I went for an interview yesterday at a car audio place for an installer/custom job. The manager told me that if I could build a box that impressed him, I could have the job, he will train and pay for MECP certification as well. I can't mess this one up. I have one question that I am unsure about. What frequency should I tune this ported box to?
I was given a pair of Diamond CM310D2's
here are the specs..
10"DVC
SPL........84dB
Fs...........40Hz
F3 tuned at 41Hz=42Hz
The amp specs are a true 800w bridged at 1ohm with a 18dB boost @ 40 Hz.
He wants to know everything..total dB, port tuned at what freq (other than recommended)
dB dropoff and so forth.
Here is my question in depth, should I port these subs at a lower frequency than what they are rated? I was thinking 32-34Hz. If the F3 of the speaker is around 42 and the amp supplies +18dB @40, I am assuming there is a dropoff rate from that boost at around 12dB/octave, so I should still be at around a 10-14dB increase from the boost at 32Hz, and the speaker should have only lost around 10-14dB, so essentially I am extending the low frequency by 10 Hz at the same time holding at or near peak dB. Am I close with this one?
My other option is to try to match curves with the amp.. ie port the speakers to the frequency of the bass boost of the amp, would this be too overpowering at 40Hz, and too much of a dropoff with the sub dropping power below 40, and the amp dropping at the same rrate and time?
Replies (13)
Swez on 12/22/2003 17:22:22
Hey CPL,
I responded to this earlier but sede it did not post... Here are some thoughts on your senario:
1. Get the build specs and plots from Cadence. If they reply well, you will know the port tuning recommendations, F3 and how much power these subs can handle safely below F3
2. Get your hands on a speaker design program called WinISD. There are several verssions out there and this program will allow you to use T/S parameters to plot projected frequency response curves, F3 and X-max at all bass range frequencies
3. The other way I see it, you can run the Cadence recommended enclosure and port dimensions, but use an RTA and signal generator to manually plot output on semi-log graph paper.
Finally, note that if you use EQ boost to extend the low end SPL of these subs, you run the risk of exceeding X-max of the drivers at moderately low SPL levels. This can ultimately destroy the subs if high power input makes the subs go beyond max excursion. (X-max) The Fs/F3 tells us how low the subs will go in free air. But if you electronically try to boost the low end via bass boost EQ, go easy on same or the subs will be toast in no time.
Swez
cplkittle on 12/22/2003 18:02:29
how accurate is winisd? I have version .50, and I did input the parameters of this woofer. With the auto calculate unknown values box checked, everything matched up pretty well as I entered the values, the ones I had not entered yet were already configured pretty close to the given parameters. Only on this speaker has that ever happened. All Audiobahn values are waaaay off, or they are incorrect in the owners manual. Just wondering how much I can trust this program.
ttocs on 12/22/2003 20:50:27
wait, when he says impress him, does he mean sonically, visually, or both???????? You can build a square box that sounde perfect, but you will loose style points...... If I put that challenge down, I would expect to be amazed...
Swez on 12/22/2003 21:50:06
WinISD does have some quirks I am told and newer versions are supposedly debugging them, but in general terms... the program has been pretty favorable to those who know it well. (I do not..) So my opinion is only 2nd hand at best.
Ttocs makes a good point too... performance is probably most important to one type of person while style and originality may be more important to others. Would be a good idea to clarify this aspect as well. If both of you don't see the same page well... missing the intended goal is a real possibility.
Also, what is the budget and time table for this enclosure? It does not seem reasonable to put too much time and money into a box that will look great, sound great but lose money via extensive labor. A mass production box will look OK, sound OK and be reasonably cheap... ($85 -150.00)
But, if you go whole hog and spend 10 hours of labor and the box must sell for under $125.00 + drivers, you've spent $70.00 IN MATERIALS AND GET PEANUTS ($5.50/hr.) FOR YOUR TIME. That's worth clarifying too. It's got to make sense sonicaqlly, visually and economically speaking too huh? THINK ???
Swez
cplkittle on 12/23/2003 11:58:02
It is going in a customer's car and I have to finish it by Jan 5. They get the car on the 3rd. I was given advance notice to design and calculate the box. all work will be done under his supervision at his shop. We decided on the weekend because no one else would be there Sat. after 11, and I would have the whole install bay to myself.
