SP Technology Timepiece 2 & Continuum AD

[oneoldude]

Anybody know what brand and model drivers SP uses for the tweeter in their waveguide and for the 8" metal mid woofers?

Also, what type of bass loading do they use?

It would be interesting to know at what max SPL their speakers will play (within tweeter Xmax) since they cross them at 950 for the Timepiece and 750 for the Continuum with only 4th order LKR filters. Wow, that seems low for a 4th order filter, even with a waveguide, doesn't it?

Anybody know the shape (conical, radial, ?) and depth of their waveguide flair? Also, how large is the waveguide opening at the apex for the tweeter dome to fit in? In otherwords, how tight is the fit?

Nobody sells them around here so I have no chance to see them or hear them. But their ideas seem pretty interesting. It might be interesting to clone a pair. :T

Anybody want to critique their sound or design?

[JonMarsh]

The woofers are Seas. There's been some other threads discussing them, but we don't have some of the "hard" details you're looking for.

I'm considering trying a wavegude design with RD50's, just for fun...

The biggest advantage I see is improved radiation resistance at the low end (down to 700-800 Hz for their two ways) and lower distortion at the bottom end of the tweeter range because of the reduced tweeter excursion. Obvoiusly, if you start with a low distortion, large Xmax tweeter to begin with, you're going to be even better off. FR will NOT be flat, though, and will require some care in the crossover.

Get Gedlee's book and software if you want to get into this approach in a serious way-

~Jon

[oneoldude]

Yea, I read those threads, including yours, and they are what got me interested in waveguides. I have bought a pair of the round 90 deg horrns shown below from Steelsound (http://store.steelsound.com/Detail.bok?no=528 ). I am waiting for them as we speak.



MCM has a nice one too but it also is a screw in and costs more. Rigging the tweeter to the horn may well be a pain. What we really need is a flat flange version of these cheap horns as a beginner's guide (pun intended). That would be the cat's meow.

Flattening the response with my DCX2496 should be no problem and it has built in 8th order LKR filters. I am thinking of using an RS28A with a pair of either RS180's or RS225's per speaker. That way I can cross low with or without the waveguide.

I am also thinking of the M6A's or the M8A's. Since you have used both brands, which would you suggest as sounding better? Note that I can cross low and steep with the 2496 to get away from the RS breakup modes and will be using them bi-amped as a two way full range in a vented box with extended LF response like in your floorstanding design. I noted in another forum a picture of your boxes with RS speakers in them. Is that your preferred set up?

I only got a C in calculus and that was over 40 years ago. From what I have read about the Gedlee book, it is way over my head. Maybe someone will post a waveguide cookbook for hands-on types like me.

In the meantime I can measure what I get with the waveguides and see if I can work with what I get.

[JonMarsh]

That's pretty interesting from Steel Sound. Certainly the price is right for experimenting.

Depending on how low the tweeter works out with the waveguide and what kind of crossover you're willing to do, the RS225 might be OK, since the combo might be able to do a 1 kHz crossover or a little lower (that's what these are without a waveguide).



Xmax of 7mm, pretty nice nonlinear distortion performance. If the Peerless Nomex Exclusive 8's are ever anything besides vaporware (I'm calling Solen when I'm back in town next week), then those might be the way to go for low LF and midband distortion, albeit at a slightly higher price point.

The M6a is a bit less Xmax than the M8a, and with break up mode not that higher in frequency, so I'm not as "keen" on it.

Of course, the Seas L22 series is one to consider, but the inductive rise of the slightly longer travel L22RN4X/P gives me concern about the midband distortion- my intuition says the 2 layer version should be better in the midband.

~Jon

[Dennis H]

Carving a klone of a Geddes horn out of wood should be pretty straightforward if you have a V-groove router bit with the proper angle. From the front side, carve a cone that comes to a point where it hits the back side. From the back side, bore a hole to make the throat whatever diameter you want. Then use coarse sandpaper or whatever to round the transition between the two. It's not shown on the graphs below (made using the oblate spheroid equation) but you'd want to round the outside edge of the horn as well to limit diffraction.

