Hi guys,
I've got myself a Peerless XLS12 830500 driver and a 200 watt subwoofer plate amp. The amp has a highpass filter set at 17Hz but I'm not sure of the rate. I have decided to build a vented box of between 40 and 60 litres using flanged fort ends. The sub is for home theatre use in a room 14' x 20' with 9' ceilings.
I give WinISD a go and after a couple of goes found it pretty easy to use. I ended up with some nice coloured lines but then realised I don't know what sort of response I should be looking for.
Can anybody give me some ideas of what a good response curve and what I can expect fom this driver.
Thanks.
I've got myself a Peerless XLS12 830500 driver and a 200 watt subwoofer plate amp. The amp has a highpass filter set at 17Hz but I'm not sure of the rate. I have decided to build a vented box of between 40 and 60 litres using flanged fort ends. The sub is for home theatre use in a room 14' x 20' with 9' ceilings.
I give WinISD a go and after a couple of goes found it pretty easy to use. I ended up with some nice coloured lines but then realised I don't know what sort of response I should be looking for.
Can anybody give me some ideas of what a good response curve and what I can expect fom this driver.
Thanks.
I also have the identical combination, XLS 830500 and 200W with rumble filter. It seems this combo is ideal for vented box systems for movies. But I'm attempting to use it in a closed system for music/audio reproduction, in 80L sealed application. I haven't built it yet. If it sounds dodgey, I'll build the box as below, and find a better driver for my sealed box....
As for vented, I got some good advice from the XLS distributer:
Consider using 45L (air volume) box, a 90mm diameter pvc plumbing pipe as your port, as this is a common plumbing size and suited to this. You could attach 2 elbows to bend it around inside your box, and you need to flare the ends as much as possible to stop the pipe from chuffing. Basically, the longer you can make the pipe, the more bass extension you will get, but remember that the end of the pipe must be at least 75mm away from any wall inside your box for best performance, so this is a restriction. Also, make sure you brace the box inside and brace the port from moving, so you need to allow more volume internally for all of these extra items.
As for vented, I got some good advice from the XLS distributer:
Consider using 45L (air volume) box, a 90mm diameter pvc plumbing pipe as your port, as this is a common plumbing size and suited to this. You could attach 2 elbows to bend it around inside your box, and you need to flare the ends as much as possible to stop the pipe from chuffing. Basically, the longer you can make the pipe, the more bass extension you will get, but remember that the end of the pipe must be at least 75mm away from any wall inside your box for best performance, so this is a restriction. Also, make sure you brace the box inside and brace the port from moving, so you need to allow more volume internally for all of these extra items.
The response curve should be smooth and it's not a big problem if it droops off gradually as the room will have a boosting function of it's own that will broadly compensate.
As for the tuning, a 90mm vent is just about acceptable. Just make sure that you tune it no higher than about 35Hz or it will chuff badly and because below the tuning frequency the cone will be unloaded.
As for the tuning, a 90mm vent is just about acceptable. Just make sure that you tune it no higher than about 35Hz or it will chuff badly and because below the tuning frequency the cone will be unloaded.
According to Collo's experiments on anti-chuffing, what really matters is the ratio of cross-sectional areas of flared end of port and port itself, and the diameter of the port. Basically, the bigger the port flare the more air velocity you can have through your port without chuffing. Also, bigger port diameter allows faster flow too. You can download his calculator to determine max velocity.
Also, you can use WinISD Pro to design vented boxes and check that the max velocity through the port doesn't exceed the value given by Collo's calculator for your particular port design.
I guess the aim for vented boxes is to design a box/vent which gives maximum bass extension for your particular driver/amp without exceeding the specs for your driver, and also staying within the safe non-chuffing air velocities for your port.
Is the only reason for not having a huge box for vented systems asthetics?
Check this:
http://www.diyaudio.com/wiki/index.php?page=How+to+get+a+vent+that+doesn't+chuff!
Also, you can use WinISD Pro to design vented boxes and check that the max velocity through the port doesn't exceed the value given by Collo's calculator for your particular port design.
I guess the aim for vented boxes is to design a box/vent which gives maximum bass extension for your particular driver/amp without exceeding the specs for your driver, and also staying within the safe non-chuffing air velocities for your port.
Is the only reason for not having a huge box for vented systems asthetics?
Check this:
http://www.diyaudio.com/wiki/index.php?page=How+to+get+a+vent+that+doesn't+chuff!
