do the frequencies have to be? I have no idea of the exact number, but I would probably look for a factor of at least four.

What if one completely ignores all the graphs except the SPL response? More exactly, what is the worst case when obtaining a perfectly flat and extended SPL response and ignoring all the others? And how audible is the difference?

I am not sure I completely understand the question. The bottom line for any design is the plot you reference. The other plots help you understand why you get the final SPL trace. Can you only look at one plot? Sure, but the understanding might not be as complete. I think the goal is a flat response so I am not sure what you are asking in the second question. But remember, all of the plots assume that the sound is produced by the speaker in an infinite baffle and in the real world a baffle step response should be superimposed on the plots. I recommend after sketching the final enclosure design, that you consult "The Edge" to get a more complete representatin of the real SPL response.

Hope that helps,