I'm making plans for an enclosure to house (2) JBL wGTi15 15" subwoofers (dual 6 ohm, 800w RMS, real nice subs). I have an audiobahn amp (A1500HCT, the same one I talked about constantly the last time I used this forum) that will push them perfectly when they're hooked up for a single 1.5 ohm load to my amp...
My question concerns the box type. JBL published specific specs and dimensions for a sealed box, vented box, and sealed-bandpass box. I plugged all the thiele-small parameters into WinISD v.044, and looked at the results using the specified box parameters. Not surprisingly, the sealed box had extremely linear response. The vented box designed to spec wasn't quite as linear, but was pretty damn good for a vented box (it was much more linear than a pair of Audiobahn in a vented box I've analyzed).
So what's better to use, sealed or vented (would probably do a slot port design for each chamber)? Obviously, sealed is supposed to sound better because it has a better "transitional response" or something, and is more linear in response. But I've also read that if a ported box is built EXACTLY to spec it will distort less at most frequencies, especially when the volume is cranked up, and that there will be a noticeable volume gain. You just have to make sure not to send any signals below what the box is tuned for, because you could hurt the subs.
Some people say that if a sub's Qts parameter is higher than 0.4, then you should only use a sealed box. This sub's Qts parameter is 0.48! But JBL and a lot of other people apparently aren't worried about it, build a ported box exactly as they specify and you'll be fine....
So what's you're guys opinions/suggestions? Which box design should I go with? I want good SQ, and I also want a lot of SPL.
Replies (11)
swez on 05/7/2004 11:22:34
Vented designs are able to deliver both SPL and SQ. Most Pro enclosure are vented for that very reason.
Since you are thinking HT here, you can port the subs to a very low F3 point of say 20-25 Hz and install a Subsonic Filter to block signals below 20 Hz.
As for Qtc parameters, that's a general guide... not a hard, fast rule. If you go ported, just make sure you follow the guidelines form JBL for tuning.
Also, what is the price of these GTi subs? I see that Parts Express is offering a JBL Pro line sub for $250.00/ea. These are 4 ohm, 800 RMS subs, so a pair will net 2 ohms in parallel. Even if your amp is 1500 RMS @ 1.5 ohms, 500 RMS less output at 2 ohms, you will not really notice a decrease of 1.5 - 2dB in SPL. You'll pick up +3dB by porting, another +3dB from dual sub design and +10-15 more dB from room transfer function. (room gain effect) Combine all that extra gain and you are well over +120 dB reference level for HT applications.
Not bad for 500 RMS per sub and $500.00 for the pair.
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-750&dotd=050604
What say you?
Swez
BigJMan on 05/7/2004 11:56:55
Thanks for the swift reply.
I think I'm going to go ahead and try building the ported box. I still wnat to get the JBL wGTi15 subs, because they can use all of my amp's available power, which although, as you pointed out, might not make much of a noticeable difference, is still important to me.
The wGTi15 subs have a list price of $700.00 - yikes right? Not really, I know from painful past experiences that you definitely, definitely get what you pay for... and plus I've already found internet retailers I can buy the subs from for less than half the list price, so I'm going to stick wit em.
p.s. What's the difference between the wGTi15 sub that I'm talking about and the older JBL Pro Line 15" sub you're talking about, besides the resistance? Both are 15" subs, and both take 800w RMS. JBL says that the wGTi15 can take 5000w max power, maybe that's it (although I think that numbe is probably bull).
Thankyou
John
BigJMan on 05/7/2004 12:03:35
Another quick question,
in this pdf file
http://manuals.harman.com/JBL/CAR/Boxes%20and%20Parameters/W15GTi_rev_f.pdf
2nd page, in the "vented box volume" picture (look inside where the port is drawn), it says fo = 28.0 Hz, is this what the box is supposed to be "tuned" to, I need to know for WinISD and other reasons...
John
swez on 05/7/2004 19:57:51
Fo is port tuning frequency. This is based on T/S parameters of the sub, the enclosure design and port size.
The main difference I can see in the GTI series, it is a hybrid of JBL's newer Pro Line subs. Large frame, huge magnet structure and rapid cooling system for the 3" DVC coils. Better cooling will provide less "thermal compression" (output power reductions) at high SPL levels.
The 15" sub I mentioned is a 4" SVC design that is well suited for HT, Club monitors and modest Sound Reinforcement applications. It would probably be a good option for large car audio applications as well. This sub requires a large vented enclosure for optimal performance. A 3.926 cf internal and 3 ports; 3" (ID) x 13.66" long.
