Sanity check sonotube sub DIY project

[HMenke]

First time post here after lurking and discovering that this is the ultimate DIY forum on the web! :T

I recently acquired a BFD1124P and RoomEQ Wizard. Result: instant dissatisfaction with my old Paradigm PS-1000 10" ported box subwoofer. Output rolling off steeply below 35 Hz doesn't cut it!

For my first sonosub project, I have tried WinISD Pro, Unibox, and Adire LspCAD. I couldn't get Unibox to do anything other than load and display. WinISD Pro seems to give unexpected results (ports apparently much too long), but I like and feel comfortable with Adire LspCAD. As you know Adire LspCAD only includes generic data for their drivers. I modeled the 15" Tempest, even though the driver I think I want to use it the Soundsplinter RL-p15. I'm not as concerned about modeling the performance of the driver at the extremes as I am just getting the box properly tuned. I won't be holding any home rock concerts, just listening to movies!

I have come up with the following concept:

• tube ID 24" (I assume the concrete forming tubes are spec'd by ID?)

• tube cut length 55"

• 3/4" MDF cap each end displacing 236 in.^3 inside the tube

• RL-p15 displacing 363 in.^3

• 6" unflared PVC port (I assume PVC spec'd by OD and actual ID is about 5-1/2"?)

• Port 10" long displacing net 38 in.^3 insde the tube (not re-counting the 3/4" end cap exit length already included in end cap displacement calc)

• Resultant port tuning 17.9 Hz (according to LspCAD)

Looking for a sanity check on the above - does it look OK?

Also, how/why would one choose between the dual 4-ohm vs the dual 2-ohm voice coil option on this driver?

Thanks!

Henry

[SteveCallas]

How many layers of 3/4" MDF were you planning on using for the end caps? One probably won't be enough. I'd use at least two for the top and three for the bottom. I've modeled both the dual 2ohm and dual 4ohm versions and based on what I see, I prefer the dual 4ohm version even though it won't extend as deep. Take a look at a 7.5 cubic foot enclosure with a 6" port that is ~28" long (~17.7hz tuning) fed with 1000 watts.

Your tube wouldn't need to be nearly as large as you are thinking.

[HMenke]

My thinking was that there would be two layers of 3/4" MDF laminated together, such that one of the layers is flush inside the tube and the other is fully outside the tube.

I neglected to mention that the above works out to a net enclosure volume of 13.9 cu. ft or 383 liters, which is almost double what you estimate is needed. So you think that is too much for this driver? (I realize there may be more than a little irony in asking you "Is that too much?" after looking at your Sonosub!)

One other thing I've been wondering is how people cosmetically handle the interface of the tube covering with the overhanging end caps. Does the fabric just wrap over the end of the tube? Or is there a raw edge butted up to the end cap? I was thinking it might make sense to router another 1/8" - 1/4" out of the outer cap to let it drop down and cover the raw edge of the fabric.

Henry

[HMenke]

Two designs

Here are LspCAD screen captures from two designs, 212L and 393L. The 393L seems to have flatter extension with roughly the same rolloff.

[ThomasW]

Henry,

Since you're willing to live with a such a large enclosure you can get some interesting results.....

If you can find material for a 8" port, 33.5" long you can get some pretty low port air velocities using a 300L box ....:wink:

And if you want to run Unibox, you need to change the security setting in Excel to allow macros before loading the Unibox spreadsheet

[HMenke]

Henry,

Since you're willing to live with a such a large enclosure you can get some interesting results.....

If you can find material for a 8" port, 33.5" long you can get some pretty low port air velocities using a 300L box ....:wink:

And if you want to run Unibox, you need to change the security setting in Excel to allow macros before loading the Unibox spreadsheet

Wow Thomas, that's awesome! Yes, I am not bothered by a large enclosure. In fact, it's cooler! Fortunately I have a wife who puts up with me (we have a folded corner horn in the living room for "whole house audio"). This unit will go in the dedicated basement HT room.

I realized after looking at your post that with my LspCAD model, I had the amp power set at only 1W, so I wasn't getting a realistic port velocity. I can see that 8" would be a lot better than 6"!

Thanks for the Unibox tip: I'll give it a try.

