I'll be at the stuffing point in my Pensil 10p build pretty soon and have read about adjusting the stuffing based on listening tests.
So, what should I be listening for in determining whether or not to adjust the volume of stuffing?
Thanks,
Charlie
So, what should I be listening for in determining whether or not to adjust the volume of stuffing?
Thanks,
Charlie
Best thing to do is experiment and hear it for yourself, but here's a quick subjective take on it:
Too little damping: shouty, hollow, reverberant, harsh.
Too much damping: dull, lifeless, gray.
Also, google "click test" for the old school scientific way of doing it.
Too little damping: shouty, hollow, reverberant, harsh.
Too much damping: dull, lifeless, gray.
Also, google "click test" for the old school scientific way of doing it.
FWIW, many times early on when I'd post what seemed like an acceptable minimum amount of damping using MJK's early software, most folks would ultimately wind up removing most of it, so as GB noted/implied, listen to it empty, then very lightly stuffed and if there's any hollowness add more with it concentrated behind the driver or at least fluffed out from the top down to just below it; and if none, then start taking it out as too often it's already over-damped, so any more just starts reducing its [mid]bass output and at some point it begins 'sucking the life' out of the performance...........
If the driver is 'shouty', then some form of EQ is usually required or at least listened to off axis as required with most speakers being toe'd in such that their centerlines cross somewhere in front of the listening position [LP] 'sweet spot'. That, or if relatively close together, toe'd out such that the first side wall reflections start behind the LP.
GM
If the driver is 'shouty', then some form of EQ is usually required or at least listened to off axis as required with most speakers being toe'd in such that their centerlines cross somewhere in front of the listening position [LP] 'sweet spot'. That, or if relatively close together, toe'd out such that the first side wall reflections start behind the LP.
GM
Forget symptoms like shouty, hollow, reverberant dull, lifeless, gray and harsh. There are too many variables at play that can cause those symptoms. The thing to know is that any internal reflections or conducted vibrations are always bad. The ideal enclosure gets rid of rear energy without reflecting it back out through the diaphrams or enclosure walls. Perfect internal padding would constitute a "gausian" arrester at all frequencies.
When I attended the Syn-Aud-Con seminar, Don Davis demonstrated that acoustic padding is MUCH more effective when it is glued tight to the internal surfaces of the enclosure, rather than just fluffed up loose randomly.
I like to glue foam rubber or carpet or 1/4 inch thick wool felt (best choice) to all internal surfaces first, and then glue in place (away from drivers) a bunch of lower mass stuffing (synthetic fiberglass), to form an approximation of a gaussian arrester. I use silicone rubber glue or anything that never gets brittle hard, to keep everything in place, and I leave significant air space around the drivers so they can do their job best. jamming fiberglas equivelent right up against the back of some drivers could cause a loss of bass or higher distortion. The driver needs to breath. In the case of a bass reflex enclosure, there need to be a clear path to the port, unless the design specifically calls for something different. Foam rubber is actually an excellent damping material acoustically, but many kinds deteriorate over time. Softer foam is better.
In my midrange enclosure, I used a 4 inch internal diameter ABS plastic tube that goes all the way to the back of the enclosure, and stacked several layers of 1/4 inch thick wool felt at the bottom, then a few layers of foam rubber, then some fluffed up synthetic fiberglass, then left about 3 inches of air behind the 3 inch driver, silicone rubber glue holding everything in place, and the with the Peerless 3 inch TG or TC driver (one of my favorite drivers for mids), it measured ruler flat from about 300HZ to above 7kHZ.
I've got an 8 inch kevlar cone woofer and a vintage Peerless cone tweeter (from a McIntosh ML-1) in there with it, and it sounds VERY good. I cross the 3 inch at 500HZ (4 pole active), and 7kHZ (1 pole passive). Getting the crossover right is very important and where a lot of speaker system fall short.
When I attended the Syn-Aud-Con seminar, Don Davis demonstrated that acoustic padding is MUCH more effective when it is glued tight to the internal surfaces of the enclosure, rather than just fluffed up loose randomly.