Fb = 30 Hz and F3 is 28.46 Hz. Big box huh?
Care to share your deep discount sources so that others may benefit as well?
Good luck on your project and keep us posted as to your progress OK?
Swez
BigJMan on 05/11/2004 12:55:11
"Since you are thinking HT here, you can port the subs to a very low F3 point of say 20-25 Hz and install a Subsonic Filter to block signals below 20 Hz."
What's HT mean?
Swez, here's what my amp has to make adjustments:
Variable 24dB High-pass Crossover: 50Hz – 750Hz
Variable 24dB Low-pass Crossover: 30Hz – 120Hz
Variable Subsonic Filter: 20Hz - 45Hz
Variable Bass Boost: 0 – 18dB
Variable Bass Boost Frequency: 40Hz – 100Hz
I would use the Variable Low-pass Crossover, because I'm using subs.. so I would set it to around 80hz, because I don't want any frequencies higher than 80hz reaching my subs.
My question is, if my ported box is tuned to 28 hz, which apparently is what JBL suggests ( "Fo is port tuning frequency. This is based on T/S parameters of the sub, the enclosure design and port size" ), should I then turn on my subsonic filter and set it to 28hz, preventing any frequencies less than 28hz to play?
Also, because I like a lot of bass I always use the bass boost. When I use it, considered the box I've been discussing, what "frequency" should the bass boost be set at?
Sorry for the excessive amount of questions :)
John
swez on 05/11/2004 13:18:27
John,
HT = Home Theater applications.
Your amp setup mentioned is good. The LPF set at 80 Hz is commonly a good all around choice for best SQ. If you want more SPL, can move the LPF up to 100 or 120 Hz and see how that sounds in the sustem.
As for your SS filtering, yes, set it close to the "Fo" tuning port as possible. Ported subs go bonkers when we feed signals below Fo to them. The cones get sloppy and hard on the voice coils at high power ratings as there is little output, minmal sub excursion and poor cooling properties below Fo.
Finally, go easy on your bass boost feature. A +3,+6dB boost at 40 Hz will give more deep lows. If you adjust the boost upward to say 60 Hz, more punch bass is available.
Did we get all your questions answered?
Swez
BigJMan on 05/11/2004 14:37:31
Yes, for the time present.
Thanks for the help; I'm going to have trouble fitting this box in my trunk, but going from my measurements it will just barely fit...if I can get it INTO the trunk...I need to measure the space I have to slide it in when I open my trunk lid, I think I'll be alright.
Thanks
John
P.S. As far as my "deep discount sources" for audio equipment, they always vary depending on the piece of hardware. What I usually do is enter the Brand Name and/or model number of what I am looking for in Google, and literally go through ALL the results, looking for the dealer with the cheapest price, ensuring that I pay the least possible for something I want. Read: I'm "poor", and even if I wasn't I would still do this. I'll let you guys know where I find the best price for my JBL subwoofers....
BigJMan on 05/11/2004 14:39:28
Oh yeah, can anybody tell me why this proposed setup is like a "home theater" setup? Cause it's ported and big?
swez on 05/11/2004 19:43:08
Large box, ported and low tuning frequency are all common hallmarks of a first rate HT sub system. Most car systems are often tuned just below 40 Hz. If a high SPL machine, some use replaceable ports. Daily driver ports near 40 Hz and SPL COMPS ports are tuned close to resonance frequency of the vehicle.
Swez
Tinker18 on 05/11/2004 20:47:46
yes, i am also curious, as swez was, as to where on the internet you bought those subs for half price. im sure it would be appreciated by others as well. thanks.
BigJMan on 05/12/2004 09:56:04
Tinker18,
I haven't actually bought the JBL subs yet, because I plan the heck out of any purchase before I go through with it, and I'm still saving up some money.
As far as low-cost sources to buy w15GTi subs, heres a few I found:
list price = $700.00
$417.95 http://www.audionmore.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=ANM&Product_Code=W15GTI
$417.95 http://mainstreet-audio.com/JBL/jbl_subwoofers.shtml
$417.99 http://www.carstereoworld.com/jbl/jblsub.html
$417.95 http://www.audio-n-more.com/jbl/jbl_audio_subwoofers.shtml
and the big wammi of them all:
$369.00 http://www.carmedia1.com/en-us/dept_127.html
I guess I'm guilty of exagerrating the price savings a little bit, but most of these prices are still around roughly half the list price, which I think is pretty good.
