TH-18 Flat to 35hz! (Xoc1's design) - Page 41 - diyAudio
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Old 3rd January 2012, 01:46 PM   #401
Xoc1 is offline Xoc1  United Kingdom
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Hi PASC
Great information, thanks!
Restricting the throat is something that has been discussed in this thread. It looks like it could be needed when running these drivers at such high powers.
I am undecided which way would be the best way to restrict the throat, especially when concidering the need to let the driver reach its Xmech limits.
It might be good to retest the Keystone with the dB meter with a fresh 9V battery to check its SPL.
Kind Regards
Martin (Xoc1)
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Old 3rd January 2012, 03:04 PM   #402
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Do we care to discuss such high SPL claims from pro boxes such as the DSL TH118?
Is it really all marketing trickery??

Peak 4 cabinets for the TH-18 should be 138.2db according to PASC's measurement for one cab. That lines up pretty well with the 140db 4 cabinet goal set by You in the beginning. Great job Martin!!

Last edited by m R g S r; 3rd January 2012 at 03:07 PM.
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Old 3rd January 2012, 04:27 PM   #403
PASC is offline PASC  Brazil
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Hi!

For better ref I attach a picture from the way I put two new slots that let the botton quiet in spite of Pe applied to 18NLW9600 during the tests.

Click the image to open in full size.

Thinking if it helps fix similar slots to the sides from the front/mouth to the back to avoid any vibration at that points.
Could be thinner solid wood slots as teached by Weems in Designing Building and testing your Own speakers Systems

regards,
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Old 3rd January 2012, 05:47 PM   #404
Djim is offline Djim  Netherlands
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Xoc1: "Restricting the throat is something that has been discussed in this thread. It looks like it could be needed when running these drivers at such high powers. I am undecided which way would be the best way to restrict the throat, especially when concidering the need to let the driver reach its Xmech limits."

Hi Martin,

The problem of losing control over the excursion in that last power up stage is a driver problem. The only way to suppress it, while keeping the max SPL intact, is designing a TH in such way the excursion dips fall together (just a little above) with the most important resonances in the cone. If you want to go a step further you'll have to use dynamic eq on these spots.

Although the driver will never reach its Xmech, you are right in that the cone needs to move freely to obtain max SPL with minimal change in response, at high levels.

Last edited by Djim; 3rd January 2012 at 05:51 PM.
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Old 3rd January 2012, 05:56 PM   #405
iand is offline iand  United Kingdom
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Quote:
Originally Posted by Djim View Post
Xoc1: "Restricting the throat is something that has been discussed in this thread. It looks like it could be needed when running these drivers at such high powers. I am undecided which way would be the best way to restrict the throat, especially when concidering the need to let the driver reach its Xmech limits."

Hi Martin,

The problem of losing control over the excursion in that last power up stage is a driver problem. The only way to suppress it, while keeping the max SPL intact, is designing a TH in such way the excursion dips fall together (just a little above) with the most important resonances in the cone. If you want to go a step further you'll have to use dynamic eq on these spots.

Although the driver will never reach its Xmech, you are right in that the cone needs to move freely to obtain max SPL with minimal change in response, at high levels.
Restricting the throat is likely to cause severe power compression before it helps much with cone excursion -- you really want a strong nonlinear restoring force (rapidly increasing suspension stiffness) to limit cone travel, not an almost-linear throat restriction.

If this is a real problem then you either need drivers with more Xmax/Xmech (eg. Ficar BTL N218, Xmax=28mm) or "unbottomable" ones with a very rapid decrease in compliance at large excursions -- it's been said that the B&C drivers are almost impossible to drive to Xmech even with huge input powers.
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Old 3rd January 2012, 05:57 PM   #406
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by m R g S r View Post
Do we care to discuss such high SPL claims from pro boxes such as the DSL TH118? Is it really all marketing trickery??
Hi mRgSr,

Marketing maybe, but as long people 'forget' to read the additional info, such as measured in 1/2Pi, it's not Danley who you should blame.

It's actually similar to what happens here on DIY. Members around here compare TH's with different drivers, based on 2,83V instead of the 1W/1m. That means the driver with the highest Re will show a lower sensitivity response compared to a driver with the lowest Re.
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Old 3rd January 2012, 06:02 PM   #407
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by iand View Post
Restricting the throat is likely to cause severe power compression before it helps much with cone excursion -- you really want a strong nonlinear restoring force (rapidly increasing suspension stiffness) to limit cone travel, not an almost-linear throat restriction.

If this is a real problem then you either need drivers with more Xmax/Xmech (eg. Ficar BTL N218, Xmax=28mm) or "unbottomable" ones with a very rapid decrease in compliance at large excursions -- it's been said that the B&C drivers are almost impossible to drive to Xmech even with huge input powers.
Hi Iand,

I agree in most part. Yes, restricting the mouth or the path will result in extra (Dynamic) Power Compression. But you can design a TH in such way to restore one or max 2dB's (not over the entire bandwidth but at 'problem spots') that will be lost by Dynamic Power Compression in non-optimised TH's.

Last edited by Djim; 3rd January 2012 at 06:06 PM.
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Old 3rd January 2012, 06:03 PM   #408
iand is offline iand  United Kingdom
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Quote:
Originally Posted by Djim View Post
Hi mRgSr,

Marketing maybe, but as long people 'forget' to read the additional info, such as measured in 1/2Pi, it's not Danley who you should blame.

It's actually similar to what happens here on DIY. Members around here compare TH's with different drivers, based on 2,83V instead of the 1W/1m. That means the driver with the highest Re will show a lower sensitivity response compared to a driver with the lowest Re.
I had a debate with Tom about this when he started to use lower impedances; his view was that so long as the spec was clear (e.g. 105dB for 2.82V, 4 ohms impedance) this was not an issue, especially given that most (all?) amplifiers are voltage-limited -- you just need to know how many you can drive off one amplifier.

Since some of his subs are 2 ohms nominal they appear even more "efficient" if you don't read the details. But it would be more honest if he included impedance in the comparison tables like this as well as the headline figures...

Danley | Tapped Horn Comparison
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Old 3rd January 2012, 06:06 PM   #409
iand is offline iand  United Kingdom
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Quote:
Originally Posted by Djim View Post
Hi Iand,

I agree in most part. Yes, restricting the mouth or the path will result in extra (Dynamic) Power Compression. But you can design a TH in such way to restore one or max 2dB's that will be lost by Dynamic Power Compression in 'non' optimised TH's.
All that means is you've lost 1-2dBs off a figure that is higher to start with -- either way you're getting lower output than you could get.

It's still the wrong approach in my view, you want something that doesn't reduce output with normal drive but limits excursion under extreme drive, and throat restriction will never be able to do this, it's down to the driver.
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Old 3rd January 2012, 06:09 PM   #410
epa is offline epa  Netherlands
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question,shouldn't we look at the impedance graph to determen the minimum impedance?
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