Tweeter Location?

[wyomingbob]

WAF is in play here. I'm designing a folded TQWT 2-way that will be a maximum 40" high (that's the WAF part), with an internal CSA of 9"x11". Using MJK's worksheets, the [truncated] 6.5" woofer is centered 5" from the top. If I mount the [truncated] dome tweeter directly below, its center would be at a height of 30" -- which is 9" below ear height.

QUESTION: Can I mount the two drivers side-by-side on the wider side of the cabinet? I've searched the forums here, and found one response that said yes and one that said no.

BTW, if it comes into play here, the x-over is 4th order Butterworth lowpass and 2nd order LR, at 1900 Hz.

[CLS]

How about this:

Build the whole thing EXCEPT the baffle hole of the tweeter -- leave the tweeter movable, then you can do any experiments you want (by tape or glue or hung by strings to anywhere temporarily... )

If the tweeter is small (shallow) enough, it should be OK with the imperfect alignment for the time being. Above, under, or even side/up firing... feel free to try any possibilities.

Find what you like then cut the hole and fix.

Have fun.

[wyomingbob]

Originally Posted by CLS

How about this:

Build the whole thing EXCEPT the baffle hole of the tweeter -- leave the tweeter movable, then you can do any experiments you want

Thank you. That WAS my first thought -- to just deal with the tweeter last. However, I was stricken (as in afflicted) by the idea that the woofer and tweeter occupied only 10" of space horizontally...so why not mount them side by side?

[AEIOU]

Did you know that if you mount a tweeter below a woofer the polar axis tilt (lobe), is actually pointed upwards? While you can mount a tweeter to the left or right of a woofer, that usually affects imaging and arrival time because of the horizontal displacement.

Originally Posted by wyomingbob

WAF is in play here. I'm designing a folded TQWT 2-way that will be a maximum 40" high (that's the WAF part), with an internal CSA of 9"x11". Using MJK's worksheets, the [truncated] 6.5" woofer is centered 5" from the top. If I mount the [truncated] dome tweeter directly below, its center would be at a height of 30" -- which is 9" below ear height.

QUESTION: Can I mount the two drivers side-by-side on the wider side of the cabinet? I've searched the forums here, and found one response that said yes and one that said no.

BTW, if it comes into play here, the x-over is 4th order Butterworth lowpass and 2nd order LR, at 1900 Hz.

[wyomingbob]

Originally Posted by AEIOU

While you can mount a tweeter to the left or right of a woofer, that usually affects imaging and arrival time because of the horizontal displacement.

Had to think about that for a moment or two, but it's starting to become clear now....the sound would change when you walked past a speaker or moved to another listening position.

Back to the drawing board.

[sreten]

Hi,

Why can't you mount the tweeter above the bass/mid ? I very much
doubt moving the bass/mid down a little will change things much at all.

Your description of the crossover is ringing arm bells ....
What are the two drivers and how have you arrived at the "c/o" ?

rgds, sreten.

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[wyomingbob]

Originally Posted by sreten

Why can't you mount the tweeter above the bass/mid ? I very much
doubt moving the bass/mid down a little will change things much at all.

Your description of the crossover is ringing arm bells ....
What are the two drivers and how have you arrived at the "c/o" ?

Hi. Did some further tweaking in MathCad (about 20 tries!) and managed to move the woofer down. It shows a new 2dB dip between 100-200hz -- but an overall gain of 4dB!!! Looks like I can get that tweeter on top!

The drivers are:
(1) Peerless 831735 - Fs 40Hz, Re 5.1, Le .88, SPL 86.5, VAS 25 L, Qms 3.02, Qes .36, Qts (as actually measured by others) of .31, BL 7.9, R-xover 9.02 (1900 Hz), Sd 140
(2) Dayton Dc28fst - Fs 749Hz, Re 5.6, Le .09, SPL 89, Qms 1.97, Qes 1.6, Qts .88, R-xover 6.345 (1900 Hz)

The crossover is actually a 3rd order Butterworth LP, with 2nd order LR HP. Tweeter polarity is reversed. Crossover includes a Zobel, a series-parallel L-pad and a 3dB BSC. I spent about 2 months reading about crossovers but didn't document my sources or decision-making process...I'm a retired electrician who has often had to improvise, and this looked like a workable solution.

I built a mock-up cabinet, a 42"x9"x11.5" straight MLTL, a month ago for testing the drivers and crossover. It is elevated 2" with a bottom-firing port, which takes the overall height to 47". Don't have testing capabilities, but it DOES sound great. However, it is a little weak in the bass compared to my old Advent speakers.

Additionally, the mock-up's size is just a little too much for the wife. It's the beast in the room (see below). I've modeled a folded TQWT with an F3 at 32Hz. That should compare well with the Advents. It also has the WAF advantage of being 20% shorter. The FR from 400 to 1000Hz doesn't model quite as flat, but I guess that's the compromise I have to make.

One caveat about my design process is that I have peripheral neuropathy and can't spend much time on my feet. So I need to have an exact plan when I start doing the construction....this particular affliction has stolen my ability to fiddle around and make changes in the workshop.

Thanks for your suggestions. Two mock-up pics below. The rough-looking back side is actually a 3/4" plywood scrap added to tame the OSB resonance. The speaker cable is 18 AWG copper-braid-shielded telephone wire, probably dating from the 1940s. Yes, I used 12 AWG solid Cu to wire the crossover. Old electrician habits die hard.

[wyomingbob]

BTW, the speaker lying down in the background is an old Pioneer. Per the manual from 1975, that's an approved position. Advents were being refoamed at the time.

[sreten]

Originally Posted by wyomingbob

Hi.
The crossover is actually a 3rd order Butterworth LP, with 2nd order LR HP. Tweeter polarity is reversed. Crossover includes a Zobel, a series-parallel L-pad and a 3dB BSC. I spent about 2 months reading about crossovers but didn't document my sources or decision-making process...I'm a retired electrician who has often had to improvise, and this looked like a workable solution.

Hi,

Are these the electrical functions or your target acoustic functions ?

rgds, sreten.

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[wyomingbob]

They are electrical, based on the FRD & ZMA files and some advice received on these forums. Decisions were also based on keeping the number of capacitors to a minimum.

The LP was designed to achieve adequate rolloff well before the woofer's 5kHz breakup. The woofer does have a rising dB level above 200Hz, but the speaker would not be too far from the wall, so only a 3dB BSC.

The HP needed to bring the tweeter in at about 2.5x its Fs. There's also a 2.5 Ohm difference between the drivers at the 1.9kHz x-o point, and a 3dB difference in their efficiency.

I've tried the crossover with and without the Zobel and L-pad. Heard no audible difference, but maybe I don't hear so well, so I kept them anyway.

Acoustic target? I'm working on achieving that through the combination of drivers and enclosure (and room environment ).

Thank you for your interest in this uphill battle of mine. Perhaps I should have copied a proven design as my first project....but I've always found more satisfaction in the creative process.