Sonotube Questions & Suggestions

[Big-Al]

I am upgrading my subwoofer. The posts here on Sonotube Subs have helped me decide to use that as a Design model. I have a dedicated theater room but its only 14' wide with a 120" 16:9 screen so I dont have much width left.

Hence I think a 20" or 22" Sonotube Sub would fit nicely but it can be up to 80" high. I have an Adcom 5802 (450 WPC x2 amp) and NHT controller.

After reading through the Sonotube posts here a couple questions still nag at me.

Why stick to 260 l? The modeling I have looks better at 500+ l

At 260 l why tune to 15 Hz?
(Using Win ISD that curve looks poor to me using the reccomended SS 15P)
I assume I am doing something wrong in Modeling because the curve looks like this (below)

Secondly: Is there a downside to making a Sonosub 22" W at 80" high (500+l) ?

Third: Is there a better 15" driver under $250 than the SS 15p ?

Thanks,

-Al

[ThomasW]

I know of no better driver at the $250 price point than the RL-p15"

22" tube is great to work with since all the cuts work with cutdown 24" dimensions.

Don't know about WinISD since I don't use it.

The only downsize to a huge tube is simply it's size.

People forget that the plots from any computer sim are anechioc. In the real world vs anechoic sim, room gain fills in a ton of the low end.

Here's an real world example not a computer sim. Ignore the null that's mic placement issue. The blue line is a nearfield plot of my small IB. The magenta line is the same output level but measured 13' from the IB. That increase in output is typical of what happens when a sub is in a room.



If you really want to go with a huge tube, drop the tuning to 12Hz-13Hz and use 10" ports.

[Big-Al]

Thomas Thanks for the info!

The only downsize to a huge tube is simply it's size.

:T Thats exactly my understanding. If I make this 500 L then its only better, hence I fail to see any advanage to limiting it to 260 L.

People forget that the plots from any computer sim are anechioc. In the real world vs anechoic sim, room gain fills in a ton of the low end.

I understand, thats why I would like to design an enclosure that allows the RL -p15 to perform -3db at 20 Hz anechioc then allow room compensation to create "Riddicu-Bass"

If you really want to go with a huge tube, drop the tuning to 12Hz-13Hz and use 10" ports.

Based on your post on another topic I was considering a 10" port; but why tune it to 12Hz? I mean whats the acoustic advantage? Seriously unless you are an Organ affecianado there is little music info below 20Hz. Even many of the HT Fx occur above 20Hz.

Edit: I forgot to mention that my NHT subwoofer controller has boundary compensation, there is no exact description in the manual of what it does techically but I know it reduces the "boomy-ness" caused by room placement. So I have some control over the room/boundary issues.

[ThomasW]

but why tune it to 12Hz? I mean whats the acoustic advantage? Seriously unless you are an Organ affecianado there is little music info below 20Hz. Even many of the HT Fx occur above 20Hz.

Plenty of effects stuff at 15Hz as well. Just depends on where you want to set the subsonic filter. These drivers need protection below the tuning point.

Some drivers won't 'bottom' due to their design, that doesn't mean they won't 'oilcan' or something else nasty if they unload.

[Big-Al]

Just so I understand then... Your suggestion for tuning at 12 Hz was for protection reasons and not necessarily for acoustic reasons ???

[Big-Al]

Getting Closer

I would really apprciate feedback from those who have done this to make sure I have a solid design before I start... ;x(

Ok after further research and measuring my spacing down stairs, here is what I am thinking:

I like the look of Chuck's (Chasw98 ) 20" tube design w/ RL-p15.
The width of the 20" will fit nicely in the front or back of my room or both :E
However I still want to make it 80" tall for more low frequency extension and I think a sub taller than most people would just be wicked :evil:

Sonotube comes in only 60" lengths, however Easy Pour forms come in 12' sections so cool I just need to find them locally.

Based on the SonoSub Calcualtor http://www.quux.net/roo/diy/sonosub/sonocalc.html

20" Tube at 80" less a
8" x 31" vent (16 Hz tune)
and 15" driver space
Yeilds a useable volume of = 380 l

I was hoping form more volume but 24" tubes get a bit bulky for my room.