Ok, I've come to a nice compromise with 2 designs using the Peerless XLS 830500 driven by 200Wrms plate amp with 17Hz hp:
Critical Q=0.5 sealed sub: 32.5L box
or
Vented 65L (tuned to 18.5Hz)
Port: 100mm diameter Pvc pipe x 1.0m long
Flares: 50mm each end
This vented arrangement including the highpass filter at 17Hz ensures that the cone stays within its excursion limits below 20Hz. Also, the port velocity never exceeds 20m/s so port flare of 50mm at each end is heaps to prevent chuffing (should be fine up to 30m/s, will make bigger if I can be bothered).
Group delay is a maximum at 48ms at 16Hz, which, according to the GD wiki, should be unnoticable at such a low frequency.
Here is a graph of group delay vs frequency for the 2 subs above:
Critical Q=0.5 sealed sub: 32.5L box
or
Vented 65L (tuned to 18.5Hz)
Port: 100mm diameter Pvc pipe x 1.0m long
Flares: 50mm each end
This vented arrangement including the highpass filter at 17Hz ensures that the cone stays within its excursion limits below 20Hz. Also, the port velocity never exceeds 20m/s so port flare of 50mm at each end is heaps to prevent chuffing (should be fine up to 30m/s, will make bigger if I can be bothered).
Group delay is a maximum at 48ms at 16Hz, which, according to the GD wiki, should be unnoticable at such a low frequency.
Here is a graph of group delay vs frequency for the 2 subs above:
Attachments
I see you have included a high-pass filter in the model. This does make the initial design harder IMO. I start off by getting the low end right then doing another pass at the design with the filter added. You may have done that, I don't know.
Both of those designs are going to need EQ. I think you can shrink the vented box down a bit.
Yes a comparative test is a great idea.
Both of those designs are going to need EQ. I think you can shrink the vented box down a bit.
Yes a comparative test is a great idea.
I was hoping that maybe there is enough room gain not to include EQ. Otherwise I'm in a spot of strife.
Btw here is an updated graph showing the theoretical fitted curve of inaudible group delay superimposed on the graph above:
(NB: Paul Spencer says these extrapolations are purely experimental, there have been no tests to verify this. Still, it's good to fall below these values i think.)
Btw here is an updated graph showing the theoretical fitted curve of inaudible group delay superimposed on the graph above:
(NB: Paul Spencer says these extrapolations are purely experimental, there have been no tests to verify this. Still, it's good to fall below these values i think.)
Attachments
Over here (the Netherlands) most people seem to use, GD max= Frequency x Delay = <400, i.e. 10 ms at 40 Hz. The shape would matter here. Rather a smooth GD as one that is peak like.
The line as in the thumbnail above would suggest that the GD of about any 6th order bandpass would stay well below audibility while it's supposed not to be. Even more so, it would be rather difficult to create a sub with audible GD if this truly is the case.
The groupdelay as showed looks like as it is without lowpass filter? In that case you can add an aditional portion of GD to the graph. If you cross the sub lowish the overal GD will (in lots cases) be high enough to delay the top with 6-10 msec. Which would ultimately result in a relative very low GD.
Are you seriously going to compare the 2 design on difference in GD? Or am I missing out on a joke here?
Wkr Johan
The line as in the thumbnail above would suggest that the GD of about any 6th order bandpass would stay well below audibility while it's supposed not to be. Even more so, it would be rather difficult to create a sub with audible GD if this truly is the case.
The groupdelay as showed looks like as it is without lowpass filter? In that case you can add an aditional portion of GD to the graph. If you cross the sub lowish the overal GD will (in lots cases) be high enough to delay the top with 6-10 msec. Which would ultimately result in a relative very low GD.
Are you seriously going to compare the 2 design on difference in GD? Or am I missing out on a joke here?
Wkr Johan
I left out the lowpass filter on the graph of GD yes, I will try again and post a new one. I'm trying to make sense of the advice in Paul Spencer's group delay wiki page found here. If you have better advice on GD please update the wiki.
I wanted to explore audible GD because it seems to be the main difference between a vented sub and a closed sub... of course I would expect any vented sub has much larger GD than a closed one. But if it's possible to reduce GD in a vented sub, it would be better sounding bass for music reproduction correct?
The whole point is that you can get higher SPL for the same driver if you make a clever ported box, but at a cost of introducing unwanted delay.
So you are saying relative GD is what's important not the actual GD. How can I draw a graph of relative GD? Relative GD = GD / GD @ crossover freq ?
I wanted to explore audible GD because it seems to be the main difference between a vented sub and a closed sub... of course I would expect any vented sub has much larger GD than a closed one. But if it's possible to reduce GD in a vented sub, it would be better sounding bass for music reproduction correct?
The whole point is that you can get higher SPL for the same driver if you make a clever ported box, but at a cost of introducing unwanted delay.
