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Old 20th September 2004, 05:02 AM   #11
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Default Re: Re: baffle step

Quote:
Originally posted by sbolin
Well, two speakers is an expensive solution to the problem.
You already have 2 drivers if you are talking MTM... my feeling is just that it is better on the back than on the front -- an MTM usually forces you to cross the tweeter really low which i try to avoid.

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Old 20th September 2004, 05:15 AM   #12
sbolin is offline sbolin  Thailand
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Quote:
Originally posted by piro
what drivers do you use?
At the moment, none . I am still designing, thus all the questions about the crossover. I have not decided which drivers to use, but I really like the AudioTechnology units (but very expensive), and also the Seas Excel line (expensive, but not so bad). I originally wanted to use Accuton, but it seems they are a bit noisier than their website indicates, and they are also coming out with a new line of speakers, so I will hold off on them. In fact, I really like the Thor speaker kit, it is exactly what I am looking for. Except maybe using the AT drivers...
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Old 20th September 2004, 05:51 AM   #13
sbolin is offline sbolin  Thailand
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Default Re: Re: Re: baffle step

Quote:
Originally posted by planet10


You already have 2 drivers if you are talking MTM... my feeling is just that it is better on the back than on the front -- an MTM usually forces you to cross the tweeter really low which i try to avoid.

dave
I guess I should say first off that I am not sure I will do an MTM setup, I was interested in it on a conceptual level - I wanted to know what its benefits were compared to a usual configuration. That said...



I don't understand what you mean. Being MTM doesn't (I think) require much of a change in where you cross over to the tweeter, usually about 2500-3000Hz from what I have seen, this is the same as most two way systems.

But what I really don't understand is putting the driver on the back. Do you mean having the usual MTM on front, and a single "M" on the rear, or do you mean the T on the front with the "MM" on the rear? Or (worse, money wise) MM on both front and rear? One advantage of the MTM seems to be that since you have two low frequency drivers, you have already offset 3db of the about 6db baffle step response you have with a single driver - or is this wrong?

I don't know if the www.t-linespeakers.org site is yours or not, but I really like it, I like transmission line speakers.
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Old 20th September 2004, 06:43 AM   #14
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Default Re: Re: Re: Re: baffle step

Quote:
Originally posted by sbolin
But what I really don't understand is putting the driver on the back. Do you mean having the usual MTM on front, and a single "M" on the rear, or do you mean the T on the front with the "MM" on the rear? Or (worse, money wise) MM on both front and rear? One advantage of the MTM seems to be that since you have two low frequency drivers, you have already offset 3db of the about 6db baffle step response you have with a single driver - or is this wrong?
MT on the front, M on the back. No bafflestep, and you can take advantage of push-push loading. The maximum XO in an MTM is determined by the spacing of the 2 Ms. To get an XO as high as 2.5-3k (which i consider too low) you can only use a 5" M or smaller (maybe a 6). With only one driver on the front, you have much more flexibility.

Quote:
I don't know if the www.t-linespeakers.org site is yours or not, but I really like it, I like transmission line speakers. [/B]
Yes that is mine. Thanx.

dave
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Old 20th September 2004, 07:12 AM   #15
sbolin is offline sbolin  Thailand
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Default Re: Re: Re: Re: Re: baffle step

Quote:
Originally posted by planet10


MT on the front, M on the back. No bafflestep, and you can take advantage of push-push loading. The maximum XO in an MTM is determined by the spacing of the 2 Ms. To get an XO as high as 2.5-3k (which i consider too low) you can only use a 5" M or smaller (maybe a 6). With only one driver on the front, you have much more flexibility.



Yes that is mine. Thanx.

dave
Regarding the x-over in the MTM, does that mean the crossover point should be at the same frequency as the speaker spacing? That would work out to about 138mm spacing for a 2500 Hz crossover. On the other hand, the Seas Thor kit crosses over between two 18W units ( which are 6-7") at 2800 Hz, so maybe it is one of those rules that is broken - probably because it isn't very practical to follow.

