View Full Version : Speaker Box Suggestions Request
Hi Clever People,
I have just come across 2 pairs of Infinity 655i Co-Axial car speakers in my loft - I had forgotten that they were up there (since 1998!!!), and I was wondering if some kind soul might suggest a suitable box dimension for them. I reckon they'd sound fairly good (if memory serves me well, which is most definitely NOT to be assumed!!!).
Thanks in hopeful anticipation!!!https://uploads.tapatalk-cdn.com/20180130/59400b8fbc4912d9f9bf62c07c4b448c.jpghttps://uploads.tapatalk-cdn.com/20180130/8a9897cb2871ae957dd1307804141eda.jpg
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How about these for a cheap project http://www.ebay.co.uk/itm/SLIM-PAIR-of-5-BOX-ENCLOSURES-FOR-5-CAR-AUDIO-SPEAKERS-x2-BOXES/162495955581?hash=item25d583827d:g:vuIAAMXQYwFRhmY ~ :) Probably a tad small for home use but it will give you a taster.
Tried the Infinity Kappas 6x9 in the oval alternatives to these boxes on a big class A ss amp in the front room,:eek: be fun, with a woofer, in an open baffle.
RothwellAudio
31-01-2018, 09:31
Some drive units are best suited to ported enclosures and others are best suited to sealed boxes. Some will be ok in either. Lets assume yours will be ok for either. A sealed box is simpler and a lot less likely to go horribly wrong because there's only one parameter to worry about - box size. Ported enclosures are a lot more complicated because you have the box size to get right and the port size to get right, and if you get them wrong you can end up with a horrible bass boom. For that reason I'd be tempted to go for a sealed box. If the box is too small you'll get a bass hump and if the box is too large you'll get clean but possibly weak bass. Fortunately, there's some latitude so there's a good chance the performance won't be too far off.
Personally, I'd guess at a box size that looks a bit on the large side for the drivers and hope for the best. Of course, if you can find the driver parameters online somewhere you can eliminate a lot of guesswork.
No way to calculate the box sixe without the driver parameters.
You could try fitting them into the end of a very long length of plastic drainpipe and try to make a 'true' transmission line. In theory it should work and a lot less hassle than knocking up cabinets.
RothwellAudio
31-01-2018, 13:20
I looked up those speakers and found this spec sheet:
https://www.infinityspeakers.com/on/demandware.static/-/Sites-masterCatalog_Harman/default/dw2d24500f/pdfs/Infinity-Primus-OM.PDF
Your particular model isn't on the list but I'd take a guess that other speakers from the same manufacturer have similar specs - after all, they're all intended for use in a car so there's no room for enormous cabinets and I doubt the different models would be wildly different.
You could use those specs and a simple piece of software such as this...
http://www.mh-audio.nl/CBC.asp
... to calculate the box size.
Using the specs for the Infinity PR6512is and a ten litre box the software predicts a 4dB bass hump at 100Hz. A twenty litre box gives a 3dB hump at about 95Hz. The software predicts that the box has to be enormous to eliminate the hump completely. 200L gives a hump about 1.7dB.
That's all for a sealed box btw.
I would just make a box about as big as you think practical for the space you have - and hope for the best :)
BTW, all the above is based on what I would with a pair of old speakers which I'd found in the loft. Bear in mind I don't claim to be a loudspeaker expert and I'm sure there are plenty of forum members with more knowledge and experience in speaker design/building than me.
200 litres! That sounds about right for a decent speaker.
walpurgis
31-01-2018, 13:49
200 litres! That sounds about right for a decent speaker.
Or coal bunker.
You want to keep a bit of a bass hump around 100hz anyway. Otherwise will sound a bit light in the bass.
RothwellAudio
31-01-2018, 14:18
You want to keep a bit of a bass hump around 100hz anyway. Otherwise will sound a bit light in the bass.
Yes, I agree. No point in aiming for a ruler-flat bass response and building enormous cabs when in fact a slight bass hump is beneficial.
BTW, those calculations are worth double checking. I bunged the figures into the software pretty quickly and might have made a mistake.
Infinitely Baffled
31-01-2018, 20:34
I have got a pair of recently vacated sealed-box speaker enclosures you are welcome to have for the purposes of experimentation if you want. They are ex-KEF Celestes, so about 1965, built like a brick what-not and about 14 litres in capacity. They are not in bad nick either. Yours for the price of getting them to you (or you are welcome to collect if you would prefer). PM me if interested.
IB
Thanks all for the comments!
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fatmarley
01-02-2018, 07:54
Because they are designed for car use, there will be no baffle step compensation. They would sound best fitted flush to a wall or you could build a very slim box and put that tight against a wall.
If you're ever near Cheltenham I could measure the t/s parameters In seconds (well, minutes actually because I like to warm the driver up for a few mins first).
