Some Thor models to mull over

[imjatse]

All of the bracing should be swiss-cheesed (if that's a word). Lots of different size holes in the brace, aiming for, if I recall correctly, about 35-50% empty space in the brace. There are pictures of my braces in my build thread (link in signature) and elsewhere on the site. Hollar if you still have questions.

 

[jhnmdahl]

All of the bracing should be swiss-cheesed (if that's a word). Lots of different size holes in the brace, aiming for, if I recall correctly, about 35-50% empty space in the brace. There are pictures of my braces in my build thread (link in signature) and elsewhere on the site. Hollar if you still have questions.

So it's not actually a folded line design like the original Thor, then? Now it's easier to see why people are comparing it to a bass reflex design, as the box looks more like a traditional bass reflex enclosure than the folded line I was expecting. Thanks for the feedback,

John

 

[Steve M]

Good discussion here on whether the Thor variations especially the Small Thor are true Transmission Lines or Bass reflex, I suspect somewhere in between.

An interesting analogy is the Proac Response 2.5 and its clone. I have heard both and the bass is superb, reaches incredibly low for its given 30L enclosure and 6.5" Scanspeak driver - and its bass signature is similar to a TL box I've built using a Focal 8K5412 driver. Funny enough the P2.5 box dimensions are similar to the Small Thor, long and tall with not too much stuffing.

So, it begs the question is the Proac 2.5 enclosure a Quarter Wave TL as described by Scottmoose & Planet 10 Hi-Fi 'Dave' ??

BTW, I have heard Niall Haywood's Madisound Odin kit speakers and understand his desire to look at constructing an alternative Small Thor box ...the Odin is not a good speaker, IMHO. Especially considering the pin-point imaging and freedom from box attributes attained by ESLs, Apogee ribbons, Magneplanars, Accutons and single drivers like Fostexes/Goodmans Axiom 80 & Corals etc.

Regards,

Steve M.
System Pics at: http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1146370182&view

 

[jackinnj]

All of the bracing should be swiss-cheesed (if that's a word).

We would call that a "neo-logism"

 

[Scottmoose]

The Small & Short Thor are not bass reflex cabinets, but nor can they strictly be called transmission-lines either. Don't you just love it when things get complicated...

OK, they're technically mass-loaded quarter wave resonators. I don't know the Proac box, but from your description Steve, it sounds very much like you're spot on, and that they've taken a similar approach, & gone for a resistively loaded QW design. It's generally quite under-used, especially by the commercials, but can be very effective.

All QW design seemed to be lumped under the transmission line moniker about 30 years back, mainly due to a mis-interpretation of Bailey's original articles, despite the fact that by any logical definition, the term 'transmission line' only applies to one very specific sub-set of enclosures. Leaving specifics such as length, taper etc aside, a genuine TL would feature a completely sealed, damped line, which absorbs the entire back-wave of the driver, & thereby presenting a near flat impedence curve to the amplifier: the ~'ideal load.' Most of what we've come to know as TLs are in fact aperiodic lines, where a damped line, open at one end, absorbs most of the driver back-wave and the line harmonic modes, but preserves a degree of the line's fundamental resonance to support the LF output. Before either of these came into being there was the QWR -a deliberately resonant line, with only the minimal quantity of damping inside necessary to damp the unwanted harmonics. From the 1960s onward, but far more recently thanks to Martin King's work, we've seen the added twist of mass-loading, where the terminus CSA is restricted into a vent, the air-mass in the constrained area providing a resistive load on the QW resonance of the cabinet, lowering the fundamental and helping supress the higher harmonic resonances.

 

[planet10]

a genuine TL would feature a completely sealed, damped line, which absorbs the entire back-wave of the driver, & thereby presenting a near flat impedence curve to the amplifier: the ~'ideal load.'

And by that definition even Bailey's TLs cannot be called TLs because they in fact get some bass augmentation from the terminus.

dave

 

[planet10]

An interesting analogy is the Proac Response 2.5 and its clone. I have heard both and the bass is superb, reaches incredibly low for its given 30L enclosure and 6.5" Scanspeak driver - and its bass signature is similar to a TL box I've built using a Focal 8K5412 driver. Funny enough the P2.5 box dimensions are similar to the Small Thor, long and tall with not too much stuffing.

So, it begs the question is the Proac 2.5 enclosure a Quarter Wave TL as described by Scottmoose & Planet 10 Hi-Fi 'Dave' ??

There are an aweful lot of tall-skinny floorstanders that were originally concieved as bass-reflex with the port at the far end. When these were built, amazingly the designers found that they had to retune the box -- and ended up with more bass extension -- to make the measured response what they wanted. Inadvertently they were building an ML-TL, but still called it a BR.

Martin in his ML-TQWT article has some ANYS sims that clearly show the dramatically deferent behavior of an ML-TL vrs a box of the same volume with dimensions closer to cubic.

dave

 

[Scottmoose]

No difference at all really is there...

