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Bronze Member Username: CaddycadPost Number: 13 Registered: Jul-05 | Ok in the morning im going to a audio shop to have a custom box built for my 2 15" L7's.. I'm going for SPL and i like my bass to have that BOOM effect. Soooo talking with the guy he says theyre going to build a box with the subs facing the cabin instead of the tail lights, vented, and something about tunneling? Anyway is this really the best way? he says it will eliminate cancelation and make it louder.. just wondering what the pro's think.. thanks for your time |
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Gold Member Username: Taylor17Kopperl, Texas Post Number: 2705 Registered: Jan-05 | When you say, "vented" I'm guessing they mean a slot vented ported box? They are building a ported box right? A ported box will give the most spl, and sense you like the boomy sound, I'd tune around 45HZ But then again, I'm not box expert though... |
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Bronze Member Username: AcevolkovSpringfield, Missouri United Stated Post Number: 44 Registered: Jul-05 | they are gonna tunnel the subs into your car i think, so your subs dont have to fight through the back seat to be heard in the cabin. sounds like they are doing the best they can with a given situation. |
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New member Username: 02gsxrPost Number: 6 Registered: Jul-05 | Umm first of all, what kind of car? Second of all, your subs should be facing either back or straight up, unless you have a wall but that's a whole other story. Also, the port should be on the same face as the sub - never port out the side or the back if the sub is up. 3rd, you want a very large box for those subs - like 4-5cu ft per if possible, and you want the port to be as large AS POSSIBLE without it having to be too long for the box. For strictly SPL competition, you'd want to tune the box to about 45-55hz depending on the car. If you are talking about SPL for your personal enjoyment and everyday use, you want to tune it much lower (35-40hz). There is a very big difference. 35-40 will sound and feel much louder to you, but 45-55 will be much louder to a microphone, but sound like crap to you. Find out what size box (cu ft) they are building, what size port, how long, and tuning frequency. I will be able to tell you wether it is good or not. If you'd like, I'll design something for you and you could just have them build it. |
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Silver Member Username: Riebread77Post Number: 475 Registered: Jun-05 | i'd put it on a 45 degree angle between facing straight up and directly out...as a rule...you want the box near the taillights facing in or near the back seat facing out...because low frequencies are the longest of them all... |
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Bronze Member Username: CaddycadPost Number: 14 Registered: Jul-05 | its going in a 1996 chevy caprice, it wont be for strictly SPL competition, personal every day use I just want a high SPL to the ear. so facing the subs toward the cabin is a bad idea? I have no idea what size box theyre going to build im going there in the morning to talk to them about it and theyre going to go to work on it right away.. what about venting the top of the box? so that the air moves toward the rear deck.. also i see that porting/venting adds 3db but is that only at the tuned frequency? what will happen to 30hz if i tune for 40hz? this is going to be built tomorrow, so i just want to make sure im not spending my money and letting them make a design mistake i appreciate the help |
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Bronze Member Username: CaddycadPost Number: 15 Registered: Jul-05 | bump |
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Bronze Member Username: CaddycadPost Number: 16 Registered: Jul-05 | LoL HELP! 8hrs before my appointment! |
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New member Username: 02gsxrPost Number: 7 Registered: Jul-05 | Ahh precisly the problem. If you tune the box to 40hz, and play 30hz the sub will lose all of it's power handling. The problem is that the air pressure has no resistance while entering/exiting the box at that frequency. You will probably end up blowing the sub if you have sufficient power. That is why I asked if you want this box for competition use or street use. By building a strictly competition box you can gain much higher SPL, but lose your "streetability". They are meant to play a single note, and nothing less. By playing regular songs you lose your power handling at the lower freq's and ruin subs very easily. That is the reason most people build sealed boxes. They have much higher power handling than a ported some ported boxes. However a properly designed ported box can do the same thing. You mentioned that you heard you can gain 3db by going to a ported box. This is true to a point. By building a ported box you have much more control over what gain or loss you take. You can lose 3db, but gain a lot more low end, or you can gain 10db, but have a huge peak at certain frequencies. The bigger box (to a point) you have, the more spl you will generally have. Also, the higher tuning frequency, the more SPL you will gain (again, to a point). These are just general rules of thumb. Everything has a trade off. A bigger box gives you more spl, or lower bass, but takes up more space. A higher tuned box will give more SPL, but less "streetability". A lower tuned box will be deeper and louder