The Metronome

[schro20]

Originally posted by Scottmoose
That's why in-room response plots are really only useful to the person who owns the speaker & the room.

Ok. Fair enough. But the goal of doing the gated measurements (if I understand ARTA correctly) is to get a plot (from 200Hz onward in my case) which effectively gets a free field measurement. I could move the whole things out to the driveway...

You can see a degree of step-loss coming in from about 480Hz

Help me understand what makes you say that.

As for trying to measure damping, you'll want to be measuring cabinet (i.e vent) output & look for unwanted harmonic resonances. If there are any, it's not sufficiently damped.

Ok. If I measure there (I did that a few days ago but didn't know what to make of it), what am I looking to find and what would raise suspicion?

TBH, the more important thing is whether you enjoy the sound. If you do, it doesn't matter one jot what a graph says.

I actually agree. My problem is that I am new to this game. I don't know what I am listening for. And if there is something I don't like I have no idea what sort of thing might change that. (That's the primary motivation for me to approach this from a measurement point of view.)

So, let me say this differently. If I want to learn about the kinds of things that are involved in making Mets sound good, what should I try? Right now I am using an essentially unlined cabinet as a starting point. I can listen for a while and then try something that gives me another data point. What should that be? I seem to recall someone suggesting to line 3 of the interior walls from the top down to the height of the driver. (I have some single and double layer Whispermat, the polyurethane 1in foam, and also some 1in felt to play with; which one should I try?)

peter

[schro20]

Based on Scootmoose's observations here are octave and 1/3 octave averaged plots. (I took a closer look at the Fostex plots and they hae some of the same characteristic features in the higher frequencies I see here as well; good catch!)

The new plots show the 1m measurement straight on raw and gated as well as a direct measurement very close at the port. What is the double hump that appears twice in the port picture in the 1/3 octave average? What should I see on the port?

Peter

[schro20]

Second set of plots.

[Scottmoose]

What you are seeing in the vent output plots are the undamped harmonic resonances of the enclosure, as well as the fundamental cabinet resonance. These are what you ideally want to damp out, although they're not too bad as-is.

Re step loss, take a look at your FR response. Note the drop-off in SPLs, which will begin at approximately that point (it's usually easier to tell on a more heavily smoothed graph), but, ROT: -3db point due to step loss occurs in free-space at 4560 / baffle width at the driver height in inches.

I'd be inclined to use the felt. Not all damping materials are created equal & they all have their different requirements. That's usually one of the better materials, although it's a bit thick, so go easy with it.

[schro20]

So, I put together the second speaker (clamped on back side). This time I put 1in acoustic foam stuffing on the front and back starting at the top and going to the bottom of the driver rim. The last 40cm I put stuffing also on the side walls. I have taken measurements again with 1/1 and 1/3 averaging of the 1m gated response on the direct port readout. Note that the measurements of the unstuffed speaker and the stuffed speaker do not share a common absolute calibration (small horizontal offsets in the graphs overall do not mean anything).

Most noticeable (to me) is the markedly different behavior of the port up to 500Hz visible in the 1/3 plots. What am I seeing there? (aside from the obvious: stuffing... )

I also notice that the high frequencies fall off more in the stuffed line. Is that expected? Or am I looking at something likely due to variations in the drivers?

Now. Listening. One thing I can say already (for both of them): I am surprised by the bass authority on these! Ok. The driver is large, so there better be *some* bass, but it seems unexpectedly "present." There is also a sense (with both of the speakers) that there is a noticeable distinction between a certain range of sounds coming out of the little hole in the driver and then other sounds not coming from there. Hard to put my finger on it, but a disjunction somehow. These are just rough impressions though. I have not really sat down with specific material.

To help me learn what the perception differences are between stuffed and unstuffed, I am thinking of doing some a/b comparisons between the two speakers. What am I listening for? What sort of material might be good in revealing the differences due to stuffing? How do I decide whether I have enough or too little stuffing?

Your help, as always, is much appreciated.

Peter

[schro20]

The 1/1 averaged plots.

(Just noticed a typo in my previous post: the measurements are a) 1m gated, and b) direct from the port; NOT "gated on the port")

[Scottmoose]

What I told you before -damps out line the unwanted harmonic resonances. Re any slight discontinuity between driver & vent output, this will likely be an issue with damping quantity & positioning, which we can't really help with -it's something you'll have to do in the physical domain.

How can you tell when you've got enough? When you like it most. As is always said, damp them to your own taste.

[briandk]

Hi

I have a pair of these drivers and would like to know if any of you guys have tried them in the Metronome?

Brian

[Scottmoose]

TBH, I'd suggest a TL would be a better bet -like Bob's FTA-2000: http://www.geocities.com/rbrines1/Pa...2000/Main.html

[schro20]

Originally posted by Scottmoose
...an issue with damping quantity & positioning, which we can't really help with -it's something you'll have to do in the physical domain.

How can you tell when you've got enough? When you like it most. As is always said, damp them to your own taste.

Dear Scottmoose,

I am happy to try various things and then listen. I just do not know what to try. Question: can you or someone else make some suggestions. As I indicated I lined the front and back walls (and a bit of the side walls near the driver). If I am not happy with that, what should I do? Line more of the walls? Less? Using different material?

What I was hoping for from this forum was something more descriptive then "line them to your taste." Was I naive? Seriously, if the Mets are to be attempted only by someone who already has lots of stuffing experience, someone please say so and I'll shut up.

Thank you.

peter