TH or T-TQWP or ????

[revboden]

Hey josh,

The problems I ran into modeling this driver at full tilt was the compromise between vent length and airspeed. The size and tuning you suggest 320L/20hz with two 6" ports 29" long + flair would start to detune at 23m/s and at 32m/s the tuning would shift ~10Hz up (30hz tuning) which would send the cone into destruction mode. I did model a vent that would handle the airspeed and not detune but it would cost thousands to build and the vent would be 67" long (port and flairs) and would resemble a double tractrix horn as the opening would be 22" across at the mouth of the vent just to decelerate the air before it decoupled from the port.

That said, I was trying to model a BR that would compete with the T-TQWP from 13hz to 60hz. If I was only tuning to 20hz and 118db was the goal from 25Hz to 80Hz a BR would work just as well, possibly better.

I suspect one of the advantages of T-TQWP is ease of build and low cost.

 

[NWCgrad]

Hello Bjorno, or anyone else who wants to discuss.

I do not have hands on experience with one of these designs yet but they seem to be quite popular on this forum so I am interested in why. From looking at quite a few simulations I would list very limited bandwidth as issue #1. Also sensitivity seems to be lower than an equivalent sized TH. Response in the time domain appears to be much worse than a sealed or ported alignment same as with a TH or FLH. Ringing abounds anywhere other than over the almost 2 octave wide bandwidth where the alignment is most effective. In this case maybe 16-60Hz.

Since this seems to be essentially a reverse TH with many shared characteristics. I suspect that the distortion and compression might trend the same in general ways. That is to say that the distortion will be very low in some areas typically below the 5th harmonic of a TH it will be very low in THD which would mean the same for these and at the 5th and above THD is much higher and wildly varying with frequency and power above that point. Of course the TQWP is completely unuseable much above that point anyway, but a TH can potentially be beaten into submission with EQ, damping and perhaps internal pipe resonance cancellation (DTS-20) enough to work, ok. Potentially the THD might possibly be even lower for a TQWP over the useful bandwidth due to the cancellation effects of the enclosure on frequencies corresponding to the harmonics.

Are their any in depth investigative measurements of a TQWP that someone can point me to?

A basic 320L total volume, 20Hz tuned vented alignment utilizing a vent of 365cm (Equivalent to 2 6" flared ports) seems to have just as much sensitivity and maximum output as the TQWP presented here over it's useful bandwidth. In addition the vented alignment will have better response in the time domain and could potentially be used up till 150Hz or higher if needed.

The TQWP seems quite similar in operation to a 6th or even 4th order BP. What are it's advantages against them?

Josh, I modeled the 320 L vented alignment in WinISD (attached) and it looks pretty good. It is also quite a bit smaller, which may be of importance in many rooms. For my particular requirements I think the TQWP is better suited as its - 3 dB extension is around 13 Hz vice - 14 dB for the vented alignment at 13 Hz (- 22 dB w/ 15 Hz HPF, 4th order LR required to maximize SPL). To match my 4 sealed LAB-12 subs I need an output of 120 dB - not that I will ever play it that loud as I tend to listen to movies below THX reference level as I find THX level to loud (I must be getting old!)

The limited range is not important for my needs, but I can see where it could be a significant limitation for a person wanting to use a single sub. My days of single subs are long gone, having tried the flanking sub approach of Wayne Parham (similar to the multi-sub approach of Geddes, Toole etc.).

Hopefully your questions can be answered because I would also like to learn as much about this design as possible.

I suspect one of the advantages of T-TQWP is ease of build and low cost.

Rev, You nailed it for me. A TH build would take up less real estate, but would require considerably more woodworking skill. I can cut pretty accurately using my circular saw and a DIY saw guide (measure 6 times and cut once - yes I may be a bit obsessive about measuring, but I have made so many dumb measurment errors over the years I don't trust myself) so the TQWP build should go smooth.

I hope this thread continues to attract these great discussions!

 

[Josh Ricci]

Hey josh,

The problems I ran into modeling this driver at full tilt was the compromise between vent length and airspeed. The size and tuning you suggest 320L/20hz with two 6" ports 29" long + flair would start to detune at 23m/s and at 32m/s the tuning would shift ~10Hz up (30hz tuning) which would send the cone into destruction mode. I did model a vent that would handle the airspeed and not detune but it would cost thousands to build and the vent would be 67" long (port and flairs) and would resemble a double tractrix horn as the opening would be 22" across at the mouth of the vent just to decelerate the air before it decoupled from the port. .

Actually I mispoke. What I was looking at in comparison was a 290L system with 30L of port, or a 320L total system not 320L plus port. Not that it changes much. Apparently I wasn't comparing to the current TQWP proposed either!

