So here's the problem. I spend perhaps 12 nights a month away from home in camp accommodation for work. It's an itty-bitty 2m x 3m room with a king-single bed, cupboard, telly and attached ensuite. Very small. Alas it's in a block of four other similar rooms, and they're not well acoustically separated.
Over the years that I've been there, I've customised my room somewhat. One of the customisations was to put up some sound absorbing sheet, covered with a layer of gyprock, between my bed and my immediate neighbour on the other side of the wall. That reduced the sound quite well, both ensuring I don't annoy him when listening to music or movies, and also so I didn't hear him as much. Carpet also helped.
I mounted some little Cambridge Audio Lynx speakers to a plank behind my head to allow me to listen to music at very low level late at night - they're glorified headphones - when watching telly or reading etc they're about 50cm from my ears. They're okay, but they've got absolutely no bass. They fall in a very big heap at 120Hz. I tried some equalisation to push them down further, but they just rattle.
Time for new speakers.
I want something to provide very good reproduction, with good bass, down a fair way further than the Cambridge Audio speakers, but all at quite low level. The room isn't big, I don't need 100dB SPL, and indeed would get in a lot of trouble if I did wind the wick up. 70 or 75 is oodles as my head is generally right next to the drivers.
I reckon this is the job for a full-range TL speaker. I found some nice full-range drivers on-line, the TG9FD10-04, which are 3.5" round, offer a reasonably flat response out to ~12-13KHz, and Fs at 115Hz.
Sticking with the bedhead idea (makes room renovations straightforward) a plank 113cm x 16cm x 6cm is doable - the noisePlank. Doing a single fold gives me a tapering line 1m long from about 45cm^2 at the driver end to 9cm^2 at the open end.
I prototyped in 9mm MDF, and it sounded pretty good. I was able to get bass down to 45Hz with 12dB of equalisation using a miniDSP, without the distortion products blowing everything away.
The final speaker is shown. Inside dividers and rear in 9mm MDF, outside in Tassie Oak (random SE Aust Eucalypt). I planed the front down to about 12mm and mounted the drivers, and added a little 3/8" felt plus some stuffing for 2/3rds of the line.
Anyway the real thing sounds very nice - good transient response and heaps of bass for such a teensy driver. I've got a 100Hz low shelf with Q of 1 and 12dB gain, and that's it). It's a massive improvement over the little Cambridge Audio cubes, at any rate.
Over the years that I've been there, I've customised my room somewhat. One of the customisations was to put up some sound absorbing sheet, covered with a layer of gyprock, between my bed and my immediate neighbour on the other side of the wall. That reduced the sound quite well, both ensuring I don't annoy him when listening to music or movies, and also so I didn't hear him as much. Carpet also helped.
I mounted some little Cambridge Audio Lynx speakers to a plank behind my head to allow me to listen to music at very low level late at night - they're glorified headphones - when watching telly or reading etc they're about 50cm from my ears. They're okay, but they've got absolutely no bass. They fall in a very big heap at 120Hz. I tried some equalisation to push them down further, but they just rattle.
Time for new speakers.
I want something to provide very good reproduction, with good bass, down a fair way further than the Cambridge Audio speakers, but all at quite low level. The room isn't big, I don't need 100dB SPL, and indeed would get in a lot of trouble if I did wind the wick up. 70 or 75 is oodles as my head is generally right next to the drivers.
I reckon this is the job for a full-range TL speaker. I found some nice full-range drivers on-line, the TG9FD10-04, which are 3.5" round, offer a reasonably flat response out to ~12-13KHz, and Fs at 115Hz.
Sticking with the bedhead idea (makes room renovations straightforward) a plank 113cm x 16cm x 6cm is doable - the noisePlank. Doing a single fold gives me a tapering line 1m long from about 45cm^2 at the driver end to 9cm^2 at the open end.
I prototyped in 9mm MDF, and it sounded pretty good. I was able to get bass down to 45Hz with 12dB of equalisation using a miniDSP, without the distortion products blowing everything away.
The final speaker is shown. Inside dividers and rear in 9mm MDF, outside in Tassie Oak (random SE Aust Eucalypt). I planed the front down to about 12mm and mounted the drivers, and added a little 3/8" felt plus some stuffing for 2/3rds of the line.
Anyway the real thing sounds very nice - good transient response and heaps of bass for such a teensy driver. I've got a 100Hz low shelf with Q of 1 and 12dB gain, and that's it). It's a massive improvement over the little Cambridge Audio cubes, at any rate.
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Nice results.
Am curious about your 1/4 wave baffles setup.
I thought that one typically fitted the Driver at the other end the angles, rather than in the base ?
Am curious about your 1/4 wave baffles setup.
I thought that one typically fitted the Driver at the other end the angles, rather than in the base ?
You can taper the line either way, or not at all. Space constraints in this case pretty-much dictate tapering the line with the driver at the wide end.
Nice work! I have made many similar speakers with TG9FD and TC9FD. Great drivers.