Hope this helps.
My question concerns the box type. JBL published specific specs and dimensions for a sealed box, vented box, and sealed-bandpass box. I plugged all the thiele-small parameters into WinISD v.044, and looked at the results using the specified box parameters. Not surprisingly, the sealed box had extremely linear response. The vented box designed to spec wasn't quite as linear, but was pretty damn good for a vented box (it was much more linear than a pair of Audiobahn in a vented box I've analyzed).
So what's better to use, sealed or vented (would probably do a slot port design for each chamber)? Obviously, sealed is supposed to sound better because it has a better "transitional response" or something, and is more linear in response. But I've also read that if a ported box is built EXACTLY to spec it will distort less at most frequencies, especially when the volume is cranked up, and that there will be a noticeable volume gain. You just have to make sure not to send any signals below what the box is tuned for, because you could hurt the subs.
Some people say that if a sub's Qts parameter is higher than 0.4, then you should only use a sealed box. This sub's Qts parameter is 0.48! But JBL and a lot of other people apparently aren't worried about it, build a ported box exactly as they specify and you'll be fine....
So what's you're guys opinions/suggestions? Which box design should I go with? I want good SQ, and I also want a lot of SPL.
Replies (11)
swez on 05/7/2004 11:22:34
Vented designs are able to deliver both SPL and SQ. Most Pro enclosure are vented for that very reason.
Since you are thinking HT here, you can port the subs to a very low F3 point of say 20-25 Hz and install a Subsonic Filter to block signals below 20 Hz.
As for Qtc parameters, that's a general guide... not a hard, fast rule. If you go ported, just make sure you follow the guidelines form JBL for tuning.
Also, what is the price of these GTi subs? I see that Parts Express is offering a JBL Pro line sub for $250.00/ea. These are 4 ohm, 800 RMS subs, so a pair will net 2 ohms in parallel. Even if your amp is 1500 RMS @ 1.5 ohms, 500 RMS less output at 2 ohms, you will not really notice a decrease of 1.5 - 2dB in SPL. You'll pick up +3dB by porting, another +3dB from dual sub design and +10-15 more dB from room transfer function. (room gain effect) Combine all that extra gain and you are well over +120 dB reference level for HT applications.
Not bad for 500 RMS per sub and $500.00 for the pair.
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=299-750&dotd=050604
What say you?
Swez
BigJMan on 05/7/2004 11:56:55
Thanks for the swift reply.
I think I'm going to go ahead and try building the ported box. I still wnat to get the JBL wGTi15 subs, because they can use all of my amp's available power, which although, as you pointed out, might not make much of a noticeable difference, is still important to me.
The wGTi15 subs have a list price of $700.00 - yikes right? Not really, I know from painful past experiences that you definitely, definitely get what you pay for... and plus I've already found internet retailers I can buy the subs from for less than half the list price, so I'm going to stick wit em.
p.s. What's the difference between the wGTi15 sub that I'm talking about and the older JBL Pro Line 15" sub you're talking about, besides the resistance? Both are 15" subs, and both take 800w RMS. JBL says that the wGTi15 can take 5000w max power, maybe that's it (although I think that numbe is probably bull).
Thankyou
John
BigJMan on 05/7/2004 12:03:35
Another quick question,
in this pdf file
http://manuals.harman.com/JBL/CAR/Boxes%20and%20Parameters/W15GTi_rev_f.pdf
2nd page, in the "vented box volume" picture (look inside where the port is drawn), it says fo = 28.0 Hz, is this what the box is supposed to be "tuned" to, I need to know for WinISD and other reasons...
John
swez on 05/7/2004 19:57:51
Fo is port tuning frequency. This is based on T/S parameters of the sub, the enclosure design and port size.
The main difference I can see in the GTI series, it is a hybrid of JBL's newer Pro Line subs. Large frame, huge magnet structure and rapid cooling system for the 3" DVC coils. Better cooling will provide less "thermal compression" (output power reductions) at high SPL levels.
The 15" sub I mentioned is a 4" SVC design that is well suited for HT, Club monitors and modest Sound Reinforcement applications. It would probably be a good option for large car audio applications as well. This sub requires a large vented enclosure for optimal performance. A 3.926 cf internal and 3 ports; 3" (ID) x 13.66" long.
