Dear forum, I got two 15" inch coaxial drivers (RCF CX15N351) quite cheaply, so I would like to use them to build two active speakers in a closed cabinet. Since these speakers will be my first DIY, I unfortunately have a few questions. Maybe you can give me a few tips/answers regarding literature, videos, tutorials that could be helpful for the first start.
So far the plan is to build a loudspeaker very similar to the Martion Bullfrog loudspeaker, but with a built-in active module:
- Closed cube design
- RCF CX15N351 with modified 3D printed horn
- Hypex FA 503 (New one with FIR Filter)
- Hypex OLED display
The whole thing should be controlled via SPDIF and possibly supplemented with a suitable subwoofer in the future.
The following questions have already arisen:
- Regarding the cabinet: Unfortunately I have problems determining the volume (liters) for the driver. The comparison speaker “Martion Bullfrog” has external dimensions of 45x45x45 cm. Does anyone have experience with a 15" coax in a closed housing? Does it make sense to line the inside with insulating materials? If so, what would you recommend?
- The horn of the RCF CX15N351 has a cutoff frequency of 800hz. According to the information, the Bullfrog's crossover frequency is already at 680hz. The horn was probably enlarged by the aluminum ring. I would like to make a new horn using 3D printing and would have the opportunity to customize it even further. What do I have to pay attention to if I want the cutoff frequency to be lower? Larger horn opening? Are there programs that can simulate horns? And has anyone ever created a horn using 3D printing? Are there preferred materials?
- How do I set the limiter of the Hypex so that the chassis is protected? Simply enter the wattage of the AES / RMS / OHM value?
- Is it possible for me as a “beginner” to calibrate the loudspeaker with free programs (REW / rephase) and create a crossover with Fir filters after watching some tutorials / videos?
I know that it is a very ambitious project for a beginner, but I would also like to learn the basics and measure the speakers myself in the future. Please give me honest answers if the project is too big for me and you think I would despair about it, then I would rather sell the chassis 😀
Thank you very much in advance!
So far the plan is to build a loudspeaker very similar to the Martion Bullfrog loudspeaker, but with a built-in active module:
- Closed cube design
- RCF CX15N351 with modified 3D printed horn
- Hypex FA 503 (New one with FIR Filter)
- Hypex OLED display
The whole thing should be controlled via SPDIF and possibly supplemented with a suitable subwoofer in the future.
The following questions have already arisen:
- Regarding the cabinet: Unfortunately I have problems determining the volume (liters) for the driver. The comparison speaker “Martion Bullfrog” has external dimensions of 45x45x45 cm. Does anyone have experience with a 15" coax in a closed housing? Does it make sense to line the inside with insulating materials? If so, what would you recommend?
- The horn of the RCF CX15N351 has a cutoff frequency of 800hz. According to the information, the Bullfrog's crossover frequency is already at 680hz. The horn was probably enlarged by the aluminum ring. I would like to make a new horn using 3D printing and would have the opportunity to customize it even further. What do I have to pay attention to if I want the cutoff frequency to be lower? Larger horn opening? Are there programs that can simulate horns? And has anyone ever created a horn using 3D printing? Are there preferred materials?
- How do I set the limiter of the Hypex so that the chassis is protected? Simply enter the wattage of the AES / RMS / OHM value?
- Is it possible for me as a “beginner” to calibrate the loudspeaker with free programs (REW / rephase) and create a crossover with Fir filters after watching some tutorials / videos?
I know that it is a very ambitious project for a beginner, but I would also like to learn the basics and measure the speakers myself in the future. Please give me honest answers if the project is too big for me and you think I would despair about it, then I would rather sell the chassis 😀
Thank you very much in advance!
I'll give this a go.
Short answer: If you're starting at or near ground zero, as your questions imply, jumping straight to the solution you are proposing is almost certainly out of reach and a recipe for frustration. And yes, there are (several) horn simulators, people here design their own horns and 3D print them all the time.
But please don't start there!
