so i was playing with the DCTT setup with kel (whos car its in) and it seems to hit everything 28-35hz like a beast, then dips in db till the low high forties where it gets pingy when it hits, just a feeling if inconsistent sound, sometimes loud and sometimes not. i'm giong to do some more experimenting with the Slot Vent Version to see if i can bring the tune a little closer together to raise the "dip" a bit and hopefully make a smoother curve.
(sorry i got a bit side tracked)
ok, to the point of the thread.
we listened to a prefab set of 10s in an acura and was impressed, and decided to try a higher tuned box for that same 10 to see what kind of sound that same woofer in the same car would make with a completely different box, so i designed this-
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL2.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL1.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL4.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL3.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL5.jpg
RF recommends 1.4cuft tuned to 40hz
this box is 1.5cuft tuned to 39hz
port is 4x10x42.75
-Drew
Replies (12)
swez on 01/21/2008 23:41:56
Wow... why the 4" port? The larger the port, the longer it needs to be and the more displacement in the box too. (For the port and sub)
Also, how are you measuring/guestimating the low end bass at 28-35 Hz.?
1. Test tones and SPL meter
2. RTA and calibrated mike
3. S.W.A.G. (Scientific Wild-Azz Guessing)
The typical 4-string bass is tuned at low "E" to 41.3 Hz. To go lower, the 5, 6 and 7 string bass were employed. Few Jazz bassists went in that direction. Many stuck to 4-5 string bass options as skill levels were considerable to master use of additional bass strings.
The "C# contra-bass" was a 11-12 string bass that emulated a Grand Piano that bottomed out at 17.32 Hz. Very few bassist could manage that range with any real degree of mastery.
If we are talking synth-bass tones, that is another issue.
Comments?
Swez
newB on 01/21/2008 23:47:59
SWAG at its finest, but my primitive method is downloading a series of tones from ROE and plugging my Laptop straight into the Head unit and going through the tracks (each one dropping say 3hz) from 45-28 and that way if say track 6 is week i'll know XYhz is weak, purely by ear.
i do have an RTA on my laptop as well, but no calibrated mike.
how would that box perform??
the reason for the 4inch port is thinking moving the most air would be best, and because it is a single 10 in a very large trunk i can manage using the 4inch while still keeping the size of the box within reason compared to say his old dual 12, or dual 10 box.
-Drew
swez on 01/22/2008 06:08:16
OK, Swag it is and yes, our ears can hear that low, but acquity is limited as hearing rolls of fast below ~35 Hz.
Consider a 2.5" vent width here as the vent area is a bit large for a single 10" sub. When using a 15-18" sub, a 4" vent is appropriate, but not for a single 10.
Swez
newB on 01/22/2008 11:03:18
WHY?
the only thing i can think of is that the 10 doesnt push enough air, and port velocity would be very, very, low.
-Drew
swez on 01/22/2008 18:31:46
That is exactly the issue... Back pressure levels on a 10" cone are minimal in this size/enclosure design noted.
With a 10" sub, we want some back pressure from the port to keep the cone excursion in check and not flapping in the wind like a "free air" install. The bass is likely to be very sloppy and can only handle about 40-50% power rating before the sub cone reaches X-max.
Sure, you can try it if you like. But physics and the Theil/Small parameters will give us a better plan on how to pressurize a given sub and still maintain cone control and adequate power handling.
The Vb and tuning specs are pretty close to RF specs as noted. But there is little back pressure in such a large vent to keep the cone in check. That could come back to bite later.
Swez
newB on 01/22/2008 19:38:56
makes sense, I'm also getting from other forums that 2.5 is a more realistic number to go with, will hold more power and play better on music (although it will only be getting 300watts on a good day)
-Drew
MrBrownstone on 01/24/2008 16:54:35
I'm not sure with a port the size of the woofer cone that there's even ANY back pressure :-)
swez on 01/25/2008 09:35:07
Intuitively speaking, I'd almost agree with you B. The vent/port dimensions are used to tune the enclosure and acts more like a "resonator" at PTF. (Port Tuning Frequency +/- some percentage)
How much back pressure is actually seen by the sub(s), is a function of the vent/port area and Vb of the enclosure. Am sure it is measurable and somewhat predictable too.