[oneoldude]

Jon,

Beautiful work on your speakers. Kudos! :T

I finally modelled your CE filters in CALSOD. It picked them up nicely and was able to quickly optimize them to a beautiful LKR 8. Your filters are slick! My only problem has been minimizing the "kickback". I cannot get kickback as low as you do, even if the inductors are at zero resistance. Hmmm, more work to do. :E

BTW, since you have used both the M8A and RS225 drivers in those boxes, why will you not tell us which you prefer and why? Perhaps a mini audio review of both drivers, as used in your boxes, is in order. After all, you surely have heard them. :B

[oneoldude]

Dennis,

Thanks for your post. :T

From it, and from some thought experiments, it seems to me that, for a beginning discussion, some rules of thumb for tweeter waveguides might be as follows:

1. The general shape of the guide should be a straight sided cone (?). :huh:

2. The angle of the cone should be an angle such that the polar response of the tweeter and of the mid-range driver are the same at crossover frequency. For example, first measure the polar response of the mid, then match the tweeter to it with the waveguide. As a first cut, if you want 90 deg. polar response from the tweeter, use a 90 deg. guide, then measure and iterate (?). :huh:

3. The circumference of the guide mouth should be the same as the nominal diameter of the mid-range driver. This will make the guide circumference larger than the mid piston diameter and will give the guide a lower cutoff frequency than the intended crossover frequency. That would be a very good thing (?). :huh:

4. The guide mouth should be given a generous radius to minimize reflections unless sharp filters are used substantially above the guide mouth cutoff frequency (?). :huh:

5. The throat aperture should be big enough to allow free movement of the tweeter dome, but not too much bigger (?). :huh:

6. The throat may be either a truncation of the guide's apex at the throat (a clean cut simple hole) or a gentle radiused transition from the throat aperture to the flair of the guide as shown in your post (?). :huh:

I am proposing these rules as a starting point for discussion. That is why there are question marks in the rules. I hope there will be corrections and additions to this list as well as some practical solutions to development problems. :T

[AJINFLA]

Hi Oldude,

Hopefully you read through the thread near the bottom of the (front)page "Waveguide benefits/drawbacks". Much of what you're asking was discussed. The answers to most of your questions are yes, but... There really is no single "blueprint" for what you want. Experimentation (mucho) is in your future. I saw the guides that you bought when I was searching for mine. IMHO 90deg coverage is too narrow. I could go on, but let me just point you to a link where someone other than me has taken the time to record his findings (something I'm allergic to )

http://www.zaphaudio.com/hornconversion.html

I should also let you know that I caught the attention of Ken Kantor over on the Mad board. He said ironically, while I was asking about waveguides and showing a pic of the Mackie HR824 (as an example), he was talking with Terry Wetherbee (who now works for him @ Tymphany) - one of the lead designers of the HR824. Ken said he would give some consideration to what I was asking, which was Waveguide faceplate options for current drivers. We'll just have to wait and see. Very nice gentleman to even entertain the thought. In the mean time, you'll have to do it the way I did. Cut and measure :B . I really haven't done any more work to mine since I'm working on another project, time being measured in lightyears rather than days - as usual.

Cheers & good luck,

AJ

[AJINFLA]

BTW,
the SPTech is a terrific sounding speaker, as are some (if not all) Genelecs and Mackies. Some Amphions are pretty good also. Unfortunately, the're all boxes :W . I listened to them mainly to hear how they produced treble (with their waveguides). You can see I liked what I heard. The (waveguide) theory is sound IMHO :B .

Cheers,

AJ

[oneoldude]

AJINFLA,

Hi from another Floridian.

Your speaker work is really great. Congratulations! :T

Are you using the same MCM 90 deg horn (54-580) that Zaph used?

Whatever horn you are using, will you please share the tweeter mounting method you used? A description and some closeup pics would be great. From what I can see in your pictures, it is a very clean installation on the horn but I cannot quite make out how you actually did it. ;x(

And yes, I did read the thread you mentioned. The rules of thumb above were partially generated from that thread. You said most of what I listed was correct. That leaves a shoe to be dropped. What is incorrect or incomplete? Constructive criticism is always useful to me. It teaches me where I went wrong. :B

[goskers]

I ordered the book from Geddes and all I have to say is holy crap that's a lot of math. Not a simple read if I may say so.

My plan of attack for making a cheap diy version that fits a RS28a is to make a stair step effect and then fill the stairs with bondo; I will explain. I will use autocad to fit my profiles the way I want them to look. Since you need what appears to be a straight cone with flared throat and mouth area you need to fit different diameter circles to roughly match the profile needed. I will use 3/4" mdf for the cone portion and 1/4" masonite for the flared mouth.

Next, adhere the concentric cones together into the rough shape needed. Cut the profile desired out of a strip of wood or metal. Bondo the steps on the inside of the rough cuts. When enough bondo is placed inside the cone you can use the profile to 'pull' the shape desired. I believe this will be similar to what a plaster worker would do.