Specs:
Dimensions: Tube 20" Dia x 80" Height + 6" for Base
Vent: 8" x 31" Sonotube
Effective Volume: 380 l (13.4 ft^3)

Driver: SS RL-p15
EQ: Behringer DSP-1124P (If needed)
Existing Amp: Adcom 5802 Eventually the Adcom will power my mains and I will get a Carvin HD-1800 For the SonoSub.

Do you see any problem and or have any further advice on this design?

Also a good friend of mine runs Lucid Acoustics He has some awesome CNC routers and finish ability. I am going to ask him cut the top and bottom shapes. I think he will keep the Sonosub file database so if anyone out there wants a 20" Sonosub wood parts you should be able to call him and have him make the wood parts for you, after I am done with my project.

Thanks,
-Al

[ThomasW]

Make the bottom plate about ~2" larger in diameter than the top. This adds stability and IMO improves the looks.

[SteveCallas]

Per your request Big-Al, I'll comment. You can go with as much or as little volume as you like and make it "work", I suggest 260 effective liters with the RL-p15 D2 tuned to ~15hz because I feel it is the most balanced all around performer. Your proposed design looks to have a noticable resurgence in output at tuning which will make meshing it in naturally with room gain difficult. The goal is to have a flat in room FR, and while no two rooms are alike, there is common ground between most. A shallow rolloff into the low frequencies is what you want, not a resurgence in output. Going too large in a ported design causes that port output to be almost undamped.

I'd like to see a snapshot of the modeling you have done to show 500 liters working well with the RL-p15 D2, just out of curiousity. You may find some of the last few paragraphs in my explanation here interesting.

[ThomasW]

Your proposed design looks to have a noticable resurgence in output at tuning which will make meshing it in naturally with room gain difficult.

In 40+ yrs of speaker building I've never come across the term "resurgence" used when referring to the performance of a ported loudspeaker.

Also I can guess what you're referring to with the use of the term "meshing", but his model is anechoic, and only some aspects of room gain is predictable.

A shallow roll-off into the low frequencies is what you want, not a resurgence in output.

Again I'm not sure what you're saying here?

[cobbpa]

Maybe by resurgence he is referring to a peak? Just my guess.

[Big-Al]

I suggest 260 effective liters with the RL-p15 D2 tuned to ~15hz because I feel it is the most balanced all around performer.

Thanks Steve I am just trying to understand why 260 l is the magic number I will read through your other posts, thanks for the link.

Thomas is right I am just looking at WinISP anechocic with the aforementioned roll off at low frequencies and thinking why not increase the sonotube length for more low freq extension if you have the space? The plots are on my home computer I will post them up later.

Perhaps more specifically my question is what are the predicted negative effects of a Sonosub larger than 260 L with the RL-p15 D4 ?

Thanks for all your input!

[soho54]

I believe this graph shows the FR in question.
Resurgence peak whatever. :B
This is only an example, not to OP's responce.

[Big-Al]

Again thanks for the link Steve. Excellent write up!! :T

Sorry for all the questions them seem redundant now that I have read what you authored! Consider adding a link in your Signature and or putting it on your website, that answered most all my questions!

For the benefit of this thread discussion I will attempt to answer my own questions based on Steves LLT Explained thread

This shallow roll off area is key, as most rooms typically yield about 4-8db of room gain/octave. The lower your sub can extend while maintaining an anechoic FR with this shallow roll off, the more solid and flat you’re in room response will be. This is the main reason LLT owners have such extremely flat and low extending in room FR measurements - measurements that are almost too good to be true without the use of EQ.

Based on the assumption that that you want a flat FR curve you are compensating for the predicted room gain at low frequencies with an even roll off.

Hence the best curve for a LLT (large and low tuned ported)design looks as you showed (Plots from Steve's full post)



So to answer my own question; 260 l with a RL-p15 gives the desired nice roll off with out any rise in FR at the tuning frequency (too High or too Low)

I hope thats at least in the ball park...

Hmm now to rethink my design a bit.

[ThomasW]

Without seeing all the data used to create the sims it's difficult to know the specifics. What's obvious from the plots are the following...

#1 is typical of a ported box with a 20Hz port tuning.
#2 is the typical of a sealed box. If this is a supposed to represent a ported box, it's one that's badly miss-tuned
#3 is the response of a ported box with a low tuning.

Any attempt to characterize these as good, better, or best is comparing apples to oranges.