Regarding the two speakers - now I understand, that is a good idea. You lose some of the benefits to the MTM configuration, but gain others. But how to put it in a t-line?
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Old 20th September 2004, 08:31 AM   #16
Jennice is offline Jennice  Denmark
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Default Re: Re: Re: Re: Re: baffle step

Quote:
Originally posted by planet10


MT on the front, M on the back. No bafflestep, and you can take advantage of push-push loading. The maximum XO in an MTM is determined by the spacing of the 2 Ms. To get an XO as high as 2.5-3k (which i consider too low) you can only use a 5" M or smaller (maybe a 6). With only one driver on the front, you have much more flexibility.

dave

Dave,

Why does moving one M to the back give more flexibility when designing the XO? Wouldn't you cross over at the Baffle Step frequency anyhow, or would you design as an "ideal" 2-way (TM on the front) as the drivers allow, and then use the second M on the back with a totally independent LP filter (which is dependent of the BS frequency)?

Jennice
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Old 21st September 2004, 12:02 AM   #17
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Default Re: Re: Re: Re: Re: Re: baffle step

Quote:
Originally posted by Jennice
Why does moving one M to the back give more flexibility when designing the XO?
Because you are no longer forced to XO really low.

Take for example a pair of Vifa P13s and the matching tweeter. If in an MTM you are going to need to XO at something like 2.5k. This low you are going to need a 3rd or 4th order XO + baffle step compensation. Move the M to the back and you can use my favourite XO for this combo -- a 5 uF cap on the tweeter. You can roll the back P13 off at the bafflestep with an inductor if you want (ie 2.5 way without the inherent phase issues) or let it run full-range if your room will support it.

Now your amp is much-much happier without all the reactive components between it and the speaker and it all sounds more lively and dynamic.

dave
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Old 21st September 2004, 06:30 AM   #18
Jennice is offline Jennice  Denmark
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Dave,

I like the way you think (and your illustrative way of explaining things).

Originally I tyhought of making a MTM or TMM, in order to make a slim floor speaker without the need for a wide baffle and a 8" or bigger woofer. My concern was that a single driver (maybe 5" or 6") would not move enough air for the room size.
If I understand your concept correctly (with the second M moved to the back), I will have the same bass capability as a baffle-step corrected MTM, but with more freedom to design simpler and better XO. Is that correctly understood?

I recon that the overall sensitivity will be a little lower? My M's aren't working in parallel, and the tweeter will need a series resistor to match it's sensitivity to the single M, as it would when designing an ordinary 2-way speaker, right?

Also, if I understand you correctly, I can use a lower order ( == simpler) XO when crossing higher, or even use the M's natural roll-off, which will make the entire XO and BSC circuit much simpler and cheaper. Consequently, I think a second M isn't that much more expensive than all the (otherwise needed) extra XO omponents... Am I on the right track?

Jennice
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Old 21st September 2004, 07:45 AM   #19
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Quote:
Originally posted by Jennice
If I understand your concept correctly (with the second M moved to the back), I will have the same bass capability as a baffle-step corrected MTM, but with more freedom to design simpler and better XO. Is that correctly understood?

I recon that the overall sensitivity will be a little lower? My M's aren't working in parallel, and the tweeter will need a series resistor to match it's sensitivity to the single M, as it would when designing an ordinary 2-way speaker, right?

Also, if I understand you correctly, I can use a lower order ( == simpler) XO when crossing higher, or even use the M's natural roll-off, which will make the entire XO and BSC circuit much simpler and cheaper. Consequently, I think a second M isn't that much more expensive than all the (otherwise needed) extra XO omponents... Am I on the right track?
Same bass capabilities, same sensitivity (ignoring any losses in the more complex XO), no BSC required at all -- but the tweeter padded instead (the BSC in an MTM essentially pads the tweeter along with the upper range of the mids).

More flexibility with XO, including using Ms natural roll-off and lower order XOs.

Plus you gain with an easier load for the amp (not to be underestimated), and the benefits of push-push (more downward dynamic range & less energy transfer to the cabinet reducing its colorations.

dave
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Old 21st September 2004, 08:01 AM   #20
Jennice is offline Jennice  Denmark
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Quote:
Originally posted by planet10

...
Plus you gain with an easier load for the amp (not to be underestimated), and the benefits of push-push (more downward dynamic range & less energy transfer to the cabinet reducing its colorations.

dave
Why should less energy be transferred to the cabinet with this push-push design? If I understand you correctly, the speakers are electrically in phase, so there's the same air preassure change in the cabinet, so the sides should have the same preassure that causes them to vibrate... I don't get the point!?

Jennice
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