[SteveCallas]

I may be way off, but isn't it best to avoid any kind of a bump, or resurgence in output once the FR has started rolling off - in other words blend in the port's output so that it mates with the initial rolloff? I realize the room will make any anechoic response one is shooting for somewhat null and void, but in regards to overall performance, isn't the bump is undesirable? With the SS RLp15, especially the dual 2 ohm version, I find you can't really avoid that when you try to start using very large enclsoures. Yes, no?

[ThomasW]

Steve,

It's not a problem I'm aware of.... Many designs have a relatively big 'saddle' or dip between the driver roll-off and the output of the port. It's filled in by room gain

Here's a plot of the original Stryke cube sub. This was the quickest example I could locate...

[HMenke]

I may be way off, but isn't it best to avoid any kind of a bump, or resurgence in output once the FR has started rolling off - in other words blend in the port's output so that it mates with the initial rolloff? I realize the room will make any anechoic response one is shooting for somewhat null and void, but in regards to overall performance, isn't the bump is undesirable? With the SS RLp15, especially the dual 2 ohm version, I find you can't really avoid that when you try to start using very large enclsoures. Yes, no?

My theory is that you want the port to kick in and augment the driver's output when the driver starts to roll off. If you could achieve an ideal match, the combined response would stay flat and then roll of steeply at some point. In practice it seems like the combined response shows a shallow rolloff, a small bump, and then a steep rolloff.

I am using a Behringer Feedback Destroyer Pro DSP1124P as a subwoofer parametric equalizer. I can measure the in-room response with RoomEQ Wizard and an RS SPL meter, tweak the filter settings in REW for a flat or house curve, and then upload the settings into the BFD via MIDI. I expect the initial non-EQ'd room response to be pretty bumpy with room mode peaks that need to be cut and nulls that need to be (within reason) boosted. I can handle any bump in output with a cut, but due to headroom I can't boost enough to create more output where the sub doesn't have enough response to begin with.

[HMenke]

Question re: amp power

Thomas, I got Unibox working in Excel with your tip and was able to duplicate your 300L 8" x 33.5" port model, so I feel pretty good that I'm on the right track now. Peak cone excursion at 25Hz is only 17.5mm at 500W so the RL-p15 is hardly straining. Can you check my RL-p15 model parameters (attached). Some of the quantity names in Unibox don't appear on the SoundSplinter T/S parameters page so I "guessed" at what they might be called by SS.

I've modeled the 4-ohm and 2-ohm versions of the driver and I think Steve is right, the 4-ohm looks better. The 2-ohm generates more of a bump for soem reason.

Question: when you enter "500W" into Unibox, are you saying 225W into each 4-ohm voice coil?

Henry

[ThomasW]

Here's what I used, I rounded some of them off since I'm lazy.

[HMenke]

Are there other good 15" drivers in the $250-$275 range that I should consider?

[ThomasW]

At this time I don't know of any better drivers in that price range. The RL-p 15"s are pretty state of the art. They're built like a tank, with anodized aluminum cones, double spiders, and speaker leads woven into the spider.

[Bent]

I'd concur, I received my second 15" RL-p two weeks, or so, ago, I'll be likely buying the 3 sheets of mdf this week, building a sealed box at 22" x 22" x 46" (outer dimensions), sealed and seeing how I like it. if it doesn't dig deep enough, the I'll build a mirror-image of my AS-15 Klone and shouldn't see any need to "wonder" again.

[HMenke]

Good, one more thing to check off the list! This is starting to get pretty exciting. I am going to get everything on order and then I'll be traveling for a while before I can start building. Thomas I appreciate your help getting me going in the right direction. I think this sub is going to be awesome!

[chasw98]

I just built my sonotube sub using the RL-p15 dual 4 version with a Behringer EP2500 running one channel to each voice coil. There is a picture of it in the DIY Sub showcase at the beginning of this thread or you can go here and see all my info http://www.cwitt.com/building_a_sonotube_subwoofer.htm. Steve and Thomas will let you know what to build. It is a great driver. I had 8 AVS people over for a "meet" this weekend and some of them brought there HSU VTF Mk 2 and SVS tubes. My DIY made them look (and sound) weak for a lot less money.

Chuck

[HMenke]

Chuck, it was your subwoofer in the AVS DIY gallery that prompted me to embark on this project!

Is the fan on your Behringer noticeable during quiet passages in movies? Does it change speed at low power? Do you have to switch the amp on/off manually?