[ThomasW]

I believe this graph shows the FR in question.
Resurgence peak whatever. :B
This is only an example, not to OP's responce.

The 'saddle' (not my term) seen in computer sims results from several situations.

One is when the effect of VC heating hasn't been taken into account by the computer model.

Another is the typical situation where there's a wide gap between the driver's Fs and the port tuning. The effect of this is such that the sim replicating the natural roll-off of the driver, shows a dip in output before the effect of the port kicks in. Once again this is a situation where the sim's anechoic response doesn't reflect the 'real world', where room-gain fills the 'saddle'.

[Big-Al]

Any attempt to characterize these as good, better, or best is comparing apples to oranges.

Appologies, I am using this a bit out of context from Steves full explination post. Steve is outlining his guiding principles in designing the LLT subwoofer and to achieve his stated goal there is a specific roll off that needs to be in place.

Its only Good / Bad as relating to the design of the LLT, not in general..

[Big-Al]

T Once again this is a situation where the sim's anechoic response doesn't reflect the 'real world', where room-gain fills the 'saddle'.

Thomas thanks and interesting. I have designed numerous subs in a previous job for HT use I just used the default -3db point of the system as my vent tuning point. What you are suggesting is that there can be a larger gap between Fs and Vs and that room gain will "fill in" to some deree even when the anechoic FR shows a "saddle"...

That just makes the LLT design sound that much better to me..

[ThomasW]

What you are suggesting is that there can be a larger gap between Fs and Vs and that room gain will "fill in" to some deree even when the anechoic FR shows a "saddle"...

I'm saying there's a balance to be struck when chosing the tuning point in relation to the Fs of the driver. As a result one shouldn't dismiss a design simply because there's a saddle in an anechoic sim.

[Big-Al]

Oh I agree... I have designed some "flat" subs that souned like crap and a couple with spikes in Anechoic FR ended up sounding much better than I expected... Room loading and subs is almost its own science...

[ThomasW]

Oh I agree... I have designed some "flat" subs that souned like crap and a couple with spikes in Anechoic FR ended up sounding much better than I expected... Room loading and subs is alsmost its own science...

......:agree:

[SteveCallas]

#2 is the typical of a sealed box. If this is a supposed to represent a ported box, it's one that's badly miss-tuned

All three designs were using the same size enclosure, all that was changed was the tuning frequency. Design #2 was simply tuned to some very low frequency, maybe 5hz or so.

Any attempt to characterize these as good, better, or best is comparing apples to oranges.

How so? Again, all rooms are different, but assuming 4-8db of room gain/octave kicking in ~25hz isn't really going out on a limb. Designing with this in mind is a good idea.

Another is the typical situation where there's a wide gap between the driver's Fs and the port tuning. The effect of this is such that the sim replicating the natural roll-off of the driver, shows a dip in output before the effect of the port kicks in. Once again this is a situation where the sim's anechoic response doesn't reflect the 'real world', where room-gain fills the 'saddle'.

If room gain fills in the saddle, it also affects the peak just below the saddle, resulting in a large peak. This can be resolved by using less volume and a lower tune.

[Big-Al]

I'd like to see a snapshot of the modeling you have done

I have overlayed the plots in WinISD 0.44 beta. The Blue was the defalut in WinISD so I just left it for reference to a traditional vented design with this woofer.

I realize that the 380 l may not meet your definitions of a "True LLT" however I think the extra output 25~15 Hz could be fun for a HT subwoofer. If I dont like it the cool thing is that I can just cut the Sonotube down and change the port length with a minimum of effort. The end caps all remain the same. :B

As always thanks for your input and ideas!

[SteveCallas]

I see the discrepancy - you are using a D4 - I was referring to a D2. The D4 wants more volume than the D2.

[ThomasW]

Large enclosures with low tunings and big ports have been around a while. They're a good choice in the situation where one has enough room and isn't subject to SAF issues. These designs do not change the laws that govern ported designs. So as with any ported alignment, care must be taken to protect the driver from unloading. If this is ignored, a very unpleasant surprise is waiting in the wings....

When looking a sims and considering the effects of room gain, one must factor in how humans perceive low frequencies. With subsonic tunings, if one design has a saddle and another doesn't, isn't an indicator they will sound radically different, or that one design is inherently superior.

