Member
Joined 2009
Hi everyone,
This design will incorporate known solutions to control directivity over most of the audible range. It's currently only a concept but I'm looking to construct a prototype soon. It will be a slow advancing endeavor with projected completion for the late summer. If someone else likes my plan and decides to pursue something similar at a faster rate I will be happy to exchange observations and ideas. Constructive suggestions are welcome although I already have my mind set on how to achieve most of my goals.
- Goals:
I believe the perfect speaker should be able to play well in most listening environments. I want a solution that reduces the negative effects of the listening room while retaining most of the positive ones. Although there is much disagreement and mystery surrounding the human auditory perception I think there is considerable consensus on the following topics:
Constant Directivity - In the highly reflective environment of the typical home, the quality of sound that speakers radiate off-axis is almost as important as it is on-axis. Differences in the direct and reflected sound are audible and detrimental for stereo imaging. Constant directivity designs are often difficult but reduce the impact of other aspects of concern such as cabinet reflections and the need for room treatment.
Floor and ceiling reflections - Ideally, one would want to eliminate all unwanted reflections but in practice our auditory perception is less sensitive on the vertical axis than the horizontal. For that reason and in order to reduce the complexity of the design, I choose to relax the requirements on the vertical response to what is generally acceptable. The vertical lobe resulting from the tweeter-mid crossover should allow at least a 30 degree listening window to accommodate a seated position. Ceiling reflections will not be addressed, however I aim to eliminate the "floor bounce" problem which is known to negatively affect the perception of midbass.
Reducing reflected sound - Very often home speakers end up in the worst acoustic place - close to a room corner. While subwoofers can happily utilize corner loading for extra gain, the region between 50-500Hz can suffer serious irregularities. Waveguide based designs control dispersion well at the high end but their mids and bass are not immune to this phenomena. Dipole designs reduce lateral radiation but there is still considerable amount of energy at the rear of the speaker which can become a problem. My goal is to extend unipolar dispersion to the lower frequencies. The listener will be able to control the amount of room interaction by toeing in the speaker.
Flat frequency response - I aim for a very linear response on axis (+-1.5dB) while allowing for progressively relaxed limits off-axis to +-3dB at 45deg. I might be setting very strict requirements but I feel that this is doable with the help of DSP filters and quality drivers.
Low frequency extension - Based on personal preference I would like to have an F3 of 30Hz and I'm afraid I will need a dedicated subwoofer to reach that. A well designed 12" monopole subwoofer will be able to get there and multiple subs will be even better. I think it will be best to relieve the speaker from the stress of reproducing low frequencies in controlled directivity at the point where the effects of the room begin to matter less. Ideally this speaker should be able to cross over to a sub at 80Hz or lower. However, I will leave this requirement somewhat open for now because I'm not sure what the optimal crossover point is. Also I would like to run some experiments and get real-life data on the low end extension without a sub.
SPL - I don't play very loud and this is a low priority for me. I'm much more concerned with minimizing audible distortion. I will be satisfied if the system is able to hit peaks of 105dB without running out of excursion or power.
Linear phase - Currently I'm using IIR filters in my main system to arrive at a fairly linear phase response through the critical 300-3000Hz range. It's admittedly hard to hear phase distortion but since I'm spoiled with it now, it will be difficult to justify building a new speaker without it. Linear phase will be easy with FIR filters and they are quickly becoming more available so that's an option to consider as well.
Space considerations - Many households don't have the luxury of a large living room. Unless high efficiency is desired there is no need for refrigerator size monsters. In terms of size I feel that the typical floorstander speaker with a slim baffle is good reference point.
- Design:
To control the directivity at the highs and mids this speaker follows the design ideas developed by MarkK for the popular ER18DXT. At first I thought that I can easily come up with a more original driver pair but eventually I came to understand just how many considerations went into Mark's decision. There aren't many tweeters that license the DXT technology and I didn't want to use a large waveguide because I prefer to keep the drivers as close as possible. The Seas 27TBCD/GB-DXT is probably the best option for a tweeter because of it's excellent directivity control and a small package.
As for a midwoofer there are a lot of capable drivers at the <$100 price point. The underhung Tangband W6-1721, the Pierless Exclusive HDS 830883, the SB17NRX35 and the Dayton RS180 can all work in this application. But after much consideration I could not pick a replacement for the Seas ER18RNX. Honestly, I don't think I can pass on the looks of that reed/paper cone.
- MarkK's ER18DXT: The Seas ER18DXT ported two way
MarkK's ER18DXT succeeds in keeping excellent directivity control from the high end down to about 800Hz where the woofer begins to radiate in full space. My goal is to extend the half-space radiation pattern as low as possible. Running the ER18RNX in an open baffle configuration can retain a constant directivity pattern because energy from the back of the driver will interfere with the front wave and prevent sound radiation to develop into full space. One way to get a cardioid radiation pattern at low frequencies is to build a lossy box with holes and fill it with absorbing material. The idea is to attenuate the sound energy at the back of the driver but not fully absorb it. There are a few existing designs and experiments with lossy boxes that show very promising results.