So you are saying relative GD is what's important not the actual GD. How can I draw a graph of relative GD? Relative GD = GD / GD @ crossover freq ?
It is promising to see GD being considered seriously in a design but focusing on this aspect alone is sure to be a bad idea. You need to consider a balance of parameters.
You will not have sufficient room gain to naturally EQ your design because it begins rolling off from such a high frequency. Room gain is a bit of a red herring IMO anyway. If you listen with a door open or you have a fairly open plan house it can negate a lot of the effect anyway.
Depending on the type of music you listen to and your tastes in sound you might actually want an anechoically flat design and take advantage of the extra bass from room gain. In my own case I like a bassy sound at times and I can set my sub to be anechoically flat to 20Hz. My room gain begins around 33Hz in my 17x12 ft lounge, so I can get a real impact when watching movies and when real deep bass comes in on music!
You will not have sufficient room gain to naturally EQ your design because it begins rolling off from such a high frequency. Room gain is a bit of a red herring IMO anyway. If you listen with a door open or you have a fairly open plan house it can negate a lot of the effect anyway.
Depending on the type of music you listen to and your tastes in sound you might actually want an anechoically flat design and take advantage of the extra bass from room gain. In my own case I like a bassy sound at times and I can set my sub to be anechoically flat to 20Hz. My room gain begins around 33Hz in my 17x12 ft lounge, so I can get a real impact when watching movies and when real deep bass comes in on music!
Interesting... So what are the tradeoffs for using EQ in a sealed sub? Surely something is lost by doing this.
Is there a simple kit I can buy from Jaycar or something for EQ? I am using a plate amp with L/R line inputs. I heard maybe a linkwitz transform circuit? How do you incorporate one of those into a plate amp?
Is there a simple kit I can buy from Jaycar or something for EQ? I am using a plate amp with L/R line inputs. I heard maybe a linkwitz transform circuit? How do you incorporate one of those into a plate amp?
I'm a vent head so won't comment on the sealed.
Jaycar do sell a nice sub processor kit KA1814 and works well in the right application such as in conjuction with a power amp, but will not help you here. The equaliser in it will not do the job and only the LT will help.
http://sound.westhost.com/project71.htm
Have a read of that and the links on the page as it's very informative... they go in at line level before the amp.
Jaycar do sell a nice sub processor kit KA1814 and works well in the right application such as in conjuction with a power amp, but will not help you here. The equaliser in it will not do the job and only the LT will help.
http://sound.westhost.com/project71.htm
Have a read of that and the links on the page as it's very informative... they go in at line level before the amp.
Ok, I read all that info and played with the Linkwitz-Tr spreadsheet calculator. It seems I'll need a maximum of 12dB of boost down the bottom end to roughly flatten the response curve down to 20Hz, in a critical q=0.5 box (35L).
When I tested this with WinISD it's telling me that the cone excursion will be up around 40mm with 200W passing through it! (surely will destroy the cone) Only 20Wrms gives the full recommended cone movement in the simulation down at 20Hz, but this only allows 96dB SPL at maximum output at 20Hz.
Does this mean I can't get a useful closed sub from this driver? Or is there something wrong with the sim?
When I tested this with WinISD it's telling me that the cone excursion will be up around 40mm with 200W passing through it! (surely will destroy the cone) Only 20Wrms gives the full recommended cone movement in the simulation down at 20Hz, but this only allows 96dB SPL at maximum output at 20Hz.
Does this mean I can't get a useful closed sub from this driver? Or is there something wrong with the sim?
Damo, please don't call it my curve regarding the GD!!! It is based on the study by Bauert and Laws, and a relationship was found with frequency and audible GD and it was related as cycles. It was not purely based on a linear relationship between frequency and GD, but rather there was a number of cycles which reduced as you went lower in frequency. John Murphy made a suggestion as to how you would extrapolate down further, and I merely calculated some values following his suggestion.
As for the other suggestion, I don't know where it came from.
I think you will find that 60L will be the minimum practical for XLS to get a vent that won't chuff. Also a 90mm vent may prove a challenge. Larger flares have more compression, so you should have the vent as large as you can manage. But it really comes down to balancing factors out. Try both 90mm and 100mm and keep in mind that a 1m vent won't easily fit inside a 60L box, and you will have a lot of bends. Upsize the box and the vent will then be shorter and you will have more room to fit it in as well. Lower tuning reduces vent velocity as well. Quite a lot of juggling is required.