Many of the disciplines you mention (measurement, FIR filter design, speaker/crossover modeling, horn design, 3D printing of said designs) are all rabbit holes that, depending on your baseline of applicable knowledge, could take months (each!) to get a handle on. Note that I didn't say master, just 'get a handle on'.
The standard advice is that the best way to dip one's feet in this hobby is to find a fairly simple known-good design and follow it. That's good advice.
That said, a simple active two-way coax in a sealed cabinet... minus the FIR filters, custom horn, etc, might not be a bad place to start if you want to roll your own. If you stick with it and find it fun, you could take a basic implementation and then incrementally head in the direction you outlined.
I own/use a several pro coax drivers, primarily for live performance stage monitors. My favorite ones happen to be made by Radian, and they don't have a real horn on the HF section. There are downsides to that, but I've found them to be the simplest speaker type, by far, for getting to a listenable tuning, particularly when using an active conventional (IIR) DSP crossover with fine-grained delay controls for the two 'ways'.
The saving grace (or bane!) of a coax is that a bunch of otherwise endless variables (driver choice & spacing) have been cemented in place by the manufacturer... and you've already bought the drivers. So you can't (productively, anyway) drive yourself crazy thinking about them.
Additionally, their very coax-i-ness means that you can usually look for / measure crossover-related problems (slopes/phase/driver delay timing... all interrelated) in a frequency range (ca 400Hz and up) that is fairly easy to measure even in a modestly sized room, and IMO, you only have to care about a fairly narrow range of angles near where you're listening.
So you have to learn to measure, but maybe you don't have to be absolutely great at it right away. Half a rabbit hole.
I believe it's accurate to say that on the first order, with coincident drivers, you have to get the FR and driver offset compensation correct on or near axis, so you just do it, and unless/until you start getting fancy, you're kind of stuck with what happens elsewhere as a consequence of the driver, cone, & horn shape.
This has, at least, been my experience with the Radian coaxes I mostly use, which again, don't have a big horn on the HF section. For this reason, I feel no compelling need to model these speakers in detail, I just measure them as part of the crossover tuning.
That defers your learning one other rabbit hole skill-set (advanced cabinet & crossover modeling) for now.
So sure, there's plenty you can get wrong, but if you don't go off the deep end right away, you will probably be able to come up with something OK sounding pretty quickly. You may spend the rest of the decade fiddling with it afterwards, but at least you'll have something to listen to in the meantime. I think that's a great thing about DSP crossovers; it's really easy to get back to a known baseline to see if you're fooling yourself when making 'improvements'.
But before you start, please go read a good book (like "The Loudspeaker Design Cookbook") or some similar online resource to get the lay of the land. This forum is full of fantastic information, but IMO, you'll spin round in circles if you don't (linearly) read an overview first.
My rough steps for a basic sealed-box active coax design:
Learn what T-S parameters are, look them up for your driver (or measure them with something like the Dayton Audio DATS or your own jig).
Learn to use a speaker modeling program (or cheat and use an online woofer design calculator) and come up with a reasonable volume for your coax's woofer. Advanced topic: use a more advanced modeling program (ie, VituixCAD) to find out approximately how various choices of front panel dimensions will impact the LF driver's frequency response and directivity.
Build the box. Your stated desire to use a sealed cabinet makes it harder to completely screw things up, but it probably is going to sound very thin without a sub, and/or EQ.
Put a protective capacitor in series with the tweeter sized to create an electrical low frequency rolloff on the tweeter well below your intended crossover (maybe 300Hz).
This is so you don't kill it while you're measuring it, and so you don't kill it later, when drunkenly fumble-fingering your active crossover control program at 2AM (don't ask!). Leave it in place afterwards; you measured with it, so consider it part of the driver.
Learn to measure. (Big rabbit hole).
Easy way is with the Dayton OmniMic. Very turnkey, low basic learning curve, but cost some $$$, and not always the best tool for getting the 'time/phase accurate' info for tweaky crossover modeling (another side rabbit hole... read REW's manual, etc, for reasons why).
I switch between the OmniMic and a fairly expensive calibrated measurement mic + REW depending on mood & need. The REW rig is very fiddly to keep calibrated; I'm glad I have the OmniMic (and a mic calibrator!) as a sanity check.
