Enclosure recommendations

[riverwolf]

That port is far too small and will have a vent air velocity of 40 m/sec. That will give huge port compression and chuff like a steam locomotive.

The optimal box for that driver is one of my designs on my web site. That driver needs a slot vent of 2" X 14" X 50"

Picking nits: I think "my preferred" or "recommended" would be a better choice of wording than "optimal". A chosen speaker alignment is just one point on a curve of possible alignments. All engineering solutions are a set of tradeoffs needed to meet an end result.

I wouldn't have recommended the solution I did without checking the air velocity numbers. I don't disagree that lower is better, but I also don't believe it's quite the issue that some make it out to be. And lower air speed means bigger ports which means a bigger gross box to yield the required net...one of those annoying tradeoffs one has to make.

Food for thought...

A) You appear to have run your model without the BASH300's subsonic filter. That knocks the peak air velocity down to 35m/s, right in line with Peerless (now Tymphany) recommendation for an upper limit and also roughly in agreement with Collo's efforts to correlate port diameter/velocity/audible noise.

B) In a s/w simulation, the air velocity is a worst case number. In this scenario, that peak occurs at 17Hz...not a lot of content there, relatively speaking. Real world content is also transient in nature, not steady state power. Even a 2dB reduction from max power brings the velocity down into the upper 20s.

C) Use of a flared port will lower the potential for port noise even more although I think a straight port will get the job done for this alignment.

D) Personal experience. I used to run a 15" driver with a 4" PSP. According to the models, my air velocity crossed the 34 m/s threshold at 18Hz and was climbing fast (no rumble filter). Yet, I never heard any port noise in real world useage due to the lack of significant content in that frequency range that would excite the noise and real world playback levels that were probably significantly lower than max theoretical numbers.

Similarly, SVS' earlier PB10-NSD and PB12-ISD/NSD used single 3" and 4" ports respectively with drivers that offered equal or more excursion than the Titanics. I've not seen anyone complaining about port noise from these subs...yes, they can be made to chuff, especially in bench testing, but it's not a real world problem.

-Brent

 

[BrianJ]

Holy Cow! You guys totally lost me I suppose I need to do more research to better understand alot of the lingo.

I'm thinking that im gonna put the sub box in the corner next to my couch seeing how its pretty much wated space right now therefore i can make the box a bit larger. Maybe in the 4.5-5 cu. ft range and also make a table top out of it as i need an end table anyways

I'll post a pic of the space tomorrow with accurate measurements.

Thanks,
Brian

 

[riverwolf]

Port resonance will be 132Hz. It is the almost the same as a 4' organ stop, the port being an open pipe.

So it will be fine with a fourth order low pass at 80 Hz. The driver will already be 3 db down at that point so by 132 Hz the driver will be 18 db down by port resonance frequency. So there will be little to excite port resonance. If he uses a 60 Hz crossover point there will be no excitation. This trade off is much better than having high port air velocity, and the port dimensions are as short as they can be compatible with little port compression and no noise.

The port resonance will also be excited by subharmonics of its resonant frquency. So 66 Hz, 33 Hz, and 16.5 Hz fundamentals (all well within the pass band of this alignment) will excite a 132 Hz resonance. Audibility depends on the harmonic distortion profile of the driver itself, something that can't be filtered by the lowpass.

-Brent

 

[TLS Guy]

Picking nits: I think "my preferred" or "recommended" would be a better choice of wording than "optimal". A chosen speaker alignment is just one point on a curve of possible alignments. All engineering solutions are a set of tradeoffs needed to meet an end result.

I wouldn't have recommended the solution I did without checking the air velocity numbers. I don't disagree that lower is better, but I also don't believe it's quite the issue that some make it out to be. And lower air speed means bigger ports which means a bigger gross box to yield the required net...one of those annoying tradeoffs one has to make.

Food for thought...

