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Old 19th February 2013, 03:56 AM   #361
nycello is offline nycello  United States
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Dave,

Many of us are unable to actually experience an FH3 before committing time and money to a project, so we need to rely on opinions and data to guide us. Would you please publish FR graphs for the FH3 - maybe just a couple with the Fostex and Mark Audio drivers? I know this doesn't tell the whole story, but it would provide some standard measurement which we could interpret in light of the excellent discussion here.

Thanks.
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Old 19th February 2013, 04:02 AM   #362
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I have no FR graphs of the FH3 at this time.

And as Ed Schilling says of any rear mouth horn, what do you wantit to look like, i'll move the mic (or speaker) a bit.

The enclosure only has significant effect below ~300 Hz, where the room dominates. So above 300 Hz a FR of the driver in almost any enclosure will bemuch the same. This enclosure uses the room as part of the horn. Each room will be different. The only FR curves that will be anywhere near valid for you will be in your room. And since the room dominates we end up back to the Ed Schiling quote.

Catch 22.

dave
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Old 19th February 2013, 04:11 AM   #363
nycello is offline nycello  United States
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Thanks for your reply. The standard practice is to place the microphone 1 meter from the driver on axis and then to take readings with 1 watt or 2.82 v at a distance of 1 meter. An anechoic chamber is not necessary, just a reasonably quiet listening room. Being Canadian myself, I understand your reluctance to do this outside.
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Old 19th February 2013, 04:20 AM   #364
nycello is offline nycello  United States
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So you actually edited the post to which I responded after my reply. Interesting - like re-writing history.
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Old 19th February 2013, 04:37 AM   #365
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Quote:
Originally Posted by nycello View Post
The standard practice is to place the microphone 1 meter from the driver on axis and then to take readings with 1 watt or 2.82 v at a distance of 1 meter.
That is how it is presented, not the way it is properly measured. The proper way to do itis to take the response in the far field and scale the results to give a 1m response.

FR measures of a rear-mouth horn are a can of worms.

An in-room FR response measure is only valid (roughly) above the frequency of the 1st reflection. A nearfield measure below that is next to useless in predicting the response in your room.

Since the box does not affect the response significantly above about 300 Hz just look at any measured response. Mark's graphs for the MA drivers are very good. The factory ones for the Fostex are less reliable due to heavy smoothing. Any FR presented by a diyer with the usual candidate budget measuring mics are only good to about 10k if calibrated and less if not.

A nearfield LF measurement of a sealed box is fairly straight forward. The math to sum a BR vent and the driver output is well worked out but subject to a greater margin of error. Trying to do that in a rear firing horn that uses the room to complete the horn is not at all worked out. And each room will be different. It ends up being a smulation.

I could provide FR measures but peple would actually think they mean something when they are much more likely to be invalid for your room.

dave
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Old 19th February 2013, 04:39 AM   #366
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Quote:
Originally Posted by nycello View Post
So you actually edited the post to which I responded after my reply. Interesting - like re-writing history.
I edited it immediately after posting (before your post) to better explain things. You posted while i was diting it.

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Old 19th February 2013, 05:01 AM   #367
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I should also add that an on-axis response, even if valid, is not very useful without off-axis results as well.

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Old 19th February 2013, 09:39 AM   #368
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Quote:
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Since the box does not affect the response significantly above about 300 Hz just look at any measured response. Mark's graphs for the MA drivers are very good.
Here for instance is the anechoic measure of A7.3. The FH3 with A7.3 will have similar response above the red line. Below the red line, the box gives gain and more extension but is dominated by the room and the placement in the room. It is also affected by the amount of damping used below the driver.

Click the image to open in full size.

dave
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File Type: gif Alp7-gen3-fr1530-june2011-s.gif (92.2 KB, 664 views)
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Old 19th February 2013, 01:58 PM   #369
nycello is offline nycello  United States
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Thanks for addressing my question. I guess I was looking for something like the modeled FR curves that are on the Frugal Horn Dalek and Metronome pages. BTW I am thinking about building a Metronome - the link to the plan seems to be down unless I am looking in the wrong place.
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Old 19th February 2013, 07:00 PM   #370
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Quote:
Originally Posted by nycello View Post
I guess I was looking for something like the modeled FR curves that are on the Frugal Horn Dalek and Metronome pages.
That i have (and must have posted somewhere sometime). Scott frrely posted those in the early days, but they are subject to the same caveats as a real FR measure. We have been much more careful for the last wall as people were more often then not mis-interprting them.

With MJK it is possible to specify part of a room with speaker placement and do a sim. The walls thou are perfectly stiff (not achievable in a real room). I do not know what simuated room these were in, but they are minimal damped. All the ripple above a couple hundered Hz will not be there in reality, and the LF will be modified by your room, placement and how much damping is actually used.

Quote:
BTW I am thinking about building a Metronome - the link to the plan seems to be down unless I am looking in the wrong place.
What link where? All the links on the Met data page work

dave
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