You could easily leave a mounting ring on the throat edge by cutting the outer portion of wood to match the outside diameter of tweeter being used. A lot of work, I know, but it's just a thought. :huh:

[JoshK]

Joel,

I like your idea, I thought of something like that too. I also considered using a 45º or whatever degree chamfner bit to angle the rough cuts and less if any bondo would be needed. Just another idea.

[goskers]

I thought of that as well but then I have to spend another x amount of dollars the the chamfer bit. You still have to deal with the flares though. We are both on the same page though. :T

[JonMarsh]

Dennis,

Thanks for your post. :T

From it, and from some thought experiments, it seems to me that, for a beginning discussion, some rules of thumb for tweeter waveguides might be as follows:

1. The general shape of the guide should be a straight sided cone (?). :huh:

2. The angle of the cone should be an angle such that the polar response of the tweeter and of the mid-range driver are the same at crossover frequency. For example, first measure the polar response of the mid, then match the tweeter to it with the waveguide. As a first cut, if you want 90 deg. polar response from the tweeter, use a 90 deg. guide, then measure and iterate (?). :huh:

3. The circumference of the guide mouth should be the same as the nominal diameter of the mid-range driver. This will make the guide circumference larger than the mid piston diameter and will give the guide a lower cutoff frequency than the intended crossover frequency. That would be a very good thing (?). :huh:

4. The guide mouth should be given a generous radius to minimize reflections unless sharp filters are used substantially above the guide mouth cutoff frequency (?). :huh:

5. The throat aperture should be big enough to allow free movement of the tweeter dome, but not too much bigger (?). :huh:

6. The throat may be either a truncation of the guide's apex at the throat (a clean cut simple hole) or a gentle radiused transition from the throat aperture to the flair of the guide as shown in your post (?). :huh:

I am proposing these rules as a starting point for discussion. That is why there are question marks in the rules. I hope there will be corrections and additions to this list as well as some practical solutions to development problems. :T

I think you're on the right track here as a general direction and methodology- you're at the point, though, where it will take some calculation, construction, measurement, and validation of each concept to get to where you ultimately want to be. But I think your working assumptions, as a path for investigation, are sound.

I'm planning on getting the Gedlee software (have a copy of his book on loan- it's very comprehensive, but not for the non-technical DIY'er- i.e., it's for an EE or physicist.)

Still, this will be a major learning project for all involved- I hope that we can each share our experiences, experiments, and data as we move forward.

~Jon

[jdybnis]

Along the lines of using the chamfer bit to cut the straight part of the horn, I emailed MLCS (www.mlcswoodworking.com) about a custom router bit for the mouth. I sent them one of the pictures Dennis posted. They didn't give me an exact quote but they said it would cost 4-5 times as much as a regular bit. So somewhere around $120. That's not so bad if you can use the same bit for any tweeter of the same size.

[JoshK]

heck you could loan it out to others on this board too, maybe for a $20 fee to spread the cost around and only have to acquire one for the group.

[goskers]

I like this idea. I will chip in 40$ for the startup and usage fee.

[oneoldude]

First, check this out for some help with this thread :T . http://www.pispeakers.com/AES_v31_n6_p408.pdf

Second, what is the theory for driver spacing in MTM and TM designs re: crossover freq. vs driver spacing vs lobeing? I am concerned that when a waveguide is used its size is so large that the driver spacing will result in serious lobeing unless the crossover freq is very low like in the SP products. But I am not sure what the rule is to keep out of trouble. Is there a mathematical formula that will help? I have searched the net and this forum and found nothing on this issue. ;x(

[jdybnis]

I'll follow up with the company that actually makes the custom bits to get an exact quote. I'll ask about prices for quantity too.

A couple of questions for the board:

1. The OS waveguide looks like it starts out with a special curve and quickly converges to a straight conical horn. The router bit will cut the special part of the curve. How deep does it need to cut before a straight chamfer is a good enough approximation for the rest of the horn. The price of the router bit we're looking at seems to be proportional to the radius of the bit. So the sooner we can transition to a chamfer bit the cheaper it will be.

2. What determines the shape of the throat? Does it depend on the total depth of the horn? The size of the driver? The upper cutoff frequency? The lower cutoff? The coverage angle? I'd like to figure out how general purpose we can make a given bit.