- Keyser: http://www.diyaudio.com/forums/multi-way/192737-2-way-waveguide-cardioid-like.html
- Kimmo Saunisto: Cardioid bass
A great amount of displacement is required with the lossy box method in order to retain decent sensitivity at low frequencies. Since I want a slim baffle for aesthetic reasons I decided to have a group of four 8" woofers handle the low end. I have my heart set on the Dayton RS225 but I didn't make a final decision yet because of the price for 8 of these. The lossy box construction will undoubtedly hinder bass performance. If an additional subwoofer is need to cover the lowest octave, it's more sensible to use much cheaper guitar speakers instead. On the other hand it might be possible to get satisfactory bass from four 8" drivers at normal listening levels. I don't expect to get much output below 50Hz even with a Linkwitz Transform but even a little may turn out to be acceptable in a small living room like mine.
The crossover will be implemented in DSP using the KX-Project driver for the prototype speaker. I plan to upgrade to miniDSP or another suitable platform later on. On my current system I implemented a phase linear crossover designed by Jean-Michel LeCleac'h. It uses 3rd order Butterworth slopes with a calculated offset and a digital delay to align the phase response. It produces excellent results but I didn't have to worry about the vertical lobe in my previous speaker. With this new design I'm concerned that the digital time delay may result in an undesirable tilt of the vertical response.
Le Cleac'h crossover: Expanded Soundstaging and 3D-Imaging
- Prototype:
There are still many unknowns surrounding this design so building a prototype and taking measurements is of high priority. I hope to get insight in the following areas of concern:
- Will damping the rear wave result in the desired cardioid response? How does the composition, thickness and placement of the absorbing material affect the response?
- What will the vertical polar response look like? Will the mid-tweeter crossover allow a good listening window? Will the bass array integrate well with the midwoofer?
- What are the best crossover points and slopes?
- Will the off-axis response remain linear throughout the entire system bandwidth?
- How can I improve the construction of the box to address vibration issues? I want to experiment with magnet-mounting the woofers. Some dipole designs run woofer arrays in alternate polarities (push-pull) to reduce vibrations and I wonder if that approach will work here?
- What is the low end limit of this speaker in terms of safe driver excursion? Will I be happy without an extra subwoofer?
- Most importantly, does cardioid midbass reduce room interactions enough to be worth the extra work?
This design will incorporate known solutions to control directivity over most of the audible range. It's currently only a concept but I'm looking to construct a prototype soon. It will be a slow advancing endeavor with projected completion for the late summer. If someone else likes my plan and decides to pursue something similar at a faster rate I will be happy to exchange observations and ideas. Constructive suggestions are welcome although I already have my mind set on how to achieve most of my goals.
- Goals:
I believe the perfect speaker should be able to play well in most listening environments. I want a solution that reduces the negative effects of the listening room while retaining most of the positive ones. Although there is much disagreement and mystery surrounding the human auditory perception I think there is considerable consensus on the following topics:
Constant Directivity - In the highly reflective environment of the typical home, the quality of sound that speakers radiate off-axis is almost as important as it is on-axis. Differences in the direct and reflected sound are audible and detrimental for stereo imaging. Constant directivity designs are often difficult but reduce the impact of other aspects of concern such as cabinet reflections and the need for room treatment.
Floor and ceiling reflections - Ideally, one would want to eliminate all unwanted reflections but in practice our auditory perception is less sensitive on the vertical axis than the horizontal. For that reason and in order to reduce the complexity of the design, I choose to relax the requirements on the vertical response to what is generally acceptable. The vertical lobe resulting from the tweeter-mid crossover should allow at least a 30 degree listening window to accommodate a seated position. Ceiling reflections will not be addressed, however I aim to eliminate the "floor bounce" problem which is known to negatively affect the perception of midbass.
Reducing reflected sound - Very often home speakers end up in the worst acoustic place - close to a room corner. While subwoofers can happily utilize corner loading for extra gain, the region between 50-500Hz can suffer serious irregularities. Waveguide based designs control dispersion well at the high end but their mids and bass are not immune to this phenomena. Dipole designs reduce lateral radiation but there is still considerable amount of energy at the rear of the speaker which can become a problem. My goal is to extend unipolar dispersion to the lower frequencies. The listener will be able to control the amount of room interaction by toeing in the speaker.
Flat frequency response - I aim for a very linear response on axis (+-1.5dB) while allowing for progressively relaxed limits off-axis to +-3dB at 45deg. I might be setting very strict requirements but I feel that this is doable with the help of DSP filters and quality drivers.
