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Red Spade Audio

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    Paul

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  1. The absorption isn't normally considered because the transmission is so high. Glass has approximately four times the density of bricks but as it's always thin the mass is still quite low. All practical windows perform very poorly in terms of keeping bass in the room - even acoustic windows with a high STC rating. Rooms with lots of openings and many large windows and light construction can actually perform quite well in the bass due to being lossy. Some of us are music lovers who don't care for the technical. Some of us are gear junkies who love our shiny hifi toys. Some of us are tech nerds who enjoy learning about the science. I'd say most of us are some kind of mix. Music is often the excuse that justifies our love of tech and toys but in reality I'd argue that any mix of the above is a perfectly valid interest for anyone to take on.
  2. The article is written for studio owners. It makes sense in that context where it's about mixing decisions and getting SBIR to behave is more important. In that context, the speakers might either be soffit mounted or on a mixing desk not far from the front wall - a nearfield monitoring situation where you don't get the kind of sound stage we all want at home. At home, the offset from the wall behind the speakers has more impact on the sound stage. For many, getting this aspect right trumps SBIR.
  3. In that room it would be worth considering an AT screen with black acoustic panels across the entire front wall - hiding everything so that your wife no longer cares what is behind. You could hide it all behind there - speakers at the right height, all equipment, as many subs as you want and a bass trap across the entire front wall. A room of those dimensions will have heavy duty room mode peaks in the midbass. Just one Ultimax 15" in a sealed box with 500W would most likely give you loads of punch due to the midbass room modes. Ultimax drivers don't tend to work well in horn sub designs. Horn sub designs are usually not limited to just one driver and in some cases, you can also use a different size. But it's never a random swap - there are many cases where a design will work very poorly with a different driver. When you put a horn sub in an Australian room, the bass extension will typically be close to how it measures outdoors. Hence, if you want to get down to 20 Hz, the sub needs to be tuned that low. If you put a 30 Hz horn sub into a small room like this, you will likely get loads of midbass, which you would need to EQ out. At 20 Hz it may not be so impressive. Keep in mind that horn subs tend to have upper bass resonances which limit their bandwidth. If you run it with audible resonances, the bass won't sound articulate and refined - it might even sound like a $500 sub. Consider also the middle position across the front wall. Sometimes it can work well but that depends on both your room and seating layout. With a pair of horn subs behind a screen you can hit both corners, the centre or the centre and a corner. It's always best to test! If you are buying Dayton drivers, buying local from LSK will save you shipping them back to the US in the event of warranty claims. When it comes to choosing a design for a horn sub, there are two things you want to avoid. One is a design that lacks the extension you are targeting. The other is audible resonances within the passband of the sub. Both are difficult to avoid. A few of the BFM subs were tested here: http://prosoundshootout.com/ It's a bit of a maze of forum posts to get to the results, but they are in there.
  4. You can export sims from Hornresp into REW so you then see your model against the measurements. Hornresp models often look worse due to the scale, with 5 dB divisions over a smaller range on the y scale.
  5. Intuition tells us that if a thick absorber is better and density helps, then we want more of both. But it's slightly more complex. For any given absorber, there is a point where it becomes thicker than optimal and this effect varies with frequency. You can end up with an absorber that might perform poorly in either bass, low midrange or even both, in comparison to one with less material and a smarter design. The worst case scenario (aside from doing nothing at all), is a very high density absorber filling the entire area. There isn't an easy to define limit here because there are several variables. If there is no front reflective baffle, it's not a baffle wall but rather a very large absorber. Both are very desirable.
  6. If I were using this driver in a home system, I'd use a sealed enclosure which gives you 80 Hz extension, perfect for working with a sub. Smaller size doesn't just keep your wife happy. It's easier to work with and as you start to look at making the box inert with bracing and thick walls, the weight is not so prohibitive. A sealed enclosure also allows you to fill the entire enclosure rather than just lining it. No matter what you do, a 15 is big! Even in the smallest possible enclosure, it's a beast! You can squeeze out another octave with a ported design - many people think this is what they want before they hear it. But unless you have a lot of midbass boost from the room, it's probably not going to be very satisfying or full bass. In a home theatre it's a no brainer. Even in a music system, I'd still go with "compact" sealed, using your sub to set the bass level as it sounds right. 45L sealed with light fill should work well. If you really must have as much extension as possible, 150L tuned to 40 Hz reaches 40 Hz. You don't need to go any larger unless you are looking for an EBS (extended bass shelf), which trades box size and max SPL for extension. 100L tuned to 39 Hz gives you 50 Hz.
  7. The backing you use isn't acoustically significant - the issues are all pragmatic. Did you try corflute and if so, how did it work for you? I did a trial with corflute before 3mm MDF with velcro strips. The idea was appealing for the weight - it's extremely light. However, it has no stiffness. This means, when you remove the panels, either to take them down, move or to re-position you have to be careful your backing doesn't come off. Velcro strips take a fair bit of force to pull apart. Since the corflute bends, it pulls at the glue in the area around the velcro strips and you really test the bond. 3mm MDF has enough stiffness to ensure that as you remove the panels, the strain on the adhesive is spread over a much wider area. In terms of adhesive from the backing to the foam, you can use either contact adhesive or a construction adhesive - liquid nails fast is ideal and I would use a LOT more than shown in the photos here. If you're using contact adhesive, you'll need to spread it on and you use much more than you think you will. The foam tends to soak it up. If you're using the liquid nails (or an equivalent), 24 hours with weight applied is essential. It's not actually very fast in this application. Quite a bit of care is needed to protect the front surface yet apply adequate weight across the entire surface. After 24 hours, you flatten out the gap between backing and the foam. You can use both, contact adhesive around the edge, construction adhesive in the middle. Always buy the biggest strips you can find - gives you more margin for error and on really hot days, the strips can fail as the adhesive weakens, especially if you haven't cleaned each point of contact adequately with alcohol. Keep in mind there is risk with this type of mounting. If you want a more reliable method, use the backing but mount with button head screws going into wall anchors. On your backing you need a keyhole cutout and this does also rule out using corflute.
