Some questions about enclosure for SR124

monologuist

1.To fit ideally against the back of my rear seats in the hatch area of my Saab, the back of the box would have to be angled. Does anyone have any insights as to whether this will compromise sound quality and if so, how? This is, relative to a square or rectangular box.
2. If slanted back is a no-no (and one builder has warned me against it already), then what about a rectangular vs. square box (rectangular so as to preserve depth of space in the hatch by going wider but shallower)?

This is all assuming I stick with a net volume of 1.25 cubed which I've been told is the absolute optimal size for the SR124.

Oh yeah, am I to assume it's 1.25 cubed net, including the thickness of the MDF (so measured from the outside), or is it measured from the inside, so not including the thickness of the MDF?

MacLeod

The shape of the box doesnt affect SQ so long as its not a perfect square. Other than that, it wont affect SQ.

monologuist

MacLeod wrote: »

The shape of the box doesnt affect SQ so long as its not a perfect square. Other than that, it wont affect SQ.

you mean ideally you DON'T want a perfect square? This box-builder was trying to convince me that I shouldn't go with a slanted back, that it would detract from SQ. But I think he might have been saying this only b/c I as originally looking for a builder in my local vicinity (L.A.), and I put an ad up looking for one on Caraudio.forum....and he replied but was out of state and wanted to build me one and ship it.

Greg Peters

monologuist wrote: »

1.To fit ideally against the back of my rear seats in the hatch area of my Saab, the back of the box would have to be angled. Does anyone have any insights as to whether this will compromise sound quality and if so, how? This is, relative to a square or rectangular box.
2. If slanted back is a no-no (and one builder has warned me against it already), then what about a rectangular vs. square box (rectangular so as to preserve depth of space in the hatch by going wider but shallower)?

I am curious as to why your box builder has warned against enclosures with slanted backs (my last two subs have had enclosures like that ). I can think of a few reasons where that would be a good thing...in a perfectly square enclosure you'd be encountering some destructive reflections from the back wave of the sub's cone that could adversely affect the sub's performance. A slanted rear panel on the enclosure ensures that reflections from the back of the cone are dispersed.

monologuist wrote: »

This is all assuming I stick with a net volume of 1.25 cubed which I've been told is the absolute optimal size for the SR124.

Oh yeah, am I to assume it's 1.25 cubed net, including the thickness of the MDF (so measured from the outside), or is it measured from the inside, so not including the thickness of the MDF?

The 1.25 cubic foot measurement (earlier suggested by Mac, I believe) is definitely a good idea- would be internal measurements not including the displacement of the sub (M-Vd), .14 cubic feet. Polk recommends internal airspace requirements for the SR124 as being between .88 (minimum, plus M-Vd of the driver, .14 cubic feet= 1.02 cubes total airspace) and as large as 1.5 (plus M-Vd of driver .14= 1.64 cubes total airspace).

Enclosures on the smaller end of the spectrum will raise the resonant frequency of the enclosure (giving a "punchier" response) and allow for maximum power handling, while enclosures on the larger end of the spectrum will maximize the sub's low end extension. Modeling the SR124's response with both extremes of enclosure size using enclosure design software doesn't really show drastic performance differences between using .88 and 1.5 cubic feet of internal airspace, though modeling software only gives you a general indication of performance...building different sized enclosures will show some real-world differences. 1.25 cubic feet is a nice happy medium for enclosure size that should work well.

If you're the experimental type, you could build the larger 1.25 cube enclosure and simulate the response of smaller enclosures by adding objects that displace some airspace to give you an idea of what differences the smaller enclosure has on the sub's performance. Should you decide you prefer the sound of the smaller enclosure and want to modify it for slightly punchier response afterwards, additional internal bracing could be added to displace some air available to the sub and tailor it to your needs.

I personally went with an enclosure with 1.20 cubic feet (internal measurements including the SR124 DVC's displacement) and find low end extension is not a problem- I intended to post a review, but some other "issues" not related to the sub will have to be cleared up first...a long, involved story .

PoweredByDodge

... no no's =

1= perfect square
2= perfect globe (circle)

You can fix problem #1 by simply putting a handfull of poly-fill in there.

You're box builder is an idiot.

MacLeod

PoweredByDodge wrote: »

... no no's =

1= perfect square

Yup

2= perfect globe (circle)

Tell that to Gary Biggs. 7 SQ World Championships and he uses a round enclosure.

You're box builder is an idiot.

Yup, again.

monologuist

thanks guys..I had a feeling this was bogus advice. I think he was just trying to get my business as I put an ad out saying I wanted a LOCAL builder and he is on the other side of the country. So maybe he figured I would be scared to order a box with custom slanted back to accomodate the specific angle of my rear seats? I dunno...I could be reading too much into it. I still haven't found someone to do the box yet here in L.A. I have no time or I'd do it myself.

OK. so the volume is measured using the inside seams, thus not including the thickness of the MDF itself. Good thing I asked...I had assumed it was measured form the outside edges of the box. As far as smaller vs. bigger, I'm trying to find the most linear response, combined with lowest extension possible, but also quickness and handling of fast transient bass information is a must. This system will be used to reference various forms of studio productions primarily in electronic genres. Sounds like it's better to go too big rather than too small, and have the flexibility of adding stuffing inside if the sound is too loose or not punchy enough?

