Coming off three good builds, I am looking to my next project. Instead of another build, maybe a little research project. I did a simple test to see the relative performance of different stuffing on Fs. I guess I could do one on dampening reflections. I was thinking about internal diffusers. Any ideas? Any pressing questions an armature can take on? Any SOP that has not really been verified?
Suppressing standing waves with the minimum amount of fibrous material could be a worthwhile research project.This is in the context of vented boxes where excess material results in Qb losses.James Moir advocated,many years ago,that a single sheet of material stretched diagonally from the top of a rectangular enclosure,to an opposite diagonal at the bottom,is to be preferred over the usual practice of lining the walls.Basically the standing wave has to pass through the half spiral curtain,twice, and the wave will have a higher velocity at this point than at the cabinet rear surface. Also a layer of material cowled over the rear of a speaker(like a teapot cosy)may also be part of the experiment.
Or Rear baffle removable which would place less strain on the speaker fixing over time.
Either is reasonable if using T-nuts or similar
No question on a test box. Stuffing and accessing the crossover through a 4 inch hole is not fun. Removable baffle means easy to switch drivers, but as mentioned and I have confirmed, weak and resonance prone. So I have wound up with completely glued boxers. For testing, back access seems most logical.
It is a logical step to do similar tests on a vented box. I much prefer low Q sealed, but space and drivers available keeps making my use vented. Fill, lining, shapes, curtains. A lot of options out there. I'll think about that. I try to combine a few woodworking skills with every one too. I am still in the regular polygon space.
Three builds:
1: Started with Zaph SR-71 parts (good discount) and changed tweeters to the metal dome version of the same motor and slight box differences. Passes my wife's critical ear but something very slight is not right in Join Mitchel's voice. Confirmed the larger radius on all 12 edges of the box had a major improvement in diffraction induced response issues. 3/4 inch beats 1/2 by a lot. Also confirmed I still can't get a decent painted finish on MDF as it soaks in the seams. More work to do.
2: Fountek 85's for my desk. Applied what I learned trying to damp the breakup modes of the Fostex to the 85's pretty well. Good enough for the use for half-decent to listen to classes online. 100 to 12K speakers driven by a little USB DAC/Amp.
3: Rebuild of my old Dayton RS-150/Vifa with Seas tweets and total new crossover. Voicing came out excellent. It is within 1 dB 100 to 18K. I used what I learned on stuffing to reduce the hump before roll-off and reduce the mid range reflections. This is the first time I was successful with combining the BSC into a third order crossover. ( second order on the tweet). I went from hating metal cones on anything to coming to terms with them. No notch on the 150, as the crossover is low and steep enough.
It is a logical step to do similar tests on a vented box. I much prefer low Q sealed, but space and drivers available keeps making my use vented. Fill, lining, shapes, curtains. A lot of options out there. I'll think about that. I try to combine a few woodworking skills with every one too. I am still in the regular polygon space.
Three builds:
1: Started with Zaph SR-71 parts (good discount) and changed tweeters to the metal dome version of the same motor and slight box differences. Passes my wife's critical ear but something very slight is not right in Join Mitchel's voice. Confirmed the larger radius on all 12 edges of the box had a major improvement in diffraction induced response issues. 3/4 inch beats 1/2 by a lot. Also confirmed I still can't get a decent painted finish on MDF as it soaks in the seams. More work to do.
2: Fountek 85's for my desk. Applied what I learned trying to damp the breakup modes of the Fostex to the 85's pretty well. Good enough for the use for half-decent to listen to classes online. 100 to 12K speakers driven by a little USB DAC/Amp.
3: Rebuild of my old Dayton RS-150/Vifa with Seas tweets and total new crossover. Voicing came out excellent. It is within 1 dB 100 to 18K. I used what I learned on stuffing to reduce the hump before roll-off and reduce the mid range reflections. This is the first time I was successful with combining the BSC into a third order crossover. ( second order on the tweet). I went from hating metal cones on anything to coming to terms with them. No notch on the 150, as the crossover is low and steep enough.
Hi,
If I was testing damping material at various densities I'd use PVC piping
components with a small test driver about 2x the Vas of the main pipe,
not as easy as it sounds to get a suitable low Fs / high Vas test driver.
You can look at the optimum density for various materials to minimise
the sealed box resonance. By leaving the pipe open at the other end you
look at the shift in the 1/4 wave resonant frequency, i.e. the velocity drop,
and more contentiously (i.e. more difficult to measure) the damping effect
at higher frequencies compared to lower frequencies, and if they diverge
or correlate well with the low frequency result.
Pulse testing might give some idea of attenuation loss.
IMO regarding damping materials there is little useful testing you could
with a vented box in terms of identifying damping material properties.
It depends on the nature of the information you want to ascertain.
rgds, sreten.
