Please comment on my DIY Bass module plans

[TLS Guy]

How much bass people need is always a tough one. People often ask if what they are buying is enough and it's always hard to tell. I have done an infinite baffle system recently with 8 of our IB15's in a large theater room and for most people it would be ridiculous. Others may believe it is not enough. For a large room though, a pair of 12" drivers like the kappa perfects will likely not be enough. There are much better drivers, much lower distortion, lower inductance, better power compression out there.

I do find it somewhat interesting that the AV woofers were stated as "car woofers" when they aren't necessarily intended for that but at the same time the Kappa Perfects clearly are car woofers but they are recommended. Our AV12X has nearly identical motor strength to their "low Q" option while it has about only about 25% of the inductance and 40% more Xmax. It will also have significantly better heat transfer from the coil due to the thicker gap plate and full copper sleeve on the pole to pull heat from the coil quickly.

John

Your web site is rudimentary, and has bare bones information. The AV-15-H, is really only a sub woofer with your passive radiators, PR18-1600. Not to point out that two of those passive radiators are required to give that unit sub woofer performance, is in my view obtuse.

I have confirmed your modeling for this driver.

Your AV15-X looks more promising with a Qt optimal for reflex loading.

10 cu. ft. seems optimal. I think an enclosure of 10 cu.ft. with a slot vent 2.5" X 12" X 31.5" gives the best response.

F3 is 21.5 and there is minimal ripple.

The use of the passive radiators does extend the response to 15 Hz, however for audio systems I consider this no practical significance. The extension is bought at the price of significant ripple and lowered sensitivity.

I have added all of this to my sub woofer page. It is all down at the bottom.
You are welcome to link to it.

 

[TLS Guy]

I've been toying with the dimensions again, and at 10 cu. ft. I won't be able to fit the 15" driver and 8" port in a design with those "magic" numbers (.7*1*1.4).

I could go with a similar design as the Tremor Twins... how much does the ratio matter? Isn't it just to ensure that they are different because of resonance?

I think you 10 cu. ft. box will be fine.

I have added both those drivers to my sub page.

I think the best results for that driver are achieved with a slot vent 2.5" X 12" X 31.5". The F3 is a very acceptable 21.5 Hz, with minimal ripple.

 

[VERTIGGO]

Thanks for the dimensions... however I was hoping to hit 16Hz, which means something like 2.5x15.5x28. This is for movies, so the LF extension is a priority, and the DSP will be able to correct the slope from low to high.

 

[John_E_Janowitz]

Your web site is rudimentary, and has bare bones information. The AV-15-H, is really only a sub woofer with your passive radiators, PR18-1600. Not to point out that two of those passive radiators are required to give that unit sub woofer performance, is in my view obtuse.

There is a lot more information on our forum. I've hoped to have time to update the site forever but just have not been able to manage it with as crazy as things have been. There is no reason you cant' go with a larger enclosure and tune lower. The bump you see at tuning will be nearly removed if you implement a proper highpass filter to control excursion of the woofer anyway. The AV15H works extremely well for what it was designed to do. That is to work in a small enclosure. PR's aren't necessarily a requirement. A port can give you the same tuning and output, it just needs to get huge to do so. It would need to be a 4x15 slot vent 102" long. To take a 5 cubic foot enclosure and add another 4 cubic feet of port volume to it isn't very practical, so adding PR's is generally a better option.

10 cu. ft. seems optimal. I think an enclosure of 10 cu.ft. with a slot vent 2.5" X 12" X 31.5" gives the best response.

You'll want to go much larger on the vent than 2.5 x 12". You ideally want to keep vent velocity below 10m/s. This 10m/s is the point that Klipsch and others had determined distortion set in due to the port. With 16hz tuning this would limit you to less than 100W input before surpassing that 10m/s point. With 1000W input the vent velocity would surpass 40m/s. At 35m/s is the point where airflow becomes turbulent and no further output can be gained.

While 10m/s may not always be practical to achieve, you should still seek to keep it as low as possible and well below 35m/s. Going with a 15x4 slot vent 61" long will get you the same tuning but keep vent velocity right around 20m/s at 1000W input a down to about 14m/s at 500W input. This will give a huge increase in output over the smaller slot vent proposed.

F3 is 21.5 and there is minimal ripple.

The use of the passive radiators does extend the response to 15 Hz, however for audio systems I consider this no practical significance. The extension is bought at the price of significant ripple and lowered sensitivity.

I have added all of this to my sub woofer page. It is all down at the bottom.
You are welcome to link to it.

The ripple isn't of much serious consequence. The most detrimental factor is that the bump at tuning can often be overbearing. Again, a highpass filter that also addresses this bump can take care of the problem. I do agree though that the AV15X is a better option, as this is more the application it was intended for.