to the ear, but less SPL on a meter. As far as porting the box up, and sub facing back, that is not something you generally want to do. Each frequency has a different length. Lower frequencies have a much longer path than a high frequency. This means that it will take xx amount of feet to "fully develop". In a sound wave, frequency measures the number of waves sent out per second and in effect can be used to measure the length of the individual waves (the wavelength). Since a sound signal travels at a certain speed, it can travel a specific distance in one second. Since the distance then is set for one second and the frequency measures cycles in a second, the frequency measurement dictates how many cycles or individual waves are placed into that length. If we divide the distance the sound wave travels in one second by the number of cycles (the frequency as measured in Hz), we get the size of the individual waves (the wavelength). Sound travels about 3,960,000 feet per hour or 1,100 feet per second. By dividing the feet per second by a frequency of 20 Hz we get a wavelength of about 55 feet (the true value is given as 56 feet). At 20 kHz (20,000 cycles per second), the wavelength is about 0.66 inches or two thirds of an inch. In any car however, none of them are 55 feet long, so we use a measurement called "quarter wave". Assuming your woofer is in phase (0 degrees), this would mean that a quarter wave is 90 degrees. so 1/4 of 55 feet is 13.75 feet. In the case you would want to play 20hz you would want the woofer and port to be 13.75 feet from the listening point. However, 20hz is not audible to most humans so this would not really be a real life example. In your case, lets say 35-40hz is the most common sounds your woofer is going to be playing that you will hear. This would mean it would have a wavelength of 27-31ft. So in this case you would preferably have a distance of 27-31ft. However a 1/4 wave is going to be about 7-8 feet in this case meaning your sub would have to be in the back seat. So in this case, we will use a 1/2 wave which would be 14-16 feet. In most cars, the distance from the driver seat to the place where your box would be is only about 10 feet. So you want the woofer to aim back, and reflect off of the back of the trunk giving you 2-3 feet in each direction, which would put you at 14-16 feet. The other problem you will run into is the direction the port is facing. If your sub is wired properly in phase, the front of the woofer will be 0 degrees phase. The back of the woofer will be exactly opposite "out of phase" meaning it is at 180 degrees phase. Therefore you want the distance from the back of the woofer, to the back of the enclosure, to the front of the port to be 2 times the distance. Essentially, you are setting your own "time delay" for the back of the woofer so that it is at the same phase when it gets to the same point as the front of your woofer. This gets rid of phase cancellation and will make your woofer louder. By putting a port anywhere but the same side as the woofer, changes your phase and can cause cancellation making your sub quieter. The reason you may see some people putting a port somewhere else is because their box is so big that porting to the front would be out of phase, but in a case of a non competition enclosure, this would not be the case. Let me get the theile small (mechanical) properties of your sub, and I'll try to come up with something tonight. Then you can just let the guys know what you want when you have them build it for you. |
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Bronze Member Username: CaddycadPost Number: 17 Registered: Jul-05 | wow jon thanks for the in-depth reply.. now you have me thinking about a big sealed enclosure instead.. mainly because i would also like to hit 30hz-40hz and dont want to blow my new subs.. I play alot of music called "screwed and chopped" with continuous low notes that put serious strain on subs.. do you think i would be happy with a sealed box 2-3cu ft? here are the specs [img]http://www.picture-portal.net/images/l7-specs.JPG[/img] also, polyfil? if i do 2-3cu ft sealed per sub should i add it anyway? to make it deeper.. i appreciate your time and reply, if you could come up with a design that would be great too! |
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Bronze Member Username: 02gsxrPost Number: 12 Registered: Jul-05 | No, I would still stick with a ported box with those subs. Some subs are just meant to be in a sealed box, others are meant to be in a ported. Also, by going with too big of a sealed box, you can do very negative things also. Too big of a Sealed box and your Qtc value will be too low. Most listeners prefer a Qtc around .7 or so. If your Qtc gets too low (big box) it will sound extremely "muddy" and very "boomy". Also, a sealed box does essentially the same thing as a ported box, only a little differently. Instead of a port/vent controlling the resistance on the driver, it does essentially the same thing as trying to squeeze a plastic soda bottle with the cap on. However, gasses can be compressed. Therefore, the more air or "gas" in the enclosure, the more it can be compressed. Unfortunately, you will have the same problem with too large of a sealed box as you would with the ported box. The more the air can compress, the less resistance your driver will have. Therefore, your power handling will go down because of this also. Your best bet with those subs is to use a ported box. However, they need a box that's a little on the large side. Tune it very low and you