I like to glue foam rubber or carpet or 1/4 inch thick wool felt (best choice) to all internal surfaces first, and then glue in place (away from drivers) a bunch of lower mass stuffing (synthetic fiberglass), to form an approximation of a gaussian arrester. I use silicone rubber glue or anything that never gets brittle hard, to keep everything in place, and I leave significant air space around the drivers so they can do their job best. jamming fiberglas equivelent right up against the back of some drivers could cause a loss of bass or higher distortion. The driver needs to breath. In the case of a bass reflex enclosure, there need to be a clear path to the port, unless the design specifically calls for something different. Foam rubber is actually an excellent damping material acoustically, but many kinds deteriorate over time. Softer foam is better.
In my midrange enclosure, I used a 4 inch internal diameter ABS plastic tube that goes all the way to the back of the enclosure, and stacked several layers of 1/4 inch thick wool felt at the bottom, then a few layers of foam rubber, then some fluffed up synthetic fiberglass, then left about 3 inches of air behind the 3 inch driver, silicone rubber glue holding everything in place, and the with the Peerless 3 inch TG or TC driver (one of my favorite drivers for mids), it measured ruler flat from about 300HZ to above 7kHZ.
I've got an 8 inch kevlar cone woofer and a vintage Peerless cone tweeter (from a McIntosh ML-1) in there with it, and it sounds VERY good. I cross the 3 inch at 500HZ (4 pole active), and 7kHZ (1 pole passive). Getting the crossover right is very important and where a lot of speaker system fall short.
Stuffing vs. Felt Dampening
Stuffing in a full range enclosure (normally a transmission line style), and dampening on the internal cabinet walls are for 2 different purposes.
The felt or other dampening on the inside walls of a cabinet near the driver is to stop back reflections from returning to the speaker cone.
The stuffing in a Transmission Line enclosure is to control and even out the bass response.
Many cabinets use both. An example is the Frugel-horn 3 which has felt around the driver for back reflections, and stuffing in the tapered horn to control the bass response.
Stuffing in a full range enclosure (normally a transmission line style), and dampening on the internal cabinet walls are for 2 different purposes.
The felt or other dampening on the inside walls of a cabinet near the driver is to stop back reflections from returning to the speaker cone.
The stuffing in a Transmission Line enclosure is to control and even out the bass response.
Many cabinets use both. An example is the Frugel-horn 3 which has felt around the driver for back reflections, and stuffing in the tapered horn to control the bass response.
Charlie,
In my 10P Pensils, I have 1/2" felt on the sides and back of the cabinet around the driver area, and light stuffing from below the driver to above the vent. The speaker will have weaker bass when new, so all you need is enough to stop the "Hollow" sound from a completely empty cabinet. Pillow stuffing totally fluffed out will be fine. After about 6 months, the cones will loosen up and the bass may start to sound a bit strong and booming. At that time you add a bit more stuffing to control the sound.
Be sure to make a removable back or top on the cabinet. You do not want to be taking out the driver and risk damage to adjust the stuffing.
In my 10P Pensils, I have 1/2" felt on the sides and back of the cabinet around the driver area, and light stuffing from below the driver to above the vent. The speaker will have weaker bass when new, so all you need is enough to stop the "Hollow" sound from a completely empty cabinet. Pillow stuffing totally fluffed out will be fine. After about 6 months, the cones will loosen up and the bass may start to sound a bit strong and booming. At that time you add a bit more stuffing to control the sound.
Be sure to make a removable back or top on the cabinet. You do not want to be taking out the driver and risk damage to adjust the stuffing.
With all due respect, the OP asked for what to listen to when adjusting damping, not a theoretical rationale. Therefore some adjectives are required. I find "shouty, hollow, reverberant dull, lifeless, gray and harsh" very useful things to listen for in this process.
