Enclosure resonances, not a big deal?

[thadman]

One of the recent trends in loudspeaker design has been to incorporate dipole or open baffle alignments into the design. This has the obvious benefit of removing resonances within the body of air behind the diaphragm, but can this same result be achieved through another technique?

As far as I understand it, the behavior of the air within the enclosure and its effects on the loudspeaker can be thought of as a mass-spring system. The resonance or ringing due to the presence of modes within the enclosure space can be equalized out (by applying equal amplitude inversion signal processing of the resonances) because it is a linear phenomenon. The non-linear effects however can not. But where do the non-linear effects caused by the resonances arise? Is it because of nonhomogeneous pressure distribution over the surface of the diaphragm (ie higher damping in certain positions relative to lower damping in other positions) leading to erratic cone motion and thus non-linear distortion? If we managed to make the damping uniform over the surface of the diaphragm (by forcing the diaphragm to launch a 1 dimensional plane wave whose attributes only varied with distance from the diaphragm) wouldn't the observed non-linear effects due to the air vanish and become a linear phenomenon?

Thanks,
Thadman

[cjd]

Dipole is very much different than what you're proposing (completely different radiation pattern) - your suggestion is essentially what those of us with "IB" subwoofers are doing. And yes, it DOES help with distortion when you do that.

You may note I often play up sealed box size beyond where most folks go... there's a reason I don't just push 'em smaller and stuff...

[thadman]

Dipole is very much different than what you're proposing (completely different radiation pattern) - your suggestion is essentially what those of us with "IB" subwoofers are doing. And yes, it DOES help with distortion when you do that.

You may note I often play up sealed box size beyond where most folks go... there's a reason I don't just push 'em smaller and stuff...

I identified one particular aspect of a dipoles operation. I never claimed it was the only thing that separated it from sealed systems.

I'm confused as to how my post relates to IB subwoofer systems. Does it deal with resonances through signal processing? What resonances are present in an IB system?

[Saurav]

I've wondered about what it is that people like about dipoles. There are some that are designed with careful attention to the radiation pattern, and in those speakers, the polar response and the reduced 'box effects' probably both play a role. But there's another camp of dipole experimenters who go with very large / wide baffles, and they're pretty happy with the sound too. In those cases, I'd think the polar response wouldn't really be dipole, or at least, not as uniformly dipole.

So the question in my mind is, what plays a bigger role in creating the 'dipole sound' - the polar response, or the removal of box resonances?

[thadman]

I've wondered about what it is that people like about dipoles. There are some that are designed with careful attention to the radiation pattern, and in those speakers, the polar response and the reduced 'box effects' probably both play a role. But there's another camp of dipole experimenters who go with very large / wide baffles, and they're pretty happy with the sound too. In those cases, I'd think the polar response wouldn't really be dipole, or at least, not as uniformly dipole.

So the question in my mind is, what plays a bigger role in creating the 'dipole sound' - the polar response, or the removal of box resonances?

Most likely the polar response, but that deserves an entire discussion to itself.

[brianpowers27]

Most likely the polar response, but that deserves an entire discussion to itself.

I think so... In a nutshell... too many variables.

Jeff Bagby truely believes that small monitors image far better than large ones. The reason, he postulates, has everything to do small cabinets being easier to build rigidly.

[thadman]

Jeff Bagby truely believes that small monitors image far better than large ones. The reason, he postulates, has everything to do small cabinets being easier to build rigidly.

I'm not sure baffle resonances are a huge problem with respect to imaging. People believe dipoles lack baffle resonances, but I believe if you modeled the forces in Ansys acting on a dipole baffle (lacks rigidity) and a sealed enclosure, the sealed enclosure would resonate less. Yet people still claim dipoles lack box resonances.

Dr. Geddes spent significant effort designing structurally inert enclosures for his Summas and found little appreciable difference (in terms of perceived sound quality) between the inert enclosures and a traditional wood enclosure.

Perhaps the large distinction perceived between small monitors and large monitors is due to their dissimilar diffraction behavior and polar response?