Low frequency extension - Based on personal preference I would like to have an F3 of 30Hz and I'm afraid I will need a dedicated subwoofer to reach that. A well designed 12" monopole subwoofer will be able to get there and multiple subs will be even better. I think it will be best to relieve the speaker from the stress of reproducing low frequencies in controlled directivity at the point where the effects of the room begin to matter less. Ideally this speaker should be able to cross over to a sub at 80Hz or lower. However, I will leave this requirement somewhat open for now because I'm not sure what the optimal crossover point is. Also I would like to run some experiments and get real-life data on the low end extension without a sub.
SPL - I don't play very loud and this is a low priority for me. I'm much more concerned with minimizing audible distortion. I will be satisfied if the system is able to hit peaks of 105dB without running out of excursion or power.
Linear phase - Currently I'm using IIR filters in my main system to arrive at a fairly linear phase response through the critical 300-3000Hz range. It's admittedly hard to hear phase distortion but since I'm spoiled with it now, it will be difficult to justify building a new speaker without it. Linear phase will be easy with FIR filters and they are quickly becoming more available so that's an option to consider as well.
Space considerations - Many households don't have the luxury of a large living room. Unless high efficiency is desired there is no need for refrigerator size monsters. In terms of size I feel that the typical floorstander speaker with a slim baffle is good reference point.
- Design:
To control the directivity at the highs and mids this speaker follows the design ideas developed by MarkK for the popular ER18DXT. At first I thought that I can easily come up with a more original driver pair but eventually I came to understand just how many considerations went into Mark's decision. There aren't many tweeters that license the DXT technology and I didn't want to use a large waveguide because I prefer to keep the drivers as close as possible. The Seas 27TBCD/GB-DXT is probably the best option for a tweeter because of it's excellent directivity control and a small package.
As for a midwoofer there are a lot of capable drivers at the <$100 price point. The underhung Tangband W6-1721, the Pierless Exclusive HDS 830883, the SB17NRX35 and the Dayton RS180 can all work in this application. But after much consideration I could not pick a replacement for the Seas ER18RNX. Honestly, I don't think I can pass on the looks of that reed/paper cone.
- MarkK's ER18DXT: The Seas ER18DXT ported two way
MarkK's ER18DXT succeeds in keeping excellent directivity control from the high end down to about 800Hz where the woofer begins to radiate in full space. My goal is to extend the half-space radiation pattern as low as possible. Running the ER18RNX in an open baffle configuration can retain a constant directivity pattern because energy from the back of the driver will interfere with the front wave and prevent sound radiation to develop into full space. One way to get a cardioid radiation pattern at low frequencies is to build a lossy box with holes and fill it with absorbing material. The idea is to attenuate the sound energy at the back of the driver but not fully absorb it. There are a few existing designs and experiments with lossy boxes that show very promising results.
- Keyser: http://www.diyaudio.com/forums/multi-way/192737-2-way-waveguide-cardioid-like.html
- Kimmo Saunisto: Cardioid bass
A great amount of displacement is required with the lossy box method in order to retain decent sensitivity at low frequencies. Since I want a slim baffle for aesthetic reasons I decided to have a group of four 8" woofers handle the low end. I have my heart set on the Dayton RS225 but I didn't make a final decision yet because of the price for 8 of these. The lossy box construction will undoubtedly hinder bass performance. If an additional subwoofer is need to cover the lowest octave, it's more sensible to use much cheaper guitar speakers instead. On the other hand it might be possible to get satisfactory bass from four 8" drivers at normal listening levels. I don't expect to get much output below 50Hz even with a Linkwitz Transform but even a little may turn out to be acceptable in a small living room like mine.
The crossover will be implemented in DSP using the KX-Project driver for the prototype speaker. I plan to upgrade to miniDSP or another suitable platform later on. On my current system I implemented a phase linear crossover designed by Jean-Michel LeCleac'h. It uses 3rd order Butterworth slopes with a calculated offset and a digital delay to align the phase response. It produces excellent results but I didn't have to worry about the vertical lobe in my previous speaker. With this new design I'm concerned that the digital time delay may result in an undesirable tilt of the vertical response.
Le Cleac'h crossover: Expanded Soundstaging and 3D-Imaging
- Prototype:
There are still many unknowns surrounding this design so building a prototype and taking measurements is of high priority. I hope to get insight in the following areas of concern:
- Will damping the rear wave result in the desired cardioid response? How does the composition, thickness and placement of the absorbing material affect the response?
- What will the vertical polar response look like? Will the mid-tweeter crossover allow a good listening window? Will the bass array integrate well with the midwoofer?
- What are the best crossover points and slopes?
- Will the off-axis response remain linear throughout the entire system bandwidth?
