by lowering distortion you are also lowering distortion, if you get the same output with less cone movement thats less distortion(im sure youre famliar with this), plus youd have more headroom, plus you can get gd very close, oh yeah and a flatter FR curve to boot. People normally dismiss a ported design cause they think its high q, boomy, and has high gd, but a well implicated vented design can sound just as good as a sealed design IMO. oh and proably a little edge in output(like you need it hahaha)
paul has posted this link before, but i'll repost it. i thought it was great to read about all the different designs out there, see test data (and at far greater levels than 1W in), and hear listening reviews of all these different subs.
http://www.ultimateavmag.com/features/604way/
in my own experience, i'm much more sensitive to distortion than to group delay.
perhaps you should design for both ported and sealed. use the same size box for both. make one ported and the other sealed and do some a/b testing.
- Robert
http://www.ultimateavmag.com/features/604way/
in my own experience, i'm much more sensitive to distortion than to group delay.
perhaps you should design for both ported and sealed. use the same size box for both. make one ported and the other sealed and do some a/b testing.
- Robert
Yeah, after more thinking about it, I think I am going to go with the ported enclosure. And I also think I can still use 8 cu.ft., gain a little more output (not really needed at this point... LOL), lower the excursion conciderably which will ultimately lower the distorsion. The gd is still low, around 11m/s @ 20Hz!
The only problem is, I need someone to help me figure out the actual displacement that the port and drivers are going to take up so I don't loose too much airspace for the drivers. I want the drivers to have a total of 8 cu.ft, so the enclosure will probably have to be in the neighborhood of 9.5 cu.ft. or something which I think is about the MAX size I can go. I'll have to double check though.
The mouth of the port (inside dimentions) is going to be 2.5" x 13" and I think the total length is going to be right around 60". Oh, and if I can find it, I will be using 1" MDF, but if not it will be the typical .75" MDF.
To help save some space, I'm going to try placing my center channel vertically to see how it sounds. Def Tech claims that it can be used either way with great results. We'll see.
If I have time at lunch today, I'll try taking some more measurements to see how much space I have to work with.
The only problem is, I need someone to help me figure out the actual displacement that the port and drivers are going to take up so I don't loose too much airspace for the drivers. I want the drivers to have a total of 8 cu.ft, so the enclosure will probably have to be in the neighborhood of 9.5 cu.ft. or something which I think is about the MAX size I can go. I'll have to double check though.
The mouth of the port (inside dimentions) is going to be 2.5" x 13" and I think the total length is going to be right around 60". Oh, and if I can find it, I will be using 1" MDF, but if not it will be the typical .75" MDF.
To help save some space, I'm going to try placing my center channel vertically to see how it sounds. Def Tech claims that it can be used either way with great results. We'll see.
If I have time at lunch today, I'll try taking some more measurements to see how much space I have to work with.
I have another question, however I'm not sure if it should be posted here or in the amplifier section, but...
The two possible amps that I'm looking at to power these subs are:
1) Crown XLS - 402 (570W @ 2 ohms x 2 ch / 1140W @ 4 ohms mono)
Damping Factor: (8 ohm) 10 Hz to 400 Hz: >200.
2) QSC RMX - 850 (430WW @ 2 ohms x 2 ch / 830W @ 4 ohms mono)
Damping Factor: Greater than 300 at 8 ohms from 1000Hz and below.
Now I know that the damping factor is what helps control the movement of the driver(s) in some way, but according to this site, they claim it's not AS important as people think.
http://www.audioholics.com/techtips/audioprinciples/amplifiers/dampingfactor.php
How much attention should I pay to the damping factor? The amp will only be receiving a signal of 80Hz and below.
The two possible amps that I'm looking at to power these subs are:
1) Crown XLS - 402 (570W @ 2 ohms x 2 ch / 1140W @ 4 ohms mono)
Damping Factor: (8 ohm) 10 Hz to 400 Hz: >200.
2) QSC RMX - 850 (430WW @ 2 ohms x 2 ch / 830W @ 4 ohms mono)
Damping Factor: Greater than 300 at 8 ohms from 1000Hz and below.
Now I know that the damping factor is what helps control the movement of the driver(s) in some way, but according to this site, they claim it's not AS important as people think.
http://www.audioholics.com/techtips/audioprinciples/amplifiers/dampingfactor.php
How much attention should I pay to the damping factor? The amp will only be receiving a signal of 80Hz and below.
hopefully it wasn't peer pressure that led you to go ported. 
that port sounds really long though, and i suspect you'll need to bend it to fit. collo pointed out (or some of the other research papers did) that bends in a port are not so good. i'd tune just a bit higher to avoid the bend.
the general internet consensus is that the crown xls stuff shouldn't be labeled crown and should be avoided. for all i know that could just be internet legened as well.
qsc rmx stuff seems to have a better reputation. there's a ton of decent used stuff on ebay, so that may open a few more options as well. just look in the musical instruments / pro audio / power amplifers category. (as opposed to the relatively sissy stuff in consumer electronics) be aware most pro amps have cooling fans, so you may have to deal with some fan noise.
if you look at specs for amps, most are frequently rated power at 1kHz. in some cases they also list power from 20hz-20khz and it's always lower than the power at 1kHz. if you look at either the xls or rmx specs, you'll see they conviently don't list the 20Hz-20kHz power. this makes me suspicious. so i'm not sure you should expect to toss 2-ohm subwoofer duty on the cheapo amps and expect to have anywhere near the rated 1kHz power.
for example, note qsc doens't list a power value for 2-ohm, 20hz-20khz here http://www.qscaudio.com/pdfs/rmxspc.pdf.
if i were in your shoes i'd consider (assuming used ebay prices, not new) a crest ca4 http://www.crestaudio.com/media/pdf/ca4_11-25-97.pdf or perhaps some older yamaha stuff (cheap for what you get).
i don't have a clue how much attention you should pay to damping factor. generally better amps have higher damping factors.
