Port Surgery... does moving the port change speaker performance?

ryanosaur

ryanosaur

Audioholic Overlord
I found this older thread: https://forums.audioholics.com/forums/threads/changing-rear-port-speakers-to-front-ported-speakers.107246/
...Didn't seem completely right re-appropriating it, considering some friends here are adamant of starting a new thread for various reasons.

Long story short: First Question is about moving the port on existing Dayton-Tweeter AAs and on a second pair that I may build from BR1 Kit, assuming the Murphy Blaster XO schematic is the same as what I have existing.
OK? Or horrible idea?
(Yes, I understand everything involved in what would be required, just want to make certain if I do it, I won't be fundamentally altering the actual performance. I will even go so far as to keep the port about the same distance from the back of the woofer... just rolling it around to the side and still behind the tweeter.)

Randomly, with another pair of speakers, a simple 2-way design with woofer-tweeter center aligned, I may have reson to use them elsewhere, hanging, but I would need to turn them upside down. I know better than to put a speaker on its side... But tweeter on bottom, woofer on top... no other changes.
Thoughts, please?


Many thanks, all!
 
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ryanosaur

ryanosaur

Audioholic Overlord
Managed to find some info on my second question about turning the speaker upside down... general consensus is that it shouldn't affect anything. Examples were cited of monitors in studios being turned upside down to get the tweeters more in line with the engineers ears. So not a big deal it seams.

Though lots of jokes about music being upside down. *facepalm Anybody that's studied serial composition knows inversion doesn't turn music upside down! Duh. :rolleyes::p ('Had a lot of theory-comp courses in music school... :cool:)
 
Verdinut

Verdinut

Audioholic Spartan
I found this older thread: https://forums.audioholics.com/forums/threads/changing-rear-port-speakers-to-front-ported-speakers.107246/
...Didn't seem completely right re-appropriating it, considering some friends here are adamant of starting a new thread for various reasons.

Long story short: First Question is about moving the port on existing Dayton-Tweeter AAs and on a second pair that I may build from BR1 Kit, assuming the Murphy Blaster XO schematic is the same as what I have existing.
OK? Or horrible idea?
(Yes, I understand everything involved in what would be required, just want to make certain if I do it, I won't be fundamentally altering the actual performance. I will even go so far as to keep the port about the same distance from the back of the woofer... just rolling it around to the side and still behind the tweeter.)

Randomly, with another pair of speakers, a simple 2-way design with woofer-tweeter center aligned, I may have reson to use them elsewhere, hanging, but I would need to turn them upside down. I know better than to put a speaker on its side... But tweeter on bottom, woofer on top... no other changes.
Thoughts, please?


Many thanks, all!
I don't see any problem with moving the port to one of the sides provided that you properly block the existing port and build the new port of similar exact dimensions as the original.

With regard to installing a pair of surround speakers upside down, there is an advantage if it allows the tweeter to be closer to ear level than the other way. As a matter of fact, in my HT, the surround left and right speakers are installed upside down for that purpose. Also, I installed the surround back bookshelves on their sides and changed the orientation of the air motion ribbon tweeters appropriately.
 
Swerd

Swerd

Audioholic Warlord
First Question is about moving the port on existing Dayton-Tweeter AAs and on a second pair that I may build from BR1 Kit, assuming the Murphy Blaster XO schematic is the same as what I have existing.
OK? Or horrible idea?
(Yes, I understand everything involved in what would be required, just want to make certain if I do it, I won't be fundamentally altering the actual performance. I will even go so far as to keep the port about the same distance from the back of the woofer... just rolling it around to the side and still behind the tweeter.)

Randomly, with another pair of speakers, a simple 2-way design with woofer-tweeter center aligned, I may have reson to use them elsewhere, hanging, but I would need to turn them upside down. I know better than to put a speaker on its side... But tweeter on bottom, woofer on top... no other changes.
Thoughts, please?
I'm confused.

First, where is the port on your existing speakers? Front or back? If the port is on the back behind the tweeter, as I suspect, the answer is no you cannot move them to the front, unless there already is room on the front baffle for the same sized port. If the existing port is on the rear, and if the front baffle lacks space for tweeter, woofer and port, you must build a new taller cabinet. In the new cabinet, it's important to keep the cabinet's internal volume the same, keep the front baffle width the same, and keep the layout of the tweeter and woofer the same as on the original cabinet. I hope that's clear.

Edit: I agree with Verdinut's comment, "I don't see any problem with moving the port to one of the sides provided that you properly block the existing port and build the new port of similar exact dimensions as the original." These 2-way speakers are in small cabinets. Is there room on the side? Don't forget to include room for the port's tube length inside the cabinet.

If your tweeter is above the woofer, and you invert them, it will alter how they interact with each other. If the crossover is Linkwitz-Riley 4th order (that's Dennis's usual design starting point),that will be within the range of the crossover frequency ± one octave. So that goes from half of the crossover frequency to double. If that crossover is, for example at 2000 Hz, that includes all sound from 1000 to 4000 Hz. In short, I'd avoid inverting the woofer and tweeter, unless you redesign the crossover to account for the woofer-tweeter inversion.
 
