Looks a lot better, no problems at all! How does it sound? Can you overlay the start setting to the latest one? It looks like the bottom (port output) wasn't affected much at all? Nice!
No idea how it sounds as yet! Sure, here are the 3 comparisons - poly batting / rockwool / rockwool and poly batting in middle
To me it looks like the drop in vent ouput could be made up by tuning a little higher.
To me it looks like the drop in vent ouput could be made up by tuning a little higher.
Goals / R&D / Minutiae
Frustratingly I feel I have already failed at this project and it's pretty close to being done. That sounds pretty dramatic but it might help me to put this down and get some perspective.
This is the largest speaker cabinet I have made at 30L. Previously the largest vented box I had made was 10L but this, seemingly, came with none of the issues I am having now. Maybe I didn't see them before but trying to make a perfect midbass cabinet to use for a long while has certainly brought them into focus.
Stupidly, I made the box 300x400x400mm. I hadn't expected standing waves as I had never had any I didn't expect before and that couldn't be dealt with by way of a bit of stuffing etc. However, what I didn't account for is the bigger the cab, the lower the standing wave, the harder they are to remedy and ergo, the thicker and more effective the damping needs to be.
So, this 400x400 standing wave showed up bang on time around 400hz. I have finally remedied it but at the cost of the low end extension and that is where I feel this has failed. I wanted the vented alignment to be acoustically on target. As it stands, with the standing wave entirely eliminated, I have lost about 10hz and a couple of db to the low end output. In turn this means I have to correct it with DSP which is what I wanted to avoid doing in the first place. Had I wanted to use DSP on the alignment I wouldn't have built such a large box. Drat.
This crude diagram shows what I did to smooth it out but for some box geometry reason has cost the vent output:
This is the measured NF response:
This is the current response vs previously damped response:
I have learnt a few things though:
Frustratingly I feel I have already failed at this project and it's pretty close to being done. That sounds pretty dramatic but it might help me to put this down and get some perspective.
This is the largest speaker cabinet I have made at 30L. Previously the largest vented box I had made was 10L but this, seemingly, came with none of the issues I am having now. Maybe I didn't see them before but trying to make a perfect midbass cabinet to use for a long while has certainly brought them into focus.
Stupidly, I made the box 300x400x400mm. I hadn't expected standing waves as I had never had any I didn't expect before and that couldn't be dealt with by way of a bit of stuffing etc. However, what I didn't account for is the bigger the cab, the lower the standing wave, the harder they are to remedy and ergo, the thicker and more effective the damping needs to be.
So, this 400x400 standing wave showed up bang on time around 400hz. I have finally remedied it but at the cost of the low end extension and that is where I feel this has failed. I wanted the vented alignment to be acoustically on target. As it stands, with the standing wave entirely eliminated, I have lost about 10hz and a couple of db to the low end output. In turn this means I have to correct it with DSP which is what I wanted to avoid doing in the first place. Had I wanted to use DSP on the alignment I wouldn't have built such a large box. Drat.
This crude diagram shows what I did to smooth it out but for some box geometry reason has cost the vent output:
This is the measured NF response:
This is the current response vs previously damped response:
I have learnt a few things though:
- big boxes aren't like little boxes
- always make a test box even if it will cost £50 to get low quality material delivered
- the nagging feeling that your assumptions are wrong is to be listened to
- being a perfectionist maintains its miserable grip on me
- I'm a big cry baby
I have three potential angles of attack to this.
1. Eq the BSC to augment the bass:
2. EQ the bass end with a 3db parametric:
3. Get a grip my son.
1. Eq the BSC to augment the bass:
2. EQ the bass end with a 3db parametric:
3. Get a grip my son.
So the bigger the box the bigger the damping material simply means your damping should be a fraction of the box dimensions. Therefore it's not like there is an actual problem.
Actually, it could be said that the proximity of your standing wave frequency to your box resonance frequency happens to be a factor, and that is completely coincidental.
In any case, compromising the standing wave situation to ensure proper reflex action isn't always the best choice 😉
May I suggest you decide on the overall response you want. The way you go about achieving that ought to be less of the point, until you've made that decision. In other words, if the way you go about it gives you different results (and not saying they should but sometimes it happens), then it's those results which tell you what you'll get.
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Cheers for the input! Would you mind elabourating on this a touch, pelase?
Yes, perhaps my bad communication is the problem here. I pretty much wanted what I had in the previous measurements without damping - a shallow roll off that with room/boundary gain I can EQ down rather than up. As it stands I'm not sure there is enough fat in the low end to cut away but instead add to.
