Steering advice for those serious about DIY speakers.

[Phil Graham]

Before this forum ever existed, Jeff B approached me to see if I would be interested in contributing designs to a DIY audio forum, and I politely declined. Some of the reasons I cited for this were:

1. Desire to be paid for expertise
2. Lack of desire to provide "tech support" for every bad copy of a design
3. The economic realities of DIY projects rarely being cheaper than commercial products
4. Lack of learning from merely presenting finished designs
5. Changing driver availability

As I suspected, the speaker design tumbleweeds have quickly rolled in here, and the one proposed project is much more complicated than what should be considered by those starting in speaker design. It appears that most of that thread relates to selecting drivers, which is only a tiny fraction at the outset of speaker design project.

Real speaker design requires, at a minimum, test and measurement equipment and pretty extensive knowledge that is not easy to accumulate from a single source. One must able to take acoustic and electrical measurements and know how to act on them.

Further, the majority of those measurements must be taken in the box of interest, as the cabinet has substantial effects on the responses of the drivers, and the crossover cannot be considered in isolation from the box. Indeed crossover design should be undertaken in the cabinet of choice.

Finally, passive crossovers quickly become extremely complex and potentially unwieldy if you don't know how to design cleverly.

Rather than being purely pessimistic in this post, let me try to give some actionable advice for a serious starter project:

1. Only consider three way designs, as this gives a reasonable chance of decent performance with unexceptional drivers
2. Always utilize two LF drivers (e.g. 2 10" or 2 15") as this will minimize your mid/hi resistive padding
3. Sealed boxes are often better than poorly designed ported cabinets
4. Frequency response plots on datasheets are nearly meaningless for driver evaluation, though some more subtle effects on them do matter.
5. Don't spend more than $3-400 on drivers per cabinet
6. Keep reasonable expectations
7. Listen to the drivers first, if possible (especially HF drivers)

The best DIY projects serve the bottom end of the market space. Retail driver costs are simply too high to build a competitive high-end product for less money than a competent manufacturer can produce the same, even with their profit margin.

A sample high ROI DIY project would be a 2-15" 8" 1" 3 way that was always out on rentals for DJs. This is the kind of low end project that many forum readers would keep busy renting from their shops, and represents a much more rational first project goal than a high-end coaxial stage monitor.

 

[Jeff Babcock]

Re: Steering advice for those serious about DIY speakers.

As I suspected, the speaker design tumbleweeds have quickly rolled in here , and the one proposed project is much more complicated than what should be considered by those starting in speaker design. It appears that most of that thread relates to selecting drivers, which is only a tiny fraction at the outset of speaker design project.

Hi Phil,
Agreed, the coaxial project is not a "starter" project by any means. While most of the discussion thus far has been surrounding drivers, that is OK, this project is still a LONG way away from completion. Certainly you don't seem optimistic about a good outcome. I feel otherwise, but even if things bomb, it will still be a great learning experience.

Real speaker design requires, at a minimum, test and measurement equipment and pretty extensive knowledge that is not easy to accumulate from a single source. One must able to take acoustic and electrical measurements and know how to act on them.

Further, the majority of those measurements must be taken in the box of interest, as the cabinet has substantial effects on the responses of the drivers, and the crossover cannot be considered in isolation from the box. Indeed crossover design should be undertaken in the cabinet of choice.

Again, agreed, however I do believe that most of the required resources and knowledge exist within the members of this community and there is capability of a good quality outcome, even if that outcome is only a good learning experience.

Finally, passive crossovers quickly become extremely complex and potentially unwieldy if you don't know how to design cleverly.

Indeed this is true. This has not been discussed in much detail yet, but if this task is beyond the capabilities of those involved then we have resources who we may consider employing for such purposes.