For a music only system, there isn't a lot of program material below the Low B on a bass guitar at 30.87hz. This is what most people target as a bottom end for music only systems unless they listen to electronic music or pipe organs. This link here shows what frequencies correspond to given notes on different instruments:
http://www.contrabass.com/pages/frequency.html

Now for home theater use there is a lot of material under 30hz and as far down as 10hz or so. The ability to reproduce the sub 20hz stuff is what really will differentiate a good subwoofer from an average one. For most home theaters I see people targeting 16hz or so as the required bottom end. Tom Danley has some recordings of fireworks, a harley, and a train that will really put a subwoofer to the test at those frequencies.

http://www.danleysoundlabs.com/technical downloads.html

John

 

[VERTIGGO]

What do you use to calculate the vent? This may be a shady source, but it's the easiest calculator I've found. However, it gives different numbers... even Win ISD gives me 4x15x54. I have to get this right before I can determine the length of the box (my simplest adjustment dimension). In WinISD I get mach .15 from 2.5x15.5x33, and it's green (I assumed that meant ok).

BTW, what volume would you use for the cone of the AV15-X? I was using 175 cui.

 

[TLS Guy]

There is a lot more information on our forum. I've hoped to have time to update the site forever but just have not been able to manage it with as crazy as things have been. There is no reason you cant' go with a larger enclosure and tune lower. The bump you see at tuning will be nearly removed if you implement a proper highpass filter to control excursion of the woofer anyway. The AV15H works extremely well for what it was designed to do. That is to work in a small enclosure. PR's aren't necessarily a requirement. A port can give you the same tuning and output, it just needs to get huge to do so. It would need to be a 4x15 slot vent 102" long. To take a 5 cubic foot enclosure and add another 4 cubic feet of port volume to it isn't very practical, so adding PR's is generally a better option.



You'll want to go much larger on the vent than 2.5 x 12". You ideally want to keep vent velocity below 10m/s. This 10m/s is the point that Klipsch and others had determined distortion set in due to the port. With 16hz tuning this would limit you to less than 100W input before surpassing that 10m/s point. With 1000W input the vent velocity would surpass 40m/s. At 35m/s is the point where airflow becomes turbulent and no further output can be gained.

While 10m/s may not always be practical to achieve, you should still seek to keep it as low as possible and well below 35m/s. Going with a 15x4 slot vent 61" long will get you the same tuning but keep vent velocity right around 20m/s at 1000W input a down to about 14m/s at 500W input. This will give a huge increase in output over the smaller slot vent proposed.



The ripple isn't of much serious consequence. The most detrimental factor is that the bump at tuning can often be overbearing. Again, a highpass filter that also addresses this bump can take care of the problem. I do agree though that the AV15X is a better option, as this is more the application it was intended for.

For a music only system, there isn't a lot of program material below the Low B on a bass guitar at 30.87hz. This is what most people target as a bottom end for music only systems unless they listen to electronic music or pipe organs. This link here shows what frequencies correspond to given notes on different instruments:
http://www.contrabass.com/pages/frequency.html

Now for home theater use there is a lot of material under 30hz and as far down as 10hz or so. The ability to reproduce the sub 20hz stuff is what really will differentiate a good subwoofer from an average one. For most home theaters I see people targeting 16hz or so as the required bottom end. Tom Danley has some recordings of fireworks, a harley, and a train that will really put a subwoofer to the test at those frequencies.

http://www.danleysoundlabs.com/technical downloads.html

John

My vent has a vent velocity of 18 m/sec at full power. A vent 4' X 15" X 65" has a vent velocity of 9 m/sec at full power.

I seriously doubt that a difference of 4 or 5Hz in a domestic room will be audible. The optimal tuning for a 10 cu.ft. box with that driver is with an Fb or 20 to 21 Hz.

Frankly that is a large enclosure. That much volume would be much better used as an aperiodic transmission line. The bass would then be non resonant with a Qt of 0.5, and roll off would be second order rather than fourth.

If an enclosure of that size is required, then my recommendation would be for a TL sub, which would give by far the greatest and most natural bass output. The driver being augmented smoothly over an octave and a half, not just over a narrow frequency range.

 

[John_E_Janowitz]

My vent has a vent velocity of 18 m/sec at full power. A vent 4' X 15" X 65" has a vent velocity of 9 m/sec at full power.

Something doesn't seem right with your modeling then. The AV15X in 10cf tuned to 16hz with a 2.5" x 12" x 32.5" vent gives a vent velocity of 40.6m/s with 1000W input. With a 4" x 15" vent 62" long gets down to 20m/s. Keep in mind that you are taking up a lot of box volume at the same time so you either need to make the gross volume of the enclosure larger, or account for this loss of volume and adjust tuning accordingly. I'll check my model with the other version of bassbox at the shop to make sure it is consistent, but velocities seem correct.