Port velosity is one aspect enclosure designers have to be very aware of. Too small a port/vent, we'll get unwanted port noise as air velosity is greater in small ports/vents at high SPL levels. (Chuffing or whistling sounds are not desirable)
At the same time, if the port/vent is too large, there is little or no back pressure to the sub and X-max is reached well before the rated power is applied to a give sub. Here, the system acts more like a "free-air" design. Bass is sloppy, poorly defined and as input power is increased, the sub mechanical support structures just fall apart and the cone has lost all control. (That often leads to motor structure failures at the coil/cone joint... typically the spider will fracture or separate from its mount or at the cone glue joint) This is a common failure to SPL Comp geeks.
Swez
MrBrownstone on 01/25/2008 13:52:36
I'd have to crunch some numbers, but am frankly too lazy. It would appear, eyeballing it, that a 4" Round port, 12 sqin would be better than 48 or whatever you have going there (42.75? is that it?)
Your woofer is 78sq inch, and essentially you have the equivalent of a hole the size of an 8" woofer in your box.
I know it may sound smartarsish, but the manufacturers provide recommendations for a reason--to allow you to get the best overall performance for your speaker. Enclosures that attempt to 'maximize' on the efficiency of a woofer typically end up 1 note wonders.
Perhaps that's what's happening here.
newB on 01/25/2008 20:05:03
so whats the rule of thumb for sqin of woofer : sqin of port????
-Drew
cplkittle on 01/25/2008 23:30:05
I don't know if there is a rule of thumb, but if you multiply the diameter by 2, that seems to come out pretty well.
10" sub = 20 sq in = 2x10 port
12" sub = 24 sq in = 2x12 port
15" sub = 30 sq in = 2x15 port
Or you can go by 1/4 of the surface are of the sub
10" sub = 78.5 sq in /4= 19.625 = 2x10 port
12" sub = 113.04 sq in /4= 28.26 = 2x14 port
15" sub = 176.625 sq in /4= 44.156 = 3x15 port
I personally like the 1/4 surface diameter method, the first method seems a bit small.
If you are experimenting, a 4" port would be good for an internal volume of .75 or less, or if you are tuning below 25 Hz.
newB on 01/26/2008 00:08:09
i like the second, i'll use that for my general rule of thumb. thanx for that valuable piece of advice cplkittle
-Drew
(sorry i got a bit side tracked)
ok, to the point of the thread.
we listened to a prefab set of 10s in an acura and was impressed, and decided to try a higher tuned box for that same 10 to see what kind of sound that same woofer in the same car would make with a completely different box, so i designed this-
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL2.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL1.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL4.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL3.jpg
http://i40.photobucket.com/albums/e216/saxwonder05/audio/P3SPL5.jpg
RF recommends 1.4cuft tuned to 40hz
this box is 1.5cuft tuned to 39hz
port is 4x10x42.75
-Drew
Replies (12)
swez on 01/21/2008 23:41:56
Wow... why the 4" port? The larger the port, the longer it needs to be and the more displacement in the box too. (For the port and sub)
Also, how are you measuring/guestimating the low end bass at 28-35 Hz.?
1. Test tones and SPL meter
2. RTA and calibrated mike
3. S.W.A.G. (Scientific Wild-Azz Guessing)
The typical 4-string bass is tuned at low "E" to 41.3 Hz. To go lower, the 5, 6 and 7 string bass were employed. Few Jazz bassists went in that direction. Many stuck to 4-5 string bass options as skill levels were considerable to master use of additional bass strings.
The "C# contra-bass" was a 11-12 string bass that emulated a Grand Piano that bottomed out at 17.32 Hz. Very few bassist could manage that range with any real degree of mastery.
If we are talking synth-bass tones, that is another issue.
Comments?
Swez
newB on 01/21/2008 23:47:59
SWAG at its finest, but my primitive method is downloading a series of tones from ROE and plugging my Laptop straight into the Head unit and going through the tracks (each one dropping say 3hz) from 45-28 and that way if say track 6 is week i'll know XYhz is weak, purely by ear.
i do have an RTA on my laptop as well, but no calibrated mike.
how would that box perform??
the reason for the 4inch port is thinking moving the most air would be best, and because it is a single 10 in a very large trunk i can manage using the 4inch while still keeping the size of the box within reason compared to say his old dual 12, or dual 10 box.