- How can I improve the construction of the box to address vibration issues? I want to experiment with magnet-mounting the woofers. Some dipole designs run woofer arrays in alternate polarities (push-pull) to reduce vibrations and I wonder if that approach will work here?
- What is the low end limit of this speaker in terms of safe driver excursion? Will I be happy without an extra subwoofer?
- Most importantly, does cardioid midbass reduce room interactions enough to be worth the extra work?
Attachments
Last edited:
That's a really beautiful project, lot of good points that are barely seen on the same speaker, the cardioid bass section gives a nice touch of originality. You can expect either nice results and a lot of fun before finishing it.
But I am not so enthusiastic about the Le Cleac'h filter and it's implementation.
First, it's not a linear phase or whatever but only a "quasi optimal", more conceived by his author with in mind something easy to do and accessible to a majority of DIYers, than challenging the ultimate transient perfect.
Second point, finally it's not at all easy to do. There is a gap between the theory and it's application, the drivers have to be textbook linear, the Fc far from their natural roll offs.
In other words, the magic recipe of the spreadsheet needs a lot of measurements and a parametric EQ to comply the target...all this for at best a quasi optimal. This said for the sake of discussion, the important goal is only listening.
I have also the KX drivers on my PC, pretty amazing for a freeware. They are perfectly able to do the job.
You are right of thinking bracing and magnet mounted drivers, the side panels can be vibration friendly. Will you separate the mid cavity from the boomers ?
good luck!
But I am not so enthusiastic about the Le Cleac'h filter and it's implementation.
First, it's not a linear phase or whatever but only a "quasi optimal", more conceived by his author with in mind something easy to do and accessible to a majority of DIYers, than challenging the ultimate transient perfect.
Second point, finally it's not at all easy to do. There is a gap between the theory and it's application, the drivers have to be textbook linear, the Fc far from their natural roll offs.
In other words, the magic recipe of the spreadsheet needs a lot of measurements and a parametric EQ to comply the target...all this for at best a quasi optimal. This said for the sake of discussion, the important goal is only listening.
I have also the KX drivers on my PC, pretty amazing for a freeware. They are perfectly able to do the job.
You are right of thinking bracing and magnet mounted drivers, the side panels can be vibration friendly. Will you separate the mid cavity from the boomers ?
good luck!
Love what you've got in mind.
I think you can do a good bit better. Dave Pellegrine at Parts Express has developed a waveguide for the CSS LD25X and some other tweeters for example. Love everything else though. The CA18RLY might just make more sense than the ER18RNX as a dedicated mid though.
I think you can do a good bit better. Dave Pellegrine at Parts Express has developed a waveguide for the CSS LD25X and some other tweeters for example. Love everything else though. The CA18RLY might just make more sense than the ER18RNX as a dedicated mid though.
The DXT tweeter is very good for a 2k crossover point second order acoustic slope. I know the CSS tweeter measures very well and with a larger waveguide can cross lower but at almost 3 times the cost, not sure if its worth it.
I've built Mark's design and it easily competes with any 2-way standmount out there. The tweeter doesnt have me yearning for anything more expensive, and ive heard all the exi scan speak domes but as always, your mileage may vary!
Boris, I think this speaker will be great
Are you sure about those vertical reflections? Reading through some threads here at diyaudio left me with the impression that vertical reflections are worse than horisontal and always detrimental to sound quality (mainly in the lower mid bass region). OTOH delayed lateral reflections should be beneficial.. Maybe I should re-read the giant directivity thread again?!? 
Are you sure about those vertical reflections? Reading through some threads here at diyaudio left me with the impression that vertical reflections are worse than horisontal and always detrimental to sound quality (mainly in the lower mid bass region). OTOH delayed lateral reflections should be beneficial.. Maybe I should re-read the giant directivity thread again?!?
No, I think you have it about right. It is much more important to deal with the veritical reflections than the lateral reflections, especially if the lateral reflections can come later in time. Floor ceiling and back wall reflections are hard for the ear to seperate out and end up being perceived as frequency response errors. Late lateral reflections add spaciousness to the sound.
David S.
I am planning a very similar speaker build.
My front baffle will be slightly wider: total around 35-40cm.
And there will be no side panels.
I might experiment with damping of the rear wave too.
Driver set-up will be similar: 3 way with 4x8" woofers.
I will add two subwoofers if needed: closed box or H-frame OB.
I am going for vintage alnico Seas drivers.
Woofers are Seas 21TV-EW (I already have 8 of those).
I hate rubber/foam surround, high excursion midrangers.
My choice of midrange is a 8" cloth/paper surround widerange driver with a qts of 0.7
Mids will be either Seas 21TV-G or 21TV-GW (I have both in hand).