Rather than being purely pessimistic in this post, let me try to give some actionable advice for a serious starter project:

1. Only consider three way designs, as this gives a reasonable chance of decent performance with unexceptional drivers
2. Always utilize two LF drivers (e.g. 2 10" or 2 15") as this will minimize your mid/hi resistive padding
3. Sealed boxes are often better than poorly designed ported cabinets
4. Frequency response plots on datasheets are nearly meaningless for driver evaluation, though some more subtle effects on them do matter.
5. Don't spend more than $3-400 on drivers per cabinet
6. Keep reasonable expectations
7. Listen to the drivers first, if possible (especially HF drivers)

This advice is certainly welcome. There are plenty of ideas in the works at various stages, and a 3 way cab has already been considered and will likely receive some attention at some point in the future. The current coax project is primarily a means of getting the ball rolling with something that is a little bit less typical than most existing DIY projects. There are lots of 3 way designs, but few good compact DIY wedges that I have personally come across.

The best DIY projects serve the bottom end of the market space. Retail driver costs are simply too high to build a competitive high-end product for less money than a competent manufacturer can produce the same, even with their profit margin.

In many cases this is true. There are some exceptions however, and where those exceptions exist, I don't see a problem with using more expensive drivers. There are lots of DIY resources available if you want to build something cheap. The results of such projects can often be worthwhile, albeit limited in their use for professional or semi-professional applications.

Few resources exist for those ABOVE the bottom feeder level. I really don't care in the least if this becomes a highly popular forum or that the designs appeal to a mass market. That really is not the goal here, in fact is somewhat contrary to the approach I would envision, though this isn't just about the mod's wishes, the community will ultimately drive this in the direction that best suits their wishes.

A sample high ROI DIY project would be a 2-15" 8" 1" 3 way that was always out on rentals for DJs. This is the kind of low end project that many forum readers would keep busy renting from their shops, and represents a much more rational first project goal than a high-end coaxial stage monitor.

Certainly more rational, but IMHO, it would be a bit of a boring start. If someone wants a box like that, they are welcome to PM me for some links to existing designs from other places on the web that are quite reasonable.

Please realize that expectations are not terribly out of line here with the coax project. Are we expecting to out-do boxes like Microwedge, M2, M4, XW12/15 etc? Not at all. But I do think it's very possible to put out something that is good enough to put on a non-rider'd stage and give the muso's something that's better than what they are accustomed to. I happily acknowledge, I don't have all of the answers. But that's where the power of the community comes in. Together, our communal knowledge is quite significant.

Thanks for your comments Phil, you are certainly a highly respected member of the community and a huge intellectual asset. I hope my response helps to clarify things somewhat, if not, feel free to continue the discussion.

When we get to later stages in this project, we'd be happy to send a coax prototype your way if you wished to provide some recommendations for improvement.

Kind regards
Jeff

 

[John Roberts]

Re: Steering advice for those serious about DIY speakers.

I smiled a little when I saw Phil's post. Of course he's absolutely right, but so what?

If people want to make some saw dust and hopefully learn something along the way more power too them. If they think they're going to improve the state of the art and save money at the same time, they need to think again.

As long as everybody ends up with ten fingers it's all good...

JR (Hasn't built any DIY speakers since the early '70s... )

 

[Phil Graham]

Re: Steering advice for those serious about DIY speakers.

Certainly you don't seem optimistic about a good outcome. I feel otherwise, but even if things bomb, it will still be a great learning experience.

Its not that I am not optimistic, it is merely that a cheap speaker, built out of lower end parts, would be a lower learning curve point to get started for people to mess around.

Really, a much better way to approach people actually learning about speaker design would be to offer a kit, and then design a crossover for it "in the open" on the forum, and then everyone could implement that.

Something simple and cheap, like an 8" and a small compression driver.

If you were able to put something like that together, I could see potentially getting involved, and maybe Curtis List, too.

People learn, and they would also get some sense of the skillset needed to do passive design well, which likely means more design business for us.

Indeed this is true. This has not been discussed in much detail yet, but if this task is beyond the capabilities of those involved then we have resources who we may consider employing for such purposes.

Let me suggest Charlie Hughes and Curtis for that eventuality.

When we get to later stages in this project, we'd be happy to send a coax prototype your way if you wished to provide some recommendations for improvement.

I would be interested in that as a way to help the project, it seems like an interesting way to get involved.

 

[Jeff Babcock]

Re: Steering advice for those serious about DIY speakers.

Its not that I am not optimistic, it is merely that a cheap speaker, built out of lower end parts, would be a lower learning curve point to get started for people to mess around.