He wants origionality in design, and near perfection in parameters.
The car is an early 90's model honda accord. I was thinking on design to mount the box suspended in the trunk. directly behind the seat, and face it out by building a wall infront of the box at an angle so that the trunk arms don't hit it, or so that I don't have to cut slots to allow for the arms to pass through it. I want the wall to seal off the trunk from the front of the car, and the speakers to be mounted in the wall, using the trunk as a simulated box. I wanted to port the box through the rear armrest (2- 3"x3" square ports one on top of the other, or 2- 3"round ports dressed out in a flat piece of wood.) I was told that the customer was interested in mostly spl, and had no preference as to design other than "origional"
I am carpeting the box in black to match the trunk, and adding a silver diamond made of diamond tuft in the center of the box with the low point of the diamond being on the centerline of the speaker placement. A diamond because of the brand name and that just happens to be one of the company logos as well.
I have decided to tune the box to 36Hz (10% below Fs) this gives me (according to winisd) a max SPL of 96.2dB. The only thing I am worried about is the cone excursion, it peaks at 38mm@18Hz. The speaker max is 20mm, but since the speaker's Fs is 40Hz, I am hoping that at the 18Hz, there should be enough drop in power from the speaker and the amp that this wll not be a problem.
I chose a smaller end box also to provide more air resistance hopefully to prevent overexcursion. This raised my port air velocity to 94mph, so I have to be careful to get perfectly round inside corners if I go with the square ports (read yesterday that the closer to square the better on slotted ports). (JL website)
ryan on 12/23/2003 14:02:55
Since you have the box tuned to 36hz you wouldnt want the sub to play down to 18hz anyways. Its not good for the sub and you could toast it.
cplkittle on 12/23/2003 19:10:24
I do plan to filter it if it distorts below 30Hz, I want to see what it will do first. One thing I did not mention, I have a $200 budget on materials not counting the speakers or amps.
Old_man_audio on 12/24/2003 20:00:54
Interesting project so far. So looks and sonic ability are all important.
Quote: "I have decided to tune the box to 36Hz (10% below Fs) this gives me (according to winisd) a max SPL of 96.2dB. The only thing I am worried about is the cone excursion, it peaks at 38mm@18Hz. The speaker max is 20mm, but since the speaker's Fs is 40Hz, I am hoping that at the 18Hz, there should be enough drop in power from the speaker and the amp that this will not be a problem."
Not sure on that one since this is a ported enclosure right? When ported, we do not get that natural -12dB rolloff curve below Fs. (as in sealed boxes) Also, the port velosity should be well below 20 mph to prevent port noise... if I recall that parameter correctly.
Try using larger ports or fewer of them if possible.. tuned to 36 Hz seems very reasonable though. You can (should) filter off the low end stuff below port tuning frequency . Anything below tuned frfequency will cause the subs to go spazz and excursion issues will definitely do them in at high SPL levels below ~40 Hz.
This is where many generic box makers goof up! They only look at a few basic parameters, then formulate a "close enough to sound good" to the masses, but not great (optimized) for a specific sub brand/specs. Here, the opportunity and a decent budget to get these results are all in place. But the know how may be a bit steep a learning curve. I don't have that knowledge specifically and would have to research same as you... this is where time, research and experience meet the pavement to success.
cplkittle on 12/25/2003 12:16:16
That was a concern (96mph) I was hoping that this would produce some resistance since it is a ported box to cut down on the overexcursion, but I don't know if I can do it without port noise. 3X3 ports give me a length of 16" for 36hz, 4X4 would give me a length of around 38" and a port velocity of 48mph.
Also I will have a slight 'dog leg' in my ports. I planned to use 2 45 degree angles instead of 2 90's to prevent port noise. I may have to go with the 4x4 ports though. I hope to have some time to tweak it, I am taking at least 2 similar designs with me so that I can experiment.
I have pretty much decided from all the responses that a filter is necessary. I am thinking of setting it at 40 Hz, this should still have enough power at 36Hz (tuned freq) and raise the cutoff frequency enough to protect the speakers from the lower freqs. Any suggestions on this?
swez on 12/26/2003 08:53:14
I don't recall where I read this, but it seems to me that a port velosity under 15 mph is a good target. It may have been a Bahn site, Kicker or Adire that recommended that infor. If I run past it again, will pass on the details.
