A Cardioid mid Coax 3 way speaker

[Vineeth Kumar V]

I calibrated SPL on my measurement mic using a minidsp UMIK-1+SPL meter in REW. Here is the result with the current crossover in place (It is 86dB SPL at 1m at 1kHz)

Hope this is fine.
This itself was uncomfortably loud for me and others at home and for the listening situation of this speaker, which is mid to nearfield.
So I won't take a measurement at anymore louder SPL

 

[voodooless]

Maybe only show THD, 2nd 3rd harmonic, and noise floor Especially below about 60hz, it looks like the noise floor is drowning most of the harmonics.

Overall though, it doesn't look too bad. The small coaxial does about the same distortion as the woofer it seems, but it also shows that the cardioid configuration makes coaxial work quite a bit harder than usual. Something, we've also seen in the D&C C8 review a while back. It may be interesting to see what happens if you raise the X-over a bit more. You may be able to trade some directivity for lower distortion. Not sure what the best tradeoff would be, probably the better directly

 

[sigbergaudio]

That same coax in a cardioid enclosure (crossed over at ~600hz). This is at 100dB/1m.

 

[voodooless]

That same coax in a cardioid enclosure (crossed over at ~600hz). This is at 100dB/1m.

That's quite a big difference. There may be other sources of distortion in @Vineeth Kumar V measurements?

 

[sigbergaudio]

Well, first of all a wideband cardioid system will have more distortion / be less efficient (not sure where the driver is crossed over?), second the UMIK-1 adds some distortion all on its own, so it's not a great device for accurate THD measurements. Beyond that I can only speculate.

 

[Vineeth Kumar V]

@sigbergaudio: My coax is crossed over at 300Hz..Probably this has an effect too.
About the mic, I have no idea how good it is for distortion measurements.. By the way the distortion measurement was done using the Sonarworks soundID mic and not minidsp umik-1. My UMIK-1 has other issues, So I cant use it for this purpose. I just used it for SPL calibration of the XLR mic

 

[sigbergaudio]

@sigbergaudio: My coax is crossed over at 300Hz..Probably this has an effect too.
About the mic, I have no idea how good it is for distortion measurements.. By the way the distortion measurement was done using the Sonarworks soundID mic and not minidsp umik-1. My UMIK-1 has other issues, So I cant use it for this purpose. I just used it for SPL calibration of the XLR mic

I'm not familiar with that microphone, but it is likely it's not perfect in this regard either.

Anyway, above 300hz you're mostly at 1% or below at what I'm guessing is perhaps louder than you typically listen, so it shouldn't be of much concern.

 

[Vineeth Kumar V]

oops, I forgot to say that two of the output channels connected to the woofer driver, on my audio interface have gone bad..
It has constant 2% THD across full spectrum. This might definitely have some effect on that 300Hz bump. Need to get a better interface...

 

[abdo123]

@abdo123: Thanks
The coaxial driver at the top is in a passive cardioid "enclosure".
55mm thick basotect melamine foam rings surround the back of the driver (under a sock cloth)
View attachment 323133
Here is the absorption efficiency of basotect
View attachment 323134

This should not work as well as it does hahaha.

 

[abdo123]

Maybe only show THD, 2nd 3rd harmonic, and noise floor Especially below about 60hz, it looks like the noise floor is drowning most of the harmonics.

Overall though, it doesn't look too bad. The small coaxial does about the same distortion as the woofer it seems, but it also shows that the cardioid configuration makes coaxial work quite a bit harder than usual. Something, we've also seen in the D&C C8 review a while back. It may be interesting to see what happens if you raise the X-over a bit more. You may be able to trade some directivity for lower distortion. Not sure what the best tradeoff would be, probably the better directly

I don’t think the industry ever picked better directivity over output.

 

[Vineeth Kumar V]

but it also shows that the cardioid configuration makes coaxial work quite a bit harder than usual.