For HF I will start with the Seas 9TV-LG and 5TV-HF combination (I know that makes it 4 way).
Seas 21-9-5 combo works very well with first order CO as used in many commercial speakers of 1970s.
I will initially try first order for the woofers too. Might end up going active/dsp for them.
For HF I will later try Heil AMT (small one, I have in hand) and perhaps B&G Neo3.
My front baffle will be slightly wider: total around 35-40cm.
And there will be no side panels.
I might experiment with damping of the rear wave too.
Driver set-up will be similar: 3 way with 4x8" woofers.
I will add two subwoofers if needed: closed box or H-frame OB.
I am going for vintage alnico Seas drivers.
Woofers are Seas 21TV-EW (I already have 8 of those).
I hate rubber/foam surround, high excursion midrangers.
My choice of midrange is a 8" cloth/paper surround widerange driver with a qts of 0.7
Mids will be either Seas 21TV-G or 21TV-GW (I have both in hand).
For HF I will start with the Seas 9TV-LG and 5TV-HF combination (I know that makes it 4 way).
Seas 21-9-5 combo works very well with first order CO as used in many commercial speakers of 1970s.
I will initially try first order for the woofers too. Might end up going active/dsp for them.
For HF I will later try Heil AMT (small one, I have in hand) and perhaps B&G Neo3.
Member
Joined 2009
Yes, it sounds like we are working on very similar designs. I'm looking forward to share experiences.
I am considering not having side and rear panels as well. I'm thinking of building the whole thing around a rigid skeleton that holds the woofers and the front baffle. Absorbing material can be secured to the driver basket and the rear of the speaker can be covered with fabric.
----
Here is a quick simulation I did with DSP that you might find interesting. It looks at how 1st order filters may crossover in an open baffle. Let me state however, that although the simulation looks good electrically, I did not verify it acoustically and I give no guarantees that it works as shown.
My baffle size causes a natural response roll-off to occur at 500Hz. I'm using a 1st order high-pass filter on all simulated drivers to account for that. The red trace represents the midwoofer. The green trace represents 4 woofers on the same baffle. I discovered that in order to sum all of them flat the 4 woofers require a 1st order filter low pass filter at 125Hz. So in essence, when dealing with 1st order slopes, quadrupling the number of woofers on the low end allows the crossover point for the LP to be moved back 2 octaves.
Attachments
I've got a 2-way thing developing right now, so this will be a very interesting project to follow. Little if any of what I've done/noticed so far will apply directly to what you've proposed here but I'd still like to offer up a couple of points FWIW.
My bass is handled with a 0.47Qt driver (12") firstly on pure OB with minimal support below which evolved into full length wings @10" of depth, a narrower cap above for tweeter support and a bottom of roughly the same depth as the sides as the speaker is elevated off the floor about 10". Bass response was enhanced with the bigger wings ... wing resonance seemed to be confined to a small frequency area and was only really problematic at pretty high SPL.
The damping was tried as per various www resources (keysers thread, johnk, and many others) The thing, for me, that changed with all of the usual damping attempts .. just from a purely listening perspective now ... is that the speaker begins down the road to "sounding like a box". More damping, more box sound ... dead/lifeless .. especially in the mid range. Even just adding the full length wings changed the sound from pure OB to more like a box ... and it EQ's like that as well.
EGDE, at least, was not at all helpful in modeling an expected response with a "U" frame. My suspicion is that as side wings fold more toward the perpendicular ... the driver(s) sound characteristics, that you'd hear in a box alignment, become more "enhanced". I think the amount of damping might therefore become more room dependent than anything else as far as listening enjoyment is concerned. More of a "valve" for spacial level than anything.
Sadly, I don't have any hard data to share as I'm just getting deeper into this fascinating hobby. Good luck with your project boris81 !
My bass is handled with a 0.47Qt driver (12") firstly on pure OB with minimal support below which evolved into full length wings @10" of depth, a narrower cap above for tweeter support and a bottom of roughly the same depth as the sides as the speaker is elevated off the floor about 10". Bass response was enhanced with the bigger wings ... wing resonance seemed to be confined to a small frequency area and was only really problematic at pretty high SPL.
The damping was tried as per various www resources (keysers thread, johnk, and many others) The thing, for me, that changed with all of the usual damping attempts .. just from a purely listening perspective now ... is that the speaker begins down the road to "sounding like a box". More damping, more box sound ... dead/lifeless .. especially in the mid range. Even just adding the full length wings changed the sound from pure OB to more like a box ... and it EQ's like that as well.
EGDE, at least, was not at all helpful in modeling an expected response with a "U" frame. My suspicion is that as side wings fold more toward the perpendicular ... the driver(s) sound characteristics, that you'd hear in a box alignment, become more "enhanced". I think the amount of damping might therefore become more room dependent than anything else as far as listening enjoyment is concerned. More of a "valve" for spacial level than anything.