As for a SS filter, pretty close to 40 Hz., will be good for these subs. It needs to be at, or a hair below the port tuning frequency to protect subs from overexcursion at low frequencies... even at lower power output. If the SS filter is variable, you have some tweaking room as you observe cone movement.
What does WinISD say about port velosity proposed? I would hope it will flag it and suggest mods to correct this???
Swez
cplkittle on 12/27/2003 03:22:23
haven't seen any recommendations on winisd, but I've only been using it for about a week. All I see is the port velocity peak and excursion goes off the charts around 16Hz.
cplkittle on 01/1/2004 02:38:19
Going to try WinISD pro now. not much help on the winisd I have.
I did run across some interesting information though, WinISD uses some sort of transmission line equation to configure port length. The basic recommendation for transmission line length is 1/4 the length of the frequency. To get that you have to divide the speed of sound (1,100fps) by the frequency in Hz. This will give you the wavelength in feet.
1100fps / 20Hz = 55 ft TL length = 13.75 ft
1100fps / 40Hz = 27.5 ft TL length = 6.875 ft
1100fps / 60Hz = 18.33ft TL length = 4.58 ft
etc...
just thought that might be useful info for someone.
I know the speed of sound is affected by elevation, temperature, and relative humidity, but it dosen't make much of a difference (+ or - 30fps at extremes)
cplkittle on 01/17/2004 16:30:47
Got the job, haven't had much time to visit the site recently...
Bossman sat in the car when I was through, and told me it sounded about right for 12's, and that he wasn't that impressed until I told him that we put 10's in the car, not 12's.
I did the transmission line theory, found out you can come down to 1/12 the length with similar results, this matched winisd's port length to a T. I went with 5x5 square ports, and actually built them on a seperate piece of wood, then attached them to the box. I ended up with 31" of a maze for the ports. Upon further research, since the free air resonance of the speaker was 40Hz, if the trunk is sealed with dynamat, I will have around 6^ft of a sealed enclosure, this gives me close to the tuned frequency for a sealed box of that recommended for a 4th order bandpass.
Swez, you said you were interested in transmission lines.. try it, they are impressive! those 2 10's make my teeth rattle in that car.
I was given a pair of Diamond CM310D2's
here are the specs..
10"DVC
SPL........84dB
Fs...........40Hz
F3 tuned at 41Hz=42Hz
The amp specs are a true 800w bridged at 1ohm with a 18dB boost @ 40 Hz.
He wants to know everything..total dB, port tuned at what freq (other than recommended)
dB dropoff and so forth.
Here is my question in depth, should I port these subs at a lower frequency than what they are rated? I was thinking 32-34Hz. If the F3 of the speaker is around 42 and the amp supplies +18dB @40, I am assuming there is a dropoff rate from that boost at around 12dB/octave, so I should still be at around a 10-14dB increase from the boost at 32Hz, and the speaker should have only lost around 10-14dB, so essentially I am extending the low frequency by 10 Hz at the same time holding at or near peak dB. Am I close with this one?
My other option is to try to match curves with the amp.. ie port the speakers to the frequency of the bass boost of the amp, would this be too overpowering at 40Hz, and too much of a dropoff with the sub dropping power below 40, and the amp dropping at the same rrate and time?
Replies (13)
Swez on 12/22/2003 17:22:22
Hey CPL,
I responded to this earlier but sede it did not post... Here are some thoughts on your senario:
1. Get the build specs and plots from Cadence. If they reply well, you will know the port tuning recommendations, F3 and how much power these subs can handle safely below F3
2. Get your hands on a speaker design program called WinISD. There are several verssions out there and this program will allow you to use T/S parameters to plot projected frequency response curves, F3 and X-max at all bass range frequencies
3. The other way I see it, you can run the Cadence recommended enclosure and port dimensions, but use an RTA and signal generator to manually plot output on semi-log graph paper.
Finally, note that if you use EQ boost to extend the low end SPL of these subs, you run the risk of exceeding X-max of the drivers at moderately low SPL levels. This can ultimately destroy the subs if high power input makes the subs go beyond max excursion. (X-max) The Fs/F3 tells us how low the subs will go in free air. But if you electronically try to boost the low end via bass boost EQ, go easy on same or the subs will be toast in no time.