I don't want to get too far into a discussion of port performance but I have never seen any system detune a half an octave! And I have went through a bunch of vented systems including small 3" ports on up through 10" flared ports attached to systems more powerful than this proposed one and tunings between 11 and 40Hz. At most I've seen maybe 2-3Hz of shifting in the tuning at maximum power levels for any vented system so far. Also the tuning shifts downward at high power not up. I have yet to one shift upwards that I can remember. Also the larger the port area the higher the airspeed that can be supported before compression, noise and overload. See Collo's port tests for evidence of that. He stopped at 6" but everything I have tested has followed this trend as well. A 4" does not support 20m/s the same way that an 8.5" port does.

I suspect one of the advantages of T-TQWP is ease of build and low cost.

I don't see where this comes from honestly. If a TQWP is a reverse TH why would it be simpler or cheaper? You could make a TH with the same size/materials and construction costs right? Cheaper and simpler than a regular old vented build?

 

[Josh Ricci]

I hope this thread continues to attract these great discussions!

Hey sorry about the off topic stuff. I'm not trying to derail your thread or talk you out of the TQWP either for that matter. I'm more interested in the alignment itself than your particular app...No offense. Yours just happens to be a handy scenario.

Here is a vented system to compare to the proposed TQWP. Sensitivity and output headroom seem to be virtually the same as does driver excursion at the same input voltage. The vented system could be used up to 125Hz instead of maybe 55Hz max. Yes the port is quite large and long but it is not that difficult to pull something like that off. Many have done it. I'd expect maybe 4-6db of port compression near tuning at full tilt with that vent area and driver. The TQWP only has a 394cm mouth which isn't that much larger so there might be some compression there as well. Also all of the horn type designs that I've seen tested all have significant compression at maximum output levels too. The maximum output appears to be about the same all in all but the TQWP has much more restricted bandwidth, will probably ring mightily at 58Hz and exhibits worse group delay. I'm not seeing what the big advantage is?

 

[revboden]

Actually I mispoke. What I was looking at in comparison was a 290L system with 30L of port, or a 320L total system not 320L plus port. Not that it changes much. Apparently I wasn't comparing to the current TQWP proposed either!

I don't want to get too far into a discussion of port performance but I have never seen any system detune a half an octave! And I have went through a bunch of vented systems including small 3" ports on up through 10" flared ports attached to systems more powerful than this proposed one and tunings between 11 and 40Hz. At most I've seen maybe 2-3Hz of shifting in the tuning at maximum power levels for any vented system so far. Also the tuning shifts downward at high power not up. I have yet to one shift upwards that I can remember. Also the larger the port area the higher the airspeed that can be supported before compression, noise and overload. See Collo's port tests for evidence of that. He stopped at 6" but everything I have tested has followed this trend as well. A 4" does not support 20m/s the same way that an 8.5" port does.



I don't see where this comes from honestly. If a TQWP is a reverse TH why would it be simpler or cheaper? You could make a TH with the same size/materials and construction costs right? Cheaper and simpler than a regular old vented build?

You are absolutely correct, I wasn't feeling well last night and inverted the equation. it would detune down from 20Hz to 14.5Hz. as the boundary layer thickens with velocity.

 

[revboden]

Here is a vented system to compare to the proposed TQWP. Sensitivity and output headroom seem to be virtually the same as does driver excursion at the same input voltage. The vented system could be used up to 125Hz instead of maybe 55Hz max. Yes the port is quite large and long but it is not that difficult to pull something like that off. Many have done it. I'd expect maybe 4-6db of port compression near tuning at full tilt with that vent area and driver. The TQWP only has a 394cm mouth which isn't that much larger so there might be some compression there as well. Also all of the horn type designs that I've seen tested all have significant compression at maximum output levels too. The maximum output appears to be about the same all in all but the TQWP has much more restricted bandwidth, will probably ring mightily at 58Hz and exhibits worse group delay. I'm not seeing what the big advantage is?

A quick sorry to everyone, food poisoning and maths do not mix well.

I just redid the maths, you are spot on, the compression at full tilt would be -3.4-7.3db at 20Hz (depending on surface roughness) with two 6" ports 29" long, with 3.5" rad. flares.

Have you had pipe resonance problems going longer than 34" with ports? also, I tend to keep airspeed below 15m/s in the core to avoid compression and flow separation at the mouth, I'm curious to know what guidelines you use and why?

edit: below 115db I don't see what the advantage is as well.

 

[revboden]

sorry, that last edit should read: above 20Hz and below 120db, I don't see what the advantage is as well.

 

[NWCgrad]

Hey sorry about the off topic stuff. I'm not trying to derail your thread or talk you out of the TQWP either for that matter. I'm more interested in the alignment itself than your particular app...No offense. Yours just happens to be a handy scenario.

Here is a vented system to compare to the proposed TQWP. Sensitivity and output headroom seem to be virtually the same as does driver excursion at the same input voltage. The vented system could be used up to 125Hz instead of maybe 55Hz max. Yes the port is quite large and long but it is not that difficult to pull something like that off. Many have done it. I'd expect maybe 4-6db of port compression near tuning at full tilt with that vent area and driver. The TQWP only has a 394cm mouth which isn't that much larger so there might be some compression there as well. Also all of the horn type designs that I've seen tested all have significant compression at maximum output levels too. The maximum output appears to be about the same all in all but the TQWP has much more restricted bandwidth, will probably ring mightily at 58Hz and exhibits worse group delay. I'm not seeing what the big advantage is?

