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BioBrian

In at the deep end - SB 15 inch for sensitive bass

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Auracle   

Looks like I've made a rod for my own back.

Running an educational GTG as compared to a show-and-tell (and drink) format.

Does anyone in SNA land know if a gtg has been run along similar lines, or will this be the first?  If anyone has a suggestion for formats, let us know. Does SNA also get a portion of my apples?

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Upfront   
Looks like I've made a rod for my own back.
Running an educational GTG as compared to a show-and-tell (and drink) format.
Does anyone in SNA land know if a gtg has been run along similar lines, or will this be the first?  If anyone has a suggestion for formats, let us know. Does SNA also get a portion of my apples?
I haven't seen one. Lots of informal educational talk but not what your suggesting.

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Rob181   
4 hours ago, Auracle said:

Does SNA also get a portion of my apples?

 

What variety are the apples...

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Upfront   
 
What variety are the apples...
More importantly, can they be made in to cider before the GTG!

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Auracle   

Maybe I should start another thread on "how to make alcohol whilst listening to background music class".

 -this is Brian's thread afterall, and we really should get back on topic.

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Upfront   
Maybe I should start another thread on "how to make alcohol whilst listening to background music class".
 -this is Brian's thread afterall, and we really should get back on topic.
191aaf118d7ba5adaf6eb9e7ed234f1a.jpg

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Rob181   
7 hours ago, Auracle said:

Maybe I should start another thread on "how to make alcohol whilst listening to background music class".

 

Really looking forward top this one...give me a yell when you do start it...

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BioBrian   

 

1 hour ago, Rob181 said:

 

Really looking forward top this one...give me a yell when you do start it...

 

May I respectfully suggest you start it yourself, and leave this thread to those who don't need to be yelled at.

 

 A closer reading might reveal that Sam, who has been in consultation with me over this build, has more serious intentions in life, as do I.

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Rob181   
4 minutes ago, BioBrian said:

May I respectfully suggest you start it yourself, and leave this thread to those who don't need to be yelled at.

 A closer reading might reveal that Sam, who has been in consultation with me over this build, has more serious intentions in life, as do I.

 

May I respectfully suggest you look at who made the comment to which I referred...

That you have chosen to be a SP over a "throw away" line posted by @Auracle...

And my response to that line is your problem...no one else's...

I highly recommend you Google "sense of humour"...

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BioBrian   

You totally missed the thrust of Auracle's line. React if it pleases you.

 

I have a very busy sense of humour, but you might want to observe, as I've had to, that when a joke gets no response, it can be assumed that it was not at all appreciated.

 

I'm actually more concerned with future readers who, like me, might get very sick of the crap that invades threads and drains the good energy and direction that they can generate.

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Upfront   

So what's the next step Brian? Are you still contemplating which drivers you will use?

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BioBrian   

Well another little package came from Nigel yesterday: 3.9 mH C-coils, which are to try as ' first entry' to the 3-Way crossovers. That means dropping the DCR to the woofer, which I'm hoping might even up the balance again.

 

The previous inductor was 3.9 mH, with 0.66 Ohm DCR; these drop to 0.08 Ohm. I'll try to get them in today and have another go with just one amp running the lot - it would be great to keep it that simple.

 

For the last couple of days, I've had your Pre 1 and Parasound running the big woofers, and Cyrus on top, which I could balance, power-wise, and gave the clearest sound I've had yet. (Quite pleasing, really).

 

I still have odd tweeters, and have been playing with the balance between them - for some reason the Scanspeak one sounds more out-of-the-way and more dynamic than the SB Acoustics, but this still may be due to attenuation levels.

 

With attenuation, I've found the gap between 4.7 and 6.8 Ohms too big, so have had to calculate resistor pairs, using the formula R1 x R2 over R1 + R2. I tried 10 + 18 = 6.43 Ohms, but will go to 12 + 15 = 6.67  for the SBA tweeter.today. The SSpk one's pretty right on 3R.