Finally found some time to mount these up in the boxes very kindly donated by Infinitely Baffled - on a piece of 19mm plywood.
Just need to wire them up and give them a try now!!!https://uploads.tapatalk-cdn.com/20180428/2c8fede8d5cd37220c5a1ec5b7a88a6f.jpghttps://uploads.tapatalk-cdn.com/20180428/a7d2c3c71c634f6ccad9672102f9b9cc.jpg
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BTW, having plenty of stuffing or BAF wadding or Rockwool inside the cabinets can make them behave as if the cabinets were bigger than they actually are. I've just looked at the specs for those drivers again and I'd say the cabinet needs to be as big as possible, or appear to the drivers as big as possible, so wadding might be worth trying if you find the speakers sound a bit boomy.
My guess is the drivers were intended to be used fitted to a parcel shelf (hence the tilted tweeters) and the boot of the car would become a very large enclosure for them.Thank you. They were door speakers - originally I had them in my Nissan 200SX Turbo (which I wrote off 4 weeks after I bought it - too fast for me!).
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I'm enjoying this!https://uploads.tapatalk-cdn.com/20180428/9fde8910aa25e17c6621c07ceb2ff1e7.jpghttps://uploads.tapatalk-cdn.com/20180428/2cb8ee5adb4641642485d02edc5727e3.jpghttps://uploads.tapatalk-cdn.com/20180428/d2ca57cca4d1fc497896e301f8565ab3.jpg
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walpurgis
28-04-2018, 12:53
You need more screws through that baffle or it'll buzz and rattle.. You could experiment with a diffuser/reflector on the tweeters to redirect the output.
You need more screws through that baffle or it'll buzz and rattle.. You could experiment with a diffuser/reflector on the tweeters to redirect the output.The baffle is firmly glued in with silicone, and screwed for good measure.
The tweeters turn through almost (not quite) 360 degrees to point the way that sounds best...
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walpurgis
28-04-2018, 13:18
Actually, those drive units are almost asking for a Sonab style semi-omnidirectional cabinet.
http://i67.tinypic.com/11bkhp2.jpg
I think there's usually a pedal on the floor of those vehicles which the driver can use to control the speed. Don't press it down too far and it won't go too fast. [emoji38]I learned that - a little late!!!
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Actually, those drive units are almost asking for a Sonab style semi-omnidirectional cabinet.
http://i67.tinypic.com/11bkhp2.jpgInteresting!
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They don't sound too shoddy actually - a little strong in the midrange.
I'll hook them up to my Quad 306 next week...https://uploads.tapatalk-cdn.com/20180428/b2c354a78ab6b5addd7e704513c3be0c.jpg
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walpurgis
28-04-2018, 13:37
A forward mid makes them even better candidates for an omni type application. It may sound daft, but as an experiment, lay them on their backs with the tweeter angled so they aim towards the real wall and have a listen.
A forward mid makes them even better candidates for an omni type application. It may sound daft, but as an experiment, lay them on their backs with the tweeter angled so they aim towards the real wall and have a listen.Wow! Yes - much better!
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walpurgis
28-04-2018, 13:46
Thought the results might be interesting. The imaging will be diffuse, but that can be pleasant. You will still get a stereo image though, but a large one.
walpurgis
28-04-2018, 13:51
Another thought. Car speakers are usually well magnetically damped, enabling them to be used in all sorts of 'ill terminated' mounting positions. This means that they should respond well to reflex loading. In other words, a well chosen bass port should beef up the bass nicely.
Another thought. Car speakers are usually well magnetically damped, enabling them to be used in all sorts of 'ill terminated' mounting positions. This means that they should respond well to reflex loading. In other words, a well chosen bass port should beef up the bass nicely.This is fun!
I might hole saw a port - the 'well chosen' is the toughie though!!!
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length of port may be more important than size of hole. you can buy variable tubes that you can play around with
walpurgis
28-04-2018, 14:02
the 'well chosen' is the toughie though
You need to know the fundamental resonance of the driver and the cabinet volume.
I doubt you'll find info on the driver, but you might, T/S parameters would be handy. I can have a stab at a guesstimate if you like. What's the outside diameter of the driver? There'll be a port calculator somewhere. I have a set of ancient but very appropriate G A Briggs tables knocking about.
It's 140mm.https://uploads.tapatalk-cdn.com/20180428/06814f88b1155e290b7e9e57b4ab9d82.jpg
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I have to say, Alison Krauss and Union Station are sounding pretty damn good on them!
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walpurgis
28-04-2018, 14:32
Well it's a nominal 6.5 inch unit then. A Hi-Fi one would likely have a resonance of say 50Hz, but car speakers usually have slightly stiffer suspension to avoid cone sag when mounted vertically and to avoid damage from bumps and vibration, so add maybe another 10Hz, so call it 60 Hz.
What are the cabinet dimensions and how thick are the walls?