Then spend a little while interactively playing with your crossover's "per driver" parametric EQ while measuring the results (at low volume!).
First, flatten out the LF & HF section's responses. Don't go nuts with EQing the low end of the HF beyond where the horn stops loading, and don't go too nuts EQing the woofer at all unless you're measuring outside or have learned how to make good nearfield measurements.
Once the drivers are flat-ish, then pick some crossover slopes and play with the driver delays so that things are smooth through the crossover region.
There's a technique called 'tuning for a null' (temporarily flipping the polarity of one driver and looking for a sharp, deep cancellation at the crossover frequency) that, especially with a coax, can really make it obvious when you've got it about right.
Read up on "Baffle Step Loss", play with it in Vituix (or look for it in your measurements, if you can do them outside and way up in the air) and decide whether you care to compensate. +1 for DSP crossovers; no harm in trying.
If you get anywhere near that far, there's plenty of help available to tweak things.
FIR filtering with (the right sort of) steep slopes might be a fun way to go, but you really need to get good at making clean measurements and understand what you're doing, or you might find that you're going backwards.
The same is also true for fiddling with the HF section's horn.
I would definitely take those things on one at a time, and only after hitting a point of diminishing returns with a simpler/stock design.
Tony
Short answer: If you're starting at or near ground zero, as your questions imply, jumping straight to the solution you are proposing is almost certainly out of reach and a recipe for frustration. And yes, there are (several) horn simulators, people here design their own horns and 3D print them all the time.
But please don't start there!
Many of the disciplines you mention (measurement, FIR filter design, speaker/crossover modeling, horn design, 3D printing of said designs) are all rabbit holes that, depending on your baseline of applicable knowledge, could take months (each!) to get a handle on. Note that I didn't say master, just 'get a handle on'.
The standard advice is that the best way to dip one's feet in this hobby is to find a fairly simple known-good design and follow it. That's good advice.
That said, a simple active two-way coax in a sealed cabinet... minus the FIR filters, custom horn, etc, might not be a bad place to start if you want to roll your own. If you stick with it and find it fun, you could take a basic implementation and then incrementally head in the direction you outlined.
I own/use a several pro coax drivers, primarily for live performance stage monitors. My favorite ones happen to be made by Radian, and they don't have a real horn on the HF section. There are downsides to that, but I've found them to be the simplest speaker type, by far, for getting to a listenable tuning, particularly when using an active conventional (IIR) DSP crossover with fine-grained delay controls for the two 'ways'.
The saving grace (or bane!) of a coax is that a bunch of otherwise endless variables (driver choice & spacing) have been cemented in place by the manufacturer... and you've already bought the drivers. So you can't (productively, anyway) drive yourself crazy thinking about them.
Additionally, their very coax-i-ness means that you can usually look for / measure crossover-related problems (slopes/phase/driver delay timing... all interrelated) in a frequency range (ca 400Hz and up) that is fairly easy to measure even in a modestly sized room, and IMO, you only have to care about a fairly narrow range of angles near where you're listening.
So you have to learn to measure, but maybe you don't have to be absolutely great at it right away. Half a rabbit hole.
I believe it's accurate to say that on the first order, with coincident drivers, you have to get the FR and driver offset compensation correct on or near axis, so you just do it, and unless/until you start getting fancy, you're kind of stuck with what happens elsewhere as a consequence of the driver, cone, & horn shape.
This has, at least, been my experience with the Radian coaxes I mostly use, which again, don't have a big horn on the HF section. For this reason, I feel no compelling need to model these speakers in detail, I just measure them as part of the crossover tuning.
That defers your learning one other rabbit hole skill-set (advanced cabinet & crossover modeling) for now.
So sure, there's plenty you can get wrong, but if you don't go off the deep end right away, you will probably be able to come up with something OK sounding pretty quickly. You may spend the rest of the decade fiddling with it afterwards, but at least you'll have something to listen to in the meantime. I think that's a great thing about DSP crossovers; it's really easy to get back to a known baseline to see if you're fooling yourself when making 'improvements'.