Fb = 30 Hz and F3 is 28.46 Hz. Big box huh?
Care to share your deep discount sources so that others may benefit as well?
Good luck on your project and keep us posted as to your progress OK?
Swez
BigJMan on 05/11/2004 12:55:11
"Since you are thinking HT here, you can port the subs to a very low F3 point of say 20-25 Hz and install a Subsonic Filter to block signals below 20 Hz."
What's HT mean?
Swez, here's what my amp has to make adjustments:
Variable 24dB High-pass Crossover: 50Hz – 750Hz
Variable 24dB Low-pass Crossover: 30Hz – 120Hz
Variable Subsonic Filter: 20Hz - 45Hz
Variable Bass Boost: 0 – 18dB
Variable Bass Boost Frequency: 40Hz – 100Hz
I would use the Variable Low-pass Crossover, because I'm using subs.. so I would set it to around 80hz, because I don't want any frequencies higher than 80hz reaching my subs.
My question is, if my ported box is tuned to 28 hz, which apparently is what JBL suggests ( "Fo is port tuning frequency. This is based on T/S parameters of the sub, the enclosure design and port size" ), should I then turn on my subsonic filter and set it to 28hz, preventing any frequencies less than 28hz to play?
Also, because I like a lot of bass I always use the bass boost. When I use it, considered the box I've been discussing, what "frequency" should the bass boost be set at?
Sorry for the excessive amount of questions :)
John
swez on 05/11/2004 13:18:27
John,
HT = Home Theater applications.
Your amp setup mentioned is good. The LPF set at 80 Hz is commonly a good all around choice for best SQ. If you want more SPL, can move the LPF up to 100 or 120 Hz and see how that sounds in the sustem.
As for your SS filtering, yes, set it close to the "Fo" tuning port as possible. Ported subs go bonkers when we feed signals below Fo to them. The cones get sloppy and hard on the voice coils at high power ratings as there is little output, minmal sub excursion and poor cooling properties below Fo.
Finally, go easy on your bass boost feature. A +3,+6dB boost at 40 Hz will give more deep lows. If you adjust the boost upward to say 60 Hz, more punch bass is available.
Did we get all your questions answered?
Swez
BigJMan on 05/11/2004 14:37:31
Yes, for the time present.
Thanks for the help; I'm going to have trouble fitting this box in my trunk, but going from my measurements it will just barely fit...if I can get it INTO the trunk...I need to measure the space I have to slide it in when I open my trunk lid, I think I'll be alright.
Thanks
John
P.S. As far as my "deep discount sources" for audio equipment, they always vary depending on the piece of hardware. What I usually do is enter the Brand Name and/or model number of what I am looking for in Google, and literally go through ALL the results, looking for the dealer with the cheapest price, ensuring that I pay the least possible for something I want. Read: I'm "poor", and even if I wasn't I would still do this. I'll let you guys know where I find the best price for my JBL subwoofers....
BigJMan on 05/11/2004 14:39:28
Oh yeah, can anybody tell me why this proposed setup is like a "home theater" setup? Cause it's ported and big?
swez on 05/11/2004 19:43:08
Large box, ported and low tuning frequency are all common hallmarks of a first rate HT sub system. Most car systems are often tuned just below 40 Hz. If a high SPL machine, some use replaceable ports. Daily driver ports near 40 Hz and SPL COMPS ports are tuned close to resonance frequency of the vehicle.
Swez
Tinker18 on 05/11/2004 20:47:46
yes, i am also curious, as swez was, as to where on the internet you bought those subs for half price. im sure it would be appreciated by others as well. thanks.
BigJMan on 05/12/2004 09:56:04
Tinker18,
I haven't actually bought the JBL subs yet, because I plan the heck out of any purchase before I go through with it, and I'm still saving up some money.
As far as low-cost sources to buy w15GTi subs, heres a few I found:
list price = $700.00
$417.95 http://www.audionmore.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=ANM&Product_Code=W15GTI
$417.95 http://mainstreet-audio.com/JBL/jbl_subwoofers.shtml
$417.99 http://www.carstereoworld.com/jbl/jblsub.html
$417.95 http://www.audio-n-more.com/jbl/jbl_audio_subwoofers.shtml
and the big wammi of them all:
$369.00 http://www.carmedia1.com/en-us/dept_127.html
I guess I'm guilty of exagerrating the price savings a little bit, but most of these prices are still around roughly half the list price, which I think is pretty good.
Hope this helps.
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