@GM - TQWT with hornresp for Beta 12CX, ASD1001, & PXB2:2K5CX?

toaud

Member
2016-01-26 3:34 am
Hi GM

Freddi suggested that I reach out to you and ask if you could cook up a design/plan for a TQWT with hornresp for Beta 12CX, ASD1001, & PXB2:2K5CX?

I am currently exploring a number of build options but am pretty much a newb. I have managed to calculate and make a TL for a pair of Vifa TG9FDs and a kit sub from CSS.

My calculations for a straight TL make the speaker too big.

My struggle with this particular build is with the fold and the port placement. The calculator I have used from mh-audio.nl gave me a plan but with the port facing the top of the box.

TMLdrawing.gif


Ideally, the port would face forward(?). From the plan, I could make the port face back behind by extending the top of the cabinet and keeping the same area, but I am unsure...

I found this plan for a different speaker but I think the configuration is what I am going for, but with measurements for the Beta 12CX, ASD1001, & PXB2:2K5CX.



Thanks for your help!

:)
 
Greets!

Designed a slew of [ML] TL, [ML] TQWTs way back when Avatar/Adire was selling modified driver kits, but in a quick search couldn't find any on DIYaudio, so must have been on the old basslist and other long gone forums.

Regardless, will post back as time permits; from [very] dim memory though, they were pretty large.

GM
 

pkitt

Member
2009-02-24 12:32 am
In a TL that has a constant cross-sectional area (CSA) along its whole length, the resulting 1/4-wavelength resonant frequency is determined by the actual length of the line. If a line has a negative taper, decreasing CSA from closed (driver) end to open (opposite) end, the line has an effective length longer than its actual length, and the 1/4-wave resonance is determined by that longer effective length. If the line has a positive taper, increasing CSA from closed to open end, the has an effective length shorter than its actual length, and the 1/4-wave resonance is determined by that shorter effective length. For instance, if you wanted a 1/4-wave resonance of 30 Hz, a non-tapered line would need to be ~112" long. If the line had a negative taper of 10:1, it would need to be only ~69" long. If the line had a positive taper of 1:10, it would need to be ~159" long.
Paul

Ok .. thanks Dave! Logically is this because the taper reduces volume faster so the overall length would be longer?
 

toaud

Member
2016-01-26 3:34 am
Thanks pkitt!

... and the characteristics of the horn shape (taper vs straight vs flare) affect the pressure and the presentation/characteristics (of the affected lower frequencies)? My understanding was that with the length of the TL you could extend the Fs range of a driver, but the shape of the port could do so as well? (not just the area(^2))

**Edited** - I think I just answered a (small) part of my own questions - I went back and reread some posts and info... the shape of the port benefits certain characteristics/purpose of different drivers(?) A flared line would not affect lower bass frequencies as much as it would lower-mid and up (peaks, dips, 'chuffing') and a tapered line could create distortion...? I read, but could not quite understand the difference between a port (e.g. a rectangular opening) and a vent (e.g. a tube)... the terms seem to be interchanged.... I guess the idea is to create enough back pressure so the wave reflection is timed to reach back to the driver... something like tuning a 2-stroke exhaust on a motorcycle...

e.g. I calculated the sqcm area of the rectangular port on my TG9FD Pensil build. If I change the shape of the port but keep the same sqcm the frequency would be the same but the presentation/db would change? The bass frequencies (extended, or not) are generated at the port?

From what I can tell some of the apps (except for the Tolvan Edge and Basta, that I have seen) that help you model speaker cabinet/baffle/etc. don't necessarily give you a box design but give you the measurements you need to design your box to?

If that is the case than I am working with the overall cubic measurement given a CSA and, after determining the port size/tuning, designing the cabinet based on the number of folds, if any, and taper ratio that I want?

Thanks again to everyone for entertaining the newb questions!

:)
 
Last edited:

pkitt

Member
2009-02-24 12:32 am
Within reason the shape the port (or terminus) doesn't matter much, as long as you keep the same internal area and the same length. However, you want to avoid a large aspect ratio. For instance if the area of the port is 5 square inches, using a rectangular port you could make it 2.5" x 2", or 1" x 5" or 0.5" x 10", all having the same area, but that wide and narrow port may have noise issues. Some people recommend an aspect ratio of not more than 5:1 or thereabouts. The shape of the port (or terminus) does not extend or lessen the bass response.

On tapering a line, when you use a negative taper there are two benefits; as I stated previously the required length is shorter than the equivalent non-tapered line, and the response shape is smoother, with smoothness increasing with larger taper ratios. Personally I never use a taper ratio of less than 10:1. One constant in non-tapered lines or either type of tapering, is they will all require the same line volume for the same bass performance, f3 for instance. A non-tapered line will have several major dips in its response with the only way to smooth them out is to increase stuffing length and/or density, but that then can very detrimentally affect bass reach.
Paul

Thanks pkitt!

