# Ported main speaker roll off



## tesseract (Aug 9, 2010)

The THX electronic XO's settings that have been widely adopted set up for a 24 dB/LR4 acoustic alignment of sealed mains and subs at the XO frequency, but that is rarely the case in practice.

I am ready to purchase a pair of ported speakers that begin to roll off around 80 Hz, the CHT SHO-10. There will be no high pass XO to these speakers, they will roll off naturally. They will be paired with sealed subwoofers that use a variable 4th order low pass XO.

I have ported B&W 602S3 now. I am auditioning the sealed GR Research N2X full range and noticed that the low bass from the subs more refined with the N2X, subjectively. Which raises these questions.



1. This is a 2 channel system. What type of issues, if any, with blending the outputs of these two disparate designs can I expect? I understand that there can be problems, but it is done in many systems, albeit with a high pass on the mains usually. 

2. Modeling shows that a sealed design of this speaker in this enclosure size will raise the roll off to 200 Hz, not something I want to do. Is blocking the port going to give this same 200 Hz roll off?


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## GranteedEV (Aug 8, 2010)

1) Below tuning, vented speakers roll off at 24/db per octave. I think we recognize that part. But that doesn't mean the acoustic roll-off indicates a reduction in driver motion. Instead, the driver unloads completely below tuning, behaving like it is in free air... essentially what you've got is a driver in free air, plus the 12db/octave rolloff of a roughly 2nd order gradient system. If we use "boxes" and "resonators" to control driver motion, the driver is very much NOT under control below tuning where there is no box or resonator operating upon it. This is a great source of phase modulation distortion and worst-case scenario, driver bottoming. You absolutely need a high pass filter if you're running deep bass notes into vented speakers, especially light weight, high sensitivity, low excursion drivers such as the ones used in pro audio (including the Sho-10). Without a high pass you're effectively running the speaker full range. OTOH, a THX style speaker will have a sealed box rolloff below 80hz (12db/octave) which will give good driver protection, plus an electrical 12db/octave high pass further improving power handling. 

2) Phase tracking / smooth integration. I don't feel vents work well in blending to mains subjectively. In fact I would even say blending a woofer to midbass using 2nd order acoustic rolloff both ways is in my opinion more effective. If using a vented speaker, I would cross over still about a half-octave above tuning frequency and use a linear phase high pass filter.


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## tesseract (Aug 9, 2010)

Thanks, EV.




GranteedEV said:


> 1) Below tuning, vented speakers roll off at 24/db per octave. I think we recognize that part. But that doesn't mean the acoustic roll-off indicates a reduction in driver motion. Instead, the driver unloads completely below tuning, behaving like it is in free air... essentially what you've got is a driver in free air, plus the 12db/octave rolloff of a roughly 2nd order gradient system. If we use "boxes" and "resonators" to control driver motion, the driver is very much NOT under control below tuning where there is no box or resonator operating upon it. This is a great source of phase modulation distortion and worst-case scenario, driver bottoming. You absolutely need a high pass filter if you're running deep bass notes into vented speakers, especially light weight, high sensitivity, low excursion drivers such as the ones used in pro audio (including the Sho-10). Without a high pass you're effectively running the speaker full range. OTOH, a THX style speaker will have a sealed box rolloff below 80hz (12db/octave) which will give good driver protection, plus an electrical 12db/octave high pass further improving power handling.


Textbook, you would think that the 4th order roll off of the ported speakers would be a match for the the 4th order electronic low pass of the sub. It is not the case, at least with the B&W's. It didn't sound terrible, it worked quite well until I heard the N2X. 

The SHO-10's will be unloaded under the tuning FR of the vent, I am hoping that the low excursion of the driver can help mitigate the "loose cannon on deck" effect. I will be powering the SHO's with a mere 75 watt integrated, so the speakers won't be anywhere near xmax let alone xmech. Do you think that will be enough cushion to save the day? If not, would blocking the port with closed cell foam work to make the driver exhibit a sealed response at a reasonably low FR that would enable the sub to be XO'ed low enough to prevent localization?



> 2) Phase tracking / smooth integration. I don't feel vents work well in blending to mains subjectively. In fact I would even say blending a woofer to midbass using 2nd order acoustic rolloff both ways is in my opinion more effective. If using a vented speaker, I would cross over still about a half-octave above tuning frequency and use a linear phase high pass filter.