[Curt C]

I'm not sure baffle resonances are a huge problem with respect to imaging. People believe dipoles lack baffle resonances, but I believe if you modeled the forces in Ansys acting on a dipole baffle (lacks rigidity) and a sealed enclosure, the sealed enclosure would resonate less. Yet people still claim dipoles lack box resonances.

IMO, it appears you are considering the panel resonance, but not the standing wave phenomena, which will cause a ‘boxy’ sound even with an otherwise inert enclosure. To my mind, it would be difficult to completely ‘equalize out’ the resonance, as I suspect they will be nonlinear with respect to excitation level and polar response.

Dr. Geddes spent significant effort designing structurally inert enclosures for his Summas and found little appreciable difference (in terms of perceived sound quality) between the inert enclosures and a traditional wood enclosure.

I can’t speak for the good Dr. or the Summas, but I’ve found panel and standing wave resonance to be a high Q artifact, and as such may not be excited by a particular source material. I’ve also found these resonances can be quite audible, even in smaller, well constructed enclosures, but usually can be tracked down and attenuated by mechanical means.

Perhaps the large distinction perceived between small monitors and large monitors is due to their dissimilar diffraction behavior and polar response?

–Or perhaps the distance required for driver integration due to the larger driver offset of a larger speaker. I.e.: the ratio of the enclosure size to the room size and listening position.

C

[thadman]

IMO, it appears you are considering the panel resonance, but not the standing wave phenomena, which will cause a ‘boxy’ sound even with an otherwise inert enclosure. To my mind, it would be difficult to completely ‘equalize out’ the resonance, as I suspect they will be nonlinear with respect to excitation level and polar response.

Perhaps you did not read the thread very carefully, the first post attempts to convey the concept of mode related linear distortion by describing the relationship between the loudspeaker and the air within the enclosure as a mass-spring system.

[---k---]

Perhaps you did not read the thread very carefully,

...
:roll:

[Undefinition]

Perhaps you did not read the thread very carefully, the first post attempts to convey the concept of mode related linear distortion by describing the relationship between the loudspeaker and the air within the enclosure as a mass-spring system.

Then make the enclosure vented, and tune it very low, as Curt C does. It emulates the roll-off of a sealed enclosure, but you will not get the same sort of air-compression as you would a sealed box (you may also get the added benefit of more bass extension).

Personally, I have found sealed speakers to have a more "boxy" sound than their vented counterparts. I don't necessarily think that there is a linear causality between "sealed box" and "boxy sound," though. What I may have been hearing was could have been mechanincal resonances... but I don't know. Sort of a question I've been pondering the last few months, really.

[davey_m]

........the first post attempts to convey the concept of mode related linear distortion by describing the relationship between the loudspeaker and the air within the enclosure as a mass-spring system.

Just remember that your spring / mass model is a first order approximation of a more complex phenomenon. This is the very reason mere equalization will not solve the problem completely. You cannot simplify a problem until it is easy to solve, and then get a 100% cure.

[thadman]

Just remember that your spring / mass model is a first order approximation of a more complex phenomenon. This is the very reason mere equalization will not solve the problem completely. You cannot simplify a problem until it is easy to solve, and then get a 100% cure.

The subject of this thread is mitigating the effects of acoustic (standing wave) resonances on cone motion (leads to frequency response anomalies, ie linear distortion). Since we're considering the propagation of standing waves through the diaphragm, they can be considered one-dimensional.

If the resonance imposes a force on the cone, why couldn't an electrical signal of equal amplitude (but opposite phase) be sent to the coil. From my understanding, two forces of equal amplitude (but opposite phase) cancel. In this regard, impulse response should be able to be corrected and the effects of the resonance on cone motion reduced to zero.

[davey_m]

.......Since we're considering the propagation of standing waves through the diaphragm, they can be considered one-dimensional.

That's exactly the kind of oversimplification I'm talking about. It is a three dimensional phenomenon, with a three axis pressure distribution. The pressure distribution on the cone is in no way uniform. The cone can be bent (deformed), rocked, and axially displaced. And that's only a start.

In this regard, impulse response should be able to be corrected and the effects of the resonance on cone motion reduced to zero.

