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Alpair 7P directivity measurements
Alpair 7P directivity measurements
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Old 31st January 2015, 02:48 AM   #21
Bob Brines is offline Bob Brines  United States
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Just because you can do something does not mean that you should do it. The point is question is how low can an A7 go.

I have a cabinet that is tuned to 50Hz and with a bit of bass boost, it will do 40Hz. But at very modest SPL. I use that speaker as the top of a FAST with a 12" woofer under it. The XO is 200-250Hz, depending on how I feel on any given day. Unloading the bass from the A7 greately improves the headroom, and noticeably reduces IM distortion.

I build a pair of speakers using an 8" woofer and an A7. Crossed them passive at 700Hz. Both drivers were so far from cut-off that an electrical LR2 gave an acoustic LR2. Four parts, and of reasonable size. Integration was very good.

Where to XO depends on what you are trying to do. At the baffle step is usually convenient, particularly if bi-amping. Crossing above 300Hz runs the risk of phasing problems. Room modes might demand something else. My A10's in the HT are crossed at 165 to solve a room mode problem.

It depends.

Bob
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Old 31st January 2015, 07:47 PM   #22
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by planet10 View Post
Tom, did you modify that plan (as has been posted) for the A6p? ie leave out the vent spacer.
I removed all the vent fill, actually.

I ran the enclosure through Martin King's MathCad scripts as a sanity check and liked the simulated performance with all vent fill removed. Leaving the side fill in as, I think, is the recommendation, left me with a bit of peaking around the port resonance and a saddle in the 100-200 Hz region - in simulation. I may go back and add that port fill just to get a correlation between simulation and reality.

I'm getting a little bit of a droop in SPL in the 100-200 Hz region that adding the side fill will probably bring back up. We're talking a few dB here. Nothing earth shattering.

Quote:
Originally Posted by planet10 View Post
I should also mention that with A12pw reaching up to 10k+ that leaves a lot of XO point latitude. In this case the baffle step frequency is the prime driver determining the XO freq.
I've been drooling over that one as well. My main goal with this 2-way build is to get better time alignment between the driver and the port. I would also like to get the f3 below 40 Hz if possible. I was thinking to go full range in an MLTL, but given that I can hear the relatively short path length in the mMar-Ken6, I don't think I'll be happy with the 1-1.5 m path length in an MLTL...

A sealed enclosure solves the driver-port time alignment problem completely, at the expense of SPL below 100 Hz. One can blow $400 (per driver!) on a Seas Revelator and get f3 = 30 Hz in a 38-liter box. The Revelator I'm looking at is a 25.5 cm diameter driver, so now the baffle width blows up. Not a fan...

A less efficient way for draining one's bank account would be to go with one or two 12PWs with a port located close to the driver(s). If the port is short and close to the driver, the time alignment (or phase coherency) should be as close to a sealed box as possible, right?

~Tom
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Old 31st January 2015, 08:18 PM   #23
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by Bob Brines View Post
Just because you can do something does not mean that you should do it. The point is question is how low can an A7 go.
That is certainly true. As I have no experience with the 7P and only minimal speaker design experience, I'm just asking the what-ifs at this point.

I appreciate your insight on what's possible in reality...

Quote:
Originally Posted by Bob Brines View Post
Where to XO depends on what you are trying to do. At the baffle step is usually convenient, particularly if bi-amping. Crossing above 300Hz runs the risk of phasing problems. Room modes might demand something else. My A10's in the HT are crossed at 165 to solve a room mode problem.
Tradeoffs, tradeoffs. I would like to keep the XO frequency low to get the most out of the full-range driver. It would be nice to at least keep the XO away from the main vocal frequency range (say 200-600 Hz).

We'll see where I land. Right now, I need to hit the books and learn a few things so I can reason more clearly about the tradeoffs.

