Enclosure design help

I have a driver that I'm having a hard time simulating and enclosure for with WinISP. It is something I'm beta testing for a manufacturer, and I know it is being used in bass reflex enclosures a little larger than a cubic foot. WinISP is adamant that it needs an enclosure of about 7.75 cubic feet. Is there something I'm doing wrong? Here are the parameters I've been given.

Revc= 6.500 ohm
Fo= 41.203 hz
Sd= 22.167m M3
Krm= 124.110m Ohm
Erm= 0.306
Kxm= 1.035 H
Exm= 0.000
Vas= 105.116m M3
Cms= 1.506m M/N
Mmd= 8.006m Kg
Mms= 9.904 g
BL= 5.225 T-M
Qms= 2.880
Oes= 0.610
Qts= 0.504
No= 1.165%
SPLo+ 92.681 db

thanks,

Paul
 
Thanks for the reply.

I've been doing as much reading/searching as I can. It seems like this might be borderline for an open baffle, but would need some equalization. I've been reading about transmission lines, but designing is probably out of my league. I imagine some sort of aperiodic solution may exist as well. In any case it seems that any enclosure would either be difficult to design, domestically unacceptable, or some combination of the two.

If I'm wrong about this, feel free to chime in, otherwise I'll look for another project. Too bad creativesound is out of Jordans, my new gainclone is tiring of its present company.


Paul
 
Greets!

You're welcome! With the possible exception of a horn, all the cabs it's suitable for are simple designs, even TLs, so I'm not sure what you're referring to.

Anyway, with a 0.5 Qts, it's suitable for any box design, so it boils down to what F3 and box Q you'll settle for if the design is Vb specified. Want a low F3, the box must be large, and vice versa.

GM
 
By "simple" I was refering to my ease of design. My TL reading has been mainly restricted to MK's website, and most of the discussion is beyond my current understanding. I'm also mostly restricted to a Mac, so I can't run MathCad.

Domestic acceptability is limited to a maximum of 60 or so liters, and I can't find any tuning that seems to work for a Vb in that area. Any sealed box in that area is an awfully high Q too.

I'll be the first to admit that my knowledge is of loudspeaker design is subpar. I'm hoping to extend it with this project, but for that I need to find a suitable design. I've seen pics of this very driver playing to acclaim in vented boxes smaller than 60 liters. I expected to be able to plug the specs in to winISD and start cutting wood. Either those using this driver are modifying it, or the enclosure solution is elluding me.

I appreciate all your help; I just wish I didn't have to ask such silly questions.

Paul
 
T/S parameters check

pjanda1,

Before you give up on this project, please, doublecheck the T/S parameters you've enterd in WinISD. I'm affraid they don't match, or you have mixed the units somewhere. For example, if Sd is in cm sqared, you driver is 2.5" diameter, and then no way it has 105 liters Vas.
Check if you are running the latest version of WinISD. If not, download WinISD pro Alpha. This version checks T/S for consistency when you enter the driver parameters and will not let you save the driver file, until everything matches.

Another issue is the driver Qts. If you want to have a classic reflex box alignment, the one where you use the air VOLUME resonance, Qts of about .44 is the upper limit. Above that you will have to use some sort of Chebyshev alignment (bet that's waht WinISD suggested?) with some ripple. These require huge boxes with Vb >> Vas. I've built quite a bit of those in the beginning of this hobby. Looking back - they did not sound good. Lots of boom - not a lot of control.

However, a MLTL is a different story. It uses a quarter-wave resonance, not the volume resonance. Although it looks like a ported box, the physiscs behind it is different. This box has to be tall, to fit that quarter of the wavelength. Unfortunately, the only way I know of to model this is MKJ worksheets. It may be worth to find a PC (work, library??), download MathCAD explorer and worksheets and model it using "Ported box" sheet. The good news is - I've used this with drivers having Qts as high as .9 with decent results.

In any event, make sure the numbers and units are correct.