No

[ch83575]

That's exactly the kind of oversimplification I'm talking about. It is a three dimensional phenomenon, with a three axis pressure distribution. The pressure distribution on the cone is in no way uniform. The cone can be bent (deformed), rocked, and axially displaced. And that's only a start.

I agree; thats only the start. I am sure things change with power level and especially thermal changes in the driver and box temp ect. ect... Even correcting for the simplified version can be problematic let alone the actual phenomenon.

-Chad

[Dennis H]

The subject of this thread is mitigating the effects of acoustic (standing wave) resonances on cone motion (leads to frequency response anomalies, ie linear distortion).

Yup, that's way oversimplifying it. The box air spring isn't linear because the temperature increases as the cone moves into the box and decreases as it moves out of the box -- the old PV=nRT thing. That leads to non-linear distortion, mostly 2nd harmonic.

Box air-spring distortion % = 140 * (one-way driver swept volume) / (box volume)

[cjd]

So get rid of the tiny little box. Which was my suggestion. :P

I was responding to this part of the original post:

This has the obvious benefit of removing resonances within the body of air behind the diaphragm, but can this same result be achieved through another technique?

[thadman]

That's exactly the kind of oversimplification I'm talking about. It is a three dimensional phenomenon, with a three axis pressure distribution. The pressure distribution on the cone is in no way uniform. The cone can be bent (deformed), rocked, and axially displaced. And that's only a start.

If we restrict the wave propagation (within the enclosure) to one dimension as I suggested previously in this thread, we can assume the force distribution across its surface to be uniform and my simplification will be valid.

We can achieve this by launching a plane wave. To launch a plane wave (ie one dimensional propagation), the internal dimensions (other than the dimension of propagation) of the enclosure must not exceed 1/4 wavelength (if we assume the source is infinitely small or the source is small relative to the dimensions of the enclosure). If the dimensions are restricted to the diameter of the driver (other than the dimension of propagation), the radiating surface will encompass those dimensions and the modes related to those dimensions will sum to zero.

[Curt C]

I’m not sure where you are going with this. The wave front from any conventional driver will not exhibit planar behavior, but rectilinear propagation at each point of excitation. A point source bounded by a plane would result in a hemispherical wave front, not a planar wave front.

Conventional drivers in typical enclosures do not represent point sources, but will still produce something closer to a hemispherical wave front than a planar one. Nor, as per your assumptions, will the drivers be much smaller than the typical enclosure boundaries. Even if we restrict the enclosure boundaries to the driver diameter, the result will not be a planar wave, but individual wave fronts, which will interact coherently producing the expected interference patterns.

From a practical standpoint: How do you propose to restrict the wave propagation to planar modes only? Perhaps if you cut to the chase…

C

[thadman]

I’m not sure where you are going with this. The wave front from any conventional driver will not exhibit planar behavior, but rectilinear propagation at each point of excitation. A point source bounded by a plane would result in a hemispherical wave front, not a planar wave front.

Think about it like this. Say we have an enclosure of dimensions 1' x 1' x 1'. At frequencies whose length exceeds the wavelength of the largest dimension (in this case, 1') by a factor of 4, the pressure will be uniform throughout the enclosure and no modes will exist. I believe we can all accept this assumption as it is the same argument many make for bass in listening rooms. Below the first room mode, a dipole lacks the ability to excite the room sufficiently because it is a velocity source. A point source however does not because it is a pressure source.

If we took our example, and increased one of the dimensions (lets say depth) by a factor of 1000 for example, we would now have propagation in one dimension only over a particular bandwidth (plane wave propagation). As long as the height and width dimensions are appropriately small (< 1/4 wavelength of highest reproduced frequency), my simplification should be valid and it will exhibit plane wave propagation along its depth axis.

Conventional drivers in typical enclosures do not represent point sources, but will still produce something closer to a hemispherical wave front than a planar one. Nor, as per your assumptions, will the drivers be much smaller than the typical enclosure boundaries. Even if we restrict the enclosure boundaries to the driver diameter, the result will not be a planar wave, but individual wave fronts, which will interact coherently producing the expected interference patterns.