Here is a flat wall mount MLTL:
http://www.diyaudio.com/forums/full-range/277894-flat-wall-mount-stereo-mltl-using-tc9fds-2-a.html
If you add a 1mH and 8R to 10R BSC, if will flatten that response nicely for balanced sound.
I have used aircore coils, but find cheap $0.50 ferrrite core inductors for PCBs perfectly acceptable.
Here is a flat wall mount MLTL:
http://www.diyaudio.com/forums/full-range/277894-flat-wall-mount-stereo-mltl-using-tc9fds-2-a.html
If you add a 1mH and 8R to 10R BSC, if will flatten that response nicely for balanced sound.
I have used aircore coils, but find cheap $0.50 ferrrite core inductors for PCBs perfectly acceptable.
Cool speaker xrk.
I see our un-equalised plots are remarkably similar (mine is attached) despite very different baffle dimensions.
At the moment I'm equalising with DSP rather than a passive circuit - there's not a lot of baffle step, due to the very asymmetrical baffle I think. Really all I need is a shelving filter to extend the driver response below 100 Hz.
The linkwitz transform (Active Filters) is probably what I'll go for without using DSP.
I see our un-equalised plots are remarkably similar (mine is attached) despite very different baffle dimensions.
At the moment I'm equalising with DSP rather than a passive circuit - there's not a lot of baffle step, due to the very asymmetrical baffle I think. Really all I need is a shelving filter to extend the driver response below 100 Hz.
The linkwitz transform (Active Filters) is probably what I'll go for without using DSP.
Attachments
So here's the completed speaker, finished in polyurethane.
I tried a Linkwitz transform but found the notch wasn't really helping, so went with a very straightforward second-order low shelf, which is really what the DSP was doing anyway.
The measured results are attached - low cutoff is something like 60Hz. Beyond 92dB at 50cm it goes to custard quite rapidly. You can hear the voicecoil hitting it's limits up to about 100Hz, after which it calms down. This is earsplittingly loud at the distance these speakers will be used.
I've included a quick schematic of the equaliser, thrown together with parts I had to hand, plus the amp I'm using to test.
I tried a Linkwitz transform but found the notch wasn't really helping, so went with a very straightforward second-order low shelf, which is really what the DSP was doing anyway.
The measured results are attached - low cutoff is something like 60Hz. Beyond 92dB at 50cm it goes to custard quite rapidly. You can hear the voicecoil hitting it's limits up to about 100Hz, after which it calms down. This is earsplittingly loud at the distance these speakers will be used.
I've included a quick schematic of the equaliser, thrown together with parts I had to hand, plus the amp I'm using to test.
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@ suzyj
Congrats on the whole design & build 🙂 It's good too see ladies interested in acoustics & electronics 😉
Congrats on the whole design & build 🙂 It's good too see ladies interested in acoustics & electronics 😉
Nice setup Suzyj - you have quite the outfitted lab gear. What kind of amp is that - low res pictures so can't quite tell if it's a Class D or one of your custom Class AB's.
I have found that a simple BSC using a 1mH and 5R to 8R in parallel can flatten the response nicely in a passive manner.
I have found that a simple BSC using a 1mH and 5R to 8R in parallel can flatten the response nicely in a passive manner.
Odd about the picture res. I didn't do anything different than I usually do to upload them. I shall try again.
The amps are mine - a class AB development of David Tilbrooks AEM6000. Doing distortion plots on speakers makes me question the effort I've put into pushing my amp distortion levels down. Speakers are dreadful.
I initially built the equaliser on single-sided vero board, but found it hummed rather a lot. Rebuilding on wire wrap board, with a ground plane on the top and point-to-point (not wirewrap) connections underneath sorted the hum.
The amps are mine - a class AB development of David Tilbrooks AEM6000. Doing distortion plots on speakers makes me question the effort I've put into pushing my amp distortion levels down. Speakers are dreadful.
I initially built the equaliser on single-sided vero board, but found it hummed rather a lot. Rebuilding on wire wrap board, with a ground plane on the top and point-to-point (not wirewrap) connections underneath sorted the hum.
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Haha.... I started off in speaker design and building and then moved to amps. So I have always wondered if one really needs amps with less than 0.05% HD as even the best drivers are only -55dB at best. But the profile and relative amounts of H2/H3/H4/etc is what is important besides a fairly low HD figure better than a speaker.
However, trying to push a 3.5in driver to generate any bass below 150Hz is going to get you into the 10% HD regime very fast if above say 80dB.
Yeah, if you can ever audition a SOTA 1948 Altec 323 mono integrated amp that inflation adjusted was $8456 I imagine you'll wonder even more with specs like this: 20-20 kHz +/- 1 dB, 15 W at max 8% intermodulation and 2% harmonic distortion.
GM
Hey Suzy, this is an excellent idea, and the end result looks great - finished to your usual standard!
