Lab 12 Based Offset Driver - Mass Loaded - Transmission Line (OD-ML-TL) Design by Bj - Page 13 - diyAudio
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Old 5th May 2013, 11:39 AM   #121
DrDyna is offline DrDyna  United States
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Quote:
Originally Posted by NWCgrad View Post
Have you drilled the holes? How many of the inner partions can you reach from the driver mounting hole?

I hope we see a measurable difference, would emprically show mass loading is a real phenomenon and not just theoretical mamby pamby (precise engineering language could be substituted here).

I think two of these wil be great for the two channel rig, not sure how well they will work for HT as the don't dig below 20 Hz. The Labs 12s sound great in the temp sealed boxes I am using now, but they start rolling off to early (around 40 Hz). To counter, I have bumped up a bit with an LT via the miniDSP - but have to be careful with low end boost and cone excursion.

I don't get LT in practice. When modeling LT in winISP you have to reduce power significantly due to cone extension at the boosted frequencies, looking at before and after plots it seems it would be easier to use a shelf filter to bring down the higher frequencies instead of boosting lower. Overall the effect is almost identical if looking at max SPL at a given frequency below the LT boost due to reduced power handeling. Perhaps I am using the modeling incorrectly.
Sorry, I haven't fussed with it yet, I ended up in the middle of that bizarre may snow storm here just outside of Kansas City and wound up feeling ill this week, but I did get the wood for two new cabinets, so there should be some measurements soon. Just have to stop hacking and crooping long enough for it to be safe to use power tools :|

As far as LT, I think it's a toss up, either boosting low frequencies or cutting higher ones and then boosting everything back up to mate with mains.

I will most definitely be using these with HT, I'm going to have to confirm with measurements, but I think with the drivers I'm using, these are going almost as low as the tapped horns were pre-cataclysm, within a couple of cycles anyway, even with just one playing, they can still puff the room quite violently.

Andrea Zonn's "better be home soon" = happy fun times.
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Old 5th May 2013, 12:21 PM   #122
bjorno is offline bjorno  Sweden
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Hi All,

To answer the question of why I prefer the performance of an (OD) ML-TL versus a normal Ported BR is due to the port issues that always appear for a Driver with relative high xmax tuned low:
Over stuffing the Box and by adding Port stuffing are the only other measures that can be taken in order to keep the Port system reasonably small.

Take a serious look( zoom all the graphs) at the submitted pictures and you will find out why...

Note: The shown BR has a port diameter equal to the ML-TL.
The impact of folds in a quarter-wave enclosure are masked when stuffing is used thus can be ignored when simulating.

b
Attached Images
File Type: jpg Bends.JPG (600.8 KB, 287 views)
File Type: jpg Bends-No-Stuffing.JPG (608.8 KB, 271 views)
File Type: jpg No-Bends-its-a BR-using-Opt -Vol-and an external-port.jpg (840.8 KB, 258 views)
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Old 5th May 2013, 01:16 PM   #123
NWCgrad is offline NWCgrad  United States
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Quote:
Originally Posted by DrDyna View Post
Sorry, I haven't fussed with it yet, I ended up in the middle of that bizarre may snow storm here just outside of Kansas City and wound up feeling ill this week, but I did get the wood for two new cabinets, so there should be some measurements soon. Just have to stop hacking and crooping long enough for it to be safe to use power tools :|

As far as LT, I think it's a toss up, either boosting low frequencies or cutting higher ones and then boosting everything back up to mate with mains.

I will most definitely be using these with HT, I'm going to have to confirm with measurements, but I think with the drivers I'm using, these are going almost as low as the tapped horns were pre-cataclysm, within a couple of cycles anyway, even with just one playing, they can still puff the room quite violently.

Andrea Zonn's "better be home soon" = happy fun times.
Strange spring weather indeed, just got email from my brother in Topeka. Sorry to read you have been sick, I am on day 7 in a hospital in Bangkok. Always wanted to see Bangkok, to bad it by medical evacuation and ambulance ride. I get out and fly back to Phnom Penh tomorrow. Never thought I would be happy flying back to Phnom Penh.
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Old 5th May 2013, 01:18 PM   #124
NWCgrad is offline NWCgrad  United States
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Originally Posted by bjorno View Post
Hi All,

To answer the question of why I prefer the performance of an (OD) ML-TL versus a normal Ported BR is due to the port issues that always appear for a Driver with relative high xmax tuned low:
Over stuffing the Box and by adding Port stuffing are the only other measures that can be taken in order to keep the Port system reasonably small.

Take a serious look( zoom all the graphs) at the submitted pictures and you will find out why...

Note: The shown BR has a port diameter equal to the ML-TL.
The impact of folds in a quarter-wave enclosure are masked when stuffing is used thus can be ignored when simulating.

b
b,

Thanks for the information, when I get back to my office computer I will print and study the attachements. This has really been an education for me!