[Dennis H]

The curve of the custom bit would only be "perfect" for one throat diameter and horn angle. Working with something soft like MDF, I'd probably just round it over with sandpaper. But, with something like hard maple, it might be worth having a bit.

Here's the crude Geddes spreadsheet I cobbled together. It's not really fancied up for public consumption but you guys can figure it out.

Change the 3 numbers in blue.
theta = half angle of the horn
throat = throat diameter
offset just moves the red reference line up and down to align it with the horn

To change the depth (and outside diameter) of the horn click inside the graph. That will highlight the data range being plotted over in the rows of numbers. Grab one of the bottom handles of the highlighted data with your mouse and drag it up or down so the biggest X value is how deep you want the horn. Release the mouse button and the graph will redraw. Final step, drag the graph itself so the horizontal and vertical axes have the same scale.

http://www.crestviewcable.com/~catapult/Geddes.xls

[jdybnis]

It looks like Geddes is using a 90 degree horn in his up and coming hi-fi speaker. So I think we should stick with that too. Tweeters don't come in a awful lot of sizes. Probably a 25, 26, or 27mm is a good place to start (or maybe 28mm so it works with the RS28a). What do you think the consequences are of using a horn with a slightly larger throat diameter than the driver?

I don't have Excel on my computer. Does anyone know if one of the Open Source clones will be able to run the sheet?

[JonMarsh]

Now you see the reasons for low crossover frequency- in the example in the old AES paper, at 1 kHz, 25 degree angle between nulls requires the radiators to be within a 16 inch vertical spread- or as close as you can get. That is harder to do with an MTM, especially with a larger waveguide. A staggered arrangement like the Arvo still may be a good compromise.

[oneoldude]

Some thoughts FWIW.

I did a little math and calculated the null points at 1 kHz for a 7" guide and a nominal 7" driver as well as for an 8" guide and a nominal 8" driver. The Keele paper was based on a 15" driver and a horn about the same size! I hope I did it properly. :roll:

The respective C to C will obviously be 7" for the former and 8" for the latter. The 7" result is about 75 deg for the half angle and 150 deg for the arc between nulls and the 8" results are about 58 deg and 116 deg respectively. Both results are better than the hoped for directivity of the wave guide. :T

Moving the waveguide off center in a TM design will not move the waveguide and driver closer together because their rims will essentially be touching. Therfore it will not improve the null arc. It will however skew the nulls in a lopsided non-vertical manner that might not be good for imaging or width and smoothness of sweet spot. :M

In the case of an MTM design, there will be some closure between the M drivers (not much) and the C to C distance of the guide to the drivers will not shrink due to the rims virtually touching. But the nulls will be lopsided. It makes my head hurt to think about what the null pattern might look like in an off-center MTM design. Whatever it might be, it may not be a good thing, especially for a stable stereo image or a wide smooth sweet spot. :M

I suspect that moving a guide off center to improve diffraction might work at the cost of non-vertical lobeing. But the baffle would have to be quite wide to make room for the guide rim and the guides would have to be ineffective at controlling dispersion for the move to be beneficial. :E

If the guides work as advertised, and that is a big but, there should be little diffraction from the cabinet edge because little signal will get to the cabinet edge from the tweeter. But there may well be some from the guide mouth edge depending on the crossover frequency and guide mouth size and contour.

Thoughts anyone?

[Dennis H]

Well, thinking hurts but here goes.

Say you've got an MTM with 7" M's and a 7" waveguide on the T. Moving the T to the side and pushing the M's together will cut the M-M center-to-center distance in half from 14" to 7". Meanwhile, the M-T distance won't increase at all; they're still touching. On the horizontal axis, the MT spread will go from 0" to 6" center-to-center which still isn't too bad with a low XO on the order of 1 kHz. I think that's what Jon was getting at....

Oops, edited for bad trig.

[oneoldude]

I don't know what Jon had in mind. But if you do what you suggest, the entire concept of an MTM design is lost. :cry:

D'Appolito came up with the MTM expressly to have wide horizontal dipersion, tight vertical dispersion, symmetrical smooth off-axis response, no frequency induced lobe movement and minimal lobing when using an odd-ordered crossover. With an even-ordered crossover (LKR), you typically get one major lobe and it does not move with frequency variation. Both designs have their place. And both designs have vertical alignment of the driver centers. The reason they do is that the items above produce high order effects while diffraction results in a low order effect that happens to be easily modelled on a computer. :roll:

Not only would the benefits of the D'App MTM be lost with the plan you describe, but if you used RS180 or RS225 drivers (with like sized guides), the 180 version would be about 13.35" wide for the drivers alone. And the 225 version would be about 16.5" wide for the drivers alone. That would make for some pretty wide boxes. :E

[jdybnis]

I think your both talking about different designs. Someone needs to draw a picture.

