MY own OB speaker project

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Ray P
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#76 Re: MY own OB speaker project

Post by Ray P »

Ray P wrote: Sat Nov 11, 2017 11:39 pm Thanks for broadening the offer Colin, I would definitely take you up on it but from Somerset it's a long way so not something to be easily undertaken.

I'm really interested in this project and very tempted but for one problem I perceive; I only have around 1.5watts per channel available from my Transcendent amps!

Let's see how it develops...
Just a thought Colin, would it be possible for me to bring my Transcendent Amps up to yours to see how they fair with your OBs, perhaps in the new year?

Cheers

Ray
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#77 Re: MY own OB speaker project

Post by Toppsy »

Ray P wrote: Tue Nov 28, 2017 7:24 pm
Ray P wrote: Sat Nov 11, 2017 11:39 pm Thanks for broadening the offer Colin, I would definitely take you up on it but from Somerset it's a long way so not something to be easily undertaken.

I'm really interested in this project and very tempted but for one problem I perceive; I only have around 1.5watts per channel available from my Transcendent amps!

Let's see how it develops...
Just a thought Colin, would it be possible for me to bring my Transcendent Amps up to yours to see how they fair with your OBs, perhaps in the new year?

Cheers

Ray
Certainly Ray you are most welcome to come up to ours. Overnight sleepover available. I might have a passive version of the 2-way XO by then so you can compare the 3-way coax version with the 2-way compression horn version. Due to other paying builds I might not have had time to make up the deeper side frames and revised base, but the strategically placed LP sleeves are doing a good job to augment the bass in the meantime.
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Ray P
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#78 Re: MY own OB speaker project

Post by Ray P »

Thanks Colin. Let's see how things shape up after Christmas with the project and find a mutually convenient time when you're comfortable with progress and your bill-paying workload.

Cheers

Ray
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#79 Re: MY own OB speaker project

Post by Toppsy »

Ray P wrote: Wed Nov 29, 2017 10:00 pm Thanks Colin. Let's see how things shape up after Christmas with the project and find a mutually convenient time when you're comfortable with progress and your bill-paying workload.

Cheers

Ray
That's fine Ray, just get in touch after Christmas holiday period and we'll arrange a convenient time.

Made a small but significant modification to the speakers yesterday before Chris came around for a Friday night listening and chat evening:
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I have installed adjustable L-pads into the side frames. Originally when we played with the Fostex T90A super tweeters they were placed on top of the panels with a inline series hard wired 1uF cap and 8 ohm resistor. On the day this was the best sounding compromise of various resistor settings we tried. However, placed such they would be firing over head height when seated and when I installed the tweeters inline with the compression driver and so firing at ear level when seated I thought the tweeter was a little too much. Hence the adjustable L-Pads in place of the fixed resistor. With the help of Chris we eventually settled on a dialled in setting on the L-Pads and this has improved soundstage quite some and integrated the whole FR a lot better. A worthwhile add-on.
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#80 Re: MY own OB speaker project

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OK been a while since I did anything with these baffles so between builds of my Edingdale MKII and clone derivatives speakers I managed last week to find the time to making the MKII side frames and bases to improve the lower bass response that was a little lacking from the original side frames. At the mini gathering I had last year Nick suggested to add some LP sleeves attached by blue tack to the side frames at the base of the speakers as an experiment to to augment the bass response. This had the desired effect and below are the new bases and re-profiled side frames. They are shown next to the black finish originals.

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I managed to complete the new frames yesterday and now have them fully assembled and set up in mymusic room. They are definitely an improvement on the originals and my wife Lynn thinks they are an improvement in the looks department so a win, win result. I just need to dis-assemble the speakers and paint the new frames black. But that can wait as I'm enjoying listening to them so much.
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These will be at the next Owston meet and anyone fancy building a pair for themselves get in touch either by email or via the forum. They have been developed after all as a DIY'er project and don't rely on mini DSP's or multipleamps to drive them as they utilise a 3-way passive filter.

In the next few weeks and once Scott has finished design work on the 2-way passive filter based on the DSP experiments that Nick did I'll get that filter built and the coax driver and Fostex Supertweeter can be replaced with the horn loaded driver centre baffle. Should be interesting.
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#81 Re: MY own OB speaker project

Post by Ray P »

Interesting developments Colin and excellent work, as always. Will be good to hear how things go with horn in the 2-way.

I haven't lost interest Colin and still plan to take up your offer from before Christmas but work is a bit busy at the moment and I don't see an opportunity for a roadtrip in the next few weeks.
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#82 Re: MY own OB speaker project

Post by Toppsy »

OK guys so another update on the baffle project.

After I had completed the new frames Chris came over for a listen and thought the more powerful bass from the deeper side frames was to him swamping the lower mids some. So we did some experiments with attenuating the bass with a inline resistor placed before the 8.2mH inductor of the low frequency filter. After trying a few values we arrived at a value that to our ears seemed to address the midrange issues that Chris commented.