Have you perhaps heard of the concept of a Double Bass Array?

If not, you can read about it here: http://www.avsforum.com/avs-vb/showthread.php?t=837744

It relies on using sources placed in an array at specific distances from one another across a wall so that the LF wave propagates in only one dimension. The side walls and ceiling act to extend the array so conceptually it can be thought of as an infinite line in those dimensions (height for ceiling and width for side walls).

If a single point source is placed in a room and the highest reproduced frequency exceeds 1/4 wavelength of the largest height or width dimension, it will exhibit the same propagation behavior as an array covering the same surface. This is why my example of a point source in an enclosure is valid.

If we restrict the enclosure boundaries to the diameter of the driver and think of the surface of the diaphragm as individual sources that make up an infinitely dense array, the surface of the diaphragm is conceptually the same as the surface of the wall in the Double Bass Array. Propagation will exist in only one dimension and modes will sum to zero along the height and width dimensions. This is why my example of an enclosure restricted to the diameter of the driver is valid.

Is this more clear?

[brianpowers27]

If a single point source is placed in a room and the highest reproduced frequency exceeds 1/4 wavelength of the largest height or width dimension, it will exhibit the same propagation behavior as an array covering the same surface. This is why my example of a point source in an enclosure is valid.

Doesn't this happen all of the time? Most rooms have a 8' short boundary... 145hz.. This would mean everything above that is planar... Or are you referring to cabinet dimensions?

I believe you are going somewhere with tis but at the time I can't understand what you are trying to communicate.

[Dennis H]

Thadman, your premise that you can fix any linear distortion with EQ is flawed. Just as in a room, you can't fix a null by pumping more power into it. Here's the close-mic'd response of SL's Thor sub before any EQ. The sharp null marked 20.5" is due to the length of the box. The only way to deal with that is to use stuffing (SL doesn't use any) or, as he does, don't let it play that high.

[thadman]

Doesn't this happen all of the time? Most rooms have a 8' short boundary... 145hz.. This would mean everything above that is planar... Or are you referring to cabinet dimensions?

I believe you are going somewhere with tis but at the time I can't understand what you are trying to communicate.

The analogy refers to a listening room, but our application is loudspeaker enclosures. You have your math backwards, wavelength increases as frequency decreases. For a boundary of 8', below the frequency that corresponds to 4x that distance (32', ~35hz) pressure distribution should be uniform and modes should not exist in that dimension because a >32' wave exceeds 1/4 wavelength of that dimension.

[Curt C]

You are limiting the frequency bandwidth to wavelengths greater than 4x the enclosure height and width. I missed than in your initial post somehow… :W

At these long wavelengths I agree the wave front will somewhat resemble a planar wave. Furthermore, at those frequencies, no standing wave fundamentals can be supported. And yes, an enclosure whose characteristics emulate one of infinite depth or attenuation in that axis, would appear to propagate a linear wave front down that axis, but I’m thinking perhaps only at some distance from the source. I suspect there will still be energy near the driver that will excite the sidewalls, however this may be significantly less than a box of finite depth.

C

[thadman]

Thadman, your premise that you can fix any linear distortion with EQ is flawed. Just as in a room, you can't fix a null by pumping more power into it. Here's the close-mic'd response of SL's Thor sub before any EQ. The sharp null marked 20.5" is due to the length of the box. The only way to deal with that is to use stuffing (SL doesn't use any) or, as he does, don't let it play that high.

You are correct.

However by restricting propagation to a single dimension (we can achieve this by forcing the rear of the driver to launch a plane wave), significant attenuation is able to be achieved along that axis in the same vein as the DBA through absorption and thus FR nulls are able to be avoided.

[Dennis H]

However by restricting propagation to a single dimension (we can achieve this by forcing the rear of the driver to launch a plane wave), significant attenuation is able to be achieved along that axis in the same vein as the DBA through absorption and thus FR nulls are able to be avoided.

The null in the pic is due to your single dimension -- the wall opposite the driver. If you add stuffing to absorb it, your whole premise that resonances/reflections don't matter and can be fixed with EQ falls apart.