[Dennis H]

Browse the Arvo Part thread for pictures. The problem with the "tight vertical dispersion" of a tall MTM is it only happens as deep notches at certain frequencies which skews the in-room power response. There's a method to Jon's apparent madness.

[JohnL]

Anyone interested in waveguides might want to poke their nose in on the DIYspeakers.net list. There is a discussion going on over there that includes Earl Geddes.

FYI

[capslock]

If all you want is make the tweeter go lower while mainting low distortion, consider using 2 or 3 tweeters and use only one of these above say 3 kHz (depending on center-center distance) to avoid comb filtering.

Dynaudio use two tweeters in many models, and as I recall, the use only a first or second order low pass at 3 kHz.

[ralphs99]

I’m doing a bit of research into waveguides and thought the forum might interested in my findings.
I have a pair of Behringer B2031 powered monitors that use a waveguide loaded tweeter. I figured it would be instructive to examine them in detail.
The tweeter is a 25mm metal dome type with what looks like a plastic half-roll surround. The wave guide mates to the tweeter with a 40mm sharp-lipped throat beginning about 4mm above the level of the surround which is also the level of the tweeter face plate. The waveguide evolves in a conical expansion to a diameter of 80mm through a depth of 10mm, and then gently flares out to a 150mm mouth over the last 10mm of depth.
I surface mounted the tweeter on a 0.5m x 0.5m baffle and ran a test at 0.25m with 1/6 octave smoothing. The tweeter also is bandwidth limited to 500Hz for safety.

[ralphs99]

Not real flash at all. At first I thought my measurement setup had a problem. But that’s the true response, at least up to around 10kHz. It’s also worth pointing out that the dynamic range of the chart is quite small.
Anyway, next test is with the waveguide attached.

[ralphs99]

Wow! what difference. Behringer have obviously ordered the tweeter with a rising response to mate with the wave guide.
With a bit of imagination I can see something like a -6dB/octave effect from the waveguide. A very useful boost at the low end.
BTW, these monitors sound very average. They've been relegated to the role of computer speakers in the study. But I don't think that's the fault of the waveguides. They're just cheap 'n' nasty monitors designed to look good rather than sound good. And they don't really look very good!

Cheers,
Ralph.

[JonMarsh]

Thanks for sharing your meausrements. This is pretty much what I'd expect; you could take a pretty inexpensive, poor performing device and at least turn it into something "adequate", which looks like the case you've documented here.

With a more conventional driver, you'd have to tailer the crossover more, but you'd gain large benefits in the low end capabilities and distortio reduction.

~Jon

[AJINFLA]

Thanks Ralph.

With a more conventional driver, you'd have to tailer the crossover more, but you'd gain large benefits in the low end capabilities and distortio reduction.

~Jon

Yes, thats the idea. The waveguide used on the Behringer is very similar (size wise) to the one I used. I actually tried to get a pair of the passive version of the B2031 on ebay a while back, just for the waveguide! (I was outbid )
Ralphs results make sense to me. With a tweeter (like the XT-19) whose response is ruler flat down to 1k, the resulting boost is in the order of 15db (at 1k) with the WG, which must be compensated for. Behringer's approach is rather curious (but not too suprising). How they got a tweeter with that kind of raw response is beyond me. At first I thought Ralphs (first) graph was miscalibrated, but after seeing both posts, I see that they are not.
The benefit of that approach seems dubious, although it is possible with such a reduced output (or rising reponse), the tweeters distortion numbers are decent. Somehow I doubt it .

Cheers,

AJ

p.s. hey Oldude, attending the FL DIY in Orlando this weekend?

[JoshK]

It was threads like these that made me decide to try a waveguide with my Arvo Pärts. Fortunately with the DEQX that added countouring isn't difficult.

[oneoldude]

Hi AJ,

Thanks for thinking of me. I would really like to go. Not only because of the DIY but also to check out UCF and see what it looks like now. I graduated from there back in 1973 when it was called FTU.

I understand the DIY is Sept 3rd. Do you know what time it starts?

Is there anything I should do in order to attend? I mean is there a registration, attendance fee, or something similar? I have never attended a DIY meeting so I do not know what is expected of a visitor.

I will not be bringing anything to audition. Will you?

