Scottmoose said:
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...
Help me understand what makes you say that.
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?
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
more measurements
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
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
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.
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.
comparison of stuffed and unstuffed
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
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
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.
How can you tell when you've got enough? When you like it most. As is always said, damp them to your own taste.
TBH, I'd suggest a TL would be a better bet -like Bob's FTA-2000: http://www.geocities.com/rbrines1/Pages/FTA-2000/Main.html
Dear Scottmoose,Scottmoose said:
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
Read this , http://web.mac.com/scress1958/iWeb/Steves_Tube_Trials/Metronome-Speaker.html (link is to the first metronome) and search for other threads on the metronome to find what other have done with this cabinet.
If I recall of what I read in my searches in the past is that the metronome doesn't require much dampening and most that have built them overdamped them and had to remove dampening for best results. I would start with no dampening, then maybe line the wall directly behind the the driver or just use stuffing above the driver then go from there.
I think you are over thinking this one. I understand you wanting to learn taking and understanding the measurements, but the real test is your ears. You have to have an idea of whether or not you like how they sound? I am not the best at or like to decribe how amps, speakers, etc. sound because usaually it comes down to personal preferance, but I do know what I like and don't.
If I recall of what I read in my searches in the past is that the metronome doesn't require much dampening and most that have built them overdamped them and had to remove dampening for best results. I would start with no dampening, then maybe line the wall directly behind the the driver or just use stuffing above the driver then go from there.
I think you are over thinking this one. I understand you wanting to learn taking and understanding the measurements, but the real test is your ears. You have to have an idea of whether or not you like how they sound? I am not the best at or like to decribe how amps, speakers, etc. sound because usaually it comes down to personal preferance, but I do know what I like and don't.
Hi Peter,
I've only just come across this as I've been quite busy over the past few weeks.
The bass discontinuity you are hearing sounds to me like the third harmonic of the cabinet/driver resonant frequency escaping from the base. If that is the true problem (not saying it is) then it is pretty easy to overcome.
What you need to do is stuff the top third of the cabinet or better still lightly stuff with BAF wadding down to the top of the driver opening. Don't compress the stuffing too much or you will kill the sound stone dead, producing a hard, shrill balance. Try taking out the lining and replacing with the wadding in the top half as I have suggested.
There are not a lot of these larger Mets around. The only other one I know of at the moment is Bill's (lousymusician) hemp 8 inch driver Metronome. His driver is different so his stuffing regime won't really help you. However he did a lot of tweaking with stuffing until he got the balance he wanted. His speakers made quite an impression at the 2007 San Francisco Burning Amp Festival, probably due to the work he put in tuning them to his tastes.
What Scott and others have said is quite true. Because the cabinets are designed to suit a range of drivers then the stuffing has to be worked out carefully, case by case, by listening rather than measuring until the most pleasing tonal balance is obtained. What we have tried to do with these cabinets is to make them suitable for a whole bunch of full range drivers. The downside of this versatility is that the stuffing regime is bound to be different for each driver mounted in the cabinet, so the listener has to tune them according to their room and their personal tastes. A pure engineering solution to this problem is not possible.
However I will say that when optimally stuffed these speakers are capable of stunning sound quality. I don't know of anyone who has built them being disappointed with the sound obtained.
Steve
I've only just come across this as I've been quite busy over the past few weeks.
The bass discontinuity you are hearing sounds to me like the third harmonic of the cabinet/driver resonant frequency escaping from the base. If that is the true problem (not saying it is) then it is pretty easy to overcome.
What you need to do is stuff the top third of the cabinet or better still lightly stuff with BAF wadding down to the top of the driver opening. Don't compress the stuffing too much or you will kill the sound stone dead, producing a hard, shrill balance. Try taking out the lining and replacing with the wadding in the top half as I have suggested.
There are not a lot of these larger Mets around. The only other one I know of at the moment is Bill's (lousymusician) hemp 8 inch driver Metronome. His driver is different so his stuffing regime won't really help you. However he did a lot of tweaking with stuffing until he got the balance he wanted. His speakers made quite an impression at the 2007 San Francisco Burning Amp Festival, probably due to the work he put in tuning them to his tastes.
