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post #1 of 23 Old 11-05-2019, 08:25 PM - Thread Starter
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Need help with Quasi Marty

Hello Everyone,

Been lurking for awhile trying to obtain all the information needed to make a couple of Quasi Marty subs. Everything I find, including the flat packs are just to wide for my space. Been trying to figure out what I need to create the cut list and start, but unfortunately my cup of knowledge seems to have a leak. I can't quite put it together. I am hoping that someone out there can help me figure out what it is that I am missing so I can finally get this project of the ground. The largest box I can fit in my space (X2) is about 7.5 gross internal volume per the cut sheet. I will be using the Dayton UM18-22. Subs will be used mostly for HT, I would say with around an 80/20 split and I definitely want to feel the T-Rex and the jet engines (given the size constraints of the space).

I am having an issue with:

1. Vent length. I am not sure what port size I will need since the results I am getting from WinISD don't make much sense to me. Maybe I entered something incorrectly but the default box is something like 120 cuft with a fairly long vent length. I know I can change it but seems odd to get started with such a drastic recommendation. Is this normal? Can someone tell me what the correct size and length for this arrangement is? Or maybe explain what I am doing wrong?

2. Also don't know what to tune it to given the size of the box and the ideal port size/length. Same deal. Can anyone tell me what's needed?

I am sure I will have other questions later but hopefully this will get me started.

Thanks in advance,

260
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post #2 of 23 Old 11-06-2019, 05:42 AM
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Unfortunately, we are not mind-readers. Either post your winisd files so someone can take a look at them, or post the dimension details you're using in winisd. It would also help if you provided a layout of your space or at least the dimension restrictions you have to work with. A 17hz tune works well with the um18-22.

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post #3 of 23 Old 11-06-2019, 09:59 AM
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Quote:
Originally Posted by 260guy View Post
1. Vent length. I am not sure what port size I will need since the results I am getting from WinISD don't make much sense to me. Maybe I entered something incorrectly but the default box is something like 120 cuft with a fairly long vent length. I know I can change it but seems odd to get started with such a drastic recommendation. Is this normal? Can someone tell me what the correct size and length for this arrangement is? Or maybe explain what I am doing wrong?

2. Also don't know what to tune it to given the size of the box and the ideal port size/length. Same deal. Can anyone tell me what's needed?

260
You'll want to swap the order of your questions as they are closely related - your selected tune will impact your port diameter and length necessary to hit what you want. At 7.5 ft^3 with the UM18-22 I'd think you'll be looking at an 18-19 hz tune if you're wanting it to dig deep. Once you have your driver loaded in WINISD go to Box and set the volume you have (7.5) and your tuning frequency (18); from there you can play with the vents making sure to keep an eye on your Port Air Velocity (try to keep it under 18 to avoid port noise.

Enjoy the rabbit hole!
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post #4 of 23 Old 11-06-2019, 11:28 AM - Thread Starter
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Hello,

@johnson636 - Sorry about that, I guess it didn't occur to me. My WinISD files below. The room is 2200^3.

@Aural_Sex - Thanks for the input. Figuring out the vent is part of the problem. I don't see how to get the port to come down to a reasonable size. I have tried changing the height/width/qty of the slots. Best I have come up with is air velocity 19.3 at 20.15 Hz. Would this be acceptable? It only has a 2" high port though. The cab size is more like 5.6^3 and not 7.5^3.

Many thanks,

260
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Instead of using your net volume (5.697) use your gross volume (7.598) and your port length should come down.

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post #6 of 23 Old 11-06-2019, 01:11 PM
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Quote:
Originally Posted by johnson636 View Post
Instead of using your net volume (5.697) use your gross volume (7.598) and your port length should come down.
This ^. Also, if you raise your tune to 19 or 20 you'll see the length of the port come down as well, it's a balancing act knowing that you will also be reducing interior volume with longer ports (unless you want to do something funky with external ports ).
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post #7 of 23 Old 11-06-2019, 04:41 PM - Thread Starter
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Which value to use as box volume was something else that I had questions about. I read several articles indicating to use the net value. In other words a value with driver, bracing, ports etc already added. I also read the WinISD FAQ and came away with the same conclusion. I may be totally misunderstanding. Can you please confirm.

Q. Does WinISD add brace/driver/port displacements to calculated box volume?
A. From Janne Ahonen ([email protected])
No. WinISD doesn't do guessing, and therefore shows net volume for your box. It would be hard to predict, how you are going to mount your driver. Or the port. Or how much and which kind of bracing you are going to use inside your box. For example, you could mount port completely external to the box, which case "usual" guess would be completely wrong. Bottom line is, that you must calculate and add any displacements by yourself to calculated box volume.
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post #8 of 23 Old 11-06-2019, 04:44 PM
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Need help with Quasi Marty

Quote:
Originally Posted by 260guy View Post
Which value to use as box volume was something else that I had questions about. I read several articles indicating to use the net value. In other words a value with driver, bracing, ports etc already added. I also read the WinISD FAQ and came away with the same conclusion. I may be totally misunderstanding. Can you please confirm.



