Hi all, a while ago I purchased a very lightly used set of, all Morel, ET 338, CAW 538 and CAW 938. My intention was and still hopefully is to pack these drivers into a nice 3 way speaker.
I have been learning VituixCAD but am a bit stumped with designing an enclosure for the CAW 938. I have a few questions about this regarding simulated SPL, Xmax and overall rules around these topics.
Please correct me if I'm wrong with anything above. Please see some enclosure simulations below and also some nearfield measurements of the CAW 938 and 538 test enclosures, these measurements are also gated from memory.
Hopefully this data is enough to go on, let me know if not or you need any more info. All measurements in REW have 1/24th smoothing applied.
EDIT: Sorry I also forgot to add the nearfeild accuracy cut off's.
Thank you!
I have been learning VituixCAD but am a bit stumped with designing an enclosure for the CAW 938. I have a few questions about this regarding simulated SPL, Xmax and overall rules around these topics.
- What SPL should these speakers be able to play up to, as in max db SPL for loud listening in a medium to large lounge at between 3-5m listening distance? Or if there is a standard for general high end home audio speaker I would be happy to aim for that.
- In terms of woofer roll off at what point do you not need to worry about cone excursion, weather that's referencing the SPL roll off, the power dip at the impedance spike, cone force or velocity. I have looked around but cannot find any solid information on what is safe in terms of Xmax, everything from sealed enclosure to bass reflex and band pass all pass the rated Xmax of driver even at fairly low wattage, why is this not a big concern. What are some good rules or parameters to follow in terms of this while getting the desired SPL output.
- I really want to do a nice job with these speaker as it will be the first I have designed myself and will be my daily drivers. Keeping this in mind they will be mainly used for music and watching movies. I would ideally like the qtc to be reasonably balance around 0.707 to avoid sloppiness or compression.
- I have built and done some measurement on some test enclosures. The volumes and dimensions are listed below:
- CAW 938: 320mm x 730mm x 436mm, built in 18mm OBS, the volume is 76.5L with a qtc around 0.71.
- CAW 538: 260mm x 320mm x 210mm built with the same 18mm OBS, the volume is 10.5L giving a qtc of 0.5 to hopefully keep the mids nice and dynamic.
- Finally, is the CAW 938 not suited for a low range woofer, my initial goal was anywhere from 500 to 250Hz down to the driver roll off with no HPF. If this does not seem viable I could definitely use it for a 2 way using it with a beyma compression driver.
Please correct me if I'm wrong with anything above. Please see some enclosure simulations below and also some nearfield measurements of the CAW 938 and 538 test enclosures, these measurements are also gated from memory.
Hopefully this data is enough to go on, let me know if not or you need any more info. All measurements in REW have 1/24th smoothing applied.
EDIT: Sorry I also forgot to add the nearfeild accuracy cut off's.
- CAW 938: 655Hz
- CAW 538: 1023Hz
Thank you!
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Hello
It's more like can they meet your SPL requirements in your room at a given distance. For example what are your Peak SPL requirements at the given listening distance? You can use the calculator to help work it out. Just drop in sensitivity, distance, placement and power available to get the max SPL. The other question is for example do you plan on using them to watch movies at THX levels? In that case SPL requirements are clearly defined. So you plug it in and see if you can meet them.
This should help on this:
WRT X-Max just design not to exceed it for your chosen peak SPL. You can for brief periods as there is an X-Mec which you avoid exceeding at all cost. Just use common sense. You should have displacement vs frequency and power in your sims as a reference. The obvious is you need to know again what the target peak SPL requirement is.
Rob 🙂
https://mehlau.net/audio/spl/
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There's no obvious answer to this question. It comes down to how you intend to use the driver. If you model with excessive power levels at low frequencies, you're definitely going to exceed Xmax in lots of conditions. A 9 inch woofer is only going to do so much. At low frequencies, it's mostly about volume displacement in the end. Each octave you go down requires 4x the volume displacement to maintain the same SPL level. So at Xmax that driver might be able to run you out of the room at 200 Hz, but it's going to be much more polite at 20 Hz.
For normal home audio, there's typically a handoff in the midbass or bass region where you switch from excursion limiting output to thermal considerations limiting output. So at higher frequencies the wattage limit of the voicecoil comes into play more directly, but at lower frequencies it's more to do with the enclosure and excursion.
To me, that woofer looks best for what you originally described: a 3-way. The impedance and frequency response discontinuities starting at 800 Hz would give me some concern from a general design standpoint. Maybe you can stretch the usable range to 1500 Hz, but it's something I'd listen to and measure before committing to. It comes down to what you find important from a design standpoint.
https://www.parts-express.com/pedocs/specs/297-086--morel-caw-938-spec-sheet.pdf
A 9-inch woofer also isn't that large in the grand scheme of things, so it's unlikely to be "loud" at 20 Hz. My idea of loud and your idea of loud may be two completely different things though. Do you have experience with any speakers you think were loud enough for your listening style? That might help set a reasonable target for what SPL you want. Erin's Audio Corner has quite a few speaker tests up that include distortion (86 and 96 dB at 1 meter) and dynamic range testing (76, 86, 96, 102 dB at 1 meter).
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My main concern is around the woofer being safe from mechanical damage from over excursion and also have low compression as to keep dynamic. I will be using them for both music and home theatre as I said previously. Which leads me to the concern of not being able to play them loud enough before distortion starts to affect the low from mechanical limits. I don't mind if it only plays to 60Hz as I will definitely be building some subs in the future to good bass extension.
Yes, that is exactly what I'm going for but don't have a calibrated SPL meter so can't tell what is "loud enough" for myself. So I do think following what reference levels for movies, such as Dolby and THX, including the headroom, is a good baseline as this is likely the loudest it would be comfortable to play would be.
From what it looks like is an average level of 85dB at the listening position with 20dB headroom, taking it to 105dB. Below is a chart of SPL loss due to distance to the listening position.
| Listening Distance | SPL Loss | Required Speaker Output at 1m |
|---|---|---|
| 2m | -6 dB | 91 dB |
| 3m | -9.5 dB | 94.5 dB |
| 4m | -12 dB | 97 dB |
| 5m | -14 dB | 99 dB |
| 6m | -15.5 dB | 100.5 dB |
| 7m | -17 dB | 102 dB |
| 8m | -18 dB | 103 dB |
| 9m | -19 dB | 104 dB |
| 10m | -20 dB | 105 dB |
So I'm wondering if this is the main this I should be simulating to. Or am I needing to simulate everything to the peak/headroom of 105dB at the listening position? Here is the chart for 105dB at listening position.
| Distance (m) | SPL Loss (dB) | Required Speaker SPL @ 1m (dB) |
|---|---|---|
| 2m | -6.02 | 111.0 |
| 3m | -9.54 | 114.5 |
| 4m | -12.04 | 117.0 |
| 5m | -13.98 | 118.98 |
| 6m | -15.56 | 120.56 |
| 7m | -16.90 | 121.9 |
| 8m | -18.06 | 123.1 |
| 9m | -19.08 | 124.1 |
| 10m | -20.00 | 125.0 |
This however looks unrealistic to achieve even at 2m for even the caw 938 which does not hit Xmax at its RMS of 150W, with a 1st order HPF at 250Hz, and only achieves about 107dB. In the headroom aspect does it only need to be under peak power ratings and X_mech?
Cheers!
