A couple of points about Iso. This bass improvement is due to the effective doubling of the BL. We normally think of Iso to help with the deep end of bass and of course it does, but with a few caveats. 1. the distance between the drivers cause a smearing of sound if not compensated in time eg front delayed to placement distance of driver behind primary. Secondly this distance the rear Iso would also require a low pass if used in your configuration. This prevents upper range harmonics from being passed through the primary driver albiet reduced level. Iso only improves bass alignment and has no use in upper frequencies as they are not subject to T/S alignments. To pull this off one would need to use an active crossover (MiniDSP and the like) or a combination of electronic crossover with a delay line added to compensate. Biamped of course
Most people familiar with this won't do it outside of an auto environment because it can easily impede SQ if not done correctly. In this case a driver that has a significantly higher BL will perform better without the complications is normally chosen.
Most people familiar with this won't do it outside of an auto environment because it can easily impede SQ if not done correctly. In this case a driver that has a significantly higher BL will perform better without the complications is normally chosen.
Thanks Greebster, won't go there.
I had a pair of of Iso subs in a 5.2 and was always happy with the bass (but not using any of it now).
Tunnels are fun to make; measure carefully, cut rings, glue them together, then glue the stack to back of baffle - easy.
To wrap this up, if I get time someday and don't sell this 8" MTM black pair, I'll rebuild the boxes, double size, in the 3ft3 range.
I had a pair of of Iso subs in a 5.2 and was always happy with the bass (but not using any of it now).
Tunnels are fun to make; measure carefully, cut rings, glue them together, then glue the stack to back of baffle - easy.
To wrap this up, if I get time someday and don't sell this 8" MTM black pair, I'll rebuild the boxes, double size, in the 3ft3 range.
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Time to beat a dead horse.
I have always wondered what the reasoning (grounded in physics) is for criticizing an MTM design with large woofers solely due to driver spacing. I know there is a supposed "rule of thumb" floating around out there that you don't want the distance from the acoustic center of your tweeter or your woofer to be greater than 1/2 WL at the crossover frequency. But why? What does this give you, really, so long as you listen on-axis and your crossover design accounts properly for the path length distance to each driver? The most that driver spacing can do is affect the speaker's power response, so the sound you hear on-axis might be affected slightly if your room is very live. But unless you like to stand up and sit down repeatedly while listening, or listen in a room lined with ceramic tile, why is it an issue if the vertical off-axis response begins to suffer? (Some would call this vertical pattern control.) You (most people) don't listen there. You listen in your chair, with your ears at one height off the ground for the entire session. To me, the only thing this can possibly be about is phase relationships between the output of each driver, and when you're on-axis, those line up anyway once the crossover work has been done.
I know that as DIYers, we tend to cling to every morsel of engineering information we can get our hands on, including placing high importance on mere rules of thumb that make design 'easier', but I think it's ridiculous to declare that someone's design is no good just because the drivers are spaced too far apart according to a 'rule' that is really only a recommendation for what will "usually" work well with most drivers in most speakers in most rooms. I think this is a case when a 'rule' isn't really a rule, and the designer should enjoy the results of his hard work.
I have always wondered what the reasoning (grounded in physics) is for criticizing an MTM design with large woofers solely due to driver spacing. I know there is a supposed "rule of thumb" floating around out there that you don't want the distance from the acoustic center of your tweeter or your woofer to be greater than 1/2 WL at the crossover frequency. But why? What does this give you, really, so long as you listen on-axis and your crossover design accounts properly for the path length distance to each driver? The most that driver spacing can do is affect the speaker's power response, so the sound you hear on-axis might be affected slightly if your room is very live. But unless you like to stand up and sit down repeatedly while listening, or listen in a room lined with ceramic tile, why is it an issue if the vertical off-axis response begins to suffer? (Some would call this vertical pattern control.) You (most people) don't listen there. You listen in your chair, with your ears at one height off the ground for the entire session. To me, the only thing this can possibly be about is phase relationships between the output of each driver, and when you're on-axis, those line up anyway once the crossover work has been done.
I know that as DIYers, we tend to cling to every morsel of engineering information we can get our hands on, including placing high importance on mere rules of thumb that make design 'easier', but I think it's ridiculous to declare that someone's design is no good just because the drivers are spaced too far apart according to a 'rule' that is really only a recommendation for what will "usually" work well with most drivers in most speakers in most rooms. I think this is a case when a 'rule' isn't really a rule, and the designer should enjoy the results of his hard work.
Play in a simulation program like edge that can actually show you what happens to the response when you move off axis with big MTM designs, and you will quickly learn that all of the garbage "rules of thumb" are based on some very unusual requirements... Who needs 120 degree vertical dispersion? Most of the rules of thumb thrown around here as based on the premise that the speaker should behave as a point source with no directivity or "design axis" whatsoever. As soon are you are prepared to accept the notion that there is nothing wrong with having a limited vertical axis, the sooner you can move forward with a nice dynamically capable speaker.
An 8" MTM with 11" C-C spacing crossed over at ~1700hz will provide +/-10 degree vertical axis response with very minor effects on the response. (at 15 degrees off axis, there would be a few dB droop just below the tweeter crossover). If the listening position is 3M back or more, then the response is pretty good everywhere from sitting on the floor to standing up.