A) You appear to have run your model without the BASH300's subsonic filter. That knocks the peak air velocity down to 35m/s, right in line with Peerless (now Tymphany) recommendation for an upper limit and also roughly in agreement with Collo's efforts to correlate port diameter/velocity/audible noise.

B) In a s/w simulation, the air velocity is a worst case number. In this scenario, that peak occurs at 17Hz...not a lot of content there, relatively speaking. Real world content is also transient in nature, not steady state power. Even a 2dB reduction from max power brings the velocity down into the upper 20s.

C) Use of a flared port will lower the potential for port noise even more although I think a straight port will get the job done for this alignment.

D) Personal experience. I used to run a 15" driver with a 4" PSP. According to the models, my air velocity crossed the 34 m/s threshold at 18Hz and was climbing fast (no rumble filter). Yet, I never heard any port noise in real world useage due to the lack of significant content in that frequency range that would excite the noise and real world playback levels that were probably significantly lower than max theoretical numbers.

Similarly, SVS' earlier PB10-NSD and PB12-ISD/NSD used single 3" and 4" ports respectively with drivers that offered equal or more excursion than the Titanics. I've not seen anyone complaining about port noise from these subs...yes, they can be made to chuff, especially in bench testing, but it's not a real world problem.

-Brent

For subs vent velocity should be no higher than 18 m/sec.

The whole point of a DIY sub is to exceed the performance of commercial subs, which by and large are not very good.

He has a large room and he will be pushing that sub to the limit. He needs a slot vent period.

 

[TLS Guy]

The port resonance will also be excited by subharmonics of its resonant frquency. So 66 Hz, 33 Hz, and 16.5 Hz fundamentals (all well within the pass band of this alignment) will excite a 132 Hz resonance. Audibility depends on the harmonic distortion profile of the driver itself, something that can't be filtered by the lowpass.

-Brent

Balls! Utter rubbish! Harmonics are multiples of the fundamental, they are NEVER lower than the fundamental.

So even harmonics are fundamental X 2, X 4, X 6 etc. An open pipe which a slot vent fits the category of has only even harmonics. It does not have harmonics F/2, F/4 F/6 etc.

A closed pipe (closed one end) has odd order harmonics, F X 3, F X 5, F X 7 etc. The intensity of all harmonics decreases with frequency. So in an open pipe the second harmonic has the greatest intensity an for a closed pipe the third.

 

[BrianJ]

Heres the spot where I would like to put my box. You can see where there's a TV tray. That area is roughly 35"deep x 28"wide x 26"high. So I have plenty of room for a large box. The 35 and 28 are max dimensions so I would have to subtract space for wall and couch clearance but I would like to keep the 26" overall height because it works good with the height of the arm rest on the couch. Also I would like to somewhat mimic the stlye of my TV stand but I can do without the shelf underneath.

SO based on those measurements should I go bigger on the box? I could easily get in the 7-8cu ft range. Also would you suggest down firing or firing out one of the sides which means either forward or into one of the 2 walls or int the side of the couch?

 

[TLS Guy]

Heres the spot where I would like to put my box. You can see where there's a TV tray. That area is roughly 35"deep x 28"wide x 26"high. So I have plenty of room for a large box. The 35 and 28 are max dimensions so I would have to subtract space for wall and couch clearance but I would like to keep the 26" overall height because it works good with the height of the arm rest on the couch. Also I would like to somewhat mimic the stlye of my TV stand but I can do without the shelf underneath.

SO based on those measurements should I go bigger on the box? I could easily get in the 7-8cu ft range. Also would you suggest down firing or firing out one of the sides which means either forward or into one of the 2 walls or int the side of the couch?

It is hard to know from pictures how a sub will sound in any location. You will get some corner loading, but it is a room that will have a lot of bass leakage anyway.

