Lab 12 Based Offset Driver - Mass Loaded - Transmission Line (OD-ML-TL) Design by Bj - Page 10 - diyAudio
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Old 22nd April 2013, 10:27 PM   #91
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Something is way off with those impedance measurements. There's no reason why they should look so ragged, unless the box is very poorly built and full of resonance modes, which I doubt.
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Old 22nd April 2013, 10:30 PM   #92
_henry_ is offline _henry_  Australia
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i think i know, dave forgot to calibrated the test lead
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Old 23rd April 2013, 01:36 PM   #93
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Originally Posted by _henry_ View Post
shadydave,

thank you for posting these details. its very interesting the impedance behaviour heavily altered in this box. i think this was the case with the original LABhorn, as i remember the impedance on the box will be around 8ohms with the LAB12 6ohm.

in this case, you can save the 1ch from your amp by driving the 2 LAB12 with single channel with similar power and SPL, isnt it?

the room response is very flat, is that EQ'ed?

cheers
henry
No EQ.
I was driving the amp with the output of the USB pre.
All sweeps posted since Jan. of this year are with a 20 Hz BW, 24 dB/octave HP filter and no low pass filter.
It is unsmoothed, or 1/48th octave which is what REW calls unsmoothed.
.
My house has an inroom hole at about 34 Hz and I found that moving the speaker around the room while maintaining the 1 M mic distance would change this hole.
I attached an example of 2 sweeps, one showing the hole prominently and the other with the hole somewhat reduced.
Also, I am rather sure of the SPL calibration on these sweeps.
I did the cal using an EBAY new (NOS) "Shack" SPL meter.
.
I think I may have hurt the USB port that I am using for DATS as I have seen several anomalous results from DATS lately, including the in box Re of over 12 ohms. Both Lab12 sub boxes read this way.
.
The thing that I am worried about is the falling low end in the outdoor response.
I thought it should look closer to the output of HRSP SPL chart.
.
Am I correct in thinking that the outdoor SPL sweeps should be allot flatter?
.
I attached 2 sweeps made indoors (in my concrete house) done in Jan where I moved the cabinet around the room. One shows the prominent hole at 34 Hz, the other shows a different looking "hole response".
It is definitely a room mode.
.
Also
Quote:
Brian Steel says: Something is way off with those impedance measurements. There's no reason why they should look so ragged, unless the box is very poorly built and full of resonance modes, which I doubt.
I agree that something is wrong.
I do not think it is the box construction, 18 mm 13 ply BB glued with Urethane glue, clamped and screwed together using #6 square drive screws and stuffed with long hair wool (this time to Bjorno's specs).
.
I even pulled out some stuffing and the Speakon connector to use larger wire (was 16, went to 12 gauge appliance wire) when I saw the 12.4 ohms on the first box but this changed nothing.
.
I expected the Impedance curve to look similar to the HRSP chart with maybe the magnitude of the impedance off a little and the frequency of the peaks to be close to the HRSP prediction.
.
I am really stumped by the lower peak being so much lower in magnitude, so much wider and the general waviness of the trace.
.
I don't seem to have them with me but the bare Lab12 driver makes a single peaked impedance plot that looks just like what I would see on a spec sheet.
I need to do some more testing and figure out what is going on.

The only thing I can say is they, both, sound impressive

Dave

Time for more testing
PS..I assume that testing the impedance through a 4 pole Speakon connector, both sides using 12 gauge wire, and only about 12 ft. of it is OK..??
Attached Images
File Type: jpg Jan 12 sweeps.jpg (117.3 KB, 326 views)
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Last edited by Shadydave; 23rd April 2013 at 01:55 PM. Reason: too many mistakes
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Old 23rd April 2013, 10:39 PM   #94
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Originally Posted by Shadydave View Post
..I assume that testing the impedance through a 4 pole Speakon connector, both sides using 12 gauge wire, and only about 12 ft. of it is OK..??
It should be fine. A few times I've gotten similar crazy graphs from my WT3/DATS system and the only resolution was a PC restart and ensuring that I use the same USB port every time for measurements.

BTW, In my (albeit limited) experience, a lower impedance peak that's much lower and flatter than expected can be caused by too much damping material in the box. If the center frequency is shifted upwards, it could also be caused by a leak near the driver.
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Old 23rd April 2013, 11:48 PM   #95
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Quote:
Originally Posted by Shadydave View Post
The thing that I am worried about is the falling low end in the outdoor response.
I thought it should look closer to the output of HRSP SPL chart.