If I was testing damping material at various densities I'd use PVC piping
components with a small test driver about 2x the Vas of the main pipe,
not as easy as it sounds to get a suitable low Fs / high Vas test driver.
You can look at the optimum density for various materials to minimise
the sealed box resonance. By leaving the pipe open at the other end you
look at the shift in the 1/4 wave resonant frequency, i.e. the velocity drop,
and more contentiously (i.e. more difficult to measure) the damping effect
at higher frequencies compared to lower frequencies, and if they diverge
or correlate well with the low frequency result.
Pulse testing might give some idea of attenuation loss.
IMO regarding damping materials there is little useful testing you could
with a vented box in terms of identifying damping material properties.
It depends on the nature of the information you want to ascertain.
rgds, sreten.
Last edited:
Who obliges you to put it inside the box ?
This is DIY and you're not selling the box as it is ( a...box)
reflective damping or diffusion of reflection is a good test, there are many you have mentioned. Skyscraper diffusors, holey 'helmholtz' absorbers with damping, or a 'pierced' inner cavity wall with absorbent in the cavity. These are things that i would find interesting to investigate. In particular the last one.
Ker,
I think the age old answer to that one is " it depends". I use different materials for different size boxes. There is no right answer.
Mondog,
Some ideas there. Your last idea is quite appropriate for room size absorbers, but I don't think that scales to the inside of a 15L box. A bit of visualation is in order. Think about how the different frequencies will radiate from the back of a driver. Logically, the further the effective distance is before a reflective surface, the longer the path so the lower the frequency that is absorbed.
Sreten,
Kind of confused on the vented box. It is not as easy as stuff and measure like a sealed box. Just like sealed boxes, I have seen everything from bare walls to full blocks of foam, light stuffing and tight stuffing. Years ago, a gradient stuffing was all the rage.
So, lots to think about. If I am staying in the stuffing topic, I need to find a driver that the frame is not a bigger problem than the box. That probably means a "decent" driver so I don't have one on the shelf. It probably should be a reasonably wide band driver so I can see if there is a point where it no longer matters. ( an octave above the crossover would be a rule of thumb I bet. I should get the paid version of ARTA so I can save charts. Printing and holding to the light works fine, but not easy to post. Side note, I am finding ARTA so much easier to use that I have not bothered with Sound Easy at all.
I have a couple of woodworking ideas. The first is how to get MDF sealed so finishes don't sink into the seams. I have tried a lot of things; all fail, even though some took a year or so. I have not ventured into non-regular shapes yet. I have had skill issues with angle repeatability on the saw so I just bought a digital tilt gauge. I have an idea for box that is basically the intersection of two ellipses. Not sure how to make it, but the result would only have simple curves so it could be veinered. I already concluded a 3/4 radius edge is a lot better than a 1/2 inch. I don't know what a flat angle as is used frequently does. As so much as the fit of the tweeter in the baffle is measurable, I have a feeling it is not as good as expected.
Another subject on which I have only seen subjective testing is decoupling the drivers from the baffle. Never seen a method that I actually believe achieves this in the first place.
A trend here. I only have interest in things that apply to something that fits into my rooms. That translates into a box-ish shape of bookshelf size. I have no room for floor standers anywhere. Even my subs are all under two cubic foot.
I think the age old answer to that one is " it depends". I use different materials for different size boxes. There is no right answer.
Mondog,
Some ideas there. Your last idea is quite appropriate for room size absorbers, but I don't think that scales to the inside of a 15L box. A bit of visualation is in order. Think about how the different frequencies will radiate from the back of a driver. Logically, the further the effective distance is before a reflective surface, the longer the path so the lower the frequency that is absorbed.
Sreten,
Kind of confused on the vented box. It is not as easy as stuff and measure like a sealed box. Just like sealed boxes, I have seen everything from bare walls to full blocks of foam, light stuffing and tight stuffing. Years ago, a gradient stuffing was all the rage.
So, lots to think about. If I am staying in the stuffing topic, I need to find a driver that the frame is not a bigger problem than the box. That probably means a "decent" driver so I don't have one on the shelf. It probably should be a reasonably wide band driver so I can see if there is a point where it no longer matters. ( an octave above the crossover would be a rule of thumb I bet. I should get the paid version of ARTA so I can save charts. Printing and holding to the light works fine, but not easy to post. Side note, I am finding ARTA so much easier to use that I have not bothered with Sound Easy at all.
I have a couple of woodworking ideas. The first is how to get MDF sealed so finishes don't sink into the seams. I have tried a lot of things; all fail, even though some took a year or so. I have not ventured into non-regular shapes yet. I have had skill issues with angle repeatability on the saw so I just bought a digital tilt gauge. I have an idea for box that is basically the intersection of two ellipses. Not sure how to make it, but the result would only have simple curves so it could be veinered. I already concluded a 3/4 radius edge is a lot better than a 1/2 inch. I don't know what a flat angle as is used frequently does. As so much as the fit of the tweeter in the baffle is measurable, I have a feeling it is not as good as expected.