I reported this back to Scott to which he commented that the resistor mod is perhaps not the best way to address the midrange swamping issue and suggested a 22uF cap placed before the first inductor of the bass section of the coax driver a better solution and or try replacing the 8.2mH inductor with a 5.6mH. Doing this one component change at a time and listen to which sounds best. So I ordered a couple the Monacor 5.6mH Transformer Core Coils having some 22uF polyprop caps in stock.

In the interim Scott had sent me the 2-way passive filter to mimic the mini DSP experiments that Nick carried out late last year. Having ordered the components from NickL at HFC these had arrived earlier in the week and set about building these into a spare ply boxes I had from a previous mock-up build. Photo below:

Image

Thursday evening Chris came over to try the new 2-way filter and 3-way baffle minor XO mods suggested by Scott. First we tried the 22uF cap on the bass section of the coax to reduce the amount of lower frequencies generated by the coax driver. We both thought this an improvement on our ill informed attempts at addressing the over bass issue. So out came the 22uF cap and the 8.2mH inductor replaced with the 5.6mH. Chris almost instant response to this change was on the lines 'that's nailed it. The changes though both gave improved results were quite interesting and have nailed the sound the 3-way baffles and increased further my understanding of how filter work. So apart from painting the new frames matt black the 3-way baffles are sorted.

Next we replaced the coax driver baffles with the compression driver/horn baffles and hooked up the new 2-way passive filters.
Wow! We were both blown away how good these sounded apart from some harshness of the high frequencies - cymbals and the like. We were using NickG's P6 amps and both thought that good as the P6 amps are they perhaps were not the best choice for with what are near 100dB efficient 2-way speakers. So the P6's were replaced with my 300B SET amps.

This nailed the combination and Chris commented that originally he was not that impressed with the sound quality of mini DSP experimental set up for the 2-way baffles but this Scott passive filter is something else. I have to agree. Scott has done wonders with this filter and it just goes to confirm my suspicions that the mini DSP modules are adding colouration to the detriment of the sound quality and that a well designed passive filter with quality components will better an all digital DSP XO. Perhaps the new generation of DSP modules are better in the sound quality department?

Having spent most of yesterday listening to different genres of music through the 2-way baffles with the 300B amps I can hear still some harshness and shrill from the very high frequencies through the horn. One some my torture tracks cymbals can be a little too much. Scott has promised a minor mod to the high pass filter to address this but before that suggested I try a different horn. The one I have installed (Monacor MRH-200) Scott says was really designed for PA use and has suggested a more modern design horn in the Monacor MRH-180 might address the minor HF shrillness without having to mod the filter.

Image
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The specs for this are:
PA mid-high range horn
• Diecast aluminium horn
• Resonance-free due to rubber elements used
• Can be mounted turned by 90°
• 25 mm (1") flange connection with standard 2-hole screw connection (hole spacing: 76 mm)
• Consistent radiation pattern due to the latest FEA and CAD 3D developments
• Frequency range 1,000-20,000
• Mounting cutout 155mm dia.
• Mounting depth 86mm
• Radiation angle (vert./hor.) 50deg/70deg
• Dimensions 180x180x90mm

So I have a couple these on order and shall be making up some new mounting baffles.
So watch this space for further development updates.
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#83 Re: MY own OB speaker project

Post by chris661 »

Just a thought, Colin, that the harshness you're hearing might actually be resonances in the 10-20kHz range. The titanium diaphragms used in compression drivers often have some ringing up there, which is fine when you're pushing >120dB to a drunk audience, but perhaps not so great for home HiFi.

If it's of interest, I've a couple of B&C DE250 1" drivers here that I'd be happy to loan out for a month or two for you to play with. They're polyimide diaphragms, which I think is softer than titanium, but also much better damped. Consider it the difference between a metal and paper-coned driver.
http://bcspeakers.com/en/products/hf-driver/1-0/8/de250
You'll likely want to cross them over lower than they're rated for, but so long as you don't ask PA levels of them, it'll be fine.

Chris
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#84 Re: MY own OB speaker project

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Chris,
Many thanks for the offer but having just checked the manufacturers datasheet for the compression driver we are using it would appear to have a One piece Polyimide diaphragm and surround.https://celestion.com/product/128/cdx11747/

Scott thinks it may be the actual horn shape the throat tapering from a 25mm circle to a square shape over around 70mm then tapering to the large rectangular final. Perhaps as Scott said more suited to PA use and perhaps not in keeping with latest oval shape horn designs. We'll see anyway next week when I get the new oval horns.

