LLT Explained

**SteveCallas** · **01-10-07, 10:18 AM**

Wow Chris, I'm not just saying this, but you almost couldn't have asked for a driver more suited to this type of application (ported IB design) except for something like the LMS 4000. That Vas is very high for a 15" driver, making proper porting and low end sensitivity a sinch. More excursion woulda been nice, but can't complain.

Let me first collect a little more information though. With that 16db boost at 20hz, in all honesty, have you ever experienced any bottoming? You can get 120db+ levels at mid to high bass frequencies, but there is heavy compression going on below that, and your natural response shows this. Without exceeding excursion limits, and taking into account electronics rolloff, that IB is limited at ~9.5hz to 170 watts. So assuming you watch the typical WOTW, Incredibles, and other such low bass intensive movies at spirited levels (-10 or higher), if there has never been any bottoming, I can factor in more electronics rolloff than I am now. Or do you not really listen that loud (-10 or higher)? And are these sweeps corrected or not? Using Sonnie's correction files if so?

As far as room gain, doesn't really look like you are getting any. In fact, at the listening position, seems like you are losing a touch of low end. See the attached picture, it is what the rolloff should look like without any room influence, 12db/octave. This may also be incluenced partly by electronics rolloff.....my fingers would point in the direction of that standalone crossover and the BFD

It would also seem that the response looks more like the enclosure volume was 14 cubic feet as opposed to 600 based on where the rolloff begins (40hz) - that probably means the driver suspension isn't nearly as loose as AE claims.

Anyway you could take a 75db sweep from 10-100hz without that crossover or BFD in the chain? As in unplug them and go dvd player - processor - amp - sub? If not, no big deal, but the better idea I have of your electronics rolloff, the more performance I can extract. Make sure you are using Sonnie's RS spl meter correction file.

I'll wait to finalize the ported design until you can respond to some of those, but from an intial look, you won't need to partition off more than ~150 cubic feet, and you'll have up to 10db more headroom down low.

**SteveCallas** · **01-10-07, 10:38 AM**

Ok, another question. Does this thing:

Stay attached at all times? If it does, even when opened, it might explain some of the discrepancy in the rolloff starting so early. What would the dimensions of this wooden baffle cavity be?

**Chrisbee** · **01-10-07, 05:26 PM**

Hi Steve

Firstly I hardly ever get any cone movement at all.

I often do watch films at somewhere between -10 and -5.

I have watched WOTW "machine emerging" at reference without any obvious problems except abject fear.

With no house curve I have to listen loud to get any floor vibration. My SVS cylinder can shake the floor on solo piccolo!

This suggests that there is plenty of room gain. Over 20dB gain rising to 15Hz in the case of the cylinder!

The louvered panel is a permanent feature to keep off birds, prevailing sunshine and insects. The open area area is 5.5 x Sd. My IB enclosure is a glazed gable end and can reach 100F so I wanted to protect the divers from direct afternoon sunshine.

Careful listening tests on difficult material (classical organ) suggests no difference with the panel in place. Thomas didn't like the louvered panel either.

I should have tried an REW sweep without the Behringer boxes ages ago given the very early roll off. But having read the thread on non-spec IB15's I have assumed my own drivers have an Fs up around 35Hz. It would be nice to be proved wrong.

I am using the proper REW correction file for my new RS SPL meter.
My old RS meter was much more flattering. I used the correct file for that one too.

Now the (very) bad news: 150cu ft would completely fill the entire volume to one side of my glazed double doors. It just isn't going to happen! A sealed triangular enclosure 7 feet high x 7 feet deep x 7 feet wide in our sun room will never be acceptable to my wife. Or me, I'm afraid.

Thankyou for your interest, Steve.

I shall just have to find another way to turbo the bottom end of my IB.

If the REW sweep sans CX and BFD proves nothing I shall just have build an opposed driver manifold and/or buy some real IB drivers.

**SteveCallas** · **01-10-07, 11:04 PM**

Oh come on man, we were this close to making something like the first ported IB that I know of

It would have shown that it can be done, and the benefits are real. Maybe just wall it off so that it looks like a small equipment room? That would protect the drivers from everything.

5.5 x Sd? I'm not sure what you mean, I'm referring to the height, width, and depth of that section right behind the drivers - not the large open space, just that wooden area that has the louvered pannel.

I'm not saying your room can't give gain, it just doesn't look like it is for the location of the IB measured at your seat.