I suggest designing with all the filters included. Once you start including filters, GD goes up a lot and you see a more complete picture of the performance. Try a sealed sub with a linkwitz transform and you will find if you match the response that the GD is about the same but that max SPL is 6db less. All you have gained is a smaller box!
It's easy to say you have a low GD vented sub until you add filters! As others have commented, don't compare while only considering one factor. There are a lot of opinions on GD, but there doesn't appear to be any credible well established research prove where it is actually audible.
What is certain is that high GD goes hand in hand with 20 Hz extension.
Don't count on room gain. If you live in a typical Australian house you may not have any at all. My room is ~4x5m and I have no room gain, just a room mode peak at 35 Hz. I understand a lot of US homes are more solid, have worse room modes and more room gain, hence many of their comments in this area won't relate as much to Aussie homes.
If anyone else has other recommendations on GD that is audible, please feel free to add it. But also include what it is based on.
As for the other suggestion, I don't know where it came from.
I think you will find that 60L will be the minimum practical for XLS to get a vent that won't chuff. Also a 90mm vent may prove a challenge. Larger flares have more compression, so you should have the vent as large as you can manage. But it really comes down to balancing factors out. Try both 90mm and 100mm and keep in mind that a 1m vent won't easily fit inside a 60L box, and you will have a lot of bends. Upsize the box and the vent will then be shorter and you will have more room to fit it in as well. Lower tuning reduces vent velocity as well. Quite a lot of juggling is required.
I suggest designing with all the filters included. Once you start including filters, GD goes up a lot and you see a more complete picture of the performance. Try a sealed sub with a linkwitz transform and you will find if you match the response that the GD is about the same but that max SPL is 6db less. All you have gained is a smaller box!
It's easy to say you have a low GD vented sub until you add filters! As others have commented, don't compare while only considering one factor. There are a lot of opinions on GD, but there doesn't appear to be any credible well established research prove where it is actually audible.
What is certain is that high GD goes hand in hand with 20 Hz extension.
Don't count on room gain. If you live in a typical Australian house you may not have any at all. My room is ~4x5m and I have no room gain, just a room mode peak at 35 Hz. I understand a lot of US homes are more solid, have worse room modes and more room gain, hence many of their comments in this area won't relate as much to Aussie homes.
If anyone else has other recommendations on GD that is audible, please feel free to add it. But also include what it is based on.
For me, the size of the box is irrelevant, I just want a good sounding sub!
Thanks Paul, yes it appears that a closed box will end up 5-6dB quieter after the linkwitz transform for the same input power! And there is very little benefit in group delay after all the filters! I would prefer the extra 6dB at 20Hz, and I'd rather spend my efforts on building a nice box than fancy filters, (besides, my plate amp already has a rumble filter at 17Hz) so it looks like I'm building a vented one:
65L 100mm pipe x 900mm long. Massive flares > 60mm to reduce port noise.
Thanks Paul, yes it appears that a closed box will end up 5-6dB quieter after the linkwitz transform for the same input power! And there is very little benefit in group delay after all the filters! I would prefer the extra 6dB at 20Hz, and I'd rather spend my efforts on building a nice box than fancy filters, (besides, my plate amp already has a rumble filter at 17Hz) so it looks like I'm building a vented one:
65L 100mm pipe x 900mm long. Massive flares > 60mm to reduce port noise.
Damo, assuming that you have the regular XLS (not the car version and not the XXLS), then 65L with 100mm vent with large flares and 900mm long looks like it will work well. I did a quick model and looked at response, excursion, GD and vent velocity. They all look ok.
It would be tuned at 19 Hz which with a 17 Hz rumble filter (3rd order?) ... will keep cone excursion no more below tuning than it is above.
GD is 50ms @ 20 Hz which I think is ok ... 35ms with the rumble filter off. Hopefully it is defeatable so that you can compare and see what you think. If it is a problem then for music you can turn it off.
Vent velocity peaks at 25 m/s which is ok with a 100mm vent if the flares are large enough.
A 2nd order filter set at 50 Hz gives you -3db points at 20 and 80 Hz anechoic, lower if you have the rumble filter off and more so with room gain potentially.
It would be tuned at 19 Hz which with a 17 Hz rumble filter (3rd order?) ... will keep cone excursion no more below tuning than it is above.
GD is 50ms @ 20 Hz which I think is ok ... 35ms with the rumble filter off. Hopefully it is defeatable so that you can compare and see what you think. If it is a problem then for music you can turn it off.
Vent velocity peaks at 25 m/s which is ok with a 100mm vent if the flares are large enough.
A 2nd order filter set at 50 Hz gives you -3db points at 20 and 80 Hz anechoic, lower if you have the rumble filter off and more so with room gain potentially.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.