As a quick experiment earlier I swapped out the shunt L-Pad resistor for the next value size up and to all extent and purposes this has practically cured the high frequency shrill of cymbals I was hearing, but then on the tracks the drummer is quite forward in the mix. Having said that this was only on a couple of high energy torture tracks I use and I was playing them rather load :shock: Reducing the volume to more akin to normal listening levels and the shrillness goes away. Still on occasion I do like to turn the volume up. Still it may be that a 1dB attenuation of the tweeter may be in order but before that I'll try the oval shaped horn and see where to go from there.
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#85 Re: MY own OB speaker project

Post by chris661 »

Fair enough, must've missed the datasheet for your driver.
From reading around about Geddes' work on horns, it looks like a horn needs to be as smooth as possible, particularly towards the driver end where pressure levels are highest. The one you've linked a couple of posts above looks just the job.
I did note that some of the horns I've tried are particularly bad-sounding, even if you force them flat with EQ. All the sharp edges results in diffraction, so you've got a mess of secondary sources and a load of time-smearing.

Treble balance can be a peculiar thing. I find playing with the switches on the back of my monitors (which only alter by 2dB at a time) can make the sound go from "relaxed", to "about right" and then "forward". I suppose it's the level change over a fairly broad area that does it.

Chris
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#86 Re: MY own OB speaker project

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Toppsy wrote: Sat Feb 24, 2018 4:22 pm Scott thinks it may be the actual horn shape the throat tapering from a 25mm circle to a square shape over around 70mm then tapering to the large rectangular final. Perhaps as Scott said more suited to PA use and perhaps not in keeping with latest oval shape horn designs.
This is more or less what the Yuichi horn does ( the 415Hz ones I built ) and these sound less harsh than the Azura axi-symmetric horns. It may be this horn is either a constant-directivity horn or a bit too small for the job. Best way to check if a horn is causing the harshness is to listen to the driver without the horn ( ! ) . Yes I can hear Chris gearing up to tell me about the FR not being flat .... no, I'll leave that one ...... but if the apparent distortion or intermodulation distortion goes away and the tone is clearer and the sound cleaner, then you've learnt something - like I did testing the Radian 745 Be's with/without the Azurahorn.
ps. It may be that Geddes points out horn transitions need to be smooth, but it wasn't him who discovered this, for sure ! ( Bruce Edgar, Jean Michel le Cleac'h and probably other before them were the experts ) .
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#87 Re: MY own OB speaker project

Post by Scottmoose »

Excellent day yesterday at Colin's place with Chris listening to the 2-way baffles with the new horn.

Short version = they're bloody good. One of the few 2-way baffles I've heard that I could live with if I had the space. Good extension at both ends -especially with the supertweeters added in, which is the excellent icing on the cake. Integration between the bass units & the compression tweet is nice & smooth; they seem at home with most any genre. Very low distortion levels, lots of weight down to below open E double bass & clean as you like; it's very easy to pick up on the compression levels in recordings etc. as their own dynamic range is high -those bass units really don't move much. That high sensitivity makes them an ideal match to SET amps; we were running them purely off Colin's 300b. Not as good off PP valves or SS, but that's to be expected.

I liked the new oval horn a lot; there seems to be very little colouration from it relative to some I've heard. The other horn isn't bad (it's actually pretty good), but this one is perhaps a little closer to a waveguide in its characteristics; it doesn't use quite such an efficient / high gain profile, but it's a lower distortion design & isn't really giving anything away in sensitivity in this application. No shout, no honking, no uneasy reflections etc. The 15s do a good job up to the XO point too & the compression tweet itself is very well behaved; you can hear some of the finer details on recordings that only a few high-end conventional dome tweeters can manage. I like the looks too -for baffles they're fairly compact & I like that smaller central horn -reminds me of an inflated conventional MTM.

All told -impressed. :^)
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#88 Re: MY own OB speaker project

Post by iansr »

I only visit the forum infrequently and yesterday I popped on to place a wanted ad for some Fostex super tweeters. In the process I stumbled upon this thread. I was interested because I too have been inspired by the PAP Trio15 Horn1 to have a go at DIYing some (3 way) OB woofer / horn speakers, hence the Fostex ad. My aim is to make them as good as I possibly can. I’m not going to go TAD mad (have I just coined a new phrase?) but I am prepared to throw a bit of money at it. I think I’ve settled on the drivers I’m going to be using and am actually in the process of buying some used woofers and comp drivers - fingers crossed those deals don’t fall through. If there was interest I could start a separate thread . . .
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#89 Re: MY own OB speaker project

Post by Ali Tait »

Always an interest here for projects, so please do.
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#90 Re: MY own OB speaker project

Post by Toppsy »

Ian,
As Ali has said please do post up details and progress of your OB project when it gets started. Too few speaker projects of late and as winter is in full swing and generally the time folk think about a winter build project it will be good to read of your efforts.

It's been a while since I last visited my OB speakers and your posting Ian has prompted me to reconfigure the baffles back into the 2-way configuration and reinstall them into my listening room. Forgotten just how good they sound and yes the super tweeters do add the cherry on the cake as they say. Have been thoroughly enjoying most this afternoon.

Having re-read the last few pages on this thread I realise I hadn't posted any photos of the finished 2-ways baffles. So to set the record straight:

Image

I might do some further experiementation with these baffles to see if I can further improve them. It will give me something to do this winter.
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