 

I had a mail from Per Skaaning last night with more info on the lusted-after drivers. Plan had been to use the (23 cm diameter - 8") 23 I 52 in the 30 litre sealed box, but he said it needs vented, as its EBP is about 140. EBP is Fs over Qes, and I don't come across this as an important design consideration very often. Troels seems to ignore it when doing his 100-200 Hz sealed boxes for tight punchy upper-bass/lower-mid. I'm hoping the EBP thing is only important in getting efficient bass out of a driver, which I don't need, but would like to hear from any readers here, who may throw some light on it.

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lusk   

HI Brian,

 

Been trying to follow where your at the moment, 15" bass driver active + 3way troels (8" SB acoustics?? or Jantzen??) is this correct?

 

So the new inductor 3.9mH with lower DCR is for the 8" to get slightly more output?

 

Re:AT drivers

Will you be using the sealed box to act as the high pass (like Troels design) or using a crossover filter? The driver will be different for each, EBP will need

to drop so driver pushes lower in sealed box so then you add your crossover filter.

 

 

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BioBrian   
9 hours ago, lusk said:

HI Brian,

 

Been trying to follow where your at the moment, 15" bass driver active + 3way troels (8" SB acoustics?? or Jantzen??) is this correct?

 

So the new inductor 3.9mH with lower DCR is for the 8" to get slightly more output?

 

Re:AT drivers

Will you be using the sealed box to act as the high pass (like Troels design) or using a crossover filter? The driver will be different for each, EBP will need

to drop so driver pushes lower in sealed box so then you add your crossover filter.

 

 

 Hi Lusk, and anybody with else with the patience, it's been a long day in the chariot for a recently-dissected specimen (I meant me, but the speakers too).

 

Quite a few changes, quite a few loose ends sorted:

 

The new 3.9 mH C-coils went in, as inductors for the 8" woofer. These have done the job of raising the sensitivity of the upper 3-ways, better matching the bottom 15" woofers.

 

I put the Scanspeak tweeter back in its little L-frame to return for duty as part of my Centre speaker, in the 7.1 system at the house.

 

Fitted the other SB tweeter back in the 3-ways, so they're now symmetrical again.

 

Put the 12 + 15 R = 6.67 R resistor parallel pairs in, as tweeter attenuation. This worked:  it sounds more like a proper working system with the symmetry. May need to go back to 6R8 if it stays this bright, but will wait till it's played in a bit more.

 

Fitted new 39 uF Cross Caps to the bottom 4th Order passive LP filter. It had been a bit of a bird's nest with paralleled caps, so is now one level neater.

 

The upper 3-way is still based on Troels' SB 3-way crossover. This remains all 2nd Order, with no HP woofer filter, other than acoustic roll-off by the sealed 40 litre box. Main changes to the design are:

 

-  SBA TW29RN tweeter, instead of cheaper SB29RDC-C000-4.

-  SBA SATORI MW16P-8 mid, instead of smaller SB12MNRX25-4.

-  Troels Gravesen/SEAS JA8008 woofer (94 dB, as opposed to 88.5 for the original SBA SB23NRXS45-8).

-  8" Woofer C-coil has much lower DCR, and nearly double the mH, due to using the JA8008 driver. Also to cut its mid-range output to suit XO to mid.

-  Mid gets 50% more uF in HP section to lower crossover point to woofer. Also a CR across its LP coil, to tame upper roll-off and XO point.

-  Attenuation adjustments, and placement of resistors within filters.

 

- And of course addition of the bottom SBA SB42FHC75-6 15" woofer below, in its 240 litre vented box. It has 4th Order passive filter.

 

Today I re-wired the whole caboodle to run as a 4-way passive again, all off Linc's Bel Canto Pre 1 and the Parasound A 21 power amp. (I think the A 21 enjoys having something to do for a change).

 

Sorry, pictures might be a better way of presenting all that, but I'm not skilled in doing hybrid photos with text added.

