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andreasmaaan

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About andreasmaaan

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  1. I'd also suggest that if you're going for the tube/horn sound you might want to consider ditching the MLs completely and building one or two decent quality 12 or 15 inch woofers into a box to handle frequencies below 500hz. The larger woofer will (all things being equal) be more efficient, have less thermal compression, and have a beamwidth (off-axis response) more similar to the the beamwidth of the horn at the crossover point. This should result in a lower midrange with dynamics and directivity that better match those of the horn. And the other advantage is that you could get the CD and woofer closer this way. The martin logans have their bass drivers right at the bottom of a tall box. The great distance between the woofers and the CD if you mounted it on top of the boxes would make it very hard to get the crossover right.
  2. Any of the three horns you've selected look capable of playing down to 500hz, but (without having off-axis measurements available) I'd guess that the smaller horns will have poorer directivity control in the lower region of their passbands, which would result in less smooth off-axis response. As a rule of thumb, a horn with a 300mm mouth will control directivity down to 1000hz, while a 600mm horn will control directivity down to 500hz. Another thing to consider is that the three horns each have different throat sizes and would therefore require different sized compression drivers. The AH550 has a 1 inch throat, the AH425 has a 1.4 inch throat, and the AH340 has a 1.5 inch throat. In general, it would be hard to imagine a 1 inch exit CD managing well below 1000hz (I think some of the Radians claim to be rated down to 800hz but this seems optimistic to me). Larger (1.4 or 1.5 inch) exit CDs will more comfortably play down to 500hz, but may struggle in the top octaves, both in terms of beaming (narrowing directivity) and in terms of resonances. It does depend partly on the driver you choose to use though. If I had to make an educated guess, I'd suggest probably the AH425 with a 1.4 inch exit CD might be the best balance of compromises. If you can find reliable measurements online of the particular CD/horn combos you're looking at, which include polar response measurements, this would be very helpful in making your decision.
  3. Yeh absolutely, it all depends on the particular limitations of the room. I'd say if you have a room with distances between any two walls/surfaces of 3m or more (i.e. most rooms), you'd be best off measuring a metre away from the speaker -- the first reflection should arrive around no less than about 5-6ms later than that, giving (hopefully) reliable measurements down to about 200hz-ish with 200hz-ish resolution.
  4. Hi Jbyhwn, I'm not sure of the answer to your question, but I can say that that wiring the speakers the wrong way in theory won't result in any audible difference for music, so long as you wire both speakers the same way and are running them full-range (i.e. no crossovers to other drivers). This article gives an interesting intro to the topic: http://www.stereophile.com/content/absolute-phase-fact-or-fallacy#Q7BoMmbJM0muTUHb.97 If you are running them with a crossover and other drivers, you can probably extrapolate the polarity by taking measurements of both drivers with crossover, with the polarity switched both ways and looking at whether the drivers are summing correctly. Cheers, Andreas Cheers, Andreas
  5. To an extent, but you don't want to get too close for a couple of reasons. The main reason is to do with the relative distances between the drivers and the mic. Any multi-way speaker will be designed so that the output from all drivers sums flat at a particular point in the far-field. This point could be at a distance of around 1-3 metres, depending on the speaker. By getting significantly closer to the speaker than this point, you are going into a region where the outputs from the drivers don't sum correctly due to incorrect relative distances and offsets between the drivers. To illustrate, imagine you're measuring a two-way speaker. Picture an imaginary triangle with the acoustic centre of the woofer at one corner, the acoustic centre of the tweeter at another corner, and the mic at the third corner. By moving the mic closer to the speaker, the angles of the triangle change, and the lengths of each side of the triangle do too. The result is that the relative phase between the drivers changes. This will cause the crossover to sum the drivers incorrectly if it was designed to sum the drivers at a different distance from the speaker. Or to cut to the point, I'd suggest measuring from at least 1 metre from the speakers for a small-medium sized 2 way, or, for a larger 3 or 4 way with greater distances between the drivers, maybe more like two metres. Cheers, Andreas
  6. Ah well, problem (more or less) solved for now. Cheers everyone
  7. Great question, hadn't thought of that. Here is just the blue woofer and I think this give us an explanation: The software is tracking the blue woofer +3db to model the power response for some reason. I have no idea why it's doing this but it does seem to clear up that it's not to do with the phase relationship between the drivers particularly. What do you think @davewantsmoore?