Swez
cplkittle on 12/22/2003 18:02:29
how accurate is winisd? I have version .50, and I did input the parameters of this woofer. With the auto calculate unknown values box checked, everything matched up pretty well as I entered the values, the ones I had not entered yet were already configured pretty close to the given parameters. Only on this speaker has that ever happened. All Audiobahn values are waaaay off, or they are incorrect in the owners manual. Just wondering how much I can trust this program.
ttocs on 12/22/2003 20:50:27
wait, when he says impress him, does he mean sonically, visually, or both???????? You can build a square box that sounde perfect, but you will loose style points...... If I put that challenge down, I would expect to be amazed...
Swez on 12/22/2003 21:50:06
WinISD does have some quirks I am told and newer versions are supposedly debugging them, but in general terms... the program has been pretty favorable to those who know it well. (I do not..) So my opinion is only 2nd hand at best.
Ttocs makes a good point too... performance is probably most important to one type of person while style and originality may be more important to others. Would be a good idea to clarify this aspect as well. If both of you don't see the same page well... missing the intended goal is a real possibility.
Also, what is the budget and time table for this enclosure? It does not seem reasonable to put too much time and money into a box that will look great, sound great but lose money via extensive labor. A mass production box will look OK, sound OK and be reasonably cheap... ($85 -150.00)
But, if you go whole hog and spend 10 hours of labor and the box must sell for under $125.00 + drivers, you've spent $70.00 IN MATERIALS AND GET PEANUTS ($5.50/hr.) FOR YOUR TIME. That's worth clarifying too. It's got to make sense sonicaqlly, visually and economically speaking too huh? THINK ???
Swez
cplkittle on 12/23/2003 11:58:02
It is going in a customer's car and I have to finish it by Jan 5. They get the car on the 3rd. I was given advance notice to design and calculate the box. all work will be done under his supervision at his shop. We decided on the weekend because no one else would be there Sat. after 11, and I would have the whole install bay to myself.
He wants origionality in design, and near perfection in parameters.
The car is an early 90's model honda accord. I was thinking on design to mount the box suspended in the trunk. directly behind the seat, and face it out by building a wall infront of the box at an angle so that the trunk arms don't hit it, or so that I don't have to cut slots to allow for the arms to pass through it. I want the wall to seal off the trunk from the front of the car, and the speakers to be mounted in the wall, using the trunk as a simulated box. I wanted to port the box through the rear armrest (2- 3"x3" square ports one on top of the other, or 2- 3"round ports dressed out in a flat piece of wood.) I was told that the customer was interested in mostly spl, and had no preference as to design other than "origional"
I am carpeting the box in black to match the trunk, and adding a silver diamond made of diamond tuft in the center of the box with the low point of the diamond being on the centerline of the speaker placement. A diamond because of the brand name and that just happens to be one of the company logos as well.
I have decided to tune the box to 36Hz (10% below Fs) this gives me (according to winisd) a max SPL of 96.2dB. The only thing I am worried about is the cone excursion, it peaks at 38mm@18Hz. The speaker max is 20mm, but since the speaker's Fs is 40Hz, I am hoping that at the 18Hz, there should be enough drop in power from the speaker and the amp that this wll not be a problem.
I chose a smaller end box also to provide more air resistance hopefully to prevent overexcursion. This raised my port air velocity to 94mph, so I have to be careful to get perfectly round inside corners if I go with the square ports (read yesterday that the closer to square the better on slotted ports). (JL website)
ryan on 12/23/2003 14:02:55
Since you have the box tuned to 36hz you wouldnt want the sub to play down to 18hz anyways. Its not good for the sub and you could toast it.
cplkittle on 12/23/2003 19:10:24
I do plan to filter it if it distorts below 30Hz, I want to see what it will do first. One thing I did not mention, I have a $200 budget on materials not counting the speakers or amps.
Old_man_audio on 12/24/2003 20:00:54
Interesting project so far. So looks and sonic ability are all important.
Quote: "I have decided to tune the box to 36Hz (10% below Fs) this gives me (according to winisd) a max SPL of 96.2dB. The only thing I am worried about is the cone excursion, it peaks at 38mm@18Hz. The speaker max is 20mm, but since the speaker's Fs is 40Hz, I am hoping that at the 18Hz, there should be enough drop in power from the speaker and the amp that this will not be a problem."