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ryanosaur

ryanosaur

Audioholic Overlord
Hey Swerd... was thinking the sides of the BR1 cabinet, not the front... its pretty deep so I could roll the placement around to the "inside" face of the cabinets, the port would likely end up being ever so slightly closer to the woofer, but we are still talking probably an easy 6" of distance separating them... Likewise, there is ample space to keep the port at its same vertical location on the box, and I should be able to have 3" clearance from the port and any existing wall.

No desire to play with the front baffle. But when I mount them for atmos, they will be two close to other surfaces for the rear ports to operate properly.

I do like the idea of building a new box and have thought of that. In order to pull off what I want, it would need to be a trapezoid shape to help cut back a little on the depth, but yes... would have to maintain exact baffle dimensions as is, as well as internal volume! Completely tuned in to that. :)

The other question I posed and retracted, was just about turning a surround speaker upside down... separate situation entirely. Verdinut and my continued research seem to line up that it shouldn't affect anything.
Would love to hear your thoughts if you disagree, though! :)
 
Verdinut

Verdinut

Audioholic Spartan
I'm confused.
If your tweeter is above the woofer, and you invert them, it will alter how they interact with each other. If the crossover is Linkwitz-Riley 4th order (that's Dennis's usual design starting point),that will be within the range of the crossover frequency ± one octave. So that goes from half of the crossover frequency to double. If that crossover is, for example at 2000 Hz, that includes all sound from 1000 to 4000 Hz. In short, I'd avoid inverting the woofer and tweeter, unless you redesign the crossover to account for the woofer-tweeter inversion.
If you just turn a speaker cabinet upside down, please explain how that changes the interaction between the drivers. I don't understand how it would, nothing is changed except the orientation of the enclosure. Polar response remains the same.
 
Swerd

Swerd

Audioholic Warlord
If you just turn a speaker cabinet upside down, please explain how that changes the interaction between the drivers. I don't understand how it would, nothing is changed except the orientation of the enclosure. Polar response remains the same.
I'm on softer ground trying to answer this, but here goes.

In theory, turning the cabinet upside down shouldn't matter if the speaker is a 2-way with a 4th order crossover. The acoustic lobes in the crossover frequency ±1 octave range have no tilt – they project directly in front of the baffle at 90° to it – in theory.

When Dennis Murphy designs a crossover he usually starts with a textbook Linkwitz-Riley 4th order design, and then (among other things) he carefully adjusts the roll-off curves such that the woofer roll-off and tweeter roll-in curves are as symmetrical as possible on either side of the crossover frequency. He usually does this by placing LCR traps in parallel to each driver. He spends time tweaking these until he's satisfied that the sound is as flat as possible, ie there are no additions or cancellations. Now, here's the important part, he also tweaks those LCR traps so the resulting roll-off/roll-in curves arrive in phase with each other at the designed listening distance. If I've correctly described what I understand that Dennis does, this contributes in a major way to the creation of a focused image, and when listening is stereo, to a realistic sound stage. The net result of all this is a somewhat modified LR 4th order crossover where there can be some tilt to the acoustic lobes.

If I understood this better, I be able to describe it with fewer words. Dennis once carefully explained his thinking on this to me, and I only partially understood it.

As is often said, in theory there is no difference between theory and practice. But in practice, there almost always is.
 
ryanosaur

ryanosaur

Audioholic Overlord
I'm on softer ground trying to answer this, but here goes.

In theory, turning the cabinet upside down shouldn't matter if the speaker is a 2-way with a 4th order crossover. The acoustic lobes in the crossover frequency ±1 octave range have no tilt – they project directly in front of the baffle at 90° to it – in theory.

When Dennis Murphy designs a crossover he usually starts with a textbook Linkwitz-Riley 4th order design, and then (among other things) he carefully adjusts the roll-off curves such that the woofer roll-off and tweeter roll-in curves are as symmetrical as possible on either side of the crossover frequency. He usually does this by placing LCR traps in parallel to each driver. He spends time tweaking these until he's satisfied that the sound is as flat as possible, ie there are no additions or cancellations. Now, here's the important part, he also tweaks those LCR traps so the resulting roll-off/roll-in curves arrive in phase with each other at the designed listening distance. If I've correctly described what I understand that Dennis does, this contributes in a major way to the creation of a focused image, and when listening is stereo, to a realistic sound stage. The net result of all this is a somewhat modified LR 4th order crossover where there can be some tilt to the acoustic lobes.

If I understood this better, I be able to describe it with fewer words. Dennis once carefully explained his thinking on this to me, and I only partially understood it.

As is often said, in theory there is no difference between theory and practice. But in practice, there almost always is.
Ah! Cool, thank you for elucidating on that. I only loosely (like so many things here, recently) understand.
Any idea if it’s likely an upward tilt, or downward?
 
Verdinut

Verdinut

Audioholic Spartan
Ah! Cool, thank you for elucidating on that. I only loosely (like so many things here, recently) understand.
Any idea if it’s likely an upward tilt, or downward?
The polar response will be reversed. For example, if there is an upward tilt in the normal position, then it will be downward if the cabinet is upside down. That would be the only difference.
 