[thadman]

The null in the pic is due to your single dimension -- the wall opposite the driver. If you add stuffing to absorb it, your whole premise that resonances/reflections don't matter and can be fixed with EQ falls apart.

Perhaps there has been a miscommunication or a wording error on my part. My premise was that if we force the rear of the driver to launch a planar wave, the effects of the body of the air behind the diaphragm would become one-dimensional and would decompose to a linear phenomenon (which you so aptly demonstrated through your citation), not that it would be able to be corrected. The purpose of this thread was to determine if it was possible to mitigate the effects of enclosure resonances that are absent in open baffle designs ... to see if we could isolate the enclosure resonances into something that is able to be manipulated to our liking. The anticipated discussion that followed my initial post was to determine what techniques we could use to correct the linear distortion. Signal processing was proposed as a possible technique to achieve that goal, but following the discussion it is found to be inadequate in dealing with nulls.

[Dennis H]

I see that as a distinction without a difference. If you have to stuff the box, it really doesn't matter what size or shape the box is or whether you're generating simulated plane waves or whatever. It could be a tower design where the height dimension is critical and the same principle applies -- stuff the box to reduce resonances. All the rest is just a distraction from the big picture.

[thadman]

Is there a reason this thread (Enclosure resonances, not a big deal?) was moved to the Audio Hideout section? I'm confused as to how this thread is more relevant to:

Audio Hideout
For the connoisseur of fine audio. Whether 2 channel and multichannel format, solid state and tube electronics, discuss it here. Also, hardware related SACD, DVD Audio, vinyl, high end speakers and audio enhancements including high end cables.

than

Mission Possible DIY
DIY (Do it yourself): Cabinetry, speakers, subwoofers, crossovers, measurements. Jon and Thomas have probably designed and built as many speakers as any non-professionals. Who are we kidding? They are pros, they just don't do it for a living. This has got to be one of the most advanced places on the net to talk speaker building, period.

[AJINFLA]

This has got to be one of the most advanced places on the net to talk speaker building, period.

Correct. Not discussing the inane, post upon post over the years.
If you have ever actually built a loudspeaker system, let's see it.

[thadman]

Correct. Not discussing the inane, post upon post over the years.
If you have ever actually built a loudspeaker system, let's see it.

Here's a link to my last build thread

http://www.emsqforum.com/forum/showthread.php?t=334

It utilizes 13 individual layers stacked horizontally. A Matrix bracing system encompasses the volume of the cabinet. The Y(top to bottom) and Z(front to back) directions are braced by planes with 1-1/4" circles routed out every 1/2". 39 dowel rods spaced every inch (X and Y direction) brace the structure in the X(side to side direction) and penetrate every panel.

The top (front and back) and bottom (front and back) utilize a 1-1/2" roundover, while the sides utilize a 3/4" roundover.

Corning Owens 703 permeates the the entire matrix, disrupting any resonances that may be present in the enclosure.

I do not have finished (Drivers installed, High Gloss Piano Black finish) photos on the net yet, however that can be arranged.

Here is a photo of the matrix bracing system (without stuffing)

initial wood (367lbs!) :E




The panels that require routing :E



Template




Routing Template


Drill Bits Used



Bare, unrouted X,Z matrix panels



Routed, Drilled X,Z matrix panels



Interior Routing Template


Bare, unrouted interior panels


Routed Internal Panels














External Structure (not sanded)







Just because I haven't posted a construction thread on this forum, does not mean I'm not an active speaker builder.

Is that sufficient enough for you?

[AJINFLA]

Here's a link to my last build thread
http://www.emsqforum.com/forum/showthread.php?t=334

Never heard of that forum and do not intend to join just to see what you should have posted on other forums. Including this one.

Is that sufficient enough for you?

It's not for me. It's for you.
So you have built and listened to enough speakers now to where you have all the basics comfortably squared away and can now obsess with these minutiae?
When you make statements that belie an understanding of the fundamentals (yes, I read other forums)?
Can we see how you got to this point? What came before this exotic (and IMO, completely unnecessary) construction? On what basis do you believe that this will improve the sound in your room (you know, the part coming off the front of the cone and baffle)? Or is that even a goal?

