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Midrange driver to match with planar ribbon tweeter

Certainkindoffool

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Currently I own 2 pairs of Clements RT-7 speakers - which I love. However, I have found, when using REW and ARC that I have a drop from around 800hz to 1800hz on both pairs(peaking at about -6db). The specifications for the speakers list the crossover point at 1575. My assumption is that, either through degradation or design, the driver and 7" ribbon tweeter aren't capable of being matched at this point.

I am thinking about constructing a separate enclosure to handle the mid range, and using a dcx 2496 as a 3way active crossover. My only investment will be the drivers, and I would prefer not to spend more than $500US on the pair.

I was hoping to get some advice regarding a mid range driver that would match well with a 7" ribbon tweeter within this price range.

Clements RT-7 is a 2 way transmission line speaker rated +/- 3db from 26hz - 20khz using an 8" woofer and 7" direct inductance planar ribbon tweeter. Though in my measurements I would say that it doesn't get much lower than 30hz before dropping off sharply.

Edited to correct misleading wording.
 
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RayDunzl

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#2

Certainkindoffool

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Poorly structured sentence.

According to the manufacturer, the frequency response of the tweeter is 1500hz-100khz +/- 0.5db(was used in some experiments with bats). I would disagree with that...they flutter about, most severely in the range cited above, and start to drop off after 15khz.

Rating for the speaker is 26hz-20khz.
 

Certainkindoffool

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That looks promising. I will do some research and see where it leads. Couldn't find any reviews or measurements on those speakers. Drivers are reasonably priced though.

Thanks
 

HammerSandwich

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You should probably post some details about how you measured. And the measurements. :)

Because you're trying not to waste money, are you sure that all 4 of your original drivers are working well? Replacing the crossover will help, unless the XO isn't the problem...

An 8" woofer + smaller ribbon sounds difficult to me. Most such ribbons do not like low crossovers, and polar mismatch probably will happen with 2-way XO at 2kHz, if not lower. But adding a mid can't hurt, and you like your speakers. Good enough starting point, then.

What are you thinking for the mid's bandpass? 700Hz up to 2, maybe 2.5kHz? Find a good 4-5". For an active speaker, you don't care (much) about sensitivity or impedance, so I'd prefer the smaller ones. You don't need a bigger driver's bass or SPL, and the ribbon will have wide horizontal dispersion at crossover.

So... Scan 10F or 12W, Peerless HDS, Wavecor 120BD, SB12... Faital's 4FE & 5FE are good value. Feleppa liked the cheap Dynavox, and his measured really well. Or a small dome such as Dayton RS52 or Morel MDM55 would work here. Spend a few hours at Hificompass & Dibirama, and you'll have more options than you can count.

Now, where are you going to put the thing? Your speakers have the usual TM layout? Be aware that you may create some lobing issues. A pic of the front of your speaker would help.
 

PaulD

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#8
I can't help thinking that if you have a 6dB dip 800-1800Hz (just over an octave), then you are probably better off with EQ rather then trying to redesign your speakers, which is an expensive and time-consuming undertaking, and more hit-and-miss without the proper tools. Just my 2c (undithered).
 

Certainkindoffool

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I am away from home at the moment, but will add some pictures and measurements later.

@PaulD - arc does a pretty good job of flattening out the response. This is more of a learning exercise as I would like to try my hand at building a pair of speakers from scratch in the future.

@HammerSandwich - one of the pairs was an early version that looks like an industrial prototype that was severely abused. I've really just been keeping it around for the parts(which may be unobtainable) and a future project.

That speaker is already somewhat modular, the tweeter housing is just sitting on top of the transmission line box. I figured I would just build a midrange enclosure and either put it on top or between. I can play around with position before affixing them. Aesthetics aren't a concern, as the speakers are extremely unattractive and will never be allowed out of the basement.

My thought for the crossover point was to find a good driver aimed for an approximate range of 500- 2500hz. Design the enclosure around it, then use the active crossover to fit in in where/if it works.

Here is a random picture of a pair that arent so compromised.
218960_thumb_9d7dda95986c617cd0643c41c27dc2c7.jpg
 

Certainkindoffool

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@HammerSandwich

I haven't yet tried directly connecting the active crossover to the drivers. I was unsure what, if anything, I should put in the signal line of the tweeter. Most of my reading has suggested placing a capacitor and resistance in the path to protect them. I am still reading up on this.
 