So I don't get ripped off, what's a fair price for such a build? Also, would it be stupid to consider a pre-fab box, something like :
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=013&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=230149322396&rd=1&rd=1

or

http://www.woofersetc.com/index.cfm?fuseaction=product.display&Product_ID=3623

or

http://www.sonicelectronix.com/item_7590_Sonic+Sub+Box-+1H12-1.0.html


???

MacLeod

Just for the record, I didnt just pull that 1.25 out of me arse.

In the review CA&E did on the SR124, they stated they called the man himself, Polk Paul DiComo and he recommended a 1.25 sealed for best SQ. So I figure if thats the size box they want a magazine reviewer to use, well then its good enough for me!

If youre handy with power tools, you could run down to Home Depot and grab some 3/4" MDF, some screws and wood glue and build the thing yourself for $30'ish.

Otherwise it should run you close to $100 for a QUALITY premade box.

300m

A sphere is a BAD idea for an enclosure. Gary's enclosure is sphereish on the outside, however he has a lot going on inside the box. Non-parallel sides, and/or irregular "interior walls" will net the best results.

Greg Peters

MacLeod wrote: »

Just for the record, I didnt just pull that 1.25 out of me arse.

I wouldn't dream of insinuating that (Mac's bigger than me).

MacLeod wrote: »

In the review CA&E did on the SR124, they stated they called the man himself, Polk Paul DiComo and he recommended a 1.25 sealed for best SQ. So I figure if thats the size box they want a magazine reviewer to use, well then its good enough for me!

If youre handy with power tools, you could run down to Home Depot and grab some 3/4" MDF, some screws and wood glue and build the thing yourself for $30'ish.

Otherwise it should run you close to $100 for a QUALITY premade box.

I read that article too. The folks at CA&E felt bigger was better, and in reading between the lines it suggested the SR124 didn't lack in the impact department.

Greg Peters

monologuist wrote: »

thanks guys..I had a feeling this was bogus advice. I think he was just trying to get my business as I put an ad out saying I wanted a LOCAL builder and he is on the other side of the country. So maybe he figured I would be scared to order a box with custom slanted back to accomodate the specific angle of my rear seats? I dunno...I could be reading too much into it. I still haven't found someone to do the box yet here in L.A. I have no time or I'd do it myself.

A wedge shaped box is a touch harder to build, in that you have to cut some edges on an angle for them to mate properly with opposing edges- more work than a quick and dirty traditional enclosure, plus more math :mad:. What you need is a typical carpenter's protractor to grab the required angle, then you can download some enclosure design software (plenty of free versions online) and factor the angle plus available dimensions into the software. I don't advocate pirating software, but Bassbox Pro is a wonderful (and expensive) program that will actually do a blueprint for you, complete with external dimensions, angles, measurements...everything you need to DIY, or provide to a local enclosure guru. Just enter TS parameters of sub, angle required, thickness of MDF etc. and you can juggle all other variables until you get something that makes best use of space for your cargo area and the sub .

monologuist wrote: »

OK. so the volume is measured using the inside seams, thus not including the thickness of the MDF itself. Good thing I asked...I had assumed it was measured form the outside edges of the box. As far as smaller vs. bigger, I'm trying to find the most linear response, combined with lowest extension possible, but also quickness and handling of fast transient bass information is a must. This system will be used to reference various forms of studio productions primarily in electronic genres. Sounds like it's better to go too big rather than too small, and have the flexibility of adding stuffing inside if the sound is too loose or not punchy enough?

So I don't get ripped off, what's a fair price for such a build? Also, would it be stupid to consider a pre-fab box, something like :
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ih=013&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=230149322396&rd=1&rd=1

or

http://www.woofersetc.com/index.cfm?fuseaction=product.display&Product_ID=3623

or

http://www.sonicelectronix.com/item_7590_Sonic+Sub+Box-+1H12-1.0.html


???

Quickness and handling of transients is partially a function of the sub's design, and partially a function of the enclosure (group delay). Software can model the group delay your enclosure will exhibit, and you can see how it can change in relation to enclosure size/stuffing.

Just so you're clear, "stuffing" an enclosure is used with a smaller than optimum box, to mimic the response of a larger one- it won't work if your airspace is way too small, but if you're close, adding polyfill stuffing will trick your sub into performing like it's in a larger box than actual. Adding hard, non-compressing material like additional bracing will effectively shrink the airspace available inside the enclosure. If you build your box on the larger side, stuffing it with polyfill is probably not a great idea. Polyfill will effectively increase the airspace seen by the woofer through the magic of complicated physics .

My local enclosure wiz whips a custom sealed box out for $80, "in the raw". The ones he's built for me needed finishing (carpet/paint/vinyl, terminal cup etc.) and some seam sealing, but they're bang-on with internal dimensions and finished almost good enough to paint- rounded edges, smoothed joints. He's got a F/T job plus lots of enclosure work on the side, so he's very busy as a result- it takes weeks to track him down. If I catch him on a slow day, my enclosure's usually done in a couple of hours.

Pre-fab enclosures are not usually well made- some are better than others. Expect to do some seam sealing with silicone caulk if you go that route, and expect the internal volumes to be approximate rather than exactly what you need. They're not usually real sturdy, and are fairly easy to damage in transit. Buying a pre-fab enclosure online can really cost a bundle in shipping- MDF is heavy. For example, my 3/4" MDF box (double thickness front panel, recessed for sub) loaded with the SR124 weighs 50 lbs . Custom box designed for your sub > cheaply made assembly line "generic" box.