I seriously doubt that a difference of 4 or 5Hz in a domestic room will be audible. The optimal tuning for a 10 cu.ft. box with that driver is with an Fb or 20 to 21 Hz.

A tuning of 4-5hz when were are talking sub 20hz range makes a huge difference in excursion of the driver. It can make a large difference in terms of playing these sub 20hz frequencies and that makes a large difference in the tactile sensation created by those frequencies. Tuning slightly lower than "optimal" has no negative effects on the system.

Frankly that is a large enclosure. That much volume would be much better used as an aperiodic transmission line. The bass would then be non resonant with a Qt of 0.5, and roll off would be second order rather than fourth.

If an enclosure of that size is required, then my recommendation would be for a TL sub, which would give by far the greatest and most natural bass output. The driver being augmented smoothly over an octave and a half, not just over a narrow frequency range.

You will always have a tradeoff between efficiency and enclosure size. The larger the enclosure, the more efficient. This means you need less power input to get the same output levels. This is good on all fronts. It lowers thermal issues and less current in the coil means less flux modulation, both meaning lower distortion. Going smaller with the enclosure requires more power to get the same levels. It's a direct tradeoff between the two. Some people want smaller enclosures. That is exactly why we offer the AV15H as mentioned before.

The transmission line could work well, although you'll end up with a lot more than 10cubic foot of volume to do a 16hz transmission line. It's also much more difficult to build than a vented enclosure. If you wanted to model one up I'd be interested in seeing it though. A tapped horn is another that could work if someone wanted to model it up.

John

 

[VERTIGGO]

I'll look into bassbox then (I take it that's your software). WinISD doesn't seem to change when I adjust the Pe (from 100W to 1000W etc.) so I doubt it's accurately portraying that. Right now I have a master equation with a 20"x30" front (outer dimensions, minus 3/4" ply and 3/4" MDF thats 17x29) and the product is the length of the box with the only variables being port dimensions. Once I settle on a port size I'll be all set.

Do I measure an "L" shaped port by the shortest side or as if I was taking the distance down the exact center line of the tunnel? (A 60" port will have to extend along the bottom and up the back end of the enclosure)

 

[annunaki]

I'll look into bassbox then (I take it that's your software). WinISD doesn't seem to change when I adjust the Pe (from 100W to 1000W etc.) so I doubt it's accurately portraying that. Right now I have a master equation with a 20"x30" front (outer dimensions, minus 3/4" ply and 3/4" MDF thats 17x29) and the product is the length of the box with the only variables being port dimensions. Once I settle on a port size I'll be all set.

Do I measure an "L" shaped port by the shortest side or as if I was taking the distance down the exact center line of the tunnel? (A 60" port will have to extend along the bottom and up the back end of the enclosure)

With WinISD if you do not have Le, Re, SD, & Xmax parameters, it will hold you back a bit from more accurate modeling. Leaving out Le hurts a bit there.

 

[lsiberian]

I'm salivating at the idea of a DYI sub... but I have to rebuilt some WAF...

Flowers, Musicals, chocolates. Notes left for them. Come one pursue her again. It will be well worth it. In more ways than one.

 

[lsiberian]

Something doesn't seem right with your modeling then. The AV15X in 10cf tuned to 16hz with a 2.5" x 12" x 32.5" vent gives a vent velocity of 40.6m/s with 1000W input. With a 4" x 15" vent 62" long gets down to 20m/s. Keep in mind that you are taking up a lot of box volume at the same time so you either need to make the gross volume of the enclosure larger, or account for this loss of volume and adjust tuning accordingly. I'll check my model with the other version of bassbox at the shop to make sure it is consistent, but velocities seem correct.



A tuning of 4-5hz when were are talking sub 20hz range makes a huge difference in excursion of the driver. It can make a large difference in terms of playing these sub 20hz frequencies and that makes a large difference in the tactile sensation created by those frequencies. Tuning slightly lower than "optimal" has no negative effects on the system.



You will always have a tradeoff between efficiency and enclosure size. The larger the enclosure, the more efficient. This means you need less power input to get the same output levels. This is good on all fronts. It lowers thermal issues and less current in the coil means less flux modulation, both meaning lower distortion. Going smaller with the enclosure requires more power to get the same levels. It's a direct tradeoff between the two. Some people want smaller enclosures. That is exactly why we offer the AV15H as mentioned before.

