Just for the sake of asking... (about Bass)

[BAM]

Finally, here is a diagram to show about the wiring. Note that the crossover network only affects the drivers on the front baffle, not the rear driver. The rear driver is allowed to run through its full range.

[7V]

Originally posted by BAM
7V Steve: So, to get the required enclosure volume, I should model a ported enclosure, with a port that tunes the enclosure to a certain frequency, but instead of the reflex port I should substitute the line, correct? And perhaps the line should be the length of a quarter of the wavelength of what would otherwise be the enclosure's tuning frequency. Also correct?

Please bear in mind that when I built the System IVs, there was very little reliable theory on TL speakers. That's why I built the variable prototypes to test the bass response. I took the speakers up to John Collinson (ex Wharfedale and Castle Acoustics) for measurement but making nearfield measurements wasn't so easy, particularly as there were four drivers and the line exit was designed to be as far as possible from the drivers.

Unfortunately, I can't lay my hands on the resulting measurements at the moment so I'll rely on my memory. Of course the Bandor units that I used at that time are not the units available today.

The first thing to say is that, as I played with the prototype, varying the box size and opening & closing the port (switching the line on or off) it became clear that I wasn't modelling the system on a ported enclosure but rather a sealed box.

There was definitely deeper and 'more' bass with the line open but it was difficult to determine accurately as opening the line also resulted in a significant reduction in the 2nd harmonic distortion so the bass sounded deeper anyway. In any case, there was plenty of scope for tuning the line by varying the amount and positioning of the stuffing (long-haired wool).

The line cross section was very slightly under the combined cone area and the port in the cabinet had the same area as the line.

I chose a relatively large box size to get the overall (sealed box)Q down to about 0.6. This was because the speaker was designed to work alone without any bass or subs and I preferred the sound like this. The cost was greater cone excursion. My new speakers, designed for use with bass speaker(s) are in a smaller enclosure with the Q nearer to 0.7.

The line was, as you correctly surmise, a quarter wavelength design. Again I could vary the length of the line (by opening different ports at the line end). Subjectively, a shorter line didn't seem to work as well, although in the end I did choose a compromise based partly on the aesthetics of the thing (I'm so ashamed)

As I said, I don't entirely believe the theory put forward by the original Daline designer although I had owned two pairs of his original designs and was very fond of them. However, when I played with my prototypes I found that closing the port opening to the line by up to about 50% made no material difference. This made me sceptical that there was a normal ported box principle at work here. Nevertheless, the port and line definitely behaved as a low pass filter just as you would expect from any line. I couldn't detect any difference whatsoever in the mid-range with the port (and line) open or closed.

So BAM, I would build a box size based on the Qts that you would choose for a sealed box and then add a quarter wavelength line and tune with the line stuffing.

There you have it. Sorry I'm a bit vague but come back if you have any more questions and I'll try to dig deeper to see if I can find the measurements taken at the time or remember any more. I'm also going to visit a friend who has a pair of operational System IVs and he has some photos of the variable prototypes. I'll see if I can borrow them and post them here. Should give everyone a laugh.

[BAM]

I must say, this has been an intensely mind-expanding experience for me, and I appreciate the opportunity to rack the brains of professionals in this which is my first foray into the area of transmission line loading.

Here's the extent of my understanding of Daline theory:

1. Model a sealed box with the appropriate Qtc for the desired response.
2. Add a quarter-wavelength transmission line, using traditional quarter-wavelength transmission-line theory to determine the area of the line. The opening into the box should be no less than 50% of the line area.

But there's a problem.

In modeling my NSBs in a sealed box of 33 liters, I get a Qtc of about 0.8, which means boom, boom, boom. The dimensions of the upper enclosure for this simulation are 16" high, 18" deep, and 7 inches wide (yielding 2016 cu. in., or 33 liters.) This does not look good for Homestar Runner. Should I worry about the Qtc of the system if my goal is to get lots of bass from this? Or will adding stuffing to the line tighten things up?

[kelticwizard]

BAM:

Have you checked the specs for the NSB's you are talking about? I postem them in post #15, here's the link:
http://www.diyaudio.com/forums/showt...207#post205207

The Vas of the woofer is not 0.8 cu ft. It is 0.08 cu ft, or 20% less than 0.1 cu ft. The Vas of the two NSB's is 276 cu in. so the box you modeled is over 7 times larger than the speakers' Vas. You can make the box much smaller and still have the same numbers-the Qts won't go up much even if you make the box 17 liters instead of 33.