... and the characteristics of the horn shape (taper vs straight vs flare) affect the pressure and the presentation/characteristics (of the affected lower frequencies)? My understanding was that with the length of the TL you could extend the Fs range of a driver, but the shape of the port could do so as well? (not just the area(^2))

**Edited** - I think I just answered a (small) part of my own questions - I went back and reread some posts and info... the shape of the port benefits certain characteristics/purpose of different drivers(?) A flared line would not affect lower bass frequencies as much as it would lower-mid and up (peaks, dips, 'chuffing') and a tapered line could create distortion...? I read, but could not quite understand the difference between a port (e.g. a rectangular opening) and a vent (e.g. a tube)... the terms seem to be interchanged.... I guess the idea is to create enough back pressure so the wave reflection is timed to reach back to the driver... something like tuning a 2-stroke exhaust on a motorcycle...

e.g. I calculated the sqcm area of the rectangular port on my TG9FD Pensil build. If I change the shape of the port but keep the same sqcm the frequency would be the same but the presentation/db would change? The bass frequencies (extended, or not) are generated at the port?

From what I can tell some of the apps (except for the Tolvan Edge and Basta, that I have seen) that help you model speaker cabinet/baffle/etc. don't necessarily give you a box design but give you the measurements you need to design your box to?

If that is the case than I am working with the overall cubic measurement given a CSA and, after determining the port size/tuning, designing the cabinet based on the number of folds, if any, and taper ratio that I want?

Thanks again to everyone for entertaining the newb questions!

:)
 
Ok .. thanks Dave! Logically is this because the taper reduces volume faster so the overall length would be longer?

No. it is because the line used “classic” design o come up with the dimensions. Modern modelers have shown very clearly that “Classic Design” produces almost universally not very good results. Your box needs to be modeled.

I see Paul has stepped in, he has a good handle on using modern modelers.

dave
 
Within reason the shape the port (or terminus) doesn't matter much, as long as you keep the same internal area and the same length. However, you want to avoid a large aspect ratio. For instance if the area of the port is 5 square inches, using a rectangular port you could make it 2.5" x 2", or 1" x 5" or 0.5" x 10", all having the same area, but that wide and narrow port may have noise issues. Some people recommend an aspect ratio of not more than 5:1 or thereabouts.

Paul, seeing your name, i was ready to draw the box you threw out.

The bit about the vent is a generalization, that is both waranted and unwarranted. A high aspect ratio vent can be used to advantage if you know how to deal (in the design phase) with the extra R the highRatio vent brings to the equation.

We have almost always coneverted Scott’s circular vents to slots with the desired results. We also use long high ratio vents in our miniOnkens to bring positive benefits to a nominally BR enclosure.

In a TL, which is often heavily stuffed, any long vent resonances get eaten up by the damping.

dave
 

pkitt

Member
2009-02-24 12:32 am
Not having ventured into ports or termini with large aspect ratios for my personal builds, I relied on guidance from Martin King whose opinion I respect very, very highly, and simply passed that on. Others have made comments about potential port noise issues based on the ports' profiles and aspect ratios, not on higher frequency resonances typical from long ports. I always try to avoid using stuffing length or density to "fix" a TL design if I can because of the detrimental effect on bass reach.
Paul

Paul, seeing your name, i was ready to draw the box you threw out.

The bit about the vent is a generalization, that is both waranted and unwarranted. A high aspect ratio vent can be used to advantage if you know how to deal (in the design phase) with the extra R the highRatio vent brings to the equation.

We have almost always coneverted Scott’s circular vents to slots with the desired results. We also use long high ratio vents in our miniOnkens to bring positive benefits to a nominally BR enclosure.

In a TL, which is often heavily stuffed, any long vent resonances get eaten up by the damping.

dave
 
...from Martin King whose opinion I respect very, very highly…

Me too. I worked closely with him durin gthe 1st release of his software. A brilliant man, but like all, not without prejudice or weak spots. We all have them.

I am guessing he is looking at the numbers/sims and not actually tried them.

You can see the slot vent at the bottom of these Woden specced ML-TLs (converted from a circular vent)
A12pw-MTM-comp.jpg


But an integral feature of our miniOnkens. You cn hardly see the vents in this — they are Onken-style down each side (the empty space at the bottom of the floorstander version is a space between the box and the stand).

MK12pwxwT-SM.jpg


The vents add R too the vent, which leads to lower gain and less sensitivity to dynamic T/S changes.

dave
 

pkitt

Member
2009-02-24 12:32 am
Yep, we all sure do. Other than following Martin's advice on port/terminus aspect ratios, I can remember reading several others comments that believed the larger the circumference was of a slot, compared to a circle with the same area, the more likely there would be increased turbulence at the internal entrance of the slot (if I recall correctly). I don't recall seeing any test results that validated this, but I decided to play it safe and create a questionable situation.
Paul

Me too. I worked closely with him durin gthe 1st release of his software. A brilliant man, but like all, not without prejudice or weak spots. We all have them.

I am guessing he is looking at the numbers/sims and not actually tried them.

You can see the slot vent at the bottom of these Woden specced ML-TLs (converted from a circular vent)

But an integral feature of our miniOnkens. You cn hardly see the vents in this — they are Onken-style down each side (the empty space at the bottom of the floorstander version is a space between the box and the stand).


The vents add R too the vent, which leads to lower gain and less sensitivity to dynamic T/S changes.

dave