-Drew
swez on 01/22/2008 06:08:16
OK, Swag it is and yes, our ears can hear that low, but acquity is limited as hearing rolls of fast below ~35 Hz.
Consider a 2.5" vent width here as the vent area is a bit large for a single 10" sub. When using a 15-18" sub, a 4" vent is appropriate, but not for a single 10.
Swez
newB on 01/22/2008 11:03:18
WHY?
the only thing i can think of is that the 10 doesnt push enough air, and port velocity would be very, very, low.
-Drew
swez on 01/22/2008 18:31:46
That is exactly the issue... Back pressure levels on a 10" cone are minimal in this size/enclosure design noted.
With a 10" sub, we want some back pressure from the port to keep the cone excursion in check and not flapping in the wind like a "free air" install. The bass is likely to be very sloppy and can only handle about 40-50% power rating before the sub cone reaches X-max.
Sure, you can try it if you like. But physics and the Theil/Small parameters will give us a better plan on how to pressurize a given sub and still maintain cone control and adequate power handling.
The Vb and tuning specs are pretty close to RF specs as noted. But there is little back pressure in such a large vent to keep the cone in check. That could come back to bite later.
Swez
newB on 01/22/2008 19:38:56
makes sense, I'm also getting from other forums that 2.5 is a more realistic number to go with, will hold more power and play better on music (although it will only be getting 300watts on a good day)
-Drew
MrBrownstone on 01/24/2008 16:54:35
I'm not sure with a port the size of the woofer cone that there's even ANY back pressure :-)
swez on 01/25/2008 09:35:07
Intuitively speaking, I'd almost agree with you B. The vent/port dimensions are used to tune the enclosure and acts more like a "resonator" at PTF. (Port Tuning Frequency +/- some percentage)
How much back pressure is actually seen by the sub(s), is a function of the vent/port area and Vb of the enclosure. Am sure it is measurable and somewhat predictable too.
Port velosity is one aspect enclosure designers have to be very aware of. Too small a port/vent, we'll get unwanted port noise as air velosity is greater in small ports/vents at high SPL levels. (Chuffing or whistling sounds are not desirable)
At the same time, if the port/vent is too large, there is little or no back pressure to the sub and X-max is reached well before the rated power is applied to a give sub. Here, the system acts more like a "free-air" design. Bass is sloppy, poorly defined and as input power is increased, the sub mechanical support structures just fall apart and the cone has lost all control. (That often leads to motor structure failures at the coil/cone joint... typically the spider will fracture or separate from its mount or at the cone glue joint) This is a common failure to SPL Comp geeks.
Swez
MrBrownstone on 01/25/2008 13:52:36
I'd have to crunch some numbers, but am frankly too lazy. It would appear, eyeballing it, that a 4" Round port, 12 sqin would be better than 48 or whatever you have going there (42.75? is that it?)
Your woofer is 78sq inch, and essentially you have the equivalent of a hole the size of an 8" woofer in your box.
I know it may sound smartarsish, but the manufacturers provide recommendations for a reason--to allow you to get the best overall performance for your speaker. Enclosures that attempt to 'maximize' on the efficiency of a woofer typically end up 1 note wonders.
Perhaps that's what's happening here.
newB on 01/25/2008 20:05:03
so whats the rule of thumb for sqin of woofer : sqin of port????
-Drew
cplkittle on 01/25/2008 23:30:05
I don't know if there is a rule of thumb, but if you multiply the diameter by 2, that seems to come out pretty well.
10" sub = 20 sq in = 2x10 port
12" sub = 24 sq in = 2x12 port
15" sub = 30 sq in = 2x15 port
Or you can go by 1/4 of the surface are of the sub
10" sub = 78.5 sq in /4= 19.625 = 2x10 port
12" sub = 113.04 sq in /4= 28.26 = 2x14 port
15" sub = 176.625 sq in /4= 44.156 = 3x15 port
I personally like the 1/4 surface diameter method, the first method seems a bit small.
If you are experimenting, a 4" port would be good for an internal volume of .75 or less, or if you are tuning below 25 Hz.
newB on 01/26/2008 00:08:09
i like the second, i'll use that for my general rule of thumb. thanx for that valuable piece of advice cplkittle
-Drew
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