Aaron,
The short answer: No.
The pulse is going to split down the two paths according to their relative cross-sectional areas. Even if you remove the bass drivers and mount fans in the openings so there is a continuous flow down the mouth pipe, there will be pressure on the back of the mid driver trying to push it out.
I think Troels may have been thinking of "venturi effect", where air blowing over the end of a pipe can "suck" air out of the pipe. This definitely does not apply in this case. For this scenario, where the bass cones move inwards, or when they are replaced by fans, the air pressure everywhere in the box will be greater than the air pressure outside, and the mid cone will move out.
I often find it helpful to visualise these scenarios as if they were waves in a tank of water. In fact, you can set the enclosure design up in a ripple tank simulator and see for yourself.
Look here:
http://www.falstad.com/ripple/
I find it a very useful tool for demonstrating all sorts of acoustic scenarios.
The short answer: No.
The pulse is going to split down the two paths according to their relative cross-sectional areas. Even if you remove the bass drivers and mount fans in the openings so there is a continuous flow down the mouth pipe, there will be pressure on the back of the mid driver trying to push it out.
I think Troels may have been thinking of "venturi effect", where air blowing over the end of a pipe can "suck" air out of the pipe. This definitely does not apply in this case. For this scenario, where the bass cones move inwards, or when they are replaced by fans, the air pressure everywhere in the box will be greater than the air pressure outside, and the mid cone will move out.
I often find it helpful to visualise these scenarios as if they were waves in a tank of water. In fact, you can set the enclosure design up in a ripple tank simulator and see for yourself.
Look here:
http://www.falstad.com/ripple/
I find it a very useful tool for demonstrating all sorts of acoustic scenarios.
Your explanation is appreciated, Don. So, under the conditions you described, would not the rear woofers movement cause some sort of distortion to be created by the front midwoofer, more so than what would be caused by that midwoofer trying to reproduce both bass and midrange frequencies on its own?. If so, the big question is would that distortion be audible?
Don Hills said:
QW
Don...
your post is not entirely true...
I.e... make a big taper of wallpaper or anything (similar to the taper in the DTQWT speaker) and then you punch a small hole somewhere on the outside of it... That small hole representing the "gap" to the midrange and tweetet from the taper in the speaker... So now you should have 3 holes... 1 big "exit" at the bottom of the taper, 1 small "entry" at the top of the taper and one small hole in the side of the taper...
Now take a cigarett or anything that produces smoke and blow in the entry of the taper and hold the cigarett outside the small hole... As you can see the smoke sucks into the taper from the small hole and comes out the exit of the taper... voilá, negative air-pressure... Now this will only occur when the velocity and pressure of the air inside the taper is below a surtent point... Ofcourse everything depends on the size of the taper and the holes, but still it proves the theory...
Now I dont have the maths for any of this and Im no expert at this subject... but just to prove Troels point this experiment is perfect...
Same thing will occur in a house when you open 3 doors somewhere in the house... eventually one of them is going to slam shut due to negative air-pressure...
Atleast thats my theory... I could be as wrong as anyone else on this subject...
Don...
your post is not entirely true...
I.e... make a big taper of wallpaper or anything (similar to the taper in the DTQWT speaker) and then you punch a small hole somewhere on the outside of it... That small hole representing the "gap" to the midrange and tweetet from the taper in the speaker... So now you should have 3 holes... 1 big "exit" at the bottom of the taper, 1 small "entry" at the top of the taper and one small hole in the side of the taper...
Now take a cigarett or anything that produces smoke and blow in the entry of the taper and hold the cigarett outside the small hole... As you can see the smoke sucks into the taper from the small hole and comes out the exit of the taper... voilá, negative air-pressure... Now this will only occur when the velocity and pressure of the air inside the taper is below a surtent point... Ofcourse everything depends on the size of the taper and the holes, but still it proves the theory...
Now I dont have the maths for any of this and Im no expert at this subject... but just to prove Troels point this experiment is perfect...
Same thing will occur in a house when you open 3 doors somewhere in the house... eventually one of them is going to slam shut due to negative air-pressure...
Atleast thats my theory... I could be as wrong as anyone else on this subject...
Re: QW
The rear woofers will have little effect on the front midwoofer. The front midwoofer will move according to its voice coil force and be little affected by the pressure from the rear woofers. It would be affected more if the enclosure were sealed, which is why you will see sealed chambers on midrange drivers to block the pressure from the bass drivers in such enclosures. But in the DTQWT case, there is little internal pressure due to the large exit vent.