I agree re your final statement. In art school we used to yawn all the way through some of our peers talks who made "process based" art. Who is leading who here, should I be more interested in you or the pencil? As you say, sometimes it works, sometimes very much not.
When you do your initial development for fixing the standing waves, ie determine the needed damping material, you shouldn't let the concern about damping the reflex resonance interfere with the answer you get. It's only after this that you have to put the compromise into place.
Up to a point the standing waves will be more of a priority than the reflex resonance, due to the nature of them as an issue and their higher frequency etc.. You'll have to determine that point and accept what you get in the bass. I don't think this is a reason to avoid larger enclosures.
Simulators these days allow you to sim a reflex box with lots of damping which I think is a better idea than the old rule of thumb to try and avoid damping.
Sorry to hear back from you with such fundamental issues. Perfectionism isn’t bad and you where going for a very well controlled acoustic system pre-EQ all the time. I would suggest to you building another box. Vituix has a build in standing waves calculator in Tools -> Auxiliary. It will be far more satisfying if you accomplish your goal. In the meantime, I want to point out you can mix both EQ strategies: limiting the boost and not loosing as much efficiency.
Can you show us the impact of the standing wave pre vs. after dampening?
Can you show us the impact of the standing wave pre vs. after dampening?
Egads! That's a midrange enclosure in my world.
Seriously, at least partially, you need to design the entire enclosure including bracing, port locations and damping as part of the whole. For example, I use matrix style bracing (not getting into bracing discussion here), but it allows me lots of small volumes that I can fill with fibre damping and then use cotton material glued and stapled to the bracing to hold it in place and still leave a clear path from the driver rear to the port. In my new surrounds (as per today's design*) the LF section is about 70L net with 400mm ports exiting the bottom of the enclosure. The entire lower part of the enclosure is filled as I mentioned up to near the port entry, plus a bit near the top, so there are no internal resonances. I factored into the initial design the clearance from the floor needed for the ports to get the MF/HF sections where I wanted them.
* I've used this basic enclosure design before several times.
PS: as I'm going to build 4 of these, I'll build a cheap mdf box to get it all right internally before I construct the finals and it means I can actually tune the porting, not rely on the sims.
What software does a whole speaker cabinet system? At the moment I use a combination of Hornresp, basta and vituixCAD.
Or the next time you use a standing wave calculator before building. Not surprising that you got bad resonance: https://vikash.info/audio/standing_...0&height=400&width=300&depth=400&threshold=50
None I'm aware of. It's mainly down to experience and trying things.
Useful, but it's only for an empty undamped box, but will help with Bob Gold's page to help work out what you need.
https://www.bobgolds.com/AbsorptionCoefficients.htm
Designing as a whole can mean doing all of the parts and processes separately, then compromising and combining them into one. (A compromise cannot be made if the properties of the individual parts aren't known, and speakers have many compromises. This doesn't always mean things have to suffer)
Egads, isn't that what I have just done (at least partially)?!
I did a lot of work before I built, I just omitted any thought to standing waves. Having had a year out from designing/making speakers some of the things on the mental checklist have faded a bit. Have got a bit rusty and found areas of weakness in my regime! 🙂
Cheers for the link. Based on this calculator I should be looking at 483hz. My problem starts from 380hz. Puzzling.
Yes, but so far you've done it once, not many times and applied what you learned from the measurements to subsequent developments, at least in this area. I started designing in the era when it was me, a pencil and the HP48G, not relying on a software suite to do it all for you. Build, measure, evaluate, modify, rinse and repeat. That's where you learn.
With my last build, pretty much everything went wrong. I tried all sorts to reduce standing waves but like you, lost the low frequencies in the process.
The drivers didn't measure anything like the datasheets suggested, some of that was because of internal cabinet reflections though.
The speakers cost me a lot of money to build, but were a complete disaster.
I know plenty of people who waste most of their disposable income on drink and drugs, so I just think of it as a learning experience.
The drivers didn't measure anything like the datasheets suggested, some of that was because of internal cabinet reflections though.
The speakers cost me a lot of money to build, but were a complete disaster.
I know plenty of people who waste most of their disposable income on drink and drugs, so I just think of it as a learning experience.
It looks to me like you changed the tuning frequency by whatever you did, if you were to lower the tuning frequency you might get back to what you wanted. Damping affects the apparent enclosure volume which if you keep the port the same length will change the tuning.
I would not be too bothered about the difference between the above graphs as below a few hundred Hz the room will be in control and the speaker is along for the ride. EQ'ing the in room response will have a lot more impact than the difference between those two curves will.
The calculator may not showing the realworld things, but i'ts a guideline. One thing is sure, don't use same dimensions for loudspeaker enclosure walls like 400x400.