Having considerable experience with SDX7 i wouldn't bother with anything but sealed.
dave
I read that somewhere else too..hence I was wondering about a TL- but then I noticed the BR on Markaudio site.. tell me more Dave😕
That sounds like an offset driver, you take a normal TL but put the driver approx 1/3 to 1/5 the way down the line, then you do have a part of the line that will be approx 20% of the total length, but will be closed at one end, then the other 80% makes up the rest of it, and is open
And it does help to reduce the ripples
The SDX7 (as with other XBL drivers i've used) has a very abrupt and sonically disturbing overload characteristic. The sealed box, like on the JXR6, provides some load to counter this behaviour.
dave
dave
🙁 damn, I had my heart set on this beautiful driver (and which I can get here in the UK).
I'm staying passive and being 6.5" it doesnt quite have the bass output i want when sealed
If only CSS made a bigger version😉
Ok, I read your informative thread - they run out of excursion with no warning in a BR- not great.
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How are you estimating bass output? Are you taking room gain into consideration? With a touch of boost, i've seen 25 Hz, lower than i could get with the TLs (which in the end had to be heavily packed to make them aperiodic, and were good to 40 Hz).
dave
dave
All BR will leave the driver unloaded below tuning, an XBL is just very linear until such time as the VC slams into the backplate. Ideally input to the loudspeaker should be limited below the BR tuning frequency.
dave
I just used winisd and the slow roll off (for a BR) looked very positive.
I'm building these for a friend and so they will need to be passive and hook up to his existing stereo (I won't give them to him unless they work properly). is there a way to 'boost' the bass without EQ?
Not effectively? How low are you trying to go? How big is the room?
Hope your XO is above 200-250 Hz.
And you are familiar with what i consider the necessary minimum mods needed for this driver?
dave
I'm probably going to go with 2x alpair 6's per side and Mark has suggested experimenting with them full range first- so the x/o would have to be way below that. I am happy to roll off the 6's at 200 hz if needed. The friend I'm making these for doesnt play music too loud (because of the wife), but he does like his dub step (!) and ska so I was thinking an f3 of around 35 hz or so- if 25-30 hz can be achieved in room sealed with this driver then great.
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ever did less than 1/4 wave length TL. put the a lot stuff in it. that makes sense but f3 still higher than 1/4 wave length a little. the sound is pretty. i also like small TL.
Back to the 1/4 vs 1/8 vs 1/2 wave stuff for a moment. I just have to point out the obvious.
The TL will have all produced frequencies in it. Therefore there is one tuned frequency that is 1/4 wave, another that is 1/2 and another that is 1/8. These are all dependent on the length. The 1/4 wave is the resonant frequency of the TL, and so will be reinforced
(?) the best (or most) and other frequencies will behave differently depending on phase relation to the length of the TL.
So a 1/4 WTL is defined as 1/4 wave since it is the behavior of the frequency response where the TL length is 1/4 of the wavelength that we care about. If you care about the frequency response at 1/8 wavelength, you could call it that, but it is against convention, as there still will be another wavelength that will resonate at the 1/4 wave frequency and be more prominent, hence the definition in the first place.
The point I may be failing to make well is that all TLs have all fractions of wavelength resonances, we simply define the response based on the 1/4 wave response, since that one probably makes the most sense in terms of the output we want, so all TLs are 1/4 wave TLs.
Hi,
If the short one is open it will simply stop the long one working properly.
If its shut it is as mentioned before effectively its an offset driver.
rgds, sreten.
Regarding the SDX7 there is no reason I can see it cannot be used vented,
but like all vented boxes without exception if you want see what it can really
do at maximum levels low down, an excursion limiting filter is needed somewhat
below the vent frequency to allow maximum vent frequency levels.
The same would and does apply to TL's, though I agree with p10 to a
degree, Zaph has shown such drivers are often suspension limited as
opposed to excursion limited, sealed will linearise the suspension limit,
and possibly allow acceptable distortion higher excursion levels.
If you don't have such a filter sealed may well work better.
I am sorry, but that makes no sense to me. There will be discrete resonances in a TL speaker system associated with the 1/4 wavelength standing waves in the pipe combining with the driver's resonance at fs, there will not be all fractions of wavelength resonances as stated in your final paragraph.
I recall a guy named Cockroft published a few articles in Speaker Builder Mag. quite some time ago utilizing very short lines. Don't know how good the designs were sound-wise though.
Check the SB indexes at audioXpress mags website. You may be able to purchase 1 or 2 back issues with Cockcrost's articles in them.
Check the '88 and '89 issues for the unline, a short TL and microline
Check the SB indexes at audioXpress mags website. You may be able to purchase 1 or 2 back issues with Cockcrost's articles in them.
Check the '88 and '89 issues for the unline, a short TL and microline
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I am going to speculate that if you are going to use 2 of the new Alpair 6, and they meet their efficiency spec (very likely) then the SDX7 won't keep up with them efficiency wise. This is one of the reasons that Tysen never got a passive XO. Single SDX7 would have required padding on the 86 dB FF85.
dave
I think Mark mentioned the efficiency issue and told me how to solve that- funnily enough I quite like the look of the old spec 6's and the higher Fs has its advantages in this design-
John Cockroft was a fine person, much fun to communicate with about TLs and speakers in general (which I had the pleasure of doing several times). That said, he was one, among others, that promoted the theory that stuffing made a line act is if it was longer than it really was, which we know is incorrect. To be completely honest, I have a pair of overstuffed "TL" speakers in my workshop built according to John's theory; they sound just fine for use in my workshop but they don't perform as he thought they should and nowhere nearly as good as those I've built after modeling them with Martin's worksheets.
Paul
Paul
Hey Jrenkin, I agree, and that was what I was trying to point out earlier. I think the first transmission lines (in the 30s) were a means of controlling cone motion and were sized to give the 1/4 wave resonance at the woofer's (high Q) resonance frequency. Since the modern approach is to have a fiarly well damped line then the frequency of 1/4 wave resonance is not the overwhelming design criterion.
Clearly any line of any length will have some frequency for which it is 1/4 wave long, 1/2 wave long, 10 waves long, etc.
David S.
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