But before you start, please go read a good book (like "The Loudspeaker Design Cookbook") or some similar online resource to get the lay of the land. This forum is full of fantastic information, but IMO, you'll spin round in circles if you don't (linearly) read an overview first.
My rough steps for a basic sealed-box active coax design:
Learn what T-S parameters are, look them up for your driver (or measure them with something like the Dayton Audio DATS or your own jig).
Learn to use a speaker modeling program (or cheat and use an online woofer design calculator) and come up with a reasonable volume for your coax's woofer. Advanced topic: use a more advanced modeling program (ie, VituixCAD) to find out approximately how various choices of front panel dimensions will impact the LF driver's frequency response and directivity.
Build the box. Your stated desire to use a sealed cabinet makes it harder to completely screw things up, but it probably is going to sound very thin without a sub, and/or EQ.
Put a protective capacitor in series with the tweeter sized to create an electrical low frequency rolloff on the tweeter well below your intended crossover (maybe 300Hz).
This is so you don't kill it while you're measuring it, and so you don't kill it later, when drunkenly fumble-fingering your active crossover control program at 2AM (don't ask!). Leave it in place afterwards; you measured with it, so consider it part of the driver.
Learn to measure. (Big rabbit hole).
Easy way is with the Dayton OmniMic. Very turnkey, low basic learning curve, but cost some $$$, and not always the best tool for getting the 'time/phase accurate' info for tweaky crossover modeling (another side rabbit hole... read REW's manual, etc, for reasons why).
I switch between the OmniMic and a fairly expensive calibrated measurement mic + REW depending on mood & need. The REW rig is very fiddly to keep calibrated; I'm glad I have the OmniMic (and a mic calibrator!) as a sanity check.
Then spend a little while interactively playing with your crossover's "per driver" parametric EQ while measuring the results (at low volume!).
First, flatten out the LF & HF section's responses. Don't go nuts with EQing the low end of the HF beyond where the horn stops loading, and don't go too nuts EQing the woofer at all unless you're measuring outside or have learned how to make good nearfield measurements.
Once the drivers are flat-ish, then pick some crossover slopes and play with the driver delays so that things are smooth through the crossover region.
There's a technique called 'tuning for a null' (temporarily flipping the polarity of one driver and looking for a sharp, deep cancellation at the crossover frequency) that, especially with a coax, can really make it obvious when you've got it about right.
Read up on "Baffle Step Loss", play with it in Vituix (or look for it in your measurements, if you can do them outside and way up in the air) and decide whether you care to compensate. +1 for DSP crossovers; no harm in trying.
If you get anywhere near that far, there's plenty of help available to tweak things.
FIR filtering with (the right sort of) steep slopes might be a fun way to go, but you really need to get good at making clean measurements and understand what you're doing, or you might find that you're going backwards.
The same is also true for fiddling with the HF section's horn.
I would definitely take those things on one at a time, and only after hitting a point of diminishing returns with a simpler/stock design.
Tony
oh wow thank you! I didn't expect such a detailed and good answer, thank you very much 🙂 I will answer it again in detail in the next few days.
Thank you again for your nice detailed answer. I almost expected that all of my questions would be about individual disciplines that would require a lot of knowledge. But I think the plan you suggested of starting with a “simple” system and specializing from there makes sense. That means I will first calculate a reasonable volume. Is there a good book that explicitly deals with closed speakers? Or should I start with the “loudspeaker design cookbook”? Then I have another question: The idea with the protective capacitor is great! As a beginner, I'm afraid of breaking something. But how do I calculate a suitable capacitor?
I think the LDC is a great place to start.
Re: sizing the capacitor... the LDC is a great place to start ;0)
You're creating a series first-order electrical high pass filter... the LDC will discuss it.
Here's a whole thread on the topic of tweeter protection caps, one of many, I suspect:
https://www.diyaudio.com/community/...eter-protection-with-active-crossover.338794/
To cheat... you have a 16 ohm tweeter, a 24uF cap in series with the driver would get you an electrical rolloff at about 400Hz.
x2 (50uF) for an 8 ohm driver (I think that's what the RCF CX15N351 has for both iLF and HF... but check yours!).
