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Old 10th October 2005, 07:27 PM   #21
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I vote for GM's solution on this one. As has been pointed out before, as the height to area ratio increases, quarter wave mode begin to appear and then to dominate. With the short pipes being discussed here, the line is being crossed toward a simple BR and looking at the port output, I think GM's box is more of an EBS BR than MLTL.

Not all drivers are suitable for MLTL's, and I think that is the case with the B102. From a practical point of view, neither my solution or GM's is suitable for a floor stander, since the driver is way too low. I try to get the driver at least 30" off of the floor for my speakers, and a better sound stage is created by getting the driver 45" or so off of the floor.

Bob
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Old 11th October 2005, 12:31 AM   #22
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Quote:
Originally posted by Bob Brines
.......I think GM's box is more of an EBS BR than MLTL.

Not all drivers are suitable for MLTL's, and I think that is the case with the B102. From a practical point of view, neither my solution or GM's is suitable for a floor stander, since the driver is way too low. I try to get the driver at least 30" off of the floor for my speakers, and a better sound stage is created by getting the driver 45" or so off of the floor.
Greets!

Actually, it's almost a perfect golden ratio (~1.567:1.000:0.618) since the routine I use reduces the aspect ratio with decreasing Qts and/or increasing Fb to keep peaking at Fb under control, so below the 'GR' point, either sealed, horn, or max flat impedance vented (aka Pi Align) is required IMO, ergo without any series R these are the best cab alignments for the B102.

True, many of the designs I post that I consider ~optimum require an extended cab with a lower cavity that needs to be filled with a massive damping material such as kitty litter, sterile sand, or similar to keep it from resonating and reduce its tendancy to tip over. Or make it an open box frame and fill it with records, books, magazines, etc. to do essentially the same thing and be a bit more space efficient.

Yeah, for best soundstaging one has to consider the room modes. For instance my 'sound' wall is ~15.50 ft x 8.17 ft and the calc'd ideal is ~5.12 ft off the floor and ~7.23 ft from a side wall. Not very practical even if I only had a mono system, though an acceptable compromise would be to invert the vertical position to ~3.05 ft since it's within the vertical 'window' for a typical seated ear height.


GM
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Old 12th October 2005, 01:49 AM   #23
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Quote:
Originally posted by Bob Brines

Not all drivers are suitable for MLTL's, and I think that is the case with the B102. From a practical point of view, neither my solution or GM's is suitable for a floor stander, since the driver is way too low. I try to get the driver at least 30" off of the floor for my speakers, and a better sound stage is created by getting the driver 45" or so off of the floor.

Bob
Is there an enclosure type that would sound better? I can deal with practicalities to some extent (as GM wrote, a subcabinet could work). I'm most interested in sonics, then maintaining efficiency and, lastly, though still important, extended bass (I can always add a subwoofer).

Would a back horn work well?

In the description of the trick Druid enclosure, the design goals seem to be minimal cone movement and minimum group delay. I don't know how that correlates to the various enclosure types. I'm not even sure I understand what group delay is .

Thanks.

Paul
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Old 12th October 2005, 02:35 AM   #24
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Default Look in latest issue of Audioexpress

I spent a couple of days modeling the B102 in a transmission line. Never got it to go as low as my Lowthers measure in room with a big TQWT.
I saw a article this week on the Omega Quarterwave Reflex. It looks better, maybe 35 -40 Hz, and for the B102 about 39 inches tall. The models, of a different cabinet matched to the Jordan show 32 Hz.
I am thinking of stuffing with Miraflex, bonded fiberglass. I calculated an area of 144 square inches.
My biggest problem is a clean way of mounting these rear mount drivers. The idea of a front panel holding the driver, and bolting this to the main cabinet seems best. That metal ring used in the Druids is not an option.
This rearmount driver is why I have a nice pair of Goodmans in the closet. I like to be able to pull the drivers, and a removeable back panel defeats the pupose of building a good box.
I bought a pair of the matching horns also. Going to first order both at 6500 - 7000 Khz. Not run the B102 fullrange. The horns look real close to the ones in the Druids also.

George
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Old 12th October 2005, 02:38 AM   #25
rjb is offline rjb  New Zealand
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Hi Bob and GM

Please can you expand a bit on your statements that not all drivers are suited to TL's and MLT's.

I have seen this stated several times, with various Qts figures suggested, but never with any justification.

Here I don't mean using dissimilar types of cabinent, obviously sealed cabinents give a different curve from resonant types, with some drivers giving more practical designs in terms of size with one type or the other, but what say makes a driver more suitable for a BR than an ML TL?

Thanks
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Old 13th October 2005, 01:20 AM   #26
GM is offline GM  United States
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Default Re: Look in latest issue of Audioexpress

Quote:
Originally posted by Panelhead
I saw a article this week on the Omega Quarterwave Reflex. It looks better, maybe 35 -40 Hz, and for the B102 about 39 inches tall.

My biggest problem is a clean way of mounting these rear mount drivers. The idea of a front panel holding the driver, and bolting this to the main cabinet seems best.
Greets!

I did an OQR for it the other day also and it's aneochoic response was abysmal IMO. In theory, if you use series resistance (SR), then calc based on the new lower Qts, this buys you only a little bit flatter response with a lower Fp, but a larger pipe and still too much of a stepped response/loss of efficiency IMO, so designing based on Qts then adding SR better mimics what response curve changes you get with BR/ML-TL.

Still, both mine and BB's designs sim as good with much less stuffing, so at a glance it doesn't appear to be a good alternative IMO.

Agreed, on my own designs I mount the driver to a sub baffle that's ~only big enough to hold the driver and leave enough room to mount it to the cab's braced/flanged baffle cutout. This allows for good cab bracing and provides the driver a really rigid 'work platform'.

GM
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Old 13th October 2005, 02:10 AM   #27
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Quote:
Originally posted by rjb
Please can you expand a bit on your statements that not all drivers are suited to TL's and MLT's.

.........but what say makes a driver more suitable for a BR than an ML TL?

Thanks
Greets!

Not sure what to add to our comments as I believe they are sufficient, so what specifically don't you follow?

WRT desirable driver specs, I've never given it much thought since pipe design is flexible enough to make any driver work OK in one, but for ML-TL I consider the theoretical ideal as being one where a T/S max flat alignment is Vb = Vas/Fb = Fs, so its Qts would be ~0.403 and Vas needs to be great enough that it's CSA isn't too small for the desired pipe length.

Performance wise, there's no such thing as too low a Qts driver, but there's a point of diminishing returns WRT efficiency loss, so 0.707x either side of ~o.403 works for me, ~0.285 min./0.57 max. where Fp is down below 40 Hz.

GM
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Old 13th October 2005, 02:52 AM   #28
rjb is offline rjb  New Zealand
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Thanks GM

Thats the clue I needed.

Ross
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Old 16th October 2005, 07:43 PM   #29
amt is offline amt  United States
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Thanks for all the help everyone. It appears that the best bet is going to be a BR since both VAS and Qts arent really ideal for a pipe. Looks like winISD is going to do the designing.

amt
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