Q. Does WinISD add brace/driver/port displacements to calculated box volume?

A. From Janne Ahonen ([email protected])

No. WinISD doesn't do guessing, and therefore shows net volume for your box. It would be hard to predict, how you are going to mount your driver. Or the port. Or how much and which kind of bracing you are going to use inside your box. For example, you could mount port completely external to the box, which case "usual" guess would be completely wrong. Bottom line is, that you must calculate and add any displacements by yourself to calculated box volume.


Yes, using the net to model is correct.

Your net volume is slightly bigger than a Marty cube, which amazingly enough runs a 20hz tune. Your numbers for 20hz look pretty good. I’d go with that.

Chris


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post #9 of 23 Old 11-06-2019, 06:43 PM - Thread Starter
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Looks like I don't have another choice. All else being equal bringing tuning down to 19 extends the port past the size of the cab.
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post #10 of 23 Old 11-06-2019, 06:53 PM
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Quote:
Originally Posted by 260guy View Post
Which value to use as box volume was something else that I had questions about. I read several articles indicating to use the net value. In other words a value with driver, bracing, ports etc already added. I also read the WinISD FAQ and came away with the same conclusion. I may be totally misunderstanding. Can you please confirm.

Q. Does WinISD add brace/driver/port displacements to calculated box volume?
A. From Janne Ahonen ([email protected])
No. WinISD doesn't do guessing, and therefore shows net volume for your box. It would be hard to predict, how you are going to mount your driver. Or the port. Or how much and which kind of bracing you are going to use inside your box. For example, you could mount port completely external to the box, which case "usual" guess would be completely wrong. Bottom line is, that you must calculate and add any displacements by yourself to calculated box volume.


Use net volume in WinISD. I agree that you are probably good to go, but that hump in your Transfer function magnitude graph means you should probably go bigger in box volume to flatten it out, and then tweak your actual box dimensions to match. Go with at lest a 3" tall port.

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post #11 of 23 Old 11-06-2019, 06:55 PM
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Originally Posted by 260guy View Post
Looks like I don't have another choice. All else being equal bringing tuning down to 19 extends the port past the size of the cab.


I assume the 20hz tune leaves the end of the port at least port-width from the side?

You can wrap ports multiple times, coming back across the top of the cab. But your port volume to enclosure volume is usually getting stupid at that point, plus you’re already loosing too much on the low end from the reduced volume. Can doesn’t mean should.

Honestly, the similarities to a marty cube tell me its a viable design. If you can’t go bigger, its probably the best set of compromises you can do.

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Use net volume in WinISD. I agree that you are probably good to go, but that hump in your Transfer function magnitude graph means you should probably go bigger in box volume to flatten it out, and then tweak your actual box dimensions to match. Go with at lest a 3" tall port.
It would make my life a whole lot simpler if that were possible. Given the area where it's going I am already at max size. Moving to 3" ports takes me even further away from where I need to be. What I don't understand is that the original Marty's had a shorter port size than WinISD is giving me, even at 3". Any ideas?

260
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I assume the 20hz tune leaves the end of the port at least port-width from the side?


Honestly, the similarities to a marty cube tell me its a viable design. If you can’t go bigger, its probably the best set of compromises you can do.

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You mean from the top? It does leave me about 5" or so from the top of the cabinet.

I agree it's close enough to the cube that I would think I can pretty much duplicate it. Unfortunately, it's not what WinISD is saying. Which leaves me wondering. Not only do I have the hump between 30-50 Hz but the first port resonance is probably borderline.

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Quote:
Originally Posted by 260guy View Post
It would make my life a whole lot simpler if that were possible. Given the area where it's going I am already at max size. Moving to 3" ports takes me even further away from where I need to be. What I don't understand is that the original Marty's had a shorter port size than WinISD is giving me, even at 3". Any ideas?



260

Port length inversely tracks net volume for given port area. So compared to a mini marty, I’d expect your port length to be longer. The marty cube ports are only 2” high, so again, the numbers make sense. If you have doubts on modeling , build a marty cube in winisd and make sure it checks out.


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You mean from the top? It does leave me about 5" or so from the top of the cabinet.



I agree it's close enough to the cube that I would think I can pretty much duplicate it. Unfortunately, it's not what WinISD is saying. Which leaves me wondering. Not only do I have the hump between 30-50 Hz but the first port resonance is probably borderline.



260

5” from top is good to go.

