What to look for in Win ISD graphs?

[darrenh]

OK... very naive with understanding what I should be looking for in Win ISD graphs...

I am putting together a sub for home cinema use, utilising a 10" Alcone driver. Limited space in the home and have been playing with subs around the 11.5 to 20 Litre size. I have used the speaker parameters to generate graphs but do not know how these relate to the reallife sound. I also do not know what tuning frequency to set the box at?

Any help appreciated with Gain, phase plot, SPL, and group delay. The group delay shows a vast difference between a sealed and ported box, as does the phase plot to 50Hz. The ported design tends to have a more rounded curve in SPL, and a sharper line to curve in Gain... what does it all mean?

[eyekode]

I cannot say what "most" are looking for. But in general people either want a flat frequency response or an EBS (extended bass shelf) for their frequency response.

Home theater guys will dismiss group delay. Some music guys say it matters and it is why they build huge sealed boxes .

Most on these boards care about f3 frequency (where the low end rolls off to 3 dB down). Most also care about SPL.

If you continue to investigate you will probably find that you cannot produce significant SPL < 30Hz with a 10" driver. Also 20 Litre is about the volume of the bracing + driver + port for most of the subs people build in these forums . You really need a larger volume to produce significant SPL at low frequencies. A 100 Litre box is considered medium to small.

That being said some sub is better then none. Keep playing with WinISD. It should set the tuning for you when you specify the alignment you want.

Have fun!

[atledreier]

The port on my current sub project is around 42 liters.. And I'm building 2....

[darrenh]

eyekode wrote:

I cannot say what "most" are looking for. But in general people either want a flat frequency response or an EBS (extended bass shelf) for their frequency response.

Home theater guys will dismiss group delay. Some music guys say it matters and it is why they build huge sealed boxes .

Most on these boards care about f3 frequency (where the low end rolls off to 3 dB down). Most also care about SPL.

If you continue to investigate you will probably find that you cannot produce significant SPL < 30Hz with a 10" driver. Also 20 Litre is about the volume of the bracing + driver + port for most of the subs people build in these forums . You really need a larger volume to produce significant SPL at low frequencies. A 100 Litre box is considered medium to small.

That being said some sub is better then none. Keep playing with WinISD. It should set the tuning for you when you specify the alignment you want.

Have fun!

Thanks very much. This really helps when knowing when to stop trying to push the boundaries and what to look for in the graphs. I was worried about the group delay and read about it on another forum - although I think these guys were speaker designers and mainly for music. I have got to find some way of getting the Win ISD pro to work on my PC as I think it may answer some of the questions I have regarding the extended bass shelf (Like what is it, how do I model it) and now I'll be looking into this f3 frequency roll off!

I am usually pretty quick to pick things up, but I have to say that this is taking me a little time to get to grips with!

[Mike P.]

To give you an idea what to look for in the graphs, pick a sub build from the database and model what the specs of the build are.
http://www.hometheatershack.com/foru...-database.html
Remember that all subs model differently, and the graphs will show you what is "acceptable" for a given sub, in a given design. A lot of sub builds in the database were designed for low end extension, and the graphs will reflect that.

[eyekode]

darrenh wrote:

Thanks very much. This really helps when knowing when to stop trying to push the boundaries and what to look for in the graphs. I was worried about the group delay and read about it on another forum - although I think these guys were speaker designers and mainly for music. I have got to find some way of getting the Win ISD pro to work on my PC as I think it may answer some of the questions I have regarding the extended bass shelf (Like what is it, how do I model it) and now I'll be looking into this f3 frequency roll off!

I am usually pretty quick to pick things up, but I have to say that this is taking me a little time to get to grips with!

My guess is your 10" driver is not a good candidate for EBS. You really need to get down into the low-mid 20's (Hz) before it starts to make sense because this is where room gain will help level out your frequency response. Also EBS tends to overall cut the SPL. And because your driver is a 10" with such small Sd (surface area) you really cannot make up the SPL with excursion (and I doubt the excursion of your driver is very large anyway).

[darrenh]

eyekode wrote:

My guess is your 10" driver is not a good candidate for EBS. You really need to get down into the low-mid 20's (Hz) before it starts to make sense because this is where room gain will help level out your frequency response. Also EBS tends to overall cut the SPL. And because your driver is a 10" with such small Sd (surface area) you really cannot make up the SPL with excursion (and I doubt the excursion of your driver is very large anyway).

