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Thanks Brent. So that begs the question - should I tune for max extension (below 20hz) or max spl (from 20hz)? Is there a THX standard for extension? Also, how important is it to get a flat curve for the transfer function magnitude & how does that curve relate to max SPL and which one is most important (I know, probably both). In fact, I've got no idea what to do with WinISD - e.g. the best tuning for my application - lost!

Blue
Tuning - It's usually trying to find a balance between max extension and max spl. In this case it would be 12.4 cubic feet tuned to 16 hz.
It's ok if the transfer function dips below 20hz because room gain will add to the output and bring it back up. Some rooms have more room gain then others so it's not very accurate. To get a flat response in room you would use the REW software to get an accurate response and use the BFD (Behringer Feedback Destroyer) to make the corrections.
 

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Discussion Starter #22
I have used REW and found that the best location for a sub is in a rear corner (otherwise I have horrendous peaks and nulls). At present, with the passive radiator sub I have, I cannot discern the location of the sub.

I read somewhere that for Hi-fi use a port velocity of around 17 m/s was recommended. For the new subs, I would place one sonotube at the rear corner and probably one in a front corner. Do you think with a port velocity of 24 m/s that I would be able to locate the sub position?

I've tried playing round with WinISD and can only get the velocity down (to 19.5 m/s) by using a 9 inch wide port of 47.24 inches long with a tuning of 16hz (box vol 351 litres). Would that work? What is the reason to keep ports less that 36 inches long?
 

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The reason to keep ports less that 36 inches long is because of the first port resonance. One 8 inch port would meet the requirements. At maximum power to the sub, the air speed would be 24 m/s at 14.5 hz. The question is how often would you be driving a sub to those extremes at that frequency. Even if you did while playing a movie, a frequency at that level would only be for a second or 2. If you were playing a 14 hz sine wave then it might be a problem. If you reduce the input power to 500 watts the air speed drops to 20 m/s. I have 6 subs and modelled them to have a maximum air speed of 30m/s and have never heard port chuffing while wartching a movie.
Here is a thread on port air speed and port resonance. Note post #3 by Brent who gives an excellent explaination.

http://www.hometheatershack.com/forums/diy-subwoofers/8249-avoiding-port-noise-churf-resonance.html
 

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Discussion Starter #24
Thanks for the link to that thread. Yes, I don't think I'll be running full volume much, if at all. More like -6db (master volume) is my normal max listening level, and -12 to -20 (if the baby's asleep) normal listening. So your recommended 24m/s sounds fine (no pun intended).

Regarding the following:

The lower frequency first resonance starts at the higher order crossover you will need to use to avoid reaching this band. I have heard and am currently building a pair of subwoofers whose first port resonance is about 120Hz. Due to this resonance happening at a pretty low frequency I will be using an extremely steep crossover (8th Order - 48dB/octave) and crossing the subwoofers over around 60-80Hz.
"higher order crossover", "8th order - 48db/octave", "first port resonance" - what does it all mean? I'm quite new to all this. Do WinISD show these things?
 

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Thanks Brent. So that begs the question - should I tune for max extension (below 20hz) or max spl (from 20hz)? Is there a THX standard for extension? Also, how important is it to get a flat curve for the transfer function magnitude & how does that curve relate to max SPL and which one is most important (I know, probably both). In fact, I've got no idea what to do with WinISD - e.g. the best tuning for my application - lost!

Blue
Mike already chimed in, but I'll add my .02 anyway.

As in most things, subwoofer design is a collection of compromises. The beauty of DIY is you get to choose how to weight those compromises. There's no single right answer to tuning for SPL, extension, or even cabinet size. It helps if you have an objective point of reference to base your design goals on.

In my case, I established an upper limit of 6ish ft^3 (170l) gross for volume. I focus my designs on 20ish Hz performance and my SPL requirements are relatively modest compared to the efforts of a lot of DIYers. My current sub is 5.9 ft^3 net, PE DVC15 tuned to 17hz. Based on REQW measurements of my previous subs, I knew this room was giving me as much as 10dB at 20hz compared to the WinISD model for those subs. The DVC15 is about -7dB at 20hz in the model with considerably more output potential...not that I really planned to use all of the extra SPL. According to REQW using the Radio Shack SPL meter as the mic, the DVC15 ended up essentially flat to 10hz in room, at least up to 100dB at the seats.