[JohnL]

You can find some info here. I'll see ya there.

http://groups.yahoo.com/group/audioDIYflorida/

John

[jdybnis]

Back "on topic"

SP Technology just announced a new budget two-way with the same waveguide on the tweeter.

Crossover: 1000Hz 4th order L-R
Dispersion - 90 degrees Horizontal, 60 degrees Vertical
Price - $995 on up depending on finish

It looks like they are using one of the new nomex Peerless drivers.

http://www.audiocircle.com/circles/viewtopic.php?t=21240

The woofer isn't flush mounted. From the look of the box diffraction effects are eliminated by the waveguide. The sides of the box actually overhang the front of the baffle!

[AJINFLA]

Hi oldude,

I really don't think anything is required, I heard mention of a $10 fee to cover the cost of the event, which is fine with me. Gates open at 9am. 1hr chat time, then the show starts I guess. Check out the Yahoo group. I swore I was going to have even one of my thousand odd projects done in time for this event, but suprising to no one including myself, I have finished exactly zero of them
But hey, this is my first DIY event, so it might be more prudent for me to simply attend and learn something. I am looking forward to hearing what others are hearing (or think they are hearing ). Should be fun. I've also heard there may be such wonders as a "9 step CD treatment", turntables, tubes and such. I'll do my best to keep an open mind - and a straight face, during the "CD treatment" portion. The worst that could happen is that I actually hear a difference! 8O . Anyway, back to the thread. Thats an interesting new design by SP. I think it's the first design I've seen with the new Peerless. Certainly would like to hear it. Maybe someone would be kind enough to buy a pair and review it :T

Cheers,

AJ

p.s. I'll bring the crappy ol' Sony Mavica for some (crappy ) pics of the DIY stuff.

[ralphs99]

Thanks for the link Josh.

It's really the first time I've actually been able to seen the contour of the waveguides SP use. It appears quite flat for the most part, like a conical flare with a soft transition to the flat baffle. The 90 degree included angle is obvious as well. There also appears to be a phase plug of some type which surprises me, unless that's the dome of the tweeter?

I think I will conclude that all this waveguide stuff is really rather low-tech. A simple conical expansion with the included angle of choice, rounded out to the baffle interface. Set mouth diameter to about Lambda/2. EQ to taste.

Am I missing something?

Cheers, Ralph.

[JonMarsh]

Back "on topic"

SP Technology just announced a new budget two-way with the same waveguide on the tweeter.

Crossover: 1000Hz 4th order L-R
Dispersion - 90 degrees Horizontal, 60 degrees Vertical
Price - $995 on up depending on finish

It looks like they are using one of the new nomex Peerless drivers.

http://www.audiocircle.com/circles/viewtopic.php?t=21240

The woofer isn't flush mounted. From the look of the box diffraction effects are eliminated by the waveguide. The sides of the box actually overhang the front of the baffle!

I wonder if these are designed for wall mounting or flush mounting. A 830884 won't do 90 dB/1.83VRMS with baffle step compensation.

Interesting combo- a "high power" satellite (60 Hz cutoff). Probably a pretty good way to use the 884.

[AJINFLA]

Looks like Zaphs latest project will use a WG and a SEAS (H1212?) tweeter. Probably the same off the shelf one (Pyle/MCM) I used and the one shown in his WG experiment. Too bad its still in a box . Step in the right direction though :T

http://www.zaphaudio.com/temp/waveguide-TMM.pdf

Cheers,

AJ

[noah katz]

So any updates, anyone?

oneolddude, did you ever make a waveguide?

One thing I find puzzling is how does SP Tech get away with XO'ing an 8" waveguide at 1 kHz, but it takes Geddes' Summa a 15" waveguide to do so.

[JonMarsh]

Differences in directivity control. The more directivity, the longer and larger a "waveguide" or horn mouth will have to be.

Geddes' book on acoustics design has all the messy math.

~Jon

[oneoldude]

We have put a little group with differing skills together. We plan to develop and test a variety of WG profiles to see how they actually perform. We will be using the H1212 as a foundation. I am waiting with bated breath for the first protos.

If you think that X'ing the 8" WG at 1k Hz is improbable, the handout given by SP Tech at the CES says they cross their flagship at 600 Hz! I estimate that WG to have a mouth of around 9". The MTM M's were 8". To be honest, I find it most improbable that there is enough WG lift of the T's bottom end to allow for a X at 600 Hz. But what do I know?

I will know more when I do some testing of the WG's we are working on. Results will be posted.