Really, a much better way to approach people actually learning about speaker design would be to offer a kit, and then design a crossover for it "in the open" on the forum, and then everyone could implement that.

Something simple and cheap, like an 8" and a small compression driver.

If you were able to put something like that together, I could see potentially getting involved, and maybe Curtis List, too.

People learn, and they would also get some sense of the skillset needed to do passive design well, which likely means more design business for us.



Let me suggest Charlie Hughes and Curtis for that eventuality.



I would be interested in that as a way to help the project, it seems like an interesting way to get involved.

Thanks Phil.
I realize that a more simple project might be a better learning attempt. The coax is a 1st kick at the can while relatively few are watching, allowing some time to sort out some logistical details along the way. Without getting into too much detail, there were several proposed starting points but there are some underlying reasons why those didn't get pushed to the surface at this point in time. There are a few folks around these parts who have a practical use for such a box in the near future (myself included), so it got pushed to the front of the pile, even though it might not be the simplest starting point.

Please keep in mind that currently there is ZERO budget, so it helps if those involved have an intended use for the design given that we bear the entire cost ourselves. On a personal note, I'm willing to shell out some $ on the coax project because I have an application where I could use quite a pile of these when they're done. This isn't always going to be the case, so agreed, a low cost project may be the next logical move.

We're not out to start making alternatives to the Martin MLA here...... Simpler projects will come.... perhaps the 8/1 box idea you mention could even serve to some as a front fill box, for which there are few existing suitable DIY designs. My only real insistence is that the quality of the final product be at least good enough for semi-professional or professional use. To put into perspective better, in the SRX/QRX sort of league. I realize this does make things more challenging, but I don't think most of the folks here have much use for something less than that level of performance. Thoughts?

Please, by all means, continue to share your thoughts and participate whenever you have time to do so. I hope you understand that I am for the most part in total agreement with what you have shared.

BTW, Charlie and Curtis were the exact folks in mind re crossovers.

Thanks for your offer regarding sending you a prototype. When things get to that point, we'll try to ensure that that happens, as your skillset and your clear communication with regards to teaching would be a tremendous asset.

Thanks!
Jeff

 

[Phil Graham]

Re: Steering advice for those serious about DIY speakers.

Thanks Phil.
I realize that a more simple project might be a better learning attempt. The coax is a 1st kick at the can while relatively few are watching, allowing some time to sort out some logistical details along the way. Without getting into too much detail, there were several proposed starting points but there are some underlying reasons why those didn't get pushed to the surface at this point in time. There are a few folks around these parts who have a practical use for such a box in the near future (myself included), so it got pushed to the front of the pile, even though it might not be the simplest starting point.

Starting out with a product that everyone needs makes sense, but it also makes the underlying assumption that result you produce is up to the standards of performance you have envisioned in your mind. If the product doesn't perform, you all have collectively created expensive paperweights.

Think about comparing this to the open source software (OSS) community. In the OSS community, people develop software tools that many have mutual needs for and aid their business. Examples like Apache and nginx help everyone who has serving web pages as part of their business, but didn't want to have to pay for such software. When the software is done it can be widely distributed for very little cost, recreated as many times as needed.

In contrast, you have a product that every person involved must build individually, completion of the design involves a substantial cost to each builder, and there is no easy way to divvy up the design responsibilities amongst the community.

To return to the OSS comparison, the people involved with this project don't know how to "code" (i.e. they don't deeply understand loudspeaker design). Nor do these people have the "code development/debug/etc" tools (i.e. the loudspeaker measurement and design equipment and software). Hopefully this analogy will help expand some of the potential absurdity of the project.

Please keep in mind that currently there is ZERO budget, so it helps if those involved have an intended use for the design given that we bear the entire cost ourselves. On a personal note, I'm willing to shell out some $ on the coax project because I have an application where I could use quite a pile of these when they're done.

If you need a pile of wedges, I would strongly encourage purchasing them from a manufacturer. Indeed I would posit that the very act of needing a pile of wedges would preclude one from having the time to build them! You'll be much happier if you treat your attempt at the coax design as lottery money, rather than something your business is going to need to rely on.