This box is going to come out I suspect about 5 cu.ft when you are driver, port, amp and bracing the Vb which is just under 1 liter. This box gives you an F3 of 20 Hz and very good spl off just over 110 db. The driver never exceeds xmax (maximum excursion) until below F3 which your subsonic filter will take care of. If you build that box with the slot vent carefully you will have a potent sub, that will exceed the performance of the vast majority of commercial subs.

 

[lsiberian]

Is it safe to assume that the width dimension of this box would be 14" internally? Also to get the slot to be 50" long it would probably have to wrap around 3 walls correct?

Whether it be a round port or slot port is there a industry standard for the minimum distance an inner port opening should be from an inner wall?

Square ports are a better choice because they are easier to wrap around, normally a lot cheaper and help brace the box. You'd need multiple ports for round ones for any sub worth it's salt. I'd probably go with a 3" thick port rather than the 2", but it doesn't matter all that much.

wouldn't a 50" port resonate with when using an 80hz crossover? That's what my gut tells me at least.

You are correct that it would resonate and if you are sensitive to port resonance then you would probably be better off with an LLT or sealed sub, but I know only one guy sensitive to it in the DIY community. Considering most folks have ported speakers with their own resonances I think the issues are overstated. If you don't mind ported speakers then you won't have issues. Additionally the resonance would be inaudible in most cases. Even if it was slightly audible I think it's worth the added power in that 20-30 range.

Picking nits: I think "my preferred" or "recommended" would be a better choice of wording than "optimal".
without checking the air velocity numbers. I don't disagree that lower is better
B) In a s/w simulation, the air velocity is a worst case number. In this scenario, that peak occurs at 17Hz...not a lot of content there, relatively speaking.

I'd disagree based on the measurements I've seen. I don't think anyone building a DIY sub is too worried about size. If it is a concern then I'd suggest going sealed.

Holy Cow! You guys totally lost me I suppose I need to do more research to better understand alot of the lingo.

I'm thinking that im gonna put the sub box in the corner next to my couch seeing how its pretty much wated space right now therefore i can make the box a bit larger. Maybe in the 4.5-5 cu. ft range and also make a table top out of it as i need an end table anyways

I'll post a pic of the space tomorrow with accurate measurements.

Thanks,
Brian

TLS produces designs you can go to bat with. I would build anything he recommended with confidence. He's been building speakers longer than I've been on this earth probably. Good experience is the best teacher. I'm not discounting our discourse, but I'd give that build a go if you have the space.

For subs vent velocity should be no higher than 18 m/sec.

The whole point of a DIY sub is to exceed the performance of commercial subs, which by and large are not very good.

He has a large room and he will be pushing that sub to the limit. He needs a slot vent period.

Agreed. The whole point is to make something better then you can buy. If you want an SVS sub then buy one.

 

[BrianJ]

TLS guy,
is your 3.9Vb dimension the final internal volume after deductions?

Also does it matter if your box is say 22" wide but the port is only 14" wide? Basically is it OK to have the slot port narrower then the box?

 

[TLS Guy]

TLS guy,
is your 3.9Vb dimension the final internal volume after deductions?

Also does it matter if your box is say 22" wide but the port is only 14" wide? Basically is it OK to have the slot port narrower then the box?

You have it the wrong way round! They are additions NOT deductions. So you take Vb and add them, so Vt is going to be around 5 cu.ft, which will be your final volume. Remember Vb is the volume of air in your box not including air in the port. So everything else is an addition to your final volume. The slot vent can be narrower than the box, no problem.

When you have your design we will check you math before you begin cutting.

 

[BrianJ]

OK so lets say Vb is 4cuft and your port is 1 cuft, then Vt is 5cuft. Sorry i really dumbed it down for myself.

 

[TLS Guy]

OK so lets say Vb is 4cuft and your port is 1 cuft, then Vt is 5cuft. Sorry i really dumbed it down for myself.

Now you have got it! You are on your way.

 

[GO-NAD!]