I have no way to use an active XO and still maintain my preamp switching functions, I can only dump a XO (like the one built into the Dayton SA1000 sub amp) into one input. So, unfortunately an active XO is out and honestly I would prefer not to use one anyway. There is a gentleman that owns Gedlee Abbey and SHO-10 and has said that the SHO-10 does fine running full range, I am just wondering about the textbook theory of it all, how it correlates with my recent experience, sealed vs. ported, and how a high efficiency ported design might fare.


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## tesseract (Aug 9, 2010)

Hoping to get a response like this. Graph courtesy of Linkwitzlab.


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## chashint (Jan 12, 2011)

Since the SHO-10 was specifically designed to be used in home theater applications, why buy it (unheard) with the intention of using it in a two channel setup ?
I would ask the question in reverse if you were intending to buy and use a pair of low sensitivity four ohm audiophile speakers as the front main speakers of a multi-channel home theater system.


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## tesseract (Aug 9, 2010)

chashint said:


> Since the SHO-10 was specifically designed to be used in home theater applications, why buy it (unheard) with the intention of using it in a two channel setup ?
> I would ask the question in reverse if you were intending to buy and use a pair of low sensitivity four ohm audiophile speakers as the front main speakers of a multi-channel home theater system.


"_Our very successful SHO-10 High Efficiency Monitor has proved to be highly adept at handling the subtle nuances which music demands while excelling as a system for movies and dialog and doing both with neutrality and clarity._ "

The SHO-10 isn't meant to be a HT only speaker, although that has been it's primary use. Reports from the field give it high marks for musicality, in fact a pair of ERA D4 were used to voice the midrange. I would like to explore it's potential in a minimalist 2 channel system, if you can call a system with subs "minimalist". I call subs necessary, especially with the music I listen to.

I had a chance to listen to the SHO-10's in the early stages of HuskerOmaha's theater build. I was really impressed with the dynamics and lack of horn sound, although I didn't get a chance to critically listen to music as the theater was not yet completed or dialed in optimally. I have yet to hear any negative impressions from SHO-10 owners, one owner has compared them favorably to his GedLee Abbeys and Nathan center. I have no illusions that they are at parity, but coming close at that low of a cost speaks well of the Chase design. I have a little insight about the evolution of the PRO/SHO-10, a lot of work was done by the OEM driver supplier, Rock and his son to get to that point. GedLee, Zilch's EconoWave, Wayne Parham's Pi and Duke LeJeune's AudioKinesis speakers are getting a lot of attention, the SHO-10 is an cost efficient way for me to see if high efficiency constant directivity is for me, without having to buy woodworking tools and do a build out or spend mega $$$$.

I want to try CD speakers partially because I have a very difficult room, with a 6 ft. opening to the right side of the front stage and a wall with windows on the left side. The recommended 45 degree crossfire isn't going to be happening, but hopefully CD can help with the opening, and a 48x24x6 absorption panel will be going up on the left window wall to simulate the opening on the right.

I have been reading tons on the matter, it doesn't appear I will have any problems below the vent's tuning point. A lot of speakers are ported, few have as heroic a driver as the SHO-10. 75 watts each at 8 ohms is all the power they will see, so hitting xmech will never be a problem. There is a high pass XO on the Dayton amp I can experiment with, but I would prefer to avoid that if possible, I'm a bit of a purist. I just wanted to get some feedback before I dive into this, so I started this thread. This was my main concern, the lack of a high pass XO on the SHO-10's. I have since found out that the SHO-10 is also used in large venue situations, running full range with no issues.

We'll see how it goes, I'll be gearing up for REW after this purchase and will be able to get a good look at what is happening in my system. Less cone excursion usually translates into less distortion. With the compression drivers, the 10" mid bass and the dual 18" subs, I am shooting for a clean, effortless sound.

Most of all, I intend to have fun and learn, for me that's what this hobby is all about.


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## tesseract (Aug 9, 2010)

I am running a pair of TCA WAF-1's full range in my system now. The rear firing ports were not playing well with the subs placed directly behind them. I plugged the ports and raised the subwoofer amp's XO point slightly to match the new higher roll off of the WAF-1, which is now around 75 Hz. Sounds much better.

I'm hoping that it will work the same way with the SHO-10's if any issues arise, although the B&W's front firing ports sounded better open than while plugged. :dunno:


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