So in summary, in the DTQWT, any distortion from the bass/midrange driver will be almost entirely produced by its own efforts, not by being influenced by the bass drivers.
Ipppe,
As I said in my earlier post, venturi effect does not apply here.
Imagine taking the DTQWT enclosure and removing all the drivers. Now mount fans in the bass driver holes to blow air through the speaker. I will bet you will see smoke coming out of the bass/ midrange hole, not going in. This is because of the geometry of the design.
If the bass/mid horn were to join to the main pipe through a hole in the wall part way down, then you might get venturi effect. Venturi effect requires the "side" opening to be flush with the wall. But in the DTQWT design, air flowing up from the bass horn will want to flow across into the mid horn due to momentum, rather than turn at right angles and flow down the main horn. Pressure waves are more democratic, they will tend to split between the two horns accoring to the relative areas.
Actually, even if you do set up a cone with a hole in it as you described, you may still see air flowing out rather than in. The reason is that when air flows through a tube where the diameter is increasing, its pressure increases rather than decreases. The textbook example of a venturi effect is where a tube has a narrow section in the middle, and pressure gauges attached to the wide and narrow sections. The pressure is high in the wide sections of the tube where the air is moving slowly, and the pressure is low in the narrow part of the tube where the air is moving fast.
For more, try Google search for "venturi effect".
You could start with this result:
http://en.wikipedia.org/wiki/Venturi_effect
pkitt said:
The rear woofers will have little effect on the front midwoofer. The front midwoofer will move according to its voice coil force and be little affected by the pressure from the rear woofers. It would be affected more if the enclosure were sealed, which is why you will see sealed chambers on midrange drivers to block the pressure from the bass drivers in such enclosures. But in the DTQWT case, there is little internal pressure due to the large exit vent.
So in summary, in the DTQWT, any distortion from the bass/midrange driver will be almost entirely produced by its own efforts, not by being influenced by the bass drivers.
Ipppe,
As I said in my earlier post, venturi effect does not apply here.
Imagine taking the DTQWT enclosure and removing all the drivers. Now mount fans in the bass driver holes to blow air through the speaker. I will bet you will see smoke coming out of the bass/ midrange hole, not going in. This is because of the geometry of the design.
If the bass/mid horn were to join to the main pipe through a hole in the wall part way down, then you might get venturi effect. Venturi effect requires the "side" opening to be flush with the wall. But in the DTQWT design, air flowing up from the bass horn will want to flow across into the mid horn due to momentum, rather than turn at right angles and flow down the main horn. Pressure waves are more democratic, they will tend to split between the two horns accoring to the relative areas.
Actually, even if you do set up a cone with a hole in it as you described, you may still see air flowing out rather than in. The reason is that when air flows through a tube where the diameter is increasing, its pressure increases rather than decreases. The textbook example of a venturi effect is where a tube has a narrow section in the middle, and pressure gauges attached to the wide and narrow sections. The pressure is high in the wide sections of the tube where the air is moving slowly, and the pressure is low in the narrow part of the tube where the air is moving fast.
For more, try Google search for "venturi effect".
You could start with this result:
http://en.wikipedia.org/wiki/Venturi_effect
Re: Re: QW
just for the record... I did the experiment with the "cone" as I described, and it actually sucked in the smoke... But you may be right about the geometry of the speaker, it may not do the same thing... But until anyone makes a good scale model I guess its hard to prove what actually happens with airflow...
Don Hills said:
just for the record... I did the experiment with the "cone" as I described, and it actually sucked in the smoke... But you may be right about the geometry of the speaker, it may not do the same thing... But until anyone makes a good scale model I guess its hard to prove what actually happens with airflow...
gainphile said:Hi Ipppe,
Could you please elaborate more how you do the pine wood finishing? they are very beautiful!
What are the metal wire brush for?
More pics ?
Hi...
The metal brushes are used to "brush" the surface of the pine to get the "old" effect... When you brush hard against the surface the naturally softer parts will get deep and the hard parts like the twigs and such will not get deeper... so the result looks like its been worn over a long time... and when you use the wax as I described the wax will "stick" to the deeper parts of the wood automatically and those parts will look darker, and the hard parts of the wood will look lighter... very easy and you dont have to be so careful... just go crazy and it will turn out perfect
I suppose I keep visualizing Venturi effect. Because the mid is so close to the split, I can see how it might not be the overriding physical event. But, like Ippe: seing is believing in any case.