What Scott and others have said is quite true. Because the cabinets are designed to suit a range of drivers then the stuffing has to be worked out carefully, case by case, by listening rather than measuring until the most pleasing tonal balance is obtained. What we have tried to do with these cabinets is to make them suitable for a whole bunch of full range drivers. The downside of this versatility is that the stuffing regime is bound to be different for each driver mounted in the cabinet, so the listener has to tune them according to their room and their personal tastes. A pure engineering solution to this problem is not possible.
However I will say that when optimally stuffed these speakers are capable of stunning sound quality. I don't know of anyone who has built them being disappointed with the sound obtained.
Steve
Basically, what the guys above said. It's got to be your call at the end of the day, because you're the one listening to them. i.e. damp / stuff to taste. Adding damping will progressively damp the output of the cabinet. Removing it will allow it to resonate more strongly. We can't tell you exactly what you'll like or not like though -some people prefer a slightly more resonant sound than others. The trick is not to over-damp things, which will appear to 'suck the life' out of the midrange.
So my FE127e Mets started with a lining of approx. 1cm carpet underlay on all surfaces but ended up with lining only on the back wall, and on the surfaces at the pointy end where my hand couldn't reach. How did I decide on this? It sounded better that way. Was it scientific? Not remotely. Do I have lots of experience? Nope, these were my first attempt at building speakers. My recommendation? Get on and build the things, you'll love 'em.
Cheers,
Gus
Cheers,
Gus
When I posted this I had not yet seen Scottmoose's response of "overstuffing sucks the life out." Ok. That's something I think I can listen for.schro20 said:
What does it sound like when it's overdamped? (Ok, I could put a pillow in there and find out that way...
Thanks also to Steve for his suggestion. I will try those and just listen for a while.
And I promise not to post any more measurements!
Peter
baffle step correction
Since the subject of BS (baffle step) correction is also a matter of taste it would seem that I need to try that and decide for myself (which I am eager to do). Looking at the metronome tables I find the recommendation 2.8 Ohm and 0.9 mH for a parallel RL in series with the speaker. Right now I don't plan on including the Zobel. Should I? For amps I'll start with Onyx SP3 A/B class tube amp or a
Sonic Impact gen 2 (since I have those sitting around I might as well start with them).
A couple of questions. Is this recommendation for values to be used as a starting point still considered the right place for the FE207e in particular if I don't do the Zobel at the same time? Since it is a parallel RL in series with the driver the overall response is a function of the driver as well and in that case the Zobel parallel to the driver might matter sonically. It certainly would from a filtering point of view, though I am no expert at passive filter design. What wattage on the resistor and what wire gauge on the inductance is recommended?
peter
Since the subject of BS (baffle step) correction is also a matter of taste it would seem that I need to try that and decide for myself (which I am eager to do). Looking at the metronome tables I find the recommendation 2.8 Ohm and 0.9 mH for a parallel RL in series with the speaker. Right now I don't plan on including the Zobel. Should I? For amps I'll start with Onyx SP3 A/B class tube amp or a
Sonic Impact gen 2 (since I have those sitting around I might as well start with them).
A couple of questions. Is this recommendation for values to be used as a starting point still considered the right place for the FE207e in particular if I don't do the Zobel at the same time? Since it is a parallel RL in series with the driver the overall response is a function of the driver as well and in that case the Zobel parallel to the driver might matter sonically. It certainly would from a filtering point of view, though I am no expert at passive filter design. What wattage on the resistor and what wire gauge on the inductance is recommended?
peter
Re: baffle step correction
I can't help on crossovers but I am sure that the other members can help you out with that. One thing I think that might be recommended is that a min. of 200 hrs on this driver would be needed before attempting fine tuning a crossover network. Once you get them both built I would run them 24/7 for awhile facing each other with a blanket thrown over them. I know my FE127e's had took at least 200hrs before sounding good.
I would love to hear what your final results are on the crossover when that time comes.
I can't help on crossovers but I am sure that the other members can help you out with that. One thing I think that might be recommended is that a min. of 200 hrs on this driver would be needed before attempting fine tuning a crossover network. Once you get them both built I would run them 24/7 for awhile facing each other with a blanket thrown over them. I know my FE127e's had took at least 200hrs before sounding good.
I would love to hear what your final results are on the crossover when that time comes.