Actually, a cardioid enclosure can give more output than the same driver in a sealed enclosure down to a certain frequency..
Take a look here and the following post

A 3 way design study

@mabat: Sure. I will try to measure it tomorrow.. :) But if I close the port completely, the driver will only get almost no space behind it to even act like its in a closed box I think.. :unsure:

www.diyaudio.com

In my case, there is some other distortion source(s) at work, the No.1 suspect being my audio interface used for DSP as I pointed out above. So let's not trust my distortion result for now..

 

[D!sco]

I meant to ask in the diyaudio.com thread but I might as well ask here how well the wavecor works as a midbass driver and a subwoofer. I know you've got those massive bass towers, did you consider at one point having a dedicated midbass and crossing to the subs, or was that never part of the design philosophy? Your other thread is massive and I get lost all the time trying to read it.

 

[Vineeth Kumar V]

I meant to ask in the diyaudio.com thread but I might as well ask here how well the wavecor works as a midbass driver and a subwoofer. I know you've got those massive bass towers, did you consider at one point having a dedicated midbass and crossing to the subs, or was that never part of the design philosophy? Your other thread is massive and I get lost all the time trying to read it.

So this speaker started out as a relatively low-output PC speaker build.
A larger woofer than 7-8 inches was never in the picture while the design was thought about simply because I didn't have the space to accommodate bigger speakers. But then things became more exciting, and I decided to scale up the size of the bass driver a little bit. Since I also had this driver in storage, I decided to use it in this build.

About the capability of the Wavecor SW215 driver as a midbass driver, I think it works pretty fine so far in this application. But this is still early days and I haven't compared these with anything else. I think it is better suited as a subwoofer driver for a small, relatively low-output PC speaker kind of build than as a dedicated midbass, some of the reasons being that rising impedance curve, those big rubber surrounds causing directivity issues up higher, and the relatively low(ish) sensitivity etc

 

[TKasprzak]

This design is so brilliant I can't stop thinking about it
Just an idea. This should also work great in an arrangement similar to LXmini, with woofer mounted in the pipe and coax in the foam cylinder above.

I'm long-time lurker but this is my first post. So welcome everyone, It's great such forum exists.

 

[Vineeth Kumar V]

I decided to scale up the cardioid mid-concept a little bit more..

Design iteration v2 for a big cardioid box (for Faital Pro15PR400) + EXAR 400 waveguide
The box is only about 26cm deep from the 'baffle surface' (whatever little there is).
A potential accompanying spatially distributed monopole subwoofer set-up for getting the real low frequencies is not shown here..
I like the looks of this

Driver can even be magnet mounted

 

[olieb]

I decided to scale up the cardioid mid-concept a little bit more..

Design iteration v2 for a big cardioid box (for Faital Pro15PR400) + EXAR 400 waveguide
The box is only about 26cm deep from the 'baffle surface' (whatever little there is).
A potential accompanying spatially distributed monopole subwoofer set-up for getting the real low frequencies is not shown here..
I like the looks of this

Cool speaker. Do you have a special reason to make the distance (center to center) so big?

 

[Vineeth Kumar V]

So the following is the general idea I had in mind with the C-C spacing
First, the free standing waveguide should be allowed to do its job properly. That needs bit of space. Then, the intended crossover with the horn may occur somewhere in between 600-800Hz.
The driver Centre-to-Centre (C-C) is 50cm in the pic (this will be variable though). The minimum C-C distance possible is 40cm due to driver and horn sizes (this is about one wavelength at 700Hz). The speakers are intended to be listened to at 2+ m away. The rough C-C I am targeting is between 1x to 1.4x wavelength at crossover due to the following reasons:

Some help with lobing

I think I understand the concept but can't figure out the solution. "Lobing occurs with any two drivers producing the same frequency range in parallel (identical signal) where the distance between the drivers is greater than 1/4 wavelength of any frequency they are reproducing." So if I am...

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