TLS guy,
is your 3.9Vb dimension the final internal volume after deductions?

Also does it matter if your box is say 22" wide but the port is only 14" wide? Basically is it OK to have the slot port narrower then the box?

Just take a look at the plans for the Infinity Kappa in the the DIY section. You'll see how easy it is to make the port narrower than the enclosure. You can take that whole design and adjust the dimensions to suit your driver.

 

[lsiberian]

Just take a look at the plans for the Infinity Kappa in the the DIY section. You'll see how easy it is to make the port narrower than the enclosure. You can take that whole design and adjust the dimensions to suit your driver.

This is the best way to do it. That is a picture of a good square ported sub.

 

[BrianJ]

Box Width 24 Inches
Box Height 20 Inches
Box Depth 25 Inches
Material Thickness .75 Inches (3/4 MDF)
Bracing Volume 469.686 Inches3 (2 braces)
Port Volume 1925 Inches3
Driver Volume .12037 Ft3
Number of Drivers 1 Total

Total Net Volume 4.155 Ft3 Vb (5.269 Vt)
Total Net Volume 117.646 Liters


Hows this look?

 

[riverwolf]

Balls! Utter rubbish! Harmonics are multiples of the fundamental, they are NEVER lower than the fundamental.

So even harmonics are fundamental X 2, X 4, X 6 etc. An open pipe which a slot vent fits the category of has only even harmonics. It does not have harmonics F/2, F/4 F/6 etc.

A closed pipe (closed one end) has odd order harmonics, F X 3, F X 5, F X 7 etc. The intensity of all harmonics decreases with frequency. So in an open pipe the second harmonic has the greatest intensity an for a closed pipe the third.

Say what? Did you actually read what I wrote or just decide to go on a red herring tangent when you didn't understand it? This has nothing to do with odd/even harmonics or open/closed pipes. You implied the only source of energy available to induce the pipe resonance would be filtered by the low pass xover making it a non-issue.

All drivers will produce odd and even harmonic distortion of the signal they're playing, even if it's a sine wave with no inherent harmonic signature of its own. Call it mechanical distortion if you want; it's simply not in the source signal to be filtered by the low pass, but is still present in the cabinet itself. Feed the driver a 66/44/33 Hz fundamental and you'll get 2nd/3rd/4th harmonics that also happen to be at the 132Hz fundamental of your port. Looked at the other way, they are subharmonics of the fundamental pipe resonance. The level of these harmonics relative to the fundamental will vary by driver and may or may not drive the pipe resonance to audibility.

If we're going to design for some theoretical ideal of port air velocity that may never be a problem in the real world, we should also consider other potential sources of port noise as well, non?

-Brent

 

[riverwolf]

For subs vent velocity should be no higher than 18 m/sec.

The whole point of a DIY sub is to exceed the performance of commercial subs, which by and large are not very good.

He has a large room and he will be pushing that sub to the limit. He needs a slot vent period.

Can you point me to the research or evidence behind your 18 m/s edict? Peerless did some work and wrote a whitepaper on the topic that recommends 35 m/s or .1 mach. Collo's testing showed 4" flared ports to be subjectively clean up to 25-30 m/s on test tones with listeners placed next to the sub...real world content and listening positions would allow for higher velocities (up to 40% in his estimates). Seems to work well in my real world experience (20+ years since some folks put value in that sort of thing).

I guess I got into DIY for the wrong reasons. Just like those pesky engineering tradeoffs I mentioned, we all do things for different reasons. These "bad" commercial subs are simply built with a different set of parameter prioritization than you or I would choose. I'm not arrogant enough to think I know more than the Stephen Ponte, Deon Bearden, Ed Mullen, Jack Hidley, etc. types of the audio engineering world.

Brian's going to be sitting roughly 3' from the sub, the room size will not be a limiting factor for output. With the corner loading suggested, he's easily looking at another +6 to +12dB above the models...well into OSHA regulation territory, especially if the mains and sub levels are properly calibrated. I would rather expect this sub will be loafing most of the time...unless I'm a real wimp with my idea of what loud is.