Am I correct in thinking that the outdoor SPL sweeps should be allot flatter?

I expected the Impedance curve to look similar to the HRSP chart with maybe the magnitude of the impedance off a little and the frequency of the peaks to be close to the HRSP prediction.

I am really stumped by the lower peak being so much lower in magnitude, so much wider and the general waviness of the trace.
I think I may have hurt the USB port that I am using for DATS as I have seen several anomalous results from DATS lately, including the in box Re of over 12 ohms.
Though I have not done impedance sweeps on my cabinets, I am familiar with Hornresp frequency response peaks and dips looking larger than those measured, I would not worry much about the amplitude of the peaks since they are at the correct frequencies, and stuffing is not in the Hornresp program.

The in box Re of over 12 ohms would make sense as an average that includes the 18 and 38 ohm peaks and the 5.2 dip.

As far as your outdoor measurements, (not sure which they were) "cabin gain" in a small sealed room can make a big difference in LF response.
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File Type: png Impedance.png (152.3 KB, 303 views)
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Old 24th April 2013, 02:18 AM   #96
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12gauge wire should be MORE than adequate for this setup. All connections are secure correct?

Driver bolted down firmly? Gasket in place?
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Old 25th April 2013, 12:44 PM   #97
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Originally Posted by m R g S r View Post
12gauge wire should be MORE than adequate for this setup. All connections are secure correct?

Driver bolted down firmly? Gasket in place?
10-24 Socket Head Cap Screws and I used the 1/8" X 3/8" speaker sealing foam to seal the drivers.
As far as secure I always wonder about spring loaded wire clamps, they sure are easy but...well I guess they must be proven to work well by now.
.
I used a new USB port and also noticed that I had the input level set at 0% instead of 1% as per the DATS instructions (not sure what that all means, 1% ?)
Anyway, it now makes a much cleaner looking impedance measurement.
Attached Images
File Type: jpg Lab 12 box_2_4-25-13.jpg (222.5 KB, 279 views)
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Old 25th April 2013, 01:50 PM   #98
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Originally Posted by Shadydave View Post
I used a new USB port and also noticed that I had the input level set at 0% instead of 1% as per the DATS instructions (not sure what that all means, 1% ?)
Anyway, it now makes a much cleaner looking impedance measurement.
Dave,
Looks about 1% "cleaner" to me .

Looked OK before, and virtually identical, other than the 33.65 Hz peak being about 10% higher in the 1% test.


Art
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File Type: png 1% cleaner.png (123.7 KB, 264 views)
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Old 26th April 2013, 12:54 PM   #99
DrDyna is online now DrDyna  United States
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I finished one prototype yesterday and was looking forward to doing some outdoor measurements today, but its been raining, of course.

Stupid tablet, I guess its just gonna be sideways.
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File Type: jpg 20130426_075151.jpg (315.0 KB, 259 views)
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Last edited by DrDyna; 26th April 2013 at 12:57 PM.
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Old 27th April 2013, 01:50 PM   #100
DrDyna is online now DrDyna  United States
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Alright, so a few listening impressions since I've had a chance to spend some quality time with this enclosure. First, I've only completed the one made out of scrap left over from moisture damaged tapped horns, and I'm in a different room until repairs are made to the normal one. In case you haven't seen any other posts of mine, I'm using TC Sounds epic 12 rather than the Eminence driver. I've wired the single driver with each coil having one channel of an EP 2000.

This design seems to have more in common with my other T-TQWT than any of the others. I'm not sure if its due to the front mounted driver, but this seems way, way easier to integrate with mains than the tapped horn, or even the T-TQWT. It seems like it behaves more like a standard vented enclosure in that regard. It also seems like it has more "grip" on the air, but I'm not sure if that's in my imagination or not. It seems like it keeps pace with the music better with less...uh...(sorry for all the subjective junk) flop.

Where the tapped horn was just "blam boom pow bass here I am in your face" this is quite a bit more musical, and with some careful level matching seems to have disappeared behind my mains, until something needs it. "Yello - The Expert" means something completely different on this design.

While not quite as efficient as the TH, it's growing on me. I think the trade off is well worth it. Yeah, its not going to knock pictures off my neighbor's walls, but it can still grip your guts and give you a good shake when it needs to.

I'm looking forward to a sunny day tomorrow, where I can dolly this thing out in then front yard and try to get some proper measurements, but overall, I'm very happy with it and I'm most likely going to be building a proper pair out of BB Ply in the next couple of weeks.
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