New Compact TL Project

[cs]

I have re-ran the simulation over and over trying different lengths, taper ratios. 65 is pretty much ideal for this driver. A steeper taper can result in high velocity at the mouth. However, I did increase the taper to a little over 9:1 and came up with good results. velocity at the mouth is still acceptable, and bass response is improved:

To me, your results suggest that the line is still too long, and it is heavily overdamped.

Try setting the damping to 1lb/cu ft, but only for the firat half of the line (from the driver end). Leave the second half of the line (port end) empty.

I used this approach on a Jordan JX92S TL recently, which is similarly sized to your driver, and got very good results.

 

[MJL21193]

To me, your results suggest that the line is still too long, and it is heavily overdamped.

Try setting the damping to 1lb/cu ft, but only for the firat half of the line (from the driver end). Leave the second half of the line (port end) empty.

Here it is with no stuffing at all:

 

[MJL21193]

CS: And here it is a you suggest, with stuffing at 1lb/cubic foot for the first half ofthe line:

 

[cs]

Here it is with no stuffing at all:

OK, I think this verifies that the line is tuned far too low in frequency, as even with the reinforcement from the line at the low-end, there is still a pronounced overall slope to the response.

A line length in the range 45 to 55" would be better. Also, if you put the stuffing back - but only in the first half of the line, you will find that the low-end reinforcement is maintained, but the high frequency fluctuations are greatly reduced.

 

[MJL21193]

CS: To your credit, you were right. In my haste, I forgot to change the stuffing amount through the line.
Am I wrong in thinking it looks good?
Here it is with the line length reduced to 45" unstuffed:

 

[cs]

CS: To your credit, you were right. In my haste, I forgot to change the stuffing amount through the line.
Am I wrong in thinking it looks good?
Here it is with the line length reduced to 45" unstuffed:

Yes that's much better

With the line 'half-stuffed' as before, it will probably be the best you can do with that drive unit.

 

[cs]

One more thing to check :-

What is the line cross-section at the driver end ?
I've found that it is usually best not to go below about 4*Sd.

 

[MJL21193]

One more thing to check :-

What is the line cross-section at the driver end ?
I've found that it is usually best not to go below about 4*Sd.

Unfortunately, cross section at line start has to be small, as the box is small. It is 1.8 x Sd.
Reducing the line length is going to be troublesome at this point, since the outside of the box is already built. Adding a divider to shorten it will reduce cross section and upset driver offset.
I will play with the sim some more...
Thank you for your help so far CS

 

[cs]

Unfortunately, cross section at line start has to be small, as the box is small. It is 1.8 x Sd.
Reducing the line length is going to be troublesome at this point, since the outside of the box is already built. Adding a divider to shorten it will reduce cross section and upset driver offset.
I will play with the sim some more...
Thank you for your help so far CS

OK.
Could you move the port to the back of the box ?

Then, the top edge of the internal partition could be moved right to the back of the box - increasing start cross-section. An extra partition could be put in at the port end of the line to shorten it.

 

[planet10]

acting as an infinite baffle would (the dotted line in the graph).

The dotted line is the response of a sealed box of the same volume.

dave

 

[planet10]

The best TL's eat the back wave from the driver

Aperiodic is not what I'm looking for here.

These 2 statements are contradictory. A TL stuffed until there is no backwave is an aperiodic enclosure. You get no additional bass beyond sealed, just less internal energy coming back thru the cone.

dave

 

[planet10]

Further tinkering with the simulation gives me the results I think I'm looking for. Offset the driver 12" from the start of the line, increase taper ratio to ~6:1 while maintaining the same cross sectional area at the start. With minimum stuffing I have the following result:

Can you post the impedance & excursion plots to go along with this one please.

dave

 

[MJL21193]

The dotted line is the response of a sealed box of the same volume.

Gee Dave, are you sore because I get the plywood so cheap? They deliver.

When I say the dotted line is infinite baffle, I'm only reading what it says above the chart:

 

[planet10]

When I say the dotted line is infinite baffle, I'm only reading what it says above the chart

Could be my mistake, but i've seen the blue line change around with the same driver in different size boxes, so i made the leap that Martin is using the term -- common before acoustic suspension -- of calling a sealed box that is relatively large an infinite baffle.

dave

 

[MJL21193]

These 2 statements are contradictory. A TL stuffed until there is no backwave is an aperiodic enclosure. You get no additional bass beyond sealed, just less internal energy coming back thru the cone.

I said the best TL's eat the back wave because I believe that to be true. The output from the front of the driver (if it's good enough) would be enough. I didn't say my humble creation would do this.
I wanted to build a TL, not a weezer. In further posts I admit that I missed setting the stuffing amount for each section, and that's why the simulation looks like that. Good advice from CS lead me to shortening the line (slightly) and changing the stuffing amount in the simulation.

 

[MJL21193]

Can you post the impedance & excursion plots to go along with this one please.

dave

Here's the new allignment. 60 inch line, 6:1 taper, 12 inch driver offset. The following is unstuffed:

 

[planet10]

if you post impedance & excursion we will have even more info to help....

dave

 

[MJL21193]

Patience! Here they are. You didn't say if you want acoustic or electrical impedance, electrical first:

 

[MJL21193]

Here's the acoustic impedance. Line is unstuffed.

 

[planet10]

Patience! Here they are. You didn't say if you want acoustic or electrical impedance, electrical first:

We were posting simultaneously... impedance is unstuffed? The 3rd peak is indicative of significant ripple that should go away with some stuffing.

The shape of the saddle indicates you are getting some bass reiinforcement... with appropriate room placement to about 40 Hz.

dave