Sadly, I don't have any hard data to share as I'm just getting deeper into this fascinating hobby. Good luck with your project boris81 !
Member
Joined 2009
Thank you for your input!
I'm afraid you are right that the amount of damping will have to be determined by experimentation. My idea is to start with a nice looking polar and continue from there. I have doubts about this method being able to hold a cardioid response for a wide bandwidth.
As for your design it sounds like you are working with a U-frame box. Note in JohnK's articles that a U-frame design develops a resonance above the dipole peak. He uses the U-frame only below the resonance point <100Hz. I doubt that U-frame will work well in the mids even when damped well. A damped lossy box with holes on the side behaves differently than a U-frame.
NaO U-frame
I have experimented with dipole rear wave damping in the past.
But my experience is limited to over 1500Hz, because the testing was done on my Heil AMT driver (Oskar Heil Syrinx speaker).
First of all reflections are not problematic for up to a meter of distance from the wall.
I think for lower frequencies you may go even lower.
At higher distance, perhaps because of reflection delay, the effect gets problematic.
Any damping that blocks the free air flow in the back of the driver has negative effects.
Best dipole damping that worked for me was a spheric shaped wool/sponge right behind the driver.
I am also thinking of wrapping my diy built by speaker cloth, giving it a pseudo-box look.
But my experience is limited to over 1500Hz, because the testing was done on my Heil AMT driver (Oskar Heil Syrinx speaker).
First of all reflections are not problematic for up to a meter of distance from the wall.
I think for lower frequencies you may go even lower.
At higher distance, perhaps because of reflection delay, the effect gets problematic.
Any damping that blocks the free air flow in the back of the driver has negative effects.
Best dipole damping that worked for me was a spheric shaped wool/sponge right behind the driver.
I am also thinking of wrapping my diy built by speaker cloth, giving it a pseudo-box look.
Member
Joined 2009
Thank you everyone for the encouraging comments!
Let me address some of the concerns that were raised previously.
The Le Cleac'h crossover is an topic on it's own and I would rather open a separate thread if there is enough interest. I made a 1st order Butterworth module for KX-Project, which cascaded with their LP or HP (at a Q-value of .71) gives a 3rd order Butterworth. Anyway, I have it working well already and it passes square waves but it's not perfect like you said. In any case, I'm flexible on the crossover ad I'd love to try different options as DSP makes it so easy.
Thank you for the suggestions!
I was not familiar with the CSS LD25X and after researching it, it looks like a great driver. Those waveguide experiments show some incredible results indeed! However, as "samadhi" already pointed out, it will not bring ground-breaking improvement over what I already have.
For all important parameters the CA18RLY and the ER18RNX are more or less the same. Except the ER18RNX is prettier. I believe the CA18RLY is targeted for sealed enclosures which makes no difference in my case. There are some very subtle differences that make the ER18RNX a better choice. For example the specs show better sensitivity for the CA18RLY but that's misleading because I don't have to do baffle step compensation and in my application the ER18RNX may gain a few dB.
Let me address some of the concerns that were raised previously.
The Le Cleac'h crossover is an topic on it's own and I would rather open a separate thread if there is enough interest. I made a 1st order Butterworth module for KX-Project, which cascaded with their LP or HP (at a Q-value of .71) gives a 3rd order Butterworth. Anyway, I have it working well already and it passes square waves but it's not perfect like you said. In any case, I'm flexible on the crossover ad I'd love to try different options as DSP makes it so easy.
Thank you for the suggestions!
I was not familiar with the CSS LD25X and after researching it, it looks like a great driver. Those waveguide experiments show some incredible results indeed! However, as "samadhi" already pointed out, it will not bring ground-breaking improvement over what I already have.
For all important parameters the CA18RLY and the ER18RNX are more or less the same. Except the ER18RNX is prettier.
I believe the CA18RLY is targeted for sealed enclosures which makes no difference in my case. There are some very subtle differences that make the ER18RNX a better choice. For example the specs show better sensitivity for the CA18RLY but that's misleading because I don't have to do baffle step compensation and in my application the ER18RNX may gain a few dB.Member
Joined 2009
Vertical response
There's definitely room for improvement with my design on the vertical axis. Let me elaborate my reasoning and the choices I made may become more clear.
Delayed horizontal(lateral) reflections add spaciousness and reinforce the stereo image but the off-axis frequency response must be similar to the direct one. This may or may not have to do with the fact that above 1600Hz we localize sound based on the level. In any case, successful Constant Directivity designs give evidence to that.