 

The upshot of all that is a pretty nice speaker system. I ran a few of the usual CDs through - Prokofiev, Stravinsky and Mahler, but look forward to getting the Server plugged in to deliver some Hi-Def files. Just in case there was a good drum track, I played some bits from Abbey Road, but it didn't have what I expected. But quite a shock - I've never heard such separation, such clarity, such a raw '60s sound, and all the lyrics so clear. Just goes to show how attitudes, presumptions, and memory, change over 2 years - I really need to go back to previous speakers to get this in contrast. I've created something pretty different, and I'm getting to accept that it's a big step up from what I've had in the past.

 

The voicing sort of works, with, as I mentioned above, maybe a bit too much brightness from the tweeters. The prototype tweeter 'wings' are still on, which does brighten the treble.

 

What bothers me is a kind of 'cuppy' sound from the mids. I had this complaint with the original 4" mids, but maybe this EBP thing, mentioned in my previous post, might just have the clue. Both drivers are sealed in accordance with WinISD - correct volume for Qtc of 0.707, but both sound wrong to me. I've checked their EBP numbers, and guess what? - they're both about 140, which is what Per said needs vented enclosures!

 

The new AT 8" would be expected to have as little bass as possible, so I can keep the sealed (it would reduce to about 30 litres) box and not have to make an expensive HP filter for it.

 

Another puzzle is that the 15 H 52 06 13 SDKA mids that I'm talking about with Per have an EBP of 130, and he says 4-5 litres sealed would suit them. :anyone: I have a note here saying "Glasswolf Pages", so I probably need to look that up again and try to work out something. For this mid, Troels uses an aperiodic vent in 4.9 litres, so I can build that in, with some difficulty (vent might have to be out one side).

 

Fitting a vent and doubling the inner box size for the present mids would be a major rebuild. So I'll keep considering the AT drivers, which would need a rebuild, but would be (more?) permanent. Yeah, that sounds good. Give me more of this transparency thing I keep hearing about, please Universe?

 

So @lusk, please spell it out for me simply, if you can advise on EBP - and anything else that comes to mind of course.

 

As usual, I welcome comments or advice from all readers. If you're shy, please PM. It could save a lot of dollars!

 

 

 

 

Edited by BioBrian

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lusk   
11 hours ago, BioBrian said:

 

What bothers me is a kind of 'cuppy' sound from the mids. I had this complaint with the original 4" mids, but maybe this EBP thing, mentioned in my previous post, might just have the clue. Both drivers are sealed in accordance with WinISD - correct volume for Qtc of 0.707, but both sound wrong to me. I've checked their EBP numbers, and guess what? - they're both about 140, which is what Per said needs vented enclosures!

 

 

EBP is a guide to show weather a driver is suited to sealed or ported when considering the drivers low end frequency response.

Efficiency Bandwidth Product, eg.  value of 50 = more bandwidth less efficiency, 140 = less bandwidth more efficiency

 

Using a midrange driver with EBP of 140 in a sealed enclosure doesn't matter because you may not require the

driver to go low but you want reasonable efficiency.

 

Its difficult to offer suggestions on your issue with mids without seeing measurements of each driver and total response.

 

 

 

 

 

 

 

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BioBrian   

Thanks, lusk. I need to learn more about Qes.

 

Relieved - it sounds like sealed will suit what I want from both new drivers. Using the box to control/suppress bass, but not damping dynamics too much.

 

I'll try to do a set of measurements as you suggest - the cupiness may well be due to the JA8008 going too high into the mid's territory. I haven't spent much time on it, as I'm pretty desperate for them to go back to their proper homes.

 

But I think listening to the mids on their own shows the same uncomfortable sound. I thought it might be because either the 2.6 litres is too small, or there's a reflection off the flat back wall of the mid box.

I do have a hard foam shape there to dissipate it, but it did seem a bit crazy to put this Satori driver in a box it only just fits in.

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