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Speaker Advice for Bitzie System (Take II) |
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Well, I guess this topic is on hold whilst the world reopens sometime next week...
Having a conversation with John C about wood cutting, B&Q's cutting service, and how to do round holes with rebates, it looks possible that we can make the prototype I illustrated earlier on in this topic. So we're going to have a go at making a Slee transmission line enclosure, and perhaps it might be covered better in a new topic of its own. |
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KJFAudio
Senior Member Joined: 17 Nov 2016 Location: Warwickshire UK Status: Offline Points: 119 |
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Hey Graham, looks like you've been doing a lot of reading, sorry I've made you catch the bug, it's impossible to shake now you've got it!
Don't worry about the rebate and holes etc, I'll make you another test cabinet. I've got a transmission line design for the Alpair 7 that is similar to yours, shorter but deeper and they work very well. I'll make some posts over in your new thread. Did you get a listen to the FH last Wednesday in your room? I spent some time talking with Dr. Scott at the weekend who is the FH designer about your 'Heath Robinson' experiments. Here are some thoughts on that which may or may not help your quest. One of the original requests was for as tight a bass as possible in a similar footprint to the LS3/5a which needs the lowest group delay possible. Lowest possible GD implies 'transient perfect' response through the acceleration (rising response) bandwidth which as far as boxes go is technically a sealed box with a 0.5 system Q, I made a maximally flat .707 system Q box however to get a slightly deeper and flatter bass response while maintaining excellent transient response. Of all of the vented type enclosures a transmission line, being roughly akin although it will eventually unload at 24dB/octave like any vented box variation. Since the Alpair 7 has an inherent Qt of 0.54 that defines the lowest system Q for sealed box loading, making the TL potentially a better option is terms of lower bass with decent transient response, obviously at the expense of cabinet size though. An open-back box will lurk in a similar vicinity assuming it doesn't become too deep, as would a straightforward OB, although in both cases there's the reflection of the back-wave to contend with. Scott suspects you'd like the Pensil 7 or similar since it has some of these traits, the other option being a folded TL intended as you have designed above, to suck the back-wave away, with some additional pressure-bleeds elsewhere. I failed to be able to model what you have done with the carpet, Scott couldn't either, if he can't then nobody can but this is what he had to say. 'I don't think it could be accurately modelled to be honest, since the behaviour is going to be at best random depending on the specifics of the damping, how carefully positioned it is, how much of a gap there is & whether the rear panel dangling in the breeze is going to be producing any vibration effects. YMMV on that one. About the closest thing to it that I can think of off-hand is an open-back box with variable damping, but given the number of variables at work in this instance, I don't see any way to accurately model the behaviour. It's possible that that rolled up carpet is causing some [air] mass-loading to the suspension / diaphragm, which will affect midband behaviour. I would guess something akin could be approximated by making a partially open-backed box with a heavily damped tube (open both ends) positioned directly behind the driver. Edited by KJFAudio - 30 Dec 2016 at 9:07am |
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UK/EU dealer for Mark Audio Drivers and Manufacturer of speaker kits
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KJFAudio
Senior Member Joined: 17 Nov 2016 Location: Warwickshire UK Status: Offline Points: 119 |
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I hope my answer further up helped with the treble question? I also posted a few pages ago about dynamics and how a smaller driver is actually better with a few caveats, the biggest being lower bass which you are taking care of elsewhere so no worries there. I've not seen Steve's new speakers so am not sure on how he's got those two drivers working together, be interesting to see though. I think you really should come and borrow my FHXL prototypes and have a listen at home with music and movies, give them some welly and see what you think. Stefan |
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UK/EU dealer for Mark Audio Drivers and Manufacturer of speaker kits
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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Hi Stefan, do you mean the Hurricane? I read the review at HiFi Pig but I'm a bit worried about the comment regarding rock music. When designing I am often in melody mode but with many rock music customers I need to test with this genre, and I also have a Porcupine Tree album... Wink
I can see the Pensil 7 has some similarities to a transmission line, albeit a straight one, and by my novice TL reasoning, the tuned frequency will be around 110 Hz, but by now I know there's a little more to it than meets the eye. As I may have mentioned previously, I have always found deep speakers don't image in the way I expect. Although you've said that isn't always the case, it makes me wary. The Heath Robinson experiment with the offcuts of carpet rolled up gives a pipe length of 20" which approximates a 160Hz "tuned" transmission line. This removed something which I found very objectionable, and that something is often hard to grasp by most people, but I will try to explain... I get a feeling of tenseness above each shoulder blade when something in the sound isn't quite right. I first found this with CD many years ago, and so I put it down to phase displacement between mid frequencies (in-phase) and the result of "brick wall" filters which put the highs 90 degrees out of phase. Also the pass band ripple which is quite high with such filters. This not being natural is considerably annoying. In the sealed enclosures (which might not be optimum for the Alpair 7) this is exactly what I was getting, and also some lower mid "suck out". Another thing I did was to stick felt around the driver perimeters similar to the LS35A tweeter treatment. The carpet tubes improved the lower mids and the felt took away the piercing highs IMO. I have yet to listen to the FH3's which should arrive with Chris in the next hour. |
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Dave Friday
Senior Member Joined: 07 Apr 2011 Location: Spain Status: Offline Points: 173 |
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Graham have you thought about fixing the speakers to the ceiling ( with speaker stands?)
Or upside down floor standing cabinets? |
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lp12,oc9mk3,ca610p,krimson40watt pa,kef105.4
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Graham Slee
Admin Group Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16298 |
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I haven't because knowing how ceilings are constructed, and methods changed some 30 years ago where 4x1 boards are criss-crossed under rafters, they will be highly resonant - worse than the plaster-board "tents" we get because of dot and dab walls. Some floors can be almost as bad - 18mm particle floor board on today's narrow joists on 450mm centres should do upper bass some harm (plenty of boom). One can add mass by using heavy carpet with heavy underlay, or lead-weight rubber sheeting plus heavy soundproofing underlayment under thick laminate flooring or engineered wood. Ceilings would not take that additional load, and rockwool only insulates sound passing inside the void. |
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That none should be able to buy or sell without a smartphone and the knowledge in how to use apps
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Ash
Senior Member Joined: 18 Mar 2013 Location: Dorset Status: Offline Points: 4334 |
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I prefer listening to speakers now. Sold my spare K1000 to fund a second Proprius pair for side-by-side speaker comparisons. I will sell my last K1000 soon to generate additional funds for speaker drivers. I don't need any headphones anymore as I should be able to judge speaker performance well enough without them. |
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We do not see things as they are. We see things as we are.
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