  8. Hey @davewantsmoore and @VanArn, thanks for sticking round on this one Dave, I have actually tried that. Basically the power response peak remains when the tweeter disappears. And it's there no matter whether I model the design with the 'ideal' responses I posted last, or with the modelled responses of the drivers as I posted originally. So it seems that it must be to do with the interaction between the two woofers (or any two woofers in this topology). FWIW, here is a screenshot without the tweeter: And here's a shot of the response from +45 degrees vertically off axis, which is the point at which fiddling around with the position of the imaginary mic got me the closest to the effect showing up in the power response, but still IMHO nowhere near close enough to explain it: Van, I'm not sure I understand you correctly, but I think you're relating this to the directivity of the drivers? I do understand what the power response is, and I do more or less understand the principles that affect the directivity of a driver with reference to it's radiating surface and frequency. But the phenomenon that this software seems to be pointing to (the peak in the power response that I marked in the pic) seems to me to be unrelated to this, since it appears to be the result of interaction between two drivers with identical directivity, but non-identical phase response due to differing filter slopes (i.e. a 1st order slope on the lower woofer @ 300hz or so, cascaded into a 2nd order slope over both woofers in the upper midrange). Will be interesting to get to the bottom of this... Cheers, A
  9. Hi @davewantsmoore, yes that's exactly the question So, if I believe the software, the woofers in any 2.5 way configuration have an inherent peak in the power response in the range between where the bass driver begins to roll off and where the mid-bass driver begins to roll off. And since (according to the software) this peak cannot be accounted for +/- 0-90 degrees off axis (that is far as the software allows me to model), the cause must be in the extreme off-axis response (90 degrees to 270 degrees off axis). Which I guess must be a result of the phase relationship between between the two woofers when one woofer is rolling off at 6db/octave while the other isn't.... or, the software is wrong... Can anyone explain this theoretically? Or explain why the software is wrong? Or if that's not possible, maybe someone who has other software that they use for crossover modelling could check if they get the same results? Cheers, Andreas
  10. Hey VanArn, Thanks and yes I understand that. As you picked up in your earlier post the tweeter is horn loaded, and the horn has a similar directivity profile to the 8'' woofer in the crossover region. So using the larger driver is in this case a deliberate move. And yes, the enclosure would be around that size by my calculations. Re: the 830884, it seems to be available here in Germany so I wonder if maybe it's back in production here (or if the store I'm looking at has an outdated website perhaps). I'm still having trouble understanding this power response peak in the modelled response though. The software seems to model it into every 2.5 way speaker no matter what I do. Hence my question about the power response of 2.5 way systems generally - whether this peak is a real phenomenon that is recognised and understood or a glitch in the software?
  11. Thanks for the replies everyone At this stage I haven't bought or taken my own measurements of any drivers, I've just been modelling various combinations of drivers from published measurements to try to decide on what to buy and build. The modelling is obviously of limited value for this reason, but it does incorporate modelled in box response and modelled baffle diffraction/step. But really my question is not about this particular design, it's a question about 2.5 way systems in general. That's why I posted the above modelled response using "ideal" drivers, i.e. with perfect frequency response and 0 degrees phase response 20-20,000hz, to show how the software seems to be telling me that a bump in the power response in the midrange seems to an inevitable outcome of the 2.5 way topology. Here's the screenshot again (power response in green): So I'm actually just trying to understand if the bump in the modelled power response of the ideal drivers is based on the topology itself... since it isn't something I can explain through my own understanding of phase interactions between the drivers. Cheers, Andreas Sent from my iPhone using Tapatalk
  12. Actually, here's a screenshot of the same configuration using ideal frequency responses for all drivers (and a modelled baffle step roll-off on the two woofers). So it seems that Jeff Bagby's software is trying to tell me that a bump in the power response in the upper region of the midwoofer (but not one that is caused by anything occurring within a 90 degree vertical or horizontal axis, apparently) is an inevitable outcome of any 2.5 way design. Is that right? Or is this a bug in the software? Edit: here is a screenshot from the off-axis position (within 90 degrees vertical/horizontal) which produces the greatest bump in this reason. It's at -30 degrees vertical, so it's a floor reflection, but still I don't feel that it alone can explain the modelled power response...
  13. A screenshot. Note that there is no sign of peaking beyond a decibel or so in this region at any point in the modelled off-axis response, and that there is significant off-axis dipping in this region too.
  14. Hi @davewantsmoore and @VanArn, thanks for commenting. The software is Jeff Bagby's passive xover designer and the woofers in this case are Peerless P830884. The crossover is 2nd order LR2 @ 1800hz between midwoofer and tweeter and 1st order at around 400hz on the woofer. The speakers are laid out in a TMM configuration with about 20cm between the centre of each driver. Cheers, Andreas
  15. Update: the same power response bump is there when I remove the tweeter, i.e. if it is the result of an interaction between the drivers' spatial relationship, it is a result of the relationship between the two woofers.
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