Best,
Steve
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Old 7th May 2013, 05:23 PM   #125
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Originally Posted by bjorno View Post
Note: The shown BR has a port diameter equal to the ML-TL.

b
Does the BR have the exact same flare at each end of the port as the ODMLTL?
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Old 8th May 2013, 03:30 PM   #126
DrDyna is offline DrDyna  United States
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I'm sure making sure stuffing is correct, as well as performance at higher levels should be considerations, nevertheless, here's the result of my little experiment.

All I did was rip out the piece directly behind the driver, which I figure was enough to turn it into a fairly well braced BR enclosure.

Not sure if this answers any questions or even creates more.

*shrug*
Attached Images
File Type: jpg od-turned-br.jpg (60.5 KB, 205 views)
File Type: jpg odmltl.jpg (59.6 KB, 179 views)
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Old 8th May 2013, 04:25 PM   #127
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Originally Posted by bjorno View Post
To answer the question of why I prefer the performance of an (OD) ML-TL versus a normal Ported BR is due to the port issues ...........
Right, IME anytime a < 0.5 [~17 m/s] vent mach requires a long vent, it's better overall to take the cab and vent volume [net Vb] and morph it into an inverse tapered TL.

GM
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Old 8th May 2013, 04:37 PM   #128
DrDyna is offline DrDyna  United States
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Right, IME anytime a < 0.5 [~17 m/s] vent mach requires a long vent, it's better overall to take the cab and vent volume [net Vb] and morph it into an inverse tapered TL.

GM
Inverse tapered, ahh!

I wish I knew wtf I really want to build now, to be honest I'm glad my tapped horns got wet, that was too much of a trade off to get efficiency and output I really didn't need.

I was fairly convinced I wanted to build a good pair of these OD-ML-TL enclosures, but if it's better overall for something reverse tapered (are we talking about an OD-ML with a reverse taper or are we talking about T-TQWT?
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Old 8th May 2013, 07:05 PM   #129
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Hmm, I see my response wasn’t quite ‘on track’ to bjorno’s……………

Regardless, nothing wrong with a MLTL, it's what I've mostly used, recommended over the decades since they work so well with traditional type drivers combined with the total effective system output impedance, but modern very low Vas and/or low Qt systems will spec TL length vents, so the inverse tapered TL or its tapped variant seems to me to be the obvious way to 'have my cake and eat it too' same as a TH is a morphed 6th order BP.


FWIW, I use different TL monikers for the purpose of clarity even though that technically, they are all just TLs and unfortunately are at odds with some of MJK’s monikers:

Constant [straight] taper = TL, ML-TL, etc.
Inverse taper = TQWT, ML-TQWT, etc.
Positive taper = horn, ML-horn, etc.

Where [ML = mass loaded] means a reflex vent is included to further lower system tuning.

Of course, there’s no clear cut break points WRT driver specs as to which is the best overall to use in every case, so it doesn’t hurt to try each one to see which one best overall suits the needs of the app.

As bjorno indicates, the constant tapered one covers most traditional apps and still many today and why I mostly recommend it or the ML-horn, especially since both are best overall [with a slight edge going to the latter] when a really wide BW is required with a medium Qt driver, but when there’s the need for some serious acoustical control down low, it’s hard to beat a TQWT and why I prefer it for ‘sub’ duty or getting a ‘choke hold’ on a high Qt driver.

The ‘stereo’ corner ‘subs’ I did back when other than for a few $$$ specialty R_T_R tapes, 32 Hz was pretty much the ‘bottom’ of even the best recordings, a ~16 Hz TQWT with a 15" low Qt, ~20 Hz Fs driver [or two ] at the floor and vent at the ceiling junction yielded a room enveloping, hear attack ‘fast’ bass that forced us to experiment extensively with turntable [TT] isolation.

Positively wimpy by today’s HT’s LFE channel’s standards of course, but back when the average HIFI recording was ~ –10 dB/35 Hz, it was pretty thrilling, especially if you also had chest pounding mid-bass to go along with it.

GM
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Old 8th May 2013, 07:49 PM   #130
DrDyna is offline DrDyna  United States
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...when a really wide BW is required with a medium Qt driver, but when there’s the need for some serious acoustical control down low, it’s hard to beat a TQWT and why I prefer it for ‘sub’ duty or getting a ‘choke hold’ on a high Qt driver.

The ‘stereo’ corner ‘subs’ I did back when other than for a few $$$ specialty R_T_R tapes, 32 Hz was pretty much the ‘bottom’ of even the best recordings, a ~16 Hz TQWT with a 15" low Qt, ~20 Hz Fs driver [or two ] at the floor and vent at the ceiling junction yielded a room enveloping, hear attack ‘fast’ bass that forced us to experiment extensively with turntable [TT] isolation.
So, not a tapped tqwt then, you're essentially talking about a tube with a driver at one end that inverse tapers to a slot port at the other? Or am I misunderstanding your description?
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