As I said originally, I don't disagree that lower air velocity is better, within reason. However, a port that adds 25% to the enclosure volume along with increasing the complexity of what appears to be a first time build seems a bit extreme, IMO...I would choose and recommend a different balance.

-Brent

 

[GranteedEV]

Feed the driver a 66/44/33 Hz fundamental and you'll get 2nd/3rd/4th harmonics that also happen to be at the 132Hz fundamental of your port. Looked at the other way, they are subharmonics of the fundamental pipe resonance. The level of these harmonics relative to the fundamental will vary by driver and may or may not drive the pipe resonance to audibility.

Unless the driver is really poor, AFAIK harmonics alone are going to be lower in volume as a 4th order low passed fundamental, though.

 

[TLS Guy]

Say what? Did you actually read what I wrote or just decide to go on a red herring tangent when you didn't understand it? This has nothing to do with odd/even harmonics or open/closed pipes. You implied the only source of energy available to induce the pipe resonance would be filtered by the low pass xover making it a non-issue.

All drivers will produce odd and even harmonic distortion of the signal they're playing, even if it's a sine wave with no inherent harmonic signature of its own. Call it mechanical distortion if you want; it's simply not in the source signal to be filtered by the low pass, but is still present in the cabinet itself. Feed the driver a 66/44/33 Hz fundamental and you'll get 2nd/3rd/4th harmonics that also happen to be at the 132Hz fundamental of your port. Looked at the other way, they are subharmonics of the fundamental pipe resonance. The level of these harmonics relative to the fundamental will vary by driver and may or may not drive the pipe resonance to audibility.

If we're going to design for some theoretical ideal of port air velocity that may never be a problem in the real world, we should also consider other potential sources of port noise as well, non?

-Brent

We are not talking about the driver, we are talking about the port and not the driver. The port can only be excited by the fundamental (132 Hz) and the even harmonics. A pipe can not and does not generate subharmonics. So yes the low pass filter will prevent the port generating its fundamental and the harmonics.

To generate a subharmonic you need two closely spaced tones, to generate a beat tone (the subharmonic).

You have added nothing to this discussion except confusion.

 

[lsiberian]

Can you point me to the research or evidence behind your 18 m/s edict? Peerless did some work and wrote a whitepaper on the topic that recommends 35 m/s or .1 mach. Collo's testing showed 4" flared ports to be subjectively clean up to 25-30 m/s on test tones with listeners placed next to the sub...real world content and listening positions would allow for higher velocities (up to 40% in his estimates). Seems to work well in my real world experience (20+ years since some folks put value in that sort of thing).

I guess I got into DIY for the wrong reasons. Just like those pesky engineering tradeoffs I mentioned, we all do things for different reasons. These "bad" commercial subs are simply built with a different set of parameter prioritization than you or I would choose. I'm not arrogant enough to think I know more than the Stephen Ponte, Deon Bearden, Ed Mullen, Jack Hidley, etc. types of the audio engineering world.

Brian's going to be sitting roughly 3' from the sub, the room size will not be a limiting factor for output. With the corner loading suggested, he's easily looking at another +6 to +12dB above the models...well into OSHA regulation territory, especially if the mains and sub levels are properly calibrated. I would rather expect this sub will be loafing most of the time...unless I'm a real wimp with my idea of what loud is.

As I said originally, I don't disagree that lower air velocity is better, within reason. However, a port that adds 25% to the enclosure volume along with increasing the complexity of what appears to be a first time build seems a bit extreme, IMO...I would choose and recommend a different balance.

-Brent

There is more to small ports than port noise. The main problem with small ports is they compress the air in a bass box. This compression results in suboptimal performance. I fail to see how building a slot port is more difficult than building the box itself.