Verdinut

Verdinut

Audioholic Spartan
I'm on softer ground trying to answer this, but here goes.

In theory, turning the cabinet upside down shouldn't matter if the speaker is a 2-way with a 4th order crossover. The acoustic lobes in the crossover frequency ±1 octave range have no tilt – they project directly in front of the baffle at 90° to it – in theory.
.
IMO, there shouldn't be a major difference for either a 2nd order or a 3rd order passive crossover, which are simpler designs than the 4th order type, and used in most commercial products made by major manufacturers.
 
Swerd

Swerd

Audioholic Warlord
IMO, there shouldn't be a major difference for either a 2nd order or a 3rd order passive crossover…
In a perfect world, where drivers have perfect roll-off/roll-in curves, there should be no difference. But our world isn't perfect, and that's why text book crossovers benefit from a bit of tweaking.

I should add, it's quite possible that some people might not perceive the difference between tweeter-on-top and tweeter-on-bottom and others might. In an imperfect world, such things readily occur.
 
Swerd

Swerd

Audioholic Warlord
IMO, there shouldn't be a major difference for either a 2nd order or a 3rd order passive crossover, which are simpler designs than the 4th order type, and used in most commercial products made by major manufacturers.
This morning, I thought of another point that might help with my previous explanation:

When Dennis Murphy talks about crossover slopes, he distinguishes between acoustic crossover slopes and electronic crossover slopes. By acoustic slopes, he specifically means the roll-off/roll-in slopes, measured acoustically, of the drivers combined with the electronic crossover network. Most people usually think only of the slopes of measured voltages in the electronic crossover networks. When Dennis speaks of those, he'll specify electronic slopes to avoid confusion. Because drivers have their own inherent roll-off or roll-in behaviors, a speaker's acoustic slopes and a crossover network's electronic slopes will most likely not be identical.

If you look at the schematic diagrams of crossovers Dennis has designed, they might not look like a text book 4th order filter, with two inductors and two capacitors for each driver, and with the classic 24 dB/octave slopes. But their measured acoustic slopes will be as close as possible to the electronic behavior LR 4th order filters.

I hope that helps.
 
TLS Guy

TLS Guy

Seriously, I have no life.
In a perfect world, where drivers have perfect roll-off/roll-in curves, there should be no difference. But our world isn't perfect, and that's why text book crossovers benefit from a bit of tweaking.

I should add, it's quite possible that some people might not perceive the difference between tweeter-on-top and tweeter-on-bottom and others might. In an imperfect world, such things readily occur.
You are absolutely correct that the order of the crossover affects lobing. For odd order crossovers there will be a 15 degree slope downwards if the tweeter is on top and upwards if underneath.

This Dynaudio Consequence speaker used first order crossovers and had the tweeter at the bottom.



These speakers of mine were tilted for the same reason, odd order filters.



Those same speakers used as surrounds have the lobing axis down towards the listening area.
 
ryanosaur

ryanosaur

Audioholic Overlord
Surprised that this topic is getting the play! But nice also. :) I only just read about tilt in the LDC7. His dense writing style made it difficult for me to really understand it. And though I understand that the xo can be not-a 4th order LR, yet still perform as one, I of course don’t have the experience yet or instinct to help me gauge expected performance.

With that said, I am specifically looking at mounting my Mini-Phil’s upside down, vs right side up. The location, cabinet design, and usage as rears all come together as reasons why I am considering this. Placement is wall mounted about 7’ high, on brackets aimed at my LP. By inverting them, I get the benefit of being able to use the adjustable bracket a bit more effectively, tweeter ends up aligning better with LP.
We all know the Raal to have good off-axis dispersion.
Is lobing and tilt, in this instance, a real concern?
Then, I have s slew of other questions to help me understand tilt better:
Do simulation programs model tilt? Or is it something you just have to analyze for?
Is there a good all-in-one design and modeling program that gives cabinet design, xo design and optimization, and performance modeling?
If so, which? If not, which programs are considered to be better for those different stages?
For me, I will not have a testing room... my best case is doing free range testing in a field that seems to meet the criteria of large, flat, and with no interfering objects nearby.

Thank you!
 
Verdinut

Verdinut

Audioholic Spartan
I understand that the xo can be not-a 4th order LR, yet still perform as one
Your assumption is right for a well designed 2nd or 3rd order crossover.

For the speakers that I have built so far over the years, I have designed several 2nd order Butterworth or Linkwitz-Riley crossovers, and some systems have a combination of a 2nd order L-R filter for the midrange driver or woofer with a 3rd order Butterworth for the tweeter.
Of course, there are interactions between a driver depending on its frequency range and response curve, and calculated component values often have to be adjusted to obtain a smooth overall response. With the proper testing equipment, I can measure the acoustic frequency response and proceed to slight adjustments if required.

I obtain very good results and nobody can hear where the transition occurs in the frequency range between drivers. This is what counts.
 
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