Non spec IB15s with a 35hz Fs....hmm, that's no good. Whether you still have any interest in the ported IB or not, I'd take the crossover and BFD out of the chain and do a close mic sweep and one at the seat, that will clear some things up. I would highly recommend you reconsider this ported IB idea one more time though

You could be the first of many.

**Chrisbee** · **01-11-07, 02:56 AM**

Steve

Your enthusiasm for this project exceeds my own by around seven feet cubed.

My IB enclosure doubles as a sunroom where plants can be grown and offers a nice view over the garden.

As an IB it doesn't even have to be remotely airtight. These are priceless advantages to the IB over an LLT.

Perhaps somebody else will step forwards as a willing guinea pig to build your first "ported IB"?

Put up a few likely figures as eye candy to prove your case and they might start fighting to be in your queue instead of ThomasW's.

**terry j** · **01-11-07, 03:16 AM**

geez, I'm kinda interested!

Am looking for options in the sub department, currently considering some sort of IB, will know more next week.

However, being in Australia I guess kinda limits the range of available drivers, as due to costs of shipping etc it makes most of the drivers you guys talk about prohibitive.

Anyway, as a point of discussion, what would a 'Callas' alignment consist of?? ( Did you like that? ha ha ha).

Further, how would such an alignment be evaluated?? What I mean is, say I ( or someone else) built it, and reported back that " it sounds fantastic", it wouldn't really mean much would it. And although measurements such as produced in REW tell us something about the performance, they don't really tell the whole story do they.

Intrigued.

**Chrisbee** · **01-11-07, 06:30 AM**

Hi Steve

Just to say thanks for reminding me to check for bass roll off in my IB's control electronics and any acoustic problems from my louvered rear panel.

All seems OK thanks.

I just need some room gain!

**SteveCallas** · **01-11-07, 09:25 AM**

Quote:

Put up a few likely figures as eye candy to prove your case

A simple understanding of what porting actually does and it's just common sense. The main issue is keeping the enclosure air tight and using drivers that like to see a lot of volume.

Quote:

Further, how would such an alignment be evaluated?? What I mean is, say I ( or someone else) built it, and reported back that " it sounds fantastic", it wouldn't really mean much would it. And although measurements such as produced in REW tell us something about the performance, they don't really tell the whole story do they

The sound quality would be exactly the same as a regular IB with the difference of a more solid low end. Porting in the range I am considering, 5-10hz, means that port output won't really play a role until below 20hz - above that, it is just a sealed sub. Look over post #1 in this thread for a better understanding. You would evaluate such an alignment by meauring your FR with the port(s) open vs with them stuffed, as well as max output levels, if your home could take it. The advantage in output comes from better power handling - with a sealed rolloff, you'll ultimately reach max excursion at some point with adequate power, let's just say 8hz as an example. Without some type of limiting or filtering, max power handling for the IB is based on safe playback levels to the lowest usable frequencies from your common media. By using a port, and limiting yourself to max excursion at the same point (8hz), you're able to use a fair amount more power, as the port decreases excursion use as you approach tuning. So essentially, you base max power handling on some higher frequency, like ~14hz, and you gain more headroom. See the attached picture.

The output advantage over most of the range with most IBs is moot though, because as Chris will attest to, output over most of the range isn't an issue to begin with using multiple high excursion drivers. The primary advantage is staying solid where the IB starts pooping out without having to wish for spectacular room gain or use lots of boost. Sooner or later somebody will make one. Hell, it might have to be me when I get a house

**SteveCallas** · **01-11-07, 09:30 AM**

Quote:

Just to say thanks for reminding me to check for bass roll off in my IB's control electronics and any acoustic problems from my louvered rear panel.

All seems OK thanks

Would you care to share them? I'm kinda interested in what's going on now too. Even without room gain, that rolloff is starting too early - either the drivers are far off spec or the louvered panel is somehow restricting the volume the drivers are seeing. You've got my curiosity raised

**Chrisbee** · **01-11-07, 10:27 AM**

Hi Steve

I published my new REW graphs in my "Attic" thread on the IB Cult Forum.

It took me so long to host them off group and then organize the graphs and titles that I would rather not repeat the exercise here.

I hope this link points to the thread but you may have to log in to view it.

http://ibsubwoofers.proboards51.com/...3383536&page=5

**Chrisbee** · **01-12-07, 01:16 PM**

Steve

I've been messing about with WinISD Beta and Pro (with limited success) trying to port my present 4 x 15" IB to try and develop a house curve for films.

Porting lifts the extreme bass into a hump on the WinISD graphs but I am not sure how sealed the enclosure needs to be or suitable port dimensions.