~Tom
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Old 31st January 2015, 08:25 PM   #24
planet10 is offline planet10  Canada
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Alpair 7P directivity measurements
Quote:
Originally Posted by tomchr View Post
I removed all the vent fill, actually.
...left me with a bit of peaking around the port resonance and a saddle in the 100-200 Hz region - in simulation.
No vent spacers is right for the A6p. There should be a bit of peaking just before roll-off this is flattened out by the high ratio vent.

Quote:
My main goal with this 2-way build is to get better time alignment between the driver and the port. I would also like to get the f3 below 40 Hz
Unless the enclosure is very long, frequencies at the vent are so large time alugnment is irrelevant.

F3 is not something i look at as it has no perceptional meaning... in 35 litre with the miniOnken alignment, F6 is estimated in the mod 30s, F10 in the low 30s.

Quote:
f possible. I was thinking to go full range in an MLTL, but given that I can hear the relatively short path length in the mMar-Ken6, I don't think I'll be happy with the 1-1.5 m path length in an MLTL...
You are likely assigning the wrong cause to whatever you are hearing in the mMar-Ken.

Quote:
A sealed enclosure solves the driver-port time alignment problem completely
I suspect you are just hearing what a bass reflex does -- damped back somewhat in the miniOnkens.

Quote:
One can blow $400 (per driver!) on a Seas Revelator and get f3 = 30 Hz in a 38-liter box. The Revelator I'm looking at is a 25.5 cm diameter driver, so now the baffle width blows up.
Bessel Q, A12pw hits F6 of 50, F10 in the mid 30s.

Quote:
one or two 12PWs with a port located close to the driver(s). If the port is short and close to the driver, the time alignment (or phase coherency) should be as close to a sealed box as possible, right?
Nope.

dave
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Old 1st February 2015, 06:23 AM   #25
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by planet10 View Post
No vent spacers is right for the A6p. There should be a bit of peaking just before roll-off this is flattened out by the high ratio vent.
Good point. I just read about the high aspect ratio ports this afternoon in Martin Colloms, "High Performance Loudspeakers". Pretty decent book...

Quote:
Originally Posted by planet10 View Post
Unless the enclosure is very long, frequencies at the vent are so large time alugnment is irrelevant.
Hmmm... What happens on a transient? Say a good stomp on a bass drum? That's a pretty wide-band signal. What I think I'm hearing is that the bass thump from the port arrives slightly after the thump from the driver. I don't get that with sealed boxes. I'm thinking it's probably what a bass reflex does. I'm curious to hear your interpretation, though.

Quote:
Originally Posted by planet10 View Post
F3 is not something i look at as it has no perceptional meaning... in 35 litre with the miniOnken alignment, F6 is estimated in the mod 30s, F10 in the low 30s.
I agree that F3 is largely of academic interest. It's just a handy figure of merit that's reported by just about all speaker design software.

Quote:
Originally Posted by planet10 View Post
You are likely assigning the wrong cause to whatever you are hearing in the mMar-Ken.
Could be... They're nice speakers for sure. I built the enclosures in 11-ply Baltic birch plywood with maple veneer. Gave them some 6-8 coats of polyurethane and polished them up. They turned out very nice. I like them. I needed a small bookshelf speaker. They'll work out quite nicely.

Now for my main speakers, I'd like to have deeper bass. Ah... Another day another project.

~Tom
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Last edited by tomchr; 1st February 2015 at 06:26 AM.
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Old 1st February 2015, 07:15 AM   #26
planet10 is offline planet10  Canada
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Alpair 7P directivity measurements
Quote:
Originally Posted by tomchr View Post
Hmmm... What happens on a transient? Say a good stomp on a bass drum?
A BR is a 4th order roll-off vrs the 2nd order of a sealed. Lower order filter should have better transient response.

dave
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Old 1st February 2015, 09:37 PM   #27
tomchr is offline tomchr  Canada
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Good point.

I should hit the books. I'll start a separate build thread once I get a little further. Thanks for your help.

~Tom
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