We're not out to start making alternatives to the Martin MLA here...... Simpler projects will come.... perhaps the 8/1 box idea you mention could even serve to some as a front fill box, for which there are few existing suitable DIY designs. My only real insistence is that the quality of the final product be at least good enough for semi-professional or professional use. To put into perspective better, in the SRX/QRX sort of league.

I suspect this project will increase the participants' appreciation for the actual engineering in the boxes mentioned above. There is extensive engineering in horns, driver design, and crossovers. Especially if you try to build to a similar price point, you are going to find that the passives in the XOs get pricey quickly.

I realize this does make things more challenging, but I don't think most of the folks here have much use for something less than that level of performance. Thoughts?

I don't anticipate you meeting your performance goals without hiring a third party to do your XO design, and that point, how much are you really DIYing, and which members of the build pay for those design services?

Just some counterpoints to consider...

 

[John Roberts]

Re: Steering advice for those serious about DIY speakers.

Phil is already arguing what is normally my side of the argument, while i routinely caution against second guessing the real loudspeaker engineers when it comes to dialing in DSP/crossovers, easily an order of magnitude simpler than passive crossover design**. With the new information about how small the odds are your DSP is actually doing what it says it is (thanx grasshopper) and this gets even more difficult.

But just to explore the other side of the arguement (no not trolling), there is a long tradition in small sound companies rolling their own cabinets, as a simple investment in sweat equity. Back in the old days they pretty much copied from a short list of classic proven designs, or ventured out on their own, with mixed results. More recently we saw the "will be a" classic LAB sub, thanks to the engineering talent of TD.

That LAB sub was a near ideal model to follow. A knowledgeable designer working interactively with a interested community to help define the important design targets. While for obvious reasons we aren't likely to enjoy another TD experience, we have enough collective wisdom here to at least identify the heavy lifting and seek out decent answers.

As has been already stated, this will not save you money, if you have any other productive stuff to do with your time, but if you have more time than money and access to basic woodworking tools this could be a good learning experience. You may only learn to never do something like this again, but if it turns out well, it could be worth time spent and a source of some pride of personal accomplishment.

JR

*** Back in the '70s I considered selling a time aligned hifi speaker kit, through my kit business. I had a real speaker designer who had designed bookshelf speakers for a couple companies (Ohm, Bozak, and a small company Fourier) who was willing to assist me. His weapon of choice for designing the passive crossover (recall that this was back in the '70s) was a programmable HP calculator. His crossover program took so long to run, that he would start it and let if run overnight. Today your cellphone probably has more computing power! FWIW I never did the speaker kit, so you know how my personal judgement falls on this.

PS: I got building speakers myself out of my system, earlier in the decade. Later working at Peavey it was really nice to have a whole department of competent transducer engineers that we could point at a project (For example I was able to use Charley's quadratic horn in a plastic box I was involved with), real industrial designers to make it look sexy (well sexy for Peavey).

 

[Art Welter]

Re: Steering advice for those serious about DIY speakers.

Phil is already arguing what is normally my side of the argument, while i routinely caution against second guessing the real loudspeaker engineers when it comes to dialing in DSP/crossovers, easily an order of magnitude simpler than passive crossover design**. With the new information about how small the odds are your DSP is actually doing what it says it is (thanx grasshopper) and this gets even more difficult.

But just to explore the other side of the arguement (no not trolling), there is a long tradition in small sound companies rolling their own cabinets, as a simple investment in sweat equity. Back in the old days they pretty much copied from a short list of classic proven designs, or ventured out on their own, with mixed results. More recently we saw the "will be a" classic LAB sub, thanks to the engineering talent of TD.

That LAB sub was a near ideal model to follow. A knowledgeable designer working interactively with a interested community to help define the important design targets. While for obvious reasons we aren't likely to enjoy another TD experience, we have enough collective wisdom here to at least identify the heavy lifting and seek out decent answers.

As has been already stated, this will not save you money, if you have any other productive stuff to do with your time, but if you have more time than money and access to basic woodworking tools this could be a good learning experience. You may only learn to never do something like this again, but if it turns out well, it could be worth time spent and a source of some pride of personal accomplishment.