Yes, THX does have an extension and SPL standard. Back in the old days (DolbyProLogic), I believe it was 105dB at 30hz at the seats. Somewhere after the availability of DD/DTS and the LFE channel, the spec appears to have been bumped to [email protected] Remember, these are in room numbers, not ground plane/anechoic. McIntosh actually had a THX certified sub (old days) that had an anechoic f3 of 38hz. Similarly, M&K's THX subwoofer had a switch for THX mode/normal, which functioned much like current manufacturers extension/spl modes, to roll of sub 30hz content in THX mode to allow it to meet the THX spl requirements without risk of bottoming if sub 30hz content came along...otherwise it was spec'd with an f3 of 20hz.

-Brent
 

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Discussion Starter #26
Up to the XLS12's limits, it makes a better-sounding sub than the Ascendant Avalanche 18 does...

I would consider doubling up on XLS12's, putting them in about 40L each, and using 1 PR per driver instead of importing an unknown quantity from the US.
Surely an 18" or two would reach much lower and louder - but you think the sound quality will be inferior? Mike recons that his two 18" are far superior to the 12" Shivas he has (sorry - don't want to start a war!). How do the Shivas compare to the Peerless, keeping in mind I seldom listen to music (which is sad really) and really want the shake and rumble for movies? Does anyone else have any experience with these drivers?

Nevertheless, that's an interesting suggestion which I hadn't considered (I am actually looking at the Mach5 IXL 18.4s here: http://testbed.mach5audio.com/index-1.html. Can you tell from the specs if the driver is any good?)

It certainly would be cheaper using my existing sub and resolve the problem of selling my existing sub (or parts). But I'm finding the 12" Peerless box I have now only reaches to about 24hz, then drops off dramatically (even though I tuned it to 20hz). How would putting the drivers in smaller boxes (currently 50L) with one PR each affect extension/SPL and Xmax? The design of the sub I followed did say that you could get away with one PR in the same size box. I guess 2 boxes would give me twice as much SPL, but what about extension? Could I tune them to different frequencies to complement each other - one with lower extension, the other higher SPL? Also, would I double up on amplifiers - currently I have a 240watt plate amp in the box - or use a power amp of some kind to power them both?

Alternatively, I suppose I could keep the peerless and just make an additional 18" mach5 sonotube for extended lower end - the two complementing each other. But then, buying an EP2500 would be a bit of a waste because I would only be using one channel (any suggestions for a suitable amp for this setup)? Also, I suppose I'd be limiting the system overall volume by the limits of the lesser powered 12"?

Cheers,
Blue
 

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Thanks Brent. So that begs the question - should I tune for max extension (below 20hz) or max spl (from 20hz)? Is there a THX standard for extension? Also, how important is it to get a flat curve for the transfer function magnitude & how does that curve relate to max SPL and which one is most important (I know, probably both). In fact, I've got no idea what to do with WinISD - e.g. the best tuning for my application - lost!

Blue
I don't know of a THX spec for extension though they do specify an output spec of 115db. Dolby labs will reference 120db at 20hz (though I don't know how you'd use this.. the format specs 115db). If your design hits 115 at 20hz (in room with gain) you'll be more than well on your way :bigsmile: which it looks like you are. Build thread by chance???
 

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Discussion Starter #29 (Edited)
If you want to use the subs for movies, then the EBS alignment is the way to go. The recommended box size is 350 liters tuned to 15 hz. When modelling in WinISD the goal is to keep the port length under 36 inches and to keep the air speed at a reasonable level. To make it all work together, 12.4 cubic feet tuned to 16 hz works with a 8 inch diameter port 36 inches long. With an input power of 750 watts the airspeed is 23 m/s at 14 hz.

There is a lot of material under 20hz on todays DVDs. Tuning the subs to 16 hz will allow you to experience this.
Okay, I'd like to build a LLT as per Steve Callas' definition in 'LLT explained'. Your suggested design appears to meet most of the criteria however, Steve defines a LLT as a sub that is tuned to 15hz or less. Is it not possible to get down to 15hz with the Mach5s? Would that 1hz make very much difference? Should I model another driver (eg. Fi Car audio or elemental designs)? Eg. 'LLT explained" appears to list an Avalanche 18 in 650 liters tuned to 13hz, and a TC2000 15 in 320 liters tuned to 14.5hz. Nevertheless, the Mach5s do appear attractive given the cost... freight cost is the big killer over here.:rolleyesno:

Edit: I just noticed the Mach5 Audio website recommends for the IXL 18.4 an EBS enclosure of 350 litres (12.4 cubic ft) and a 15hz tuning...
 

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Is it not possible to get down to 15hz with the Mach5s?