will not have any problems. You mentioned that you will be listening to very low bass notes, however if you can hear them, they are not as low as you may think. In 99.9% of all songs, none of them will play anything below 35hz. That is the general cutoff point for just about any song, whether it's rock, rap, metal, drum and bass, country, anything. The only time you may have a problem is one of those bass CD's people buy to impress their friends. You know the ones that actually have a warning on them saying that it plays ultra low frequencies that can damage woofers lol. If you build a properly designed ported box, you will not have any problems. Otherwise people wouldn't be using them. It is just important that the shop building the box knows what they are doing, and it takes a really good shop to build one that will yield very good SPL gains at a low frequency. Like I said, I will get the mechanical specs of your sub and put something together. I will make sure that it is not tuned too high that you have any problems. I will also ensure you that the port is large enough so that you don't have any velocity problems (port noise). If you wouldn't mind, please get me the largest desired dimesions for the box in your vehicle. Thanks. |
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Bronze Member Username: CaddycadPost Number: 18 Registered: Jul-05 | is 53" wide x 16" depth x 16" height big enough? |
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Bronze Member Username: 02gsxrPost Number: 13 Registered: Jul-05 | Hmmm, could you go 17-18"?? Also, do you mind if it's 53" wide? BTW, do you have any specs on the sub itself? You should have gotten a sheet with it with all of the Theile/Small (mechanical) properties. This would include, but not limited to: SPL/Sensitivity Vas Qts Qes Qms Sd Re Pe You should see most of those on there. If you have it that would be a great help. I'm not finding them on the web, I should be able to find them though if I have to. |
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Bronze Member Username: CaddycadPost Number: 19 Registered: Jul-05 | weird those properties are not in the owners manual.. actually i can probably only go 15" depth due to the trunk lid bars but i can go 53" wide.. |
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Bronze Member Username: CaddycadPost Number: 20 Registered: Jul-05 | also should i cut off frequencies above 40hz on the crossover? |
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Bronze Member Username: 02gsxrPost Number: 15 Registered: Jul-05 | No, it is only harmful to the woofer when you go BELOW the tuned frequency. A crossover on your amp will cut frequencies above the frequency you set. Like I said though, 99.9% of songs will not play anything under 35hz though. So if you tune it right you should not have a problem at all. If your amp has a subsonic filter however, you should turn that on. That cuts out the harmfull frequencies (usually below 30hz or 20hz) some amps even have an adjustable subsonic filter which is even better. Well, I'm gonna try and find those T/S properties. I'll post back here with some info, hopefully tonight yet so you can tell the guys what you want tomorrow. |
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Bronze Member Username: 02gsxrPost Number: 16 Registered: Jul-05 | Ok, got the specs. Is it a Dual 4ohm? or Dual 2ohm? Also, when I was asking if you had 17-18", I was talking about the height... |
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Bronze Member Username: 02gsxrPost Number: 17 Registered: Jul-05 | Wow, I never realized what a flexable sub this really was! You can actually get a very nice gain at extremely low frequencies!! They do however, require somewhat large boxes. In your case though, this is not a problem. Here's what I came up with: If you have a 4ohm... W 53" x H 16" x D 15.5" Your port will be H 14.5" x W 4" x L 23.125" If you have a 2ohm... W 53" x H 16" x D 16" You port will be H 14.5" x W 4" x L 27.25" The 4ohm box will give you a nice gain (5db) between 36hz and 63hz and very low tuning so it will be a safe box to use. The 2ohm box will give you a good gain from 30hz to 51hz and again, is very safe to use. 4ohm: (2) front/back: 53" x 16" (2) top/bottom: 53" x 14" (2) sides: 14.5" x 14" (1) port #1: 14.5" x 10" (1) port #2: 14.5 x 11.625" 2ohm: (2) front/back: 53" x 16" (2) top/bottom: 53" x 14.5" (2) sides: 14.5" x 14.5" (1) port #1: 14.5" x 10.5" (1) port #2: 14.5" x 15.25" Make sure the end of the second port piece butts up against the first port piece so that you maintain 4" of port along the back side. |
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Bronze Member Username: 02gsxrPost Number: 19 Registered: Jul-05 | Follow this link, if you'd like to see a plot: click here |
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Makavelian Unregistered guest | Idont want to be jaking your thread or anything but im in a similar situation as yourself i will be having two l7 15s in a double ported box....Low bass and is also Ported these are the specs im given if u could kindly check these for me it would be greatly apreciated thanks. (Size: Length 42-1/2" Height 17-1/4" Depth (Bottom) 22-1/2" Depth (Top) 17-1/2") |
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Bronze Member Username: 02gsxrPost Number: 45 Registered: Jul-05 | Makavelian... I need to know what size the port is. Please give me the width, height, and length. Or diameter and length if a circular port. I also need to know if you have 2ohm voice coils, or 4ohm coils... |