I'm not convinced that vertical reflections in that frequency region have a pronounced effect on sound perception. Evidence to that is the fact that almost all speakers out there are designed with severe nulls on the vertical axis. If the vertical reflections were indeed more important sideways D'Appolitos will be ruling the market
When speaking about lower frequencies I will agree that all reflections are detrimental. As the wavelength grows the room boundaries start to interact with the sound even before the waves are fully developed. The walls closest to the speaker begin to shape the sound. Reinforcements and cancellations develop both horizontally and vertically, at the same time. When I look at ripple tank simulations I find it incredible that we can hear anything at all!
Conventional speakers have omnipolar radiation at lower frequencies. They illuminate all 6 walls although the first 5 are arguably most important. In my design I'm making a priority to eliminate reflections from the floor and the back wall while reflections from the side walls are reduced. The most offensive reflections will be from the ceiling but I hope those will not be hard to equalize.
Are you sure about those vertical reflections? Reading through some threads here at diyaudio left me with the impression that vertical reflections are worse than horisontal and always detrimental to sound quality (mainly in the lower mid bass region). OTOH delayed lateral reflections should be beneficial.. Maybe I should re-read the giant directivity thread again?!?
There's definitely room for improvement with my design on the vertical axis. Let me elaborate my reasoning and the choices I made may become more clear.
Delayed horizontal(lateral) reflections add spaciousness and reinforce the stereo image but the off-axis frequency response must be similar to the direct one. This may or may not have to do with the fact that above 1600Hz we localize sound based on the level. In any case, successful Constant Directivity designs give evidence to that.
I'm not convinced that vertical reflections in that frequency region have a pronounced effect on sound perception. Evidence to that is the fact that almost all speakers out there are designed with severe nulls on the vertical axis. If the vertical reflections were indeed more important sideways D'Appolitos will be ruling the market
When speaking about lower frequencies I will agree that all reflections are detrimental. As the wavelength grows the room boundaries start to interact with the sound even before the waves are fully developed. The walls closest to the speaker begin to shape the sound. Reinforcements and cancellations develop both horizontally and vertically, at the same time. When I look at ripple tank simulations I find it incredible that we can hear anything at all!
Conventional speakers have omnipolar radiation at lower frequencies. They illuminate all 6 walls although the first 5 are arguably most important. In my design I'm making a priority to eliminate reflections from the floor and the back wall while reflections from the side walls are reduced. The most offensive reflections will be from the ceiling but I hope those will not be hard to equalize.
We may not perceive vertical reflections well for imaging but they'll cause colouration, as will the horizontal reflections. Horizontal reflections usually are treated in a constant directivity design, by way of the directivity itself.
I don't agree that the ceiling reflection will be easy to equalise.
I don't agree that the ceiling reflection will be easy to equalise.
Hello Boris,
I usually don't write much on forums at all, but this thread is interesting enough to make me write my very first post here!
I am extremely tempted to try out the resistive-vents-approach to improve the horizontal directivity in an upcoming line array build, and in the course of researching this I found this thread. I will use 28 3.5" Vifa TC9FD18/08 as full range drivers in each speaker (cf. Roger Russels IDS-25), and would aim to match the radiation at frequencies below the beaming threshold, to the dispersion of the beaming region (or at least even out the differences). Hence, resistive vents from around 2 kHz and down.
A couple of questions:
Do you have any thoughts on box size/volume and effective vent area as of yet? Kimmo Saunisto seems to imply that he likes a vent area of about 1.2-1.3*Sd, but I have seen no discussion on the geometry of the vents, for instance how far back along the box the vented area should reach. I find it hard to understand the best geometry for wide-band venting. Have you looked at the midrange box of the Gradient Helsinki, by the way?
Also, I have to ask if you have thoughts on using felt material over the vents, again like Kimmo, or do you plan for regular stuffing?
I usually don't write much on forums at all, but this thread is interesting enough to make me write my very first post here!
I am extremely tempted to try out the resistive-vents-approach to improve the horizontal directivity in an upcoming line array build, and in the course of researching this I found this thread. I will use 28 3.5" Vifa TC9FD18/08 as full range drivers in each speaker (cf. Roger Russels IDS-25), and would aim to match the radiation at frequencies below the beaming threshold, to the dispersion of the beaming region (or at least even out the differences). Hence, resistive vents from around 2 kHz and down.
A couple of questions:
Do you have any thoughts on box size/volume and effective vent area as of yet? Kimmo Saunisto seems to imply that he likes a vent area of about 1.2-1.3*Sd, but I have seen no discussion on the geometry of the vents, for instance how far back along the box the vented area should reach. I find it hard to understand the best geometry for wide-band venting. Have you looked at the midrange box of the Gradient Helsinki, by the way?
Also, I have to ask if you have thoughts on using felt material over the vents, again like Kimmo, or do you plan for regular stuffing?
Member
Joined 2009
Hello Boris,
I usually don't write much on forums at all, but this thread is interesting enough to make me write my very first post here!
