Coaxial Active Speaker Build

[IPunchCholla]

I’m starting a new build, active coaxial designed to be crossed with a sub at around 180 hZ. I have the CAD design done-ish (depending on actual speaker measurements). I thought I would share as I go. But it will likely be a slow build…

Details:

Materials: MDF cabinet, Birch plywood baffle(unless I can find some really nice wood for the baffle), acoustic foam lined interior.
Volume: 15.97887677 liters (gotta love CAD)
Driver: Lavoce CSF082.00K 8”
Amplifier: Hypex FA-122

 

[LTig]

You need 2 subs because at 180 Hz you will notice their position. They need to be placed below the sats to create a proper soundstage.

 

[IPunchCholla]

You need 2 subs because at 180 Hz you will notice their position. They need to be placed below the sats to create a proper soundstage.

These will be for an audio installation, with between 4 and 16 speakers depending on the installation space. I am planning on having a sub for each speaker, but that also depends on speaker siting. My initial sims of the box and ports show good extension down to 100 hZ. Unfortunately, LaVoce doesn’t seem to give out there FR and ZMA files so actual crossover point to the subs will have to wait until I can make my own measurements.

 

[TheBatsEar]

What frequency will you cross over? What max SPL do you expect to get out of it?
Do you have distortion measurements of the drivers?

 

[Grotti]

For what reason did you choose this particular driver? There are quite a lot of 8 inch coaxial drivers out there: why pick this one?

 

[sarumbear]

I assume you are using this driver? Have you calculated the TS parameters?

Coaxial speaker Lavoce CSF082.00K, 8+8 ohm, 8 inch

en.toutlehautparleur.com

It looks like your enclosure is too large for that driver and you will achieve a very low Qtc, which maybe difficult to cross over to the sub. A simple calculation gives Qtc=0.47 at F3=181Hz.

 

[IPunchCholla]

What frequency will you cross over? What max SPL do you expect to get out of it?
Do you have distortion measurements of the drivers?

No distortion measurements, only FR and impedance. it should be able to hit 110 dB at two meters. Recommended cross is 2200. I’m excited about the FA-122 as it will allow me to really experiment with filters.

 

[IPunchCholla]

For what reason did you choose this particular driver? There are quite a lot of 8 inch coaxial drivers out there: why pick this one?

Price (I might need 16 of them) and listed performance mostly. Kinda just winging it with this one to see what it can do Since I can’t find any measurements.

 

[sarumbear]

…I can’t find any measurements.

If this is driver, I can assure you it has one of the most comprehensive measurements you can find on any driver.

Coaxial speaker Lavoce CSF082.00K, 8+8 ohm, 8 inch

en.toutlehautparleur.com

 

[IPunchCholla]

I assume you are using this driver? Have you calculated the TS parameters?

Coaxial speaker Lavoce CSF082.00K, 8+8 ohm, 8 inch

en.toutlehautparleur.com

It looks like your enclosure is too large for that driver and you will achieve a very low Qtc, which maybe difficult to cross over to the sub. A simple calculation gives Qtc=0.47 at F3=181Hz.

I haven’t calculated them yet, just going off the specs from LaVoce. The cabs are designed as much for aesthetic reasons (this is for a generative sound piece not traditional music listening) as acoustic. It looks in my modeling that the cab should really be half that volume. I’m playing with ideas for filling it up vs. a smaller cab.

 

[sarumbear]

I haven’t calculated them yet, just going off the specs from LaVoce.

Can you share a link to the manufacturer’s specs where they suggest Vb=16L, the size you plan to use?

 

[IPunchCholla]

Can you share a link to the manufacturer’s specs where they suggest Vb=16L, the size you plan to use?

Recommended volume is 8.35 liters, I’m not planning on running it at 16 liters, but that is the volume of the cabinet as designed. I’m planning on filling it with closed cell foam (CNC’d to fit precisely) and going with the acoustically recommended volume, but keeping it the size it is for purely aesthetic reasons. Since I have my own CNC, making a smaller cabinet is no problem. I actually originally designed it with the recommended volume, but didn’t like it visually.

 

[sarumbear]

Recommended volume is 8.35 liters,

Interesting. At that volume Qtc=0.56, near to Bessel alignment, which is an odd choice as crossover to sub will not create a flat response. You need Butterworth alignment for that. Naturally you can change them using the DSP.

I ran a simple chart group. It seems the driver is designed for vented enclosures as that gives the most optimal response, though you cannot use that as your 110dBSPL @2m requirement cannot be matched below around 160Hz.

Red: 16L, your enclosure, over-damped 2nd order
Orange: 8.3L, the “recommended volume,” near Bessel 2nd order
Green: 4.2L, Max flat amplitude, Butterworth 2nd order
Blue: 10.6L vented (@ 88Hz) Max flat amplitude, Butterworth 4th order

I hope these will be helpful. Enjoy the ride

 

[IPunchCholla]

110dBSPL @2m requirement cannot be matched below around 160Hz.

That’s not the requirement, just max. They will be about 70 dB at 2 meters, max.

Thanks for the graphs! The red is what I was getting too last night on the calculators. I hadn’t had time to run the lower volumes I was planning on, but that 4th order butterworth was what I was hoping to see (hence saying I would cross at around 180 to the subs, directionality not really being important for this use, but I would love to get it down closer to 100.

 

[sarumbear]

That’s not the requirement, just max. They will be about 70 dB at 2 meters, max.

You are confusing us. In the post above you mentioned hitting 110dBSPL, which means max, in the above sentence you confirm that was indeed the max but then on the same sentence you said 70dBSPL is the max. There is 40dB difference between your two maxes. That is a 100x difference!

Thanks for the graphs! The red is what I was getting too last night on the calculators. I hadn’t had time to run the lower volumes I was planning on, but that 4th order butterworth was what I was hoping to see (hence saying I would cross at around 180 to the subs, directionality not really being important for this use, but I would love to get it down closer to 100.

If you will use the 4th order Butterworth alignment then you can simply cross over at 100Hz, which is the F3. That will simplify the sub LP as most are already 4th order.

 

[IPunchCholla]

You are confusing us. In the post above you mentioned hitting 110dBSPL, which means max, in the above sentence you confirm that was indeed the max but then on the same sentence you said 70dBSPL is the max. There is 40dB difference between your two maxes. That is a 100x difference!

Sorry, I phrased that badly! The speaker should be capable of around 110dB at 2 meters. The loudest I will actually use it in the installation is likely to be 70dB At 2 meters.

 

[Ron Texas]

Sounds like an interesting project. The subs will be a challenge themselves with a crossover as high as 180 Hz.

 

[sarumbear]

Sorry, I phrased that badly! The speaker should be capable of around 110dB at 2 meters. The loudest I will actually use it in the installation is likely to be 70dB At 2 meters.

In which case you don’t have any worries about levels. The driver is extremely efficient, you won’t need much power to drive them either.

 

[IPunchCholla]

Sounds like an interesting project. The subs will be a challenge themselves with a crossover as high as 180 Hz.

I’m definitely hoping to cross them lower than that. As per @sarumbear, it looks like 10.6 litters and a 4th order but warmth should get me to 100 hZ. Below is a pic with the air volume in red. This is 10.7 liters air volume. I still need to tweak it a bit.

 

[Ron Texas]

@IPunchCholla 100 Hz crossover is a lot easier.