Granted, a beginner may have trouble distinguishing between, for example: harshness caused by midrange reflections through the cone, and harshness from a driver break-up mode. That's why experimenting and listening - and measuring - is always a good idea.
would al this show up on rew/rata/impulse etc rather that been audible to the uninformed listner,
some people have a very different take on what sounds good.
hence if it shows up then measuring is the way forward for the (lets say persons of good intent with inexperienced quality sound reference) then to see relise what is capable.
I am at this stage myself I know a decent sound but if measurments can better it for me then i will learn upon what i am missing out🙂
some people have a very different take on what sounds good.
hence if it shows up then measuring is the way forward for the (lets say persons of good intent with inexperienced quality sound reference) then to see relise what is capable.
I am at this stage myself I know a decent sound but if measurments can better it for me then i will learn upon what i am missing out🙂
Stuff until it Sounds Right ?????
Charlie2
I know what you mean. Our instructions remind me of recipes that state "Season to taste". I can taste that something is missing, but I have no clue how to make it taste right.
Happily, unlike cooking, speaker stuffing is completely reversible. 🙂
On to your question:
I don't know if there is an easy way to objectively set the stuffing on a speaker. You are looking to even out the peaks and valleys in the bass response caused by the resonances in the tuned enclosure.
If you have a microphone and the software to measure speaker response, it would be interesting to measure the speaker's response with no stuffing, lightly stuffed, and heavily stuffed.
The theory states you should see peaks and valleys in your bass response with no stuffing, a smoother response with some stuffing, and weaker overall bass response with too much stuffing.
Perhaps somebody else can offer plots at different stuffing levels.
My "No Test Instruments" hint.
Simply stuff one speaker, and leave the other unstuffed. Sit them side by side and run the balance control from side to side. Now you are comparing two different sounds. That is much easier than listening to a single setup and trying to decide if anything should be changed.
Charlie2
I know what you mean. Our instructions remind me of recipes that state "Season to taste". I can taste that something is missing, but I have no clue how to make it taste right.
Happily, unlike cooking, speaker stuffing is completely reversible. 🙂
On to your question:
I don't know if there is an easy way to objectively set the stuffing on a speaker. You are looking to even out the peaks and valleys in the bass response caused by the resonances in the tuned enclosure.
If you have a microphone and the software to measure speaker response, it would be interesting to measure the speaker's response with no stuffing, lightly stuffed, and heavily stuffed.
The theory states you should see peaks and valleys in your bass response with no stuffing, a smoother response with some stuffing, and weaker overall bass response with too much stuffing.
Perhaps somebody else can offer plots at different stuffing levels.
My "No Test Instruments" hint.
Simply stuff one speaker, and leave the other unstuffed. Sit them side by side and run the balance control from side to side. Now you are comparing two different sounds. That is much easier than listening to a single setup and trying to decide if anything should be changed.
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Thanks for all the posts. I'll glue some kind of felt/carpet underlay or something around the driver area, then add fluffed stuffing.
I'll start with less stuffing rather than more and proceed from there.
Regards,
Charlie
I'll start with less stuffing rather than more and proceed from there.
Regards,
Charlie
Here is the hot tip: use Mr Clean Magic Eraser pads as acoustic absorber lining around driver area. It is same material as professional BASF phenolic open cell sound absorber used in sound recording studios. Works real well for preventing back reflections.
I use old pillow stuffing or pink fiberglass for stuffing.
I use old pillow stuffing or pink fiberglass for stuffing.
Here's a good one to do...
You'll need:
- click generator
- oscilloscope
- dynamic mic
Connect the dynamic mic to the input of the scope, and hold it in front of the cone.
Set the click generator to click quite often, say, once per second, and then set the timebase on the scope (assuming an analogue one) so that the waveform is stationary on-screen.
On-screen, you should see an initial spike from the driver, followed by a bunch of other smaller ones. Since you know the timebase settings, you can find out the time-of-flight for each reflection (causing the smaller spikes). Remember the click is travelling from the cone, to the reflector, and back, so halve each distance when you're calculating.
Speed of sound = 340m/s.
Round-trip distance = 340*time of flight.