[HMenke]

I had an idea to possibly improve the appearance of the port. Rather than bring the tube out flush with the outer cap, I could possibly cut the outer cap to the ID of the port and then round it over. The inner plug would be cut to the port OD, so the result is that the end of the port butts up to the outer cap and you don't see the port end. When you look down into the port, you just see a thin joint. Would this be overly difficult to accomplish? I am thinking it might be hard to align the holes so the inside joint is flush.

[HMenke]

Mike at SoundSplinter advised me to be wary of too much enclosure volume, which could result in an underdamped woofer that is boomy with muddled upper bass. I know I don't like boomy bass so I am thinking of scaling back the volume to around 250L with an 8" port 36.55" long. This is a port tuning of 18.5Hz with peak port velocity 19.5m/s.

I think I like the aesthetic proportions of a sonotube that is tall and slender as opposed to short and fat. So instead of 24" or 22" I am now thinking about a 20" tube that is 57" high.

[---k---]

Mike advises everyone of this. I think him and Thomas have a very differnt design philosphy. I'm happy with the design Thomas recommended me. I think your in good hands with Thomas.

[Bent]

Boomy bass is more the result of too small an enclosure - Mike is prolly more concerned with the excursion limits ofthe driver when there is less mechanical dampening/resistance provided by a large enclosure. the upper/mid bass will definitely be less pronounced with a larger box - but IMHO, that's a good thing.

[ThomasW]

Henry,

Sorry but I don't understand the description of the port finishing.

I agree with the aesthetics of a taller narrow tube. And 24" tube is a pain to work with because it's so big and bulky...

wary of too much enclosure volume, which could result in an underdamped woofer that is boomy with muddled upper bass

This is an illogical statement with regard to loudspeaker design.

Because.....

The size of the box has little if any impact on the upper end performance. The relatively high Le of the RL-p drivers will have a much bigger impact on the upper bass then any difference in box design.

FWIW, we've used RL-p 15"s in true IB subs (sealed enclosure volume 10 times the summed Vas of the drivers). They don't boom....

If you're still worried about the system being underdamped go with the 2 ohm version of the driver and it's lower Qts.

[chasw98]

Chuck, it was your subwoofer in the AVS DIY gallery that prompted me to embark on this project!

Is the fan on your Behringer noticeable during quiet passages in movies? Does it change speed at low power? Do you have to switch the amp on/off manually?

I do not notice the fan on my amp, but, the amp is enclosed in a cabinet with good air flow. When i have listened right next to the amp I have heard it change fan speed. I don't even notice when sitting in the room listening at low or high volume.

I used a 4PDT 120VAC 10 amp relay that turns on the amp when the AV rec. is powered on. It is controlled through the switched outlet of the AV rec.

[HMenke]

Sorry but I don't understand the description of the port finishing.

Here's a quick cross-sectional drawing. It seems like most people do it as shown on the left, and I am thinking I could do it as shown on the right and have a decent-looking port that doesn't need to be covered for aesthetics. Although it might need to be covered to prevent 8O something falling into it accidentally.

[HMenke]

This is an illogical statement with regard to loudspeaker design.

Because.....

The size of the box has little if any impact on the upper end performance. The relatively high Le of the RL-p drivers will have a much bigger impact on the upper bass then any difference in box design.

FWIW, we've used RL-p 15"s in true IB subs (sealed enclosure volume 10 times the summed Vas of the drivers). They don't boom....

Thomas,

So, in a vented design or a sealed design or an IB, in your view a larger box will yield improved low end response with no audible penalty with respect to boominess/lack of "tightness"? This seems logical to me, and in addition will not the amplifier also excert its own control over the woofer, i.e. make it move with signal and stop it from moving without signal?

[HMenke]

I found a cool local supplier, Con Quip in Burlington, KY for the Sonotube who will cut the tube to length and charge only for the needed length. They have a saw that cuts the tube straight (probably a band saw). They stock all sizes including the 20" and 8" that I am interested in. I told them I am not using this for concrete and he said, "What's it for, a table?" He had never heard of the subwoofer application.