Another subject on which I have only seen subjective testing is decoupling the drivers from the baffle. Never seen a method that I actually believe achieves this in the first place.
A trend here. I only have interest in things that apply to something that fits into my rooms. That translates into a box-ish shape of bookshelf size. I have no room for floor standers anywhere. Even my subs are all under two cubic foot.
KEF used to do effective driver decoupling. their simple sytem for wmaller woofers used rubber grommets at the holes and soft foam tape arount the perimeter. There was a sleave inside the grommet that prevented over tightening. Acelerometer tests on the cabinet showed a big difference in cabinet vibration when issolation was used.
I think a practical stuffing test would be useful. Just drill a hole in the corner of an unstuffed cabinet and insert a probe microphone. You will see all the standing waves based on the cabinet dimensions. Trial absorption samples will have varying effects on reduction of the various resonances. The test can be done on a sealed box yet give good info for a vented box, i.e. what materials work well as a lining rather than as total stuffing.
David S.
I think a practical stuffing test would be useful. Just drill a hole in the corner of an unstuffed cabinet and insert a probe microphone. You will see all the standing waves based on the cabinet dimensions. Trial absorption samples will have varying effects on reduction of the various resonances. The test can be done on a sealed box yet give good info for a vented box, i.e. what materials work well as a lining rather than as total stuffing.
David S.
Give some consideration to researching high'ish efficiency speakers with controlled directivity. There are many positive comments on the value of greater dynamics and improved low level musical details.
There are many Econowave designs based upon the low cost SEOS-12 waveguide and 10" or 12" midbass that could be sized to fit into your room and mate well with your stereo 100Hz woofers.
Plastic SEOS DIY Sound Group
You could also purchase a high'ish efficiency dome tweeter like the small SB29RDNC-4 rated 94db/watt and mate it to a high'ish efficiency 8" pro audio. Cabinet edge diffraction could also be part of your research: large radius edges; Avalon ISIS truncated pyramid; B&W 801 sphere+tapered_tube; etc...
Thinking out loud.
If I can go by The Edge, the largest refraction problem is the lowest one and it is greatly effected by the driver placement. With small cabinets and large, relative, woofers, there is not much room to play with that. Kind of forces you to do what you can with the crossover.
Subjectively, I noticed a big difference between the front baffle edges being radiused and all 12. That should not be hard to quantify.
If I can go by The Edge, the largest refraction problem is the lowest one and it is greatly effected by the driver placement. With small cabinets and large, relative, woofers, there is not much room to play with that. Kind of forces you to do what you can with the crossover.
Subjectively, I noticed a big difference between the front baffle edges being radiused and all 12. That should not be hard to quantify.
After much contemplation, I am testing MDF sealing and finish materials and will be finishing the subs I built many years ago for higher WAF. They are just black plywood on the outside. I am going to build them into Chinese type chests to make them look like just part of the decor. They have all the sound I need, now to raise the WAF. NOt exciting.
Re: sealing MDF edges.
I dont know if you've tried this, or if it has been suggested already, so bear with me. Try a 1:2 mix of PVA and any old emulsion paint. I have used this method to prime a number of times, and topcoating with regular spray cans. It takes a few coats and alot of sanding, but its miles better than car primer which i tried and became frustrated with. I have also used just regular spirit based varnish, thinned in the normal way. That finish looked rather good considering the lack of grain.
I dont know if you've tried this, or if it has been suggested already, so bear with me. Try a 1:2 mix of PVA and any old emulsion paint. I have used this method to prime a number of times, and topcoating with regular spray cans. It takes a few coats and alot of sanding, but its miles better than car primer which i tried and became frustrated with. I have also used just regular spirit based varnish, thinned in the normal way. That finish looked rather good considering the lack of grain.
Last edited:
PVA and latex paint. Never heard of that. I'll give it a try. Old style sanding sealer and auto lacquer primer look good to start, but after time, the seams sink in and show. I have tried fiberglass resin with mixed results. My first test is comparing auto spot putty with elmers wood filler in the seams. Spot putty seems better when fresh.
I like plain old auto lacquer primer, it is the base I am having so much trouble with. Most of my primer problems are my cheap gun. It is a HVLP that only works with HP. I should buy a old style gun. Not having a booth causes me much trouble.
I like plain old auto lacquer primer, it is the base I am having so much trouble with. Most of my primer problems are my cheap gun. It is a HVLP that only works with HP. I should buy a old style gun. Not having a booth causes me much trouble.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.