My plan: replace my un-scientifically designed (but good looking) rear surround speakers with new carefully designed ones. The present ones are a Voight pipe kind of guess work mis-mash that I concocted a few years ago. Without any good reason, they sound half descent. For us who are never satisfied, that's not enough though. Given the excuse to start today with everybodies favourite material: baltic birch plywood, I jumped in.
First, I'll show what I am replacing. The drivers are Vifa P13WH0008 and Seas 19TAF. A great combination IMO.
First, I'll show what I am replacing. The drivers are Vifa P13WH0008 and Seas 19TAF. A great combination IMO.
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The purpose of a transmission line, in my opinion, is not to augment the bass- its purpose to to effectively deal with internal resonances and standing waves. This improves midbass and lower midrange clarity, and makes the driver behave more as if it were in an infinitely large sealed box.
Transmission lines can, with the right drivers, be tuned to give bass augmentation comparable to a vented box- but as their performance approaches that of a vented box, so does their behavior. There's a fuzzy line between transmission lines, mass loaded transmission lines, and ported boxes. To me, the critical thing is that throughout the bandwidth of the woofer there is not a strong standing wave that can be excited, and there is no major reflection from the inside of the box to store energy.
B&W's Nautilus makes use of terminated tapered tubes to effectively absorb the rear wave of the drivers, allowing them to behave very much as though they are in infinitely large sealed boxes.
If you're not expecting bass, and you build your walls well so that everything is solid, then this looks like a fine design and should be very non-resonant.
Transmission lines can, with the right drivers, be tuned to give bass augmentation comparable to a vented box- but as their performance approaches that of a vented box, so does their behavior. There's a fuzzy line between transmission lines, mass loaded transmission lines, and ported boxes. To me, the critical thing is that throughout the bandwidth of the woofer there is not a strong standing wave that can be excited, and there is no major reflection from the inside of the box to store energy.
B&W's Nautilus makes use of terminated tapered tubes to effectively absorb the rear wave of the drivers, allowing them to behave very much as though they are in infinitely large sealed boxes.
If you're not expecting bass, and you build your walls well so that everything is solid, then this looks like a fine design and should be very non-resonant.
joe carrow said:
owdi said:
First, I'm not looking for a lot of base from these, there's only 86 sq.cm cone area. I want them to sound good, I want the bass to sound natural, not boomy or forced.
Second, sealed will not give better response, as far as bass goes. Even though it doesn't look like it in the graph above, there is some gain.
cs said:
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:
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Since the bass has such low importance in this case, I'd just say that you want to make sure that there are no likely standing waves below 1khz. If the cross section is square and a large fraction of a wavelength of something inside the bandwidth of the woofer, then that's bad, unless the line has a lot of taper. I think you're on a good track here.
If it were me, I'd probably try to optimize for the smallest reasonable box. I had these as surrounds for a while, and my girlfriend hated them.
If it were me, I'd probably try to optimize for the smallest reasonable box. I had these as surrounds for a while, and my girlfriend hated them.
joe carrow said:
If it were me, I'd probably try to optimize for the smallest reasonable box. I had these as surrounds for a while, and my girlfriend hated them.
There's something wrong with her if she doesn't like those
The box size is pretty much fixed now, as I have much of the outside complete (I have left the back off in order to install the brace and divider) Just need to determine the best taper.
I'm thinking about offseting the woofer from the start of the line by a few inches, suposed to reduce some ripple. Need to run some more sims...
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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:
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Moving the woofer more toward the centre of the box gives me the option of placing the tweeter either between the woofer and port or on the other side of the woofer, away from the port.
Is there a chance an MTM type effect with the first allignment?
The speaker will be mounted sideways (see photo in post#1)
Is there a chance an MTM type effect with the first allignment?
The speaker will be mounted sideways (see photo in post#1)
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Great, Now we know how to design a surround TL. Is this what you are aiming at:
bjorno: Not sure what you are trying to show me here. You are using a more advanced version on the mathcad models than I am. If youcare to make a comment, by all meas do so, that's why I started his thread in the first place. If I am designing a dud, let me know.
I did notice in your first chart that you have xmax at 2mm. Xmax for this driver is +/- 4mm. Do you have the right specs?
I did notice in your first chart that you have xmax at 2mm. Xmax for this driver is +/- 4mm. Do you have the right specs?
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