I am going to analyze the Focal Daline to see how that works. Be back later tonight or tomorrow.

[BAM]

I checked the T/S entries in WinISD yet again, and they agree with the specs you provided in your post #15. A Qtc of about 0.8 is the result at every reasonable enclosure size, it seems. WinISD says that this driver's EBP best suits it for a vented box.

[kelticwizard]

BAM:

The reason is that the Vas is so small, that the Qts is not going to change in any reasonable size box. When the volume of the box gets to be 3 or 4 times the Vas of the speaker, the speaker is essentially working in free air, except for the back wave being cut off.

Qtc = square root of: [(Vas/Vb) + 1] times Qts.

You have to really be twice Vas or less for the Qtc to change.

WinISD says that this driver's EBP best suits it for a vented box.

Not with a Qts of 0.79. Earlier in this thread you said it was a Qts of 0.35 or something. Please check that-Parts Express says the Qts. is 0.79, which is certainly not fit for a ported box.

EDIT: Oops. I see you mentioned that you already did re check the figures in WinISD. Sorry.

[7V]

Originally posted by BAM
Here's the extent of my understanding of Daline theory:

1. Model a sealed box with the appropriate Qtc for the desired response.
2. Add a quarter-wavelength transmission line, using traditional quarter-wavelength transmission-line theory to determine the area of the line. The opening into the box should be no less than 50% of the line area.

Originally posted by kelticwizard
I am going to analyze the Focal Daline to see how that works. Be back later tonight or tomorrow.

Yes, BAM that's my experience of the design process of the Seventh Veil - System IV, although I'd be cautious of the opening being 50% of the line area when using other drivers. I would say, that as a general rule the box opening should be approximately the same as the line cross sectional area.

I've just dug out and reread (briefly) the two original articles by the Daline designer Robert Fris (Hi-Fi News & Record Review - November 1974 and May 1975). As I said, my own findings didn't concur with everything that is said about the Daline system. The major differences between Daline and System IV were:

1. The cavity volume of the Daline appears to be less than that of the 'sealed box' model used with the System IV.

With the drivers that I used in my variable prototype I found that the bass response improved as I increased the size of the cavity/box.

2. A tapered 1/4 wave pipe was used in the Daline. I found that the taper made no material difference so I used a rectangular section steel pipe (no taper).

3. The Daline is claimed to be non-resonant or aperiodic from 20Hz upwards. I found that the System IV measured like a normal TL with the two resonant peaks that can be tempered by damping.

I did find, like Robert Fris, that less damping was needed in the line than is normally suggested for a conventional TL.

I hope that this shines more light on the subject.

Has anyone else built any Daline type speakers using different drive-units and/or dimensions than the original Robert Fris designs?

[dunderchief]

so I just read the description of these little 4" beasts. It says they would work in a line array. Any thoughts on this. I've always kind of been interested in these if nothing else, then for their visual effect. for 90 cents, can you really go wrong? Any thoughts on maybe a line of 16 drivers a piece. I wouldn't be looking for something that blew me away sound quality wise. Maybe just something that got pretty loud for all those raging college parties I'll be throwing next year ( I'm a senior in Electrical engineering HA!). Although of course I will do a search, does anybody know of a project that might be something like this?

[BAM]

@dunderchief: You could do it, but you would probably get a good deal of comb filtering. Being an EE major, though, you should know how to build an active EQ circuit to compensate for that. I understand that if you search the Parts Express message board for NSB, you should turn up all results relating to the NSBs, including several designs. One of these is a sealed enclosure. Please note, however, that the NSBs do not handle much power at all, only about 5 watts RMS. While this would be good for tube amp users, it probably wouldn't be quite so good for big, powerful solid state amplifiers.

Off topic, what college are you graduating from? This fall, I will be a freshman at Purdue University.

@kelticwizard
Above, I mentioned that I knew of a sealed enclosure project that uses the NSBs. Could I just take this sealed design and then add the line to the bottom and be done with it?

@7V
Subjectively, how would you describe the bass of the System IVs? Was it fairly deep with less control? Or was it very controlled but not quite as deep?

[7V]

Originally posted by BAM
@7V
Subjectively, how would you describe the bass of the System IVs? Was it fairly deep with less control? Or was it very controlled but not quite as deep?

I would describe the bass of the System IVs as controlled and deep (low Q) but light. It's certainly tuneful- every note is clear - but, as I said, a little light.