Zaphs measurements of the SB29RDCN show high 2nd order harmonics below 3K. It's not as dead clean as far low as the non-N variant. I've been on a search for a small flange neo tweeter myself for a TM design with a high EBP midbass unit and didn't really find any remarkable solutions so will just go with a regular full flange tweeter and be done with it.
I imagine similar 11" c-c spacing could be achieved with a "full" size flange tweeter with the tweeter offset. So this could work either way.
Eric
An 8" MTM with 11" C-C spacing crossed over at ~1700hz will provide +/-10 degree vertical axis response with very minor effects on the response. (at 15 degrees off axis, there would be a few dB droop just below the tweeter crossover). If the listening position is 3M back or more, then the response is pretty good everywhere from sitting on the floor to standing up.
Zaphs measurements of the SB29RDCN show high 2nd order harmonics below 3K. It's not as dead clean as far low as the non-N variant. I've been on a search for a small flange neo tweeter myself for a TM design with a high EBP midbass unit and didn't really find any remarkable solutions so will just go with a regular full flange tweeter and be done with it.
I imagine similar 11" c-c spacing could be achieved with a "full" size flange tweeter with the tweeter offset. So this could work either way.
Eric
Last year I built a pair of MTMs using the 8" silver flutes and a Tang Band 2" "full range" driver as the tweeter, crossed over around 700Hz. The low crossover point completely solved the issues normally associated with an MTM, and the Tang Band was able to accommodate it very well, with low distortion and extension to about 18kHz with nice off-axis dispersion.
It's very difficult to cross low enough with a traditional dome tweeter to avoid some of the well known flaws of the MTM configuration but the SB29 (the neo version is a must for its small flange) is a great unit in this application.
-Charlie
Lost Charlie....
The black 8" MTM's turned out nicely and happy to keep them, Not a lot of bass, but adequate; boxes could be larger, but would not change the front baffle. E.g. the speakers are 11" center to center. With the tight grouping, I couldn't hear anything odd moving around the room.
I do think the SF's are a little harder to work with - need a good solid box, lined with felt and/or cork.
The black 8" MTM's turned out nicely and happy to keep them, Not a lot of bass, but adequate; boxes could be larger, but would not change the front baffle. E.g. the speakers are 11" center to center. With the tight grouping, I couldn't hear anything odd moving around the room.
I do think the SF's are a little harder to work with - need a good solid box, lined with felt and/or cork.
Crazy Little Woofers
So here's an update - had these in a huge 80' x 120' x 20'H party room.
And know I know what the 8" SF's do best.
THEY PLAY LOUD
The SF's just keep impressing me. This 8" mtm pair has been wrapped in shrink wrap for 6 months and been waiting for the day to crank them up in a big room.
They were a WOW and folks just loved them, crystal clear, powerful, plenty of bass. (one was placed in corner the other 8' along a wall) One RB990 (200watt amp) which never sounded better, so again a huge success.
So here's an update - had these in a huge 80' x 120' x 20'H party room.
And know I know what the 8" SF's do best.
THEY PLAY LOUD
The SF's just keep impressing me. This 8" mtm pair has been wrapped in shrink wrap for 6 months and been waiting for the day to crank them up in a big room.
They were a WOW and folks just loved them, crystal clear, powerful, plenty of bass. (one was placed in corner the other 8' along a wall) One RB990 (200watt amp) which never sounded better, so again a huge success.
I agree that that tweeter is a good option. Stepping higher to the Satori would likely also work, short of the SS 9900 or something in that capability range.
Not many can do the close to 1000Hz requirement. That 300Hz thing is a FAST employment, and we don't have to do that. A good robust tweeter is fine.
Later,
Wolf
Thanks Wolf
We we curious if the compact sb tweeter was up to the challenge; good to know.
Woo-ah $500 a pair for SS9900's
I bet they sound great but I don't know
View attachment 449931
Just meaning that it would take a ultra-robust tweeter to get low enough to meet the 8" in a lot of cases, and you can pretty much count those on one hand.
Later,
Wolf
So here's an update - had these in a huge 80' x 120' x 20'H party room.
And know I know what the 8" SF's do best.
THEY PLAY LOUD
The SF's just keep impressing me. This 8" mtm pair has been wrapped in shrink wrap for 6 months and been waiting for the day to crank them up in a big room.
They were a WOW and folks just loved them, crystal clear, powerful, plenty of bass. (one was placed in corner the other 8' along a wall) One RB990 (200watt amp) which never sounded better, so again a huge success.
That's a good test for how robust the tweeter is. Glad to hear they survived a setting like that!
Another update, going back through the flurry of speaker builds for the last couple of years and mic testing.
This is a little unusual, the tweeter has a dip at 4.500hz (top graph), I'm curious if that is a placement/cancellation issue?
The SB29 graph (specs) looks a little different now also.
[vs. post #76]
This is a little unusual, the tweeter has a dip at 4.500hz (top graph), I'm curious if that is a placement/cancellation issue?
The SB29 graph (specs) looks a little different now also.
[vs. post #76]
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Single wavelength spacing has some advantages:
1) it creates off-axis nulls that you can use to reduce output to the ceiling and to the floor
2) It's a lot easier to do. For instance, with an 8" woofer you'd use a crossover of 1688hz
3) With a 4th order xover you'd need a significant backwards offset to get the tweeter in phase. About 8". Due to this, the use of a waveguide is an obvious choice.
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