JR

*** Back in the '70s I considered selling a time aligned hifi speaker kit, through my kit business. I had a real speaker designer who had designed bookshelf speakers for a couple companies (Ohm, Bozak, and a small company Fourier) who was willing to assist me. His weapon of choice for designing the passive crossover (recall that this was back in the '70s) was a programmable HP calculator. His crossover program took so long to run, that he would start it and let if run overnight. Today your cellphone probably has more computing power! FWIW I never did the speaker kit, so you know how my personal judgement falls on this.

PS: I got building speakers myself out of my system, earlier in the decade. Later working at Peavey it was really nice to have a whole department of competent transducer engineers that we could point at a project (For example I was able to use Charley's quadratic horn in a plastic box I was involved with), real industrial designers to make it look sexy (well sexy for Peavey).

Funny, after realizing some design errors in horns I had built, I recently built a version of Charley's quadratic horn, it sounds very good. After an extended time spent designing and testing a passive crossover for it, (still not done to my satisfaction, and the two driver types I have to stick on it require completely different crossovers even though they are both 1 inch exit titanium drivers) I put that project aside and immersed myself in the study, design and building of tapped horns, they do better in smaller packages than standard horn designs.

There was a reason Tom didn’t mind giving away the "will be history" LabSub, which is very similar to many other bass horn designs.

Below is a list of my hours designing and building eight 2 x8” monitors using passive crossovers, built in 2002.

I did the original crossover design starting with a basic values from a crossover component chart. Then using an RTA, my ears and a lot of substitution of parts, I honed in on something that looked fairly flat and sounded decent.

I try to keep learning, I certainly knew a lot more about crossover design in 2002 than I did in the 1970s when I built my first passive crossovers. One of those lessons was a passive crossover “mistake” in the 1980’s which cost me six JBL 2421 diaphragms after about 16 hours making them, and a fair amount of cost in capacitors, inductors and L pads.

Fast forward to entry 1100 on my New Mexico work log, late 2008.
I had acquired Smaart several months before, and learned to use it.
That was easy, since I had 30 years of measuring speakers it probably took no more than 100 hours to become somewhat competent in its use. Well, maybe 200, but who's counting ?

After testing my venerable 2x8T monitors, found the low end to be consistent, but the tweeter range measured slightly different for each unit, and the crossover region on all had a big phase glitch.

First problem was to choose a representative driver, since they all measured differently, I had to choose one “in the middle” to design a crossover around.

Turned out my careful listening and RTA observations in 2002 had not caught a polarity reversal hidden at the acoustic crossover frequency between the 3.15 and 4K 1/3 octave ISO centers. However, reversing the tweeter polarity, while “fixing” the phase glitch, now made the frequency response terrible around the crossover point.
The crossovers, even though not a single client had complained in the course of six years, were not “right”.

Also found the porting I decided on in 2002 could have been improved for the range the monitors are used in, I had tuned them low, but always ended up using a cut off above the port tuning. Porting them higher would have given about 3 dB more level where it would be more useful, and make the midrange more clear as the cones wouldn’t have to move as far to produce that level.

After 17 days of part time work I came up with a crossover that used about half the parts, and had a smoother response than the old ones. After all that work, I now try to match pairs of monitors, the driver differences were such that three different crossover designs would have been needed to compensate.

Oh, by the way, two brand new drivers fit somewhere in the deviation range of the eight old ones, since they did not match each other, they became part of the "average" I designed for.

I have thought of going to an 8 inch coaxial design for my monitors, but can’t justify the cost, since no one has ever complained about my monitors.

Coaxial crossover design is even more demanding than a standard horn/cone crossover.

If I did decide to spend the money, I would probably purchase the coaxial 8” Ramsdell makes, which would also probably cost less money than building them myself.

But then I'd miss out on the endless hours of fun of DIY :^).

Art (DIY from when that was the way the big boys all dun it) Welter

 

[John Roberts]

Re: Steering advice for those serious about DIY speakers.

Funny, after realizing some design errors in horns I had built, I recently built a version of Charley's quadratic horn, it sounds very good.
====
There was a reason Tom didn’t mind giving away the "will be history" LabSub, which is very similar to many other bass horn designs.
=====

Yup all speakers are basically the same.. while the details matter.

