Port Issues in Tower Design?

[Mattcc22]

In this design would there be issues with the port being at the bottom. I have seen people say it might act more like a transmission line with a long enclosure. I like the look of it at the bottom, but I don't want to have any bass issues with it. Any thoughts appreciated.

[LouC]

Re: Port Issues in Tower Design?

Probably not. It shouldn't be a "problem", it may marginally change response. If you have small critters (like cats) that may present an invitation to investigate.

[Paul K.]

Re: Port Issues in Tower Design?

With the internal height of your cabinet ~40" or so, the 1/4-wavelength resonant frequency of it will effect the overall tuning frequency. If you base the tuning frequency solely on the enclosed volume to determine the port's dimensions, it won't be tuned optimally. Perhaps as important, the location of the port won't necessarily be optimum if the system isn't modeled as an ML-TL. As Lou said, there won't be a large difference but there will be a difference. I would be happy to model your design as an ML-TL if you send me the T/S values you will be using for the midwoofers, the internal cabinet dimensions and the tweeter's center location vertically. I could work first with what you plan and show you those results, then make some modifications.
Paul

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In this design would there be issues with the port being at the bottom. I have seen people say it might act more like a transmission line with a long enclosure. I like the look of it at the bottom, but I don't want to have any bass issues with it. Any thoughts appreciated.

[fastbike1]

Re: Port Issues in Tower Design?

Paul, why the tweeter's location vice the midwoofers? Isn't the location of the mid-woofs w/ respect to the line a critical dimension?

I would be happy to model your design as an ML-TL if you send me the T/S values you will be using for the midwoofers, the internal cabinet dimensions and the tweeter's center location vertically. I could work first with what you plan and show you those results, then make some modifications.
Paul

[diy speaker guy]

Re: Port Issues in Tower Design?

Paul, why the tweeter's location vice the midwoofers? Isn't the location of the mid-woofs w/ respect to the line a critical dimension?

The tweeter location has nothing to do with anything (as far as the line is concerned). I suspect that he is asking for the tweeter location simply because it's easier than asking for the physical midpoint between the mids, which is where the tweeter happens to be located, and what he will actually be simulating.

[fastbike1]

Re: Port Issues in Tower Design?

Doesn't seem like that is harder ask for. Seems to be clearer.
How much spacing can one have between the woofs before this approximation befor we aren't tuned "optimally".

.... I suspect that he is asking for the tweeter location simply because it's easier than asking for the physical midpoint between the mids, which is where the tweeter happens to be located, and what he will actually be simulating.

[Mattcc22]

Re: Port Issues in Tower Design?

The design is Jeff Bagby's MTM using the RS180S-8 and RS28F from this thread:

http://techtalk.parts-express.com/sh...light=RS180S-8

I'm not sure if I want to stay with the posted design or not, but if I do the internal dimensions would be 7.5"W x 8.75"D x 43.25"H

Baffle dims:

[diy speaker guy]

Re: Port Issues in Tower Design?

Doesn't seem like that is harder ask for. Seems to be clearer.
How much spacing can one have between the woofs before this approximation befor we aren't tuned "optimally".

Perhaps not harder to ask for, but it's certainly easier to understand for the person that has to answer the question, assuming he might not know much about mltl simulations or the reason why Paul needs this info.

How much space between drivers before the assumption becomes inaccurate depends on the frequencies being played. I've never done a study on this but I'm assuming it's 1/4 wavelength. This is moot anyway, since you are never going to place the drivers far enough apart to void the assumption. (The assumption being that you can simulate 2 drivers by simulating them as a single lumped driver at the physical midpoint of the 2 drivers.)

[Paul K.]

Re: Port Issues in Tower Design?

I made two assumptions; the midwoofers are equally spaced relative to the tweeter and, that, they're also located close to the tweeter. The tweeter's center, then, becomes the TL's design center as if there is a single woofer, with the twice the Sd and Vas, located where the tweeter's center is. I asked the question that needed to be answered for me to do the modeling.
Paul

Paul, why the tweeter's location vice the midwoofers? Isn't the location of the mid-woofs w/ respect to the line a critical dimension?

[Paul K.]

Re: Port Issues in Tower Design?

If you do decide to build Jeff's design and want me to model it as an ML-TL, let me know.
Paul

The design is Jeff Bagby's MTM using the RS180S-8 and RS28F from this thread:

http://techtalk.parts-express.com/sh...light=RS180S-8

I'm not sure if I want to stay with the posted design or not, but if I do the internal dimensions would be 7.5"W x 8.75"D x 43.25"H

Baffle dims:
[ATTACH]21784[/ATTACH]

[fastbike1]

Re: Port Issues in Tower Design?

Thanks for the answer. Perhaps it wasn't clear but I was asking to learn/ make sure I understood some basic MLTL issues.

I made two assumptions; the midwoofers are equally spaced relative to the tweeter and, that, they're also located close to the tweeter. The tweeter's center, then, becomes the TL's design center as if there is a single woofer, with the twice the Sd and Vas, located where the tweeter's center is. I asked the question that needed to be answered for me to do the modeling.
Paul

[Paul K.]

Re: Second thoughts...

Since this is Jeff's design, which I didn't realize at first, I'm not going to second guess him. I have too much respect for his knowledge, experience and skills at speaker design. Therefore, I withdraw my offer to model it as an ML-TL.
Paul

If you do decide to build Jeff's design and want me to model it as an ML-TL, let me know.
Paul

[Paul K.]

Re: Port Issues in Tower Design?

Fair enough. If you've never visited Martin King's site, doing so will provide you with a lot of reading material about TLs, as well as other types of enclosures, which will help you learn more about them.
Go to: http://www.quarter-wave.com/
Paul

Thanks for the answer. Perhaps it wasn't clear but I was asking to learn/ make sure I understood some basic MLTL issues.

[diy speaker guy]

Re: Port Issues in Tower Design?

I'll do it if I have time. I will need all the driver specs posted here though (including Sd and Bl), I don't want to go searching for them with my slow dial up. Measured t/s parameters are even better if you have them.

I don't see this as stepping on Jeff's toes at all, it's just a simulation of a dayton driver in an mltl box. I'm not going to comment on the suitability of using Jeff's crossover on an entirely different box (other than to say it might turn out worse than following the plans) but I can't see anything taboo about simulating this.

[Mattcc22]

Re: Port Issues in Tower Design?

I don't see this as stepping on Jeff's toes at all, it's just a simulation of a dayton driver in an mltl box. I'm not going to comment on the suitability of using Jeff's crossover on an entirely different box (other than to say it might turn out worse than following the plans) but I can't see anything taboo about simulating this.

In Jeff's original design he used the PE 1.0 cu ft cabinet, ported in the back. but I was under the impression that you can take that same design and crossover and turn it into a tower as long as you correct the tuning based on box volume. The baffle layout from the top will be identical, I was just going to turn it into a tower and tune a little lower. Similiar to turning the Nat P. into a tower design. The only thing I was worried about was the port being at the bottom and acting like a TL. I haven't read much about that so wasn't sure. If it's going to be too much trouble I can just put the port in the rear behind the drivers as in the original design.