Well it's a nominal 6.5 inch unit then. A Hi-Fi one would likely have a resonance of say 50Hz, but car speakers usually have slightly stiffer suspension to avoid cone sag when mounted vertically and to avoid damage from bumps and vibration, so add maybe another 10Hz, so call it 60 Hz.
What are the cabinet dimensions and how thick are the walls?Inches, or millimeters?
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walpurgis
28-04-2018, 14:35
Doesn't matter.
Doesn't matter.Inches then - being British from the '60s, seems appropriate!
18" × 10 3/4" x 7 ". Wall thickness 3/4" plywood.
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The original Kef label showed the LF resonance as 29 Hz - it was a big oval driver!
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https://uploads.tapatalk-cdn.com/20180428/752dca5960db391d3d172bdc8612bd2c.jpg
walpurgis
28-04-2018, 19:39
The original Kef label showed the LF resonance as 29 Hz - it was a big oval driver
That was an early B139 bass driver. The 29Hz relates to its free air resonance and has no bearing on the volume of these cabinets.
That was an early B139 bass driver. The 29Hz relates to its free air resonance and has no bearing on the volume of these cabinets.Ah, right!
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walpurgis
28-04-2018, 19:47
Inches then - being British from the '60s, seems appropriate!
18" × 10 3/4" x 7 ". Wall thickness 3/4" plywood
Right.
Done a bit of research and working out. The cabinet volume is just under 18 litre. Taking the bass driver resonance as 60 Hz, it may be wise to tune the port slightly below that to avoid the box resonance overlapping that too much and creating larger than desirable 'hump' (there wiil be a slight one), so I'd aim for 50Hz, that will also allow the bass to extend down a bit further, there will certainly be sufficient output from the driver at that frequency to excite the reflex action. This will require a tubular bass port of 6 inches length and 2 inches inside diameter. There will be roll off below 50 Hz, but you should still get some output at 40Hz, maybe even lower if you're lucky.
I use usually use cheap plastic waste piping from places like B&Q for ports, but as Grant says, there are custom ports available that can be adjusted for length, allowing cabinet tuning to be played with.
Right.
Done a bit of research and working out. The cabinet volume is just under 18 litre. Taking the bass driver resonance as 60 Hz, it may be wise to tune the port slightly below that to avoid the box resonance overlapping that too much and creating larger than desirable 'hump' (there wiil be a slight one), so I'd aim for 50Hz, that will also allow the bass to extend down a bit further, there will certainly be sufficient output from the driver at that frequency to excite the reflex action. This will require a tubular bass port of 6 inches length and 2 inches inside diameter. There will be roll off below 50 Hz, but you should still get some output at 40Hz, maybe even lower if you're lucky.
I use usually use cheap plastic waste piping from places like B&Q for ports, but as Grant says, there are custom ports available that can be adjusted for length, allowing cabinet tuning to be played with.Thank you for the effort!
I won't have 6" front to back - the box is 7" deep outside, minus 2 × 3/4" only leaves 5 1/2" inside. How much gap to the inside of the back is required?
Could I run the pipe in at an angle?
Should I still use wadding?
Thanks for your knowledge!
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walpurgis
28-04-2018, 20:44
The port can go anywhere, as long as the internal end is not right by the back of the driver. It does not need to be at the front, you can bung it in the side if that suits.
Yes, you still use wadding, but probably less and around the walls of the cabinet leaving space in the middle. You can experiment with quantity.
walpurgis
28-04-2018, 20:54
You can if need be try a slightly shorter port and part plug it with rolled resistive open cell foam. This effectively makes the port narrower, but retains the bass tuning.
This kind of stuff: https://www.ebay.co.uk/itm/ACTIVATED-CARBON-FOAM-FILTER-SHEET-Various-Sizes-and-Apps-filter-foam-Foam-UK/131848661543?hash=item1eb2caea27:m:mYsDn0I4e1GSjec LSvo5V3Q You may find it cheaper elsewhere.
It would be trial and error though. i.e., how much to shorten the port and how tight to pack the foam. Obviously not so tight as to stop air movement.
Hope your ears are good enough to judge what goes on! :)
You can if need be try a slightly shorter port and part plug it with rolled resistive open cell foam. This effectively makes the port narrower, but retains the bass tuning.
This kind of stuff: https://www.ebay.co.uk/itm/ACTIVATED-CARBON-FOAM-FILTER-SHEET-Various-Sizes-and-Apps-filter-foam-Foam-UK/131848661543?hash=item1eb2caea27:m:mYsDn0I4e1GSjec LSvo5V3Q You may find it cheaper elsewhere.
It would be trial and error though. i.e., how much to shorten the port and how tight to pack the foam. Obviously not so tight as to stop air movement.
Hope your ears are good enough to judge what goes on! :)Ha!
My ears aren't what they once were!
Thanks for all the great advice!
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