Vadim
 
Wow, somebody did some digging to bring this up. Heres the deal. This was an early version of the Hemp Acoustics driver. I couldn't come out and say it at the time. I wondered if someone would read my later posts and put it together.

I'm not sure why Sd was quoted the way it was. It is an 8" driver, and 221cm (squared) is a better spec (that's how I entered them). I tried them both in a 50L enclosure, both sealed and tuned to 40ish hertz. I know it wasn't ideal, but I had the box. It worked either way, obviously with more bass in the later. The response of this driver closely mirrored that of the Fostex FE206E, and was ultimately too hot for my tastes in a BR or sealed enclosure. The current Hemp Acoustics drivers are a couple of generations beyond this.

I've still got the drivers. I've toyed with the idea of building a compensation network to tame them, and ultimately a more suitable enclosure. I think a TL of some sort woudl be ideal, but with that compliance, it would be big. I've been too happy with the newer Hemp Acoustics 8's to give it much thought.

thanks for checking up,

Paul
 
This was an early version of the Hemp Acoustics driver. I couldn't come out and say it at the time. I wondered if someone would read my later posts and put it together.

Aha! I thought the spec looked familiar. The thing is, I am working on a disign for the same driver. It will, probably, be the newer version, since I am still waiting for Hemp's shipment to a distributor for several weeks now.
I, actually, want to try it in a back-loaded horn - believe it or not. This weekend I'm gonna try to get the new version of MJK's worksheets ($25 is a bargain for what they can do) and model my horns. The hope is to skip the baffle step compensation.

So, what is a difference between older and newer versions of the Hemp FR8?

Vadim
 
I'll be curious to see what you come up with for a BLH. I really need to buy an old PC so I too can run mathcad. You should give them a shot in a BR first if you have time. I completely understand your hopes of eliminating the need for BSC. I try and help the situation by using a wide baffle and place them close to the rear wall. I've wondered if a really well engineered bass hump (too small an enclosure, too high a tuning or something) in a BR would work. I know it would hurt transient response, but more than a BLH?

I also want to minimize excursion. Smaller lower tuned BR's (like I was using; 50L 40hz) appear to unload a bit around 60-70hz, and it doesn't take much power to exceed Xmax. With larger enclosures there is still musical content below the point the driver unloads. In any enclosure, we're still taking very high output for a FR driver. I'm just trying to get the maximum possible dynamic range.

I'll use a sub either way, because nothing short of the BIB will create the sort of bass I'm after (into the 20's). I like the Hemps because they will hit the magical sub integration point of 80hz in a sealed box. Sealed it will take more power without exceeding Xmax a some point between 40 and 100hz than most any BR aligment I've looked at.

If you have driver design questions, give Hemp Acoustics a call after the Montreal show is over. Also, I've been thinking we should start a Hemp alignments thread. GM proposed a really neat sounding TL in the BIB thread, and addition to a BIB size. A singular location for ideas would help folks find them in the future.
 
Case building

I built my own speaker case. I got a general book on speaker building at the library. After learning the basics I used a Jensen bookshelf speaker as a base. I built it using solid pine and used a rear port. I installed Jensen 2-way car speaker and it sounds just as good as my Cerwin Vega 3-way floor speakers.:smash:
 
Hemp FR8 enclosure

I've tried, and it didn't look as good as I wanted. I think the Q is a little too high. BIB is a different story, but... well it's big.

The best solution I found was a BLH. My design is available at E-speakers: "http://www.e-speakers.com/", as 'Vadim Horn project'.
If interested, click on download Info Package:
http://www.e-speakers.com/pdf/vadim-infopack.pdf

It's free and has details on why this alignment was choosen, as well as quite a bit of measurements and FR plots.
All I can say is that I like my horns quite a bit, especially after about half a year of break-in. The imaging is fantastic if you keep them away from the back wall.