 

[jackinnj]

Martin in his ML-TQWT article has some ANYS sims that clearly show the dramatically deferent behavior of an ML-TL vrs a box of the same volume with dimensions closer to cubic.

dave

Dave, pardon my ignorance, but what exactly do the colored pix represent and from where is it sourced?

 

[Scottmoose]

They're acoustic finite element models seen in Martin King's Project 2 ML TQWT write up: the 2.11mb pdf file is here: http://www.quarter-wave.com/Project02/ML_TQWT.pdf

Of particular interest to you will be pages 14 - 15, and Attachments 1 & 2 at the end of the file. The different colours in the picture Dave extracted from these show the different natural frequencies mode shapes, & normallised pressure distributions at work in (in this exemplar case) an ML TQWT and a BR cabinet of the same Vb and vent CSA / length. The linked pdf has the colour key & tabulated data with the drawingas, as well as a discussion on the aforementioned pp.14 - 15.

 

[MJK]

Jack,

You can find those plots attached at the back of my ML TQWT article. They were generated by modeling the air volume with acoustic elements using the ANSYS finite element program. Basically, they show the pressure profile of the different standing waves that exist in the two types of boxes at the applicable resonant frequencies. They are normalized mode shapes so the absolute value of the pressure is not presented, the relative values of the pressure at different positions in the box is what is being shown.

Also from the plots you can assess where the velocity maximums and nulls are located in the boxes. At a pressure maximum the velocity will be zero. Where the pressure is zero the velocity will be a maximum. Look at the output of the port (borrom front edge modeled as a slot) to see where the velocity is a maximum in each of the fundamental frequency plots. In the higher frequency plots there will be velocity maximum and minimums inside the box.

Hope that helps,

 

[Niall Hayward]

Hi guys back again I have finally started working on my Thor project, as I do not have a workshop I have been dependent on weather conditions (never seen so much rain ) the drawings for the small Thor tell me the port should be four inches long can someone tell me if this length is measured from the inside wall of the cabinet or does it include wall thickness, which in the case of my cabinets is 1" thick.
Many thanks
Niall

 

[imjatse]

Total port length is 4". At least that is how I made mine. Since the internal volume is the same regardless of wall thickness, the port length is constant too. I had this same question when I was building mine. Can't wait to see the work and your reviews of the speakers!

 

[planet10]

Port length will always be specified as the length of the port,,, it is from the outside of the cabinet to the inside end of the port.

dave

 

[Niall Hayward]

Thanks Dave and Patric, for your rapid and invaluable advice.
Niall

 

[cnankervis]

Small Thor Dimensions

Short Thor is also on that thread -post 122. I've attached Dave's drawing of it. Small THor has not yet been drawn -it's in the waiting list for Dave's Thor Revisited article I understand, but it's dimensions are described in post 231. It's 48" tall, 7.5" wide x 10.5" deep (internal). The tweeter centre is 12" down from the top of the line. The port is on the front panel, 3" diameter, 4" long, positioned 4" up from the internal base. Stuff 0.35lbs ft^3 from the top to 20" above the internal base.

However: you design and engineer an enclosure for a specific driver combination, so you can't just stuff any drivers into an enclosure and hope it will work -if only life were that simple! Send me a private email and we'll see if we can come up with something specifically for the drivers you're looking at.

Of course, when you get to gigantic sized rooms things start to vanish. A Linn Kan mini-monitor in Wembly Arena doth not a sensible combination make. But as a room becomes smaller, low frequencies are progressively attenuated, meaning you need more power needs to be fed into the speaker if you want to maintain bass levels. So, up to a point, a small room with sound 'louder', but only until you reach that point where attenuation begins. From then on, it's dependant upon how much air your drivers can shift (preferably without distorting) and how much current your amplifier can pump. A big driver will almost invariably have an easier time of it than a small one, in any size room (though common-sense dictates a monster speaker is not always appropriate in a small room, usually more for practical than for sonic reasons). There's no accurate way of simulating a room's resonant qualities, as you note, because although we can get a good idea from the dimensions, it's construction materials and furnishings all play a big part. There's still art there in this respect.

Best
Scott

Hi Scott,

I am a newby on diyaudio.

I have been researching TL designs for a while now as I am looking to build my second set of floor standing speakers. This time I would like to up the ante on things and build some higher end speakers.

I have been looking at the designs and there seems to be only brief dimensions marked. I particular I would like to know the dimensions for the swiss cheese hole cutouts for the braces and the length and diameter of the port used?

I will intend to use the Seas kit from Madisound, however I'm located in Brisbane Australia. Is there anywhere in Australia that you may know that can supply the items in the kit from Madisound to save me on posteage costs?

You assistance with this would be greatly appreciated.

Kind regards,

Christian

 

[JC]

Linolll

I don't know if you are still following this thread from several years ago, but I am curious as to the details of your crosover mod. I had the same reaction to the sound as you did with the original crossovers.