Not sure on that one since this is a ported enclosure right? When ported, we do not get that natural -12dB rolloff curve below Fs. (as in sealed boxes) Also, the port velosity should be well below 20 mph to prevent port noise... if I recall that parameter correctly.
Try using larger ports or fewer of them if possible.. tuned to 36 Hz seems very reasonable though. You can (should) filter off the low end stuff below port tuning frequency . Anything below tuned frfequency will cause the subs to go spazz and excursion issues will definitely do them in at high SPL levels below ~40 Hz.
This is where many generic box makers goof up! They only look at a few basic parameters, then formulate a "close enough to sound good" to the masses, but not great (optimized) for a specific sub brand/specs. Here, the opportunity and a decent budget to get these results are all in place. But the know how may be a bit steep a learning curve. I don't have that knowledge specifically and would have to research same as you... this is where time, research and experience meet the pavement to success.
cplkittle on 12/25/2003 12:16:16
That was a concern (96mph) I was hoping that this would produce some resistance since it is a ported box to cut down on the overexcursion, but I don't know if I can do it without port noise. 3X3 ports give me a length of 16" for 36hz, 4X4 would give me a length of around 38" and a port velocity of 48mph.
Also I will have a slight 'dog leg' in my ports. I planned to use 2 45 degree angles instead of 2 90's to prevent port noise. I may have to go with the 4x4 ports though. I hope to have some time to tweak it, I am taking at least 2 similar designs with me so that I can experiment.
I have pretty much decided from all the responses that a filter is necessary. I am thinking of setting it at 40 Hz, this should still have enough power at 36Hz (tuned freq) and raise the cutoff frequency enough to protect the speakers from the lower freqs. Any suggestions on this?
swez on 12/26/2003 08:53:14
I don't recall where I read this, but it seems to me that a port velosity under 15 mph is a good target. It may have been a Bahn site, Kicker or Adire that recommended that infor. If I run past it again, will pass on the details.
As for a SS filter, pretty close to 40 Hz., will be good for these subs. It needs to be at, or a hair below the port tuning frequency to protect subs from overexcursion at low frequencies... even at lower power output. If the SS filter is variable, you have some tweaking room as you observe cone movement.
What does WinISD say about port velosity proposed? I would hope it will flag it and suggest mods to correct this???
Swez
cplkittle on 12/27/2003 03:22:23
haven't seen any recommendations on winisd, but I've only been using it for about a week. All I see is the port velocity peak and excursion goes off the charts around 16Hz.
cplkittle on 01/1/2004 02:38:19
Going to try WinISD pro now. not much help on the winisd I have.
I did run across some interesting information though, WinISD uses some sort of transmission line equation to configure port length. The basic recommendation for transmission line length is 1/4 the length of the frequency. To get that you have to divide the speed of sound (1,100fps) by the frequency in Hz. This will give you the wavelength in feet.
1100fps / 20Hz = 55 ft TL length = 13.75 ft
1100fps / 40Hz = 27.5 ft TL length = 6.875 ft
1100fps / 60Hz = 18.33ft TL length = 4.58 ft
etc...
just thought that might be useful info for someone.
I know the speed of sound is affected by elevation, temperature, and relative humidity, but it dosen't make much of a difference (+ or - 30fps at extremes)
cplkittle on 01/17/2004 16:30:47
Got the job, haven't had much time to visit the site recently...
Bossman sat in the car when I was through, and told me it sounded about right for 12's, and that he wasn't that impressed until I told him that we put 10's in the car, not 12's.
I did the transmission line theory, found out you can come down to 1/12 the length with similar results, this matched winisd's port length to a T. I went with 5x5 square ports, and actually built them on a seperate piece of wood, then attached them to the box. I ended up with 31" of a maze for the ports. Upon further research, since the free air resonance of the speaker was 40Hz, if the trunk is sealed with dynamat, I will have around 6^ft of a sealed enclosure, this gives me close to the tuned frequency for a sealed box of that recommended for a 4th order bandpass.
Swez, you said you were interested in transmission lines.. try it, they are impressive! those 2 10's make my teeth rattle in that car.
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