Josh, no issues on my end as I am exploring the options so that I can make an informed decision on my next build. When I followed the crowd and built a sealed 24" cube for the driver I did not model the response. This configuration would be great in multiples, but a single one does not allow me to fill in the missing octaves below the LAB-12's. I modeled it with LT and could get down deep, but excursion limited output to 110 dB or less.

The HR program models the vented enclosure you show a lot better than WinISD. I am having a hard time figuring out the port size from the input screen shot - I am not very good with HR.

I think these discusions are valuable for a lot of people like me, who want great performance but don't have the time or inclination to master the skill sets required to design a great sub enclosure.

 

[manuelbauwens]

I'm watching close, because I do not know yet what I will do for my two subs... BR or TQWP, Bjorno made a nice calculation, but I'm trying to get as much info on TH and TQWP as possible

 

[tb46]

Hi Y'all,

I have been watching bjorno's T-TQWT with interest too. I have a drawing that is almost a match for
his simulation. I do not have the dimensions for the driver, but, for what it's worth I'll attach it here:

Regards,

 

[NWCgrad]

Hi Y'all,

I have been watching bjorno's T-TQWT with interest too. I have a drawing that is almost a match for
his simulation. I do not have the dimensions for the driver, but, for what it's worth I'll attach it here:

Regards,

Thanks for the drawing, I have not seen a folded T-TQWT. Ity does make for a smaller enclosure. For now, I would build the dimensions provided by bjorno as it can be either put in a rear corner of the room or lying across the front wall under the screen.

 

[GM]

Search bjorno's posts, he's posted pics of some of his builds IIRC.

GM

 

[zobsky]

Here's one I built a while back http://www.diyaudio.com/forums/subwoofers/170277-opinions-needed-tapped-horn-drivers-2.html

 

[manuelbauwens]

Here's one I built a while back http://www.diyaudio.com/forums/subwoofers/170277-opinions-needed-tapped-horn-drivers-2.html

Were you happy with that build?

 

[zobsky]

Were you happy with that build?

Yes. Since I haven't junked it yet, it must be worth keeping.

That said, ..
1. T-TQWT's work very well with low-mid efficiency mains, preserving that "tight" sound that I like about horn subs, in a smaller package. OTOH, I wouldn't use them with high efficiency mains (say 95 db/W/m or above as they can run out of steam trying to keep up, depending on what the mains and the amps are). Definately superior to reflex designs. I don't know if it's obvious from my diagram but if the driver access panel is removed (i.e. decouple the "tap", the design resembles a conventional negative taper transmission line sub.


2. If I had to rebuild this design, I'd tweak the design slightly to incorporate a gentle drop in SPL with decreasing frequency response to account for room gain. Not hard to do, just something that needs to be worked into the design.

Build one, keeping in mind (1) and (2). You won't be disappointed. Hope my TH folding clarified things somewhat.

 

[NWCgrad]

Half-way through my tour in Cambodia. I am still planning on building the box based on Bjorno's inputs when I return to the US next summer.

I think that Kevin Haskins, seller of the maelstrom, recommended a minimal 4" clearance behind the driver for airflow. Could this be a problem? If so, how can I minimize its impact?

 

[bjorno]

Half-way through my tour in Cambodia. I am still planning on building the box based on Bjorno's inputs when I return to the US next summer.

I think that Kevin Haskins, seller of the maelstrom, recommended a minimal 4" clearance behind the driver for airflow. Could this be a problem? If so, how can I minimize its impact?

Hi NWCgrad,

It looks like tb46 drawing(.pdf) show an inch less internal dimension behind the driver(without clearance) than whats necessary to fit the driver.

The proposed thickness of wood is ~18mm(0.72"). I suggest at least a 3 times thicker.for the baffle and second of dividers = (~11 cm in total) ~1.88" added for driver clearance.

b

PS: 3" clearance is IMO quite adequate.

 

[NWCgrad]

Bjorno,
Thanks for all your assistance on the design. I do not think I will try to fold the design as the tall, but fairly small width and depth, provides greater flexibility in my room.

Cannot wait to start cutting wood next summer!!!

 

[NWCgrad]

I spent about 6 hours today trying to fold this enclosure. After failing to do so I decided to medel a straight pipe, I was successful if I wanted a sub that is 72" tall AFTER folding.

I guess I need to learn how to use sketchup, the only software I have for drawing is PowerPoint.

 

[tb46]

Hi NWCgrad,

Assuming this is still about the 18" Maelstrom (I guess it has been discontinued), if you can get me clear sideview, frontview and rearview pictures, and accurate dimensions for the driver dimensions, I'll see what I can come up with. Without these dimensions it's just guesswork.

Regards,