- Robert
that port sounds really long though, and i suspect you'll need to bend it to fit. collo pointed out (or some of the other research papers did) that bends in a port are not so good. i'd tune just a bit higher to avoid the bend.the general internet consensus is that the crown xls stuff shouldn't be labeled crown and should be avoided. for all i know that could just be internet legened as well.
qsc rmx stuff seems to have a better reputation. there's a ton of decent used stuff on ebay, so that may open a few more options as well. just look in the musical instruments / pro audio / power amplifers category. (as opposed to the relatively sissy stuff in consumer electronics) be aware most pro amps have cooling fans, so you may have to deal with some fan noise.
if you look at specs for amps, most are frequently rated power at 1kHz. in some cases they also list power from 20hz-20khz and it's always lower than the power at 1kHz. if you look at either the xls or rmx specs, you'll see they conviently don't list the 20Hz-20kHz power. this makes me suspicious. so i'm not sure you should expect to toss 2-ohm subwoofer duty on the cheapo amps and expect to have anywhere near the rated 1kHz power.
for example, note qsc doens't list a power value for 2-ohm, 20hz-20khz here http://www.qscaudio.com/pdfs/rmxspc.pdf.
if i were in your shoes i'd consider (assuming used ebay prices, not new) a crest ca4 http://www.crestaudio.com/media/pdf/ca4_11-25-97.pdf or perhaps some older yamaha stuff (cheap for what you get).
i don't have a clue how much attention you should pay to damping factor. generally better amps have higher damping factors.
- Robert
batdorf9 said:hopefully it wasn't peer pressure that led you to go ported.
- Robert
Well that's one of the nice things about building a slot port that's large enough to have a low air velocity. Having one bend it in should effect the performance of it that much, if any at all.
Update, Update, Update!
Just an update here...
I just ordered all three 15" Dayton drivers this morning, so they should be getting here in about a week or so and I can finally start this little project.
Also, I have once again slightly changed the design of the enclosures. I moved my projector screen a little higher up on the wall, so now I can build these enclosures to a usable volume of 12 cu.ft each, and still tuned to 12Hz.
With the vent opening staying at 2.5" x 12", the new length of the port will only be 42" long. Air velocity is at an all-time low of 7.5 s/m @ 20Hz, 11.8 s/m @ 15Hz, and cone excursion reaches 26.5mm p-p @ 24Hz!
Yeah.... These are going to be some good times pretty soon.
Just an update here...
I just ordered all three 15" Dayton drivers this morning, so they should be getting here in about a week or so and I can finally start this little project.
Also, I have once again slightly changed the design of the enclosures. I moved my projector screen a little higher up on the wall, so now I can build these enclosures to a usable volume of 12 cu.ft each, and still tuned to 12Hz.
With the vent opening staying at 2.5" x 12", the new length of the port will only be 42" long. Air velocity is at an all-time low of 7.5 s/m @ 20Hz, 11.8 s/m @ 15Hz, and cone excursion reaches 26.5mm p-p @ 24Hz!
Yeah.... These are going to be some good times pretty soon.
dont be a wuss! just buy two 4x8s and attatch them to the car as wings...anndd er fly home? i dont know really.
no offence, but i wouldnt expect someone who drives such a small efficient car to have such large burly subwoofers! not hating on mazda, both my parents own one...but with a sub like that id guess you drive a hummer :|
no offence, but i wouldnt expect someone who drives such a small efficient car to have such large burly subwoofers! not hating on mazda, both my parents own one...but with a sub like that id guess you drive a hummer :|
xstephanx said:
Yeah well, none taken. And you should have seen what my plans were for the stereo system in that Miata. I was going to be pumping about 1000 watts into two 12" Treo subs with a 54mm Xmax! But I decided that might be a little too much for the trunk and car, so I sold it all before I ever installed it and used the money to put towards my home stereo and a healthy computer upgrade.
Quick question...
I'm going to be building these subs pretty soon and just wanted to know how exactly to figure out the air displacement of the port. It's going to be in the neighborhood of 2.5"W x 13"H x 46"L.
Do I just figure it out like building a normal exclosure (0.87 cu.ft.) taken away from the internal air space of the sub enclosure?
The drivers NEED 12 cu.ft. per pair, so I would have to build the enclosure out to almost 13 cu.ft. so the subs have 12 cu.ft. of air space after driver and port displacement?
Does all of this sound right to you guys?
Thanks!
I'm going to be building these subs pretty soon and just wanted to know how exactly to figure out the air displacement of the port. It's going to be in the neighborhood of 2.5"W x 13"H x 46"L.
Do I just figure it out like building a normal exclosure (0.87 cu.ft.) taken away from the internal air space of the sub enclosure?
The drivers NEED 12 cu.ft. per pair, so I would have to build the enclosure out to almost 13 cu.ft. so the subs have 12 cu.ft. of air space after driver and port displacement?
Does all of this sound right to you guys?
Thanks!
sounds perfect to me. alot fo people dont knwo this but theres alto fo leeway with ports because the sims you get arent perfect, and becuase usually port tubnings are LOWERR than what calculations woudl suggest. and are you sure thats not 70 some od mm both ways? if thats 6" p-p LINEAR..... i think ill soil myself.
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