Winkleswizard

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You would be correct that you should protect the ribbon with a capacitor before doing anything else with it. The value would depend on the resistance of the ribbon, but expect somewhere between 10-20 uF. Before you spend any money on new drivers, you need to measure each existing driver. If they are all ok, then the next step would be to insert your active crossover and see if you can get some decent results with it. Your best bet would be to try to emulate the passive crossover electronically at least initially.

A solid redesign of this speaker to a 3-way is a non-trivial task. You would have to have equipment to measure driver parameters, the experience to know how to how to design a speaker (electrically and acoustically) and build a nice cabinet. Suggest you read this: http://www.linkwitzlab.com/Fitz/considerations.htm

OTOH, if this is mainly a salvage job/learning experience, go for it!
 
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ctrl

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However, I have found, when using REW and ARC that I have a drop from around 800hz to 1800hz on both pairs(peaking at about -6db). The specifications for the speakers list the crossover point at 1575.
How did you measure? It's quite possible that vertical cancellations are causing the dip.

Due to the large dimensions of the speaker, a gated measurement should be taken at a distance of at least 1-1.5m (the speaker should be as far away as possible from any boundary surface).
 

Certainkindoffool

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@ctrl I just took measurements from a few different speaker positions via ARC. Double checked with REW, but my mic is not calibrated for REW, so it was mostly for curiosity about the software. Speakers were certainly not ideally located. I will take more ideal measurements Monday morning. However, I do not currently have the capacity/know how to test beyond a response graph. Part of this exercise is just to provide a reason to explore the software and concepts behind the hobby. Hopefully at the end of it I will at least have improved my ability to make informed purchases.

@Winkleswizard this is definitely just a learning exercise. My only purchase will be the drivers, which I plan on reusing for a future build. If it doesn't work out, I will not be at all upset.
 

ctrl

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However, I do not currently have the capacity/know how to test beyond a response graph. Part of this exercise is just to provide a reason to explore the software and concepts behind the hobby. Hopefully at the end of it I will at least have improved my ability to make informed purchases.
In this case, you should take some time to deal in detail with measuring loudspeakers.

Even for an active crossover you need reliable measurements of the individual drivers, if possible 0-90° horizontally and vertically.

These measurements are then entered into a simulation program such as VituixCAD where the active crossover is developed.

You can find a lot of information about the correct measurement of loudspeakers here:
http://www.artalabs.hr/download/ARTA-user-manual.pdf
http://www.artalabs.hr/AppNotes/AN4-FreeField-Rev03eng.pdf
 

Winkleswizard

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Save your money then. You can learn plenty just converting these to active speakers and reap some major benefits.

Do you have schematic of the existing crossover?
 

Certainkindoffool

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@ctrl Thanks for the reading material. Looks like I need to brush up on my math if I'm going to understand any of that. It's been awhile, pretty much quit cold turkey after taking differential equations.
 

Certainkindoffool

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@Winkleswizard I do not have a schematic, so I would have to reconstruct it. Also, there was variation in the crossover design through different iterations of the speaker. At least one version had some tone controls.

The attached picture us from the oldest version. Apologies for the dust, I didn't want to blow it out in the house.
20200208_152936.jpg
 

HammerSandwich

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Save your money then. You can learn plenty just converting these to active speakers and reap some major benefits.
Hard to argue with that.

If you're really set on adding mids, get a pair of Vifa TC9s to learn on. That's a $10 version of the 10F, and it performs far better than its price would suggest.
 

Certainkindoffool

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@HammerSandwich Thanks, that is a very well reviewed driver for an extremely low price. In the meantime, I will get on with my reading before deciding on any course of action.

Part of the issue is my schedule. I have a ton of free time until mid April. After that I wont have a chance to do anything until November. If I do nothing but read, I doubt I'll remember much come November without some sort of practical application.

@Winkleswizard Converting them to active speakers is probably the best place to start.

I will instal a second set of binding posts that bypass the passive crossover next week. Seems like an easy first step while I figure out the measurement software.
 

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