I had a sort of similar situation to design for recently, I needed something to go under the TV, as unobtrusive as possible, and low SPL only, so I made up a dual transmission line speaker like yours, except flat and short, 2xTG9FD drivers and the small Dayton tweeters (which I never hooked up) pics below. It sounds very good, much better than the crap drivers in the TV. I haven't measured it yet.
I based the transmission line dimensions on the German wall mounted design that xrk971 referenced earlier. I'd made a pair of these earlier (pics below), and mounted hard against a wall they sounded good with no BSC needed. Under the TV the flat horizontal version, sticking some 24" out from the wall did need quite some BSC.
Why am I mentioning this? Because I found that the white pair, when mounted hard against a wall didn't need any BSC correction. I guess this is because they are always driving into half space with the wall right behind and they have a very slim enclosure. It looks to me like your placement above the bed head will be very similar. Do yours need any BSC when placed above the bed like that? I would think not.
Graham.
I had a sort of similar situation to design for recently, I needed something to go under the TV, as unobtrusive as possible, and low SPL only, so I made up a dual transmission line speaker like yours, except flat and short, 2xTG9FD drivers and the small Dayton tweeters (which I never hooked up) pics below. It sounds very good, much better than the crap drivers in the TV. I haven't measured it yet.
I based the transmission line dimensions on the German wall mounted design that xrk971 referenced earlier. I'd made a pair of these earlier (pics below), and mounted hard against a wall they sounded good with no BSC needed. Under the TV the flat horizontal version, sticking some 24" out from the wall did need quite some BSC.
Why am I mentioning this? Because I found that the white pair, when mounted hard against a wall didn't need any BSC correction. I guess this is because they are always driving into half space with the wall right behind and they have a very slim enclosure. It looks to me like your placement above the bed head will be very similar. Do yours need any BSC when placed above the bed like that? I would think not.
Graham.
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Good point Graham. I've only tested them perched on the edge of the desk. I'll drag my measurement mic out to work when I'm next there and test them in-situ when I install them. It's straightforward to change shelf frequency and gain to suit the install, or simply do without if that's better...
I like your tabletop speaker. That looks really cool. I imagine the crossover for your tweeters could be very simple, as you wouldn't need a fast rolloff on the TG9.
I like your tabletop speaker. That looks really cool. I imagine the crossover for your tweeters could be very simple, as you wouldn't need a fast rolloff on the TG9.
Oldvinylplayer:
Very beautiful finish work - how do you get that gloss piano look? It almost looks like you made these out of sheets celluloid (billiard balls and piano keys). The German TL design is open ended so not technically a mass-loaded TL. That's why I added a small port constriction and drove the tuning down to 55Hz. I second your observation that when wall mounted needs no BSC.
Very beautiful finish work - how do you get that gloss piano look? It almost looks like you made these out of sheets celluloid (billiard balls and piano keys). The German TL design is open ended so not technically a mass-loaded TL. That's why I added a small port constriction and drove the tuning down to 55Hz. I second your observation that when wall mounted needs no BSC.
Thanks xrk,
I don't want to hijack Suzy's thread so I'll be brief. If anyone wants more detail on the finish I'll start another thread with some better photos.
But in summary:
Simple MDF joinery, no rabbets, no screws, glue joints trenched out with router, polyester filler in trenches, sanded flat, roundovers done with router, 2 coats of laminating epoxy to fill MDF end grain, 1 coat of laminating epoxy wiped on to fill the large faces, sanded, multiple coats of automotive spray putty then primer with sanding in between, 5 or 6 coats of gloss black automotive acrylic enamel with progressively finer sanding in between ending at 1200 grit, machine buffed with 3M marine buffing compound, polished with automotive wax polish. The end result is a deep black gloss, indistinguishable from my actual piano. I did it to match the Sony blueray player and the black on the TV. It did the trick.
Graham.
I don't want to hijack Suzy's thread so I'll be brief. If anyone wants more detail on the finish I'll start another thread with some better photos.
But in summary:
Simple MDF joinery, no rabbets, no screws, glue joints trenched out with router, polyester filler in trenches, sanded flat, roundovers done with router, 2 coats of laminating epoxy to fill MDF end grain, 1 coat of laminating epoxy wiped on to fill the large faces, sanded, multiple coats of automotive spray putty then primer with sanding in between, 5 or 6 coats of gloss black automotive acrylic enamel with progressively finer sanding in between ending at 1200 grit, machine buffed with 3M marine buffing compound, polished with automotive wax polish. The end result is a deep black gloss, indistinguishable from my actual piano. I did it to match the Sony blueray player and the black on the TV. It did the trick.
Graham.
I put those tweeters in there in case the off axis response lost too much at the top end. We also need to listen to these speakers when sitting off to one side at the dining table, the TV swivels but the speaker pair stays still. In practice, for the audio content that comes off the TV, the little TG9s didn't sound too bad off axis, so I never hooked up the tweeters. So I never had to design a suitable crossover🙂
One day I may fiddle around with two more amp channels for the tweeters and a miniDSP, but the tweeter's placement off horizontally from the main drivers will introduce it's own set of problems.
Graham.
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