After 17 days of part time work I came up with a crossover that used about half the parts, and had a smoother response than the old ones. After all that work, I now try to match pairs of monitors, the driver differences were such that three different crossover designs would have been needed to compensate.

Oh, by the way, two brand new drivers fit somewhere in the deviation range of the eight old ones, since they did not match each other, they became part of the "average" I designed for.

Art (DIY from when that was the way the big boys all dun it) Welter

I don't know about those particular drivers (and I'm not a speaker guy) but one concept I had a very hard time explaining to old school Peavey dealers, whenever we would try to make a more professional offering, that to buy drivers that didn't vary a lot and would array together, cost more money. The dealers thought I was pulling their leg (if so somebody pulled mine first, but they didn't have any good reason to lie to me.).

JR

PS At least with active crossovers the driver impedance variations don't alter the crossover frequency, just levels.

 

[Art Welter]

Re: Steering advice for those serious about DIY speakers.

Yup all speakers are basically the same.. while the details matter.

PS At least with active crossovers the driver impedance variations don't alter the crossover frequency, just levels.

Unfortunately, impedance variations between drivers will still alter the Acoustic crossover frequency, as a driver with a lower impedance at X (electrical crossover) frequency will typically be louder at X frequency than it's sibling that has a higher impedance at X frequency.
If a HF driver is louder at X frequency, the acoustical crossover will shift up.

The variations with active crossovers are much less than when the same drivers are used with passive crossovers, but are still there if the drivers impedance curves do not match each other.

An extra turn of wire when a HF voice coil only has 20 turns can make a difference..

 

[Jeff Babcock]

Re: Steering advice for those serious about DIY speakers.

To return to the OSS comparison, the people involved with this project don't know how to "code" (i.e. they don't deeply understand loudspeaker design). Nor do these people have the "code development/debug/etc" tools (i.e. the loudspeaker measurement and design equipment and software). Hopefully this analogy will help expand some of the potential absurdity of the project.

Putting analog crossover design aside for a moment, consider that a single coax driver in a relatively small ported box is really not that absurd of an undertaking.

Even if the design is not absolutely optimal, I think you are seriously overstating the downside. The reality is, that a good driver, in a reasonable box, combined with use of measurements and reasonably well derived DSP settings is certainly not going to be a paperweight. I have used the homebrew wedges of several companies in my time in this industry and some of them were actually quite good despite them being given a lot less design thought than the coax project will put forth.

If you need a pile of wedges, I would strongly encourage purchasing them from a manufacturer.

Sure, but where is the fun in that?

I don't anticipate you meeting your performance goals without hiring a third party to do your XO design, and that point, how much are you really DIYing, and which members of the build pay for those design services?

On a personal note, I would not require passive XO for my intended use of these. But if the crossover is going to be too expensive for some, we might also consider a rudimentary crossover that is supplemented with additional single channel DSP. Many manufacturers have DSP presets for their products regardless of whether or not they are passive.

I totally get what you are saying, I just think you underestimate the folks here. I am no speaker design guru nor will I ever claim to be. But there's enough knowledge in this community to do something that's pretty solid IMHO.

 

[John Roberts]

Re: Steering advice for those serious about DIY speakers.

Unfortunately, impedance variations between drivers will still alter the Acoustic crossover frequency, as a driver with a lower impedance at X (electrical crossover) frequency will typically be louder at X frequency than it's sibling that has a higher impedance at X frequency.
If a HF driver is louder at X frequency, the acoustical crossover will shift up.

The variations with active crossovers are much less than when the same drivers are used with passive crossovers, but are still there if the drivers impedance curves do not match each other.

An extra turn of wire when a HF voice coil only has 20 turns can make a difference..

Yes, perhaps only a semantic distinction on my part. Changing the level of any bandpass changes the effective crossover frequency. I guess to be rigorous I would have to inspect if the driver impedance shifts the crossover frequency and bandpass level in the same direction or opposite, while it seems it would never fully cancel.

Just the old engineer in me, preferring one less variable to deal with.

JR

 

[Jack Arnott]

Re: Steering advice for those serious about DIY speakers.

I have thought of going to an 8 inch coaxial design for my monitors, but can’t justify the cost, since no one has ever complained about my monitors.