The Marty cube is not at all an optimized box for the UM18, the mini marty is much better. However, when you can’t fit a larger box, you make compromises. Where’s the resonance at?

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port length inversely tracks net volume for given port area. So compared to a mini marty, i’d expect your port length to be longer. The marty cube ports are only 2” high, so again, the numbers make sense. If you have doubts on modeling , build a marty cube in winisd and make sure it checks out.





5” from top is good to go.

The marty cube is not at all an optimized box for the um18, the mini marty is much better. However, when you can’t fit a larger box, you make compromises. Where’s the resonance at?

Chris



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Any better choices than the UM18 that you can recommend?
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Need help with Quasi Marty

With the generic 80hz lpf, that resonance shouldn’t be a big deal.

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Any better
choices than the UM18 that you can recommend?
Sure, SI HST18 and double the amplifier. But that costs way more and now your port velocity is going to be stupid.

The UM18 is the best bang for the buck you’re going to find for a HT woofer.

Since you’re constrained to those dimensions, I’m assuming additional boxes are out. And higher performance subs need a larger box due to port velocity. So I really don’t see you finding a better option than the UM.

You can model the Dayton HO, I can’t remember off hand if its happier in a smaller enclosure.

EDIT: Check out GSG’s performance table here:

https://shop.gsgad.com/pages/perform...mparison-table

It shows quite a few of the popular and highly regarded woofer options. Remember, your box falls between a cube and a mini, closer to the cube side.

Based on that, I’d model the SAF184.03 as well. Its out of stock everywhere till the end of the year though. Its also an 8ohm driver, so may cause you amplifier issues.

Chris

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Thanks for the feedback. Looks like my options are somewhat limited. I did download the HO specs and am now testing both in sealed and vented. Let's see where this goes.

I'm thinking of doing two of these so doubling/tripling the price is really not an option right now. Who knows, maybe running two sealed subs will work. The room is only 2200^3 so maybe.

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Edited my last post with some additional info you may be interested in.

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Quote:
Originally Posted by 260guy View Post
Thanks for the feedback. Looks like my options are somewhat limited. I did download the HO specs and am now testing both in sealed and vented. Let's see where this goes.



I'm thinking of doing two of these so doubling/tripling the price is really not an option right now. Who knows, maybe running two sealed subs will work. The room is only 2200^3 so maybe.



260


The HST comment was more to demonstrate that a “better” woofer isn’t the solution in this case. So even if you could swing the cash, I wouldn’t recommend it. Port velocity will be unusable, sub will be choked.

Your limiting factor is box volume. The UM is already too much sub for that box, hence the degradation of performance. Yet its price point, durability, and impedance still makes it a good choice.

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I am still a little bothered given the difference in what I see in WinISD and the original cube cut list. I think there is a difference of at least 13" in the port. Maybe they were using a different driver. One more thing to look at.

I will definitely compare what's available but would really like to get something going now. Who knows what can happen between now and the holidays
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Need help with Quasi Marty

Quote:
Originally Posted by 260guy View Post
I am still a little bothered given the difference in what I see in WinISD and the original cube cut list. I think there is a difference of at least 13" in the port. Maybe they were using a different driver. One more thing to look at.



I will definitely compare what's available but would really like to get something going now. Who knows what can happen between now and the holidays


Its possible that your issue is due to WInISD not factoring in the increased wall friction encountered due to the surface area to port volume increase found in narrow slot ports.

Here’s a calc that includes the option to crudely compensate for it, see if it comes up with closer to the original length with slot port checked yes. With the slot port checked no, it should match winISD.

http://www.mobileinformationlabs.com...0lenth%201.htm

I’ve never seen a conclusive argument for which way is correct. And I don’t have an impedance measurement rig to experiment for myself.

I certainly understand wanting to build quickly, I usually have that issue as well.

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post #23 of 23 Old 11-07-2019, 05:11 AM
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Quote:
Originally Posted by 260guy View Post
Which value to use as box volume was something else that I had questions about. I read several articles indicating to use the net value. In other words a value with driver, bracing, ports etc already added. I also read the WinISD FAQ and came away with the same conclusion. I may be totally misunderstanding. Can you please confirm.

Q. Does WinISD add brace/driver/port displacements to calculated box volume?
A. From Janne Ahonen ([email protected])
No. WinISD doesn't do guessing, and therefore shows net volume for your box. It would be hard to predict, how you are going to mount your driver. Or the port. Or how much and which kind of bracing you are going to use inside your box. For example, you could mount port completely external to the box, which case "usual" guess would be completely wrong. Bottom line is, that you must calculate and add any displacements by yourself to calculated box volume.
Of course use net volume to model in winisd. My post suggesting you to use your gross volume was merely to illustrate the relationship between box volume and port length.

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