The transmission line could work well, although you'll end up with a lot more than 10cubic foot of volume to do a 16hz transmission line. It's also much more difficult to build than a vented enclosure. If you wanted to model one up I'd be interested in seeing it though. A tapped horn is another that could work if someone wanted to model it up.

John

Welcome to the forum. Interesting posts.

 

[VERTIGGO]

Well I'm gluing my 2.5x15.5x32 port section now (it will be 33.5" long with front thickness of cabinet). Hopefully I estimated my driver sized fairly accurately, because it will be tough to change the port once it's made!

 

[TLS Guy]

Well I'm gluing my 2.5x15.5x32 port section now (it will be 33.5" long with front thickness of cabinet). Hopefully I estimated my driver sized fairly accurately, because it will be tough to change the port once it's made!

Sorry to ignore you, but I have been under the weather these past days, and had a procedure today. The fentanyl and midazolam are just wearing off.

I messed up the previous alignment a little, as I inadvertently had two slot vents specified. I have corrected my web site.

Now there is no free lunch. The F3 of a driver pretty much determines the LF extension possible within 3 Hz or so.

Here is your driver in a 10 cu.ft box with optimal porting of 6" x 16" x 49"

F3 is 21 Hz. Vent velocity is 10 m/sec at full power.

Here is your current alignment.

There is gradual roll off below 100 Hz, with an F3 of 41 Hz. Roll off is rapid at 16 Hz were the output is 7 db down.

Now the two alignments have virtually identical output at 16 Hz, 2 db greater for your alignment, but the optimal alignment has 6 db greater output at 21 Hz.

Your vent velocity is 25 m/sec, which is too high and will result in port compression.

So I would maintain that the optimal extended bass alignment will actually produce the best performance.

I'm sorry for the mix up on vent numbers.

 

[TLS Guy]

What do you use to calculate the vent? This may be a shady source, but it's the easiest calculator I've found. However, it gives different numbers... even Win ISD gives me 4x15x54. I have to get this right before I can determine the length of the box (my simplest adjustment dimension). In WinISD I get mach .15 from 2.5x15.5x33, and it's green (I assumed that meant ok).

BTW, what volume would you use for the cone of the AV15-X? I was using 175 cui.

I have been under the weather lately, and had a procedure today. The drugs are just wearing off.

I inadvertently had two vents specified which accounts for the discrepancies.

I will do TL calculation for you, when I get feeling better. The aperiodic lines have to be calculated the old fashioned way, with a wet towel!

The F3 will be a little higher, but the roll off will be 12 db per octave. It will produce more low bass, in a non resonant with greater authority than BB4 or passive radiator box.

For optimal TL results Fs should be 20 Hz or lower and Qt about 0.4 to 0.44.

 

[VERTIGGO]

Well first off I hope you feel better! And thanks so much for the technical help... I have been confused by too many "right" answers.

I guess I could make a new port to 6x16x49, but I still haven't heard how to measure a wrap-around port. My box was going to be 48" long OD, which means the port has to wrap up the back end. How far up should it go?

I can adjust other dimensions to make it 10'^3 np.

 

[TLS Guy]

Well first off I hope you feel better! And thanks so much for the technical help... I have been confused by too many "right" answers.

I guess I could make a new port to 6x16x49, but I still haven't heard how to measure a wrap-around port. My box was going to be 48" long OD, which means the port has to wrap up the back end. How far up should it go?

I can adjust other dimensions to make it 10'^3 np.

Sorry not to answer that question! Put it down to the drugs.

You measure the length of all folded pipes, and that includes ports, by the length of the center line.

 

[VERTIGGO]

ha ha it happens.

Also, your recommendation actually shows 2 ports at 4x15x64, so I don't know what I would get from 6x16x49...

I'm sorry I have so many questions, but there's just no clear answer; every recommendation is different.

 

[TLS Guy]

ha ha it happens.

Also, your recommendation actually shows 2 ports at 4x15x64, so I don't know what I would get from 6x16x49...

I'm sorry I have so many questions, but there's just no clear answer; every recommendation is different.

Sorry! I linked the wrong pdf.

The drugs are well worn off now! Here is the correct pdf.

I have changed it on my site also.

This is your current vent.

Sorry about that!

 

[VERTIGGO]

Thanks. I took the recommendation but tweaked it a little to my taste. I finally found 6" PVC at Loews so I'm going with round instead, but the tuning is almost the same. At 20840.2 cubic inches with 2 6" diameter by 30" ports I should get approximately 19Hz tuning, keep the response curve above -6db, and keep the port velocity at no more than about 10 m/s at 1000W. The box is half built and I'll have pics up in a fresh thread soon. I'm just waiting on the driver at this point...

 

[VERTIGGO]

See my build thread here:
http://forums.audioholics.com/forums/showthread.php?t=53564