Coaxial crossover design is even more demanding than a standard horn/cone crossover.

Art (DIY from when that was the way the big boys all dun it) Welter

Hello Art,

Would you please explain why the coaxial is more demanding?

Regards, Jack

 

[Phil Graham]

Re: Steering advice for those serious about DIY speakers.

Hello Art,

Would you please explain why the coaxial is more demanding?

Regards, Jack

Jack,

I'm not Art, but the short answer is thus: impedance behavior of a compression driver on a coax near cutoff is generally more complicated than that when a compression driver is on a "proper" horn.

Concessions on horn flare for a coax lead to compression driver impedance behavior that requires more skill to manage, and all of this generally occurs very near the desired XO frequency.

A standard 2 way is generally easier.

 

[Art Welter]

Re: Steering advice for those serious about DIY speakers.

Jack,

I'm not Art, but the short answer is thus: impedance behavior of a compression driver on a coax near cutoff is generally more complicated than that when a compression driver is on a "proper" horn.

Concessions on horn flare for a coax lead to compression driver impedance behavior that requires more skill to manage, and all of this generally occurs very near the desired XO frequency.

A standard 2 way is generally easier.

In addition to the difficulties you mention, if the coaxial horn is independent of the cone, reflections from the cone off the back of the horn will cause peaks and dips that need to be addressed. Some of those problems can be helped with damping materials surrounding the horn, those materials become part of the passive crossover. Change those materials, and a new crossover needs to be cooked up.

Another difficulty is the fixed distance between the two co-axial drivers, a separate horn and driver allow some spacing leeway for time alignment. A longer or shorter horn can be chosen, woofer front or rear mounted, facilitating time alignment at the acoustical crossover point . With a fixed driver to driver relationship, time alignment needs to be done with passive components, very tricky and increasing the parts count.

And all those increased parts interact with each other, fix one problem and two others often pop up, and no program written can account for all the complex interactions.

 

[Curtis H List (Too Tall)]

Re: Steering advice for those serious about DIY speakers.

Jack,

I'm not Art, but the short answer is thus: impedance behavior of a compression driver on a coax near cutoff is generally more complicated than that when a compression driver is on a "proper" horn.

Concessions on horn flare for a coax lead to compression driver impedance behavior that requires more skill to manage, and all of this generally occurs very near the desired XO frequency.

A standard 2 way is generally easier.

Hi Phil and Jack,
It comes down to how you approach the problem.
Back in the late 70s I met up with someone who had a talent for building passive xovers. I suppose it helped that there was next to nothing on the market for active analog that had any flexibility.

In the early 80s I built him a HUGE crossover substitution box.
With that an Apple II, RTA and a FFT analyzer he was a force to be reckoned with.

He has forgotten more then I have learned in the last 15 years on the technical aspects of xover design.

That said if you gave us one week to design a 2-way passive xover the best he could hope for is a tie and I would not bet money on him.

The reason being the modern modeling program I have allows me to solve problems without me seeing what is going on “Under the Hood”.

I give it a target and it moves the values on my caps, inductors and resistors around till I have the solution.
So I don’t need to figure out what to do when the impedance goes nuts. That is what the modeling program is for.

In the end it is more complicated than that. If I just shove all the data into the program, hit start and go get a cup of coffee it will most likely go down a “Blind Alley” of one kind or another, but I am a LONG WAY from looking at radical impedance change and knowing which part to change to get a better result.
My friend might be able to do that…

I do eventually get to that point. Tweaking the values by hand (an ear) is one of the last things I do. If nothing else I move the values to part values that are for sale. I HATE unwinding inductors!!!

 

[Brian Oppegaard]

Re: Steering advice for those serious about DIY speakers.

Hello Art,

Would you please explain why the coaxial is more demanding?

Regards, Jack

Hi Jack,

I'm not Art either, but having built left center right speakers for my HT over the holidays using your excellent BMS 8 inch neo coax I do have a perspective. With a coax, the off axis response is consistent due to the geometrical advantage inherent in the design. But the inevitable effect on the frequency response of the discontinuity in the horn makes getting a flat frequency response with a passive crossover much more challenging. I am very happy with the results I got with DSP, but I would hesitate to attempt it otherwise.