For finishing like Ippe's another nice effect I just did on a jewelry box for my wife is to ceruse the surface. Oak is nice when done this way. You brush out the softer grain with a stiff brass brush, then back fill with wood filler/glaze/paste wax, lightly sand, and finish...
http://www.wooddigest.com/print/Finishing-Magazine/Step-By-Step--Weathered-Ceruse/1$1262
Ebonizing the oak or using a blackening stain (Ebony or ink) is a very nice effect.
For finishing like Ippe's another nice effect I just did on a jewelry box for my wife is to ceruse the surface. Oak is nice when done this way. You brush out the softer grain with a stiff brass brush, then back fill with wood filler/glaze/paste wax, lightly sand, and finish...
http://www.wooddigest.com/print/Finishing-Magazine/Step-By-Step--Weathered-Ceruse/1$1262
Ebonizing the oak or using a blackening stain (Ebony or ink) is a very nice effect.
gainphile said:
Do you cover it with veneer afterwards?
No veneer used...
All you have to do is wipe off the abundance of wax with some rag after 10 minutes then after a couple hours you can polish it slightly with a rag to get it more shiny... the result is really cool and very easy to achieve... and you can improve the surface anytime you want using the same method...
Ipppe,
Back in the 1970s, I think it was about then, I have trouble remembering those days , a similar finish was popular for a while. You ran a blowtorch over the wood surface to char it. Then you wire brushed away the charred parts. The soft parts of the grain charred deeper, causing the same profile as on your speaker baffle. It was usually done to soft woods with coarse grain such as pine, and often repeated to make the grooves 1/4" deep or more.
The effect looks much more subtle and elegant on your baffles. You can't beat the spousal acceptance factor of cabinets that look like fine pieces of furniture. The name plates are a very nice finishing touch.
Back in the 1970s, I think it was about then, I have trouble remembering those days
, a similar finish was popular for a while. You ran a blowtorch over the wood surface to char it. Then you wire brushed away the charred parts. The soft parts of the grain charred deeper, causing the same profile as on your speaker baffle. It was usually done to soft woods with coarse grain such as pine, and often repeated to make the grooves 1/4" deep or more. The effect looks much more subtle and elegant on your baffles. You can't beat the spousal acceptance factor of cabinets that look like fine pieces of furniture. The name plates are a very nice finishing touch.
Beautiful work Ippe!
Could you please comment on room placement experience with the speakers, especially on the bass response?
I havent tried so many placements exept the distance to rear wall with my current position, my furniture and my room prevents me from placing the speakers any differently than they are placed now... But I can tell you that Troels is right when he recommends to use a minimum 20-25cm distance to rear wall, any closer than that and the bass gets extremely "boomy", dont know why, im no expert in acustics... But I did compare between placing them 20cm from the rear wall and 50-60cm from the rear wall, and to my ears there is no difference in sound... Perhaps an expert would tell the difference but I couldnt so im currently keeping them 20cm from the rear wall to save space... My room is probably no way near perfect for these speakers but as long im satisfied with the sound I wont make any big changes...
I also can tell you that now when ive played them for a few hours every day the past month the midrange and bass have really improved from my first setup (break-in i guess)... The midrange has really "opened" and the bass is deeper and stronger... In the beginning I had to turn the bass up a bit on my amplifier to get the sound which I preffered but now i keep my amplifier at neutral and the bass is really nice...
Thanks, Ipppe
I'm really getting wormed up to make those speakers, and since I'm a professional doublebass player I'm really interested in good natural deep bass. I was a bit disappointed to read PK comment in another thread http://www.diyaudio.com/forums/showpost.php?p=1798299&postcount=13 that bass doesn't go super low. Yet on Troel's site there are some in room measurements that show bass all the way to 20HZ...
Thanks, Ipppe
I'm really getting wormed up to make those speakers, and since I'm a professional doublebass player I'm really interested in good natural deep bass. I was a bit disappointed to read PK comment in another thread http://www.diyaudio.com/forums/showpost.php?p=1798299&postcount=13 that bass doesn't go super low. Yet on Troel's site there are some in room measurements th
at show bass all the way to 20HZ...
I have no fancy measuring equipment but when I use TrueRTA to generate frequencies I can hear all the way down to 24hz, anything below that is just silent but the drivers are "moving"... I dont know if thats means the drivers go down to 24hz or not but that proves 24hz frequencies are atleast detectable with my ears
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