The distance to the reflecting surface is half of the round trip distance, as I mentioned above.
Since you know the dimensions of the cabinet, you've just got a map of what's reflecting, and can add lining accordingly. NB - the larger the peak on the 'scope, the more severe the reflection. I also believe later reflections are more detrimental than earlier onces.
HTH
Chris
You'll need:
- click generator
- oscilloscope
- dynamic mic
Connect the dynamic mic to the input of the scope, and hold it in front of the cone.
Set the click generator to click quite often, say, once per second, and then set the timebase on the scope (assuming an analogue one) so that the waveform is stationary on-screen.
On-screen, you should see an initial spike from the driver, followed by a bunch of other smaller ones. Since you know the timebase settings, you can find out the time-of-flight for each reflection (causing the smaller spikes). Remember the click is travelling from the cone, to the reflector, and back, so halve each distance when you're calculating.
Speed of sound = 340m/s.
Round-trip distance = 340*time of flight.
The distance to the reflecting surface is half of the round trip distance, as I mentioned above.
Since you know the dimensions of the cabinet, you've just got a map of what's reflecting, and can add lining accordingly. NB - the larger the peak on the 'scope, the more severe the reflection. I also believe later reflections are more detrimental than earlier onces.
HTH
Chris
Its a bit of a myth that an over-stuffed cabinet sounds 'lifeless". If you are relying on internal reflections and resonances to inject 'life' then you are on to the wrong idea.
If you overstuff the first thing that happens it that you approach the perfomance of a sealed box and the internal volume can be reduced. This could adversely affect the bass extension but should not effect the dynamics at anything other than the required tuning frequency (as you really don't want other frequencies eminanting from the port anyway).
Too much stuffing is far better than too little (apart from in the port assistance region).
If you under stuff you won't reach the optimal lowest tuning frequency as the stuffing effectively raises the virtual cabinet volume if it is effective, providing greater bass extension for a given cabinet size. This is adding life, not sucking it out!
Also with a well-designed longitudinal cabinet with small panel widths and well braced the panel resonances won't be much of a problem so you are really looking at reducing internal reflections, transmission-line resonances eminanting from the port and through driver diaphram. With a transmission line you really have to fill most of the cabinet with an effective stuffing material to this effect and it solves most of these issues.
If you overstuff the first thing that happens it that you approach the perfomance of a sealed box and the internal volume can be reduced. This could adversely affect the bass extension but should not effect the dynamics at anything other than the required tuning frequency (as you really don't want other frequencies eminanting from the port anyway).
Too much stuffing is far better than too little (apart from in the port assistance region).
If you under stuff you won't reach the optimal lowest tuning frequency as the stuffing effectively raises the virtual cabinet volume if it is effective, providing greater bass extension for a given cabinet size. This is adding life, not sucking it out!
Also with a well-designed longitudinal cabinet with small panel widths and well braced the panel resonances won't be much of a problem so you are really looking at reducing internal reflections, transmission-line resonances eminanting from the port and through driver diaphram. With a transmission line you really have to fill most of the cabinet with an effective stuffing material to this effect and it solves most of these issues.
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A bit late to the party here, but I found this thread before starting a new one. I've been tuning my recently built FH3 speakers. After initial recommended damping and listening over a couple of weeks or so, I finally settled that less was more, with Nothing being used, being the outcome!
The sound just opened up completely but without the usual resonance issues and hollowness which I have had with other designs previously and sounded so natural in comparison? I can't help wondering if the reason is, maybe, it works (the frugal horn) more like a horn than the hybrid design that it is? Any thoughts?
Was Don stuffing a TL? Or a BR?
My first question, how well teased is your stuffing?
Amount will depend on the quality of the poly-fluff.
It should be evenly spread thruout the Pensil, somewhat less dense right behind the driver.
Typically, it seems, about 2/3rds of specified is often where people end up.
dave
It's basically a mass loaded re-entrant horn and fundamentally the same as some of the pioneer's designs such as this crude W.E. version.