Here is their pricing:

20"
6-ft cut-to-length $36.00
12-ft $62.40

8"
4-ft cut-to-length $8.00
12-ft $26.68

[SteveCallas]

Here's a quick cross-sectional drawing. It seems like most people do it as shown on the left, and I am thinking I could do it as shown on the right and have a decent-looking port that doesn't need to be covered for aethetics. Although it might need to be covered to prevent something falling into it accidentally.

I did it as you are showing on the right, and you be surprised to find that quite a few people do it that way. When you get up to large diameter ports, you basically have to create your own flare, and this seems like the best way. Yes, you will want to cover it - I used one of these:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-426

[ThomasW]

First yes you can make the port like that. Just factor the flare into the total length of the port

So, in a vented design or a sealed design or an IB, in your view a larger box will yield improved low end response with no audible penalty with respect to boominess/lack of "tightness"? This seems logical to me, and in addition will not the amplifier also excert its own control over the woofer, i.e. make it move with signal and stop it from moving without signal?

'Boomy' response is primarily a function of the room geometry reinforcing a particular frequency, or an improperly designed ported box.

Box size has no impact on the sound quality of the high end of the woofer's passband.

A bigger box gives better low frequency boost, and allows larger ports, that mean lower mach numbers.

[HMenke]

Yes, you will want to cover it - I used one of these:
http://www.partsexpress.com/pe/showd...number=260-426

Steve, looks good. I thought that the DIY grille on this box subwoofer looks pretty cool too. If it was close to the OD of the top cap, it would eliminate some of the finishing and look cool.

I also like the type of textured paint found on the second photo of the black box sub - the craftsmanship on this unit is first-rate. I think I will shoot for this finish on the end caps etc.

[HMenke]

First yes you can make the port like that. Just factor the flare into the total length of the port

'Boomy' response is primarily a function of the room geometry reinforcing a particular frequency, or an improperly designed ported box.

Box size has no impact on the sound quality of the high end of the woofer's passband.

A bigger box gives better low frequency boost, and allows larger ports, that mean lower mach numbers.

Alright, this is good. I agree about the room being a culprit in boominess, as I discovered with RoomEQ Wizard and corrected with a BFD. Once the peaks are tamed, the level can be brought up without sounding boomy. I could also see how a bad port design could have its own response peak (like a jukebox) and sound like a one-note boom-boom-boom.

[HMenke]

I did it as you are showing on the right, and you be surprised to find that quite a few people do it that way.

Steve, this small flare radius doesn't have much practical effect, does it? I read somewhere that the flare radius has to be pretty large relative to the port dia. to be effective. A small radius like this would be mainly cosmetic, no?

[HMenke]

Well, a dual 4-ohm RL-p15 is on its way to be powered by a Samson S700 that delivers 350W/ch into 4 ohms. Thanks for your help and advice everyone - I'm sure I'll be checking back with questions once I get going on the build phase.

Henry

[SteveCallas]

How large of a radius are you using? My outer layer of 3/4" MDF is completely rounded over and then I did some "artistic" filing and sanding :B

Does it have much of an effect? Probably not - the port is 8" in diameter to begin with, so air velocity never gets very high in the first place. But it has to be better than nothing.

[HMenke]

How large of a radius are you using? My outer layer of 3/4" MDF is completely rounded over and then I did some "artistic" filing and sanding

That's alll the radius I would give it too. I think such a small radius would be almost completely cosmetic because (acknowledging that I'm no expert on fluid mechanics) the difference in terms of air turbulence caused by zero radius and a 3/4" radius has got to be insignificant. I'd think you'd need at least a 2" radius to make any real difference. The key here as you say is going to be the 8" diameter where the air velocity is just plain low to begin with.

[HMenke]

Here's a look at what I have drafted in AutoCAD so far. I don't have a CAD model or detailed dimensions on the woofer, so I will have to wait until I get delivery to take measurements and improve the woofer details. Drawn to scale, the port looks pretty big but it still fits the enclosure nicely. This is 22" dia. x 56.5" Sonotube for 315L, and the port is 8" x 31.75" for a tune of 17.5 Hz.

How high do you guys recommend the support posts to be? Currently I have them at 4" tall.

[ThomasW]

4" is fine. The design looks good.... :T

[HMenke]

I may have to scale it back just a bit - I found out I have a slight height restriction due to the mounting location of my left rear surround speaker, under which the sonosub will go.