[Big-Al]

I see the discrepancy - you are using a D4 - I was referring to a D2. The D4 wants more volume than the D2.

Yea I prefer the higher damping factor (Amplifier Damping Factor) when connectd to 4 or 8 Ohm woofers. I have seen soooo many car designs and when the guys strap them to 2 Ohms the Amps loose control. Most guys think it sounds great but it bugs the crap out of me. I like overkill bass but I like it under control. The other thing I have experienced is that the Z curve for 2 Ohm woofers can get wierd and go below 2 Ohms and even the best amps dont like that, especially when you are driving them hard...

I know I am a bit quirky on this but I have never met a 2 Ohm driver / Amp combination that I really liked. So I trade a bit less max ouput for more woofer control at all frequencies...

[Big-Al]

So as with any ported alignment, care must be taken to protect the driver from unloading. If this is ignored, a very unpleasant surprise is waiting in the wings....

I agree I will use steep filter below tuning Freq. This is one I learned the hard way when I was demonstrating my 2nd subwoofer design at a CES and "Whack!!!!" the VC hit the back plate with my hand still on the volume control...In fact it damaged the woofer, good thing I had brought a couple extras just in case. Its REALLY loud when you push a vented woofer beyond its XMAX or clip the amp.... Scared the crap out of me (well some of it) DOH :E Ever since I am a believer in protecting vented designs below tuning.

[Big-Al]

EQ w/ Low Pass Filter

Found a good EQ with built in low pass filter at 10 hz -12db/oct
only $89

http://www.behringer.com/PEQ2200/index.cfm?lang=ENG

For anyone who needs just a subsonic filter under 20 Hz they are hard to find but here is one from the Car world PIE Ld-1

http://www.discountcarstereo.com/detail.aspx?ID=317

[ThomasW]

On page 10 of the manual #5 regarding the LOW CUT control it says "In the 10Hz position the signal passes unchanged"

System Specs listed as 18Hz - 30kHz +/-3dB

And in the parametric filter section the lowest frequency is band #1 20Hz-400kHz?

That seems a bit odd?

[Big-Al]

hmm the Spec sheet says:

Adjustable 10 - 400 Hz , 12db/Oct butterworth

So I guess you set it to 15 Hz and your fine ????
Thats odd...

[Big-Al]

And in the parametric filter section the lowest frequency is band #1 20Hz-400kHz?

None of the EQ's I have seen Rane, Behringer, etc have EQ range under 20 Hz and 99% of the products with sub sonic filter stop at 20 Hz or higher.

The DSP 1124p that is also reccomended does not have EQ under 20 Hz according to thier specs (maybe an owner can tell me otherwise??)
And it does not have and subsonic filter according to the manual.

[soho54]

On page 10 of the manual #5 regarding the LOW CUT control it says "In the 10Hz position the signal passes unchanged"

System Specs listed as 18Hz - 30kHz +/-3dB

Maybe it has a natural 12db/oct roll off at 10hz, and the FR's F3 is 18hz. :B

[ThomasW]

The 1124P has 20Hz as the lowest hinge point

This 1/3rd octave graphic EQ has a 10Hz slider and a separate low cut filter that starts at 10Hz. Frequently these go on sale for $70

http://www.musiciansfriend.com/product/Furman-Q1311-Single-Channel-31Band-Equalizer?sku=181227

[---k---]

Was Chuck a while ago talking about a subsonic filter project that he said he would be willing to sell them?

It seems silly to me to put another eq in a chain to get a highpass filter. Can't they be made pretty easily and cheaply?

[ThomasW]

There's always this solution

http://sound.westhost.com/project99.htm

[Big-Al]

There's always this solution
http://sound.westhost.com/project99.htm

Yea I saw that but I would prefer a single box solution a good EQ & filter all in one box..

Thanks for the suggetions guys!

[Big-Al]

It seems silly to me to put another eq in a chain to get a highpass filter. Can't they be made pretty easily and cheaply?

I am not suggesting 2 eq's just trying to find one good EQ that also has a sub sonic filter at 10 Hz.

Thomas the Furman is a discontinued product, ovbiously that particluar company may have them in stock but in reading through the manual its pretty similar to the Behringer. I hope I only need 1 or 2 bands of EQ in the sub range.