  8. It sounds like your baffle wall is actually more like a big bass trap that essentially fills in the void between the speakers, with no actual reflective membrane on the front. It's a great opportunity to get in a big bass trap. You might consider also using fairly dense panels in front, like rigid fibreglass (48kg/m3) or any of the polyester options in a similar density. They hold their shape well and stand on their own without a frame. In fact, you can stand up a full 1.2 x 2.4m 50mm thick panel and it won't collapse like fluffy insulation. A little velcro can easily attach them to a frame. My triple leaf comment only applies where your baffle wall has a sealed and solid reflective membrane with a cavity behind. Otherwise it makes no sense at all!
  9. You could say that! We use them in our PSE-144 horn. I've worked with many Acoustic Elegance drivers over the years, all of them are excellent. They are expensive but they are worth it. You can pay much more for inferior drivers.
  10. Your modified plan is a clear improvement over the original. I would orient the room just as you have as it's by far the best layout. Intuition and observation often work against you with acoustics. Often there are a few things going on at the same time. Yes, bass is omni but it's also modal. Hence, you need the speaker outdoors to appreciate the dispersion without room effects obscuring the picture. No matter how you build your baffle wall or how much fill you use, its impact on sound isolation is not very significant in the most critical bass region. Keep in mind that if you create a sealed cavity, you can accidentally engage the triple leaf effect with respect to your front wall. When you consider your front wall, keep in mind it's also about keeping external noise out. The location of your speakers isn't significant in sound isolation terms. I'd call that good news as you can focus on how you prefer to lay out your room. Looks like a great system and room in the making!
  11. TD18H+ is an exceptional driver and if I had to pick one favourite out of them all, regardless of price, this would be the one. A vented enclosure can give you extension to 36 Hz with 160L tuned to 38 Hz. That's a good starting point for your modelling. A passive implementation takes the sensitivity down to around 94 dB. That might be a problem if you're intending to use that same 10W amp to drive your horns.
  12. In that theoretical scenario, I'd say no - they should be fairly comparable, if we are just talking about performance in one position. In practice, we often find some products differ from expectations. It may be that either the 12" or the 18" in that particular range perform better, for reasons that aren't obvious. When it comes down to specific choices, it could go either way. Definitely!
  13. The size of the drivers tells you very little about the sound quality of the sub. Neither the size nor the moving mass are good predictors of any subjective quality that audiophiles are looking for. Myths abound here and quite often it's because they are very often quite intuitive - they feel like they should be true! My experience in building, testing and integrating many different subs over the years suggests two things that contradict expectations: 1. Subs that appear radically different can be made to sound near identical within their linear range. An extreme example might be an open baffle sub vs a huge horn sub. Most of the differences can be removed with calibration. 2. Larger and heavier subs are more likely to perform better in any measure, whether subjective or objective. Yes, it sounds like a contradiction to my previous point! However, this has been my experience generally. Let's suppose we could compare a pair of sealed subs, using drivers from the same range. One is 8" sealed, the other is 18" sealed. Cabinets equally solid. Placed in the same position. Calibrated so they have the same frequency response. Operating at exactly the same level - let's say 90 dB which both could handle. I'd expect the bigger sub to sound cleaner and more accurate but it would be a subtle difference. It's only when you move beyond the limits of the smaller sub that they start to sound very different. The extra clean output of the bigger sub in actual use translates into an experience of greater authority and punch. You find yourself turning it up more, without realising. It doesn't sound louder, Instead, it feels more full, powerful and clean. This is why many audiophiles would actually be well served with a sub that is bigger than they think they need. When it comes to the choice of a sub in terms of its size, I'd suggest you have two main things to think about. Keeping things simple, big enough to give you satisfying bass depth and output. Small enough that you can live with it in your room. Getting the balance right is a fairly personal decision.
  14. If you're building a horn sub that will sit under a floor or in a garage, formply is worth considering. It's inexpensive and pre finished, which is handy. You can glue and screw, getting around the need for a lot of large clamps. If it's always going to be indoors, MDF is easier to work with as long as you don't attempt to screw into it. With MDF, I prefer to use brads with a nail gun. It's very quick and if you're working without another pair of hands on something huge, it's a problem solver. You lay down the big side panel on a pair of dollies - you're probably building it in the garage. The brads hold a big panel in place so you can then grab some big F clamps. You want some long pine studs on edge for clamping these up, unless you plan to visit every Bunnings in Victoria to find enough F clamps! If you're taking your time on the build, you can ditch the brads and screws with MDF. You would probably start with the largest panel laying down, with two sides forming a corner. Any wood glue is fine here but I like to use Titebond. If you can live with the size, using a pair of drivers dual opposed reduces vibration dramatically. So you can cut down on bracing to make the build easier. Or you can end up with something quite a bit more inert. Worth considering even more if you are going to say put it in a garage with the mouth coming into the room, hence you're attaching the horn to the room itself. Every build is different and the bracing design has a big impact on the best build sequence. If you have leaks, blu tak and REWs signal generator are your friends! If your design has a hatch to access the driver, that's the most likely location for leaks. Also the driver mount to the baffle. If you build with ply, variations in thickness can cause you some problems - vernier calipers are often needed here. If you're using low grade ply, you will often have voids and thin layers on the faces. Often you won't get away without painting it if your jointing isn't spot on.
  15. Are the drivers from the same manufacturer? If they aren't, it's not a safe assumption that they are comparable.
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