My fuzzy logic suggests I need a port with some length rather than a simple hole in the wall. Otherwise the hole will simply leak the higher frequencies giving me an odd response compared with the IB. I can get the port only about 6-8 feet away from the drivers.

Perhaps my 600 cu.ft. (17000L) box is simply too big to fit a port anyway?

The large size of the enclosure may mean perfect airtightness is not really necessary? I'm thinking that lining the enclosure with taped, thick polythene sheet might be sufficient since pressures are likely to be so low.

I doubt an LLT of this size has ever been tried before with 4 x 15" drivers.

Any useful thoughts?

Thanks

**Sonnie** · **01-12-07, 04:19 PM**

Quote:

Chrisbee wrote:

It took me so long to host them off group and then organize the graphs and titles that I would rather not repeat the exercise here.

I can grab it, copy and paste that for you over here if you want. It would probably be nice to see some more REW graphs on IB's in the REW forum... or here in the DIY Subwoofer area.

**Chrisbee** · **01-12-07, 04:47 PM**

Quote:

Sonnie wrote:

I can grab it, copy and paste that for you over here if you want. It would probably be nice to see some more REW graphs on IB's in the REW forum... or here in the DIY Subwoofer area.

Hi Sonnie

If you have the skill and expertise then please feel free to do so.

Provided the original post remains on the Cult I hope Thomas won't mind you "borrowing" a copy in the interests of science and education.

**Sonnie** · **01-12-07, 07:20 PM**

Okay Chrisbee, your thread is started here. You can edit it as you see the need. You can also use those image links... and if you need images hosted, just let me know... that's not a problem. If you want the title of the thread changed, let me know as well.

**Sonnie** · **01-12-07, 09:07 PM**

Steve... would an LLT get me into that 10Hz range at respectable levels with one of the SoundSplinter Rl-p15 drivers?

**SteveCallas** · **01-12-07, 10:22 PM**

Quote:

My fuzzy logic suggests I need a port with some length rather than a simple hole in the wall. Otherwise the hole will simply leak the higher frequencies giving me an odd response compared with the IB. I can get the port only about 6-8 feet away from the drivers.

Perhaps my 600 cu.ft. (17000L) box is simply too big to fit a port anyway?

Yeah, you definitely don't want to use all 600 cubic feet for such a sub. I'm on a different computer now, but the model I was working with was somewhere under 150 cubic feet, used two 10" diameter ports that were less than 30" long, and was tuned somewhere around 8-10hz. I'll get on my laptop tommorrow if you want the exact figures I was working with, but just adding a port to your 600 cubic foot enclosure isn't a good idea. If those drivers really have a Fs of 35hz, scratch the idea all together

Quote:

Steve... would an LLT get me into that 10Hz range at respectable levels with one of the SoundSplinter Rl-p15 drivers?

No, I don't see that happening, not with a single driver if you want a legitimate subwoofer. If you want something like a badpass that focuses just on a small area down low that you can try to integrate with another sub, that might be possible, but even then, the RLp15 isn't very well suited to such a task and that kind of a sub is pretty wasteful when taking work and size into consideration, in my opinion. And though you didn't mention it, trying to port a multidriver RLp15 IB wouldn't work out too well either, the driver isn't suited to it unfortunately. Those IB15s are almost perfect though, if they actually meet their spec.

**Sonnie** · **01-13-07, 12:58 AM**

IB15's??? Which drivers are you referencing?

Is there a good driver for me to accomplish this with? What I'd like to do is work on the response from 10-18Hz and with one driver if possible.

**SteveCallas** · **01-14-07, 09:15 PM**

Just about any sub you can build that will be solid from 10-18hz will also typically be a good overall sub....not just in that region, cause if it has headroom to spair that low, it definitely should have headroom to spare above that region. Is your IB not keeping you flat down low too, or is this for a different room?

**Sonnie** · **01-15-07, 09:22 AM**

I don't have an IB.... I use two SVS PB12-Plus/2 subs. They extend down to about 16-18Hz comfortably. Awesome subs, but I would like to add something to reach down to 10Hz.

**SteveCallas** · **01-15-07, 09:06 PM**

I coulda sworn you tried an IB

Thread overload for me I guess.

Well, assuming you sold the two Plus/2s, you should have a pretty good chunk of change to work with, and you would easily be able to outperform them....easily. I know you'd probably be pretty reserved about selling your commercial subs to go DIY, but you can check the impressions of any multitude of people who have done the same thing and marveled at the improvement. Anyway, on to the two main questions:

What are your size and cost limits?

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