I guessed as much... I don't expect major bass from a 10" driver, but I would like to be able to learn from playing with different box types... so the plan is to build a sealed box, vented box and sonotube to see how they sound.

[Warmon]

Actually, any driver suited for ported can be used in a EBS type alignment, however best results will be with a Qts of around .30. The driver he's working with has a Qts of .34 - it will work okay. The biggest problem is over excursion - making sure you don't give it to much power the driver bottoms out.

Another bit of info for you guys is that the smaller the box, the more difficult it is to tune - that's why you see these massive boxes being built: let's say you got a box of 30liters and a 3" port at 42" - you can see how one is going have some serious issues on how to make that work. One way is to bend the ports and another is to take the port external out of the box..sometimes it can take both strategies together.

[darrenh]

Warmon wrote:

Actually, any driver suited for ported can be used in a EBS type alignment, however best results will be with a Qtc of around .30. The driver he's working with has a Qts of .34 - it will work okay. The biggest problem is over excursion - making sure you don't give it to much power the driver bottoms out.

Another bit of info for you guys is that the smaller the box, the more difficult it is to tune - that's why you see these massive boxes being built: let's say you got a box of 30liters and a 3" port at 42" - you can see how one is going have some serious issues on how to make that work. One way is to bend the ports and another is to take the port external out of the box..sometimes it can take both strategies together.

I have to say that taking the ports outside could actually look quite cool! (Please dont berate me for introducing some vanity to a scientific discussion!)

[Mike P.]

Outside ports have been done. Check out Collo's site.

http://www.subwoofer-builder.com/vent-options.htm

[darrenh]

Mike P. wrote:

Outside ports have been done. Check out Collo's site.

http://www.subwoofer-builder.com/vent-options.htm

Not sure I would go that far!!! but a couple of ports that exit the toop of the cabinet may look cool! Also, I have aatached some further graphs... is the 4th order bandpass the same as the EBS type? Look at tha Qi though!!!

[darrenh]

darrenh wrote:

Not sure I would go that far!!! but a couple of ports that exit the toop of the cabinet may look cool! Also, I have aatached some further graphs... is the 4th order bandpass the same as the EBS type? Look at tha Qi though!!!

Should be better resolution!

[Warmon]

What you want to do is change the tune to 30hz and them change the volume [Vb] up or down until you get a curve that looks like the yellow one in the graph below.

[darrenh]

Warmon wrote:

What you want to do is change the tune to 30hz and them change the volume [Vb] up or down until you get a curve that looks like the yellow one in the graph below.

Which one of these? Should I be looking to hit the -3dB line (Blue), or getting a line that sits further down the frequency range (Yellow)?

[Mike P.]

Using WSinISD Pro this sub models to 55 liters tuned to 26hz. With manimum input power of 150 watts SPL is still 100 db at 23 hz without room gain. Xmax isn't exceeded untol 20hz. The use of a subsonic filter would be required for frquencies below 20 hz. When modelling subs for HT use, you can get more low end output with a bigger box and a lower tuning point at the expense of power handling. It's a trade off. Finding the "balance" of box size, tuning frequency and power handling for a specific sub for HT use is the challenge.

[darrenh]

Mike P. wrote:

Using WSinISD Pro this sub models to 55 liters tuned to 26hz. With manimum input power of 150 watts SPL is still 100 db at 23 hz without room gain. Xmax isn't exceeded untol 20hz. The use of a subsonic filter would be required for frequencies below 20 hz. When modelling subs for HT use, you can get more low end output with a bigger box and a lower tuning point at the expense of power handling. It's a trade off. Finding the "balance" of box size, tuning frequency and power handling for a specific sub for HT use is the challenge.

Thanks Mike.

Any idea why I might be having a problem with Win ISD pro? I get an error when closing it and it doesn't want to go away!

I'll try the figures you supplied in Win ISD Beta....

[Mike P.]

No idea why WinISD is not working properly for you. It works fine on my 1 Gig Dell laptop with XP Home Edition. You might try uninstalling the program and then reinstalling it. I'm not sure if you can install over top of a previous edition. Check the WinISD forum to find out.