[thadman]

Never heard of that forum and do not intend to join just to see what you should have posted on other forums. Including this one.


It's not for me. It's for you.
So you have built and listened to enough speakers now to where you have all the basics comfortably squared away and can now obsess with these minutiae?
When you make statements that belie an understanding of the fundamentals (yes, I read other forums)?
Can we see how you got to this point? What came before this exotic (and IMO, completely unnecessary) construction? On what basis do you believe that this will improve the sound in your room (you know, the part coming off the front of the cone and baffle)? Or is that even a goal?

Why all of the hostility?

To be honest, during my last build I wasn't very concerned with whether or not my construction was unnecessary or excessive. It was simply my attempt at building the most structurally inert enclosure I could design based on the research I had done and the tools I had access to. Following my research, I believed the matrix bracing system to be an improvement over traditional bracing techniques, which offered me the peace of mind of knowing that cabinet resonances present in my system would be a non-issue relative to other systems. I wasn't sure if my efforts would lead to an appreciable difference in sound quality relative to a more traditional braced enclosure, but that was a non-issue for me as I was interested in the design/construction of the loudspeaker. Besides, how would I know without trying it? It's not like I'm trying to convince a group of investors to fund this project, it's my personal loudspeaker.

[brianpowers27]

Thadman,

Don't sweat AJ. He is quite helpful, when you change your perspective. If you are easily offended, he will offend you. Otherwise he will challenge you.

That is a mightily reinforced cabinet. Were you concerned that the bracing structure would create it's own set of unique resonances?

If I understand you correctly you are saying that a box with speakers limited to a frequency whose wavelength is no more than 4x times the least dimension of the box will result in a rear planar wave. This wave should be absorbed by the cabinet without a great amount of resonance.

Maybe I am missing the next detail. Is the back of the cabinet open?

[brianpowers27]

Here's a link to my last build thread

http://www.emsqforum.com/forum/showthread.php?t=334

No one can view the page without an account. Accounts are granted by invitation only.

[thadman]

Yup, that's way oversimplifying it. The box air spring isn't linear because the temperature increases as the cone moves into the box and decreases as it moves out of the box -- the old PV=nRT thing. That leads to non-linear distortion, mostly 2nd harmonic.

Box air-spring distortion % = 140 * (one-way driver swept volume) / (box volume)

This is very interesting. So basically the maximum output capability (below distortion threshold) of a system (displacement=SPL) is limited by the compression of mass of air behind the diaphragm.

I'm assuming the distortion is due to the difference in pressure between the sides of the cone. Or is that an incorrect assumption?

What effect will the decay of the temperature within the volume of air have on the system?

[AJINFLA]

Btw, congrats thad. You've changed the format of the forum .
Got a question. I see you are in Indiana. Will these be ready for Dayton DIY?

[brianpowers27]

Btw, congrats thad. You've changed the format of the forum .
Got a question. I see you are in Indiana. Will these be ready for Dayton DIY?

No doubt. The newbie comes in and changes everything. Not a bad change though!

What part of Indiana? Fort Wayne? :W

[thadman]

Btw, congrats thad. You've changed the format of the forum .
Got a question. I see you are in Indiana. Will these be ready for Dayton DIY?

When / Where is Dayton DIY? I will be in Munich from July 13th to August 12th.

I'm perfectly satisfied with my current monitors on most content, but the single midwoofers strain at higher amplitudes (>100dB), especially if the signal contains a lot of LF content. Supermodified by Amon Tobin is a supreme example ... my midwoofers aren't a big fan of this record at higher amplitudes.

For the most recent build, I picked up a pair of TD15M Apollo drivers as well as a pair of Beyma TPL-150 AMTs. I'd like to do a 2-way, but I have some reservations. A PHL 1120 (or AE TD6.5M if its EVER released) could potentially be added as a transition driver if synergy is not achieved between the TD15M and TPL150.

The TD15M with its unique cone profile and corresponding modal behavior makes polar response calculations quite difficult. John has mentioned that it is flat to 4khz and suitable off-axis to 2khz. We'll soon see how true this claim is. Polar response measurements will have to be taken to see how suitable it is as a midrange driver and how high it can really reproduce off-axis.