Yes, with the right combination of box size, and port diameter. The port length should be kept under 36 inches due to port resonances. I'm not sure what Steve recommends for the IXL-18 in a LLT. Hopefully he'll join in with a recommendation.
 

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Just by remembering discussions when it first came out about its Le (and knowing it has no Faraday ring in the motor) I can tell you it won't sound as good as the XLS12, though everybody's right that it'll get (much) louder and go lower with meaningful SPL...
That in itself is quite subjective.. ;)
 

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Discussion Starter #33 (Edited)
I think I recall Steve recommending the IXL 18.4, so I guess it can suit a LLT...

I did try modelling the Mach5 in WinISD but I seem to remember (I don't have WinISD to hand) every time I changed the tuning to 15hz the port length would go way past 36". Changing the port diameter to 10" didn't seem to make any difference.

I've noticed that the power graph (I don't recall exactly which one - handling?) sometimes exhibits a u shaped dip (50-100 watts I think), with the rest being a straight line, depending upon the tuning etc. What is ideal here? (sorry, this is turning into a WinISD tutorial).

Also, does it matter if the transfer function (going in the 100hz down to 15hz direction) gradully rolls off, then starts to climb back up again a little around 20hz, peaking at around 15hz?

425l at 15hz!? How does that work (sounds cool though)? I definately would like a big one (no jokes please), as long as it will fit (2.3m ceiling). Does the 8" port get below 190hz resonance?

By the way, I'm looking forward to reading your LLT build thread Thxgoon - I think I might pick up some good info.
 

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Discussion Starter #34
That in itself is quite subjective.. ;)
Mark from Mach5 Audio gave me the details of the IXL 18.4 driver build:

"The IXL's have a 6 spoke cast basket, CCAW voice coil wire, black aluminum
former, four layer winding. I have the drivers built to my spec by a
buildhouse in China."

Does that mean much to anyone - in terms of quality? I know I can't expect the most expensive technology for the money.
 

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Mark from Mach5 Audio gave me the details of the IXL 18.4 driver build:

"The IXL's have a 6 spoke cast basket, CCAW voice coil wire, black aluminum
former, four layer winding. I have the drivers built to my spec by a
buildhouse in China."

Does that mean much to anyone - in terms of quality? I know I can't expect the most expensive technology for the money.
Six spoke cast basket just means.... its a 6-spoke cast basket. CCAW = Copper Clad Aluminum Wound voice coil. Nothing wrong with that. Black aluminum former & four layer winding are just basic parts and build process.

They are probably great quality. Mark has been selling woofers for awhile and if they sucked he would have all kinds of negative feedback. That doesn't seem to be the case.
 

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Six spoke cast basket just means.... its a 6-spoke cast basket. CCAW = Copper Clad Aluminum Wound voice coil. Nothing wrong with that. Black aluminum former & four layer winding are just basic parts and build process.

They are probably great quality. Mark has been selling woofers for awhile and if they sucked he would have all kinds of negative feedback. That doesn't seem to be the case.
I can vouch for that. I've been working mine hard since I built them. It's getting better and better now that the suspensions are loosening up. Definitely a good valve for the money.
 

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IXL 18 doesn't want a huge enclosure, and even at 400+ liters the tuning region starts to get peaky. I like the looks of ~365 liters with a ~15hz tune. You can't get away with an 8" port that way, but since it "only" has a claimed xmax of 22mm, air movement shouldn't be so bad as to cause problems. So it looks like three 4" diameter ports that are each 32" long works best. Two of those and an EP2500 will definitely do the trick. I wouldn't worry about sound quality for one second, as you'll have lots more headroom, lower distortion, much deeper extending FR, and faster overall transient response, all of which work to define accuracy. The most accurate subwoofer doesn't always sound the best subjectively though, based on what you are used to and what kind of music you like. However, over time, for a combination of both music and movies, accuracy tends to win out. A 12" simply can't keep up with two high excursion 18s in LLT form, not by a long shot.
 

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Discussion Starter #39
Thanks Steve,

I'm planning on building x2 sonotubes, so what would the port length & diameter work out to? Or would I use 3, 4" ports at the top of the sonotube?


And thanks for the advice about sound quality, it's always a worry when you can't hear them before buying - and I've never heard an LLT for that matter either. :T

Cheers
 

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Per each sub, you would want to use three 4" diameter ports that are 32" long for the design I mentioned. You would want to make sure you have at least 4" spacing between the edge of each port as well as the sonosub walls. Shouldn't be a problem with something like 28" diameter tube, you should be able to get a good 6" spacing between each port and the walls.
 
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