I am extremely tempted to try out the resistive-vents-approach to improve the horizontal directivity in an upcoming line array build, and in the course of researching this I found this thread. I will use 28 3.5" Vifa TC9FD18/08 as full range drivers in each speaker (cf. Roger Russels IDS-25), and would aim to match the radiation at frequencies below the beaming threshold, to the dispersion of the beaming region (or at least even out the differences). Hence, resistive vents from around 2 kHz and down.
A couple of questions:
Do you have any thoughts on box size/volume and effective vent area as of yet? Kimmo Saunisto seems to imply that he likes a vent area of about 1.2-1.3*Sd, but I have seen no discussion on the geometry of the vents, for instance how far back along the box the vented area should reach. I find it hard to understand the best geometry for wide-band venting. Have you looked at the midrange box of the Gradient Helsinki, by the way?
Also, I have to ask if you have thoughts on using felt material over the vents, again like Kimmo, or do you plan for regular stuffing?
Hi,
unfortunately I can't answer any of your questions. I have no experience with this type of speakers and I'm perusing this project solely based on data published by Kimmo, Keyser, JohnK and others. Progress relies entirely on the outcome of my experiments. At this point I don't know if my proposed design will work as intended.
I have even less grasp on the resistive vent approach. If I understand correctly the resistive vent is not meant to absorb the sound energy but to restrict air-flow. In that application the box acts somewhat like a soft spring on the back of the driver (as opposed to a sealed box which would act as a stiff spring). I have no idea what the polar response of that configuration will be.
For my application I'm strictly after a cardioid response and I'm not set on any particular way to achieve it. I may remove the side and rear panels and not use a box enclosure. I'm gravitating towards something like this:
http://www.diyaudio.com/forums/multi-way/142691-adventures-cardioid.html#post1808314
I wish I could give you more relevant information but I don't know much on the topic of absorption materials and vent sizes. What I would do in your case is start with a small-scale model and experiment with different configurations. Measurement equipment is essential but thankfully not difficult to acquire.
Hi,
And thanks for replying. I have the same feeling like you do, that it might take a lot of experimenting to tune something like this. In my case that might be exactly what prevents me from doing it. On the other hand, the fine results in the threads you link to stem from seemingly simple and straightforward means.
In any case, my intuition tells me the boxless/muffler approach is qualitatively equivalent to the box-with-sidevents approach, maybe with edge diffraction playing some role in the difference? Topologically they seem equivalent to me, at least. The effective distance the air needs to travel between front of membrane to vent of course also determines the dipole step frequency; i.e. the highest frequency at which you can expect to "cardio-ize" your response -- but I cannot quite get a feel for bandwidth versus vent geometry (yet).
Anyway, my goal would be cardioid dispersion as well, just like you. Hope you make progress, I would be quite interested to see it. Love your idea and your box design looks great! The thread is subscribed to.
Cheers,
Member
Joined 2009
Correct, when it comes to a cardioid response the boxless/muffler approach produces similar results to the box with side holes that is stuffed with absorbing material.
I was thrown off by the term "resistive vent" because that is used in an Aperiodic Loudspeaker Enclosure Design for bass tuning. With resistive ports on the side of the box an aperiodic enclosure should theoretically produce some type of cardioid response. Unfortunately, I'm not familiar with any research that specifies how different parameters can be optimized to arrive at a desired response.
I was thrown off by the term "resistive vent" because that is used in an Aperiodic Loudspeaker Enclosure Design for bass tuning. With resistive ports on the side of the box an aperiodic enclosure should theoretically produce some type of cardioid response. Unfortunately, I'm not familiar with any research that specifies how different parameters can be optimized to arrive at a desired response.
I'm not convinced that vertical reflections in that frequency region have a pronounced effect on sound perception. Evidence to that is the fact that almost all speakers out there are designed with severe nulls on the vertical axis. If the vertical reflections were indeed more important sideways D'Appolitos will be ruling the market
Not following your logic here. I think you are saying all would be well if the floor reflections have flat response, or that if speakers send messy response towards the floor that proves it must be inconsequential. That isn't true. Floor and ceiling bounce energy, no matter what the spectrum, will arrive at the ear just enough delayed to give very significant comb filtering.
The issue is one of psychoacoustics. We are inundated with reflections from all directions. If they come from the sides our binaural hearing lets us separate them very well from the frontal sound. We perceive them as added spaciousness or image spread. Anything that arrives on the median plane (the plane halfway between the two ears) we will have a hard time seperating out. It will be combined with the direct sound as a nonflat, comb filtered composite.
Vertical directivity of any form is useful. Lateral reflections, if sufficiently delayed, are pleasant and add spaciousness. Toole writes a lot about this, you should read his book.
D'Appolitos should be vertical!
David S.
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