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Old 31st March 2009, 03:32 PM   #11
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Quote:
Originally posted by RobWells
Hi Mark,

I've not had bad results just measuring groundplane in my garden. Here's a measurement of one of my labs taken with the mic on the ground at 2m.
snip
Cheers,

Rob.
Given my own inability to measure well, your results seem really good and promising. Not sure how it translates to a horn in a corner in a room. Footnote: I am also taking part in a discussion of the many artifacts of measuring motorcycle HP on a dyno. Many. Relevant, eh.

But there's a lot I don't understand: "lab" official" "labforum", what's the frequency range, etc. Is one of those curves (which one?) simply a tone sweep trace taken with a high-class ground plane mic in your garden? Is one theoretical? Or can you direct me to a write-up?

Thanks.
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Old 31st March 2009, 05:01 PM   #12
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Hi Mark,

It's just coming into spring in the UK too... Have started tidying the garden just in case we get something resembling summer this year!

If you can wait a couple of months I'll be trying some tapped horn proof of concepts so will be able to post some measurements then.

Cheers,
Rob.
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Old 31st March 2009, 05:14 PM   #13
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Quote:
Originally posted by bentoronto



But there's a lot I don't understand: "lab" official" "labforum", what's the frequency range, etc. Is one of those curves (which one?) simply a tone sweep trace taken with a high-class ground plane mic in your garden? Is one theoretical? Or can you direct me to a write-up?

Thanks.

Hi Ben,

The 'lab' I referred to was a Labhorn, or Labsub. It is a subhorn designed to be used in groups of 6 by Tom Danley. Frequency range was pretty much 32Hz- ~80Hz

It was concieved and designed over at the Labsub forum

The top graph was a measurement of one of my labsubs with the 'official' Labsub forum measurement underneath it. My measurement was taken with pink noise.

Hope that answers most of your Q's

Rob.
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Old 31st March 2009, 05:27 PM   #14
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Quote:
Originally posted by bentoronto


Not sure how it translates to a horn in a corner in a room.

It doesn't, that's the point. If you want to measure a sub you cannot do it in room without measuring the room modes aswell. Therefore you'd have to 'subtract' the room from the measurement for it to be meaningfull.

So we either take Toms advice and go for the professional set up, or do what most DIY'ers do which is groundplane.

If you model as Mark suggested in halfspace and measure in halfspace then you should get pretty consistant results.

Thinking about if you wanted to measure in 1/8 space then perhaps find a very large empty warehouse and place the speaker in the corner with the mic at 2m from the corner, equally distant from the floor and the 2 side walls. Try and use some form of gating to cut down on reflections and measure fairly quietly to make any reflections come back lower than the noise floor. Just an idea I'd try if desperate to measure in 1/8 space...


Rob.
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Old 31st March 2009, 05:33 PM   #15
jbell is offline jbell  United States
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I've done some horn sub testing (correct or incorrect) and have always relied on this approach.

Outdoors, 28.3 volts, 10m, sine wave, and a spl meter that is either calibrated, or has a known calibration offset file to correct to flat. I also remeasure a known sub to make sure it matches what I measured last time, to know if my meter is drifting.

The only reason why I'm adding my 2c, is that I use notes.... yes sine wave tones that start at A0, 27.5 hz, and go on up. I don't pay much attention to peaks or dips between notes. Personally I feel that if my sub has a big response dip between notes, and the bass player is out of tune... I don't want to hear that note anyway...

For some reason, I like to have a sine wave 'sit' on a note for a few seconds before I declare a value.. not sure if that's more scientific than a tone sweep or not, but it makes me feel better.

And the only way I know of to do a 1/8th space measurement, is to find an outdoor racquetball court.
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Old 31st March 2009, 06:32 PM   #16
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Very nice of Rob and jbell to try to help me - I appreciate the help and feel pretty out of date. I've been curious about these horns (on a grouchy day, I'd say, "so-called" horns) and look forward to learning more. The labforum is bit too far downstream for a beginner, but I'll persevere.

Some further questions, please.

1. How are you doing that pink noise test - swept 1/3 octave source or 1/3 octave analyzer or what?

2. Not sure what an outdoors racquetball court is - how many walls - might be a cultural thing.

Back to dyno testing of motorcycles: a dyno test is run full throttle from idle to screaming top in fourth gear. Not a bad simulation of a drag race but not too useful to tune for street riding.

I can see the many measurement benefits of measuring speakers out of doors and I can see the ungeneralizability of testing them in your music room. But the music room performance is all that counts in DIY.

Nor am I optimistic about "... well, you just subtract out the room response." Is there a way of doing so?
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Old 31st March 2009, 06:55 PM   #17
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Quote:
Originally posted by bentoronto


1. How are you doing that pink noise test - swept 1/3 octave source or 1/3 octave analyzer or what?

2. Not sure what an outdoors racquetball court is - how many walls - might be a cultural thing.


I can see the many measurement benefits of measuring speakers out of doors and I can see the ungeneralizability of testing them in your music room. But the music room performance is all that counts in DIY.

Nor am I optimistic about "... well, you just subtract out the room response." Is there a way of doing so?
Hi Ben,

1) full range pink noise into the speaker under test with no crossovers connected. Measured using treRTA 1/24th octave version.

2) Think it's like a squash court without a ceiling ?

You seem to be wanting to know how to take in-room measurements of your system rather than how to accurately measure a sub..

What exactly do you want to achieve by taking measurements in room ?

Rob.
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Old 31st March 2009, 07:15 PM   #18
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Thanks for answers. Yeah, I'm living in the old days when you'd have a nice 1/3 filter analyzer in an awful green case.... when I was at Bell Labs.

This thread was about measuring horns. The output of a horn is very dependent on the room in which it is installed and kind of "undefined" to measure it elsewhere. As measurements go, rather soft relationship between the horn in the backyard and your living room (much more so than other freq bands or other enclosure types). Like an automotive dyno run. Again, the difference between a manufacturer's perspective and a DIY perspective.
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Old 31st March 2009, 07:20 PM   #19
jbell is offline jbell  United States
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yes an open Tri-corner of sufficient size was what I was referring to. Racquetball was what came to mind. I would guess in toronto, where you have the underground tunnels connecting buildings for weather reasons... that outdoor courts are not popular...

An open concrete tri-corner is the only way I can think of to measure a sub that depends on a corner (ala, K-horn) to complete the horn path.
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Old 31st March 2009, 07:27 PM   #20
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Really ?

Here's my 2 labs as measured across my couch in 3 positions. In room doesn't look hugely different to outdoors.

Again, what are you trying to achieve by the indoor measurement ? Maybe measure a sealed sub outside, then indoors in the same place as you'll place your horn. Compare indoors to out, this will show the rooms effects. Then put your horn in and measure at exactly the same position. You'll have some idea of the rooms effects from the sealed measurement..

Rob.
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