Vadim
 
The VAS makes any enclosure large. Sim a few BR alignments, and then realize that a TL of any sort would need to be bigger and you see the issue. Obviously I settled with the BIBs, and I'm thrilled. Back in the BIB thread, GM proposed a straight TL that looks really interesting.

http://www.diyaudio.com/forums/showthread.php?s=&postid=870235&highlight=#post870235

GM always seems to be right, so I am sure it is worth building. Like the BIB, the design relies on available corners to work best. It should be easy enough.

Also keep in mind that MLTL's are often employed when the driver just won't work in a simple BR. (Of course that's not the only circumstance they are employed given their benefits.) The Hemps work really well in a standard reflex enclosure, so it doesn't need to be more complicated. Of course, with a BR (or an MLTL) you'd be best to use some BSC, whereas GM's triangular line, the BIBs or Vadim's horn won't need it.

good luck,

pj
 
Just to clarify, GM's triangular cross section enclosure for the Hemp FR8 is not a MLTL but a conical horn. In GM's own words:

Technically it's a corner loaded 90 deg wall angle conical horn with an acoustic pathlength = to whatever the ceiling height is plus an end correction, or ~35 Hz for an 8 ft height.

I think it is a great design for the Hemp and plan to build a pair as soon as I finish my current work projects and can find the top of my desk.

James
 
jimmyd53 said:
Just to clarify, GM's triangular cross section enclosure for the Hemp FR8 is not a MLTL but a conical horn. In GM's own words:

Technically it's a corner loaded 90 deg wall angle conical horn with an acoustic pathlength = to whatever the ceiling height is plus an end correction, or ~35 Hz for an 8 ft height.

I think it is a great design for the Hemp and plan to build a pair as soon as I finish my current work projects and can find the top of my desk.

James

Thanks for the replies. Corners are not an option in my room. I am using FE206Es in the alternative BR enclosure on the PDF. They are 45 liters and the port is tuned according to the PDF.

http://www.fostexinternational.com/docs/speaker_comp/pdf/recom_enclose/206e_enclrev.pdf

I am using the BSC circuit from MJKs site. I may just try the Hemps in my enclosure and see how it goes. I'm tired of the shouting 206s. I haven't tried phase plugs though. I haven't worked up the nerve to do surgery on $160.00 worth of speakers yet.:bigeyes: :whazzat: The cabinets are made of 1" plywood with a sprayed in damping material on the inside. No stuffing or frame dampening. Maybe I should tweak them out first before dropping 250.00 on new drivers huh? Oh yeah. I am using a little M&K sub and my room is small so thundering bass is not really needed. 50 - 60 Hz is fine.
 
The VAS makes any enclosure large. Sim a few BR alignments, and then realize that a TL of any sort would need to be bigger and you see the issue.

Vas alone doesn't make the enclosure large. Take any Fostex driver with Qts=.20 and you will end up with very small optimum box. F3 would be high, though. With Qt of .5 the only ported alignment that works would be a Chebyshev, where Vb has to be larger than Vas.

But, even this is not a problem. Hemp FR8 models quite OK in a 72 liters box, tuned to 43Hz with a broad hump of only .3dB. The probelm is Xmax of this driver being 1.9mm. It will bottom out in this alignment at only 3W of power anyhwere from 100 to 60 Hz. BTW, Fostex is even worst in this regard. That's why I settled on the horn

Vadim
 
Here is a cabinet worth mentioning:

http://www.frugal-horn.com/metronome.html

There is a thread nearby on the design, and others that mention it. It is probably the smallest footprint design for the Hemps that will give you real bass. It should control excursion much better than a BR. And it looks just plain neat. It looks like a simple build and it will need BSC.

In my experiance, the Qts. of .4 isn't that unusual. The VAS of 90ish (cu ft) is, unless your 'usual' includes pro audio drivers. That's why I singled it out, not because I'm under the impression that any one parameter will determine cabinet requirements on it's own. It's the combination that gets ya'.

pj