StigErik (over on DIYAudio) uses a pair of TPL-150s in his current design and has them crossed to a Seas W22 around 1400hz without issues. I've got a few ideas for potential tweaks that may benefit performance.

I plan on removing the rear enclosure of the TPL-150 and instead of operating them dipole, I'll place them in a 16" stuffed transmission line. The attenuation should be significant above 200hz, as 16" is roughly 1/4 wavelength of 200hz.

I'm also interested in placing the TPL-150 in a DIY waveguide. Due to the drivers dimensions, construction of the waveguide should be relatively straightforward and painless. With 90* horizontal and 30* or so vertical, a 1khz crossover shouldn't be a problem. The commercial waveguides (TPL-150H) could be ordered if the DIY version doesn't measure up.

Fuzzmeasure Pro software has been purchased for measurements along with an Apogee Duet. The microphone however has not. I'd like to purchase an Earthworks product, but haven't found a good deal yet.

Any input?

[thadman]

No doubt. The newbie comes in and changes everything. Not a bad change though!

What part of Indiana? Fort Wayne? :W

Fort Wayne / West Lafayette

[A9X]

StigErik (over on DIYAudio) uses a pair of TPL-150s in his current design and has them crossed to a Seas W22 around 1400hz without issues. I've got a few ideas for potential tweaks that may benefit performance.

I plan on removing the rear enclosure of the TPL-150 and instead of operating them dipole, I'll place them in a 16" stuffed transmission line. The attenuation should be significant above 200hz, as 16" is roughly 1/4 wavelength of 200hz.

I'm also interested in placing the TPL-150 in a DIY waveguide. Due to the drivers dimensions, construction of the waveguide should be relatively straightforward and painless. With 90* horizontal and 30* or so vertical, a 1khz crossover shouldn't be a problem. The commercial waveguides (TPL-150H) could be ordered if the DIY version doesn't measure up.

I have been thinking about doing something similar with the TPL, a handmade OS WG (balsa and resin was my working idea) but crossing to a TD10M, which I already own. The drivers are expensive, and I just bought a new apartment so funds prohibit until I can sell some of my surplus drivers and parts (and finish my Unity's). The terminated transmission line is something I have done with mids with success, but it never occurred to me to use it with the Beyma.

I'll watch you progress with keen interest.

Fuzzmeasure Pro software has been purchased for measurements along with an Apogee Duet. The microphone however has not. I'd like to purchase an Earthworks product, but haven't found a good deal yet.

Any input?

I'm a PC guy and have Soundeasy, but I have a new calibrated measurement mic from IBK in Germany, same unit Illka used for his sub tests. Much cheaper than Earthworks, which are very expensive down here.

[Smokinghot]

No doubt. The newbie comes in and changes everything. Not a bad change though!

If they really wanted to clean up Mission Impossible. All they'd really need to do is create a place for all the Statement builds.

[brianpowers27]

When / Where is Dayton DIY? I will be in Munich from July 13th to August 12th.

Here is a link to the Official Dayton 2009 DIY thread. July 11, Dayton, OH

http://techtalk.parts-express.com//showthread.php?t=210790

Fort Wayne / West Lafayette

I am a FW resident myself.

[Dennis H]

Last I heard, B&H Photo had the best price on Earthworks mics, something like $440 for the M23 and $550 for the M30. You have to call them to get the good price.

[thadman]

I have been thinking about doing something similar with the TPL, a handmade OS WG (balsa and resin was my working idea) but crossing to a TD10M, which I already own. The drivers are expensive, and I just bought a new apartment so funds prohibit until I can sell some of my surplus drivers and parts (and finish my Unity's). The terminated transmission line is something I have done with mids with success, but it never occurred to me to use it with the Beyma.

What curve were you interesting in using?

Some options:

Rectangular waveguide.
Pros

Easy to construct
Cheap to build (mdf/BB ply)

Cons

may not be the last word in uniform directivity control

Elliptical waveguide
Pros

improved radiation pattern

Cons

Fiberglass construction (no previous experience)