Typical 'textbook' crossover cheat site, useful for this purpose, but not much else, IMO...
https://www.diyaudioandvideo.com/Calculator/SpeakerCrossover/
You can put a few smaller caps in parallel to make up your final value (it's additive); that will give you some flexibility to change your rolloff point without buying all new parts.
As to what frequency... it depends.
If you keep it a few octaves below your 'real' DSP + acoustic (driver+horn rolloff) crossover, the cap won't have much of an effect on the crossover, but it also won't provide as much protection from mistakes. Still way better than nothing. In this case, you might be able to remove the cap afterwards and not disturb your crossover too awfully much.
Personally, I'd plan to leave the cap in place forever, and put its rolloff about 1-2 octaves below the lowest realistic crossover point you'll want to try.
If you place the capacitor's rolloff anywhere near the intended crossover point, it becomes an integral part of the design and you have to leave it there permanently.
There's nothing inherently wrong with that. You'll be measuring your driver's 'raw' response with it in place, & optimizing your DSP settings around it. This is workable if your methodology is "measure + modelling", "measure-twiddle-measure", or some combination thereof.
Note that capacitor type & brand selection is its own rabbit hole... be careful. You could go broke or crazy before you even start ;0)
You either need a non-polarized electrolytic (cheapest), or if that bothers you, some sort of film cap (100V or up). I use 250V metallized polypropylene caps, mostly because that's what I have on hand. Maybe something like this:
https://www.parts-express.com/Dayto...0V-Polypropylene-Capacitor-027-443?quantity=1
That's not hideously expensive, but it makes me look differently at the big shoebox full of Erse caps that I stumbled across in my lab the other day... and then misplaced again!
Re: sizing the capacitor... the LDC is a great place to start ;0)
You're creating a series first-order electrical high pass filter... the LDC will discuss it.
Here's a whole thread on the topic of tweeter protection caps, one of many, I suspect:
https://www.diyaudio.com/community/...eter-protection-with-active-crossover.338794/
To cheat... you have a 16 ohm tweeter, a 24uF cap in series with the driver would get you an electrical rolloff at about 400Hz.
x2 (50uF) for an 8 ohm driver (I think that's what the RCF CX15N351 has for both iLF and HF... but check yours!).
Typical 'textbook' crossover cheat site, useful for this purpose, but not much else, IMO...
https://www.diyaudioandvideo.com/Calculator/SpeakerCrossover/
You can put a few smaller caps in parallel to make up your final value (it's additive); that will give you some flexibility to change your rolloff point without buying all new parts.
As to what frequency... it depends.
If you keep it a few octaves below your 'real' DSP + acoustic (driver+horn rolloff) crossover, the cap won't have much of an effect on the crossover, but it also won't provide as much protection from mistakes. Still way better than nothing. In this case, you might be able to remove the cap afterwards and not disturb your crossover too awfully much.
Personally, I'd plan to leave the cap in place forever, and put its rolloff about 1-2 octaves below the lowest realistic crossover point you'll want to try.
If you place the capacitor's rolloff anywhere near the intended crossover point, it becomes an integral part of the design and you have to leave it there permanently.
There's nothing inherently wrong with that. You'll be measuring your driver's 'raw' response with it in place, & optimizing your DSP settings around it. This is workable if your methodology is "measure + modelling", "measure-twiddle-measure", or some combination thereof.
Note that capacitor type & brand selection is its own rabbit hole... be careful. You could go broke or crazy before you even start ;0)
You either need a non-polarized electrolytic (cheapest), or if that bothers you, some sort of film cap (100V or up). I use 250V metallized polypropylene caps, mostly because that's what I have on hand. Maybe something like this:
https://www.parts-express.com/Dayto...0V-Polypropylene-Capacitor-027-443?quantity=1
That's not hideously expensive, but it makes me look differently at the big shoebox full of Erse caps that I stumbled across in my lab the other day... and then misplaced again!