One low impedance amp channel, double the power for two drivers.
You are right, I didn't quite gain 5dB before the spacing started to work agaist me. You will find an optimum spacing for your drivers that will likely be somewhere aproaching the driver diameter.
I believe the measured gain is simply from the increased path length of driver one rear to driver two rear as opposed to driver one front to rear. Linkwitz calls this "D" in his calculations. A second driver, a larger baffle or a winged arrangement (eg H baffle) can be used to increase D. A second driver can only increase D by so much.
D increases.
You are right, I didn't quite gain 5dB before the spacing started to work agaist me. You will find an optimum spacing for your drivers that will likely be somewhere aproaching the driver diameter.
I believe the measured gain is simply from the increased path length of driver one rear to driver two rear as opposed to driver one front to rear. Linkwitz calls this "D" in his calculations. A second driver, a larger baffle or a winged arrangement (eg H baffle) can be used to increase D. A second driver can only increase D by so much.
D increases.
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This is all so interesting I have just pulled these beauties out of my spare parts drawer.
So I will also get to some more experimenting!
This is proper interesting stuff
I agree. Nothing like real measurements.
Andrew - so where does this put us?
Are we saying that the clamshell configuration is the same as an isobaric configuration - because if we are, I do not understand the 6dB increase in output we saw when I double the amps and drivers - as this implied increased output with the same excursion?
Also, if you are say this clamshell is the same as an isobaric setup......and given you had the same increased output at your furthest spacing (accounting for the increased acoustic source distance given your close mike measurements) then how far can you seperate the drivers and they still behave like a 'slug of air' is between them (back to my earlier thought experiment)!
Are we saying that the clamshell configuration is the same as an isobaric configuration - because if we are, I do not understand the 6dB increase in output we saw when I double the amps and drivers - as this implied increased output with the same excursion?
Also, if you are say this clamshell is the same as an isobaric setup......and given you had the same increased output at your furthest spacing (accounting for the increased acoustic source distance given your close mike measurements) then how far can you seperate the drivers and they still behave like a 'slug of air' is between them (back to my earlier thought experiment)!
Thanks for the measurements William,
so, the gain is between something as 2dB and 4-5dB, depending on the distance. Looking back at my own measurements, I got a bit more than 3dB, but measured with a single distance only, probably around some 30mm. I am sort of relieved that my measurement was not off, again.
I am looking forward to more measurements, and hope to be able to contribute some myself.
so, the gain is between something as 2dB and 4-5dB, depending on the distance. Looking back at my own measurements, I got a bit more than 3dB, but measured with a single distance only, probably around some 30mm. I am sort of relieved that my measurement was not off, again.
I am looking forward to more measurements, and hope to be able to contribute some myself.
No worries Erik
There is probably an optimum driver spacing based on diameter. This is something the folk who are using nude clam shell arrangements should explore before comitting to a spacing. There is a very good chance a larger driver could achieve a >6dB output gain with the right spacing. An H frame baffle arrangement could give you even more.
There is probably an optimum driver spacing based on diameter. This is something the folk who are using nude clam shell arrangements should explore before comitting to a spacing. There is a very good chance a larger driver could achieve a >6dB output gain with the right spacing. An H frame baffle arrangement could give you even more.
We are squinting at these charts - William has shown a 4.5-5dB increase in output.
I have shown an ~6dB increase.
There is 1-2dB differences here that we are drawing conclusions from.
I am the only one to use two separate amps with the same power and output with the same ohms per amp - a proper, like with like comparison.
Can someone please repeat my measurements with two amps and the same loads per driver?! Please?
I have shown an ~6dB increase.
There is 1-2dB differences here that we are drawing conclusions from.
I am the only one to use two separate amps with the same power and output with the same ohms per amp - a proper, like with like comparison.
Can someone please repeat my measurements with two amps and the same loads per driver?! Please?
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William,
another question on your measurements. I thought: look, dipole peak at circa 650Hz, the null afterwards. Then I did a quick simulation in edge.exe and found that the dipole peak for the 150mm driver should be at about 1k8. So do you think that the measured peak and valley are due to the magnet being between driver and mic?
thanks!
Erik
another question on your measurements. I thought: look, dipole peak at circa 650Hz, the null afterwards. Then I did a quick simulation in edge.exe and found that the dipole peak for the 150mm driver should be at about 1k8. So do you think that the measured peak and valley are due to the magnet being between driver and mic?
thanks!
Erik
I still feel that this configuration is *NOT* behaving in the same way as an isobaric config.....
Initially there was scepticism that there would be anything beyond the expected 3dB increase in output due to a doubling of amplifier power - there are multiple comments to this effect earlier in the thread.
Now we are concluding there is indeed up to 6dB to be gained from the compound woofer arrangement but probably not a 6dB increase in max SpL as it behaves the same as the isobaric configuration.
I think there is also a concurrent increase in max SpL too......
How do we drill down to this guys?
Initially there was scepticism that there would be anything beyond the expected 3dB increase in output due to a doubling of amplifier power - there are multiple comments to this effect earlier in the thread.
Now we are concluding there is indeed up to 6dB to be gained from the compound woofer arrangement but probably not a 6dB increase in max SpL as it behaves the same as the isobaric configuration.
I think there is also a concurrent increase in max SpL too......
How do we drill down to this guys?
Oh s**t, sorry!
I've been called lots of odd names before, but I've never been called Andrew!
It's all good. Funny how the others followed along
I've been called lots of odd names before, but I've never been called Andrew!
It's all good. Funny how the others followed along
Absolutely - I thought I was being polite *Andrew*
The dipole peak was indeed just below 2K, I saw it before rescaling. The wavelengths are around driver diameter there and things were starting to get a little messier. The dip may have been magnet related or a numer of other things. It was a ground plane measurement with no other reflective surfaces within 1M
I've been called lots of odd names before, but I've never been called Andrew!
It's all good. Funny how the others followed along
Yes, but credit where it is due - it was Juhazi who started the confusion!
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