I am going to use a Samson S700 amp for this project. It seems to me it should be close to the speaker, and I have been wondering where to put it nearby. Has anyone considered, or tried, putting their amp in a bracket mount on top? If yes I'm wondering how much gap needs to be left above the port. If it is inadvisable to mount it on top, I will probably make a wall shelf for it near the sub.

Chuck, what 120VAC coil relay are you using to remotely power your amp from a switched 120VAC outlet on your receiver?

Henry

[ThomasW]

The port needs room to breath so the amp should be no closer than 6"-9".

BTW, I wouldn't want my amp exposed to the direct output of a port.

[HMenke]

That's what I needed to know. I just got the Samson S700 amp today. I hadn't looked at the weight in the spec sheet but this thing is 31 lbs! Probably not a good idea to put that much weight that high either. Anyway the amp looks really well-made; I'm very pleased with the quality. The woofer is on the truck in CA so it's going to be a few days until I have it here in KY.

[chasw98]

I may have to scale it back just a bit - I found out I have a slight height restriction due to the mounting location of my left rear surround speaker, under which the sonosub will go.

I am going to use a Samson S700 amp for this project. It seems to me it should be close to the speaker, and I have been wondering where to put it nearby. Has anyone considered, or tried, putting their amp in a bracket mount on top? If yes I'm wondering how much gap needs to be left above the port. If it is inadvisable to mount it on top, I will probably make a wall shelf for it near the sub.

Chuck, what 120VAC coil relay are you using to remotely power your amp from a switched 120VAC outlet on your receiver?

Henry

I used OMRON 6C884 4PDT 120 VAC coil relays rated at 10A/240VAC. The mounting socket for this model is an OMRON 2XC09. If you buy a piece of DIN rail, the socket will clip into the rail making for a nice mountable piece.

[HMenke]

I used OMRON 6C884 4PDT 120 VAC coil relays rated at 10A/240VAC. The mounting socket for this model is an OMRON 2XC09. If you buy a piece of DIN rail, the socket will clip into the rail making for a nice mountable piece.

Thanks Chuck. After thinking about it, I decided to go with a solid state AC relay so it will operate silently (no relay click when I turn on the receiver). I was just poking around on the internet and found a place called electronicsurplus.com. I bought an SPST AC-input / AC-output 15A solid state relay for $15 plus $6 shipping:

http://www.electronicsurplus.com/com...=1141715220006

I wrote them to confirm before shipping that it will accept 120VAC input and switch 120VAC output. The description implies that it will accept 90-250VAC input, and will switch up to 250VAC at up to 15A.

These solid state relays typically have four screw terminals (2 in/2 out) so I plan to just mount it in a handy box behind my rack, with a 120V plug going from the switched outlet on my receiver to the relay input, a 120V grounded plug going from the GFCI power outlet behind my rack to one terminal on the output of the relay, and Romex running from the other relay output terminal to a new dedicated switched power outlet for the Samson S700 sub amp. The grounds will be tied together at the handy box and the neutrals will be wire nutted in the box as well.

I am using a GFCI outlet because if I get 60Hz hum through the amp due to a ground loop, I will install a cheater plug at the outlet. Then if there is ever a ground fault in the amp, the GFCI breaker will trip at 4-7mA for safety.

[chasw98]

Good idea. Let us know how it works.

[Kingdaddy]

A long 8" diameter port hanging from the top plate is a problem if you don’t secure it well, that’s a heavy port. I went through several different ideas until I cam up with one that worked well and was still easy to install. The attached picture shows how I did it as my 8” port weighed about 35lbs. Once the saddle was mounted the all-thread rod holes are sealed with silicone and screws can be used to fasten the saddle face to the inside of the top cap.

[ThomasW]

Most people aren't using schedule 60 pipe for their ports ...:wink:

[HMenke]

I'm having trouble locating wide (>60") black carpet. I found a couple of places:

http://www.speakercity.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=SC&Product_Code=SH-1048&Category_Code=SP

72" wide but it doesn't specify how long the "bolt" is. I assume one yard, but if I order 3 yards will I get one piece or 3 pieces? I don't know because the co. hasn't answered my email.

http://cgi.ebay.com/ws/eBayISAPI.dll...ory=29914&rd=1

This eBay stuff sounds like it could be ugly ("indoor/outdoor synthetic fibre").